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Sample records for chert

  1. Shikarpur lithic assemblage: New questions regarding Rohri chert blade production

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    Charusmita Gadekar

    2014-03-01

    Full Text Available Recent excavations at Shikarpur, a fortified Harappan site situated near the Gulf of Kuchchh in Gujarat, Western India, brought to light a large collection of Rohri chert blades.  Chert found in the Rohri hill near Sukkur in Sindh, central Pakistan is distinctive and easily identifiable. The wide distribution of standardized Rohri chert blades is often regarded as a testimony to the Harappan efficiency in long distance trade and craft production.  The possibility of localized production of Rohri chert blades in Gujarat is often negated due to the constraints of raw-material availability.  The absence of Rohri chert working debitage from most of the sites in Gujarat, has lent support to this position. The Shikarpur Rohri blade assemblage however incorporates more than 650 blades, a large fluted blade-core and a few Rohri chert debitage.  These have led the excavators to suggest that some of the blades found at Shikarpur were locally produced from raw materials brought to the site from the Rohri hills.  Typo-technological features of the Rohri chert assemblage from Shikarpur have been analysed in this background. These along with metrical features of the assemblage are compared with Rohri chert assemblages from other major Harappan sites in the region to check the validity of the proposed ‘limited local production’.

  2. Germanium/silicon of the Ediacaran-Cambrian Laobao cherts: Implications for the bedded chert formation and paleoenvironment interpretations

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    Dong, Lin; Shen, Bing; Lee, Cin-Ty A.; Shu, Xu-jie; Peng, Yang; Sun, Yuanlin; Tang, Zhuanhong; Rong, Hong; Lang, Xianguo; Ma, Haoran; Yang, Fan; Guo, Wen

    2015-03-01

    Sedimentary strata of the terminal Ediacaran (635-542 Ma) to early Cambrian (542-488 Ma) Laobao-Liuchapo bedded cherts in the South China Block include the Ediacaran Oxidation Event and the Cambrian explosion. Understanding the origin and depositional environment of the bedded cherts may provide insight into how the Earth's surface environment changed between the Proterozoic and Phanerozoic. We measured major and trace element compositions and Ge/Si ratios of the Laobao cherts from northern Guangxi province. The Laobao cherts were deposited in the deep basinal environment of the South China Block. We show that the composition of the Laobao cherts is determined by a mixture of four components: quartz, clay, carbonate, and pyrite/iron-oxide. The quartz component is the dominant component of the Laobao cherts. The maximum estimated Ge/Si of the quartz component is between 0.4 and 0.5 μmol/mol, which is close to the Ge/Si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids. These Ge/Si systematics suggest that normal seawater rather than mid-ocean ridge hydrothermal fluids is the primary Si source for the Laobao cherts. The Ge/Si of the clay component varies between 1 and 10 μmol/mol, which is comparable to the Ge/Si of typical marine clays, but 10-100 times lower than that of chert nodules from early Ediacaran beds (the Doushantuo Formation) predating the terminal Ediacaran Laobao cherts studied here. Our observations indicate that the clay component Ge/Si ratio decreased from the early Ediacaran to the late Ediacaran. We speculate that high Ge/Si ratios in clays reflect the preferential chelation of Ge by dissolved organic compounds adsorbed onto clays. If so, this suggests that the decrease in Ge/Si ratio of the clay component in the Ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the Ediacaran-Cambrian transition, consistent with oxidation of the oceans during the

  3. Dating carbonaceous matter in archean cherts by electron paramagnetic resonance

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    Bourbin, Mathilde; Gourier, Didier; Binet, Laurent; Le Du, Yann; Derenne, Sylvie; Westall, Francès; Kremer, Barbara; Gautret, Pascale

    2013-01-01

    Ancient geological materials are likely to be contaminated through geological times. Thus, establishing the syngeneity of the organic matter embedded in a mineral matrix is a crucial step in the study of very ancient rocks. This is particularly the case for Archean siliceous sedimentary rocks (cherts), which record the earliest traces of life. We used electron paramagnetic resonance (EPR) for assessing the syngeneity of organic matter in cherts that have a metamorphic grade no higher than gre...

  4. Sedimentary environments of the Middle Permian phosphorite chert complex from the northeastern Yangtze platform, China; the Gufeng Formation: a continental shelf radiolarian chert

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    Kametaka, Masao; Takebe, Masamichi; Nagai, Hiromi; Zhu, Sizhao; Takayanagi, Yukio

    2005-02-01

    Radiolarian chert deposited on a continental shelf occurs in the Middle Permian Gufeng Formation on the northeastern Yangtze platform, China. The sedimentary environments of radiolarian cherts from accretionary complexes have been well studied; however, there are few studies about radiolarian chert deposited on continental shelves. Therefore we have completed a sedimentological and geochemical study of the Gufeng Formation. The Gufeng Formation is subdivided into the Phosphate Nodule-bearing Mudstone Member (PNMM) and the Siliceous Rock Member (SRM) in ascending order. The basal PNMM consists of glauconite-bearing mudstone, which indicates deposition under aerobic shallow-marine conditions, whereas the upper PNMM is composed of mudstone including abundant phosphate nodules, suggesting deposition near the outer shelf in suboxic conditions. The SRM consists mainly of alternating beds of black chert, mudstone, and siliceous mudstone, with minor tuffaceous mudstone and porous chert beds. The black chert contains abundant radiolarians, sponge spicules, and organic matter. Framboidal pyrite occurs in the black chert. Porous chert in the SRM includes abundant rhombohedral cavities, which are dolomite moulds surrounded by quartz, suggesting dolomitization before silicification during early diagenesis. The Gufeng Chert is characterized by high Si, Mo, Ni, Cu, and Zn contents, and extremely low Mn content. The Gufeng Chert has high normal paraffin concentrations with petroleum-like markers. These geochemical features suggest that the Gufeng Chert was deposited under sulfate-reducing conditions; and is not hydrothermal, but rather biogenic in origin. The sedimentological and geochemical data suggest that the Gufeng Formation was deposited mainly on the outer shelf in suboxic-anoxic conditions caused by organic matter produced during upwelling. The upwelling probably led to high radiolarian productivity. Abundant silica and organic matter were deposited in the Gufeng basin

  5. Neutron activation analysis of chert artifacts from a Hopewell mound

    International Nuclear Information System (INIS)

    Six artifacts from a Hopewell mound located near Mt. Vernon, Indiana, and 21 geologic specimens from three different chert sources in the Ohio River Valley were analyzed by instrumental neutron activation analysis. Principal components analysis and posterior classification of the artifacts on the basis of Mahalanobis distance calculated probabilities were used to determine the most probable source for each of the artifacts. (author)

  6. "Mucientes Chert" in the Northern Iberian Plateau (Spain

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    M. Natividad Fuertes-Prieto

    2014-03-01

    Full Text Available The so-called “Mucientes chert" is a variety that appears in the central area of the Iberian North Plateau, in theDueroBasin. It is widely known in the geological and archaeological literature and its use for knapping was especially important in Prehistory. From a macroscopic point of view it is a nodular chert, with white and very porous cortex, and brown to blackish or beige colour in the inner part.In this work we carried out a more accurate petrographic, mineralogical and chemical characterization of this lithology using SEM, XRD and XRF techniques in samples coming from “Las Canteras” (Mucientes village, a chert outcrop of the “Cuestas” Unit (Vallesian-Aragonian, Miocene Age. Also, we have made a review of its geological occurrence and archaeological distribution areas.  It is intended to sketch the delimitation of the geographical area of occurrence taking into account the geological and archaeological references. 

  7. Archean cherts from the Barberton Greenstone Belt (3.5-3.2Ga), South africa. Formation process and usability as paleo-environmental proxies

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    Ledevin, Morgane,

    2013-01-01

    Archean cherts potentially constrain the primitive environment in which life emerged and evolved. These siliceous rocks formed by three processes : C-cherts (primary cherts) formed by the chemical precipitation of oceanic silica, either as a siliceous ooze (or silica gel) on the seabed, or as cement within still soft sediments at the surface ; F-cherts (fracturefilling cherts) precipitated from circulating fluids in concordant or crosscutting veins in the shallow crust ; S-cherts (secondary c...

  8. Petrologic and Geochemical Characteristics and Origin of Gusui Cherts,Guangdong Province,China

    Institute of Scientific and Technical Information of China (English)

    EDWARDH.CHOWN; EDWARDH.CHOWN; 等

    1994-01-01

    The characteristic structures of the Precambrian cherts from the Gusui section, Guangdong ,Chi-na, include bedded structure ,laminated structure ,massive structure and pseudobrecciated structure.The chert is characterized by consistently low abundance of TiO2,Al2O3 and most trace elements.Howevver ,it is enriched in Ba,As,Sb,Hg and Se.In Al-Fe-Mn ternary diagrams,it falls into the "hydrothermal field" .Correspondence analysis and factor analysis show that many elements show up in the factor that represents the leaching of country rocks by hydrothermal solutions,and are the very characteristic element association fo the geochemically anomalous South China basement.Petrologic and geochemical evidence suggests a hydrothermal origin for the chert.The chert may have been formed in a Precambrian fift or an extension zone developed within the Yunkai marginal geosyncline, with a fault system linking it to an unknown heat source at depth.

  9. The chert quarrying and processing industry at the Piatra Tomii site, Romania

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    Otis Norman Crandell

    2015-03-01

    Full Text Available Fieldwalking surveys in 2007 and 2008 revealed a moderate sized settlement on Piatra Tomii Hill (Alba County, Romania which was considered of interest because of its location on top of a natural source of chert, and the large amount of chert artefacts found on the surface. In 2009 the site was excavated during which one of the objectives was to learn more about the chert mining and processing at the site. The ratio of artefact types and lack of use-wear suggests that not only was raw material being extracted at the site, but tools were also being produced locally before being exported. The 2009 excavations also revealed what appear to be the remains of pit quarrying and possibly fire cracked limestone and debris. These finds provide technical insight into potential chert extraction techniques utilised in the Late Chalcolithic and Early Bronze Age. As well, this is as yet the only reported settlement in the Transylvanian basin involved in chert extraction (either quarrying or mining. Given the settlement’s affluence, especially considering its relative isolation, it is likely that the chert industry here was important to communities in the vicinity. Indeed artefacts found at contemporary sites in the Mureș Valley appear to have been made from the same or a similar chert. This paper gives an introductions to the site, describes the artefacts and features found there and provides possible interpretations  regarding the processing and export industry, as well as the methods of extracting the raw material during this period.

  10. Terrestrial laser scanning for high resolution cyclostratigraphy of chert in pelagic limestone series

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    Penasa, L.; Franceschi, M.; Preto, N.

    2012-04-01

    We here propose the use of terrestrial laser scanning (TLS) for the mapping of chert on natural outcrops and for rapid extraction of its distribution along stratigraphic sections. The technique permits rapid production of high-definition time series for cyclostratigraphic analysis. Chert, sometimes referred to as flint, is a widespread component of sedimentary successions. It is often found in deep water and pelagic sediments and is constituted by cryptocrystalline varieties of quartz. It is generally accepted that the origin of chert is principally biogenic; it derives from the slow alteration, through a process called maturation, of opaline organic components as tests and spicules under the influence of pore waters. Most often, chert forms nodules of various size, or more or less continuous layers. Its color shows strong variability (white, red, gray, black). Although it could record paleoceanographic and climatic changes because of its biogenic nature, the cyclostratigraphic study of chert is largely neglected. This is mainly due to the difficulty of logging it. Hand logging is time consuming, but also, because of nodules' highly variable shape, lateral variability of chert abundance is large. Photographic image-processing techniques could help in principle, but they become difficult to use when chert has a color similar to that of the host rock. Chert is easily detectable in TLS generated images because of its very low reflectivity at infrared (IR) wavelengths, also where the color of chert in visible light is close to that of the host rock. Thus, TLS data can be used to map the distribution of chert on an outcrop, and to compute its abundance along a stratigraphic section. The ultimate result of such data processing, for which a suite of original procedures was implemented, is a stratigraphic log that is suitable for time series analysis. A section in the early Cretaceous Maiolica Formation of Central Italy (Gubbio) was considered as preliminary case study for

  11. Les cherts Archéens de la ceinture de roches vertes de Barberton (3.5-3.2Ga), Afrique du Sud. Processus de formation et utilisation comme proxys paleo-environnementaux

    OpenAIRE

    Ledevin, Morgane,

    2013-01-01

    Archean cherts potentially constrain the primitive environment in which life emerged and evolved. These siliceous rocks formed by three processes : C-cherts (primary cherts) formed by the chemical precipitation of oceanic silica, either as a siliceous ooze (or silica gel) on the seabed, or as cement within still soft sediments at the surface ; F-cherts (fracturefilling cherts) precipitated from circulating fluids in concordant or crosscutting veins in the shallow crust ; S-cherts (secondary c...

  12. GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS AND RELATED MINERALIZATION OF CHERT FORMATIONS IN SOUTH TIBET

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    There occur abundant cherts in the Mesozoic and Cenozoic strata in southern Tibet. Some of them possess characteristic hydrothermal structures such as layered, laminated, massive and breccia structures.Ratios of Al/(Al+Fe+Mn), Co/Ni, Fe/Ti and TiO2-Al2O3 demonstrate that their origin is related to hydrothermal sedimentation. The chert formations have close relationship with Sb, Au and poly-metallic mineralization, and the ore-forming fluid show strong correlation with fossil hydrothermal water.

  13. Thermoluminescence dating of burnt cherts from the Alice Boer site (Brazil)

    International Nuclear Information System (INIS)

    More than 40 culturally burnt cherts from the Alice Boer site near Rio Claro, Sao Paulo State, have been studied by thermoluminescence (TL). Nine of these were found to be sufficiently heated by early man to reset the TL clock to zero and thereby be suitable for TL dating. These cherts define, for the upper half of the uppermost cultural layer (layer III), a time scale for the presence of man from 2,220 to 11,000 years. This time range is in essential agreement with the geological-paleoclimatological age estimate for the end of deposition of this layer, as well as with radiocarbon dates. In particular, it lends support to a radiocarbon age of 14,000 BP for a deeper level. The overall geochronologic results are not in contradiction with earlier statements that the deepest cultural layer (layer V) at Alice Boer might have been deposited at least 20,000 years ago. (Author)

  14. Detecting human mobility in the Pyrenees through the analysis of chert tools during the Upper Palaeolithic

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    Marta Sánchez de la Torre

    2014-03-01

    Full Text Available The purpose of this paper is to present the preliminary results of PhD research focused on hunter-gatherer groups that occupied the Central and Eastern Pyrenees during the Magdalenian period. This research aims to improve the knowledge we have about those Magdalenian groups, specifically concerning their lithic procurement strategies. The core of the study is based on the lithic tools collected from two archaeological sites - Alonsé Cave and Forcas I Shelter, both in Huesca, Spain-, and in particular those made from chert, because they are both a spatial and a cultural marker at the same time. These cherts have been studied using petroarchaeological methods, and as a result, it has been possible to detect the type of procurement strategies carried out and to guess the relation existing between those human groups and their environment, especially in what refers to mobility strategies.

  15. The noble gas isotope geochemical composition of chert at the bottom of Cambrian in Tarim Basin,China

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In the Tarim Basin,black shale series at the bottom of Cambrian is one of the important marine facies hydrocarbon source rocks. This research focuses on the analysis of the isotope of noble gas of 11 cherts. The R/Ra ratio of chert in the Keping area is 0.032―0.319,and 40Ar/36Ar is 338―430. In Quruqtagh the R/Ra ratio is 0.44―10.21,and 40Ar/36Ar is 360―765. The R/Ra ratio of chert increases with 40Ar/36Ar from the west to the east accordingly. They have evolved from the crust source area to the mantle source area in a direct proportion. Surplus argon 40ArE in chert is in direct proportion to the R/Ra ratio,indicating that it has the same origin of excess argon as in fluid and mantle source helium. Comparison of the R/Ra ratios between the west and the east shows that the chert in the eastern part formed from the activity system of the bottom hydrothermal venting driven by the mantle source,where the material and energy of crust and mantle had a strong interaction in exchange;whereas in the western part,chert deposited from the floating of hydrothermal plume undersea bottom,which is far away from the centre of activities of the hydrothermal fluid of ocean bottom. In addition,from noble gas isotope composition of chert,it is suggested that the ocean anoxia incident happened at the black shale of the Cambrian bottom probably because of the large-scaled ocean volcanoes and the followinghydrothermal activities.

  16. The rheological behavior of fracture-filling cherts: example from Barite Valley dikes, Barberton greenstone Belt, South Africa.

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    Ledevin, Morgane; Arndt, Nicholas; Simionovici, Alexandre

    2014-05-01

    A 100m-thick complex of black carbonaceous chert dikes marks the transition from the Mendon to Mapepe Formations (3260 Ma) in the Barberton Greenstone Belt, South Africa. Fracturing was intense in this area, as shown by the profusion and width of the chert dikes (ca. 1m on average) and by the abundance of completely shattered rocks. Similar structures occur in many greenstones worldwide. Here we investigate (1) the origin of the dikes and (2) the nature of the material that precipitated to form the fracture-filling chert. The dike-and-sill organization of the plumbing system and the upward narrowing of some of the large veins indicate that at least part of the fluid originated at depth and migrated upward. Abundant angular fragments of silicified country rock are suspended and uniformly distributed within the larger dikes. Jigsaw-fit structures and confined bursting textures indicate that hydraulic fracturing was at the origin of the fractures, a particularity attributed to the confinement of the hydrothermal system below an impermeable cape of chert. The location of the dikes beneath an impact spherule bed leads us to propose that the hydrothermal circulation was related to the impact. The present site may have been located at the external margin of a large crater. The geometry of the dikes and the petrography of the cherts indicate that the fluid that invaded the fractures was thixotropic. The injection of black chert into extremely fine fractures is evidence oflow viscosity at the time of injection while the lack of closure of larger veins below eroded country blocks and the suspension of fragments in a chert matrix provides evidence of high viscosity soon thereafter. The inference is that the viscosity of the injected fluid increased from low to high as the fluid velocity decreased. Such rheological behavior is characteristic of media composed of solid and colloidal particles suspended in a fluid. The presence of abundant clay-sized particles of silica

  17. New data about Cenomanian and Turonian chert from the Charente basin (France

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    Mar Rey-Solé

    2014-03-01

    Full Text Available Prehistoric studies in lithic raw materials have experienced some methodological innovations that have resulted in research breakthroughs. The transfer of methods from Geology to Archaeology has led to the development of a new discipline, Petroarcheology, which has allowed to go beyond the study of chert as a raw material, providing archaeological responses from Petrography’s own methods.Why did we choose the Charente’s basin samples?The history of research goes back to early 2000, with works like the PCR led by Anne Delagnes “Paléolithique Moyen dans le bassin de la Charente” and the doctoral thesis of Seon-Jing Park (2007, in relation to the question of Neanderthal human mobility and potential mineral resources of that basin. These works led to the initiation of different geoarchaeological surveys in search of quality siliceous raw materials for the manufacture of stone tools, whose positive results led, in 2002, to the creation of the regional lithothèque of Charente (Angoulême, France.This lithothèque, located at the Museum of Fine Arts in Angoulême and with a collection of 183 samples of siliceous rocks - chert, jasper (Riba, 1997 and claystones (Riba, 1997-, has become over the years an essential and very important tool for scholars interested in siliceous raw material availability and procurement in that region.Our study has combined petrologic and micropalaeontological (both macroscopic and microscopic analysis of all samples recovered from two of the four geological stages of the Upper Cretaceous represented in the lithothèque - Cenomanian and Turonian.We’ve described some different kind of chert and we’ve made location maps with the aim, in the future, of compare and relate to archaeological studies on the origin of lithic industries recovered in the archaeological deposits of the area.

  18. Characteristics, distribution and diagenetic stages of chert in the La Silla Formation (Lower Ordovician, Argentine Precordillera

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    Mariana M. Raviolo

    2009-12-01

    Full Text Available The late Cambrian - late Tremadocian La Silla Formation is a carbonate unit of the eastern Precordillera in Argentina whose facies indicate a shallow platform environment. Until this moment, there were no studies that referred to the diagenetic evolution of these rocks. The present study involves the characteristics and distribution of the silicification that affects this unit and determines its different diagenetic stages through petrographic (with cathodoluminescence support and stratigraphic analyses. An early diagenetic chert, in a stage previous to the compactation, was observed. This chert is related to silica-rich seawater in contact with permeable and porous sediments. A later pulse of chert, associated with fracturing, also occurs. The knowledge provided by the characteristics and distribution of chert in these carbonates is significant, especially when considering that the La Silla Formation in San Juan province is the most quarried unit for the elaboration of lime.A Formação La Silla (Neo Cambriano-Neo Tremadociano é formada por depósitos carbonáticos da região da Pré-Cordilheira leste, Argentina. As faciologias encontradas em tais depósitos indicam um ambiente de deposição caracterizado por uma plataforma rasa. Até o momento, nenhum estudo tratou especificamente da evolução diagenética dessas rochas. O presente estudo envolve as características e distribuição da silicificação que afeta esta formação e apresenta os diferentes estágios diagenéticos ocorridos, através de análises petrográficas (auxiliadas por catodoluminescência e estratigráficas. Foi identificado um pulso precoce de silicificação, anterior ao processo de compactação das rochas afetadas. Esta silicificação foi favorecida pela presença de água do mar rica em sílica em contato com sedimentos porosos e permeáveis. Também foi identificado um pulso de silicificação tardia, associado a eventos de fraturamento das rochas. O conhecimento

  19. Magadi-type chert, indicator of a lacustrine environment in the Middle Eocene McBean formation, South Carolina.

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    Houser, B.B.

    1985-01-01

    Magadi-type chert (chert derived from magadiite) occurs in the basal part of the formation at three localities in Orangeburg and Calhoun Counties. These occurrences imply that the basal part of the McBean formation was deposited here in an alkaline lake with a high silica content. Formation and filling of the lacustrine depression could have resulted from a timely combination of the following factors: an initial nearshore to estuarine depositional environment; falling sea-level; minor tectonic uplift of the Cape Fear Arch and/or the northern boundary of the south Georgia rift basin; intense chemical weathering in a tropical climate; and seasonal rainfall. The mineralogy, chemistry and genesis of the chert are considered.-R.S.M.

  20. Texture-specific Si isotope variations in Barberton Greenstone Belt cherts record low temperature fractionations in early Archean seawater

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    Stefurak, Elizabeth J. T.; Fischer, Woodward W.; Lowe, Donald R.

    2015-02-01

    Sedimentary cherts are unusually abundant in early Archean (pre-3.0 Ga) sequences, suggesting a silica cycle that was profoundly different than the modern system. Previously applied for the purpose of paleothermometry, Si isotopes in ancient cherts can offer broader insight into mass fluxes and mechanisms associated with silica concentration, precipitation, diagenesis, and metamorphism. Early Archean cherts contain a rich suite of sedimentological and petrographic textures that document a history of silica deposition, cementation, silicification, and recrystallization. To add a new layer of insight into the chemistry of early cherts, we have used wavelength-dispersive spectroscopy and then secondary ion mass spectrometry (SIMS) to produce elemental and Si and O isotope ratio data from banded black-and-white cherts from the Onverwacht Group of the Barberton Greenstone Belt, South Africa. This geochemical data is then interpreted in the framework of depositional and diagenetic timing of silica precipitation provided by geological observations. SIMS allows the comparison of Si and O isotope ratios of distinct silica phases, including black carbonaceous chert beds and bands (many including well-defined sedimentary grains), white relatively pure chert bands including primary silica granules, early cavity-filling cements, and later quartz-filled veins. Including all chert types and textures analyzed, the δ30Si dataset spans a range from -4.78‰ to +3.74‰, with overall mean 0.20‰, median 0.51‰, and standard deviation 1.30‰ (n = 1087). Most samples have broadly similar δ30Si distributions, but systematic texture-specific δ30Si differences are observed between white chert bands (mean +0.60‰, n = 750), which contain textures that represent primary and earliest diagenetic silica phases, and later cavity-filling cements (mean -1.41‰, n = 198). We observed variations at a ∼100 μm scale indicating a lack of Si isotope homogenization at this scale during

  1. A palaeotemperature curve for the Precambrian oceans based on silicon isotopes in cherts.

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    Robert, François; Chaussidon, Marc

    2006-10-26

    The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian era (before 550 million years ago), ranging from surface temperatures similar to or higher than today's to global glaciation events. The most continuous record of sea surface temperatures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian era shows that the observed silicon isotope variations imply seawater temperature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago. PMID:17066030

  2. Far-travelled Permian chert of the North Fork terrane, Klamath Mountains, California

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    Mankinen, Edward A.; Irwin, William P.; Blome, Charles D.

    1996-04-01

    Permian chert in the North Fork terrane and correlative rocks of the Klamath Mountains province has a remanent magnetization that is prefolding and presumably primary. Paleomagnetic results indicate that the chert formed at a paleolatitude of 8.6° ± 2.5° but in which hemisphere remains uncertain. This finding requires that these rocks have undergone at least 8.6° ± 4.4° of northward transport relative to Permian North America since their deposition. Paleontological evidence suggests that the Permian limestone of the Eastern Klamath terrane originated thousands of kilometers distant from North America. The limestone of the North Fork terrane may have formed at a similar or even greater distance as suggested by its faunal affinity to the Eastern Klamath terrane and more westerly position. Available evidence indicates that convergence of the North Fork and composite Central Metamorphic-Eastern Klamath terranes occurred during Triassic or Early Jurassic time and that their joining together was a Middle Jurassic event. Primary and secondary magnetizations indicate that the new composite terrane containing these and other rocks of the Western Paleozoic and Triassic belt behaved as a single rigid block that has been latitudinally concordant with the North American craton since Middle Jurassic time.

  3. Electron Paramagnetic Resonance Study of a Photosynthetic Microbial Mat and Comparison with Archean Cherts

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    Bourbin, M.; Derenne, S.; Gourier, D.; Rouzaud, J.-N.; Gautret, P.; Westall, F.

    2012-12-01

    Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.

  4. Silica precipitation triggered by clastic sedimentation in the Archean : new petrographic evidence from cherts of the Kromberg type section, South Africa

    OpenAIRE

    M. Ledevin; Arndt, N.; Simionovici, A.; Jaillard, Etienne; Ulrich, M.

    2014-01-01

    The Kromberg Formation (ca. 3432 Ma) in the Barberton Greenstone Belt, South Africa, contains well-preserved chert beds at the tops of turbidite deposits. At the interface, siltstone, which consist of Kfeldspar, K-mica, microquartz with minor lithic fragments and heavy minerals, grades into chert, which consists of microquartz and minor K-mica (

  5. The rheological behavior of fracture-filling cherts: example of Barite Valley dikes, Barberton Greenstone Belt, South Africa

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    M. Ledevin

    2014-05-01

    Full Text Available A 100 m-thick complex of near-vertical carbonaceous chert dikes marks the transition from the Mendon to Mapepe Formations (3260 Ma in the Barberton Greenstone Belt, South Africa. Fracturing was intense in this area, as shown by the profusion and width of the dikes (ca. 1 m on average and by the abundance of completely shattered rocks. The dike-and-sill organization of the fracture network and the upward narrowing of some of the large veins indicate that at least part of the fluid originated at depth and migrated upward in this hydrothermal plumbing system. Abundant angular fragments of silicified country rock are suspended and uniformly distributed within the larger dikes. Jigsaw-fit structures and confined bursting textures indicate that hydraulic fracturing was at the origin of the veins. The confinement of the dike system beneath an impact spherule bed suggests that the hydrothermal circulations were triggered by the impact and located at the external margin of a large crater. From the geometry of the dikes and the petrography of the cherts, we infer that the fluid that invaded the fractures was thixotropic. On one hand, the injection of black chert into extremely fine fractures is evidence for low viscosity at the time of injection; on the other hand, the lack of closure of larger veins and the suspension of large fragments in a chert matrix provide evidence of high viscosity soon thereafter. The inference is that the viscosity of the injected fluid increased from low to high as the fluid velocity decreased. Such rheological behavior is characteristic of media composed of solid and colloidal particles suspended in a liquid. The presence of abundant clay-sized, rounded particles of silica, carbonaceous matter and clay minerals, the high proportion of siliceous matrix and the capacity of colloidal silica to form cohesive 3-D networks through gelation, account for the viscosity increase and thixotropic behavior of the fluid that filled the

  6. The rheological behavior of fracture-filling cherts: example of Barite Valley dikes, Barberton Greenstone Belt, South Africa

    Science.gov (United States)

    Ledevin, M.; Arndt, N.; Simionovici, A.

    2014-05-01

    A 100 m-thick complex of near-vertical carbonaceous chert dikes marks the transition from the Mendon to Mapepe Formations (3260 Ma) in the Barberton Greenstone Belt, South Africa. Fracturing was intense in this area, as shown by the profusion and width of the dikes (ca. 1 m on average) and by the abundance of completely shattered rocks. The dike-and-sill organization of the fracture network and the upward narrowing of some of the large veins indicate that at least part of the fluid originated at depth and migrated upward in this hydrothermal plumbing system. Abundant angular fragments of silicified country rock are suspended and uniformly distributed within the larger dikes. Jigsaw-fit structures and confined bursting textures indicate that hydraulic fracturing was at the origin of the veins. The confinement of the dike system beneath an impact spherule bed suggests that the hydrothermal circulations were triggered by the impact and located at the external margin of a large crater. From the geometry of the dikes and the petrography of the cherts, we infer that the fluid that invaded the fractures was thixotropic. On one hand, the injection of black chert into extremely fine fractures is evidence for low viscosity at the time of injection; on the other hand, the lack of closure of larger veins and the suspension of large fragments in a chert matrix provide evidence of high viscosity soon thereafter. The inference is that the viscosity of the injected fluid increased from low to high as the fluid velocity decreased. Such rheological behavior is characteristic of media composed of solid and colloidal particles suspended in a liquid. The presence of abundant clay-sized, rounded particles of silica, carbonaceous matter and clay minerals, the high proportion of siliceous matrix and the capacity of colloidal silica to form cohesive 3-D networks through gelation, account for the viscosity increase and thixotropic behavior of the fluid that filled the veins. Stirring and

  7. An enigmatic fossil fungus from the 410 Ma Rhynie chert that resembles Macrochytrium (Chytridiomycota) and Blastocladiella (Blastocladiomycota).

    Science.gov (United States)

    Krings, Michael; Taylor, Thomas N; Martin, Helmut

    2016-03-01

    Litter layers in the Lower Devonian (~ 410 Ma) Rhynie chert were inhabited by a wide variety of saprotrophic fungi, however, only a few of these organisms have been described formally. A new microfungus, Trewinomyces annulifer gen. et sp. nov., occurs as tufts on decaying land plant axes from the Rhynie chert. The fungus consists of an intramatrical rhizoidal system and an erect extramatrical hypha (stalk) that bears a single, terminal sporangium. One or two successive rings often are present in the stalk immediately below the sporangium base. Overall morphology of T. annulifer resembles the extant genera Macrochytrium (Chytridiomycota) and Blastocladiella (Blastocladiomycota). However, the rhizoids are septate or pseudoseptate, a feature not known in extant zoosporic fungi, and thus render the systematic affinities of T. annulifer unresolved. Trewinomyces annulifer offers a rare view of the morphology of a distinctive Early Devonian saprotrophic microfungus. PMID:26740543

  8. Dating chert (diagenetic silica) using in-situ produced Be-10 : possible complications revealed through a comparison with Cl-36 applied to coexisting limestone

    OpenAIRE

    Zerathe, S.; Braucher, R.; Lebourg, T.; Bourles, D.; M. Manetti; Leanni, Laetitia

    2013-01-01

    This paper highlights potential complications that may arise while using in situ produced Be-10 to date exposure or burial events using diagenetic silica (chert). The initiation and evolution of large gravitational collapses in sedimentary rocks were constrained using cosmic ray exposure dating. Because these collapses occurred in a stratigraphic level composed of chert (diagenetic silica) concretions interbedded in limestone layers, their development was studied by performing in situ-produce...

  9. Early diagenetic quartz formation at a deep iron oxidation front in the Eastern Equatorial Pacific – A modern analogue for banded iron/chert formations?

    OpenAIRE

    Meister, Patrick; Chapligin, Bernhard; Picard, Aude; Meyer, Hanno; Fischer, Cornelius; Rettenwander, Daniel; Amthauer, Georg; Vogt, Christoph; Ivano W Aiello

    2014-01-01

    The mechanisms of early diagenetic quartz formation under low-temperature conditions are still poorly understood. In this study we investigated lithified cherts consisting of microcrystalline quartz recovered near the base of a 420 m thick Miocene–Holocene sequence of nannofossil and diatom ooze at a drill site in the Eastern Equatorial Pacific (Ocean Drilling Program Site 1226). Precipitation seems still ongoing based on a sharp depletion in dissolved silica at the depth of the cherts. Also,...

  10. Interpretation models of the distribution of Bavarian chert and Carpathian obsidian in the Neolithic of the Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Řídký, Jaroslav; Burgert, Pavel; Končelová, Markéta

    Glasgow : University of Glasgow, 2015 - (Campbell, L.). s. 139 ISBN N. [Annual Meeting of the European Association of Archaeologists /21./. 02.09.2015-05.09.2015, Glasgow] R&D Projects: GA ČR GA15-16963S Institutional support: RVO:67985912 Keywords : Neolithic * distribution of Bavarian chert and Carpathian obsidian * chipped stone industry Subject RIV: AC - Archeology, Anthropology, Ethnology http://eaaglasgow2015.com/wp-content/uploads/2015/07/EAA-Glasgow-Abstract-Book.pdf

  11. The rheological behaviour of fracture-filling cherts: example of Barite Valley dikes, Barberton Greenstone Belt, South Africa

    OpenAIRE

    M. Ledevin; Arndt, N.; Davaille, A.; Ledevin, R.; Simionovici, A.

    2015-01-01

    In the Barberton Greenstone Belt, South Africa, a 100–250 m thick complex of carbonaceous chert dikes marks the transition from the Mendon Formation to the Mapepe Formation (3260 Ma). The sub-vertical- to vertical position of the fractures, the abundance of highly shattered zones with poorly rotated angular fragments and common jigsaw fit, radial structures, and multiple injection features point to repetitive hydraulic fracturing that released overpressured fluids trapped wi...

  12. The rheological behavior of fracture-filling cherts: example of Barite Valley dikes, Barberton Greenstone Belt, South Africa

    OpenAIRE

    M. Ledevin; Arndt, N.; Simionovici, A.

    2014-01-01

    A 100 m-thick complex of near-vertical carbonaceous chert dikes marks the transition from the Mendon to Mapepe Formations (3260 Ma) in the Barberton Greenstone Belt, South Africa. Fracturing was intense in this area, as shown by the profusion and width of the dikes (ca. 1 m on average) and by the abundance of completely shattered rocks. The dike-and-sill organization of the fracture network and the upward narrowing of some of the large veins indicate that at...

  13. Diagenetic-metallogenic ages of pyritic cherts and their implications in Mojiang nickel-gold deposit in Yunnan Province, China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Diagenetic-metallogenic ages of pyritic cherts formed by the syn-sedimentation of hydrothermal vent and ages of the Jinchang Rock Formation in the Mojiang large nickel-gold deposit in the Ailaoshan gold metallogenic belt have been discussed on the basis of chronology of isotopic geochemistry.. Nickel-gold.bearing pyritic cherts in the mining were formed by syn-sedimentation of hydrothermal vent in the Late Devonian, i.e. age by Sm-Nd isochronal method (t)= (358 4±8.6) (2σ) Ma and age by Rb-Sr isochronal method (t)= (354.74±0.72) (2σ) Ma. On the other hand, deep-water cherts from the Jinchang Rock Formation of the Upper Devonian in the area were initiated at the same time; that is,age by Sm-Nd isochronal method (t) = (359±21) (2σ) Ma and age by Rb-Sr isochronal method (t) = (358.02±0.30) (2σ)Ma.

  14. Genesis of a regionally widespread celadonitic chert ironstone bed overlying upper Lias manganese deposits, Hungary

    Science.gov (United States)

    Polgari, Marta; Hein, J.R.; Toth, M.; Brukner-Wein, A.; Vigh, T.; Biro, L.; Cserhati, C.

    2010-01-01

    Mineralogy and chemical composition are presented for a chert-ironstone bed that overlies the ??rk??t Mn deposit. This bed is mottled green-brown in its lower and upper parts, which are composed of quartz, goethite and celadonite. These parts of the bed are interpreted to be strongly altered tuffs, reflecting oxidic, low-temperature alteration of a hydrated, Fe-rich, Al-poor tuff, and K and Mg uptake from seawater. The middle part of the bed is a mineralized bacterial mat (quartz, goethite). Textures resembling bacterial cells and colonies are common, with wavy, bulbous laminations composed of mounds overlying a mesh-work stromatolite-like texture constructed of micrometre-size Fe oxides. This bed is concordant with the underlying Mn deposit and marks the termination of Mn accumulation. Although no genetic connection exists between the two, the rocks adjacent to the contact record the oceanographic and bottom-water conditions extant when accumulation of one of the major Mn deposits of Europe ended, when the Transdanubian Range was located in the middle of the Adria-Apulian microcontinent between the Neotethys and Atlantic-Ligurian seaways. A pyroclastic origin for part of the bed has significance for the Toarcian of Central Europe because evidence of volcanism occurring at that time is otherwise sparse. ?? 2010 Geological Society of London.

  15. Dolomitized cells within chert of the Permian Assistência Formation, Paraná Basin, Brazil

    Science.gov (United States)

    Calça, Cléber P.; Fairchild, Thomas R.; Cavalazzi, Barbara; Hachiro, Jorge; Petri, Setembrino; Huila, Manuel Fernando Gonzalez; Toma, Henrique E.; Araki, Koiti

    2016-04-01

    Dolomitic microscopic structures in the form of microspheres, "horseshoe- shaped" objects, and thin botryoidal crusts found within microfossiliferous chert within stromatolites of the Evaporite Bed (EB) of the Permian Assistência Formation, Irati Subgroup, Paraná Basin, Brazil, have been investigated by means of optical microscopy, X-ray fluorescence, scanning electron microscopy, Raman spectrometry and energy-dispersive X-ray spectrometry. The microspheres were identified as dolomitized coccoidal cyanobacteria based on similarity in size, spheroidal and paired hemispheroidal morphologies and colonial habit to co-occurring silicified organic-walled cyanobacteria embedded within the same microfabric and rock samples. The co-occurrence of dolomite, pyrite framboids, and abundant dispersed carbonaceous material and silicified cells is consistent with a hypersaline depositional environment with abundant cyanobacterial mats and elevated Mg2 +/Ca2 + ratios and reducing conditions with active anoxic microbial processes near the water-(bio)sediment interface. The abundance of extracellular polymeric substances facilitated anoxic microbial processes (sulfate reduction), providing essential conditions for possible primary microbially induced dolomitization. In most of the dolomitized cells dolomite occurs only as an external layer; in fully dolomitized cells magnesium is richest in the outermost layer. Presumably, the dolomitization process was favored by the presence of anoxic microbial degraders and negatively charged functional groups at the surface of the cyanobacterial cells. Botryoidal dolomite rims of silica-filled fenestrae formed by a similar process and inherited the botryoidal morphology of the cell as originally lining the fenestrae. Silicification interrupted the dolomitization of the largely organic biosediment, mostly by permineralization, but locally by substitution, thereby preserving not only dolomitic microspheres, but also huge numbers of structurally

  16. Biogenic nitrogen and carbon in Fe-Mn-oxyhydroxides from an Archean chert, Marble Bar, Western Australia

    Science.gov (United States)

    Pinti, Daniele L.; Hashizume, Ko; Orberger, Beate; Gallien, Jean-Paul; Cloquet, Christophe; Massault, Marc

    2007-02-01

    To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar formation, Western Australia, and to gain insights on their origin and potential biogenicity, we conducted nuclear reaction analyses (NRA) and carbon and nitrogen isotope ratio measurements on various samples from the 3460-Myr-old Fe-rich Marble Bar chert. The Marble Bar chert formed during the alteration of basaltic volcanoclastic rocks with Fe- and Si-rich hydrothermal fluids, and the subsequent precipitation of magnetite, carbonates, massive silica, and, locally, sulfides. At a later stage, the magnetite, sulfides, and carbonates were replaced by Fe-Mn-oxyhydroxides. Nuclear reaction analyses indicate that most of the N and C resides within these Fe-Mn-oxyhydroxides, but a minor fraction is found in K-feldspars and Ba-mica dispersed in the silica matrix. The N and C isotopic composition of Fe-oxides suggests the presence of a unique biogenic source with δ 15NAIR values from +6.0 +/- 0.5‰ to 7.3 +/- 1.1‰ and a δ 13CPDB value of -19.9 +/- 0.1‰. The C and N isotope ratios are similar to those observed in Proterozoic and Phanerozoic organic matter. Diffusion-controlled fractionation of N and C released during high combustion temperatures indicates that these two elements are firmly embedded within the iron oxides, with activation energies of 18.7 +/- 3.7 kJ/mol for N and 13.0 +/- 3.8 kJ/mol for C. We propose that N and C were chemisorbed on iron and were subsequently embedded in the crystals during iron oxidation and crystal growth. The Fe-isotopic composition of the Marble Bar chert (δ 56Fe = -0.38 +/- 0.02‰) is similar to that measured in iron oxides formed by direct precipitation of iron from hydrothermal plumes in contact with oxygenated waters. To explain the N and C isotopic composition of Marble Bar chert, we propose either (1) a later addition of N and C at the end of Archean when oxygen started to rise or (2) an earlier development of localized oxygenated

  17. Magneto-biostratigraphy of the Upper Triassic bedded chert succession from the Mino Belt, Inuyama area, central Japan: correlation to Tethyan sections

    Science.gov (United States)

    Yamashita, D.; Koji, U.; Onoue, T.

    2015-12-01

    Late Triassic magnetostratigraphy and biostratigraphy has recently been investigated in both continental and Tethyan marine sequences (Hounslow and Muttoni, 2010). However, there is no agreed on geomagnetic polarity timescale (GPTS) for the Late Triassic, because of poor age control of many Late Triassic magnetostratigraphic sections, missing or duplicated intervals, and within- section changes in sedimentation rates (Lucas, 2013). Here we present lower Carnian to upper Norian magnetostratigraphy and biostratigraphy (conodont and radiolaria) of the Upper Triassic bedded chert successions from the Mino belt, Inuyama area, central Japan. The bedded chert was deposited in a mid-oceanic basin of the Panthalassa Ocean. Chert samples were collected at two sections (Sakahogi and Momotaro sections) where Sugiyama (1997) investigated the radiolarian biostratigraphy. Based on detailed study of the conodont biostratigraphy from the study sections, five conodont zones are recognized in ascending order as follows: lower Carnian lower Quadralella polygnathiformis zone, upper Carnian upper Quadralella polygnathiformis zone, lower Norian Epigondolella quadrata zone, middle Norian Epigondolella postera zone, and late Norian Epigondolella bidentata zone. Thermal demagnetization showed four distinct remanent magnetization components from the cherts. The highest blocking temperature component shows positive reversal test and is regarded as the primary remanent magnetization, which produced a magnetostratigraphy of the lower Carnian to upper Norian. The magnetostratigraphy consists of 15 substantive normal- reverse polarity chrons, defined by sampling at 256 stratigraphic levels. Paleomagnetic polarity reversals observed at the vicinity of Carnian/Norian boundary and middle Norian/upper Norian boundary are correlated with those of Tethyan marine sections (Pizzo Mondello and Silickà Brezovà). Assuming that the rocks in the two Tethyan marine sections were deposited in the Northern

  18. Biogeochemical and micropaleontological study of black chert, Sete Lagoas Formation, Bambui Group (Late Proterozoic), Sao Gabriel (GO), Brazil

    International Nuclear Information System (INIS)

    The biogeochemical study of amorphous and structured organic matter (OM) in two samples of thinly laminated black cherts (SG-1 and SG-2) from Sete Lagoas Formation, State of Goias, Brazil, is presented. The spectra analysis of infra-red, electron paramagnetic resonance and isotope ratio of C-12 and C-13 shown that: the amorphous OM consists of a soluble fraction (SF) and a insoluble fraction (Kerogen), which only the latter is syngenetic; the allochthonous SF comes from several sources, mainly from Phanerozoic sediments and soil contamination; the SG-1 and SG-2 Kerogens have δ 13C values (-27.2 per mille and - 29.2 per mille respectively), which suggest OM photosynthetized and submitted to a mild thermal hystory; although the preserved microbiota is dominated by allochthonous elements (colonial fragments) and planktonic forms, both Kerogens were derived for the most part from photo-autotrophic benthonic communities, probably responsible for the lamination in the original carbonate rock, both SG-1 and SG-2 Kerogens exhibits O/C and H/C ratios comparable to Proterozoic humic Kerogens (type IV); the preserved microflora represents a microbial community of the chert-algae facies typical of the Middle and upper Proterozoic; and the occurence of rare acritarchs (Kildinella spp.) in the microflora is biostratigraphically significant in that it suggests a Late Riphean or Vendian age (950-570 m.y.) for the Sete Lagoas Formation. (Author)

  19. Raman Imaging Spectroscopy of a Putative Microfossil from the ∼3.46 Ga Apex Chert: Insights from Quartz Grain Orientation

    OpenAIRE

    Bower, D.M.; Steele, A.; Fries, M.D.; Green, O.R.; Lindsay, J.F.

    2016-01-01

    Abstract The utility of nondestructive laser Raman for testing the biogenicity of microfossil-like structures in ancient rocks is promising, yet results from deposits like the ∼3.46 Ga Apex chert remain contentious. The essence of the debate is that associated microstructures, which are not purported to be microfossils, also contain reduced carbon that displays Raman D- and G-band peaks similar to those seen in the purported microfossils. This has led to the hypothesis that all features inclu...

  20. EPR study of thermally treated Archean microbial mats analogues and comparison with Archean cherts: towards a possible marker of oxygenic photosynthesis?

    Science.gov (United States)

    Bourbin, M.; Derenne, S.; Westall, F.; Gourier, D.; Gautret, P.; Rouzaud, J.-N.; Robert, F.

    2012-04-01

    The datation of photosynthesis apparition remains an open question nowadays: did oxygenic photosynthesis appear just before the Great Oxidation Event (GOE) of the atmosphere, 2.3 to 2.4 Gyr ago, or does it originate much earlier? It is therefore of uttermost interest to find markers of oxygenic photosynthesis, applicable to samples of archean age. In order to handle this problem, Microcoleus Chtonoplastes cyanobacteria and Chloroflexus-like non-oxygenic photosynthetic bacteria, were studied using Electron Paramagnetic Resonance (EPR) spectroscopy, a high sensitivity technique for the study of organic radicals in mature geological samples (coals, cherts, meteorites...). M. chtonoplastes and Chloroflexus-like bacteria were sampled in mats from the hypersaline lake "La Salada de Chiprana" (Spain), an analogue to an Archean environment, and were submitted to accelerated ageing through cumulative thermal treatments. For thermal treatment temperatures higher than 620° C, a drastic increase in the EPR linewidth of the oxygenic photosynthetic bacteria (M. chtonoplastes) occurred, as compared with the anoxygenic photosynthetic one (Chloroflexus-like). The EPR study of a thermally treated mixture of the two bacteria evidences that this linewidth increase is driven by catalytic reaction at high temperatures on an element selectively fixed by M. chtonoplastes. Based on comparative EDS analyses, Mg is a potential candidate for this catalytic activity but its precise role and the nature of the reaction are still to be determined. The EPR study of organic radicals in chert rocks of ages ranging from 0.42 to 3.5 Gyr, from various localities and that underwent various metamorphisms, revealed a dispersion of the signal width for the most mature samples. This comparative approach between modern bacterial samples and Precambrian cherts leads to propose the EPR linewidth of mature organic matter in cherts as a potential marker of oxygenic photosynthesis. If confirmed, this marker

  1. Paleomagnetism of the Marble Bar Chert Member, Western Australia: Implications for apparent polar wander path for Pilbara craton during Archean time

    Science.gov (United States)

    Suganuma, Yusuke; Hamano, Yozo; Niitsuma, Sachiko; Hoashi, Masamichi; Hisamitsu, Toshio; Niitsuma, Nobuaki; Kodama, Kazuto; Nedachi, Munetomo

    2006-12-01

    The Archean Biosphere Drilling Project (ABDP) drilled a continuous 270 m long oriented core from the Towers Formation, which includes the Marble Bar Chert Member (3456.1-3476.0 Ma) in the Pilbara craton, northwestern Australia. A paleomagnetic study of 261 discrete specimens, collected from a 158.5 to 182.0 m section of the Marble Bar Chert Member, revealed two distinct magnetic components (LT and MT). The MT component yields seven different mean paleomagnetic directions clustered as MB1 to MB7. These, together with the published paleomagnetic poles of early Archean rocks from the Pilbara craton, draw a continuous paleomagnetic pole path, which likely to be regarded as the early to late Archean apparent polar wander path (APWP) for the Pilbara craton. The APWP implies that the Pilbara craton underwent a latitudinal drift of about 21° during the interval when the magnetization of the Marble Bar Chert Member was acquired. The estimated speed of the lateral drift is 12-112 cm/yr (120-1120 km/Myr), which is large compared with current plate motion velocities, suggesting that continents might have moved during the Archean faster than in the Phanerozoic.

  2. Cherts from the Yangla copper deposit, western Yunnan Province: geochemical characteristics and relationship with massive sulfide mineralization

    Institute of Scientific and Technical Information of China (English)

    PAN; Jiayong; (

    2001-01-01

    [1]Wei Junqi, Zhan Mingguo, Lu Yuanfa et al., Geochemistry of granitoid from the Yangla ore district, Geology and Mineral Resources of South China (in Chinese), 1997 (4): 50.[2]He Longqing, Zhan Mingguo, Lu Yuanfa, Division of sequence stratigraphy and study on ore-bearing beds in the Yangla copper orefield, western Yunnan, Geology and Mineral Resources of South China (in Chinese), 1998 (3): 37.[3]Zhan Mingguo, Lu Yuanfa, Chen Shifang et al., Formation condition and type of the Yangla large scale copper deposit, Western Yunnan, Mineral Deposits (in Chinese), 1998, 17 (supplement): 183.[4]Lu Yuanfa, Chen Kaixu, Zhan Mingguo et al., Geochemical evidence of exhalative-sedimentary ore-bearing skarns in Yangla copper mineralization concentrated Area, Earth Science (in Chinese), 1999, 24(3): 298.[5]Yomamoto, K., Geochemical characteristics and depositional environments of cherts and associated rocks in the Franciscan and Shimanto terranes, Sedimentary Geology, 1987, 52: 65.[6]Zhou, Y. Z., Geochemical characteristics of siliceous rocks originated from a fossil hydrothermal system in the upper Devonian strata, Guangxi, southern China, Acta Sedimentologia, 1990, 8 (3): 75.[7]Zhou Yongzhang, Geology and Geochemistry of Hetai Gold Field, Southern China, Guangzhou: South China University of Technology Press, 1993, 53-107.[8]Bostroem, K., Harold, R., Oiva, J., Provenance and accumulation rates of opaline silica, Al, Fe, Tl, Mn, Cu, Ni and Co in Pacific pelagic sediment, Chem. Geol., 1973, 11: 123.[9]Herzig, P. M., Becker, K. P., Stoffers, P. et al., Hydrothermal silica chimney field in the Galapagos rift center at 81°W, Earth Pla. Sci. Lett., 1987, 52: 65.[10] Douthitt, C. B., The geochemistry of the stable isotopes of the silicon, Geochim. Cosmochim. Acta, 1982, 16: 129.[11] Ying Hanlong, Cai Xinping, Liu Bingguang, Geochemical features and formation of auriferous cherts in Mojiang Gold Mine, Yunnan, Geochemistry (in Chinese), 1999

  3. Paleomagnetism of Jurassic radiolarian chert above the Coast Range ophiolite at Stanley Mountain, California, and implications for its paleogeographic origins

    Science.gov (United States)

    Hagstrum, J.T.; Murchey, B.L.

    1996-01-01

    Upper Jurassic red tuffaceous chert above the Coast Range ophiolite at Stanley Mountain, California (lat 35??N, long 240??E), contains three components of remanent magnetization. The first component (A; removed by ???100-???200 ??C) has a direction near the present-day field for southern California and is probably a recently acquired thermoviscous magnetization. A second component (B; removed between ???100 and ???600 ??C) is identical to that observed by previous workers in samples of underlying pillow basalt and overlying terrigenous sedimentary rocks. This component has constant normal polarity and direction throughout the entire section, although these rocks were deposited during a mixed polarity interval of the geomagnetic field. The B magnetization, therefore, is inferred to be a secondary magnetization acquired during accretion, uplift, or Miocene volcanism prior to regional clockwise rotation. The highest temperature component (C; removed between ???480 and 680 ??C) is of dual polarity and is tentatively interpreted as a primary magnetization, although it fails a reversal test possibly due to contamination by B. Separation of the B and C components is best shown by samples with negative-inclination C directions, and a corrected mean direction using only these samples indicates an initial paleolatitude of 32??N ?? 8??. Paleobiogeographic models relating radiolarian faunal distribution patterns to paleolatitude have apparently been incorrectly calibrated using the overprint B component. Few other paleomagnetic data have been incorporated in these models, and faunal distribution patterns are poorly known and mostly unqualified. The available data, therefore, do not support formation of the Coast Range ophiolite at Stanley Mountain near the paleoequator or accretion at ???10??N paleolatitude, as has been previously suggested based on paleomagnetic data, but indicate deposition near expected paleolatitudes for North America (35??N ?? 4??) during Late Jurassic

  4. 57Fe Mössbauer analysis of the Upper Triassic-Lower Jurassic deep-sea chert: Paleo-redox history across the Triassic-Jurassic boundary and the Toarcian oceanic anoxic event

    International Nuclear Information System (INIS)

    We investigated the paleo-redox change across the Triassic-Jurassic (T-J) boundary (∼200 Ma) and the Early Toarcian oceanic anoxic event (T-OAE; ∼183 Ma) recorded in the Upper Triassic to Lower Jurassic pelagic deep-sea cherts in the Inuyama area, Central Japan. The present 57Fe Mössbauer spectroscopic analysis for these cherts identified five iron species, i.e., hematite (α-Fe2O3), pyrite (FeS2), paramagnetic Fe3 + , and two paramagnetic Fe2 +  with different quadrupole splittings. The occurrence of hematite and pyrite in deep-sea cherts essentially indicates primary oxidizing and reducing depositional conditions, respectively. The results confirmed that oxidizing conditions persisted in deep-sea across the T-J boundary. In contrast, across the T-OAE, deep-sea environment shifted to reducing conditions. The first appearance of the gray pyrite-bearing chert marked the onset of the deep-sea oxygen-depletion in the middle Pliensbachian, i.e., clearly before the shallow-sea T-OAE.

  5. Petrographic and SIMS pyrite sulfur isotope analyses of Ediacaran chert nodules: Implications for microbial processes in pyrite rim formation, silicification, and exceptional fossil preservation

    Science.gov (United States)

    Xiao, Shuhai; Schiffbauer, James D.; McFadden, Kathleen A.; Hunter, Jerry

    2010-09-01

    The lower Ediacaran Doushantuo Formation in the Yangtze Gorges area contains exceptionally preserved microfossils, including the earliest known animal resting eggs and embryos. These fossils are preserved in cm-sized chert nodules, which typically have a microbial mat fragment in the center, a silica cortex, a pyrite rim, and an outer rim of blocky calcite. Petrographic analysis indicates that the formation of the blocky calcite rim postdates that of the pyrite rim and silica cortex. The pyrite rim grew centripetally during early diagenesis, representing a reaction front that was determined by the dynamics between ambient Fe 2+ and H 2S, the latter of which was derived from bacterial sulfate reduction (BSR) of mat fragment in nodule center. The silica cortex was formed pervasively through replacement of carbonate sediments prior to compaction. Secondary ion mass spectroscopy (SIMS) sulfur isotopes of individual pyrite crystals (δ 34S py - SIMS) in pyrite rims and matrices show highly positive values (15.2-39.8‰). The pyrite rims do not show an isotopic gradient between small crystals formed in outer rim during early diagenesis and large crystals formed in inner rim during subsequent overgrowth. Although rim pyrite in the same chert nodule has consistent δ 34S py - SIMS values, there are significant spatial and stratigraphic variations in δ 34S py - SIMS values of both matrix and rim pyrite. Overall, isotopic fractionation between pyrite and carbonate associated sulfate (CAS) is small (< 22‰). The isotopic and petrographic data can be interpreted as evidence for rapid BSR of highly metabolizable organic matter in a diagenetic environment with limited sulfate availability, local anoxia, high Fe 2+ concentration, and low sedimentation rate. The embryonic nodules nucleated on microbial mat fragments and stayed in the BSR zone during early diagenesis, when rapid BSR in the nodule center generated outward-diffusing H 2S that was confined by readily available Fe 2

  6. Paleomagnetism of Triassic bedded chert from Japan for determining the age of an impact ejecta layer deposited on peri-equatorial latitudes of the paleo-Pacific Ocean: A preliminary analysis

    Science.gov (United States)

    Uno, Koji; Yamashita, Daisuke; Onoue, Tetsuji; Uehara, Daiki

    2015-12-01

    Bedded chert samples from the Norian (Upper Triassic) Sakahogi section of the Mino Terrane in the Inuyama area, southwest Japan, have been collected for paleomagnetic study in order to determine the age of an impact ejecta layer interbedded within it and the paleolatitude of its deposition. Thermal demagnetization of the bedded chert samples revealed four distinct remanent magnetization components. The last demagnetized component with both polarities is interpreted to be the primary magnetization, which produced the first magnetostratigraphic data of the middle to upper Norian from Panthalassa, consistent with Tethyan magnetostratigraphic sections. Tie points were derived from paleomagnetic and paleontological data, from which the stratigraphic position of the ejecta layer was compared with the astronomically tuned geomagnetic polarity time scale (APTS). The age of ejecta layer is estimated to be about 212 Ma. This magnetostratigraphic age is consistent with the radiometric age of the Manicouagan impact that formed the second largest known crater in the Phanerozoic at Quebec, Canada. The results of this study, as well as previous studies, suggest that the chert section, which includes the ejecta layer, was deposited within a paleolatitude range of 0.3-14.4°N. This indicates that the material ejected by the Manicouagan impact event reached near the equatorial region of the paleo-Pacific Ocean.

  7. Raman Imaging Spectroscopy of a Putative Microfossil from the ∼3.46 Ga Apex Chert: Insights from Quartz Grain Orientation.

    Science.gov (United States)

    Bower, D M; Steele, A; Fries, M D; Green, O R; Lindsay, J F

    2016-02-01

    The utility of nondestructive laser Raman for testing the biogenicity of microfossil-like structures in ancient rocks is promising, yet results from deposits like the ∼3.46 Ga Apex chert remain contentious. The essence of the debate is that associated microstructures, which are not purported to be microfossils, also contain reduced carbon that displays Raman D- and G-band peaks similar to those seen in the purported microfossils. This has led to the hypothesis that all features including reported microfossils are due to compression of nonfossil carbon during crystal growth around quartz spherulites or more angular crystals. In this scenario, the precursor to this macromolecular carbon may or may not have been of biogenic origin, while the arcuate and linear features described would be pseudofossils. To test this hypothesis, we have undertaken 2-D micro-Raman imaging of the Eoleptonema apex holotype and associated features using instrumentation with a high spatial and spectral resolution. In addition to this, we utilized the ratio of two Raman active quartz mode intensities (I129/I461) to assess quartz grain orientation and grain-splitting artifacts. These data lead us to conclude that the holotype of Eoleptonema apex is a sheet-shaped pseudofossil that appears to be a carbon infilled intragranular crack; therefore other holotypes should be carefully reexamined for syngenicity. PMID:26848838

  8. Late Olenekian Radiolarians from Bedded Chert of Ashio Terrane, Northeast Japan,and Faunal Turnovers in Western Panthalassa during Early Triassic

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Anisian faunas, respectively, and is herein named the Minowa fauna. Study of the literature indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian-Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic. The first turnover is the Paleozoic-type radiolarian extinction at the Permian-Triassic boundary, the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic-type radiolarian faunas that are characterized by multi-segmented Nassellaria.

  9. Selection of Portable Spectrometers for Planetary Exploration: A Comparison of 532 nm and 785 nm Raman Spectroscopy of Reduced Carbon in Archean Cherts.

    Science.gov (United States)

    Harris, Liam V; Hutchinson, Ian B; Ingley, Richard; Marshall, Craig P; Marshall, Alison Olcott; Edwards, Howell G M

    2015-06-01

    Knowledge and understanding of the martian environment has advanced greatly over the past two decades, beginning with NASA's return to the surface of Mars with the Pathfinder mission and its rover Sojourner in 1997 and continuing today with data being returned by the Curiosity rover. Reduced carbon, however, is yet to be detected on the martian surface, despite its abundance in meteorites originating from the planet. If carbon is detected on Mars, it could be a remnant of extinct life, although an abiotic source is much more likely. If the latter is the case, environmental carbonaceous material would still provide a source of carbon that could be utilized by microbial life for biochemical synthesis and could therefore act as a marker for potential habitats, indicating regions that should be investigated further. For this reason, the detection and characterization of reduced or organic carbon is a top priority for both the ESA/Roscosmos ExoMars rover, currently due for launch in 2018, and for NASA's Mars 2020 mission. Here, we present a Raman spectroscopic study of Archean chert Mars analog samples from the Pilbara Craton, Western Australia. Raman spectra were acquired with a flight-representative 532 nm instrument and a 785 nm instrument with similar operating parameters. Reduced carbon was successfully detected with both instruments; however, its Raman bands were detected more readily with 785 nm excitation, and the corresponding spectra exhibited superior signal-to-noise ratios and reduced background levels. PMID:26060980

  10. 安徽巢湖地区中二叠统栖霞组灰岩中燧石成因%Origin of Nodular Cherts in Limestones in Middle Permian Qixia Formation,Chaohu,Anhui Province

    Institute of Scientific and Technical Information of China (English)

    杨锐; 李红; 柳益群; 雷川; 雷云; 冯诗海

    2014-01-01

    安徽省巢湖地区中二叠统栖霞组以发育一套滨海沼泽-浅海碳酸盐台地环境为主的细碎屑岩至碳酸盐岩沉积建造为特征,灰岩中常见结核状及条带状燧石。燧石多为椭球状和串珠状,部分燧石与灰岩间发育宽约0.5 cm的过渡带。镜下观察灰岩为微晶生物碎屑灰岩;过渡带也多由微晶方解石组成,多数钙质生物壳体被石英充填或半充填,扫描电镜下可见方解石微溶、石英充填溶孔的现象;燧石主要为隐晶及微晶石英,生物碎屑类型与灰岩中基本一致,且多被石英交代。岩石学特征表明死亡的生物在腐烂降解过程中形成的有机酸抑制了碳酸钙的沉淀,并使部分生物碎屑及灰泥发生溶蚀,胶质二氧化硅沉淀,形成燧石结核。燧石中w(Al)/w(Al+Fe+Mn)平均值为0.63,远大于热水沉积硅质岩的最大值0.35;Fe/Ti平均值为9.5,小于热水成因的最小值20;Al-Fe-Mn三角图投点位于非热液成因区域;燧石中Al2 O3含量平均值为0.20%,远高于MgO、Na2 O、K2 O的含量。分析认为,该区燧石结核的二氧化硅可能来源于陆源物质。%The Middle Permian Qixia Formation in Chaohu area,Anhui Province,was mainly composed of fine-grained clastic rocks and limestones which were deposited in the coastal marsh and carbonate platform. Limestones were characterized by nodular and banded cherts.Most of cherts were axiolitic and moniliform in outcrops.Among some cherts and limestones developed transitional belts with 0.5 cm width around cherts.The limestones were composed of packstone and wackestone which consisted mainly of fragments of fossils and micro-crystalline calcite through polarizing microscope observation.The transitional belts were mainly composed of mi-crites and the aragonite-shell fragments which were replaced or half replaced by quartz prior to the micrites. Meanwhile the amorphous silica was found to be

  11. Physics of crustal fracturing and chert dike formation triggered by asteroid impact, ˜3.26 Ga, Barberton greenstone belt, South Africa

    Science.gov (United States)

    Sleep, Norman H.; Lowe, Donald R.

    2014-04-01

    asteroid impacts, reflected in the presence of spherule beds in the 3.2-3.5 Ga Barberton greenstone belt (BGB), South Africa, generated extreme seismic waves. Spherule bed S2 provides a field example. It locally lies at the contact between the Onverwacht and Fig Tree Groups in the BGB, which formed as a result of the impact of asteroid (possibly 50 km diameter). Scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site, where they widely damaged Onverwacht rocks over much of the BGB. Lithified sediments near the top of the Onverwacht Group failed with opening-mode fractures. The underlying volcanic sequence then failed with normal faults and opening-mode fractures. Surficial unlithified sediments liquefied and behaved as a fluid. These liquefied sediments and some impact-produced spherules-filled near-surface fractures, today represented by swarms of chert dikes. Strong impact-related tsunamis then swept the seafloor. P waves and Rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves. The duration of extreme shaking was also far longer, probably hundreds of seconds, than that from strong earthquakes. Dynamic strains of ˜10-3 occurred from the surface and downward throughout the lithosphere. Shaking weakened the Onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open-mode fractures. Coast-parallel opening-mode fractures on the fore-arc coast of Chile, formed as a result of megathrust events, are the closest modern analogs. It is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the Onverwacht rocks.

  12. 皖南皮园村组硅岩的沉积古地理环境及其演化%Sedimentary paleogeographic environment and the evolvement of the Piyuancun chert in Southern Anhui Province

    Institute of Scientific and Technical Information of China (English)

    常华进; 陈雅丽; 刘洪舟; 冯连君; 黄晶

    2014-01-01

    The black Piyuancun chert in Southern Anhui Province was deposited in terminal ediacaran to early cambrian transition period (about 550–532 Ma). The w(Ce)/w(Ce*) and w(LaN)/w(CeN) of the Piyuancun chert samples were 0.68–1.08 (avg. 0.85) and 0.56–1.52 (avg. 1.10), respectively, which indicates that the chert was deposited in the continental margin. Chert samples from the lower part and the upper part of the Lantian section have different rare earth elements (REE) patterns: REE concentrations for chert samples in the lower section are low relative to post-Archean Australian shale (PAAS), and their REE patterns are similar to that of the modern seawater, indicating that the influence of terrigenous detrital has been trivial. Although REE patterns for the chert samples in the upper section maintain some seawater characteristics, such as negative Ce anomaly and positive Y anomaly, they have flat REE patterns that are similar to PAAS, and their REE concentrations are close to that of PAAS, indicating that the influence of terrigenous detrital has been huge. Al2O3 content also displays the characteristics that the content are low in the lower section (0.03%–0.94%, avg. 0.41%) and are high in the upper section (0.74%–5.04%, avg. 2.98%). These geochemical characteristics show that the Piyuancun chert was probably deposited in the continental margin, and the water column became shallow (from basin margin to slope) for regression. The depth of the water column in which the Piyuancun chert deposited probably prompted the water column redox condition to change, and therefore affected the survival, evolution and distribution of early life.%皖南蓝田剖面皮园村组为一套埃迪卡拉纪−寒武纪过渡期(约550∼532 Ma)沉积的黑色硅岩.皮园村组硅岩样品的w(Ce)/w(Ce*)为0.68∼1.08(平均0.85), w(LaN)/w(CeN)为0.56∼1.52(平均1.10),指示它们可能形成于大陆边缘环境.剖面下部与剖面上部样品具有明显不同的稀土

  13. 湖北嘉鱼县蛇屋山金矿硅质岩地球化学特征及成矿环境约束%Geochemistry of Cherts from Shewushan Gold Ore Deposit in Jiayu, Hubei Province and Its Metallogenic Environmental Constraints

    Institute of Scientific and Technical Information of China (English)

    徐萌萌; 徐广东; 孙祥民; 朱本杰; 刘蕴光; 肖凡; 许荣科; 徐永利; 李宝庆

    2012-01-01

    The Shewushan gold deposit is the largest laterite-type gold ore deposit in Asia, and authors discover that cherts covered on the top of the red soil in the gold ore deposit, showing a gradual transition relationship with the silicified limestone. The analysis of cherts approves that the SiO2content is from 96. 87% to 97. 90% , and that the Si/Al ratio ranges from 92. 84 to 287. 66 with average value of 173, therefore, the cherts could be classified as pure cherts. The Al/( Al + Fe + Mn) ratios of chert samples in the research area are between 0. 189 and 0. 388, and the average value is 0. 303, implying that the cherts is of hydrogenous genesis. Al-Fe-Mn diagram shows that the cherts is also hydrothermal type, and the ratios of Ni/Co, Fe/Ti, Ti/V and U/Th show that cherts from Shewushan are hydrothermally sedimentary origin. The ratios of Ce/Ce* and( La/Ce)N is 1. 05-1. 27 and 0. 84 - 1. 12 with average value of 1. 12 and 0. 98, respectively. The trace element V content is 3. 02 -4. 26 μg/g and the ratio of MnO/TiO2 is 1. 0 -2. 0, which indicated that the radiolarian chert formed in transitional environment of continental margin basin. Combining with the macro characteristics, we regard that cherts probably formed in the Carlin-type gold's stage of eliminate carbonatization, which are the product of hy-drothermal activity.%湖北蛇屋山金矿是亚洲最大的红土型金矿,矿区内硅质岩发育,覆于含矿红土层之上,并与硅化灰岩呈渐变过渡.硅质岩主要由微晶和隐晶组成,其SiO2含量为96.87%~97.90%,w( Si)/w(Al)=92.84 ~ 287.66,平均值为173,处于纯硅质岩的范畴.硅质岩样品的w(Al)/w(Al+Fe+ Mn)为0.189 ~0.388,平均值为0.303,具热液成因硅质岩的特征.根据Al、Fe、Mn三角图的投点,认为本研究区硅质岩为热液成因硅质岩.微量元素w(Ni)/w( Co)、w(Fe)/w(Ti)、w(Ti)/w(V)、w(U)/w(Th)也说明了硅质岩具有热水沉积成因.w(Ce )/w( Ce*)为1.05 ~1.27,平均值为1.12,(La

  14. 湘西地区前寒武纪-寒武纪转折期碳酸盐-硅泥质沉积体系的截然转换:地层-沉积样式,形成机理及意义%Sharp transition from carbonates to cherts across the platform margin in western Hunan,south China during Precambrian-Cambrian transition:Stratal-depositional patterns, mechanisms and implications

    Institute of Scientific and Technical Information of China (English)

    汪建国; 陈代钊; 严德天; 韦恒叶; 遇昊

    2011-01-01

    sedimentary facies and their spatial variation across this critical interval. A sharp transition from carbonates to cherts across the platform margin in western Hunan was identified in the earliest Cambrian, indicating syndepositional extensional faulting could have occurred along the transitional zone of platformbasin. Mounded chert,funnelized brecciated chert and vein chert which characterized by unique mineral compositions and internal structures in this transition zone, were formed by submarine hydrothermal venting on the fault-controlled terraces along the margin-to-slope of Yangtze carbonate platform where syndepositional fault/fracture zone could have acted as conduits channeling the hydrothermal fluids heated up by the deep-seated thermal source updip to the seafloor. The bedded chert, mainly distributed in the localities farther basinwards, implies enhanced influences of seawater away the vent fields during deposition. Considering widespread chert along the transitional zone of platform-basin in Yangtze area, intense hydrothermal venting might have occurred along the platform margin such that vast amounts of greenhouse gases,anoxic fluids rich in metal and nonmetal elements would have been released to the ocean/atmosphere, leading to climate warming, oceanic anoxia and oceanic eutrophication. As the hydrothermal activity waned, sea level would rise due to basin subsidence induced by crust cooling, abundant nutrient materials in the deep ocean were then brought to the ocean surface by upwelling currents,which could have increased primary productivity,and facilitated organic accumulation and preservation in the anoxic waters already during the Niutitang interval.

  15. Biography of Jack Holland (1926-2014: Chert expert

    Directory of Open Access Journals (Sweden)

    William Engelbrecht

    2015-03-01

    Full Text Available Jack was born and grew up in Lock Haven Pennsylvania, the son of William G. Holland and Florence (Davies Holland. He had an older brother, William and a younger brother, Donald. Jack spent much of his boyhood roaming the surrounding flood plains of the West Branch of the Susquehanna River looking for arrowheads. As Jack recalled, his parents gave him a great deal of freedom, just asking that he be home in time for dinner. Dr. T. B. Stewart, a Lock Haven dentist, encouraged Jack’s early archaeological interest, helping him to identify specimens. Dr. Stewart had an extensive archaeological collection and had worked with Donald Cadzow, Pennsylvania’s State Archaeologist (1929-1939. Dr. Stewart was also one of the founders of the Society for Pennsylvania Archaeology, an organization with which Jack would later become involved and that bestowed their J. Alden Mason Award on him as a professional who encouraged society members in the “proper pursuit of archaeology.” 

  16. Modern estuarine siliceous spiculites, Tasmania, Australia: A non-polar link to Phanerozoic spiculitic cherts

    Science.gov (United States)

    Reid, C. M.; James, N. P.; Kyser, T. K.; Barrett, N.; Hirst, A. J.

    2008-02-01

    Biosiliceous sedimentary rocks are well known from the geologicrecord and many are correctly interpreted to have formed indeep-water or cold-water environments. Shallow non-polar spiculitesare also known from the rock record, yet no modern analog hasbeen documented for such environments. Bathurst Harbour, anestuarine system in southwest Tasmania, provides this much-neededmodern analog. In this system a sharp halocline separates tannin-richlow-salinity surface waters from clear marine bottom waters.Tannins supply few nutrients and substantially reduce lightpenetration to bottom environments, resulting in a thinned photiczone and the mixing of deeper-water sub-photic biotas of softcorals, bryozoans, and sponges with other organisms more typicalof this temperate shallow-water environment. The well-definedhalocline allows a typically marine biota, including echinoderms,to live in bottom waters of this estuarine setting. The bioclasticfactory, producing both carbonate and siliceous particles, existsin marine subphotic bottom waters of incised channel and shallowrocky environments along the shoreline. Extensive organic-richsoft sediments in protected embayments generate few bioclasts,but contain allochthonous sponge spicules transported from theadjacent bioclastic factory. Trapping of organic material withinthe estuarine system lowers sediment pH and promotes dissolutionof carbonate biofragments, resulting in preferential preservationof siliceous sponge spicules. This situation implies that manybiosiliceous neritic deposits in the rock record may be theresult of similar preferential preservation.

  17. Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the ∼1.9-Ga Gunflint chert

    OpenAIRE

    Wacey, David.; McLoughlin, Nicola; Kilburn, Matt R; Saunders, Martin; Cliff, John B.; KONG, Charlie; Barley, Mark E.; MARTIN D. BRASIER

    2013-01-01

    The 1.88-Ga Gunflint biota is one of the most famous Precambrian microfossil lagerstätten and provides a key record of the biosphere at a time of changing oceanic redox structure and chemistry. Here, we report on pyritized replicas of the iconic autotrophic Gunflintia–Huroniospora microfossil assemblage from the Schreiber Locality, Canada, that help capture a view through multiple trophic levels in a Paleoproterozoic ecosystem. Nanoscale analysis of pyritic Gunflintia (sheaths) and Huroniospo...

  18. A study of the ASR of an aggregate with high chert content by means of ultra-accelerated mortar bar test and pore fluid analysis

    NARCIS (Netherlands)

    Larbi, J.A.; Visser, J.H.M.

    2002-01-01

    Various studies have indicated that the use of some ultra-accelerated mortar bar expansion test methods for assessing the alkali-silica reactivity of concrete aggregates (particularly those using 1 M NaOH solution at 80 oC) can give rise to misleading results causing certain types of aggregates to b

  19. Genesis, Provenance and Classification of Rocks within the Chert Group in Central Europe. Archaeologia Austriaca|Archaeologia Austriaca Band 97-98/2014|

    OpenAIRE

    Brandl, Michael

    2014-01-01

    Raw material determination of prehistoric stone tools is a necessary analytical process towards a fuller understanding of prehistoric resource management. However, archaeologists face a terminological predicament when analysing raw material types present within lithic assemblages. This is chiefly due to the lack of a commonly accepted classification system, further exacerbated when working on an international scale. The principle reason for this situation is the fact that SiO2 modifications w...

  20. "Ich Möchert Schon Einmal Nach Wien" – Mief Und Muff In Franz Xaver Kroetz‘ Oberösterreich (1972 Und Der Brasilianischen Übersetzung Von 1979

    Directory of Open Access Journals (Sweden)

    Werner Heidermann

    2015-06-01

    Full Text Available Alta Áustria ist das Heft No. 20 der Reihe Caderno de Teatro Alemão, die vor rund 30 Jahren von verschiedenen brasilianischen Goethe-Instituten herausgegeben wurde. Die Kroetz-Übersetzung selbst ist in Curitiba entstanden, eine Gruppe von Übersetzern zeichnet für sie verantwortlich, geleitet wurde das Projekt von Heidede Emiliy Liede. Wir gehen der Frage nach, inwieweit das fatal Kleinbürgerliche im Österreich der Siebziger Jahre überhaupt einem brasilianischen Theaterpublikum vermittelbar ist. Wird die Enge der Zweierbeziehung mit ihren Fluchttendenzen als gemeinsame soziale Erfahrung gewertet? Ist Oberösterreich ambitionierte österreichische Landeskunde? Umfassende Zivilisationskritik? Frühe Konsumismuskritik? Inwieweit steht hinter dem Erfolg des Stücks nicht auch ein perfides Behagen am Spießertum der Anderen? In derselben Publikationsreihe erschienen Mensch Meier, Das Nest, und Wer durch Laub geht – mithin ein bedeutender Teil Kroetzscher Theaterdichtung. Der Beitrag wird nach kulturellen Affinitäten fragen und Provokationen einzuordnen versuchen, auch in übersetzungstheoretischer Hinsicht.

  1. "Ich Möchert Schon Einmal Nach Wien" – Mief Und Muff In Franz Xaver Kroetz‘ Oberösterreich (1972 Und Der Brasilianischen Übersetzung Von 1979

    Directory of Open Access Journals (Sweden)

    Werner Heidermann

    2014-06-01

    Full Text Available Alta Áustria ist das Heft No. 20 der Reihe Caderno de Teatro Alemão, die vor rund 30 Jahren von verschiedenen brasilianischen Goethe-Instituten herausgegeben wurde. Die Kroetz-Übersetzung selbst ist in Curitiba entstanden, eine Gruppe von Übersetzern zeichnet für sie verantwortlich, geleitet wurde das Projekt von Heidede Emiliy Liede. Wir gehen der Frage nach, inwieweit das fatal Kleinbürgerliche im Österreich der Siebziger Jahre überhaupt einem brasilianischen Theaterpublikum vermittelbar ist. Wird die Enge der Zweierbeziehung mit ihren Fluchttendenzen als gemeinsame soziale Erfahrung gewertet? Ist Oberösterreich ambitionierte österreichische Landeskunde? Umfassende Zivilisationskritik? Frühe Konsumismuskritik? Inwieweit steht hinter dem Erfolg des Stücks nicht auch ein perfides Behagen am Spießertum der Anderen? In derselben Publikationsreihe erschienen Mensch Meier, Das Nest, und Wer durch Laub geht – mithin ein bedeutender Teil Kroetzscher Theaterdichtung. Der Beitrag wird nach kulturellen Affinitäten fragen und Provokationen einzuordnen versuchen, auch in übersetzungstheoretischer Hinsicht.

  2. SILICON AND OXYGEN ISOTOPIC COMPOSITION OF CHERTS FROM THE GACUN KUROKO-TYPE DEPOSIT, SICHUAN, AND COMPARISON WITH SILICA CHIMNEYS FROM THE MODERN SEAFLOOR%四川呷村黑矿型矿床硅质岩的硅、氧同位素组成及其与现代海底硅质烟囱比较研究

    Institute of Scientific and Technical Information of China (English)

    侯增谦; 吴世迎; T.Urabe

    1996-01-01

    本文首次报道了川西呷村黑矿型矿床硅质岩的硅、氧同位素组成,其δ18O为12.8‰-18.3‰,形成温度约99-120℃,δ30Si为0.0‰-1.5‰,与Mariana和Galapagos热液硅质烟囱的δ30Si值范围基本相当,揭示两者具相似的形成机制.硅质岩和硅质烟囱δ30Si最大值与相伴火山岩δ30Si值一致,反映硅质来自被热液淋滤交代的火山岩系.根据SiO2溶解度-温度关系提出,来自海底之下1-2km处的水-岩反应带、温度高于320℃的初始流体,通过绝热上升或传导冷凝,可在海底形成硫化物矿体,残余热液与海水大量混合及传导冷凝,可产生硅质岩和硅质烟囱.

  3. Petrogenesis and sedimentary environment of the cherts from Yutangha,western Hubei Province: Evidence from silicon, oxygen, carbon and sulfur isotopic compositions%渔塘坝富硒硅质岩成因及沉积环境探讨:硅、氧、碳和硫同位素证据

    Institute of Scientific and Technical Information of China (English)

    冯彩霞; 刘家军; 刘燊; 胡瑞忠; 池国祥

    2009-01-01

    鄂西渔塘坝含碳硅质岩段(P31m)为硒矿床的主要赋硒层位,其硅、氧同位素组成δ30Si变化范围为0.5‰~1.8‰(平均1.25‰);δ18O为22.7‰~27.1‰(平均25.3‰);硅质岩中黄铁矿δ34S的值变化范围为-27.7‰~-5.65‰,幅度大于20‰;硅质岩层位中方解石样品的δ13C值范围为4.19‰~0.52‰.综合研究表明,渔塘坝硅质岩在成因上主要表现为热水沉积特征,成岩温度为45℃,形成于半封闭的浅海至滨浅海(滞留的盆地)缺氧沉积环境.

  4. Carbon isotopic studies of organic matter in Precambrian rocks.

    Science.gov (United States)

    Oehler, D. Z.; Schopf, J. W.; Kvenvolden, K. A.

    1972-01-01

    A survey has been undertaken of the carbon composition of the total organic fraction of a suite of Precambrian sediments to detect isotopic trends possibly correlative with early evolutionary events. Early Precambrian cherts of the Fig Tree and upper and middle Onverwacht groups of South Africa were examined for this purpose. Reduced carbon in these cherts was found to be isotopically similar to photosynthetically produced organic matter of younger geological age. Reduced carbon in lower Onverwacht cherts was found to be anomalously heavy; it is suggested that this discontinuity may reflect a major event in biological evolution.

  5. Characterizing the Biological and Geochemical Architecture of Hydrothermally Derived Sedimentary Deposits: Coupling Micro Raman Spectroscopy with Noble Gas Spectrometry

    Science.gov (United States)

    Bower, D. M.; Conrad, P. G.; Steele, A.; Fries, M. D.

    2016-05-01

    The chemical species in cherts and glass fragments were analyzed using micro Raman spectroscopy in conjunction with measurements of heavy noble gas isotopes to characterize hydrothermally derived sedimentary environments.

  6. 76 FR 80392 - Notice of Inventory Completion: University of Michigan Museum of Anthropology, Ann Arbor, MI

    Science.gov (United States)

    2011-12-23

    ..., 76 chert flakes, 2 grit- tempered ceramic sherds, 7 jars of soil, 5 red ochre samples, and 3 unworked... morphology, dental traits, and pre-contact burial dates, the human ] remains are determined to be...

  7. Objev vápenců s rohovci v Boskovické brázdě

    Czech Academy of Sciences Publication Activity Database

    Krmíček, Lukáš; Bartík, J.; Bubík, M.

    2014-01-01

    Roč. 99, č. 2 (2014), s. 73-84. ISSN 1211-8796 Institutional support: RVO:67985831 Keywords : South Moravia * Boskovice Furrow * micritic-peloidal/oolitic limestone * dark chert * sabkha environment Subject RIV: DB - Geology ; Mineralogy

  8. Bavorské jurské rohovce Franské Alby v neolitu a eneolitu Čech

    Czech Academy of Sciences Publication Activity Database

    Burgert, Pavel

    2016-01-01

    Roč. 68, č. 1 (2016), s. 91-108. ISSN 0323-1267 Institutional support: RVO:67985912 Keywords : Neolithic * Eneolithic * Bohemia * chipped stone industry * Bavarian Jurassic cherts * distribution Subject RIV: AC - Archeology, Anthropology, Ethnology

  9. Geochemical characteristics of organic matter-rich strata of lower Cambrian in Tarim Basin and its origin

    Institute of Scientific and Technical Information of China (English)

    CHEN; Jianfa; SUN; Shengli; LIU; Wenhui; ZHENG; Jianjing

    2004-01-01

    The organic matter-rich strata of the Yurtusi Formation of Lower Cambrian are wildly spread and steady in the Tarim Basin, in which cherts are developed, companied with phosphorite. Al/(Al+Fe+Mn) ratio and Si/(Si+Al+Fe) ratio of cherts range from 0.0023 to 0.0046 and 0.965 to 0.98, respectively, suggesting that cherts are formed in submarine hydrothermal activity and far away from terrestrial. Trace elements, such as As, Hg, Pb, Zn, Cu, Co, P, V, Ba, etc., are markedly rich in organic matter-rich sedimentary rocks of which Ba/Sr ratios are between 21.2 and 158.1. Compared with modern hydrothermal sediments, their Ba/Sr ratios are similar, it indicates that the organic matter-rich strata have the geochemical feature of submarine hydrothermal sediments. The total content of rare earth elements (ЕREE) in cherts is from 8.81 to 56.682 μg/g, on average 31.41 μg/g and the ΕREE of cherts is between continental margin chert's and abyssal chert's. The LREE/HREE ratio of cherts varies from 1.01 to 3.56, which reveals the characteristics of hydrothermal sediments. There is positive correlation between the total organic content (TOC) and Ba/Sr ratio which is geochemical index of submarine hydrothermal activity, which indicates that the submarine hydrothermal activity obviously influences the richness of organic matter in the Yurtusi Formation.

  10. Carbonaceous matter and putative microfossils of the mid-Archean Kromberg type-section re-visited, Barberton Greenstone Belt, South Africa

    Science.gov (United States)

    McLoughlin, Nicola; Grosch, Eugene

    2014-05-01

    Silicified seafloor sediments of the Kromberg Formation from the Onverwacht Group of the Barberton greenstone belt (BGB), South Africa, have been argued to contain some of the world's oldest preserved carbonaceous microfossils. Previous studies of these cherts have reported filamentous, spheroidal and ellipsoidal microfossils in thin-section (Walsh 1992); and bacteriomorph like structures in HF-etched samples (Westall et al. 2001). These microtextural studies however, lack supporting in-situ geochemical data, and are hampered to some degree by re-mobilisation of the carbonaceous matter (Van Zuilen et al. 2007). In light of these concerns, and ongoing debates surrounding carbonaceous remains in other Archean cherts (e.g., W Australia), further in-situ data from the Kromberg is required to positively identify carbonaceous matter of biogenic origin. New data will also help to address outstanding questions regarding the relative contribution of benthic versus planktonic microorganisms, and the putative microbial metabolisms involved. This study focuses on surface samples and drill core from the Barberton Scientific Drilling Programme, (BSDP, Grosch et al. 2009) from the southeastern limb of the Onverwacht anticline of the BGB. We sampled the Footbridge chert and a second chert horizon in drill core KD1 of the BSDP in the upper Kromberg Fm; and surface outcrops of two black cherts from the lower Kromberg Fm. Sedimentological logging reveals horizons rich in volcaniclastics with interbedded finely laminated grey-black chert, also intrusive black cherts, and sulphide rich horizons. The TOC of the sampled cherts is 1.24 to 5.40 wt%. Preliminary bulk carbon isotope values range from δ13C -21.1 to -35.3o values that are consistent with organic matter produced by anoxygenic photosynthesis. Microfabrics preserved in the Kromberg cherts include, primary wispy-laminated carbonaceous films suggesting compaction of early carbonaceous laminae. Also large composite carbonaceous

  11. Early diagenetic quartz formation at a deep iron oxidation front in the Eastern Equatorial Pacific

    Science.gov (United States)

    Meister, Patrick; Chapligin, Bernhard; Picard, Aude; Meyer, Hanno; Fischer, Cornelius; Rettenwander, Daniel; Amthauer, Georg; Vogt, Christoph; Aiello, Ivano

    2015-04-01

    The mechanisms of early diagenetic quartz formation under low-temperature conditions are still poorly understood. We studied lithified cherts consisting of microcrystalline quartz recovered from ODP Site 1226 in the Eastern Equatorial Pacific. The cherts occur near the base of a 420-m-thick Miocene-Holocene sequence within unlithified nannofossil and diatom ooze. Palaeo-temperatures reconstructed from δ18O values in the cherts are near to present porewater temperatures and a sharp depletion in dissolved silica occurs around 385 mbsf indicating that silica precipitation is still ongoing. Also a deep iron oxidation front occurs at the same depth, which is caused by upward diffusing nitrate from an oxic seawater aquifer in the underlying basaltic crust. Sequential iron extraction and analysis of the X-ray absorption near-edge structure (XANES) revealed that iron in the cherts predominantly occurs as illite and amorphous iron oxide, whereas iron in the nannofossil and diatom ooze occurs mainly as smectites. Mössbauer spectroscopy confirmed that the illite iron in the cherts is largely oxidized. A possible mechanisms that may be operative is quartz precipitation initiated by adsorption of silica to freshly precipitated iron oxides. The decrease in porewater silica concentration below opal-A and opal-CT saturation then allows for the precipitation of the thermodynamically more stable phase: quartz. We suggest that the formation of early-diagenetic chert at iron oxidation fronts is an important process in suboxic zones of silica-rich sediments. The largest iron oxidation front ever occurred during the great oxidation event ca. 2.5 Ga ago, when large amounts of iron and chert beds were deposited.

  12. A Paleoarchean coastal hydrothermal field inhabited by diverse microbial communities: the Strelley Pool Formation, Pilbara Craton, Western Australia.

    Science.gov (United States)

    Sugitani, K; Mimura, K; Takeuchi, M; Yamaguchi, T; Suzuki, K; Senda, R; Asahara, Y; Wallis, S; Van Kranendonk, M J

    2015-11-01

    The 3.4-Ga Strelley Pool Formation (SPF) at the informally named 'Waterfall Locality' in the Goldsworthy greenstone belt of the Pilbara Craton, Western Australia, provides deeper insights into ancient, shallow subaqueous to possibly subaerial ecosystems. Outcrops at this locality contain a thin (metals represented by Zn. The massive black cherts were likely deposited by mixing of hydrothermal and non-hydrothermal fluids. Coniform structures in the cherts are characterized by diffuse laminae composed of sulfide particles, suggesting that unlike stromatolites, they were formed dominantly through physico-chemical processes related to hydrothermal activity. The cherts yield microfossils identical to previously described carbonaceous films, small and large spheres, and lenticular microfossils. In addition, new morphological types such as clusters composed of large carbonaceous spheroids (20-40 μm across each) with fluffy or foam-like envelope are identified. Finely laminated carbonaceous cherts are devoid of heavy metals and characterized by the enrichment of LREE. This chert locally contains conical to domal structures characterized by truncation of laminae and trapping of detrital grains and is interpreted as siliceous stromatolite formed by very early or contemporaneous silicification of biomats with the contribution of silica-rich hydrothermal fluids. Biological affinities of described microfossils and microbes constructing siliceous stromatolites are under investigation. However, this study emphasizes how diverse the microbial community in Paleoarchean coastal hydrothermal environment was. We propose the diversity is at least partially due to the availability of various energy sources in this depositional environment including reducing chemicals and sunlight. PMID:26189535

  13. Syn-thrusting polygonal normal faults exposed in the hinge of the Cingoli anticline, northern Apennines, Italy

    Science.gov (United States)

    Petracchini, Lorenzo; Antonellini, Marco; Billi, Andrea; Scrocca, Davide

    2015-11-01

    The Cingoli arcuate anticline is part of the Apennines fold-thrust belt in Italy. The anticline involves sedimentary carbonate strata generally affected by syn-thrusting contractional structures such as bed-normal pressure solution seams, folds, and reverse faults. An exception is constituted by an outcrop in the anticline hinge, where sub-horizontal carbonate and chert beds are affected by joints and intraformational short normal faults. These faults are poorly-systematic and conceivably polygonal in map view. They cut through the carbonate beds while usually stop against the chert layers that are bent and extended along the faults themselves. At the fault tips, the displacement is generally transferred, via a lateral step, to an adjacent similar fault segment. The fault surfaces are often characterized by slickolites, greenish clayey residue, and micro-breccias including chert and carbonate clasts. Fault displacement is partly or largely accommodated by pressure solution. The faults, in effect, are usually accompanied by bed-parallel pressure solution seams in the two contractional quadrants located at the present or past fault tips. The pressure solution features fade away departing from the faults. This evidence and others are analytically explained with fault tip stress distributions. The faults are interpreted as polygonal normal faults syn-tectonically (syn-thrusting) nucleated in response to multi-directional stretching processes occurred at the Cingoli triple-folded anticline extrados. The faults then grew through a four-stage process: (1. stop) the faults stopped at the competent chert beds; (2. shrink) faulting produced shrinkage (pressure solution) of carbonate beds at the fault compressive tips; (3. shrink and step) the faults stepped laterally at the competent chert beds; (4. shatter) the chert beds were shattered along the fault surfaces. The case presented constitutes the first reported one of syn-thrusting non-diagenetic polygonal normal faults.

  14. Schattenwirtschaft und Arbeitsplatzbeschaffung

    OpenAIRE

    Merz, Joachim

    1996-01-01

    Ziel dieser Studie ist die empirisch fundierte Auseinandersetzung mit dem Thema Schattenwirtschaft und Arbeitsplatzschaffung. Die hier aufgefächerte Diskussion des Themas in Wirtschaft, Sozialpolitik und Gesellschaft, der weitere Diskurs und die empirische Fundierung erfordern eine klare und dann folgende begriffliche Abgrenzung der Schattenwirtschaft. Argumente der Diskussion zu Ursachen und positiven und negativen Wirkungen der Schattenwirtschaft auf die Arbeitsplatzbeschaffung werden im An...

  15. Rezension: Daten, Drohnen, Disziplin. Ein Gespräch über flüchtige Überwachung.

    Directory of Open Access Journals (Sweden)

    Valeska Ringhof

    2014-03-01

    Full Text Available Ein Gespräch über Überwachung und Macht in unserer Gegenwart. Die Soziologen Zygmunt Bauman und David Lyon zeigen wie breit dieses Thema gefächert ist und beleuchten unterschiedliche historische Aspekte, aktuelle Tendenzen und mögliche Weiterentwicklungen.

  16. General Projective Synchronization and Fractional Order Chaotic Masking Scheme

    Institute of Scientific and Technical Information of China (English)

    Shi-Quan Shao

    2008-01-01

    In this paper, a fractional order chaotic masking scheme used for secure communication is introduced. Based on the general projective synchronization of two coupled fractional Chert systems, a popular masking scheme is designed. Numerical example is given to demonstrate the effectiveness of the proposed method.

  17. Revisions to the stratigraphic nomenclature of the Abiquiu Formation, Abiquiu and contiguous areas, north-central New Mexico

    Science.gov (United States)

    Maldonado, Florian; Kelley, Shari A.

    2009-01-01

    Stratigraphic studies and geologic mapping on the Abiquiu 7.5-min quadrangle have led to revision of the stratigraphic nomenclature for the Oligocene to Miocene Abiquiu Formation in north-central New Mexico. The Abiquiu Formation had previously been defined to include informal upper, middle (Pedernal chert member), and lower members. The basement-derived conglomeratic lower member in the northern Jemez Mountains and Abiquiu embayment is here redefined. We propose removing the "lower member" from the Abiquiu Formation because provenance of these coarse sediments is dramatically different than the volcaniclastic strata of the "upper member." Furthermore, we propose that the term "lower member of the Abiquiu Formation" be replaced with an existing unit name, the Ritito Conglomerate of Barker (1958), and that the name Abiquiu Formation be restricted to the volcaniclastic succession. The lower part of the Ritito Conglomerate in Arroyo del Cobre on the Abiquiu quadrangle is 47 m (155 ft) thick and is composed of arkosic conglomeratic beds interbedded with arkosic sands and siltstones. Clasts include, in descending order of abundance, Proterozoic quartzite, granite, metavolcanic rocks, quartz, schist, and gneiss and a trace of Mesozoic sandstone and Paleozoic chert. Clasts are predominantly of pebble and cobble size but range from granule to boulder size. Paleocurrent data collected in the Arroyo del Cobre area indicate that the Ritito Conglomerate was deposited by a south-flowing river system during the Oligocene, eroding Laramide highlands such as the Tusas Mountains to the northeast, which contain predominantly Proterozoic rocks. This depositional setting has also been suggested by previous workers. The middle member or Pedernal chert member is present both at the top of the Ritito Conglomerate and as lenses within the lower part of the Abiquiu Formation. This post-depositional diagenetic chert remains an informal unit called the Pedernal chert.

  18. Volcanic degassing, hydrothermal circulation and the flourishing of early life on Earth: A review of the evidence from c. 3490-3240 Ma rocks of the Pilbara Supergroup, Pilbara Craton, Western Australia

    Science.gov (United States)

    Van Kranendonk, Martin J.

    2006-02-01

    New data gathered during mapping of c. 3490-3240 Ma rocks of the Pilbara Supergroup in the Pilbara Craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism. For most cherts, fossil hydrothermal fluid pathways are preserved as silica ± barite ± Fe-bearing veins that cut through the footwall and up to the level of individual bedded chert units, but not above, indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events. Silica ± barite ± Fe-bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units, and occurred under alternating high-sulphidation and low-sulphidation conditions. These veins provided pathways to the surface for elements leached from the footwall (e.g., Si, Ba, Fe) and volcanogenic emissions from underlying felsic magma chambers (e.g., CO 2, H 2S/HS -, SO 2). Stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of Warrawoona Group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and/or degassing of these magmas. Heat from these intrusions drove episodes of hydrothermal circulation. Listric normal faulting during caldera collapse produced basins with restricted circulation of seawater. Eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components, thereby providing habitats suitable for early life forms. Fossil stromatolites from two distinct stratigraphic units in the North Pole Dome grew in shallow water conditions, but in two very different geological settings with different morphologies. Stratiform and domical stromatolites in the stratigraphically lower, c. 3490 Ma, Dresser

  19. Potential siliceous sources during Prehistory: Results of prospecting in the East margin of the Ebro Basin (NE Iberian Peninsula

    Directory of Open Access Journals (Sweden)

    María Soto

    2014-03-01

    Full Text Available We present the results of prospecting in the NE of the Iberian Peninsula, with the aim of identifying the  siliceous sources potentially used by the populations that occupied the marginal basins of the Ebro depression during the Middle and Upper Palaeolithic.We intend to define the main characteristics of the cherts in the region studied, taking into account the palaeoenvironment in which silicifications are mainly formed, and the premise that siliceous rocks acquire the attributes of enclosing rocks.The cherts studied are the products of early diagenesis by replacement of carbonate and evaporite sediments. Petrological analyses show that they are made up of microquartz, with high proportion of fibrous forms silica, carbonates, ferric oxides and evaporite relicts. In the future, these characteristics will be useful for ascribing archaeological materials in both geological and geographical terms.

  20. Blueschist metamorphism in the Yreka-Fort Jones area, Klamath Mountains, California

    Science.gov (United States)

    Hotz, Preston E.

    1973-01-01

    Blueschist is plentiful in the Yreka-Fort Jones area, eastern Klamath Mountains, adjacent to a belt of serpentinite that marks the boundary between two fundamental lithologic units, an eastern belt of early Paleozoic sedimentary and metamorphic rocks, and a western greenstone-chert assemblage of late Paleozoic and Triassic(?) age. The blueschists, which contain lawsonite and glaucophane or crossite, occur with phyllitic quartzite and siliceous phyllite of the Stuart Fork Formation, which is overthrust northwestward on the greenstone-chert terrane. The blueschist facies metamorphism probably was synchronous with Middle and Late Jurassic metamorphism of the Stuart Fork Formation. The blueschist-serpentinite terrane possibly marks the site of collision between the eastern Klamath plate and an oceanic western Paleozoic and Triassic plate.

  1. Fósiles deformados y otras estructuras microtectónicas en la formación hiló (albiano) alrededores de sasaima, cundinamarca (colombia)

    OpenAIRE

    Mojica, Jairo; Adrian E. Scheidegger

    2012-01-01

    The Hiló Formation (middle to upper Albian) consists of dark bitominous sediments which include mainly calcareous shales, fine-grained sandstones and calcareous to arenaceous cherts. The rocks of the Hiló Formation contain many deformed elements that were affected by tectonic processes. Among these we note: elongated fossils (ammonites and bivalves), elongated pyrite nodules, microfolds, horizontal stylolites, folding striations and vertical sub-horizontal joints.The systematic measurement of...

  2. Mineralogy, geochemistry, genesis, and industrial application of silica in Arefi area, south of Mashhad

    OpenAIRE

    Mohammad Hassan Karimpour; Azadeh Malekzadeh Shafaroudi; Saeid Saadat

    2014-01-01

    Introduction Arefi quartz-bearing conglomerate (Middle Jurassic) is situated within Binalud structural zone. The unit is trending NW-SE located 25 km south of Mashhad. More than 97% of the pebbles are quartz as mono-crystalline, poly-crystalline, and minor fragments of chert, quartzite, and mica schist. Less that 3% of the remaining minerals are feldspar, mica, chlorite, hornblende, tourmaline, zircon, sphene, and opaque minerals. The cement is mainly silica. Hashemi (Hashemi, 2004) sugges...

  3. Earth-atmosphere evolution based on new determination of Devonian atmosphere Ar isotopic composition

    Science.gov (United States)

    Stuart, Finlay M.; Mark, Darren F.; Gandanger, Pierre; McConville, Paul

    2016-07-01

    The isotopic composition of the noble gases, in particular Ar, in samples of ancient atmosphere trapped in rocks and minerals provides the strongest constraints on the timing and rate of Earth atmosphere formation by degassing of the Earth's interior. We have re-measured the isotopic composition of argon in the Rhynie chert from northeast Scotland using a high precision mass spectrometer in an effort to provide constraints on the composition of Devonian atmosphere. Irradiated chert samples yield 40Ar/36Ar ratios that are often below the modern atmosphere value. The data define a 40Ar/36Ar value of 289.5 ± 0.4 at K/36Ar = 0. Similarly low 40Ar/36Ar are measured in un-irradiated chert samples. The simplest explanation for the low 40Ar/36Ar is the preservation of Devonian atmosphere-derived Ar in the chert, with the intercept value in 40Ar-39Ar-36Ar space representing an upper limit. In this case the Earth's atmosphere has accumulated only 3% (5.1 ± 0.4 ×1016 mol) of the total 40Ar inventory since the Devonian. The average accumulation rate of 1.27 ± 0.09 ×108 mol40Ar/yr overlaps the rate over the last 800 kyr. This implies that there has been no resolvable temporal change in the outgassing rate of the Earth since the mid-Palaeozoic despite the likely episodicity of Ar degassing from the continental crust. Incorporating the new Devonian atmosphere 40Ar/36Ar into the Earth degassing model of Pujol et al. (2013) provides the most precise constraints on atmosphere formation so far. The atmosphere formed in the first ∼100 Ma after initial accretion during a catastrophic degassing episode. A significant volume of 40Ar did not start to accumulate in the atmosphere until after 4 Ga which implies that stable K-rich continental crust did not develop until this time.

  4. Possible thermal spring deposit in the Arad area, Israel

    Energy Technology Data Exchange (ETDEWEB)

    Issar, A. (Geological Survey of Israel); Eckstein,Y.; Bogoch, R.

    1969-01-01

    A dolomite-chert breccia body, cemented by a hematite-geothite-barite-calcite mineral assemblage was found in the Arad area. This assemblage, plus the presence of anomalous quantities of various elements, particularly molybdenum, and the goethite-hematite relationship, suggest a thermal mineral spring deposit from a hypogene water source. The mineralogy and paragenesis of the deposit are discussed, and a normative analysis is tabulated.

  5. The oldest synallactid sea cucumber (Echinodermata: Holothuroidea: Aspidochirotida)

    OpenAIRE

    Reich, Mike

    2010-01-01

    Aspidochirote holothurian ossicles were discovered in Upper Ordovician-aged Öjlemyr cherts from Gotland, Sweden. The well-preserved material allows definitive assignment to the family Synallactidae, a deep-sea sea cucumber group that is distributed worldwide today. The new taxon Tribrachiodemas ordovicicus gen. et sp. nov. is described, representing the oldest member of the Aspidochirotida. The further fossil record of Synallactidae and evolutionary implications are also discussed.

  6. Geology of carbonate aggregate resources of Illinois, Illinois mineral notes

    Science.gov (United States)

    Goodwin, J. H.

    Carbonate rocks ranging in age from Pennsylvanian through Ordovician provide the principal resources for crushed stone production in Illinois. In the northern third of Illinois, dolomite and calcareous dolomite of the Silurian and Ordovician Systems from the bedrock surface are the basis of a large quarrying industry. One of the largest quarries in the United States wins stone from Silurian reefal dolomite at Thornton, near Chicago. Aggregate for skid-resistant asphalt pavement is produced from Devonian chert in extreme southern Illinois.

  7. Significance of age relations above and below upper Jurassic ophiolite in the Geysers--Clear Lake region, California

    Energy Technology Data Exchange (ETDEWEB)

    McLaughlin, R.J.; Pessagno, E.A. Jr.

    1978-01-01

    In The Geysers--Clear Lake area of northern California, a fragmented Upper Jurassic ophiolite overlain depositionally by the Great Valley sequence is juxtaposed over deformed and metomorphosed rocks of the Franciscan assemblage along the Coast Range thrust. The basal strata of the Great Valley sequence consist of thick breccias of mafic clasts, identical in composition to the upper part of the ophiolite. These breccias and their contact relations suggest that more than 1 km of the upper part of the ophiolite was locally eroded in early Tithonian time. On the basis of their radiolarian faunas, cherts in the Franciscan assemblage below the ophiolite range in age from Late Jurassic (early Tithonian) to Late Cretaceous (early Cenomanian). Of particular significance is an individual chert body (=The Geysers chert) of this age range. The early Cenomanian radiolarians, except for two occurrences associated with pelagic limestone, are significantly younger than those previously reported from the Franciscan assemblage. The existence of a sequence of Late Jurassic to Late Cretaceous radiolarian chert places critical constraints on subduction models for emplacement of the Franciscan assemblage beneath the Coast Range ophiolite and Great Valley sequence in The Geysers--Clear Lake area. From early Tithonian to post-early Cenomanian time, the Franciscan assemblage received pelagic sedimentation far from any site of subduction. By other data, blueschist metamorphism of subducted Franciscanstrata also occurred during this time. The radiolarian data from The Geysers area permit a correlation with Upper Cretaceous pelagic limestones in the Laytonville area northwest of The Geysers and also imply that the Great Valley sequence was never depositionally in contact with the Franciscan assemblage.

  8. Polymere und Nanopartikel - Verfahren für die Chemische Nanotechnologie

    OpenAIRE

    Thiessen, Wladimir

    2011-01-01

    In der vorliegenden Arbeit soll das weit gefächerte Thema der chemischen Nanotechnologie um neue Resultate bereichert werden. Im Einzelnen handelt es sich um neue Synthesemethoden für magnetische Nanorods (Nanoteilchen mit länglicher Form) und Nanoshells (oxidische Nanokristalle mit einer Hülle aus Edelmetall), ein Verfahren zur Modifizierung diverser Oberflächen mit heterogenen Polymerbürsten durch kontrollierte binäre radikalische Polymerisation, neuartige Copolymere zur Stabilisierung und ...

  9. Resonante Konverter höherer Ordnung für die kontaktlose induktive Energieübertragung

    OpenAIRE

    Bucher, Alexander

    2014-01-01

    Die kontakt- bzw. drahtlose Energieübertragung über kurze Distanzen basierend auf der induktiven Kopplung zwischen zwei Stromkreisen stellt für ein sehr breit gefächertes Anwendungsspektrum eine interessante Alternative gegenüber der drahtgebundenen Versorgung von elektrischen Verbrauchern dar. Durch den vollständigen Verzicht auf galvanische Kontakte und der damit einhergehenden Möglichkeit, Quelle und Verbraucher komplett mechanisch trennen zu können, ergeben sich vielfältige Anwendungsszen...

  10. Stone Tool Production

    OpenAIRE

    Hikade, Thomas

    2010-01-01

    In ancient Egypt, flint or chert was used for knapped stone tools from the Lower Palaeolithic down to the Pharaonic Period. The raw material was available in abundance on the desert surface, or it could be mined from the limestone formations along the Nile Valley. While the earliest lithic industries of Prehistoric Egypt resemble the stone tool assemblages from other parts of Africa, as well as Asia and Europe, the later Prehistoric stone industries in Egypt had very specific characteristics,...

  11. Busse als Wegbereiter: Zu einem frühen Markt für alternative Antriebe

    OpenAIRE

    Aigle, Thomas; Krstacic-Galic, Ante; Marz, Lutz; Scharnhorst, Andrea

    2008-01-01

    Gegenwärtig beginnt sich ein Paradigmenwechsel in der Automobilität zu vollziehen, weg vom Benzin- und Diesel-Verbrennungsmotor hin zu alternativen Antriebs- und Kraftstofftechnologien. Dieser Prozess verläuft widersprüchlich. Einerseits ist die F&E-Arbeit der Automobilindustrie nach wie vor auf die Optimierung des konventionellen Verbrennungsmotors fokussiert. Diese Optimierung bremst den Paradigmenwechsel. Andererseits hat sich im letzten Jahrzehnt ein breitgefächertes Feld antriebs- und kr...

  12. An iron shuttle for deepwater silica in Late Archean and early Paleoproterozoic iron formation

    OpenAIRE

    Fischer, Woodward W.; Andrew H. Knoll

    2009-01-01

    Iron formations are typically thinly bedded or laminated sedimentary rocks containing 15% or more of iron and a large proportion of silica (commonly > 40%). In the ca. 2590-2460 Ma Campbellrand-Kuruman Complex, Transvaal Supergroup, South Africa, iron formation occurs as a sediment-starved deepwater facies distal to carbonates and shales. Iron minerals, primarily siderite, define the lamination. The silica primarily occurs as thin beds and nodules of diagenetic chert (now microcrystalline qua...

  13. Overlapping of pedogenesis and meteoric diagenesis in distal alluvial and shallow lacustrine deposits in the Madrid Miocene Basin, Spain

    OpenAIRE

    Bustillo, María Ángeles; Alonso-Zarza, Ana María

    2007-01-01

    The Miocene distal alluvial fan and palustrine deposits of the Madrid Basin (Paracuellos de Jarama area) were examined to establish the sequence of its pedogenic–diagenetic processes and the main factors controlling them. In this area the diagenetic processes operated not only on carbonates, as commonly studied, but also in high magnesium clays and opaline cherts. This paper provides a dynamic model for saline–alkaline lake margins that complements the existing freshwater palustrine ...

  14. Petrology, Magnetic susceptibility, Tectonic setting and mineralization associated with Plutonic and Volcanic Rocks, Eastern Bajestan and Taherabad, Iran

    OpenAIRE

    Malihe Ghoorchi; Sayide Saadat; Alireza Ashouri

    2009-01-01

    Study area is located in district of Bajestan and Ferdows cities, NE of Iran. Structurally, this area is part of Lut block. The oldest exposed rocks, to the north of intrusive rocks and in Eastern Bajestan, are meta-chert, slate, quartzite, thin-bedded crystalline limestone and meta-argillite. The sedimentary units are: Sardar Formation (Carboniferous), Jamal Formation (Permian), Sorkh Shale and Shotori Formations (Triassic), carbonateous rocks (Cretaceous) and lithostratigraphically equivale...

  15. Magnetic signatures recorded in rocks and trees located inside the Tunguska blast 100 years ago, implications for Mirror Matter, Comet, and Kimberlitic Pipe explosion hypotheses

    Science.gov (United States)

    Kletetschka, G.

    2008-12-01

    Hundred years ago an unknown object impacted in Siberia, Tunguska region and created a seismic signature 100-1000 times stronger that the Hiroshima explosion. To this day, nothing has been found to suggest a foreign material (e.g. meteoritic) dispersion during this event. Various hypotheses were put forward, for example: Comet impact, Kimberlite Pipe explosion, and Mirror Matter interaction with the regular matter. We collected samples of black chert, conglomerate and wood from 5 different locations within 2 km from the epicenter. We used these samples for magnetic analysis and searched for any evidence of magnetic contamination that may date the Tunguska blast. All samples, wood, chert, and conglomerate showed sufficient content of magnetic material that should be capable of recording strong magnetic pulse. Our analysis shows no evidence of magnetic enhancement recorded in any of the three types (Chert, wood and conglomerate) of Tunguska samples. We will discuss this result in terms of three possible hypotheses of the created the Tunguska event.

  16. Depositional model of Early Permian reef-island ocean inEastern Kunlun

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Many fusulinid fossils have been found in thin- to middle-bedded limestones which aredistributed between the Early Permian limestone hills and formerly considered as Early Triassic.The fusulinid fossils, identified as Neoshwagerina sp., Verbeekina sp. and Schwagerina sp., canalso be found in massive limestone hills. At the same time, Early Permian radiolarian chert of deepbasin facies was discovered in Animaqing. All the above show that the massive limestone hills,thin- to middle-bedded limestones and radiolarian chert belong to syndeposits in Early Permianocean. The sediments in the study area can roughly be divided into three types: shallow facies,basin facies and transitional facies. The carbonate buildup can be subdivided into massive bioclas-tic limestone and reef framestone. Basin facies contains thin- or middle-bedded limestone, abyssalred mudstone or ooze, blue-green mudstone and radiolarian chert. Transitional facies includes reeftalus and platformal skirt facies. The Early Permian ocean in Eastern Kunlun is recognized as akind of reef-island ocean environment according to distribution and composition of different facies.The reef-island ocean in Eastern Kunlun is characterized by reef islands (or carbonate buildups)alternating with basins, complicated sea-floor topography, sharp facial change and well-developedreefs

  17. Lithofacies, age, and geochemistry of the Otuk Formation (Triassic) in the Red Dog District, northwest Alaska

    Science.gov (United States)

    Dumoulin, Julie A.; Burruss, Robert A.; Blome, Charles D.

    2011-01-01

    A complete penetration of the Otuk Fm. in continuous drill core (DH 927) from the Red Dog District illuminates the facies, age, source rock potential, and isotope stratigraphy of this unit in northwest Alaska. The section, in the Wolverine Creek plate of the Endicott Mountains Allochthon, is ~82 m thick. It gradationally overlies undated gray siliceous mudstone of the Siksikpuk Fm. and underlies undated black organic-rich mudstone of the Kingak(?) Shale. Shale, chert, and limestone members of the Otuk are recognized in DH 927 but the Blankenship Member is absent. The lower (shale) member consists of 28 m of variegated, silty shale with up to 6.9 wt % TOC; thin limy layers near the base contain bivalve fragments (Claraia sp.?) consistent with an Early Triassic (Griesbachian-early Smithian) age. Gray radiolarian chert dominates the middle member (25 m thick) and yields radiolarians of Middle Triassic (Anisian, Ladinian) and Late Triassic (Carnian-Norian) ages; a distinctive, ~2.5-m-thick interval of black shale and calcareous radiolarite ~6 m below the top has 9.8 wt % TOC. The upper (limestone) member (29 m thick) is lime mudstone with monotid bivalves and late Norian radiolarians, overlain by gray chert that contains the first Rhaetian (latest Triassic) radiolarians recognized in the Otuk. Rare black shale interbeds have up to 3.4 wt % TOC. Regional correlations indicate that Otuk lithofacies vary with both structural and geographic position.

  18. Late Jurassic-Early Cretaceous radiolarian age constraints from the sedimentary cover of the Amasia ophiolite (NW Armenia), at the junction between the Izmir-Ankara-Erzinçan and Sevan-Hakari suture zones

    Science.gov (United States)

    Danelian, T.; Asatryan, G.; Galoyan, Gh.; Sahakyan, L.; Stepanyan, J.

    2016-01-01

    The Amasia ophiolite, situated at the northernmost corner of Armenia, is part of the Sevan-Hakari suture zone which links with the Izmir-Ankara-Erzinçan suture zone in northern Turkey. Three new radiolarian assemblages have been extracted from siliceous sedimentary rocks that accumulated on the Amasia ophiolite in an oceanic setting. Two of these assemblages were extracted from red-brownish bedded cherts overlying basaltic lavas; one of these is likely to be middle Oxfordian to early Kimmeridgian in age, while the second correlates with the Berriasian. Similar time-equivalent lava-chert sequences have been dated recently using radiolarians from the Stepanavan, Vedi and Sevan ophiolite units, where they are considered to relate to submarine volcanic activity in the back-arc marginal basin in which the Armenian ophiolites were formed. The third radiolarian assemblage, of late Barremian age, was extracted from a more than 15-m-thick volcaniclastic-chert sequence. The related volcanic activity is likely to have been subaerial and probably relates to the formation of an oceanic volcanic plateau; no Cretaceous subaerial volcanism has been previously recorded in the Lesser Caucasus area.

  19. Palaeobiology of Mesoproterozoic Salkhan Limestone, Semri Group, Rohtas, Bihar, India: Systematics and significance

    Indian Academy of Sciences (India)

    Mukund Sharma

    2006-02-01

    Mesoproterozoic (∼1600 Ma old) Salkhan Limestone (Semri Group)of the Vindhyan Supergroup, exposed in Rohtas district of Bihar,India,preserves an abundant and varied ancient microbial assemblage.These microfossils are recorded in three distinctly occurring cherts viz.,bedded chert, stromatolitic chert and cherty stromatolites.27 morphoforms belonging to 14 genera and 21 species have been recognized.Six unnamed forms are also described. The microbial assemblage,almost exclusively composed of the remnants of cyanobacteria,is dominated by entophysalidacean members and short trichomes and can be termed as ‘typical Meso-proterozoic microbiotas ’.The assemblage includes characteristic mat-forming scytonematacean and entophysalidacean cyanobacteria. Eoentophysalis is the dominant organism in the assemblage. Ellipsoidal akinetes of nostocalean cyanobacteria (Archaeollipsoides) and spherical unicells also occur;both are distinct from mat forming assemblage,allochthonous and possibly planktic.Co-occurrence of the microbiotas and precipitates is related to the depositional environment of the Mesoproterozoic tidal flats with high carbonate saturation.

  20. The Rhynie hot-spring system: implications for the Devonian timescale, development of Devonian biota, gold mineralization, evolution of the atmosphere and Earth outgassing

    Science.gov (United States)

    Mark, D.; Rice, C.; Stuart, F.; Trewin, N.

    2011-12-01

    The Rhynie cherts are hot spring sinters that contain world-renowned plant and animal remains and anomalously high quantities of heavy metals, including gold. The biota in several beds is preserved undeformed with plants in life positions thus establishing that they and the indurating hydrothermal fluids were coeval. Despite the international importance of the Rhynie cherts their age has been poorly constrained for three reasons: (1) lack of a precise radio-isotopic age, (2) low resolution of spore biostratigraphic schemes for Devonian terrestrial deposits, with only one to a few zones per stage, and (3) poor resolution of the early Devonian timescale. Wellman (2004) assigned a Pragian-?earliest Emsian age to the Rhynie cherts on the basis of the spore assemblage. An 40Ar/39Ar dating study targeting Rhynie chert yielded an age of 395 ± 12 Ma (1σ) (Rice et al., 1995). This contribution discusses a new high-precision 40Ar/39Ar age (407.1 ± 2.2 Ma, 2σ) for the Devonian hot-spring system at Rhynie (Mark et al., 2011) and demonstrates that a proposed U-Pb age (411.5 ± 1.1 Ma, 2σ) for the Rhynie cherts (Parry et al., 2011) is inconsistent with both field evidence and our interpretation of the U-Pb data. The 40Ar/39Ar age provides a robust marker for the polygonalis-emsiensis Spore Assemblage Biozone within the Pragian-?earliest Emsian. It also constrains the age of a wealth of flora and fauna preserved in life positions as well as dating gold mineralization. Furthermore, we have now determined the Ar isotope composition of pristine samples of the Rhynie chert using an ARGUS multi-collector mass spectrometer and a low blank laser extraction technique. 40Ar/36Ar are systematically lower than the modern air value (Lee et al., 2006), and are not accompanied by non-atmospheric 38Ar/36Ar ratios. We conclude that the Rhynie chert captured and has preserved Devonian atmosphere-derived Ar. The data indicate that the 40Ar/36Ar of Devonian atmosphere was at least 3 % lower

  1. Palaeoarchean Barite Deposits in the Barberton Greenstone Belt: Origin and Links to Early Microbial Life

    Science.gov (United States)

    Mason, P. R.; Peters, A.; Nijman, W.; Reimer, T. O.; Whitehouse, M. J.

    2008-12-01

    Barite deposits are considered important for identifying microbial S cycling in Archean rocks since they can provide information about S isotopes in coexisting sulfate and sulfide minerals. However the degree to which barite and pyrite in metasedimentary rocks are related remains unclear. In this study we have investigated the origin of barite and pyrite in four main horizons seen in both outcrop and fresh drill core material from the Lower Mapepe formation (3.26 to 3.23 Ga), Barberton Greenstone Belt, South Africa. Host rocks include shales, cherts, tuffs and conglomerates that are variably silicified and/or affected by carbonate alteration. The high-energy depositional environment of the host rocks, mineralogical textures, barite chemistry and the occurrence of feldspars from the rarely-found celsian-hyalophane-orthoclase series suggest a seafloor exhalative origin for the barite. In contrast pyrite is closely associated with cherts and dolomitic units where rare earth element and Y data support a marine influence. Pyrite chemistry (Co/Ni= 0.1-1, Se/S <5 x 10- 5) also indicates a low temperature sedimentary origin. Multiple S isotope data (32S, 33S, 34S, determined by SIMS) for pyrite indicates a number of arrays with limited δ34S fractionation at constant Δ33S associated with individual syn-sedimentary microcrystalline pyrite layers. Isolated euhedral pyrites in massive chert and barite rich units show much more scatter and larger degrees of Δ33S variation (-1 to +4 ). Our results are consistent with models invoking microbial mass dependent fractionation of a heterogeneous elemental sulfur source derived from atmospheric photolysis. The sulfate reservoir can also be linked to photolysis but there is no clear relationship between the barite and pyrite S isotope data, suggesting that microbial (or abiotic) sulfate reduction was absent at this time or that the basinal sulfate concentration must have remained significantly lower than the mM level prior to barite

  2. LATE TRIASSIC (LATE NORIAN-RHAETIAN RADIOLARIANS FROM THE ANTALYA NAPPES, CENTRAL TAURIDES, SOUTHERN TURKEY

    Directory of Open Access Journals (Sweden)

    UGUR KAGAN TEKIN

    2002-11-01

    Full Text Available The Hocaköy section measured from the Alakirçay Nappe (middle nappe of the Antalya Nappes contain rich radiolarian fauna ranging from late Norian (Late Triassic to middle-late Cenomanian (mid Cretaceous. At the basal part of the section, the Late Triassic (late Norian-Rhaetian Gökdere Formation is characterized by gray to beige cherty limestone at the base and pinkish red chert- gray to beige limestone alternation at the top, with moderately to well-preserved radiolarians in the red chert beds. The overlying Jurassic - Middle Cretaceous Hocaköy Radiolarite is mainly represented by chert-mudstone alternations with some limestone interlayers. Radiolarians of the Gökdere Formation can be well correlated with that of the fauna from the Mino Terrane, central Japan and the fauna from the Queen Charlotte Islands, British Columbia, Canada. Four radiolarian zones from central Japan are recognized in the fauna obtained from Gökdere Formation such as “Praemesosaturnalis multidentatus Lowest Occurrence Zone (TR8A” (late Norian, “Praemesosaturnalis pseudokahleri Lowest Occurrence Zone (TR8B” (late Norian, ? “ Skirt F lowest Occurrence Zone (TR8C” (late Norian-Rhaetian and partly “Haeckelicyrtium breviora Taxon Range Zone (TR8D” (Rhaetian. In comparison with the Queen Charlotte fauna, the two zones “Betraccium deweveri Zone” (late Norian and “Proparvicingula moniliformis Zone” (early Rhaetian are also encountered in the Gökdere Formation. Radiolarians of the uppermost part of the Gökdere Formation indicate that “Globolaxtorum tozeri Zone” defined in Queen Charlotte Islands corresponding to the late Rhaetian, is not present in the section. Five new taxa, Capnuchosphaera okayi, Bistarkum rhaeticum, Praemesosaturnalis heilongjiangensis aksekiensis, P. nobleae, Veghicyclia sanfilippoae were determined within the late Norian-Rhaetian radiolarian fauna of the Gökdere Formation in Hocaköy section.   

  3. Geological Setting of Diamond Drilling for the Archean Biosphere Drilling Project, Pilbara Craton, Western Australia

    Science.gov (United States)

    Hickman, A.

    2004-12-01

    The Archean Biosphere Drilling Project (ABDP) is a collaborative international research project conducting systematic (bio)geochemical investigations to improve our understanding of the biosphere of the early Earth. The Pilbara Craton of Western Australia, which includes exceptionally well preserved 3.52 to 2.70 Ga sedimentary sequences, was selected for an innovative sampling program commencing in 2003. To avoid near-surface alteration and contamination effects, sampling was by diamond drilling to depths of between 150 and 300 m, and was located at sites where the target lithologies were least deformed and had lowest metamorphic grade (below 300°C). The first of five successful drilling sites (Jasper Deposit) targeted red, white and black chert in the 3.46 Ga Marble Bar Chert Member. This chert marks the top of a thick mafic-felsic volcanic cycle, the third of four such cycles formed by mantle plumes between 3.52 and 3.43 Ga. The geological setting was a volcanic plateau founded on 3.72 to 3.60 Ga sialic crust (isotopic evidence). The second hole (Salgash) was sited on the basal section of the fourth cycle, and sampled sulfidic (Cu-Zn-Fe), carbon-rich shale and sandstone units separated by flows of peridotite. The third hole (Eastern Creek) was sited on the margin of a moderately deep-water rift basin, the 2.95 to 2.91 Ga Mosquito Creek Basin. This is dominated by turbidites, but the sandstones and carbon-rich shales intersected at the drilling site were deposited in shallower water. The fourth and fifth holes, located 300 km apart, sampled 2.77 to 2.76 Ga continental formations of the Fortescue Group; both holes included black shales.

  4. Organic / inorganic carbon content and isotope analysis of 3.1Ga Cleaverville Formation in Pilbara, Australia: Result of DXCL project

    Science.gov (United States)

    Miki, T.; Kiyokawa, S.; Ito, T.; Yamaguchi, K. E.; Ikehara, M.

    2014-12-01

    DXCL project was targeted for 3.2-3.1 Ga hydrothermal chert-black shale (Dixon Island Formation) and black shale-banded iron formation (Cleaverville Formation). CL3 core (200m long) was drilled from 1) upper part of Black Shale Member (35m thick) to 2) lower part of BIF Member (165m thick) of the Cleaverville Formation. Here, the BIF Member can be divided into three submembers; Greenish shale-siderite (50m thick), Magnetite-siderite (55m thick) and Black shale-siderite (60m) submembers. In this study, we used bulk samples and samples treated by hot hydrochloric acid in order to extract organic carbon.  The Black shale Member consists of black carbonaceous matter and fine grain quartz (laminated greenish sideritic shale and white chert (lamination with inter-bedded greenish sideritic shale and siderite lamination. Hematite is identified near fractured part. The Black shale-siderite submember is composed of black shale, siderite and chert bands.  1) Siderite layers of these three submembers showedδ13Ccarb value of -14.6 to -3.8‰. Corg and δ13Corg content are 0.2% and -18.3 to -0.3‰. 2) Siderite grains within greenish sideritic shales showedδ13Ccarb value of -12.9 to +15.0‰. 3) Black shale of Corg and δ13Corg content in the BIF Member are 0.1% and -36.3 to -17.1‰ respectively.  We found great difference in values of δ13Ccarb of siderite. One is Corg-rich shale (up to +15.0‰) and the other is Corg-poor siderite layers (up to -3.8‰). The lighter value of siderite layers may be originated from precursor organic carbon which is strongly affected by biological activity.

  5. Lithofacies and stratigraphy of the Lisburne and Etivluk groups in the Lisburne 1 well and adjacent outcrops

    Science.gov (United States)

    Dumoulin, Julie A.; Bird, Kenneth J.

    2002-01-01

    The Lisburne 1 well in the thrust belt of the central Brooks Range penetrated 17,000 ft of imbricated, chiefly Ellesmerian sequence strata in the Endicott Mountains allochthon. Five thrust repeats of the Lisburne Group (Carboniferous) and overlying Etivluk Group (Permian-Jurassic) were drilled. Lithofacies analyses of >350 thin sections of cores and cuttings, and biostratigraphy based on foraminifers and conodonts, allow detailed correlation with coeval units in adjacent outcrops and provide data on the depositional setting and reservoir and source rock potential of these strata. The late Early- Late Mississippian (Osagean-Chesterian) Lisburne Group consists mainly of skeletal wackestone to grainstone, locally completely dolomitized. An interval of abundant glauconite and detrital quartz in the lower Lisburne may mark a sequence-bounding unconformity. Dolostone in the upper part of the unit has maximum porosities of 10-13% and common residual hydrocarbons. The uppermost Lisburne is thinly interbedded mudstone, chert, and shale that are locally dolomitic, phosphatic, spiculitic, and organic-rich; conodonts from this interval in outcrop represent an outer shelf to slope biofacies. The Etivluk Group here encompasses the Siksikpuk and Otuk Formations. The Siksikpuk is mainly varicolored shale and radiolarian chert, with a basal interval of glauconitic, pyritic sandstone. Phosphatic and organic-rich shale, radiolarian chert, and pelecypod coquinas make up the Otuk. Outcrop and subsurface data indicate that the Lisburne Group in this area accumulated near the seaward margin of a shallow-water carbonate platform that drowned during the Late Mississippian; outer shelf or deeper conditions predominated throughout deposition of the upper Lisburne and the Etivluk Group.

  6. A Rare Glimpse of Paleoarchean Life: Geobiology of an Exceptionally Preserved Microbial Mat Facies from the 3.4 Ga Strelley Pool Formation, Western Australia

    Science.gov (United States)

    Duda, Jan-Peter; Van Kranendonk, Martin J.; Thiel, Volker; Ionescu, Danny; Strauss, Harald; Schäfer, Nadine; Reitner, Joachim

    2016-01-01

    Paleoarchean rocks from the Pilbara Craton of Western Australia provide a variety of clues to the existence of early life on Earth, such as stromatolites, putative microfossils and geochemical signatures of microbial activity. However, some of these features have also been explained by non-biological processes. Further lines of evidence are therefore required to convincingly argue for the presence of microbial life. Here we describe a new type of microbial mat facies from the 3.4 Ga Strelley Pool Formation, which directly overlies well known stromatolitic carbonates from the same formation. This microbial mat facies consists of laminated, very fine-grained black cherts with discontinuous white quartz layers and lenses, and contains small domical stromatolites and wind-blown crescentic ripples. Light- and cathodoluminescence microscopy, Raman spectroscopy, and time of flight—secondary ion mass spectrometry (ToF-SIMS) reveal a spatial association of carbonates, organic material, and highly abundant framboidal pyrite within the black cherts. Nano secondary ion mass spectrometry (NanoSIMS) confirmed the presence of distinct spheroidal carbonate bodies up to several tens of μm that are surrounded by organic material and pyrite. These aggregates are interpreted as biogenic. Comparison with Phanerozoic analogues indicates that the facies represents microbial mats formed in a shallow marine environment. Carbonate precipitation and silicification by hydrothermal fluids occurred during sedimentation and earliest diagenesis. The deciphered environment, as well as the δ13C signature of bulk organic matter (-35.3‰), are in accord with the presence of photoautotrophs. At the same time, highly abundant framboidal pyrite exhibits a sulfur isotopic signature (δ34S = +3.05‰; Δ33S = 0.268‰; and Δ36S = -0.282‰) that is consistent with microbial sulfate reduction. Taken together, our results strongly support a microbial mat origin of the black chert facies, thus

  7. Growing up green on serpentine soils: Biogeochemistry of serpentine vegetation in the Central Coast Range of California

    Science.gov (United States)

    Oze, C.; Skinner, C.; Schroth, A.W.; Coleman, R.G.

    2008-01-01

    Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability, etc.) controlling and affecting plant growth. Here, the uptake, incorporation, and distribution of a wide variety of elements into the biomass of serpentine vegetation has been investigated relative to vegetation growing on an adjacent chert-derived soil. Soil pH, electrical conductivity, organic C, total N, soil extractable elements, total soil elemental compositions and plant digestions in conjunction with spider diagrams are utilized to determine the chemical relationships of these soil and plant systems. Plant available Mg and Ca in serpentine soils exceed values assessed in chert soils. Magnesium is nearly 3 times more abundant than Ca in the serpentine soils; however, the serpentine soils are not Ca deficient with Ca concentrations as high as 2235 mg kg-1. Calcium to Mg ratios (Ca:Mg) in both serpentine and chert vegetation are greater than one in both below and above ground tissues. Soil and plant chemistry analyses support that Ca is not a limiting factor for plant growth and that serpentine vegetation is actively moderating Mg uptake as well as tolerating elevated concentrations of bioavailable Mg. Additionally, results demonstrate that serpentine vegetation suppresses the uptake of Fe, Cr, Ni, Mn and Co into its biomass. The suppressed uptake of these metals mainly occurs in the plants' roots as evident by the comparatively lower metal concentrations present in above ground tissues (twigs, leaves and shoots). This research supports earlier studies that have suggested that ion uptake discrimination and ion suppression in the roots are major mechanisms for serpentine vegetation to tolerate the chemistry of

  8. Stratigraphy of the Kapalga Formation north of Pine Creek and its relationship to base metal mineralization

    International Nuclear Information System (INIS)

    The lithology, stratigraphy and mineralization of the Kapalga Formation (South Alligator Group) is described from the Margaret Syncline in the Pine Creek area of the Northern Territory of Australia. An interdigitation of carbonaceous siltstones and mudstones, chert, ashstones and tuffaceous chert, greywacke, siltstone, mudstone and minor banded iron formation (b.i.f.) characterises the Formation. These rocks define a vertical facies transition between low energy sediments of the underlying Koolpin Formation, and high energy sediments of the overlying Burrell Creek Formation. This transition is interlayered with numerous ashstone-tuffaceous chert horizons which were deposited during the waning stage of Gerowie Tuff sedimentation. The boundary between the Kapalga Formation of the South Alligator Group and the Burrell Creek Formation of the Finniss River Group is strictly conformable in this part of the Pine Creek 'Geosyncline'. Relict devitrified shards have been recognised in the Gerowie Tuff in the Margaret Syncline and these observations along with whole-rock chemical analyses conclusively support claims by previous investigators that these rocks are volcanic derivatives. Base metal mineralization at Iron Blow and Mt. Bonnie occurs as massive, stratiform, sulphide-silicate-carbonate lodes. The deposits are at the same stratigraphic level towards the base of the Kapalga Formation and minor stratification parallel with bedding has been observed. These features, and the association of the lodes with mud-flow breccias, lead to the conclusion that the lodes are syngenetic in origin. Thermochemical consideration of the sulphide assemblages together with the temporal relationship between the mineralization and Gerowie Tuff point to diagenetic devitrification of the underlying tuffaceous rocks as the source of the mineralization. Recent publications of experimental data from reaction of seawater and volcanic glass provide information which supports this thesis, and

  9. A stacked Late Quaternary fluvio-periglacial sequence from the Axe valley, southern England with implications for landscape evolution and Palaeolithic archaeology

    Science.gov (United States)

    Brown, A. G.; Basell, L. S.; Toms, P. S.

    2015-05-01

    The current model of mid-latitude late Quaternary terrace sequences, is that they are uplift-driven but climatically controlled terrace staircases, relating to both regional-scale crustal and tectonic factors, and palaeohydrological variations forced by quasi-cyclic climatic conditions in the 100 K world (post Mid Pleistocene Transition). This model appears to hold for the majority of the river valleys draining into the English Channel which exhibit 8-15 terrace levels over approximately 60-100 m of altitudinal elevation. However, one valley, the Axe, has only one major morphological terrace and has long-been regarded as anomalous. This paper uses both conventional and novel stratigraphical methods (digital granulometry and terrestrial laser scanning) to show that this terrace is a stacked sedimentary sequence of 20-30 m thickness with a quasi-continuous (i.e. with hiatuses) pulsed, record of fluvial and periglacial sedimentation over at least the last 300-400 K yrs as determined principally by OSL dating of the upper two thirds of the sequence. Since uplift has been regional, there is no evidence of anomalous neotectonics, and climatic history must be comparable to the adjacent catchments (both of which have staircase sequences) a catchment-specific mechanism is required. The Axe is the only valley in North West Europe incised entirely into the near-horizontally bedded chert (crypto-crystalline quartz) and sand-rich Lower Cretaceous rocks creating a buried valley. Mapping of the valley slopes has identified many large landslide scars associated with past and present springs. It is proposed that these are thaw-slump scars and represent large hill-slope failures caused by Vauclausian water pressures and hydraulic fracturing of the chert during rapid permafrost melting. A simple 1D model of this thermokarstic process is used to explore this mechanism, and it is proposed that the resultant anomalously high input of chert and sand into the valley during terminations

  10. Geschlecht und Technik: eine gesellschaftliche Praxis im Blick feministischer Erkenntnistheorie

    Directory of Open Access Journals (Sweden)

    Carola Schirmer

    2001-07-01

    Full Text Available Die Rezension stellt ein vielschichtiges Buch mit sehr unterschiedlichen Beiträgen zum Thema Geschlecht und Technik vor. Das breitgefächerte Spektrum der Aufsätze bietet einen guten Überblick über sehr verschiedene Forschungsansätze. Mehrere Autorinnen analysieren Geschlecht und Technik erkenntnistheoretisch-historisch, z.B. anhand der Begriffsentwicklung in verschiedenen naturwissenschaftlichen Disziplinen wie der Mathematik, Physik, Genetik und der Künstlichen Intelligenz. Eine Reihe andere Beiträge erforscht die Seite subjektiver Erfahrungen von Frauen in technisch geprägten Arbeitsfeldern mittels empirischer Studien.

  11. A Gunflint-type microbiota from the Duck Creek dolomite, Western Australia

    Science.gov (United States)

    Knoll, A. H.; Barghoorn, E. S.

    1976-01-01

    Two-billion-year-old black chert lenses from the Duck Creek formation, northwestern Western Australia, contain abundant organically preserved microorganisms which are morphologically similar to fossils of approximately the same age from the Gunflint formation, Ontario. Entities include a relatively small (5-15 micron) coccoid taxon morphologically comparable to Huroniospora Barghoorn, a larger coccoid form comparable to an apparently planktonic alga from the Gunflint, Gunflintia Barghoorn, and Eoastrion Barghoorn (Metallogenium Perfil'ev). Gunflint-type assemblages had a wide geographic distribution in middle Precambrian times, and these assemblages may eventually prove useful as biostratigraphic indices.

  12. Evaluation of modeling approaches to simulate contaminant transport in a fractured limestone aquifer

    DEFF Research Database (Denmark)

    Mosthaf, Klaus; Fjordbøge, Annika Sidelmann; Broholm, Mette Martina;

    of field data is the determination of relevant hydraulic properties and interpretation of aqueous and solid phase contaminant concentration sampling data. Traditional water sampling has a bias towards fracture sampling; however, concentrations in the limestone matrix are needed for assessing......Understanding the fate and transport of contaminants in limestone aquifers is important because they are a major drinking water resource. This is challenging because they are often heavily fractured and contain chert layers and nodules. Several modeling approaches have been developed to describe...

  13. Transformation of montmorillonite to kaolinite during weathering

    Science.gov (United States)

    Altschuler, Z.S.; Dwornik, E.J.; Kramer, H.

    1963-01-01

    Extensive deposits of kaolinite in Florida are formed by transformation of montmorillonite during low-temperature supergene weathering. The transformation occurs by intracrystalline leaching of interlayer cations and tetrahedral silica layers. Interposition of stripped layers within montmorillonite creates a regular 1:1 mixed-layered montmorillonite-kaolinite, a new clay structure. Kaolin-like layers are nourished by lateral epitaxy, as the iron-rich montmorillonite decomposes. Hexagonal outgrowths of new kaolinite develop at the edges of montmorillonite flakes and nucleate new vertical growth. Kaolinitic sands impregnated with goethite are ultimately formed, and the released silica enriches groundwater and forms secondary chert.

  14. Hydrothermal alteration at the Panorama Formation, North Pole Dome, Pilbara Craton, Western Australia

    CERN Document Server

    Brown, Adrian J; Walter, Malcolm R

    2014-01-01

    An airborne hyperspectral remote sensing dataset was obtained of the North Pole Dome region of the Pilbara Craton in October 2002. It has been analyzed for indications of hydrothermal minerals. Here we report on the identification and mapping of hydrothermal minerals in the 3.459 Ga Panorama Formation and surrounding strata. The spatial distribution of a pattern of subvertical pyrophyllite rich veins connected to a pyrophyllite rich palaeohorizontal layer is interpreted to represent the base of an acid-sulfate epithermal system that is unconformably overlain by the stromatolitic 3.42 Ga Strelley Pool Chert.

  15. Early Archaean collapse basins, a habitat for early bacterial life.

    Science.gov (United States)

    Nijman, W.

    For a better definition of the sedimentary environment in which early life may have flourished during the early Archaean, understanding of the basin geometry in terms of shape, depth, and fill is a prerequisite. The basin fill is the easiest to approach, namely from the well exposed, low-grade metamorphic 3.4 - 3.5 Ga rock successions in the greenstone belts of the east Pilbara (Coppin Gap Greenstone Belt and North Pole Dome) in West Australia and of the Barberton Greenstone Belt (Buck Ridge volcano-sedimentary complex) in South Africa. They consist of mafic to ultramafic volcanic rocks, largely pillow basalts, with distinct intercalations of intermediate to felsic intrusive and volcanic rocks and of silicious sediments. The, partly volcaniclastic, silicious sediments of the Buck Ridge and North Pole volcano-sedimentary complexes form a regressive-transgressive sequence. They were deposited close to base level, and experienced occasional emersion. Both North Pole Chert and the chert of the Kittys Gap volcano-sedimentary complex in the Coppin Gap Greenstone Belt preserve the flat-and-channel architecture of a shallow tidal environment. Thickness and facies distribution appear to be genetically linked to systems, i.e. arrays, of syn-depositionally active, extensional faults. Structures at the rear, front and bottoms of these fault arrays, and the fault vergence from the basin margin towards the centre characterize the basins as due to surficial crustal collapse. Observations in the Pilbara craton point to a non-linear plan view and persistence for the basin-defining fault patterns over up to 50 Ma, during which several of these fault arrays became superposed. The faults linked high-crustal level felsic intrusions within the overall mafic rock suite via porphyry pipes, black chert veins and inferred hydrothermal circulations with the overlying felsic lavas, and more importantly, with the cherty sediments. Where such veins surfaced, high-energy breccias, and in the

  16. Testing the survival of microfossils in artificial martian sedimentary meteorites during entry into Earth's atmosphere: the STONE 6 experiment

    OpenAIRE

    Foucher, Frédéric; Westall, Frances; Brandstätter, Franz; Demets, René; Parnell, John; Cockell, Charles S.; M. Edwards, Howell G.; Bény, Jean-Michel; Brack, André

    2010-01-01

    Abstract If life ever appeared on Mars, could we find traces of primitive life embedded in sedimentary meteorites? To answer this question, a 3.5 billion-year-old volcanic sediment containing microfossils was embedded in the heat shield of a space capsule in order to test survival of the rock and the microfossils during entry into the Earth?s atmosphere (the STONE 6 experiment). The silicified volcanic sediment from the Kitty?s Gap Chert (Pilbara, Australia) is considered to be an ...

  17. Minor and trace element composition and age of Yukon probable-microtektites

    Science.gov (United States)

    Boundy-Sanders, S. Q.; Hervig, R. L.

    1993-01-01

    Major, minor, and trace element composition of the candidate micro tektites from Yukon Territory suggest a possible impact site of hydrothermally altered limestone and sand or chert, or possibly a carbonatite. Their REE/chondrite curve is similar in character to, but higher than, shale composites of North America, Australia, and Europe. Relative to these same composites, the Yukon droplets are enriched in Y, F, S, Sr, P, Mn, Mg, and Ca. They are depleted in Rb, Li, Th, Nb, Ti, K, Na, Fe, Si, and Al. Biostratigraphic constraints on the droplets indicate they are Middle to Late Devonian, more likely Middle Devonian, in age.

  18. Molecular dynamics simulation of Ni3Al melting

    Institute of Scientific and Technical Information of China (English)

    Rongshan Wang; Huaiyu Hou; Xiaodong Ni; Guoliang Chen

    2008-01-01

    With the Voter-Chert version of embedded-atom model (EAM) potential and molecular dynamics, the melting of Ni3A1 alloy was simulated by one-phase (conventional) and two-phase approaches. It is shown that the simulated melting point is dependent on the potential and the simulation method. The structures of the melts obtained by different simulation methods were analyzed by the pair correlation function, the coordination number, and the distribution of atom pair type (indexed by the Honeycutt-Andersen pair analysis technique). The results show that the structures are very similar.

  19. Revised radiocarbon dates for Mwanihuki, Makira : a c. 3000 BP aceramic site4 in the southeast Solomon Islands

    International Nuclear Information System (INIS)

    Excavation of three middens on Mwanihuki, located on the north coast of Makira in the southeast Solomon Islands has returned radiocarbon dates that show an initial occupation bracket between 3351 ± 42 BP and 2975 ± 21 BP (uncalibrated). The material culture of this phase consisted of a small amount of subsistence shell and worked chert, and an absence of any ceramics. This date range, along with the absence of the distinctive Lapita type dentate stamped pottery has aligned phasing of this site with the contemporaneous aceramic Vatuluma Posovi cave site in central Guadalcanal. (author)

  20. Origin and variability of the late Precambrian-Cambrian Athel Silicilyte, South Oman Salt Basin

    OpenAIRE

    Al Rajaibi, Ibrahim Mohamed amur

    2011-01-01

    The Precambrian-Cambrian Athel Silicilyte is an enigmatic chert unit of up to 390 m thick found as slabs (each slab typically 2 × 6 km across) entrapped within salt domes at a depth of 4-5 km in the South Oman Salt Basin. This formation is a prolific self-charged reservoir with high porosity (up to 34 %) and high oil saturation (80 %). Despite its economic value, the origin and the variability of this formation are not fully understood. This study therefore aims to investigate the variability...

  1. CyLaw-Report XXVII: Zu Art. 10 GG bei der "Beschlagnahme" von E-Mails auf dem Mailserver des Providers und beim Zugriff des Arbeitgebers auf E-Mails des Arbeitnehmers : Entscheidungen des Bundesverfassungsgerichts (BVerfG) vom 16.06.2009 - 2 BvR 902/06, des Verwaltungsgerichtshofs (VGH) Kassel vom 19.05.2009 - 6 A 2672/08.Z und des Verwaltungsgerichts (VG) Frankfurt vom 06.11.2008 - 1 K 628/08.F

    OpenAIRE

    Schmid, Viola

    2009-01-01

    Im Sachverhalt der Entscheidung des BVerfG nehmen die Ermittlungsbehörden Zugriff auf E-Mails, die nicht auf einem Rechner des Durchsuchten, sondern nur beim Provider gespei-chert sind. Die Herrschaft des E-Mail-Account-Inhabers ist also nicht absolut, sondern von der Entscheidung des Diensteanbieters über die Preisgabe der Daten abhängig. Im Sach-verhalt der Entscheidung des VG Frankfurts verlangt die Bundesanstalt für Finanzdienstleis-tungsaufsicht (BaFin) von einem Arbeitgeber, der die Pri...

  2. Application of Mössbauer spectrometry to geochemistry and environmental chemistry. Estimation of sedimentation environments using chemical states of iron in the sediments as a probe

    International Nuclear Information System (INIS)

    Iron is one of the major constituents of the earth's crust and is commonly contained in various geochemical and environmental samples such as rocks, soils and sediments. Since iron exists in various chemical states according to the ambient environment, it may serve as a probe for monitoring the chemical changes taking place in the environment and/or for estimating the origin of iron containing samples. In this paper, I introduce the application of 57Fe Mössbauer spectroscopy to the sediments under hypoxia in Tokyo bay, the Antarctic Ocean sediments and the deep-sea pelagic cherts in order to estimate the sedimentation environments. (author)

  3. Ophiolitic association of Cape Fiolent area, southwestern Crimea

    Science.gov (United States)

    Promyslova, M. Yu.; Demina, L. I.; Bychkov, A. Yu.; Gushchin, A. I.; Koronovsky, N. V.; Tsarev, V. V.

    2016-01-01

    An ophiolitic association consisting of serpentinized ultramafic rocks and serpentinite, layered mafic-ultramafic complex, gabbro and gabbrodolerite, fragments of parallel dike complex, pillow lava, black bedded chert, and jasper has been identified for the first time by authors in the Cape Fiolent area. The chemistry of pillow lavas and dolerites, including REE patterns and a wide set of other microelements, indicates suprasubduction nature of the ophiolites and their belonging to a backarc basin that has reached the stage of spreading in its evolution.

  4. Why Was Silcrete Heat-Treated in the Middle Stone Age? An Early Transformative Technology in the Context of Raw Material Use at Mertenhof Rock Shelter, South Africa

    Science.gov (United States)

    2016-01-01

    People heat treated silcrete during the Middle Stone Age (MSA) in southern Africa but the spatial and temporal variability of this practice remains poorly documented. This paucity of data in turn makes it difficult to interrogate the motive factors underlying the application of this technique. In this paper we present data on heat treatment of silcrete through the Howiesons Poort and post-Howiesons Poort of the rock shelter site Mertenhof, located in the Western Cape of South Africa. In contrast to other sites where heat treatment has been documented, distance to rock source at Mertenhof can be reasonably well estimated, and the site is known to contain high proportions of a diversity of fine grained rocks including silcrete, hornfels and chert at various points through the sequence. Our results suggest the prevalence of heat treatment is variable through the sequence but that it is largely unaffected by the relative abundance of silcrete prevalence. Instead there is a strong inverse correlation between frequency of heat treatment in silcrete and prevalence of chert in the assemblage, and a generally positive correlation with the proportion of locally available rock. While it is difficult to separate individual factors we suggest that, at Mertenhof at least, heat treatment may have been used to improve the fracture properties of silcrete at times when other finer grained rocks were less readily available. As such, heat treatment appears to have been a component of the MSA behavioural repertoire that was flexibly deployed in ways sensitive to other elements of technological organisation. PMID:26867145

  5. Usage of geochemistry of uranium and associated elements to explain the anomalous non-phosphatic radiometric halo south west margins of Saba abar, Kherbet As-Sawwaneh area. Final report on scientific research

    International Nuclear Information System (INIS)

    The present research work has accomplished the whole picture of the non completed anomalous radioactive halo shown by the latest airborne radiometric survey along the extreme Southwestern corner of Saba Abar Kherbet As-Sawwaneh quadrangle. Geochemical and Carborne gamma-ray spectrometric surveys were used. The resulted radiometric maps of the radioelements U, Th, K and Ur units of the total counts assisted in achieving the completed picture of the anomalous halo towards west and north west. Thirteen anomalous spots were found in Kherbet As-Sawwaneh, Shaili and south of Abar El-Rudma Areas, especially over a cover of flint and chert blocks and stones covering the sedimentary Palaeogene rocks in close contact with volcanic basalt rocks in the vicinity of Jabal Ghurab. Upon breaking many of the chert and flint blocks and stones yellow secondary uranium mineralizations were found despite no surface indications of any mineralizations. This type of secondary uranium occurrences were never reported earlier neither in Syria no elsewhere. It is a new phenomena which deserve further investigations. In addition a few anomalous values of thorium were detected in the sedimentary rocks of the various Khebrats along the main basaltic sheet and flows. Also contamination with the isotope 136 Cs in few sampling point was still detectable in the khebrates of the area from Chernobyl fallout. (author)

  6. Organotemplate structures in sedimentary manganese carbonates of the Neoproterozoic Penganga Group, Adilabad, India

    Indian Academy of Sciences (India)

    Joydip Mukhopadhyay; Jens Gutzmer; Nicolas J Beukes

    2005-06-01

    Manganese carbonates interstratified with bedded chert in the Chanda Limestone of the Neoproterozoic Penganga Group at Adilabad, south India, have been studied for possible evidence that microbiota played a role in the mediation of early diagenetic Mn-carbonate formation in Precam- brian marine sedimentary successions. The manganese carbonate and chert beds occur within a below wave base, deep-water distally steepened ramp succession. High resolution SEM petrogra- phy of the manganese carbonates revealed two basic morphologies — spherical to oval-cylindrical shaped microconcretions, and tubular to irregular, elongated, film-like microstructures. Infolded filmy to hollow tubular strand-like internal morphologies of the spherical to oval-cylindrical shaped microconcretions suggest their microbial affinity. The tubular and film morphologies with mesh- like interconnections closely resemble architectures of microbial extracellular polymeric substance (EPS). Mineralization took place on these organotemplates by the process of permineralization as well as replacement in an early diagenetic pore-water environment with reduction of higher manganese oxy-hydroxides by organic matter and consequent increase in dissolved carbonate.

  7. Use of laboratory simulated pyrolysis in tracing the history of sedimentary organic matter

    Science.gov (United States)

    Kaplan, I. R.; Tannenbaum, E.; Huizinga, B. E.

    1986-01-01

    Results from laboratory simulated pyrolyses experiments show that in addition to depth of burial, preservation of kerogen, and hence any morphologic structure in it, is also dependent on the mineral matrix with which it is associated. In the presence of clay minerals, and especially under dry conditions, extractable lipids released during kerogen decomposition are more rapidly destroyed than in the presence of calcite or chert matrices. The result is production of gas, polar bitumen and pyrobitumen and destruction of biomarkers. During such an early reorganization of the kerogen, the biomarker constituents can be destroyed, or unrecognizably altered. The above process of organic residues maturation appears to be inhibited in the presence of water and is significantly reduced where kerogen is hosted in limestones, dolomites or cherts. These minerals have been characteristically found to be the most reliable in yielding morphological fossils and small quantities of extractable bitumen in Archean and Proterozoic rocks. To understand the validity of chemical and morphological fossils, in the early geologic record, it will be necessary to understand the process of kerogen in sedimentary rocks. To test the role of various minerals on the preservation process, kerogen extracted from a variety of rocks has been heated together with montmorillonite, illite and calcite. The kinetics of the process has been monitored and the products quantitatively identified.

  8. The use of chemical analyses of borehole samples in sub-surface mapping: an example of the Delmas-Bapsfontein area is given

    International Nuclear Information System (INIS)

    The East Rand Dolomites around Delmas-Bapsfontein underlie an area of about 1000 sq. km. but do not outcrop. An intensive ground water exploration programme had been carried out and the percussion samples obtained were analysed in an attempt to differentiate the sub-surface geology based on the chemistry of the samples. The gross chemistry of the various rock types has been well defined and various computer-aided graphical methods were used to highlight changes in the chemistry. Samples were analysed by means of x-ray fluorescence. The chert-rich dolomite formations near surface have been leached to the extent that all of the carbonate minerals have been removed, leaving a chert residium of commonly 80 m thick. The carbonates in this area can be regarded as 'pure' dolomites. There are however two discretely different CaO/MgO ratios present in the study area. Intrusives with up to 16% Na2O are noted. The effect of de-dolomitization at the contacts of the intrusives is clearly illustrated. 4 refs., 7 figs., 1 tab

  9. Reinterpretation of Mesozoic ophiolite arc, and blueschist terranes in southwestern Baja California

    Energy Technology Data Exchange (ETDEWEB)

    Sedlock, R.L. (San Jose State Univ., CA (United States). Geology Dept.)

    1993-04-01

    The nature and significance of disrupted Mesozoic oceanic rocks on Isla Santa Margarita and Isla Magdalena, western Baja California Sur, have been reinterpreted on the basis of detailed mapping and petrologic studies. Three structural units are recognized. (1) The upper plate consists of ophiolitic, arc, and forearc basin rocks. Ophiolitic rocks, including metamorphosed ultramafic rocks, gabbro, dikes, volcanic rocks, and chert, underwent strong contractional deformation and penetrative greenschist-facies metamorphism. Arc rocks, including gabbro, a dike and sill complex, compositionally diverse volcanic rocks, lahars, and volcaniclastic strata, lack a penetrative fabric and are weakly metamorphosed. Forearc basin rocks consist of unmetamorphosed conglomerated and rhythmically bedded siliciclastic turbidites. (2) The lower plate is a subduction complex consisting of weakly to moderately foliated and metamorphosed pillow and massive lavas, breccia, and tuff( ), interbedded red and green siliceous argillite, and rare radiolarian ribbon chert and limestone. Blueschist-facies metamorphism is indicated by lawsonite, aragonite, sodic amphibole, and sodic clino-pyroxene. (3) Serpentine-matrix melange crops out in shallowly dipping fault zones between the upper and lower plates. The structural and petrologic characteristics of the Mesozoic units, the geometry of contacts between them, and the age of extension are similar to those in the Isla Cedros-Vizcalno Peninsula region, 400 km to the northwest. The author infers that syn-subduction extension was a regional event that affected much of the western Baja forearc during the Late Cretaceous and Paleogene.

  10. Microscopy and Cathodoluminescence Spectroscopy Characterization of Quartz Exhibiting Different Alkali-Silica Reaction Potential.

    Science.gov (United States)

    Kuchařová, Aneta; Götze, Jens; Šachlová, Šárka; Pertold, Zdeněk; Přikryl, Richard

    2016-02-01

    Different quartz types from several localities in the Czech Republic and Sweden were examined by polarizing microscopy combined with cathodoluminescence (CL) microscopy, spectroscopy, and petrographic image analysis, and tested by use of an accelerated mortar bar test (following ASTM C1260). The highest alkali-silica reaction potential was indicated by very fine-grained chert, containing significant amounts of fine-grained to cryptocrystalline matrix. The chert exhibited a dark red CL emission band at ~640 nm with a low intensity. Fine-grained orthoquartzites, as well as fine-grained metamorphic vein quartz, separated from phyllite exhibited medium expansion values. The orthoquartzites showed various CL of quartz grains, from blue through violet, red, and brown. Two CL spectral bands at ~450 and ~630 nm, with various intensities, were detected. The quartz from phyllite displayed an inhomogeneous dark red CL with two CL spectral bands of low intensities at ~460 and ~640 nm. The massive coarse-grained pegmatite quartz from pegmatite was assessed to be nonreactive and displayed a typical short-lived blue CL (~480 nm). The higher reactivity of the fine-grained hydrothermal quartz may be connected with high concentrations of defect centers, and probably with amorphized micro-regions in the quartz, respectively; indicated by a yellow CL emission (~570 nm). PMID:26790877

  11. Tectonic evolution of the central Brooks Range mountain front: Evidence from the Atigun Gorge region

    Science.gov (United States)

    Mull, C.G.; Glenn, R.K.; Adams, K.E.

    1997-01-01

    Atigun Gorge, at the northern front of the eastern Endicott Mountains, contains well-exposed rocks of the upper part of the Endicott Mountains allochthon and rocks of the structurally higher Picnic Creek or Ipnavik River allochthon. These allochthons contain rocks as young as Early Cretaceous (Valanginian) and are separated by a nearly vertical fault zone that contains exotic blocks of Triassic and Jurassic chert and silicified mudstone. Siliceous rocks of this type are not present in the Endicott Mountains allochthon but are characteristic of the Picnic Creek, Ipnavik River, and some of the other allochthons that structurally overlie the Endicott Mountains allochthon in the central and western Brooks Range. These exotic blocks, therefore indicate that structurally higher rocks of either the Picnic Creek or Ipnavik River allochthon were emplaced during the Early Cretaceous and are preserved along the northern flank of the eastern Endicott Mountains. The deformed thickness of this higher allochthon in the subsurface north of the mountains is unknown but probably exceeds 2 kilometers. Similar relations are mapped east of Atigun Gorge in an area of structural transition from the eastern Endicott Mountains into the northern Philip Smith Mountains, which are formed by the parautochthonous North Slope stratigraphic assemblage. The allochthonous rocks at the mountain front are regionally unconformably overlain by proximal Lower Cretaceous (Albian) foredeep conglomerate at the southern flank of the Colville basin, but at Atigun Gorge, the base of these deposits is interpreted as a possible back thrust at a triangle zone. Conglomerate clasts in the foredeep deposits are dominantly chert, mafic igneous rock, and other lithologies characteristic of the Picnic Creek and Ipnavik River allochthons and scattered clasts from the Endicott Mountains allochthon. The conglomerates show that the chert-rich allochthonous rocks and the Endicott Mountains allochthon were emplaced in the

  12. Silicon and oxygen isotopic trends in Mesozoic radiolarites

    Science.gov (United States)

    Bôle, Maximlien; Baumgartner Peter, O.; Lukas, Baumgartner; Anne-Sophie, Bouvier; Rie, Hori; Masayuki, Ikeda

    2016-04-01

    Silicon and oxygen isotopes (δ30Si and δ18O) of siliceous tests (diatoms, sponges and radiolarians) preserve environmental signatures in unconsolidated sediments, but few studies show such signatures for ancient biosilicieous rocks. In Precambrian cherts from greenstone belts, small scaled isotopic variations were interpreted as a primary diagenetic feature. They were used, coupled to mean δ18O, to reconstruct seawater temperature at which cherts precipitated. Here, we examine stable isotopes in Mesozoic biogenic cherts that may also preserve an environmental signature. We measured δ30Si and δ18O in situ by SIMS, in the chalcedony of individual radiolarian tests preserved in Mesozoic radiolarites. Microanalysis of chalcedony, rather than the bulk rock isotopic composition, is likely to reveal a palaeoenvironmental signal, since it is derived from biogenic opal, the most mobile silica phase during earliest diagenesis. Our data reveal clear trends through several Mesozoic radiolarite sections from Panthalassa (Kiso River, Japan) and Western Tethys (Sogno, Italy). δ18O records measured in radiolarites show a relatively good correlation to δ18O-variations of Mesozoic low magnesium calcite shells, which are commonly used as a palaeotemperature proxy. Once these variations, attributed to seawater temperature, are removed, the residual δ18O trends are opposite to the δ30Si trends. δ30Si increases from Middle Triassic to Early Jurassic in the Kiso River sections and decrease during the Middle Jurassic in the Sogno section. The observed d30Si-trends are likely to represent a palaeoenvironmental signal, because they are not compatible with simple models of progressive diagenesis along P/T-paths (or depth below sea bottom in drill holes). Among the palaeoenvironmental factors that may have influenced these trends are the oceanic silica cycle changing though time, oceanic circulation and/or the palaeogeographic location of each studied site. Siliceous organisms are

  13. Genesis and Characteristics of the Two Sub-belts in the Western Yarlung-Zangbo Suture Zone, Tibet, China

    Science.gov (United States)

    Liu, F.; Yang, J.; Lian, D.; Dilek, Y.; Robinson, P. T.

    2014-12-01

    The Yarlung Zangbo Suture zone (YZSZ), extending more than 2000 km across southern Tibet, is thought to mark the tectonic boundary between the Indian and Asian plates. West of Saga county of the YZSZ is divided into two sub-belts (Dajiweng-Saga to the north and Daba-Xiugugabu to the south), which are separated by the Zhongba-Zhada microcontinent/terrane containing Sinian to Triassic metamorphic and sedimentary rocks. Several large ophiolitic massifs that crop out in the southern sub-belt, e.g., the Dongbo (400 km2), Purang (650km2) and Xiugugabu (700km2), have a seamount-like stratigraphy, consisting from the base upward of peridotites, mafic dikes, massive basalt and basaltic hyaloclastites, mudstone and silty shale and radiolarian chert. The sedimentary sequence also locally contains discontinuous basalt flows and siliceous to massive limestones with minor oolites. The peridotites are highly depleted harzburgites, minor lherzolites and dunites, all of which were enriched by later fluids/melts. Mafic dikes (120-130 Ma) intruding the peridotites exhibit N-MORB-like chondrite-normalized REE patterns and negative Nb anomalies in spider diagrams. These geochemical features are similar to those of volcanic-rifted margin basalts. E-MORB-like basalts (137 Ma) within the Late Jurassic to Early Cretaceous radiolarian cherts and OIB-like basalts (140 Ma) between the silty shale and peridotites reflect limited seamount volcanism. In the northern sub-belt ophiolitic peridotites, mafic dikes, cumulate gabbros, massive basalts, chert and limestone crop out discontinuously as lenses in mélange complexes. The peridotites are harzburgite and minor dunite, both of which were modified by later LREE-enriched melts/fluids. Mafic dikes (122-127 Ma) intruding the peridotites are geochemically similar to those in the southern sub-belt. A 500-meter-thick sequence of cumulate gabbro is tectonically sandwiched between the peridotites and basalts. A 1- 2 km sequence of OIB-type basalt

  14. A new occurrence of ambient inclusion trails from the ~1900-million-year-old Gunflint Formation, Ontario: nanocharacterization and testing of potential formation mechanisms.

    Science.gov (United States)

    Wacey, D; Saunders, M; Kong, C; Kilburn, M R

    2016-09-01

    Ambient inclusion trails (AITs) are tubular microstructures thought to form when a microscopic mineral crystal is propelled through a fine-grained rock matrix. Here, we report a new occurrence of AITs from a fossilized microbial mat within the 1878-Ma Gunflint Formation, at Current River, Ontario. The AITs are 1-15 μm in diameter, have pyrite as the propelled crystal, are infilled with chlorite and have been propelled through a microquartz (chert) or chlorite matrix. AITs most commonly originate at the boundary between pyrite- and chlorite-rich laminae and chert-filled fenestrae, with pyrite crystals propelled into the fenestrae. A subset of AITs originate within the fenestrae, rooted either within the chert or within patches of chlorite. Sulphur isotope data ((34) S/(32) S) obtained in situ from AIT pyrite have a δ(34) S of -8.5 to +8.0 ‰, indicating a maximum of ~30 ‰ fractionation from Palaeoproterozoic seawater sulphate (δ(34) S ≈ +20 ‰). Organic carbon is common both at the outer margins of the fenestrae and in patches of chlorite where most AITs originate, and can be found in smaller quantities further along some AITs towards the terminal pyrite grain. We infer that pyrite crystals now found within the AITs formed via the action of heterotrophic sulphate-reducing bacteria during early diagenesis within the microbial mat, as pore waters were becoming depleted in seawater sulphate. Gases derived from this process such as CO2 and H2 S were partially trapped within the microbial mat, helping produce birds-eye fenestrae, while rapid microquartz precipitation closed porosity. We propose that propulsion of the pyrite crystals to form AITs was driven by two complementary mechanisms during burial and low-grade metamorphism: firstly, thermal decomposition of residual organic material providing CO2 , and potentially CH4 , as propulsive gases, plus organic acids to locally dissolve the microquartz matrix; and secondly, reactions involving clay minerals that

  15. Oxygen isotope analysis of fossil organic matter by secondary ion mass spectrometry

    Science.gov (United States)

    Tartèse, Romain; Chaussidon, Marc; Gurenko, Andrey; Delarue, Frédéric; Robert, François

    2016-06-01

    We have developed an analytical procedure for the measurement of oxygen isotope composition of fossil organic matter by secondary ion mass spectrometry (SIMS) at the sub-per mill level, with a spatial resolution of 20-30 μm. The oxygen isotope composition of coal and kerogen samples determined by SIMS are on average consistent with the bulk oxygen isotope compositions determined by temperature conversion elemental analysis - isotope ratio mass spectrometry (TC/EA-IRMS), but display large spreads of δ18O of ∼5-10‰, attributed to mixing of remnants of organic compounds with distinct δ18O signatures. Most of the δ18O values obtained on two kerogen residues extracted from the Eocene Clarno and Early Devonian Rhynie continental chert samples and on two immature coal samples range between ∼10‰ and ∼25‰. Based on the average δ18O values of these samples, and on the O isotope composition of water processed by plants that now constitute the Eocene Clarno kerogen, we estimated δ18Owater values ranging between around -11‰ and -1‰, which overall correspond well within the range of O isotope compositions for present-day continental waters. SIMS analyses of cyanobacteria-derived organic matter from the Silurian Zdanow chert sample yielded δ18O values in the range 12-20‰. Based on the O isotope composition measured on recent cyanobacteria from the hypersaline Lake Natron (Tanzania), and on the O isotope composition of the lake waters in which they lived, we propose that δ18O values of cyanobacteria remnants are enriched by about ∼18 ± 2‰ to 22 ± 2‰ relative to coeval waters. This relationship suggests that deep ocean waters in which the Zdanow cyanobacteria lived during Early Silurian times were characterised by δ18O values of around -5 ± 4‰. This study, establishing the feasibility of micro-analysis of Phanerozoic fossil organic matter samples by SIMS, opens the way for future investigations of kerogens preserved in Archean cherts and of the

  16. Uranium roll-front deposits in the southern Black Hills, South Dakota

    International Nuclear Information System (INIS)

    In the southern Black Hills of South Dakota, uranium roll-type deposits are present in early Cretaceous Lakota Formation sandstone. Analysis of a 45-Foot drill core, representing a vertical section through the nose of the roll-front, by scanning X-ray fluorescence (XRF), standard XRF, X-ray diffraction (XRD), organic petrography, electron microprobe, and scanning electron microscopy (SEM) is underway. The core is lithologically composed of an orthoquartzite with varying amounts of chert and consists of an oxidized zone, four reduced zones, and three ore zones. The oxidized zone is characterized by medium- to fine-grained, well-sorted, well-rounded orthoquartzite with minor hermatitic kaolinite weakly cementing and coating quartz grains. Reduced zones have angular to rounded, medium- to fine-grained gray to black quartz grains; coarse-grained, angular, white to black chert; thin laminae and small isolated fragments of carbonaceous material with pyrite. Ore zones are composed of trough cross-bedded, poorly-cemented, well-sorted mixtures of rounded quartz grains and angular to rounded chert with yellow to olive-green uranium- and vanadium-rich clays, and carbonaceous material with pyrite. The chemistry of the entire core was determined by scanning X-ray fluorescence for 46 elements. In the oxidized, reduced, and ore zones, uranium and vanadium averaged 40 ppm U and 3300 ppm V, 800 ppm U and 3000 ppm V, and 3800 ppm U and 5000 ppm V, respectively. No uranium or vanadium minerals have been found by XRD or microprobe analysis. However, certain segments of the core are enriched in U and V, including those with high clay content. Preliminary SEM analyses have shown smectite, kaolinite, and possibly illite as coatings on quartz grains. U and V are present in some of the clay coatings, and probable carnotite and an authigenic vanadium mineral were found. Carbonaceous laminae are present in the reduced and ore zones and commonly contain pyrite with associated uranium. (author

  17. Palynology of Lower Palaeogene (Thanetian-Ypresian) coastal deposits from the Barmer Basin (Akli Formation, Western Rajasthan, India): palaeoenvironmental and palaeoclimatic implications

    Energy Technology Data Exchange (ETDEWEB)

    Tripathi, S.K.M.; Kumar, M.; Srivastava, D. [Birbal Sahni Instititue of Paleobotany, Lucknow (India)

    2009-03-15

    The 32-m thick sedimentary succession of the Paleocene-Eocene Akli Formation (Barmer basin, Rajasthan, India), which is exposed in an open-cast lignite mine, interbed several lignite seams that alternate with fossiliferous carbonaceous clays, green clays and widespread siderite bands and chert nodules. The palynofloral assemblages consist of spore, pollen and marine dinoflagellate cysts that indicate a Thanetian to Ypresian age. The assemblage is dominated by angiospermic pollen and specimens showing affinity with the mangrove Palm Nypa are also very abundant. The Nypa-like pollen specimens exhibit a wide range of morphological variation, some of the recorded morphotypes being restricted to this Indian basin. Preponderance of these pollen taxa indicates that the sediments were deposited in a coastal swamp surrounded by thick, Nypa-dominated mangrove vegetation. The dispersed organic matter separated from macerated residues indicates the dominance of anoxic conditions throughout the succession, although a gradual transition to oxic conditions is recorded in the upper part.

  18. Development of latent fingermarks from rocks and stones.

    Science.gov (United States)

    Hefetz, Ido; Cohen, Amit; Cohen, Yaron; Chaikovsky, Alan

    2014-09-01

    Since the beginning of recorded history, stones have been used in the commission of crimes due to their widespread availability. Stones can be used as a lethal weapon that sometimes might be the only evidence in a serious case. The common perception, even in professional fingermark circles, is that stones do not yield identifiable latent fingermarks. The authors of this research paper examined the feasibility of developing fingermarks from seven types of stones using three latent fingermark techniques: magnetic powder, cyanoacrylate fuming, and ninhydrin. The paper will demonstrate that by classifying stones and rocks according to their natural properties (porosity, permeability, and the nature of surface area), even application of the simplest development techniques can produce good results. In conclusion, chert and limestone yielded the most qualitative and quantitative results using magnetic powder. The time factor is also important in recovering latent fingermarks on stones and rocks. PMID:24502220

  19. Variation of stable silicon isotopes. Analytical developments and applications in Precambrian geochemistry

    International Nuclear Information System (INIS)

    The work presented in this thesis predominantly deals with bulk-rock measurements of silicon stable isotopes on a Multi Collector-ICP-MS. Analyses were performed in cooperation with the Royal Museum for Central Africa, Belgium. The first section describes how the first analysis of δ30Si on a conventional Nu PlasmaTM Multi-Collector ICP-MS instrument can be enabled by the elimination of 14N16O interference overlying the 30Si peak. The determination of δ30Si was rendered possible owing to new instrumental upgrades that facilitate the application of a higher mass resolution. The careful characterisation of appropriate reference materials is indispensable for the assessment of the accuracy of a measurement. The determination of U.S. Geological Survey (USGS) reference materials represents the second objective of this section. The analysis of two Hawaiian standards (BHVO-1 and BHVO-2) demonstrates precise and accurate δ30Si determinations and provides cross-calibration data as a quality control for other laboratories. The second section focuses on coupled silicon-oxygen isotopic evidences for the origin of silicification in mafic volcanic rocks of the Barberton Greenstone Belt, South Africa. In contrast to the modern Earth, silicification of near-surface layers, including chert formation, were widespread processes on the Precambrian ocean floor, and demonstrate the ubiquity of extreme silica mobilization in the early Earth. This section outlines the investigation of silicon and oxygen isotopes on three different stratigraphic sections of variably silicified basalts and overlying bedded cherts from the 3.54 Ga, 3.45 Ga and 3.33 Ga Theespruit, Kromberg and Hooggenoeg Formations, respectively. Silicon isotopes, oxygen isotopes and the variable SiO2-contents demonstrate a positive correlation with silicification intensity in all three sections, with varying gradients of δ30Si vs. δ18O arrays for different sections. Seawater has been regarded as the most likely source of

  20. Rezension von: Nadine Teuber: Das Geschlecht der Depression. „Weiblichkeit“ und „Männlichkeit“ in der Konzeptualisierung depressiver Störungen. Bielefeld: transcript Verlag 2011.

    Directory of Open Access Journals (Sweden)

    Karen Wagels

    2013-02-01

    Full Text Available Ausgangspunkt und roten Faden der Studie bildet die Frage nach einem erhöhten Depressionsrisiko von Frauen: Ist Depression als spezifische Frauenkrankheit zu verstehen, und wenn ja, warum? Mit dieser einher geht ein ausdrückliches Interesse an den gesellschaftlichen wie auch individuell verkörperten Wirkungen einer symbolischen Geschlechterordnung, die Nadine Teuber im Feld der Depression äußerst differenziert auffächert. Die Gratwanderung einer geschlechtertheoretischen Problematisierung des Phänomens Depression, in dem Spuren der Naturalisierung auf vielfältige Weise angelegt sind, gelingt ihr durch die fundierte Darstellung der diskursiven Herstellungsprozesse von Geschlechtlichkeit wie auch von Depression, die sie in einer interdisziplinären Bezugnahme auf psychologische, psychoanalytische und kulturwissenschaftliche Perspektiven herausarbeitet.

  1. The Archean Dongwanzi ophiolite complex, North China craton: 2.505-billion-year-old oceanic crust and mantle.

    Science.gov (United States)

    Kusky, T M; Li, J H; Tucker, R D

    2001-05-11

    We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike-pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting. PMID:11349144

  2. Characteristics of Albaillella (Albaillellarian,Radiolarian) Fauna from Guadalupian to Lopingian Series in Permian,South China

    Institute of Scientific and Technical Information of China (English)

    Sun Dongying; Xia Wenchen

    2003-01-01

    On the basis of establishment of radiolarian biostratigraphy and conodont biostratigraphy,a radiolarian Albaillella fauna in the transitional environment from Guadalupian to Lopingian Series in Permian was found at a pelagic chert section in southeast Guangxi, South China. Radiolarian Aibaillella is one of the most sensitive biology to the transitional environment. The Albaillella fauna shows an ecological evolutionary process from Guadalupian to Lopingian: declined stage-recovery stage-flourishing stage. The study of characteristics of the Albaillella fauna in the transitional environment may provide more information, not only for the subdivision and correlation of a high-resolution biostratigraphy, but also for influence of radiolarian Albaillella fauna on the pre-Lopingian mass extinction.

  3. Petrographic characteristic of the sandstones of the upper paleocene-middle eocene aged in the Yildizli-Aydinkent (Ereğli-Konya area

    Directory of Open Access Journals (Sweden)

    A. Müjdat Özkan

    2002-03-01

    Full Text Available In the study area, Upper Paleocene - Middle Eocene aged Halkapınar formation, was formed in a shallow and deep marine environment. The lithologies of this formation are medium - thick bedded conglomerate, thin - thick bedded sandstone, thin - very thick bedded shale, thin - medium bedded marl with chert nodules and bands. In addition olistolithes of ophiolitic melange are found at the top of the sandstones, which includes basalt interbands. Yellowish gray, greenish gray, beige, gray colored sandstones include some sedimentary structures, namely ripple - marks, graded bedding, laminate, convolute lamination, current ripple, tool marks. Constituents of the sandstones are quartz, plagioclase, sanidine, orthoclase, fragments of sedimentary and methamorphic rocks, biotite, muscovite, opaque mineral and glauconite. The sandstones, which are not matured in terms of mineralogy and texture, are mainly cemented by calcite, clay matrix and minor iron oxide and glauconite matrix. The sandstones are named lithic arenite, lithic graywacke, feldspathic litharenite and litharenite.

  4. Geochemistry of the Upper Cretaceous Oil Shale, NW-Jordan

    International Nuclear Information System (INIS)

    TheOil Shale from the Amman Formation of NW-Jordan ois mainly of calcareous oil shale type. It consists of limestone and marly limestone as major compounds beside some chert, phosphate and clay minerals and contains different amounts of organic matter up to 28% mainly of kerogen; its average is 12.12% it is mostly deposited in reducing marine shallow water environment. The minerala constituents of the studied oil shale are calcite up to 90 wt % (and quartz, beside apatite and clay minerals, and contains P2O5 (average 63.3 wt %) SO4 (average 1.53 wt %) tio2 (average 0.12 wt %) and also the trace elemments Zn, V, Pb, Ni, MO, Cu, Cr, Co, Cd, Ba. They are mainly associated with carbonates , organic matter, and/or sulphide phases. These trace elements could be partly of economic importance as byproduct. (Author's) 31 refs., 2 tabs., 3 figs

  5. SWIR Investigation of sites of astrobiological interest

    CERN Document Server

    Brown, Adrian J; Cudahy, Thomas

    2014-01-01

    Rover missions to the rocky bodies of the Solar System and especially to Mars require light- weight, portable instruments that use minimal power, require no sample preparation, and provide suitably diagnostic mineralogical information to an Earth-based exploration team. Short-wave infrared (SWIR) spectroscopic instruments such as the Portable Infrared Mineral Analyser (PIMA, Integrated Spectronics Pty Ltd., Baulkham Hills, NSW, Australia) fulfill all these requirements. We describe an investigation of a possible Mars analogue site using a PIMA instrument. A survey was carried out on the Strelley Pool Chert, an outcrop of stro- matolitic, silicified Archean carbonate and clastic succession in the Pilbara Craton, interpreted as being modified by hydrothermal processes. The results of this study demonstrate the ca- pability of SWIR techniques to add significantly to the geological interpretation of such hy- drothermally altered outcrops. Minerals identified include dolomite, white micas such as il- lite-muscovit...

  6. Using (1)(0)Be cosmogenic isotopes to estimate erosion rates and landscape changes during the Plio-Pleistocene in the Cradle of Humankind, South Africa.

    Science.gov (United States)

    Dirks, Paul H G M; Placzek, Christa J; Fink, David; Dosseto, Anthony; Roberts, Eric

    2016-07-01

    Concentrations of cosmogenic (10)Be, measured in quartz from chert and river sediment around the Cradle of Humankind (CoH), are used to determine basin-averaged erosion rates and estimate incision rates for local river valleys. This study focusses on the catchment area that hosts Malapa cave with Australopithecus sediba, in order to compare regional versus localized erosion rates, and better constrain the timing of cave formation and fossil entrapment. Basin-averaged erosion rates for six sub-catchments draining the CoH show a narrow range (3.00 ± 0.28 to 4.15 ± 0.37 m/Mega-annum [Ma]; ±1σ) regardless of catchment size or underlying geology; e.g. the sub-catchment with Malapa Cave (3 km(2)) underlain by dolomite erodes at the same rate (3.30 ± 0.30 m/Ma) as the upper Skeerpoort River catchment (87 km(2)) underlain by shale, chert and conglomerate (3.23 ± 0.30 m/Ma). Likewise, the Skeerpoort River catchment (147 km(2)) draining the northern CoH erodes at a rate (3.00 ± 0.28 m/Ma) similar to the Bloubank-Crocodile River catchment (627 km(2)) that drains the southern CoH (at 3.62 ± 0.33 to 4.15 ± 0.37 m/Ma). Dolomite- and siliciclastic-dominated catchments erode at similar rates, consistent with physical weathering as the rate controlling process, and a relatively dry climate in more recent times. Erosion resistant chert dykes along the Grootvleispruit River below Malapa yield an incision rate of ∼8 m/Ma at steady-state erosion rates for chert of 0.86 ± 0.54 m/Ma. Results provide better palaeo-depth estimates for Malapa Cave of 7-16 m at the time of deposition of A. sediba. Low basin-averaged erosion rates and concave river profiles indicate that the landscape across the CoH is old, and eroding slowly; i.e. the physical character of the landscape changed little in the last 3-4 Ma, and dolomite was exposed on surface probably well into the Miocene. The apparent absence of early Pliocene- or Miocene-aged cave deposits and

  7. Surface currents in the Arctic Ocean during the last 250 ka: Composition of ice-rafted Detritus (IRD) as a key for ice drift directions

    International Nuclear Information System (INIS)

    Eleven long sediment cores from the Arctic Ocean and Fram Strait (78 degree-86N) documenting more than 250,000 years of sedimentation history show distinct variations in the composition of coarse sand (500 pin). Ice-rafted coal fragments deposited during glacial oxygen isotope stages 6 (186-128ka) and 8 (303-245ka) are evidence for ice drift from the Eastern Arctic Ocean through Fram Strait to the Norwegian Sea. The dominating lithologies, with a high amount of sedimentary rock fragments in the IRD from interglacial stages (7, 5, 1), indicate a similar current pattern as today. Crystalline rock fragments in glacial sediments decrease from the Barents Shelf margin to the Nansen-Gakkel Ridge where they are replaced by quartzites and cherts

  8. Stable isotope composition and volume of Early Archaean oceans

    DEFF Research Database (Denmark)

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

    low-δ18O values of Precambrian sedimentary cherts and carbonates are not a consequence of isotope variability of seawater or extreme ocean temperatures [3,4], but rather are due to isotopic exchange with shallow hydrothermal fluids on the ocean floor or during diagenesis [5]. [1] Lécuyer et al. (1998......Oxygen and hydrogen isotope compositions of seawater are controlled by volatile fluxes between mantle, lithospheric (oceanic and continental crust) and atmospheric reservoirs. Throughout geologic time oxygen was likely conserved within these Earth system reservoirs, but hydrogen was not, as it can...... escape to space [1]. Hydrogen isotope ratios of serpentinites from the ~3.8Ga Isua Supracrustal Belt in West Greenland are between -53 and -99‰; the highest values are in antigorite ± lizardite serpentinites from a low-strain lithologic domain where hydrothermal reaction of Archaean seawater with oceanic...

  9. Pre-Eocene rocks of Java, Indonesia

    Science.gov (United States)

    Ketner, Keith B.; Kastowo; Modjo, Subroto; Naeser, C.W.; Obradovich, J.D.; Robinson, Keith; Suptandar, Tatan; Wikarno

    1976-01-01

    The exposed pre-Eocene rocks of Java can be divided into two compound units for purposes of reconnaissance mapping and structural interpretation: a sedimentary sequence and melange. The sedimentary sequence consists of moderately deformed and little-metamorphosed conglomerate, sandstone, mudstone, claystone, chert, and limestone. The melange consists of a chaotic mechanical mixture of rocks identical to those of the sedimentary sequence and their metamorphic equivalents, such as schist, phyllite, quartzite, and marble. In addition, it contains a large proportion of quartz porphyry and smaller amounts of granite, basalt, gabbro, peridotite, pyroxenite, and serpentinite. The sedimentary sequence is at least partly of Early Cretaceous age and the melange is of Early Cretaceous to very early Paleocene age. They are overlain unconformably by Eocene rocks. The presence in the melange of blocks of quartz porphyry and granite is not easily reconcilable with current plate tectonic concepts in which the sites of formation of melange and plutonic rocks should be hundreds of kilometres apart.

  10. Association of macro- and microfossils in the Vendian (Ediacaran) postglacial successions in Western Mongolia

    Science.gov (United States)

    Ragozina, A. L.; Dorjnamjaa, D.; Serezhnikova, E. A.; Zaitseva, L. V.; Enkhbaatar, B.

    2016-05-01

    The Vendian (Ediacaran) beds of the Zavkhan Basin, in the upper part of the Tsagaanolom Formation (<632 ± 14 Ma), yielded a new "Zavkhan" association of algae, microfossils, and problematic organisms, which is established in the series of alternating chert-carbonate shale with phosphorite interbeds. This association is distinct in the predomination of large (250 μm and over) sphaeromorphic microfossils of the genera Tasmanites, Archaeooides, and Leiosphaeridia, whereas acanthomorph acritarchs are represented by rarely found Cavaspina sp. and Tanarium sp. Multicellular algae included fragments of encrusting or foliate thalli with pseudoparenchymatous structure of polygonal cells characteristic of Rhodophyta algae ( Thallophycoides sp.), and cordlike thalli of Vendotaenid algae Tyrasotaenia podolica. These layers of siltstone contain imprints of the problematic Vendian macrofossil Beltanelliformis brunsae. In their stratigraphic position, chemostratigraphic data, and fossil assemblage, the "Zavkhan" association can be assigned to the Upper Vendian.

  11. Examining time trends in the Oldowan technology at Beds I and II, Olduvai Gorge.

    Science.gov (United States)

    Kimura, Yuki

    2002-09-01

    The lithic analysis of the Bed I and II assemblages from Olduvai Gorge reveals both static and dynamic time trends in early hominids' technology from 1.8 to 1.2 m.y.a. The Bed I Oldowan (1.87-1.75 m.y.a.) is characterized by the least effort strategy in terms of raw material exploitation and tool production. The inclusion of new raw material, chert, for toolmaking in the following Developed Oldowan A (DOA, 1.65-1.53 m.y.a.) facilitated more distinctive and variable flaking strategies depending on the kind of raw materials. The unique characters of DOA are explainable by this raw material factor, rather than technological development of hominids. The disappearance of chert in the subsequent Developed Oldowan B and Acheulian (1.53-1.2 m.y.a.) necessitated a shift in tool production strategy more similar to that of Bed I Oldowan than DOA. However, the evidence suggests that Bed II hominids might have been more skillful toolmakers, intensive tool-users, and engaged in more active transport of stone tools than the Bed I predecessors. Koobi Fora hominids maintained a more static tool-using behavior than their Olduvai counterparts due mainly to a stable supply of raw materials. They differed from Olduvai hominids in terms of less battering of cores, consistent transport behavior, and few productions of side-struck flakes, indicating a regional variation of toolmaking and using practice. However, they shared with Olduvai hominids a temporal trend toward the production of larger flakes from larger cores after 1.6 m.y.a. Increased intake of animal resources and the expansion of ranging area of Homo ergaster would have led to the development of technological organization. Technological changes in the Oldowan industry are attested at Olduvai Gorge, Koobi Fora, and Sterkfontein, suggesting that it was a pan-African synchronous phenomenon, beginning at 1.5 m.y.a. PMID:12234546

  12. Early evolution of life cycles in embryophytes:A focus on the fossil evidence of gametophyte/sporophyte size and morphological complexity

    Institute of Scientific and Technical Information of China (English)

    Philippe GERRIENNE; Paul GONEZ

    2011-01-01

    Embryophytes (land plants) are distinguished from their green algal ancestors by diplobiontic life cycles,that is,alternation of multicellular gametophytic and sporophytic generations.The bryophyte sporophyte is small and matrotrophic on the dominant gametophyte; extant vascular plants have an independent,dominant sporophyte and a reduced gametophyte.The elaboration of the diplobiontic life cycle in embryophytes has been thoroughly discussed within the context of the Antithetic and the Homologous Theories.The Antithetic Theory proposes a green algal ancestor with a gametophyte-dominant haplobiontic life cycle.The Homologous Theory suggests a green algal ancestor with alternation of isomorphic generations.The shifts that led from haplobiontic to diplobiontic life cycles and from gametophytic to sporophytic dominance are most probably related with terrestrial habitats.Cladistic studies strongly support the Antithetic Theory in repeatedly identifying charophycean green algae as the closest relatives of land plants.In recent years,exceptionally well-preserved axial gametophytes have been described from the Rhynie chert (Lower Devonian,410 Ma),and the complete life cycle of several Rhynie chert plants has been reconstructed.All show an alternation of more or less isomorphic generations,which is currently accepted as the plesiomorphic condition among all early polysporangiophytes,including basal tracheophytes.Here we review the existing evidence for early embryophyte gametophytes.We also discuss some recently discovered plants preserved as compression fossils and interpreted as gametophytes.All the fossil evidence supports the Antithetic Theory and indicates that the gametophytic generation/sporophytic generation size and complexity ratios show a gradual decrease along the land plant phylogenetic tree.

  13. Upper Cretaceous oceanic red beds in southern Tibet: Lithofacies, environments and colour origin

    Institute of Scientific and Technical Information of China (English)

    HU Xiumian; WANG Chengshan; LI Xianghui; Jansa Luba

    2006-01-01

    Application of mineralogy, geochemistry, sedimentary petrology, and sedimentology methods result in better understanding of the genesis and paleoenvironmens of the Upper Cretaceous oceanic red beds exposed in southern Tibet. The red beds comprise the Chungde Formation. Nine lithofacies recognized within this formation are: red foraminiferal packstone/grainstone, red microfossils wackestone, red marlstone with microfossils, red marlstone, red to variegated floatstone and rudstone (debris flow), red shale, red radiolarite, red chert with radiolaria, and red chert. Sedimentary structures and textures, microfossils, and carbonate content show that the Chuangde Fm was deposited near the base of a continental slope in a deep oceanic basin environment, with the basin floor below the carbonate compensation depth (CCD). Red marlstones and limestones intercalated within red shales represent slides and slumps from the upper part of the continental margin. Debris flow and turbidity deposits consist of volcaniclastic, fossilliferous rudstone and floatstone, and very thin calcareous mudstone, intercalated with red shales.The Upper Cretaceous oceanic red beds in southern Tibet are characterized by high Fe2O3, low FeO, which indicates an oxic diagenetic environment, resulting in precipitation of hematite. The latter occurs as finely, disseminated ferric oxide giving the red color to the rocks. It is concluded that the red beds in southern Tibet were deposited under highly oxygenated bottom conditions in the deep ocean basin. Such conditions not only occurred in a deep ocean basin as indicated by the occurrence of pelagic red shale deposited below the CCD, but also extended up the continental margin as indicated by the presence of red colored marlstones and limestones embedded in the Chuangde Fm. The latter were deposited above CCD, most probably on the continental slope. The oxic bottom conditions are interpreted to be a result of a combination of climate cooling, active bottom

  14. Lithological influence of aggregate in the alkali-carbonate reaction

    International Nuclear Information System (INIS)

    The reactivity of carbonate rock with the alkali content of cement, commonly called alkali-carbonate reaction (ACR), has been investigated. Alkali-silica reaction (ASR) can also contribute in the alkali-aggregate reaction (AAR) in carbonate rock, mainly due to micro- and crypto-crystalline quartz or clay content in carbonate aggregate. Both ACR and ASR can occur in the same system, as has been also evidenced on this paper. Carbonate aggregate samples were selected using lithological reactivity criteria, taking into account the presence of dedolomitization, partial dolomitization, micro- and crypto-crystalline quartz. Selected rocks include calcitic dolostone with chert (CDX), calcitic dolostone with dedolomitization (CDD), limestone with chert (LX), marly calcitic dolostone with partial dolomitization (CD), high-porosity ferric dolostone with clays (FD). To evaluate the reactivity, aggregates were studied using expansion tests following RILEM AAR-2, AAR-5, a modification using LiOH AAR-5Li was also tested. A complementary study was done using petrographic monitoring with polarised light microscopy on aggregates immersed in NaOH and LiOH solutions after different ages. SEM-EDAX has been used to identify the presence of brucite as a product of dedolomitization. An ACR reaction showed shrinkage of the mortar bars in alkaline solutions explained by induced dedolomitization, while an ASR process typically displayed expansion. Neither shrinkage nor expansion was observed when mortar bars were immersed in solutions of lithium hydroxide. Carbonate aggregate classification with AAR pathology risk has been elaborated based on mechanical behaviours by expansion and shrinkage. It is proposed to be used as a petrographic method for AAR diagnosis to complement the RILEM AAR1 specifically for carbonate aggregate. Aggregate materials can be classified as I (non-reactive), II (potentially reactive), and III (probably reactive), considering induced dedolomitization ACR

  15. Pillow basalts of Morro do Agostinho Ophiolite Suite: records of seafloor in the midwestern portion of Araguaia Belt

    Directory of Open Access Journals (Sweden)

    Luciana de Jesus Penha Pamplona Miyagawa

    2013-12-01

    Full Text Available Along the domain of low metamorphic grade (Midwestern portion of the Araguaia Belt, outcrop dozens mafic and/or ultramafic bodies of ophiolitic suites. An example is the Morro do Agostinho Ophiolite Suite, in the surroundings of the city of Araguacema (Tocantins that configures a small isolated body that sustains the Morro do Agostinho and is tectonically emplaced in meta-sandstones, slates and phyllites of Couto Magalhães Formation (Tocantins Group. The Morro do Agostinho Ophiolite Suite consists of serpentinized peridotites, basalts and ferriferous cherts. The association of basalts is characterized by a significant layer of submarine pillow lavas overlying serpentinized peridotites. The basalts were classified into massive and hialobasalts types. Massive basalts are homogenous, with intersertal texture that is essentially composed of thin laths and acicular crystals of plagioclase and clinopyroxene and present rare crystals of olivine, chalcocite and chalcopyrite. Hyalobasalt shows ultra-fast cooling features (quenching as spherulites, radial, acicular and skeletal crystals of plagioclase and clinopyroxene with forms of swallowtail. Geochemical data, including (La/Ybn and (La/Smn ratios less than 1, indicate a subalkaline-tholeiitic MORB nature of the basalts. These rocks show that during the geological evolution of Araguaia Belt, there was an oceanization stage of Araguaia Basin, with litospheric mantle’s exposure, followed by lava’s extravasation and sedimentation of cherts and banded iron formation in deep ocean environment. After sedimentary filling of the Couto Magalhães Formation (Tocantins Group, the tectonic inversion, which led to the exhumation of the ophiolitic bodies, especially along thrust surface, with fragmenting and tectonic mixing with supracrustal rocks, accompanied by regional metamorphism under conditions of low green schist facies. The Morro do Agostinho Ophiolite Suite therefore represents a small allochthonous

  16. Why Was Silcrete Heat-Treated in the Middle Stone Age? An Early Transformative Technology in the Context of Raw Material Use at Mertenhof Rock Shelter, South Africa.

    Directory of Open Access Journals (Sweden)

    Patrick Schmidt

    Full Text Available People heat treated silcrete during the Middle Stone Age (MSA in southern Africa but the spatial and temporal variability of this practice remains poorly documented. This paucity of data in turn makes it difficult to interrogate the motive factors underlying the application of this technique. In this paper we present data on heat treatment of silcrete through the Howiesons Poort and post-Howiesons Poort of the rock shelter site Mertenhof, located in the Western Cape of South Africa. In contrast to other sites where heat treatment has been documented, distance to rock source at Mertenhof can be reasonably well estimated, and the site is known to contain high proportions of a diversity of fine grained rocks including silcrete, hornfels and chert at various points through the sequence. Our results suggest the prevalence of heat treatment is variable through the sequence but that it is largely unaffected by the relative abundance of silcrete prevalence. Instead there is a strong inverse correlation between frequency of heat treatment in silcrete and prevalence of chert in the assemblage, and a generally positive correlation with the proportion of locally available rock. While it is difficult to separate individual factors we suggest that, at Mertenhof at least, heat treatment may have been used to improve the fracture properties of silcrete at times when other finer grained rocks were less readily available. As such, heat treatment appears to have been a component of the MSA behavioural repertoire that was flexibly deployed in ways sensitive to other elements of technological organisation.

  17. Albian - Cenomanian resedimented limestone in the Lower flyschoid Formation of the Mt. Mrzli Vrh Area (Tolmin region, NW Slovenia

    Directory of Open Access Journals (Sweden)

    Boštjan Rožič

    2005-12-01

    Full Text Available The Lower flyschoid formation of the Slovenian Basin is characterized by marl, shale and subordinate chert, interbedded with micritic limestone and resedimented carbonates.In the upper part of the formation marly and micritic limestones commonly prevail. The maximum range of the formation is Albian to Turonian. Contact with underlying successions is always erosional and the formation usually overlies upper Tithonian to NeocomianBiancone limestone. In the Mt. Mrzli vrh area, the formation is composed of upper Albian to lower Cenomanian resedimented limestone and upper Cenomanian to Turonian shale and marl, marly limestone and cherts. It directly overlies Lower Jurassic basinal successionor Upper Triassic platform dolomite. In this study resedimented carbonates of the formation were analyzed. A two km2 area was mapped and an 80m thick Mt. Grmuč section was studied in detail. This section consists of micritic limestone and abundant breccia andcalcarenite. Whereas the calcarenite is predominantly composed of platform-derived material, the breccia consists of slope-to-basin intraclasts and various extraclasts of older platform and basin deposits. The analyzed facies association indicates a lower slopedepositional environment. A correlation with other successions of the Lower flyschoid formation reveals that resedimented carbonates are the thickest and most abundant in the Tolmin region, that paleogeographically corresponds to the western part of the SlovenianBasin. Intense Albian – Cenomanian tectonic activity is inferable regionally, from platform as well as basinal successions, and is thought to have been the major factor causing andcontrolling the carbonate gravity-flows sedimentation in the Slovenian Basin. The Mt. Mrzli vrh area is important for paleotopographic reconstruction because it links thecentral Slovenian Basin with the margin of the Dinaric Carbonate Platform. The observed lateral facies distribution, the composition of lithoclasts

  18. Late Paleozoic accretionary complexes on the Gondwana margin of southern Chile: Evidence from the Chonos Archipelago

    Science.gov (United States)

    Davidson, John; Mpodozis, Constantino; Godoy, Estanislao; Hervé, Francisco; Pankhurst, Robert; Brook, Maureen

    The late Paleozoic "basement" rocks that crop out along the Pacific side of the Chonos Archipelago (44°-46°S) can be divided into two north-south trending belts: (1) an eastern belt formed of submarine fan-turbidites and subordinate pelagic cherts, each containing well-preserved primary sedimentary structures, and (2) a western belt, mainly formed by strongly foliated mica schists and greenschists. Trace element contents in the cherts and greenschists indicate rocks of oceanic affinity. The structures present within the eastern rock suite are principally subiso-clinal folds (with tectonic imbrication) and locally developed zones of broken formation. The transition from these rocks into the foliated schists appears to be related to a progressive increase in metamorphism and strain associated with the development of westward verging recumbent folds and a flat-lying crenulation cleavage. It is inferred that these structures developed during the construction of a Late Carboniferous-Early Permian accretionary prism (about 260 Ma Rb-Sr ages), although sedimentation may have taken place throughout the upper Paleozoic. Rb-Sr whole-rock isochrons giving Late Jurassic to Early Cretaceous ages for some localities may indicate much later development of S2 structures. Alternatively, they may represent isotopic resetting by hydrothermal effects during the emplacement of transgressive Early Cretaceous granites, one of which gives a new Rb-Sr isochron age of 125±2Ma. This overall scenario seems to be consistent with that reported in the slightly older coastal metamorphic basement north of 34°S and equivalent or younger complexes farther south in the Madre de Dios Archipelago.

  19. The silicon isotope record of early silica diagenesis

    Science.gov (United States)

    Tatzel, Michael; von Blanckenburg, Friedhelm; Oelze, Marcus; Schuessler, Jan A.; Bohrmann, Gerhard

    2015-10-01

    The heavy isotopes of silicon are strongly enriched in some of the youngest, early diagenetically formed porcellanite layers from the Southwest Indian Ridge (Pleistocene) and the Maud Rise (Pliocene). These porcellanite layers are composed of opal-CT and were formed by the conversion of amorphous silica (opal-A) from siliceous sediment via dissolution-reprecipitation. Their bulk δ30Si values range between 1.7 and 2.3‰. Detritus-poor siliceous sediment surrounding these layers is significantly lower at -0.3 to 1.5‰. Sequential chemical extractions of bulk siliceous sediment show (i) preferential dissolution of diatoms featuring higher δ30Si than radiolaria and Al-Si components. The detailed investigation of porcellanite layers by micro-scale Si isotope and Al/Si analyses using UV femtosecond laser ablation ICP mass spectrometry show that (ii) precipitation of authigenic aluminum silicates enriched in light Si isotopes drives pore waters to even higher δ30Si. We suggest that the same processes redistributed stable silicon isotopes in precursor siliceous sediments of ancient chert. We infer that past environmental conditions can be reconstructed with high fidelity from the stable Si isotope composition of chert when initial seawater Si concentrations were high (such as in the Precambrian). Exchange of Si between layers during phase transformation (from opal-A to opal-CT and from opal-CT to quartz) is impeded when variable amounts of detrital minerals are present, because they control rates of silica phase transformation and hence the timing of dissolution-reprecipitation during burial.

  20. Infrared microspectroscopy analysis of water distribution in deformed and metamorphosed rocks

    Science.gov (United States)

    Nakashima, Satoru; Matayoshi, Hiromi; Yuko, Takako; Michibayashi, Katsuyoshi; Masuda, Toshiaki; Kuroki, Noriko; Yamagishi, Hiraku; Ito, Yuki; Nakamura, Akira

    1995-05-01

    Infrared microspectroscopy has been applied to thin sections of various deformed and metamorphosed rocks in order to investigate water content of quartz in these rocks. The broad IR band absorbance around 3400 cm -1 probably due to fluid-inclusion molecular water (H 2O) was used to calculate water contents. Deformed granitic rocks from the Yanazawa-Kamimura area near the Median Tectonic Line (MTL) showed an increase of water content in quartz from about 300 ppm to 2500 ppm toward the MTL with increasing degree of deformation. Metacherts from Sambagawa metamorphic rocks (Asemigawa route) showed a systematic decrease of water content in quartz from about 1000 ppm to 200 ppm with increasing metamorphic degree from chlorite, garnet, albite-biotite to oligoclase-biotite zones. An Archaean metachert from the Napier Complex (granulite facies) has only 40 ppm water. Comparing this with an Inuyama unmetamorphosed chert sample having water contents of 3500 to 7000 ppm (a starting point of metamorphism), the systematic decrease of water in quartz with increasing metamorphic grade may extend from unmetamorphosed cherts to the highest-grade metacherts. Water contents in high-pressure metamorphic rocks in Japan are mostly of the order of 500 ppm (300-700 ppm), except for those from Kurosegawa with a water content as high as 1700 ppm. These results represent an exploratory analysis of intragranular water contents in quartz in various deformed and metamorphosed rocks. Further micro FT-IR studies of the distribution of water in crustal rocks will provide a quantitative basis for examining the geochemical cycle of water in the earth's crust.

  1. Lithofacies, age, depositional setting, and geochemistry of the Otuk Formation in the Red Dog District, northwestern Alaska

    Science.gov (United States)

    Dumoulin, Julie A.; Burruss, Robert A.; Blome, Charles D.

    2013-01-01

    Complete penetration of the Otuk Formation in a continuous drill core (diamond-drill hole, DDH 927) from the Red Dog District illuminates the facies, age, depositional environment, source rock potential, and isotope stratigraphy of this unit in northwestern Alaska. The section, in the Wolverine Creek plate of the Endicott Mountains Allochthon (EMA), is ~82 meters (m) thick and appears structurally uncomplicated. Bedding dips are generally low and thicknesses recorded are close to true thicknesses. Preliminary synthesis of sedimentologic, paleontologic, and isotopic data suggests that the Otuk succession in DDH 927 is a largely complete, albeit condensed, marine Triassic section in conformable contact with marine Permian and Jurassic strata. The Otuk Formation in DDH 927 gradationally overlies gray siliceous mudstone of the Siksikpuk Formation (Permian, based on regional correlations) and underlies black organic-rich mudstone of the Kingak(?) Shale (Jurassic?, based on regional correlations). The informal shale, chert, and limestone members of the Otuk are recognized in DDH 927, but the Jurassic Blankenship Member is absent. The lower (shale) member consists of 28 m of black to light gray, silty shale with as much as 6.9 weight percent total organic carbon (TOC). Thin limy layers near the base of this member contain bivalve fragments (Claraia sp.?) consistent with an Early Triassic (Griesbachian-early Smithian) age. Gray radiolarian chert dominates the middle member (25 m thick) and yields radiolarians of Middle Triassic (Anisian and Ladinian) and Late Triassic (Carnian-late middle Norian) ages. Black to light gray silty shale, like that in the lower member, forms interbeds that range from a few millimeters to 7 centimeters in thickness through much of the middle member. A distinctive, 2.4-m-thick interval of black shale and calcareous radiolarite ~17 m above the base of the member has as much as 9.8 weight percent TOC, and a 1.9-m-thick interval of limy to cherty

  2. Geochemical and Mineralogical Investigation for Carbon Capture and Storage, Within the Arbuckle Aquifer, Kansas

    Science.gov (United States)

    Datta, S.; Campbell, B.; Vega, M.; Barker, R. L.; Holubnyak, E.; Watney, W. L.

    2013-12-01

    A class VI permit site under U.S. Department of Energy has been proposed for carbon sequestration in south-central Kansas. In an effort to maintain environmental stability three wells have been drilled to basement rock, two being near the injection site, KGS 1-32 and KGS 1-28, and one being to the western annex, Cutter KGS #1. The western annex site, Cutter, is being utilized as a cross-comparison for mineralogical, geochemical, and structural component to the eastern sites in Wellington. A link will be determined of the continuity of three zones of interest: the Mississippian pay zone (3670'-3700'), a potential baffle zone in the upper Arbuckle (4400'-4550'), and the proposed CO2 injection zone (4900'-5050'). 11 depths within Cutter have been swabbed, and samples taken to investigate the chemistry of the subsurface formation water. The different depths will allow for a quantitative determination of how the brine composition varies with depth, and also provides a baseline for future monitoring. Initial chemical analysis by ICP-OES and HR-ICP-MS show a hyper saline brine (50,000-190,000TDS), dominated by Cl, Na, and Ca ions. pH ranges from 6.4 to 7.5, and total alkalinity from 124 and 378 mg/L of HCO¬3-. One complex, yet intriguing, species is Iron. It could potentially allow for further precipitation of the CO2¬ from the formation of Fe carbonates, such as siderite. Cores and thin sections were taken from a variety of depths ranging from 3681.9' to 5176.9' (Wellington) and 5564.3' to 7540.2' (Cutter). Dominant mineralogy consists of dolomite with varying forms of silicic intrusions, usually in the form of chert nodules with sulfide minerals and argillaceous materials in between. Extensive vugs and microfractures allow for varying porosity within each interval. Pay zone rocks typically display fine-grained cherty dolomite with subhedral to euhedral dolomite rhombs as well as oil stains oriented in parallel blotches. Characteristics such as high porosity and small

  3. New Archeointensities from Mid Holocene Archeological Materials

    Science.gov (United States)

    Kapper, K.; Donadini, F.; Hirt, A. M.

    2013-12-01

    hearth remains from central Europe, which cover a time period from 500 to 5200 BC. The ferromagnetic minerals in these materials were characterized by rock magnetic measurements. Archeointensities were obtained by using the Thellier method and the IZZI-protocol. We compare the new data with current geomagnetic field models and available archeomagnetic data. Furthermore, we demonstrate the value of burned cherts as a material that records the past geomagnetic field. We compare results of eight burned and unburned cherts to demonstrate that this material is useful for archeointensity determinations. Preliminary results show that the ceramics and slags provide reliable new archeointensity data. Hearth remains obtained in many cases a chemical remanent magnetization and therefore, do not provide useful data.

  4. Geochemistry of the Yutangba Se Deposit in Western Hubei, China

    Institute of Scientific and Technical Information of China (English)

    冯彩霞; 刘家军; 胡瑞忠; 刘燊

    2004-01-01

    The Yutangba Se deposit is a rare high-Se deposit in the world and it is well known for its high contents of Se, which reach 8590×10-6 . The ore-hosted rocks are dominated by cherts that have been well developed. Enrichment of selenium in Se-rich ores is obviously controlled by stratigraphic position and lithological character. The closer the rocks are to the Maokou Formation cherts, the more they contain selenium, but in case the stratigraphic horizons are close to one another, the enrichment of selenium would be controlled by lithological character. In the Se ores and abandoned stone coal pile at the Yutangba Se deposit there have been found large amounts of independent Se minerals, for instance, achavalite and a variety of forms of native selenium. Native selenium minerals present in the abandoned stone coal pile are the outcome of a combination of natural factors and anthropologic activities. For example, lime making will create a closed environment favoring the growth of native selenium, and the reduction of selenium will lead to its secondary enrichment. Starting with the study of ore-forming fluids. Systematic studies have been conducted on fluid inclusions separated from the main ore veins in the mining district for their homogenization temperatures, salinities and density, and the results show that fluid inclusions contained in ores from the Yutangba Se deposit are large in number and diverse in form, dominated by primary ones. The homogenization temperatures of two types of fluid inclusions are within the range of 173.2-247.5℃, individually up to 300℃ or even higher; the salinities of fluids in fluid inclusions in quartz and calcite are 5.9%-10.1% and 3.9%-4.5%, respectively; their densities vary from 0.79-0.93 g/cm3. Extensive discovery of Se minerals due to secondary enrichment of selenium in the stone coal provides important clues to the improvements on the metallurgical and recovery technologies for selenium in the black shale series of China

  5. A new method of combined techniques for characterization and monitoring of seawater interface in an alluvial aquifer

    Science.gov (United States)

    Folch, Albert; del Val, Laura; Luquot, Linda; Martínez, Laura; Bellmunt, Fabian; Le Lay, Hugo; Rodellas, Valentí; Ferrer, Núria; Fernández, Sheila; Ledo, Juanjo; Pezard, Philippe; Bour, Olivier; Queralt, Pilar; Marcuello, Alex; García-Orellana, Jordi; Saaltink, Maarten; Vázquez-Suñé, Enric; Carrera, Jesús

    2016-04-01

    Understand the dynamics of the fresh-salt water interface in aquifers is a key issue to comprehend mixing process and to quantity the discharge of nutrients in to coastal areas. In order to go beyond the current knowledge in this issue an experimental site has been set up at the alluvial aquifer Riera Argentona (Barcelona - Spain). The site comprises 16 shallow piezometers installed between 30 and 90 m from the seashore, with depths ranging between 15 and 25 meters. The seawater interface is being monitored using several techniques, the combination of which will help us to understand the spatial and temporal behaviour of the mixing zone and the geochemical processes occurring there. Specially the deepest piezometers are equipped with electrodes in order to perform cross-hole electrical resistivity tomography (CHERT). In addition, all piezometers are also equipped with Fiber Optic cable to perform distributed temperature measurements. Two single steel armoured fibre optic cable lines of around 600m length were installed in all boreholes. The objective is to use the cable both as passive and active temperature sensor. The first is being done for the continuous monitoring of temperature whereas; the second provides a higher temperature resolution used to monitor field experiments. Periodic CHERT measurements are carried out between the piezometer equipped with electrodes, resulting in parallel and perpendicular vertical cross sections of the site resistivity. The position of the fresh-salt water interface can be identified due to the resistivity contrast between the saline and fresh water. Preliminary results of periodic distributed temperature measurements will be also be used to monitor the position of the mixing zone thanks to the contrast and seasonal temperature changes. Periodic down-hole EC profiles will be used to validate the method. Acknowledgements This work was funded by the projects CGL2013-48869-C2-1 y CGL2013-48869-C2-2-R of the Spanish Government. We

  6. Diagenetic and compositional controls of wettability in siliceous sedimentary rocks, Monterey Formation, California

    Science.gov (United States)

    Hill, Kristina M.

    Modified imbibition tests were performed on 69 subsurface samples from Monterey Formation reservoirs in the San Joaquin Valley to measure wettability variation as a result of composition and silica phase change. Contact angle tests were also performed on 6 chert samples from outcrop and 3 nearly pure mineral samples. Understanding wettability is important because it is a key factor in reservoir fluid distribution and movement, and its significance rises as porosity and permeability decrease and fluid interactions with reservoir grain surface area increase. Although the low permeability siliceous reservoirs of the Monterey Formation are economically important and prolific, a greater understanding of factors that alter their wettability will help better develop them. Imbibition results revealed a strong trend of decreased wettability to oil with increased detrital content in opal-CT phase samples. Opal-A phase samples exhibited less wettability to oil than both opal-CT and quartz phase samples of similar detrital content. Subsurface reservoir samples from 3 oil fields were crushed to eliminate the effect of capillary pressure and cleansed of hydrocarbons to eliminate wettability alterations by asphaltene, then pressed into discs of controlled density. Powder discs were tested for wettability by dispensing a controlled volume of water and motor oil onto the surface and measuring the time required for each fluid to imbibe into the sample. The syringe and software of a CAM101 tensiometer were used to control the amount of fluid dispensed onto each sample, and imbibition completion times were determined by high-speed photography for water drops; oil drop imbibition was significantly slower and imbibition was timed and determined visually. Contact angle of water and oil drops on polished chert and mineral sample surfaces was determined by image analysis and the Young-Laplace equation. Oil imbibition was significantly slower with increased detrital composition and faster

  7. Pre-Ediacaran to Ediacaran Radiation in the Vindhyan Supergroup, India

    Science.gov (United States)

    Srivastava, P.

    2009-04-01

    The Vindhyan Supergroup is globally acknowledged amongst the best repositories of the Proterozoic life evidences. Fossils of the Vindhyan Supergroup exhibit extensive diversity and variable biologic affinities represented by: bacteria, cyanobacteria, algae, fungi, acritarchs, metaphytes and metazoans (including members of the Ediacaran Fauna). The size of fossils ranges from less than a micron to almost a meter. As the Ediacaran fauna has already been recorded from the uppermost Vindhyans that is from the Bhander Group, strata lying beneath and above the Ediacaran fossil bearing horizons, exhibit presence of a vast range of fossils (both micro and mega fossils) inclining towards variable biologic affinities stated earlier. Besides identified fossils, a number of peculiar morphologies (due to deviation of morphologies from conventional structures), present in various stratigraphic horizons of the entire Vindhyan Supergroup, have also been observed. It is very difficult to identify and decide biologic affinities of these peculiar morphologies or bizarre fossil forms. In thin sections of Lower Vindhyan cherts (of Semri Group), microfossils resembling, a Volvox colony like structure and a vase- shaped body without an opening, Lichen- like or fungal forms in which a sac encompassing a coiled filament may possibly indicate a symbiotic relationship are unique. Megascopic branching and associated Grypania like structure is another form preserved as an impression on a micritic limestone slab. A very unusual and interesting fossil is a transparent disc of about one mm in diameter, composed of numerous chromosome-like structures or the appendages of an unidentified mesoscopic insect- like organism. In Upper Vindhyans, microscopic unidentified forms (in thin sections of chert) include acritarchs and acanthomorphs of variable morphologies and a dividing cell like structure interpreted as rhodophycean form or a cleaving embryo of an animal affinity. Among the carbonaceous

  8. Geology and D-O-C Isotope Systematics of the Tieluping Silver Deposit,Henan,China:Implications for Ore Genesis

    Institute of Scientific and Technical Information of China (English)

    CHEN Yanjing; Franco PIRAJNO; SUI Yinghui

    2005-01-01

    The Tieluping silver deposit, which is sited along NE-trending faults within the high-grade metamorphic basement of the Xiong'er terrane, is part of an important Mesozoic orogenic-type Ag-Pb and Au belt recently discovered. Ore formation includes three stages: Early (E), Middle (M) and Late (L), which include quartz-pyrite (E),polymetallic sulfides (M) and carbonates (L), respectively. The E-stage fluids are characterized by δD=-90‰,δ13Cco2=2.0‰ and δ18O=9‰ at 373℃, and are deeply sourced; the L-stage fluids, with δD=-70‰,δ13Cco2=-1.3‰ and δ18O=-2‰, are shallow-sourced meteoric water; whereas the M-stage fluids, with δD=-109‰,δ13Cco2=0.1‰ and δ18O=2‰, are a mix of deep-sourced and shallow-sourced fluids. Comparisons of the D-O-C isotopic systematics of the Estage ore-forming fluids with the fluids derived from Mesozoic granites, Archean-Paleoproterozoic metamorphic basement and Paleo-Mesoproterozoic Xiong'er Group, show that these units cannot generate fluids with the measured isotopic composition (high δ18O and δ13C ratios and low δD ratios) characteristic of the ore-forming fluids. This suggests that the E-stage ore-forming fluids originated from metamorphic devolatilization of a carbonate-shale-chert lithological association, locally rich in organic matter, which could correspond to the Meso-Neoproterozoic Guandaokou and Luanchuan Groups, rather than to geologic units in the Xiong'er terrane, the lower crust and the mantle. This supports the view that the rocks of the Guandaokou and Luanchuan Groups south of the Machaoying fault might be the favorable sources. A tectonic model that combines collisional orogeny, metallogeny and hydrothermal fluid flow is proposed to explain the formation of the Tieluping silver deposit. During the Mesozoic collision between the South and North China paleocontinents, a crustal slab containing a lithological association consisting of carbonate-shale-chert, locally rich in organic matter (carbonaceous

  9. The Jocotán Ophiolite: A new ophiolite along the Jocotán fault, eastern Guatemala

    Science.gov (United States)

    Harlow, G. E.; Flores-Reyes, K.; Sisson, V. B.; Nelson, C.; Cacao, A.

    2011-12-01

    The North American - Caribbean plate boundary traverses central Guatemala and northern Honduras, dispersed along three left lateral faults systems, which from north to south are the Chixoy-Polochic, the Motagua, and the Jocotán-Camelecón faults, with the Motagua as the present active strand. The Motagua Suture Zone (MSZ), which encompasses this area, consists of multiple paleo-convergent boundaries. It includes slices of ultramafic-mafic complexes including both antigorite (Atg) serpentinite mélanges containing high-pressure / low-temperature (HP/LT) blocks, and lizardite-chrysotile (Lzd-Ctl) serpentinites with associated pillow lavas, radiolarian chert, and marine sediments, typically labeled as ophiolites. Guatemala Suture Zone would be a preferable term to MSZ because the area extends over all three faults, not just the Motagua. The MSZ includes the Sierra de Santa Cruz ophiolite north of the east end of the Polochic fault, the Baja Verapaz ultramafic complex (considered an ophiolite in most of the literature) lies just south of the western portion of the Polochic fault and a series of Atg-serpentinite-dominant mélanges (with HP/LT blocks) that decorate both sides of the Motagua fault. In addition, there is the El Tambor Formation, south of the Motagua fault (but west of the known limit of the Jocotán fault), which contains mafic & sedimentary units and has been called an ophiolite. However, no mafic-ultramafic bodies appear on maps that cover the Jocotán fault in eastern Guatemala. Geologic mapping by one of the co-authors located a small suite of ultramafic rocks sandwiched between the Jocotán and Camotán faults in eastern Guatemala, a short distance from the town of Camotán. Outcrops exposed for 3 km along a road and in a small river consist of sheared Lzd-Ctl serpentinite, metagabbro, overturned altered pillow lavas, listwaenite and rodingite dikes, cherts and pelagic metasediments. These units represent fault slivers subparallel to the steeply

  10. Paleomagnetism of the Astrobiology Drilling Project 8 drill core, Pilbara, Western Australia: implications for the early geodynamo and Archean tectonics

    Science.gov (United States)

    Bradley, K.; Weiss, B.; Carporzen, L.; Anbar, A.; Buick, R.

    2008-12-01

    Paleomagnetic measurements from the Archean Pilbara craton have recently been used to argue for the presence of a substantial magnetic field at 3.2 Ga (Tarduno et al., 2007), as well as for extremely fast plate motions or true polar wander (Strik et al., 2003, Suganuma et al., 2006). Paleomagnetic records in the Archean are fundamentally limited by the scarcity of well-preserved, low metamorphic grade Archean rocks. Where such rocks are exposed, paleomagnetic sampling is often difficult or impossible due to pervasive lightning remagnetization and deep weathering of the cratonic surface. More pristine samples can potentially be obtained from shallow drill cores like those obtained by the Astrobiology Drilling Project (ABDP). We present a paleomagnetic analysis of the ~350 m deep ABDP-8 drill core, which was drilled in the East Strelley greenstone belt and which penetrated the Double Bar Formation of the Warrawoona Group, as well as the unconformably overlying Euro Basalt and Strelley Pool Chert units of the Kelly Group. Full sample orientation (declination and inclination) was achieved through the use of a Ballmark orientation system. A strong drilling overprint was removed for most samples by alternating field demagnetization to 20 mT. Subsequent thermal demagnetization revealed single-polarity magnetic directions within the Euro Basalt and Double Bar Formation carried by magnetite. The directions from these two Formations are statistically different to >95% confidence, which constitutes a positive unconformity test and indicates that the Euro Basalt direction is primary. Upon tilt correction, the ~3.34-3.37 Ga Euro Basalt direction is indistinguishable from the tilt-corrected direction found previously in the ~3.46 Ga Duffer Formation of the Warrawoona Group (McElhinny and Senanayake, 1980). The Euro Basalt direction, if taken at face value, implies small relative motion of the Pilbara Craton from ~3.46 Ga to ~3.34 Ga. This is inconsistent with the apparent polar

  11. Late ordovician stratigraphy, zircon provenance and tectonics, Lachlan Fold Belt, southeastern Australia

    International Nuclear Information System (INIS)

    Ordovician quartz turbidites of the Lachlan Fold Belt in southeastern Australia accumulated in a marginal sea and overlapped an adjoining island arc (Molong volcanic province) developed adjacent to eastern Gondwana. The turbidite succession in the Shoalhaven River Gorge, in the southern highlands of New South Wales, has abundant outcrop and graptolite sites. The succession consists of, from the base up, a unit of mainly thick-bedded turbidites (undifferentiated Adaminaby Group), a unit with conspicuous bedded chert (Numeralla Chert), a unit with common thin-bedded turbidites [Bumballa Formation (new name)] and a unit of black shale (Warbisco Shale). Coarse to very coarse sandstone in the Bumballa Formation is rich in quartz and similar to sandstone in the undifferentiated Adaminaby Group. Detrital zircons from sandstone in the Bumballa Formation, and from sandstone at a similar stratigraphic level from the upper Adaminaby Group of the Genoa River area in eastern Victoria, include grains as young as 453-473 Ma, slightly older than the stratigraphic ages. The dominant detrital ages are in the interval 500-700 Ma (Pacific Gondwana component) with a lessor concentration of Grenville ages (1000-1300 Ma). This pattern resembles other Ordovician sandstones from the Lachlan Fold Belt and also occurs in Triassic sandstones and Quaternary sands from eastern Australia. The Upper Ordovician succession is predominantly fine grained, which reflects reduced clastic inputs from the source in the Middle Cambrian to earliest Ordovician Ross-Delamerian Fold Belts that developed along the eastern active margin of Gondwana. Development of subduction zones in the Late Ordovician marginal sea are considered to be mainly responsible for the diversion of sediment and the resulting reduction in the supply of terrigenous sand to the island arc and eastern part of the marginal sea. Sixty zircons from each sample were analysed and results are presented. Methods following standard procedures

  12. Geochronology and Geochemistry of the Middle Proterozoic Aoyougou Ophiolite in the North Qilian Mountains, Northwestern China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The Aoyougou ophiolite lies in an early Palaeozoic orogenic belt of the western North Qilian Mountains, near the Aoyougou valley in Gansu Province, northwestern China. It consists of serpentinite, a cumulate sequence of gabbro and diorite, pillow and massive lavas, diabase and chert. Ages of 1840±2 Ma, 1783±2 Ma and 1784±2 Ma on three zircons from diabase, indicate an early Middle Proterozoic age. The diabases and basalts show light rare-earth element enrichment and have relatively high TiO2 contents, characteristic of ocean island basalts. All of the lavas have low MgO, Cr, Ni contents and Mg numbers indicating a more evolved character. They are believed to have been derived from a more mafic parental magma by fractionation of olivine, Cr-spinel and minor plagioclase. Based on the lava geochemistry and regional geology, the Aoyougou ophiolite was probably believed to have formed at a spreading centre in a small marginal basin. Subduction of the newly formed oceanic lithosphere in the Middle Proterozoic produced a trench-arc-basin system, which is preserved in the North Qilian Mountains.

  13. Lead, cadmium, and zinc concentrations in plaster and mortar from structures in Jasper and Newton Counties, Missouri (Tri-State Mining District)

    Energy Technology Data Exchange (ETDEWEB)

    Perry, Phyllis M. [Chemistry Department, Southwest Missouri State University, 901 S. National Avenue, Springfield, MO 65804 (United States); Pavlik, Jeffrey W. [Chemistry Department, Southwest Missouri State University, 901 S. National Avenue, Springfield, MO 65804 (United States); Sheets, Ralph W. [Chemistry Department, Southwest Missouri State University, 901 S. National Avenue, Springfield, MO 65804 (United States); Biagioni, Richard N. [Chemistry Department, Southwest Missouri State University, 901 S. National Avenue, Springfield, MO 65804 (United States)]. E-mail: rnb266f@smsu.edu

    2005-01-05

    The primary goal of this study was to evaluate anecdotal evidence that within Jasper and Newton Counties, Missouri, two counties within the Tri-State Mining District, granular mine tailings were commonly used in place of river sands in wall plasters and mortar. Interior wall plaster and mortar samples from structures in this mining district were analyzed for lead, cadmium, and zinc, and compared to samples from Springfield, MO (comparison site). The Jasper and Newton County samples showed elevated concentrations of the three elements, consistent with the inclusion of mine tailings, with a number of samples containing lead and cadmium at concentrations greater than EPA remediation targets for yard soil. X-ray diffraction studies showed the presence of the zinc ore minerals, sphalerite and hemimorphite, in high level samples. Thin section optical studies identified the major component of the aggregate as chert, a mineral abundant within the tailing piles. Because dust from crumbling plaster and mortar could represent an avenue for significant heavy metal exposure to building occupants, we suggest that there may be associated health consequences that should be further evaluated.

  14. Usage of geochemistry of uranium and associated elements to explain the anomalous non-phosphatic radiometric halo south west margins of Saba Abar Kherbet As-Sawwaneh area

    International Nuclear Information System (INIS)

    The present research work has accomplished the whole picture of the non completed anomalous radioactive halos shown by the latest airborne radiometric survey along the extreme southwestern corner of Saba Abar Kherbet As-Sawwaneh quadrangle. Geochemical and various gamma-ray spectrometric surveys were used. The resulted radiometric maps of the radioelements U, Th, K and Ur units of the total counts assisted in achieving the completed picture of the anomalous halos towards west and north west. Thirteen anomalous spots were found in Kherbet As-Sawwaneh, Kherbet Shaili and south of Abar El-Rudma Areas. These anomalies were especially pronounced over a cover of flint and chert blocks and stones covering the sedimentary Palaeogene rocks in close contact with volcanic basalt rocks in the vicinity of Jabal Ghurab. Upon breaking many of the chart and flint blocks and stones yellow secondary uranium mineralizations were found despite no surface indications of any mineralizations were observed. This type of secondary uranium occurrences was never reported earlier neither in Syria nor elsewhere. It is a new phenomenon which deserves further investigations. In addition a few anomalous values of thorium were detected in the sedimentary rocks of the various Khebrats along the main basaltic sheet and flows. Also contamination with the isotope 137Cs from Chernobyl fallout in few sampling point was still detectable in the Khebrats of the area. (author)

  15. An upwelling model for the Phosphoria sea: A Permian, ocean-margin sea in the northwest United States

    Science.gov (United States)

    Piper, D.Z.; Link, P.K.

    2002-01-01

    The Permian Phosphoria Formation, a petroleum source rock and world-class phosphate deposit, was deposited in an epicratonic successor basin on the western margin of North America. We calculate the seawater circulation in the basin during deposition of the lower ore zone in the Meade Peak Member from the accumulation rates of carbonate fluorapatite and trace elements. The model gives the exchange rate of water between the Phosphoria sea and the open ocean to the west in terms of an upwelling rate (84 m yr-1) and residence time (4.2 yr) of seawater in the basin. These hydrographic properties supported a mean rate of primary productivity of 0.87 g m-2 d-1 of carbon in the uppermost few tens of meters of the water column (the photic zone) and denitrifying redox conditions in the bottom water (below approximately 150 m depth). High rain rates, onto the sea floor, of the organic matter that hosted the phosphate and several trace elements contributed to the accumulation of phosphorite, chert, and black shales and mudstones. Evaporation in the Goose Egg basin to the east of the Phosphoria basin ensured the import of surface seawater from the Phosphoria sea. Budgets of water, salt, phosphate, and oxygen, plus the minor accumulation of the biomarker gammacerane, show that exchange of water between the two basins was limited, possibly by the shallow carbonate platform that separated the two basins.

  16. A Kungurian Oceanic Upwelling on Yangtze Platform:Evidenced byδ13Corg and Authigenic Silica in the Lower Chihsia Formation of Enshi Section in South China

    Institute of Scientific and Technical Information of China (English)

    Hao Yu; Hengye Wei

    2015-01-01

    The Late Paleozoic Ice Age across Carboniferous and Permian had a significant impact on the Kungurian (Upper Cisuralian series of Permian) Chihsia Formation in South China. This re-sulted in a unique interval with features such as the lack of reef in Chihsian limestone, widespread stinkstone and nodular/bedded chert. The Chihsia limestone (Kungurian stage) deposited during a time of cooling was resulted from oceanic upwelling. Here we present evidence for this upwelling using sev-eral geochemical analyses: bulk organic carbon isotope, biomarker molecular geochemical data, and authigenic silica of the stinkstone member in the lower Chihsia Formation of the Kuangurian stage from the Enshi Section in western Hubei Province, South China. The lower part of the stinkstone member shows a rapid organic carbon isotope excursion with a-3‰shift triggered by the upwelling of 13C-depleted bottom water. The concurrent rapid increasing of authigenic silica content resulted from the enhanced supply of dissolved silica in the upwelling water mass. This upwelling at the Enshi Section also led to relative high TOC content, accounting for the widespread stinkstone in the lower Chihsia Formation during the Kungurian stage in Permian.

  17. Mid-Permian Phosphoria Sea in Nevada and the Upwelling Model

    Science.gov (United States)

    Ketner, Keith B.

    2009-01-01

    The Phosphoria Sea extended at least 500 km westward and at least 700 km southwestward from its core area centered in southeastern Idaho. Throughout that extent it displayed many characteristic features of the core: the same fauna, the same unique sedimentary assemblage including phosphate in mostly pelletal form, chert composed mainly of sponge spicules, and an association with dolomite. Phosphoria-age sediments in Nevada display ample evidence of deposition in shallow water. The chief difference between the sediments in Nevada and those of the core area is the greater admixture of sandstone and conglomerate in Nevada. Evidence of the western margin of the Phosphoria Sea where the water deepened and began to lose its essential characteristics is located in the uppermost part of the Upper Devonian to Permian Havallah sequence, which has been displaced tectonically eastward an unknown distance. The relatively deep water in which the mid-Permian part of the Havallah was deposited was a sea of probably restricted east-west width and was floored by a very thick sequence of mainly terrigenous sedimentary rocks. The phosphate content of mid-Permian strata in western exposures tends to be relatively low as a percentage, but the thickness of those strata tends to be high. The core area in and near southeastern Idaho where the concentration of phosphate is highest was separated from any possible site of upwelling oceanic waters by a great expanse of shallow sea.

  18. EPR, ENDOR, and HYSCORE study of the structure and the stability of vanadyl-porphyrin complexes encapsulated in silica: potential paramagnetic biomarkers for the origin of life.

    Science.gov (United States)

    Gourier, Didier; Delpoux, Olivier; Bonduelle, Audrey; Binet, Laurent; Ciofini, Ilaria; Vezin, Hervé

    2010-03-18

    The possibility of using vanadyl ions as paramagnetic biomarkers for the identification of traces of primitive life fossilized in silica rocks is studied by cw-EPR, ENDOR, HYSCORE, and DFT calculations. It is well-known that porphyrins, which are common to all living organisms, form vanadyl-porphyrin complexes in sediments deposited in oceans. However, the stability of these complexes over a very long time (more than 3 billion years) is not known. By encapsulating vanadyl-porphyrin complexes in silica synthesized by a sol-gel method to mimic SiO(2) sediments, we studied the structure and stability of these complexes upon step heating treatments by monitoring the evolution of the g factor and of the hyperfine interactions with (51)V, (1)H, (14)N, (13)C, and (29)Si nuclei. It is found that vanadyl-porphyrin complexes are progressively transformed into oxygenated vanadyl complexes by transfer of the VO(2+) ion from the porphyrin ring to the mineral matrix. The organic component is transformed into carbonaceous matter which contains paramagnetic centers (IOM(*) centers). To test the validity of this approach, we studied by EPR a 3490 million years old chert (polycrystalline SiO(2) rock) containing some of the oldest putative traces of life. This rock contains oxygenated vanadyl complexes and IOM(*) centers very similar to those found in the synthetic analogues. PMID:20175553

  19. ¿De dónde vienen? Aprovisionamiento de rocas sedimentarias silíceas en el yacimiento magdaleniense al aire libre de Montlleó (Prats i Sansor, Lleida

    Directory of Open Access Journals (Sweden)

    Sánchez de la Torre, Marta

    2016-06-01

    Full Text Available Results obtained after the archaeopetrological analyses of lithic tools from the open-air site of Montlleó (Prats i Sansor, Lleida are presented below. Macroscopic, microscopic and geochemical observation permitted recognitionof the textural, petrographic, micropaleontological, as well as mineralogical composition of the exploited cherts. Results confirm that Montlleó was placed at a crossroad area used repeatedly at the end of the Upper Palaeolithic. These results show that geographical barriers did not impede human mobility between both Pyrenean slopes.En este artículo se presentan los resultados obtenidos tras la caracterización arqueopetrológica de los materiales líticos del yacimiento al aire libre de Montlleó (Prats i Sansor, Lleida. El estudio desarrolla una observación macroscópica, microscópica y geoquímica para conocer las características texturales, petrográficas y micropaleontológicas, así como la composición mineralógica de los tipos de sílex explotados. Los resultados de este trabajo confirman que el yacimiento de Montlleó fue una encrucijada de caminos transitados reiteradamente al fin del Paleolítico superior, evidenciando la inexistencia de barreras geográficas que imposibilitaran la movilidad entre ambas vertientes del área pirenaica centro-oriental.

  20. Discovery of the Late Triassic (Middle Carnian-Rhaetian) radiolarians in the volcano-sedimentary sequences of the Kocali Complex, SE Turkey: Correlation with the other Tauride units

    Science.gov (United States)

    Uzuncimen, Seda; Tekin, Ugur Kagan; Bedi, Yavuz; Perincek, Dogan; Varol, Elif; Soycan, Havva

    2011-01-01

    The Kocali Complex in SE Turkey includes pelagic sediments (pelagic limestones, cherts, etc.), basic volcanic rocks of oceanic crust origin together with platform-derived sediments. Its depositional age was previously assigned as Late Jurassic-Early Cretaceous. In order to study the radiolarian contents of volcano-sedimentary sequences in this complex, six stratigraphic sections have been measured mainly at the NE and NW Adiyaman city. Radiolarian faunas from these stratigraphic sections reveal that the age of these sequences ranges from middle Carnian to Rhaetian. Based on these data, the depositional age of the complex is older than the previously assigned. Lithological characteristics (widespread Triassic basic volcanic rocks associated with pelagic sediments) and radiolarian contents of these sequences have close similarities with the sequences of the Alakircay Nappe of the Antalya Nappes in western and central Taurides. Based on taxonomic studies, 99 taxa have been determined of which one genus ( Adiyamanium) and four species ( Monocapnuchosphaera kocaliensis, Paronaella speciosa, Ferresiumokuyucui and Adiyamanium crassum) are described as new.

  1. Exchange of lyotropic series cations by micaceous vermiculite and its weathering products determined by electron microscopy and radiochemical analysis. Final technical report, June 1, 1965-October 31, 1978

    International Nuclear Information System (INIS)

    Micaceous vermiculite was found to be ubiquitous in soils, sediments, and aerosol mineral dusts and to adsorb fission product ions, particularly 137Cs+ and 90Sr2+. Crystallographic wedge zones (imaged by ultramicrotomy and electron microscopy) in micaceous vermiculite effected tight fixation of Cs+. Lowering of mica layer charge occurred in local areas, electronoscopically imaged by use of blister-swelling cations. Nuclear fission particle tracks of U enhanced translayer diffusion of elements, measured mica layer charge and age. Iron-aluminum hydrous oxide coatings adsorbed divalent cations of the alkaline earth, transition, and heavy metal elements from trace concentrations in the presence of 1 M NaNO3. Global deposition of dust by rainfall accounted for the wide distribution of Cs-fixing micaceous vermiculite in soils. Origin of the dust was traced through a method developed for isolation of fine quartz silt (1 to 10 μm diameter). Mass spectrometry of its 18O/16O isotopic ratios showed distinctly higher (delta18O = 17 to 22%0) and lower (delta18O = 9 to 15%0) ranges in the Northern and Southern Hemispheres, respectively. This difference was traced to the relative proportions of quartz from low-temperature authigenic (chert) vs igneous-metamorphic origin in the respective latitudes, hinging on trans-equatorial continental drift

  2. Curcuma nankunshanensis (Zingiberaceae), A New Species from China%中国姜黄属-新种-南昆山莪术

    Institute of Scientific and Technical Information of China (English)

    叶向斌; 陈娟; 刘念

    2008-01-01

    报道姜科姜黄属-新种-南昆山莪术(Curcuma nankunshanensis N.Liu,X.B.Ye&J.Chen).该种与近缘种广西莪术(C kwangsiensis X.X.Chen)的区别在于侧根茎分枝多,叶片阔椭圆状披针形,表面光滑无毛,不育苞片下部白色顶端深紫红色,能育苞片绿色.它与郁金(C aromatica Sahib)的区别在于根茎内面白色,不育苞片下部白色顶端深紫红色,具有种子.%A new species of Curcuma L., C. nankunshanensis N. Liu, X. B. Ye & J. Chert, is described and illustrated. The new species is similar to C. kwangsiensis X. X. Chen, but differs in its lateral rhizome multibranched, leaf blades broad-lanceolate and glabrous adaxially, coma bracts white except for purple toward the apex and fertile bracts green. It is also easily distinguished from C. aromatica by its rhizome white inside, coma bracts white except for purple toward the apex, seeds bearing.A key to Curcuma from Guangdong is provided.

  3. Earthquake lubrication and healing explained by amorphous nanosilica

    Science.gov (United States)

    Rowe, C. D.; Lamothe, K. G.; Rempe, M.; Andrews, M.; Mitchell, T. M.; Di Toro, G.; White, J. C.

    2015-12-01

    Earthquake slip and rupture propagation require fault strength to decrease during slip. Extreme shear weakening observed in laboratory friction experiments on silica-rich rocks has been explained by the formation of a hydrated amorphous 'silica gel' on the slip surface, but the mode of formation and deformation behavior of this material are not known. In addition, the wear material displays time-dependent strengthening on timescales of hours to days. We performed shearing experiments on chert rocks and analyzed the wear material formed at a range of slip rates from 10-4 - 10-1 m/s. We show by transmission electron microscopy (TEM) and X-ray diffraction that silica lubrication is the result of the formation of amorphous nanopowder rather than a gel. The nanopowder has distinct structure and properties when compared to commercially available amorphous silica nanoparticles, which result from the degree and distribution of hydration and the style of bond strain within particles (observed by Raman spectroscopy and FTIR). The lubrication effect is due to intra-particle plasticity, even at low temperature and interparticle lubrication caused by trapping of water layers between hydrated surfaces. The hours to days timescale of healing may be explained by the natural time-dependent sintering between the hydrated surfaces of the nanopowder. Formation of amorphous silica nanopowders during slip can explain the general characteristics of earthquake ruptures, including the timescales of coseismic weakening and post-seismic healing.

  4. Two new pioneer communities of Sorbus aucuparia and Sorbus aria in the southern Julian Alps

    Directory of Open Access Journals (Sweden)

    Dakskobler Igor

    2016-06-01

    Full Text Available In the southern Julian Alps we described two communities whose tree layer is dominated by species from the genus Sorbus and noted two successional stages in the overgrowing of abandoned agricultural land (pastures, hay meadows. In the secondary succession on former subalpine pastures above the alp Planina Razor und under the Breginjski Stol ridge, where potential natural vegetation consists of subalpine beech forest, dwarf pine has been overgrown with mountain ash (Sorbus aucuparia whose stands are classified into the new association Rhododendro hirsuti-Sorbetum aucupariae. Whitebeam (Sorbus aria has established itself on steep former hay meadows in the belt of altimontane beech forests under Mts. Jalovnik and Krikov Vrh, on gullied slopes on mixed geological bedrock dominated by chert, and these stands are classified into the association Calamagrostio arundinaceae-Sorbetum ariae. While occupying only small areas these two pioneer stages, as the sites of some rare or protected species, are nevertheless important biotopes and play a vital role in protection against avalanches.

  5. Distribution and diagenesis of microfossils from the lower Proterozoic Duck Creek Dolomite, Western Australia

    Science.gov (United States)

    Knoll, A. H.; Strother, P. K.; Rossi, S.

    1988-01-01

    Two distinct generations of microfossils occur in silicified carbonates from a previously undescribed locality of the Lower Proterozoic Duck Creek Dolomite, Western Australia. The earlier generation occurs in discrete organic-rich clasts and clots characterized by microquartz anhedra; it contains a variety of filamentous and coccoidal fossils in varying states of preservation. Second generation microfossils consist almost exclusively of well-preserved Gunflintia minuta filaments that drape clasts or appear to float in clear chalcedony. These filaments appear to represent an ecologically distinct assemblage that colonized a substrate containing the partially degraded remains of the first generation community. The two assemblages differ significantly in taxonomic frequency distribution from previously described Duck Creek florules. Taken together, Duck Creek microfossils exhibit a range of assemblage variability comparable to that found in other Lower Proterozoic iron formations and ferruginous carbonates. With increasing severity of post-mortem alteration, Duck Creek microfossils appear to converge morphologically on assemblages of simple microstructures described from early Archean cherts. Two new species are described: Oscillatoriopsis majuscula and O. cuboides; the former is among the largest septate filamentous fossils described from any Proterozoic formation.

  6. Terrane Boundary Geophysical Signatures in Northwest Panay, Philippines: Results from Gravity, Seismic Refraction and Electrical Resistivity Investigations

    Directory of Open Access Journals (Sweden)

    Jillian Aira S. Gabo

    2015-01-01

    Full Text Available Northwest Panay consists of two terranes that form part of the Central Philippine collision zone: Buruanga Peninsula and Antique Range. The Buruanga Peninsula consists of a Jurassic chert-clastic-limestone sequence, typical of oceanic plate stratigraphy of the Palawan Micro-continental Block. The Antique Range is characterized by Antique Ophiolite Complex peridotites and Miocene volcanic and clastic rocks, representing obducted oceanic crust that serves as the oceanic leading edge of the collision with the Philippine Mobile Belt. The Nabas Fault is identified as the boundary between the two terranes. This study employed the gravity method to characterize the Northwest Panay subsurface structure. Results indicate higher Bouguer anomaly values for Buruanga Peninsula than those for Antique Range, separated by a sudden decrease in gravity values toward the east-southeast (ESE direction. Forward gravity data modeling indicates the presence of an underlying basaltic subducted slab in the Buruanga Peninsula. Furthermore, the Nabas Fault is characterized as an east-dipping thrust structure formed by Buruanga Peninsula basement leading edge subduction beneath Antique Range. Additional geophysical constraints were provided by shallow seismic refraction and electrical resistivity surveys. Results from both methods delineated the shallow subsurface signature of the Nabas Fault buried beneath alluvium deposits. The gravity, seismic refraction and electrical resistivity methods were consistent in identifying the Nabas Fault as the terrane boundary between the Buruanga Peninsula and the Antique Range. The three geophysical methods helped constrain the subsurface configuration in Northwest Panay.

  7. Accretion, Trapping and Binding of Sediment in Archean Stromatolites—Morphological Expression of the Antiquity of Life

    Science.gov (United States)

    Altermann, Wladyslaw

    2008-03-01

    This paper reviews and discusses Archean stromatolite occurrences and their modes of growth in the context of sedimentary facies. Modes of sediment accretion and trapping and binding of sedimentary grains, together with the resulting morphology of stromatolites and microbial mats in the Archean are analysed, in order to show existing interaction between the growth patterns, morphology and facies association. Architectural elements of sediment arrangement in Archean stromatolites, together with the dependence of stromatolite distribution and morphology on sedimentary facies changes, clearly argue for a biological origin of stromatolitic lamination preserved in Archean cherts and carbonates. The observed sediment behaviour of laminae accretion and sediment precipitation, trapping and binding cannot be explained by abiogenic carbonate or silica precipitation from saturated solutions. The time-dependent, increasing complexity of stromatolitic structures in the Archean is an additional strong argument for biologic impact on stromatolite formation. Therefore, biogenic stromatolites and microbial mats were undoubtfully present at 3.5 Ga and occupied an increasingly wide range of sedimentary environments during the Archean.

  8. Depositional Environment of Permian Tak Fa Formation, Nakhonsawan, Northern Thailand

    Science.gov (United States)

    Ketwetsuriya, Chatchalerm; Nützel, Alexander; Kanjanapayont, Pitsanupong

    2016-04-01

    The carbonate rocks of the study area at Amphoe Tak Fa and Amphoe Takhli, Changwat Nakhon Sawan belong to the Tak Fa Formation, Saraburi Group. This formation crops out in the Khao Khwang Platform and consists of late Palaeozoic carbonate platform deposits. It reaches a thickness of 900 meters and crops out in a vast area. The exposures have been measured and samples were collected for petrographic study. The rock consists of limestones, argillaceous limestones, mudstones and dolomites with nodular and banded cherts, which comprise many invertebrate fossils such as fusulinids, ammonoid, pelecypod, gastropod, coral and bryozoa. Many of the fossils are silicified. The gastropod assemblage is currently under study and represents one of the most diverse faunas reported from SE Asia. The age of the rock is Yakhtashian or Artinskian (late Early Permian) to Midian or Capitanian (late Middle Permian). The study of carbonate facies and fauna indicates that the depositional environment was on shelf lagoon within the carbonate platform varying from shallow marine to barrier bar.

  9. Rb–Sr and Sm–Nd isotope systematics and geochemical studies on metavolcanic rocks from Peddavura greenstone belt: Evidence for presence of Mesoarchean continental crust in easternmost part of Dharwar Craton, India

    Indian Academy of Sciences (India)

    M Rajamanickam; S Balakrishnan; R Bhutani

    2014-07-01

    Linear, north–south trending Peddavura greenstone belt occurs in easternmost part of the Dharwar Craton. It consists of pillowed basalts, basaltic andesites, andesites (BBA) and rhyolites interlayered with ferruginous chert that were formed under submarine condition. Rhyolites were divided into type-I and II based on their REE abundances and HREE fractionation. Rb–Sr and Sm–Nd isotope studies were carried out on the rock types to understand the evolution of the Dharwar Craton. Due to source heterogeneity Sm–Nd isotope system has not yielded any precise age. Rb–Sr whole-rock isochron age of 2551 ± 19 (MSWD = 1.16) Ma for BBA group could represent time of seafloor metamorphism after the formation of basaltic rocks. Magmas representing BBA group of samples do not show evidence for crustal contamination while magmas representing type-II rhyolites had undergone variable extents of assimilation of Mesoarchean continental crust (< 3.3 Ga) as evident from their initial Nd isotope values. Trace element and Nd isotope characteristics of type I rhyolites are consistent with model of generation of their magmas by partial melting of mixed sources consisting of basalt and oceanic sediments with continental crustal components. Thus this study shows evidence for presence of Mesoarchean continental crust in Peddavura area in eastern part of Dharwar Craton.

  10. High-Ti type N-MORB parentage of basalts from the south Andaman ophiolite suite, India

    Indian Academy of Sciences (India)

    Rajesh K Srivastava; R Chandra; Anant Shastry

    2004-12-01

    A complete dismembered sequence of ophiolite is well exposed in the south Andaman region that mainly comprises ultramafic cumulates, serpentinite mafic plutonic and dyke rocks, pillow lava, radiolarian chert, and plagiogranite. Pillow lavas of basaltic composition occupy a major part of the Andaman ophiolite suite (AOS). These basalts are well exposed all along the east coast of southern part of the south AOS. Although these basalts are altered due to low-grade metamorphism and late hydrothermal processes, their igneous textures are still preserved. These basalts are mostly either aphyric or phyric in nature. Aphyric type exhibits intersertal or variolitic textures, whereas phyric variety shows porphyritic or sub-ophitic textures. The content of alkalies and silica classify these basalts as sub-alkaline basalts and alkaline basalts. A few samples show basaltic andesite, trachybasalt, or basanitic chemical composition. High-field strength element (HFSE) geochemistry suggests that studied basalt samples are probably derived from similar parental magmas. Al2O3/TiO2 and CaO/TiO2 ratios classify these basalts as high-Ti type basalt. On the basis of these ratios and many discriminant functions and diagrams, it is suggested that the studied basalts, associated with Andaman ophiolite suite, were derived from magma similar to N-MORB and emplaced in the mid-oceanic ridge tectonic setting.

  11. The Pre-Sturtian Negativeδ13C Excursion of the Dajiangbian Formation Deposited on the Western Margin of Cathaysia Block in South China

    Institute of Scientific and Technical Information of China (English)

    Lianjun Feng; Qirui Zhang

    2016-01-01

    The Dajiangbian Formation in South China is a siliciclastic-dominated sedimentary succession with low-grade metamorphism deposited on the western margin of the Cathaysia Block, and is capped by a glaciogenic diamictite (the Sizhoushan Formation). The Sizhoushan glaciogenic strata can be attributed to the Jiangkou glacial (Sturtian glacial) episode as they share stratigraphic and lithological similarities with Jiangkou strata in South China. Some carbonate, chert and shale units throughout the upper part of the Dajiangbian Formation were sampled for carbonate carbon isotope (δ13Ccarb) and organic carbon isotope (δ13Corg) analyses. A range of geochemical indices including oxygen isotopes (δ18O) and Mn/Sr (Fe/Sr) ratios suggest that primary carbon isotope values were preserved in the upper Dajiangbian Formation. The upper Dajiangbian Formation shows δ13Ccarb of-0.1‰, upward decreasing towards to-5.4‰. We suggest that the negativeδ13C excursion beneath the Sizhoushan diamictite is correlative with the Pre-Sturtian Islayδ13Ccarb anomaly and allows correlation with the global Neoproterozoic isotope stratigraphy. We find that carbonate and organic carbon isotope data of the upper Dajiangbian Formation are coupled, consistent with the δ13Ccarb-δ13Corg pattern observed on multiple continents.

  12. Für Forschung und Kultur - Öffentlichkeitswirksame Darstellung bibliothekarischer Weltschätze und bibliothekarischer Wissenschaftsservices am Beispiel der Staatsbibliothek zu Berlin

    Directory of Open Access Journals (Sweden)

    Barbara Schneider-Kempf

    2014-12-01

    Full Text Available Die Öffentlichkeitsarbeit der Staatsbibliothek zu Berlin zielt auf eine wirksame Darstellung ihrer bibliothekarischen Weltschätze und ihrer Serviceangebote für die Wissenschaft ab. Sie ruht auf drei Säulen: kulturelle Breitenbildung für wenig bibliotheksaffine Kreise, allgemeine und breit gefächerte Öffentlichkeitsarbeit sowie Aktionen, die sich an spezielle communities in der Wissenschaft richten. Der Beitrag informiert auch über die erfolgreiche Umsetzung dieser Strategie anhand zahlreicher Beispiele. Er zeigt, wie es der Staatsbibliothek in der Hauptstadt Berlin, in der viele Gedächtnisinstitutionen tätig sind, gelingt, öffentlich präsent zu bleiben und ihr Profil zu vermitteln. The public relations work of the Berlin State Library – Prussian Cultural Heritage aims at effectively presenting its globally significant treasures as well as its services for the scientific world. It is based on three pillars: cultural education for the general public, especially for people who are not naturally close to libraries; a general and wide variety of public relations work; and events which target special communities in science. The paper also presents many examples for the effectual implementation of this strategy. It shows how the State Library, in the capital city of Berlin with its many memory institutions, succeeds in keeping a strong presence and communicating its profile to the public.

  13. Petrographic and mineragraphic investigations of the archaean gold placer at Mount Robert in the Pietersburg greenstone belt, Northern Transvaal

    International Nuclear Information System (INIS)

    The fossil gold placer on Mount Robert near Potgietersrus, northern Transvaal, occurs in the Uitkyk Formation. This formation consists of arenaceous rocks with interlayered conglomerates and shales, and occurs at the top of the Archaean Pietersburg Sequence which forms the Pietersburg greenstone belt. The host rock of the occurrence consists of conglomerates. Its fragments indicate that the provenance area consisted of acid porphyritic lava, chert, banded iron-formation, quartzite, basic lava, vein quartz, and shale. It is suggested that the Uitkyk sediments were transported over short distances and originated from the erosion of a greenstone terrane. The mineralogy of the ore is relatively simply and resembles that of the much younger Witwatersrand banket. Rounded allogenic and, to a lesser extent, idiomorphic to hypidiomorphic authigenic pyrite form the main constituents. Less abundant but genetically interesting ore minerals that have been found so far are leucoxene-rutile, chromite, molybdenite, zircon, carbonaceous matter, and brannerite. The Mount Robert occurrence can be regarded as a primitive forerunner of the Witwatersrand goldfield. Ineffective sedimentary enrichment processes and an environment unfavourable for life-forms that could have acted as biogenic gold and uranium concentrators are regarded as possible reasons for the low gold content and scarcity of uranium-bearing minerals in the investigated Uitkyk conglomerates

  14. 湘赣地洼型煤田中岩浆岩的岩石学及地球化学特征

    Institute of Scientific and Technical Information of China (English)

    童玉明; 邱明

    1982-01-01

    Commonly seen in Mesozoic coal fields of Diwa type in Hunan and Jiangxi are basic, intermediate and acidic intrusive and volcanic rocks. The sequence of magmatism is from acidic to basic. The rocks show a tendency to become younger in age from west to east. Biotite granite porphyry-quartz diorite porphyrite, diorite porphyrite-diabase, diabase-porphyrite and spilite are the main rock types. These rocks are geochemically eharacterized by an evolutionary sequence from acidic to basic and by the enrichment in alkaline elements (except for biotite granite porphyry which has undergone intense alteration). In the acidic rocks K2O> Na2O whereas in the basic rocks K2O < Na2O. All the rocks are rich in non-ferrous metals and rare dements. The majority of the magmatic rocks were emplaced during the most intensive pariod of Diwa development. The rocks generally run parallel with the strike of coal basins. They were emplaced mostly along the layers or cut across coal seams. The above data on tectono-magmatic activity in coal fields of Diwa type lend great support to Prof. Chert Guoda's proposal that the history of crustal evolution is divided into three major stages -- geosyncline, platform snd Diwa.

  15. Facies and origin of triassic evaporites from the Nagra boreholes, Northern Switzerland

    International Nuclear Information System (INIS)

    The NAGRA boreholes Boettstein, Leuggern, Riniken, Schafisheim and Weiach and the NOK well Beznau cored the evaporitic succession of the Gipskeuper and of the Anhydritgruppe of the Middle Muschelkalk. These formations are relatively poorly exposed in Northern Switzerland. Detailed mineralogical, textural and sedimentological analysis of these cores enabled reconstruction of the diagenetic and depositional history of the Triassic evaporites. A complex sequence of evaporitic minerals (including calcite, dolomite, gypsum, anhydrite, halite), together with chert and talc, is interpreted to represent an eogenetic assemblage. Subsequently, during mesogenetic (burial) diagenesis, gypsum dehydrated to anhydrite. Later replacement of anhydrite by mega-quartz and dolomite is recorded by sulphate-bearing carbonate beds. Concentrations of sphalerite, fluorite and mega-quartz are also present throughout the studied sequence. Ultimately, following post-Tertiary uplift, meteoric water ingress into the shallow-buried Triassic sediments of the Beznau, Boettstein and Leuggern wells resulted in telogenetic hydration of anhydrite, causing fracturing of the host rock and extensive dissolution of the sulphates. Although most original sedimentary structures are still preserved, practically all the primary authigenic minerals have suffered subsequent diagenetic modification since eogenesis. (author) 35 figs., tabs., 252 refs

  16. Santaclaraite, a new calcium-manganese silicate hydrate from California.

    Science.gov (United States)

    Erd, Richard C.; Ohashi, Y.

    1984-01-01

    Santaclaraite, ideally CaMn4(Si5O14(OH))(OH).H2O, occurs as pink and tan veins and masses in Franciscan chert in the Diablo Range, Santa Clara and Stanislaus counties, California. It is associated with four unidentified Mn silicates, Mn-howieite, quartz, braunite, calcite, rhodochrosite, kutnahorite, baryte, harmotome, chalcopyrite and native copper. Santaclaraite is triclinic, space group B1, a 15.633(1), b 7.603(1) , c 12.003(1) A, alpha 109.71(1)o, beta 88.61(1)o, gamma 99.95(1) o, V 1322.0(3) A3; Z = 4. The strongest lines of the X-ray pattern are 7.04(100), 3.003(84), 3.152(80), 7.69(63), 3.847(57) A. Crystals are lamellar to prismatic (flattened on (100)), with good cleavage on (100) and (010); H. 61/2 Dcalc. 3.398 g/cm3, Dmeas. 3.31 (+ or -0.01); optically biaxial negative, alpha 1.681, beta 1.696, gamma 1.708 (all + or - 0.002), 2Valpha 83 (+ or -1)o. Although chemically a hydrated rhodonite, santaclaraite dehydrates to Mn-bustamite at approx 550oC (in air) . Santaclaraite is a five-tetrahedral-repeat single-chain silicate and has structural affinities with rhodonite, nambulite, marsturite, babingtonite and inesite.-J.A.Z.

  17. Ribosomal RNA gene fragments from fossilized cyanobacteria identified in primary gypsum from the late Miocene, Italy.

    Science.gov (United States)

    Panieri, G; Lugli, S; Manzi, V; Roveri, M; Schreiber, B C; Palinska, K A

    2010-03-01

    Earth scientists have searched for signs of microscopic life in ancient samples of permafrost, ice, deep-sea sediments, amber, salt and chert. Until now, evidence of cyanobacteria has not been reported in any studies of ancient DNA older than a few thousand years. Here, we investigate morphologically, biochemically and genetically primary evaporites deposited in situ during the late Miocene (Messinian) Salinity Crisis from the north-eastern Apennines of Italy. The evaporites contain fossilized bacterial structures having identical morphological forms as modern microbes. We successfully extracted and amplified genetic material belonging to ancient cyanobacteria from gypsum crystals dating back to 5.910-5.816 Ma, when the Mediterranean became a giant hypersaline brine pool. This finding represents the oldest ancient cyanobacterial DNA to date. Our clone library and its phylogenetic comparison with present cyanobacterial populations point to a marine origin for the depositional basin. This investigation opens the possibility of including fossil cyanobacterial DNA into the palaeo-reconstruction of various environments and could also be used to quantify the ecological importance of cyanobacteria through geological time. These genetic markers serve as biosignatures providing important clues about ancient life and begin a new discussion concerning the debate on the origin of late Miocene evaporites in the Mediterranean. PMID:20059556

  18. Paleocene deep-water sediments and radiolarian faunas:Implications for evolution of Yarlung-Zangbo foreland basin, southern Tibet

    Institute of Scientific and Technical Information of China (English)

    丁林

    2003-01-01

    This is the first report on the Paleocene deep-water sequences and radiolarian faunas, which are distributed along the southern side of the Yarlung-Zangbo suture zone. The Zheba group is coined to indicate these Paleocene sequences which are subsequently divided into two lithostratigraphic units based on the lithology observed in the field. The lower unit characterized by the rhythmic cherts and siliceous shales is named the Sangdanlin formation, and the upper one composed mainly of flysches is termed the Zheya formation. The radiolarian faunas from the Zheba group are assigned to the RP1-RP6 zones of the Paleocene age. The Early Paleocene ra-diolarian assemblages have the potential to be established into the low latitude radiolarian zones and to fill in the gap between the Late Cretaceous and the Late Paleocene radiolarian zonations. The radiolarian dating provides a valuable tool for the regional correlation and reconstruction of the sedimentary environment of the Neo-Tethyan Ocean. The preliminary work shows that the Paleo-cene sequences accumulated in a foreland basin resulted from the southern Asian margin loading onto the northern Indian passive continental margin. The Yarlung-Zangbo foreland basin se-quences deposited on the Indian passive continental margin also resulted in many good source- reservoir-covering assemblages for oil and gas resources.

  19. A 365-Million-Year-Old Freshwater Community Reveals Morphological and Ecological Stasis in Branchiopod Crustaceans.

    Science.gov (United States)

    Gueriau, Pierre; Rabet, Nicolas; Clément, Gaël; Lagebro, Linda; Vannier, Jean; Briggs, Derek E G; Charbonnier, Sylvain; Olive, Sébastien; Béthoux, Olivier

    2016-02-01

    Branchiopod crustaceans are represented by fairy, tadpole, and clam shrimps (Anostraca, Notostraca, Laevicaudata, Spinicaudata), which typically inhabit temporary freshwater bodies, and water fleas (Cladoceromorpha), which live in all kinds of freshwater and occasionally marine environments [1, 2]. The earliest branchiopods occur in the Cambrian, where they are represented by complete body fossils from Sweden such as Rehbachiella kinnekullensis [3] and isolated mandibles preserved as small carbonaceous fossils [4-6] from Canada. The earliest known continental branchiopods are associated with hot spring environments [7] represented by the Early Devonian Rhynie Chert of Scotland (410 million years ago) and include possible stem-group or crown-group Anostraca, Notostraca, and clam shrimps or Cladoceromorpha [8-10], which differ morphologically from their modern counterparts [1, 2, 11]. Here we report the discovery of an ephemeral pool branchiopod community from the 365-million-year-old Strud locality of Belgium. It is characterized by new anostracans and spinicaudatans, closely resembling extant species, and the earliest notostracan, Strudops goldenbergi [12]. These branchiopods released resting eggs into the sediment in a manner similar to their modern representatives [1, 2]. We infer that this reproductive strategy was critical to overcoming environmental constraints such as seasonal desiccation imposed by living on land. The pioneer colonization of ephemeral freshwater pools by branchiopods in the Devonian was followed by remarkable ecological and morphological stasis that persists to the present day. PMID:26776738

  20. Innovative Field Investigations in Limestone using a FACT-FLUTe

    DEFF Research Database (Denmark)

    Mosthaf, Klaus; Barrett Sørensen, Mie; Broholm, Mette Martina;

    2015-01-01

    Background and objective The understanding of chlorinated solvents behavior in fractured limestone aquifers is a challenging task because of the preferential flow of contaminants in fractures and the exchange with the limestone matrix. Characterization of the contaminant distribution, particularl...... sampling. It can also be applied in a matrix with strong variation in the hardness (e.g. softer limestone with interbedded chert layers). Furthermore, DNAPL presence in hydraulically active fractures can potentially be identified by high concentration peaks on the FACT.......Background and objective The understanding of chlorinated solvents behavior in fractured limestone aquifers is a challenging task because of the preferential flow of contaminants in fractures and the exchange with the limestone matrix. Characterization of the contaminant distribution, particularly...... limestone matrix and fractures as well as on the sorption to activated carbon, a modeling tool was developed (Mosthaf et al. 2014) which allows for the interpretation of field data and the analysis of the influence of various aquifer parameters. The model provides a link between sorbed concentrations on the...

  1. Re-appraisal of the Santa Rita Greenstone Belt stratigraphy, central Brazil, based on new U-Pb SHRIMP age and Sm-Nd data of felsic metavolcanic rocks

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Jost, Hardy; Fuck, Reinhardt Adolfo; Junges, Sergio Luiz [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: marcio@unb.br; Armstrong, Richard [Australian National Univ., Canberra, ACT (Australia). Research School of Earth Sciences; Resende, Marcelo Goncalves [Universidade Catolica de Brasilia, DF (Brazil). Curso de Graduacao em Engenharia Ambiental

    2000-03-01

    The Santa Rita greenstone belt represents one of the supracrustal belts of the Archaen terranes of Goias, central Brazil. The stratigraphic sequence of this greenstone belt comprises a lower of komatities and basalts and an upper metasedimentary unit made of carbonaceous schits, chert, iron formation and marble, unconformably overlain by clastic metasedimentary rocks. Felsic metavolcanics occur at the interface between the metabasalts and the upper metasedimentary pile. U-Pb SHRIMP age for zircons from the felsic metavolcanics reveal that it is not part of the Archaean sequence, but represents the product of mesoproterozoic (1580 {+-} 12 Ma) magmatic event. Sm-Nd isotopic data (initial e{sub CHUR} values between -10.5 and -14.9) and T{sub DM} values of 3.0 and 3.2 Ga, within the range of the surrounding TTG terranes, indicate that the original felsic magmas were produced by re-melting of Archaen crust. The data demonstrate that the Goias greenstone belt contains infolded and imbricated proterozoic rocks, as previously suggested by Sm-Nd isotopic analyses of some of the upper detrital metasedimentary rocks. (author)

  2. Petrography, mineralogy and geochemistry of Cretaceous sediment samples from western Khorat Plateau, Thailand, and considerations on their provenance

    Science.gov (United States)

    Saminpanya, Seriwat; Duangkrayom, Jaroon; Jintasakul, Pratueng; Hanta, Rattanaphorn

    2014-04-01

    At Mo Hin Khao on the western flank of Khorat Plateau, Thailand, the Phra Wihan Formation reveals litharenite and sublitharenite with some subarkose and arkose. A cuesta in the eroded sedimentary sequence exhibits spectacular rock pillars of considerable geotourist potential. The rock sequence is high in silica (SiO2 67-98 wt%) and contains quartz, mica, magnetite, chert fragments and accessory minerals such as zircon and tourmaline and amphibole species. These accessory minerals suggest felsic rocks, such as granite, granodiorite and pegmatite, were sources for the sandstones. Geochemical analyses of the sedimentary sequence suggest that source rocks may lie in the passive continental margin, before sediment transport and deposition in the Khorat Basin by rivers flowing across a large flood plain. Many depositional sequences/episodes formed thick beds of cross bedded clastic rocks. A high average maturity index (>5) indicates sedimentary reworking/recycling. Chemical Index of Alteration (CIA) values range from 47 to 98, suggesting variable chemical weathering within the source area rocks, largely representing moderate to high degrees of weathering. The average CIA value of these sediments (78) suggests that relatively extreme alteration factors were involved.

  3. Differentiation of naturally-occurring vs. artificial hydrocarbons in a landfill groundwater investigation

    International Nuclear Information System (INIS)

    Interpretation of groundwater sampling data at a large municipal/industrial landfill indicates contamination by both artificial and naturally-occurring hydrocarbons. Site hydrogeology consists of three different water bearing zones. The uppermost (shallow) aquifer is an unconfined unit consisting of silt, clay, and sand deposits. An intermediate depth semiconfined aquifer underlies the unconfined unit, and consists of a chert rubble zone and the upper portion of a fractured and solution-enhanced limestone formation. A regionally-extensive organic-rich shale underlies the semiconfined aquifer and separates it from the deep confined aquifer, which also consists of limestone. Groundwater investigations at the landfill have detected chlorinated and non-chlorinated hydrocarbons in the different aquifer intervals. Chlorinated hydrocarbons detected include tetrachloroethene, dichloroethene, and vinyl chloride and occur almost exclusively in the shallow aquifer. Aromatic hydrocarbons detected include benzene, toluene, ethylbenzene, and xylene (BTEX) and-occur in the intermediate and deep aquifers. The landfill was originally interpreted as the source of the contaminants. The observation of free-phase liquid hydrocarbons in the intermediate aquifer at the site, and high dissolved BTEX levels in the deep and intermediate aquifers upgradient of the landfill suggest that the aromatics were derived from a source other than the landfill. A potential source of BTEX contamination may be abandoned (pre-1930) natural gas wells located near the landfill. An additional BTEX source may be the organic-rich shale formation (a documented petroleum source rock)

  4. Archaeological salvage excavations at Patoka Lake, Indiana: prehistoric occupations of the upper Patoka River Valley. Research report (final) no. 6, Aug 77-May 80

    Energy Technology Data Exchange (ETDEWEB)

    Munson, C.A.

    1980-03-01

    An archaeological data recovery project at Patoka Lake, Indiana, was aimed toward the goals of providing a cultural-historical base for a little known area of the hill country of south-central Indiana and relating project findings to broader questions about prehistoric man's substance and settlement behaviors. Data for project studies are the result of environmental reconstructions, surface surveys at 192 sites, and salvage excavations at 11 sites. Various studies concern the cultural dimensions of both the excavated sites and the Upper Patoka Valley as a region and are based on the construction of a radiocarbon and artifact chronology, and analyses of tools and debris, features, chert utilization, botanical remains, and site location characteristics. Project findings indicate the bulk of the prehistoric occupation of the Upper Patoka Valley occurred during the Archaic, with major seasonal settlements being made during the Late Archaic, around 3,000 - 1,500 BC. For this period, the French Lick phase is defined, and a model of interregional, seasonally shifting settlements is proposed. Other interregional comparisons are identifying cultural and environmental factors which likely influenced several recognized patterns of regional land use changes between 10,000 BC and AD 1,600.

  5. The mafic-ultramafic complex of Aniyapuram, Cauvery Suture Zone, southern India: Petrological and geochemical constraints for Neoarchean suprasubduction zone tectonics

    Science.gov (United States)

    Yellappa, T.; Venkatasivappa, V.; Koizumi, T.; Chetty, T. R. K.; Santosh, M.; Tsunogae, T.

    2014-12-01

    Several Precambrian mafic-ultramafic complexes occur along the Cauvery Suture Zone (CSZ) in Southern Granulite Terrain, India. Their origin, magmatic evolution and relationship with the associated high-grade rocks have not been resolved. The Aniyapuram Mafic-Ultramafic Complex (AMUC), the focus of the present study in southern part of the CSZ, is dominantly composed of peridotites, pyroxenites, gabbros, metagabbros/mafic granulites, hornblendites, amphibolites, plagiogranites, felsic granulites and ferruginous cherts. The rock types in the AMUC are structurally emplaced within hornblende gneiss (TTG) basement rocks and are highly deformed. The geochemical signature of the amphibolites indicates tholeiitic affinity for the protolith with magma generation in island arc-setting. N-MORB normalized pattern of the amphibolites show depletion in HFS-elements (P, Zr, Sm, Ti, and Y) and enrichment of LIL-elements (Rb, Ba, Th, Sr) with negative Nb anomalies suggesting involvement of subduction component in the depleted mantle source and formation in a supra-subduction zone tectonic setting. Our new results when correlated with the available age data suggest that the lithological association of AMUC represent the remnants of the Neoarchean oceanic lithosphere.

  6. Rare earth chemistry of gold-bearing sedimentary carbonate horizons from the Abitibi Greenstone Belt, Ontario, Canada

    International Nuclear Information System (INIS)

    The ankerite, gold ore bodies of the Dome Mine, Timmins, Ontario are interflow units, 1 to 3 m thick in a sequence of tholeiitic basalts. The units consist of discontinuous layers of ferroan dolomite, chert and pyroclastic material, and laminations of iron sulfides, tourmaline, and graphite. They have been interpreted as sediments on the basis of their internal structure. Seven Rare Earth elements (REE) (Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb) were determined by instrumental neutron activation analysis, on 10 samples of carbonate material from the ankerite units. The chondrite normalized REE plots have relatively flat patterns with, in some cases, positive Europium anomalies. The flat patterns suggest that the fluids from which the carbonate precipitated was in equilibrium with volcanic rocks of tholeiitic and komatiitic composition. The positive Europium anomalies imply that the fluids were reducing at times. Such patterns are characteristic of Archaean sediments and also the precipitates associated with the discharge of hydrothermal solutions from vents on the East Pacific Rise

  7. Some masonary mortar from Hellenistic and Roman period Greece

    Energy Technology Data Exchange (ETDEWEB)

    Edwards, H.H.G.

    1985-01-01

    The Mineral Resources Research Center at the University of Minnesota has been engaged for the past six years in projects to synthesize various hydraulic cements by plasma fusion. An analytical scheme was developed to examine the plasma products. The techniques used to examine these cements were applied to five masonary mortar samples of Hellenistic and Roman periods from three sites in Greece (Olympia, Larissa, and Trikkala). These were examined by chemical, microscopical (polarized light and scanning electron), x-ray diffraction, and differential thermal analysis methods. These samples are typical sand-lime mortars: The aggregates consist of quartz with small amounts of microcline or orthoclase and, in several of the samples, rock and chert fragments. The matrix is largely fine grained calcite and a small amount of calcium silicate hydrate, a typical phase found in hydraulic cements. The sample from the Altis in Olympia (160 to 170 A.D.) is a pink, dense mortar with medium to fine grained aggregate and shows excellent workmanship. This specimen contains reddish fragments which are probably pieces of ceramics which either are used as fill or are poorly crushed material added as a pozzolana. The samples were probably emplaced as a sand and slaked-lime mixture. The limes are impure and thus have feebly hydraulic properties.

  8. Uranium and thorium enrichment in rocks from the base of DSDP Hole 465A, Hess Rise, central North Pacific

    Science.gov (United States)

    Hein, J.R.; Koski, R.A.; Morgenson, L.A.

    1982-01-01

    Uranium and thorium are concentrated in Cretaceous limestone, chert, ash, basalt, and other rock types at Deep Sea Drilling Project Site 465 located on the southern Hess Rise in the central North Pacific. U concentrations, up to 194 ppm on a carbonate-free basis, are among the highest recorded for any deep-sea deposits. U was initially derived from seawater and concentrated by absorption on terrigenous (humic) organic matter in limestone in a shallow marine environment. U and Th were probably concentrated further by low-temperature hydrothermal fluids emanating from the basaltic basement. Mainly montmorillonite, an alteration product of basalt and ash, and organic matter in sedimentary rocks acted as hosts for U and Th. The unique combination of sediments rich in humic organic matter, abundant smectite in altered ash and basalt, and warm hydrothermal solutions provided the necessary conditions for migration and concentration of U and Th. To better understand the conditions limiting the migrating and concentration of U and Th, other rocks deposited during the ocean-wide Cretaceous anoxic events should be analyzed for these elements. ?? 1982.

  9. Radionuclide sorption to rocks and minerals: Effects of pH and inorganic anions. Pt. 1. Sorption of cesium, cobalt, strontium amd manganese

    International Nuclear Information System (INIS)

    Sorption of 137Cs, 85Sr, 54Mn and 60Co to rocks (metamorphosed chert and shale, and granodiorite) and minerals (hematite, magnetite and calcite) was investigated in 0.001 N, 0.01 N and 0.1 N solutions of Na2SO, NaCl, Na2CO3 and NaHCO3. The effects of pH and co-existing anions on the sorption of these radionuclides are discussed in terms of surface complex formation. Increase in the sorption of Cs in the presence of SO42- ions is explained by preferential formation of a ternary complex, such as triple bond M-SO4-Cs. Sorption of Sr increases as the pH increases irrespective of background-anion type at the same electrolyte normality. On the whole, the sorptions of both Co and Mn increase as the pH increases, but sorption in a highly basic Na2CO3 solution sometimes is less than that in a solution of lower pH. Hydrolysis is considered to have occurred in the Na2CO3 solution, thereby generating weakly sorbed species of Mn and Co. (orig.)

  10. Isotope investigation of reduced carbon from metablack shales and black shales of Saxon Erzgebirge Mountains and other areas of GDR

    International Nuclear Information System (INIS)

    In order to examine the biogenic nature of reduced carbon the carbon isotope ratios were determined in samples of different metablack shale and black shale deposits of the Precambrium of the mountains from Saxon Erzgebirge, Schwarzburger Sattel, from the crystalline zone of Ruhla, and also from Palaeozoic layers in the Saxon Erzgebirge Mountains and from its northern border zone. The investigated rocks vary from non- or weak-metamorphic shales, alum-shales and cherts via phyllits to the stronger metamorphic quarzites, gneisses and mica-schists. The isotopic analysis of the reduced carbon indicates, that the investigated metablack shales and black shales are remarkably enriched in 12C. This result tends to an organic nature of the reduced carbon of these rocks. The 21 samples of metablack shales of the Saxon Erzgebirge Mountains yielded a mean delta13C-value of -290/00. This corresponds with delta13C-values from other deposits of the earth's crust. The isotopic abundances don't show any dependence on the carbon amount, the rank of metamorphism or the age of the rock samples. (author)

  11. PETROFACIES CHARACTERISTICS OF THE SANDSTONES OF THE UPPER MIOCENELOWER PLIOCENE AGED IN THE ULUMUHSİNE-TATKÖY (KONYA AREA

    Directory of Open Access Journals (Sweden)

    A. Müjdat ÖZKAN

    2000-03-01

    Full Text Available In the study area, Upper Miocene-Lower Pliocene aged Ulumuhsine formation, was formed in a shallow, open lake and river environment. The lithologies of this formation are thin-medium bedded, laminated and fossil rich limestone, thin-thick bedded mudstone, thin-thick bedded marl, thin-thick bedded dolomite with stromatolite interbedded limestone, tuffite, chert bands and coal-rich levels. In addition, it includes conglomerates and sandstones of underwater distrubution channels in lacustrine, and channel and bar sediments in stream environments. Red, gray, rarely green colored sandstones are thin-thick bedded, and in some levels well sorting, in some levels proorly sorting. They present sedimentary structures, as graded, herringbone cross-bedding, symmetric ripple-marks, and laminate. Sandstones are named lithic arenite and lithic graywacke and litharenite, feldspathic litharenite and sublithic arenite. These sandstones are rich rock fragments and quartzs, in addition they contain plagioclase, biotite, muskovite, opaque mineral and epidote. Binding materials of sandstones are mainly calcite cements and clay matrix, and iron oxide cement in little amount. From the mineralogical and textural point of view. As a tectonic environment, the main source of sandstones are recycled orogen (thrust, collision and land uplift and recyded lithic fragments.

  12. STRATIGRAPHIC FEATURES OF NEOGENE DEPOSITS OF DİLEKÇİ (WEST OF KONYA AREA

    Directory of Open Access Journals (Sweden)

    A. Müjdat ÖZKAN

    1999-03-01

    Full Text Available The basement of the investigated area is Silurian-Cretaceous aged basement rocks. The basement rocks consists of phillite, schist, quartzite, limestone, dolomite, spilite, diorite, gabbro, diabase and serpentinite. This basement is overlined unconformably by Upper Miocene-Lower Pliocene aged Sille formation, Yalıtepe formation, Ulumuhsine formation, Küçükmuhsine formation, Lower Pliocene aged Yürükler formation and Upper Pliocene-Quaternary aged Topraklı formation. Sille formation consists of red conglomerate, sandstone and mudstone, deposited in alluvial fan and braided stream environments. Yalıtepe formation contains cream, brown stromatolitic limestone formed in a shallow lake environment. Ulumuhsine formation is made by cream, limestone, clayey limestone, clayey limestone-mudstone alternation, mudstone, marl, dolomite, nodules and bands of chert-bearing, fossils-bearing limestone deposited in a shallow and open lake environment. Küçükmuhsine formation formed in a shallow and open lake environment consists of tuffite. Yürükler formation overlies conformably and unconformably in local Ulumuhsine and Küçükmuhsine formations, and contains conglomerate, and caliche nodulled mudstone deposited in alluvial fan and braided Stream environments. All these lithologies is overlined unconformably by Upper Pliocene-Quaternary aged Topraklı formation. Topraklı formation consists of conglomerate deposited in alluvial fan and braided stream environments. Neogene basin in the region have characteristics of an intra-mountain basin, time to time controlled by tectonics.

  13. New oil source rocks cut in Greek Ionian basin

    Energy Technology Data Exchange (ETDEWEB)

    Karakitsios, V. [Univ. of Athens (Greece); Rigakis, N. [Public Petroleum Corp., Athens (Greece)

    1996-02-12

    The Ionian zone of Northwest Greece (Epirus region) constitutes part of the most external zones of the Hellenides (Paxos zone, Ionian zone, Gavrovo Tripolitza zone). The rocks of the Ionian zone range from Triassic evaporites and associated breccias through a varied series of Jurassic through Upper Eocene carbonates and lesser cherts and shales followed by Oligocene flysch. The surface occurrences of petroleum in the Ionian zone are mainly attributed to Toarcian Lower Posidonia beds source rocks and lesser to late Callovian-Tithonian Upper Posidonia beds and to the Albian-Cenomanian Upper Siliceous zone or Vigla shales of the Vigla limestones. Oil that could not be attributed to the above source rocks is believed to have an origin from Triassic formations that contain potential source rocks in Albania and Italy. However, several samples of the shales of Triassic breccias from outcrops and drillholes were analyzed in the past, but the analytical results were not so promising since their hydrocarbon potential was low. In this article, the authors will present their analytical results of the Ioannina-1 well, where for the first time they identified some very rich source beds in the Triassic breccias formation of Northwest Greece.

  14. Mars Rover Sample Return: A sample collection and analysis strategy for exobiology

    Science.gov (United States)

    Sims, M. H.; Fischler, M.; Schwartz, D. E.; Rosenthal, Donald A.; Mancinelli, Rocco L.; Nedell, Susan S.; Gamble, E.; Mckay, Christopher P.

    1989-01-01

    For reasons defined elsewhere it is reasonable to search for biological signatures, both chemical and morphological, of extinct life on Mars. Life on Earth requries the presence of liquid water, therefore, it is important to explore sites on Mars where standing bodies of water may have once existed. Outcrops of layered deposits within the Valles Marineris appear to be ancient lake beds. Because the outcrops are well exposed, relatively shallow core samples would be very informative. The most important biological signature to detect would be organics, microfossils, or larger stromato-like structures, although the presence of cherts, carbonates, clays, and shales would be significant. In spite of the limitations of current robotics and pattern recognition, and the limitations of rover power, computation, Earth communication bandwidth, and time delays, a partial scenario was developed to implement such a scientific investigation. The rover instrumentation and the procedures and decisions and IR spectrometer are described in detail. Preliminary results from a collaborative effort are described, which indicate the rover will be able to autonomously detect stratification, and hence will ease the interpretation burden and lead to greater scientific productivity during the rover's lifetime.

  15. Middle Jurassic Radiolaria from a siliceous argillite block in a structural melange zone near Viqueque, Timor Leste: Paleogeographic implications

    Science.gov (United States)

    Haig, David W.; Bandini, Alexandre Nicolas

    2013-10-01

    Thin-bedded siliceous argillite forming a large block within a structural melange zone at Viqueque, Timor Leste, has yielded a Middle Jurassic (late Bathonian-early Callovian) radiolarian assemblage belonging to Unitary Association Zone 7. Fifty-five species are recognized and illustrated, forming the most diverse radiolarian fauna yet documented from the Jurassic of Timor. The fauna shows little similarity in species content to the few other assemblages previously listed from the Middle or Late Jurassic of Timor, and also has few species in common with faunas known elsewhere in the region from Rotti, Sumatra, South Kalimantan, and Sula. Based on lithofacies similarities and age, the siliceous argillite succession in the melange block at Viqueque is included in the Noni Group originally described as the lower part of the Palelo Series in West Timor. In terms of lithofacies, the Noni Group is distinct from other stratigraphic units known in Timor. It may be associated with volcanic rocks but age relationships are uncertain, although some of the radiolarian cherts in the Noni Group in West Timor have been reported to include tuffaceous sediment. The deep-water character of the siliceous hemipelagite-pelagite facies, the probable volcanic association, and an age close to that of continental breakup in the region suggest deposition in a newly rifted Indian Ocean. In Timor's tectonostratigraphic classification scheme, the Noni Group is here placed in the "Indian Ocean Megasequence".

  16. Application of Thermal Infrared Multiband Scanner (TIMS) data to mapping of Plutonic and stratified rock and assemblages in accreted terrains of the Northern Sierra, California

    Science.gov (United States)

    Taranik, James V.; Davis, David; Borengasser, Marcus

    1986-01-01

    The Thermal Infrared Multispectral Scanner (TIMS) data were acquired over the Donner Pass area in California on September 12, 1985. The higher peaks in the area approach 9,200 feet in elevation, while the canyon of the north fork of the American River is only 3000 feet in elevation. The vegetation is dominated by conifers, although manzanita and other shrubs are present in areas where soils have developed. The data contain noise patterns which cut across scan lines diagonally. The TIMS data were analyzed using both photointerpretative and digital processing techniques. Preliminary image interpretation and field analysis confirmed that TIMS image data displays the chert units and silicic volcanics as bright red. The imagery appears to display zoning in the batholithic and hypabyssal intrusive rocks, although this was not field checked at this time. Rocks which appear to be more dioritic in composition appear purple on the imagery, while rocks more granitic in composition appear shades of red and pink. Areas that have more than 40% vegetative cover appear green on the imagery.

  17. Cycles and events in stratigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Einsele, G.; Ricken, W.; Seilacher, A. (eds.)

    1991-01-01

    This book reviews and discusses the most up-to-date knowledge in the fields of cyclostratigraphy and event stratigraphy. The book contains 48 papers contributed by the most knowledgeable geologists and paleontologists in the fields of cycle and event stratigraphy. It is divided into two parts. Part one is concerned with the structure of individual beds and larger cycles and sequences and discusses; rhythmic stratification, event stratification, diagenetic overprint, cherts and phosphorites, and preservation and biologic destruction of laminated sediments. Part two, on larger cycles and sequences, looks at sequences, hierarchies, causes and environmental expression, and timing and correlation, i.e. the cycles of frequencies from millions of years to thousands of years (Milankovich band). Summaries on spectral analysis are also presented. There are 80 pages of references and a comprehensive index. It is extensively illustrated with line drawings and graphs. Practicing sedimentary geologists without access to a good library or find it hard to keep up with the plethora of journal articles and want a refresher in this area of stratigraphy will find the book particularly useful.

  18. The Case for a Hot Archean Climate and its Implications to the History of the Biosphere

    CERN Document Server

    Schwartzman, David W

    2015-01-01

    The case for a much warmer climate on the early Earth than now is presented. The oxygen isotope record in sedimentary chert and the compelling case for a near constant isotopic oxygen composition of seawater over geologic time support thermophilic surface temperatures prevailing in the Archean, with some support for hot conditions lasting until about 1.5 billion years ago, aside from lower temperatures including glacial episodes at 2.1-2.4 Ga and possibly an earlier one at 2.9 Ga. Other evidence includes the following: 1) Melting temperatures of proteins resurrected from sequences inferred from robust molecular phylogenies give paleotemperatures at emergence consistent with a very warm early climate. 2) High atmospheric pCO2 levels in the Archean are consistent with high climatic temperatures near the triple point of primary iron minerals in banded iron formations, the formation of Mn-bicarbonate clusters leading to oxygenic photosynthesis and generally higher weathering intensities on land. These higher weat...

  19. Mineralization Zoning in Yindongzi—Daxigou Barite—Siderite,Silver—Polymetallic Deposits in the Qinling Orogen,China

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 等

    2001-01-01

    The Yindongzi-Daxigou strata-bound barite-siderite,silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate.The orebodies occur in a series of hydrothermal depositonal rocks.Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ab→Cu-Ag→Pb→Au.This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization.In this gradational transition between Chefanggou and Yindongzi,vent-proximal mineralization consists of silver-polymetallic orebodies(Pb-Ag),which is the center of hydrothermal mineralization.The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization.Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in te east is represented by the Pb ore district.Thick massive,laminated barren albite chert and jasperite,sometimes with minor silver-ploymetallic mineralization of commercial importance,and pyritization in rocks feature more distal mineralization.Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually,Au deposits are dominantly controlled by the late brittle-ductile shear zone.

  20. 云南墨江镍金矿床主要控矿因素分析与研究%RESEARCH AND ANALYSIS ON ORE-CONTROLLING FACTORS FOR MOJIANG-YUANJIANG NICKEL-GOLD DEPOSITS IN YUNNAN, CHINA

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 谢桂青; 漆亮; 苏文超

    2001-01-01

    Based on research and analysis on ore-controlling factors and analysis of tectono-lithostratigraphic units to shed light on Ni-Au metallogenic processes, it is suggested that the main ore-controlling factors for the Mojiang-Yuanjiang Ni-Au deposits in Yunnan Province include strata-controlling and tectonics-controlling. In the Mojiang-Yuanjiang Ni-Au mine, the Upper Devonian Jinchang Formation consists of low-grade metamorphic volcano-sedimentary rocks formed in a deep-water, volcanic-related hydrothermal depositional basin. This Formation is composed of slate, chert, palimpsest siltstone and sandstone interbeded with tuff mudstone, volcanic lava and tuff. Three tectono-lithostratigraphic units (the Lanshan, Sishibaliangshan and Mahudong) can be recognized in the Jinchang Formation. The Lanshan unit (D3jy1) was formed by volcanism and volcanic-related hydrothermal deposition and is referred to as the volcanic-exhalative-genetic unit. Nickel-gold-bearing pyritic cherts in the Mojiang deposit occur in the lower part of the Lanshan rock-unit, ranging in age from 358±8.6 (2σ) Ma (Sm-Nd isochron dating) to 354.7±0.72 (2σ) Ma (Rb-Sr isochron dating). The Sishibaliangshan unit (D3jy2) consisting of slate, chert, palimpsest siltstone and sandstone, volcanic lava rock and tuff, is also referred to as the volcanic-exhalative-genetic unit. The Mahudong unit (D3jy3) is composed mainly of a suite of fine-grained turbidite rocks with acidic volcanic lava and violet-red sandstones at its top.    The ring-like clayized zone and the tectono-lithostratigraphic sequence of hydrothermal deposits are located at hydrothermal-water vents that are one of the main ore-host structures. The Yanshanian brittle-ductile shear zones that are another main type of ore-host structures are typified by the proximately horizontal tension cracks, sinistral shear fractures, close-off brittle-ductile shear zones, and Cr-illite was formed at 178 Ma to 76 Ma. The Himalayan brittle tension cleavages

  1. Mineralization Zoning in Yindongzi-Daxigou Barite-Siderite, Silver-Polymetallic Deposits in the Qinling Orogen, China

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 黄转莹

    2001-01-01

    The Yindongzi-Daxigou strata-bound barite-siderite, silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate. The orebodies occur in a series of hydrothermal depositional rocks. Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ag→Cu-Ag→Pb→Au. This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization. In this gradational transition between Chefanggou and Yindongzi, vent-proximal mineralization consists of silver-polymetallic orebodies (Pb-Ag), which is the center of hydrothermal mineralization. The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization. Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in the east is represented by the Pb ore district. Thick massive, laminated barren albite chert and jasperite, sometimes with minor silver-ploymetallic mineralization of commercial importance, and pyritization in rocks feature more distal mineralization. Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually, Au deposits are dominantly controlled by the late brittle-ductile shear zone.

  2. Sedimentary Basin Analysis and Petroleum Potential of the Cretaceous Yuchon Group In Haenam Depression, SW Korea

    Institute of Scientific and Technical Information of China (English)

    Son Jin-Dam

    2000-01-01

    The Yuchon Group in the Late Cretaceous of Haenam and Mokpo area on the southwest coast of Korea peninsula can be divided into two Formations: (1) the intermediate volcanic Formation (Hwawon Formation), about 500m thick, (2)the acidic volcanic Formation (Hwangsan Formation), about 400m thick in ascending order.The former comprises intermediate volcaniclastics interlayered with volcanic rocks, and red mudrock and tuffaceous sandstone indicating fluvial deposits. The latter is subdivided into the upper part (Hwangsan Tuff Member) consisting of subaerial pyroclastics and intercalated rhyolites, and the lower part (Byeongonri Member) including subaqueous volcaniclastics, lake deltaic sandstone and gravelstone, lacustrine black shale and limestone and chert, and lake turbidite sandstone.The Late Cretaceous basin including Haenam subbasin in southwest Korea was largely formed of extensional nonmarine depressions (volcano- tectonic) bounded by NE- SW sinistral fault system.The thermal maturation based on geochemical and mineralogical studies for the black shales and tuffaceous sandstones reached the late stage of oil generation zone or gas generation stage. It seems that black shales and limestones are fairly good as source rock. The porosity of potential reservoir sandstone and tuff ranges from 5 % to 11%, but their permeability except the fractured rocks is very low ( <1md) because of fine pore throats reduced by diagenetic cementation of tuffaceous sandstones. Numerous potential traps might have been formed by the later folding and faulting along with lateral facies change and abundant mudrocks and volcaniclastics should make excellent seals.

  3. Diagenesis of Viola Limestone (Middle and Upper Ordovician), southeastern Arbuckle Mountains, Oklahoma

    Energy Technology Data Exchange (ETDEWEB)

    Grammer, G.M.

    1983-03-01

    The Viola Limestone in the Arbuckle Mountains was deposited on a carbonate ramp within the southern Oklahoma aulacogen. A complex diagenetic history has occluded virtually all primary porosity within the Viola. Petrographic evidence suggests that the following approximate sequence of diagenetic events has occurred; (1) microboring and subsequent micritization of bioclasts to form micrite envelopes; (2) very early submarine cementation that bound the loosely sorted allochems and partly occluded porosity, characterized by drusy overgrowths on trilobite and brachiopod fragments, bladed, void-filling cement, and turbid, inclusion-rich syntaxial overgrowths on pelmatozoan fragments; (3) initial compaction evidenced by local fracturing of elongate bioclasts; (4) neomorphism, including the inversion of aragonitic allochems to calcite and the recrystallization of micrite to microspar and pseudospar in the presence of low-salinity pore fluids; (5) freshwater cementation that filled virtually all remaining pore space; (6) selective dolomitization; (7) silicification, including the formation of chert nodules and the replacement of bioclasts and calcite cements by microgranular quartz and/or lutecite; (8) compaction and pressure solution, probably due to deep burial, characterized by nonsutured seam stylolites, sutured seam stylolites oriented subparallel to bedding, and sutured grain boundaries; and (9) tectonically imposed pressure solution indicated by sutured seam stylolites oriented at high angles to bedding that developed during the late Paleozoic deformation of the Arbuckle Mountain. The Viola Limestone is known as a reservoir rock and possible source unit for hydrocarbons throughout much of south-central Oklahoma.

  4. Field trip guide to selected outcrops, Arbuckle Mountains, Oklahoma

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1991-11-17

    The Arbuckle Mountains, named for Brigadier General Matthew Arbuckle, are located in south-central Oklahoma. The formations that comprise the Arbuckle Mountains have been extensively studied for hydrocarbon source rock and reservoir rock characteristics that can be applied to the subsurface in the adjacent Anadarko and Ardmore basins. Numerous reports and guidebooks have been written concerning the Arbuckle Mountains. A few important general publications are provided in the list of selected references. The purpose of this handout is to provide general information on the geology of the Arbuckle Mountains and specific information on the four field trip stops, adapted from the literature. The four stops were at: (1) Sooner Rock and Sand Quarry; (2) Woodford Shale; (3) Hunton Anticline and Hunton Quarry; and (4) Tar Sands of Sulfur Area. As part of this report, two papers are included for more detail: Paleomagnetic dating of basinal fluid migration, base-metal mineralization, and hydrocarbon maturation in the Arbuckle Mountains, Oklahoma and Laminated black shale-bedded chert cyclicity in the Woodford Formation, southern Oklahoma.

  5. Geology and uranium mineralisation in the Deccan trap-lameta-crystalline basement at Lalbarra, Mandla district, Madhya Pradesh, India

    International Nuclear Information System (INIS)

    Proterozoic crystalline rocks of Lalbarra area comprise banded migmatites, biotite granites, and two-mica granites carrying components of pre-existing Sausar group metasediments. The biotite schists of the Sausar group had inherent anomalous radioelement contents mainly within the silicate bound structures of zircon and epidote. On being subjected to migmatisation and granitisation, the uranium has been partially re-distributed. Consequent to the emplacement of volatile rich two-mica granite (TMG) along shears, uranium is by and large partitioned from thorium and got enriched in TMG in labile state. A hiatus of long duration intervened before the Infratrappean (lametas) fresh water, sedimentary rocks with its provenance area comprising among others, the fertile TMG, were laid. Basalt flows of Deccan trap age which had covered the lametas and the basement are presently found as thin (<20 m) outliers. Uranium mineralisation is found at the Deccan trap (basalt)-lameta-crystalline basement contact zone hosted in ferruginous chert veins occupying fractures in the basal part of the flow as well as in pseudo quartzites in the lameta formation. Radioactivity is largely due to uranophane associated with ferruginous cherty matter. (author). 11 refs., 2 tabs., 2 figs

  6. Re-appraisal of the Santa Rita Greenstone Belt stratigraphy, central Brazil, based on new U-Pb SHRIMP age and Sm-Nd data of felsic metavolcanic rocks

    International Nuclear Information System (INIS)

    The Santa Rita greenstone belt represents one of the supracrustal belts of the Archaen terranes of Goias, central Brazil. The stratigraphic sequence of this greenstone belt comprises a lower of komatities and basalts and an upper metasedimentary unit made of carbonaceous schits, chert, iron formation and marble, unconformably overlain by clastic metasedimentary rocks. Felsic metavolcanics occur at the interface between the metabasalts and the upper metasedimentary pile. U-Pb SHRIMP age for zircons from the felsic metavolcanics reveal that it is not part of the Archaean sequence, but represents the product of mesoproterozoic (1580 ± 12 Ma) magmatic event. Sm-Nd isotopic data (initial eCHUR values between -10.5 and -14.9) and TDM values of 3.0 and 3.2 Ga, within the range of the surrounding TTG terranes, indicate that the original felsic magmas were produced by re-melting of Archaen crust. The data demonstrate that the Goias greenstone belt contains infolded and imbricated proterozoic rocks, as previously suggested by Sm-Nd isotopic analyses of some of the upper detrital metasedimentary rocks. (author)

  7. Late Jurassic breakup of the Proto-Caribbean and circum-global circulation across Pangea

    Science.gov (United States)

    Baumgartner, Peter O.; Rojas-Agramonte, Yamirka; Sandoval-Gutierrez, Maria; Urbani, Franco; García-Delgado, Dora; Garban, Grony; Pérez Rodríguez, Mireya

    2013-04-01

    Based on earlier plate reconstructions, many authors have postulated a circum-global equatorial current system flowing through the Pangea breakup, the Tethys - Atlantic - Caribbean Seaway, to explain changes in global climate during the Middle and Late Jurassic. While a Toarcian (late Early Jurassic) breakup is well constrained for the Central Atlantic, the place and timing of initial ocean crust formation between the Americas (Gulf of Mexico or Proto-Caribbean?) is still poorly constrained. Ar/Ar ages (190 to 154 Ma) in the Tinaquillo ultramafic complex (NW-Venezuela) have been interpreted as a result of initial Proto-Caribbean rifting. However, the Tinaquillo is clearly a subconinental block and the cited ages age cannot be related with breakup. The Siquisique Ophiolite (NW-Venezuela), long known for the occurrence of Bajocian-early Bathonian ammonite fragments found in interpilow sediments, has previously been interpreted as an early Proto-Caribbean remnant. However, the ammonite fragments were recovered from blocks in a Paleogene tectonic mélange, whereas the main Siquisique ophiolite body seems to be of middle Cretaceous age, based on a few Ar/Ar dates and poorly preserved middle to late Cretaceous radiolarians, which we recovered from black cherts interbedded with volcanics. The best record of Proto-Caribbean rifting and breakup is preserved in the Guaniguanico Terrane of NW-Cuba, which represents a distal Yucatan (N-American) passive margin segment telescoped by Tertiary nappe tectonics. In this terrane middle to upper Oxfordian pelagic limestones encroach on the E-MORB type El Sabalo Basalts which represent the oldest known remnants of oceanic crust clearly identifiable as Proto-Caribbean. Older, syn-rift sediments in the Proto-Caribbean and Gulf of Mexico are known to be deltaic to shallow marine detrital, and evaporitic. Although oceanic crust seemingly started to form in the early Late Jurassic (158 my), recent plate tectonic reconstructions show

  8. ASR potential of quartz based on expansion values and microscopic characteristics of mortar bars

    Science.gov (United States)

    Stastna, Aneta; Sachlova, Sarka; Kuchynova, Marketa; Pertold, Zdenek; Prikryl, Richard

    2016-04-01

    The alkali-silica reaction (ASR) is one of the most damaging factors for concrete structures. Different analytical techniques are used to quantify ASR potential of aggregates. The accelerated mortar bar test (ASTM C1260) in combination with the petrographic examination of aggregates by microscopic techniques belongs to the frequently employed methods. Such a methodical approach enables quantification of the ASR potential, based on the expansion values of accelerated mortar bars; and also to identify deleterious components in aggregates. In this study, the accelerated mortar bar test (ASTM C1260) was modified and combined with the scanning electron microscopy of polished sections prepared from mortar bars. The standard 14-day test period of mortar bars was prolonged to 1-year. ASR potential of aggregates was assessed based on expansion values (both 14-day and 1-year) of mortar bars and microscopic analysis of ASR products (alkali silica gels, microcracks, dissolution gaps) detected in the sections. Different varieties of quartz-rich rocks including chert, quartz meta-greywacke, three types of quartzite and pegmatite were used as aggregate. Only quartz from pegmatite was assessed to be non reactive (14-day expansion of 0.08%, 1-year expansion of 1.25%). Aggregate sections exhibited minor ASR products even after 1-year of mortar bar immersion in 1 M NaOH. Expansion values of the rest of samples exceeded the limit of 0.10% after 14-day test period indicating aggregates as reactive. The highest ASR potential was detected in mortar bars containing chert (14-day expansion of 0.55%, 1-year expansion of 2.70%) and quartz meta-greywacke (14-day expansion of 0.46%, 1-year expansion of 2.41%). The high ASR potential was explained by presence of cryptocrystalline matrix in significant volumes (24 - 65 vol%). Influence of the lengths of the immersion in the alkaline solution was observed mainly in the microstructure of the cement paste and on the extension of ASR products. The

  9. Oceanic anoxia during the Late Permian: Evidence from pyrite morphology%二叠纪末期海洋缺氧:来自黄铁矿形态的证据

    Institute of Scientific and Technical Information of China (English)

    遇昊; 陈代钊; 韦恒叶; 汪建国; 常华进

    2011-01-01

    晚二叠世是古生代环境和生物演化的重要时期,也是重要的"冰室气候"时期,但其中仍然含有大量的富有机质沉积,并发育成为我国南方扬子板块重要的烃源岩层位.为恢复这一时期古海洋氧化还原状态,我们对湖北恩施赵家坝剖面大隆组硅质岩和四川广元上寺长江沟剖面大隆组碳酸盐岩中草莓状黄铁矿的粒径大小和分布进行了测量、统计和研究.统计结果显示,这些硅质岩和灰岩样品中的草莓状黄铁矿基本为原生,少见自行晶和后期充填,具有如下特点:单体粒径普遍偏小,变化范围相当狭窄,大多数草莓状黄铁矿粒径小于5μm,80%以上的粒径小于7.7μm.这些粒径特征和分布特点表明,我国南方记录的晚二叠世大隆组烃源岩沉积于台内盆地极度缺氧(甚至硫化)的海洋环境,有利于有机质的保存.另外,该时期的极度缺氧为晚二叠世-早三叠世之交的大规模生物灭绝拉开了序幕.%Late Permian is an important stage marked by vast environmental and biological changes in the Paleozoic. Although an "Ice-House climate" predominated over the period, organic-rich sediments,which are served as important source rocks, were deposited extensively in intraplatform basins on Yangtze block, South China. In order to reconstruct the paleoredox conditions of the Yangtze sea during this period, we measured framboid size of pyrite in cherts and siliceous carbonates of Dalong Formation at Zhaojiaba section, Hubei province, and Changjianggou section,Sichuan province, respectively. Our data indicate that pyrite framboids in the cherts and carbonates are mostly of primary origin, although minor idiotopic crystals showing post-depositional transformation are observed. Pyrite framboids generally vary in a very narrow range in size,mostly smaller than 5 μm,and over 80% of which are smaller than 7.7 μm. These suggest that, during the Late Permian, the organic-rich sediments were

  10. Transformaciones edaficas y diageneticas de los depositos aluviales distales del mioceno de la cuenca de Madrid, area de Paracuellos de Jarama

    Directory of Open Access Journals (Sweden)

    Alonso-Zarza, A. Mª

    2003-08-01

    Full Text Available The distal aluvial fan and the palustrine deposits of the Paracuellos de Jarama area display a variety of specific pedogenic and diagenetic features. The processes affecting these sediments were controlled by: the sedimentary environment, the lithology and initia1 texture of the sediments and by the pedogenic-diagenetic environment in which the transformations occurred. Thus, in the distal alluvial areas (PEL profile the first processes were the formation of thin carbonate laminae and sepiolite, further, these deposits were silicified and later, a spheroidal dolomite is formed on the opaline chert. In lacustnne environments (UPC profile, drying and root activity led to the formation of palustrine carbonates that were silicified, and the initial texture and structure were preserved. The silicification consisted on a pseudomorphic replacement that produced mainly opal whereas quartz was formed mostly by cementation and ageing of previous opal. In both environments, when the silicification occurs on sepiolite, or micrite with sepiolite, atypical microfibrous opal is produced. This replacement can lead to the release of Mg, favounng a later formation of dolomite on the opaline chert, with evidence of bacteria1 activity. Al1 these processes occurred in a shallow phreatic or even vadose environment.Los depósitos distales de los abanicos aluviales arcósicos y también los carbonatos palustres del área de Paracuellos de Jarama presentan rasgos muy específicos debidos a los procesos edáficos y diagenéticos que han sufrido. Los procesos que han afectado a estos sedimentos, y su intensidad, estuvieron controlados por: el ambiente sedimentario, la litología y textura/estructura inicial del material y también por el ambiente pedogénico- diagenético superficial en el que se han desarrollado las transformaciones. Así, en las lutitas de las zonas distales de los abanicos (perfil PEL se forman inicialmente láminas de carbonato edáfico y sepiolita

  11. Silica enrichment, graphic granite and aquamarine growth: a new exploration guide

    Directory of Open Access Journals (Sweden)

    A. BHASKARA RAO

    2002-09-01

    Full Text Available Granitic pegmatites are traditionally known to contain graphic, perthitic and myrmekitic intergrowths related to quartz and K- and Na- feldspars. They are further considered to characterise the pegmatite types distinguishing them from the granites and other related plutonic rock types. Graphic granite is accepted also as a synonym to granitic pegmatite. Systematic studies, by the author and colleagues, on the granitic pegmatite gem deposits have permitted the definition of two aquamarine gem provinces in ENE Brazil, one in the NeoProterozoic and the other in the Archaean sequences. Potash feldspars in the pegmatites in the former show perthitic intergrowths, whereas in the latter graphic intergrowth dominates with anomalously coarse centimetric quartz along the cleavages of K-feldspar. Several granitic pegmatites hosted in Archaean complex, in Lages Pintadas Aquamarine Province, Santa Cruz, RN State, present this texture-structure. Graphic intergrowth is attributed to the eutectic crystallization, succeeded by hydrothermal fluids with silica enrichment permitting the growth through diffusion and nucleation of quartz and along cleavages of potash feldspar. In the Archaean terrain, the abundance of recycled chert forming metapsammitic migmatites traversed by numerous quartz veins and coarse graphic granites, has contributed to the growth of beryl and also the aquamarines.Pegmatitos graníticos são tradicionalmente conhecidos por terem intercrescimentos gráficos, pertíticos e mirmequíticos, relacionados a quartzo e feldspatos potássicos e sódicos. Também são considerados para caracterizar os tipos de pegmatitos, distinguindo-os dos granitos e outros tipos de rochas plutônicas relacionadas. Granito gráfico é aceito como sinônimo do pegmatito granítico. Estudos sistemáticos, do autor e seus colegas, sobre depósitos de pegmatitos graníticos de gemas permitiram a definição de duas províncias de gemas águas marinhas no ENE do Brasil

  12. Spatial and temporal variations of diffuse CO_{2} degassing at the N-S volcanic rift-zone of Tenerife (Canary Islands, Spain) during 2002-2015 period

    Science.gov (United States)

    Alonso, Mar; Ingman, Dylan; Alexander, Scott; Barrancos, José; Rodríguez, Fátima; Melián, Gladys; Pérez, Nemesio M.

    2016-04-01

    Tenerife is the largest of the Canary Islands and, together with Gran Canaria Island, is the only one with a central volcanic complex that started to grow at about 3.5 Ma. Nowadays the central complex is formed by Las Cañadas caldera, a volcanic depression measuring 16×9 km that resulted from multiple vertical collapses and was partially filled by post-caldera volcanic products. Up to 297 mafic monogenetic cones have been recognized on Tenerife, and they represent the most common eruptive activity occurring on the island during the last 1 Ma (Dóniz et al., 2008). Most of the monogenetic cones are aligned following a triple junction-shaped rift system, as result of inflation produced by the concentration of emission vents and dykes in bands at 120o to one another as a result of minimum stress fracturing of the crust by a mantle upwelling. The main structural characteristic of the southern volcanic rift (N-S) of the island is an apparent absence of a distinct ridge, and a fan shaped distribution of monogenetic cones. Four main volcanic successions in the southern volcanic rift zone of Tenerife, temporally separated by longer periods (˜70 - 250 ka) without volcanic activity, have been identified (Kröchert and Buchner, 2008). Since there are currently no visible gas emissions at the N-S rift, diffuse degassing surveys have become an important geochemical tool for the surveillance of this volcanic system. We report here the last results of diffuse CO2 efflux survey at the N-S rift of Tenerife, performed using the accumulation chamber method in the summer period of 2015. The objectives of the surveys were: (i) to constrain the total CO2 output from the studied area and (ii) to evaluate occasional CO2 efflux surveys as a volcanic surveillance tool for the N-S rift of Tenerife. Soil CO2 efflux values ranged from non-detectable up to 31.7 g m‑2 d‑1. A spatial distribution map, constructed following the sequential Gaussian simulation (sGs) procedure, did not show an

  13. Is There any Relationship Between the Santa Elena Depression and Chicxulub Impact Crater, Northwestern Yucatan Peninsula, Mexico?

    Science.gov (United States)

    Lefticariu, L.

    2005-05-01

    The Terminal Cretaceous Chicxulub Impact Crater had a strong control on the depositional and diagenetic history of the northern Yucatan Platform during most of the Cenozoic Era. The Chicxulub Sedimentary Basin (henceforth Basin), which approximately coincides with the impact crater, is circumscribed by a concentration of karstic sinkholes known as the Ring of Cenotes. Santa Elena Depression (henceforth Depression) is the name proposed for the bowl-shaped buried feature, first contoured by geophysical studies, immediately south of the Basin, in the area where the Ticul 1 and UNAM 5 wells were drilled. Lithologic, petrographic, and biostratigraphic data on PEMEX, UNAM, and ICDP cores show that: 1) Cenozoic deposits are much thicker inside the Basin than inside the Depression, 2) in general, the Cenozoic formations from inside the Depression are the thickest among those outside the Basin, 3) variably dolomitized pelagic or outer-platform wackestone or mudstone occur both inside the Basin and Depression, 4) the age of the deeper-water sedimentary carbonate rocks is Paleocene-Eocene inside the Basin and Paleocene?-Early Eocene inside the Depression, 5) the oldest formations that crop out are of Middle Eocene age at the edge of the Basin and Early-Middle Eocene age inside the Depression, 6) saline lake deposits, that consist chiefly of anhydrite, gypsum, and fine carbonate, and also contain quartz, chert, clay, zeolite, potassium feldspar, pyrite, and fragments of wood, are present in the Cenozoic section of the UNAM 5 core between 282 and 198 m below the present land surface, 7) the dolomite, subaerial exposure features (subaerial crusts, vugs, karst, dedolomite), and vug-filling cement from the Eocene formations are more abundant inside the Depression than inside the Basin. The depositional environments that are proposed for explaining the Cenozoic facies succession within the Santa Elena Depression are: 1) deeper marine water (Paleocene?-Early Eocene), 2) relatively

  14. A New Oceanic Anoxic Event 2 record from the Central North Atlantic at South East Newfoundland Ridge, IODP Expedition 342, Newfoundland Drifts

    Science.gov (United States)

    Junium, C. K.; Bornemann, A.; Bown, P. R.; Friedrich, O.; Moriya, K.; Kirtland Turner, S.; Whiteside, J. H.

    2013-12-01

    The recovery of Cretaceous, Cenomanian-Turonian black shales deposited during Oceanic Anoxic Event 2 (OAE 2) at Site U1407, South East Newfoundland Ridge (SENR), was an unexpected but fortuitous discovery that fills a gap in the pelagic Tethyan and North Atlantic geologic records. Drilling operations recovered the OAE sequence in all three holes drilled at Site U1407 defined initially on the basis of lithology and calcareous nannofossil biostratigraphy and confirmed by carbon isotope stratigraphy post-expedition. The SENR OAE 2 sequence is a classic chalk sequence punctuated by a prominent black band. Prior to OAE 2, greenish white pelagic carbonate is interrupted by thin, 2 to 5 cm thick organic-rich, gray calcareous clays. A sharp transition from greenish-white chalk to carbonate-poor sediments marks the occurrence of the organic carbon-rich black band. Within the black band are finely laminated to massive, pyritic black shales and laminated gray clays that are relatively organic carbon-lean, free of preserved benthic foraminifera and rich in radiolarians. Finely laminated greenish-gray marls overlay the black band and grade into approximately 1 meter of greenish white chalks with common 1cm chert layers and nodules. The remainder of the Turonian sequence is characterized by a notable transition to pink chalks. The thickness of the black band ranges from 15-40 cm between Holes A through C. The differences in the thickness of beds between Holes is due in part to drilling disturbances and mass wasting indicated by slump features in the overlying Turonian strata. Core scanning XRF and carbon isotopes can help resolve the nature of these differences and inform future sampling and study. Carbonate and organic carbon isotopes reveal that the δ13C excursion marking the initiation of OAE 2 is below the base of the black band. At U1407A the δ13C rise is immediately below (3 cm) the black shale, with δ13C maxima in the black band. At U1407C the initial δ13C rise is

  15. Sandstone provenance and tectonic evolution of the Xiukang Mélange from Neotethyan subduction to India-Asia collision (Yarlung-Zangbo suture, south Tibet)

    Science.gov (United States)

    An, Wei; Hu, Xiumian; Garzanti, Eduardo

    2016-04-01

    The Xiukang Mélange of the Yarlung-Zangbo suture zone in south Tibet documents low efficiency of accretion along the southern active margin of Asia during Cretaceous Neotethyan subduction, followed by final development during the early Paleogene stages of the India-Asia collision. Here we investigate four transverses in the Xigaze area (Jiding, Cuola Pass, Riwuqi and Saga), inquiry the composition in each transverse, and present integrated petrologic, U-Pb detrital-zircon geochronology and Hf isotope data on sandstone blocks. In fault contact with the Yarlung-Zangbo Ophiolite to the north and the Tethyan Himalaya to the south, the Xiukang mélange can be divided into three types: serpentinite-matrix mélange composed by broken Yarlung-Zangbo Ophiolite, thrust-sheets consisting mainly chert, quartzose or limestone sheets(>100m) with little intervening marix, and mudstone-matrix mélange displaying typical blocks-in-matrix texture. While serpentinite-matrix mélange is exposed adjacent to the ophiolite, distributions of thrust-sheets and blocks in mudstone-matrix mélange show along-strike diversities. For example, Jiding transverse is dominant by chert sheets and basalt blocks with scarcely sandstone blocks, while Cuola Pass and Saga transverses expose large amounts of limestone/quartzarenite sheets in the north and volcaniclastic blocks in the south. However, turbidite sheets and volcaniclastic blocks are outcropped in the north Riwuqi transverse with quartzarenite blocks preserved in the south. Three groups of sandstone blocks/sheets with different provenance and depositional setting are distinguished by their petrographic, geochronological and isotopic fingerprints. Sheets of turbiditic quartzarenite originally sourced from the Indian continent were deposited in pre-Cretaceous time on the northernmost edge of the Indian passive margin and eventually involved into the mélange at the early stage of the India-Asia collision. Two distinct groups of volcaniclastic

  16. Abiologic silicon isotope fractionation between aqueous Si and Fe(III)-Si gel in simulated Archean seawater: Implications for Si isotope records in Precambrian sedimentary rocks

    Science.gov (United States)

    Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.

    2016-08-01

    Precambrian Si-rich sedimentary rocks, including cherts and banded iron formations (BIFs), record a >7‰ spread in 30Si/28Si ratios (δ30Si values), yet interpretation of this large variability has been hindered by the paucity of data on Si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to Precambrian marine conditions. Using the three-isotope method and an enriched 29Si tracer, a series of experiments were conducted to constrain Si isotope exchange kinetics and fractionation factors between amorphous Fe(III)-Si gel, a likely precursor to Precambrian jaspers and BIFs, and aqueous Si in artificial Archean seawater under anoxic conditions. Experiments were conducted at room temperature, and in the presence and absence of aqueous Fe(II) (Fe(II)aq). Results of this study demonstrate that Si solubility is significantly lower for Fe-Si gel than that of amorphous Si, indicating that seawater Si concentrations in the Precambrian may have been lower than previous estimates. The experiments reached ∼70-90% Si isotope exchange after a period of 53-126 days, and the highest extents of exchange were obtained where Fe(II)aq was present, suggesting that Fe(II)-Fe(III) electron-transfer and atom-exchange reactions catalyze Si isotope exchange through breakage of Fe-Si bonds. All experiments except one showed little change in the instantaneous solid-aqueous Si isotope fractionation factor with time, allowing extraction of equilibrium Si isotope fractionation factors through extrapolation to 100% isotope exchange. The equilibrium 30Si/28Si fractionation between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -2.30 ± 0.25‰ (2σ) in the absence of Fe(II)aq. In the case where Fe(II)aq was present, which resulted in addition of ∼10% Fe(II) in the final solid, creating a mixed Fe(II)-Fe(III) Si gel, the equilibrium fractionation between Fe(II)-Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -3.23 ± 0.37‰ (2

  17. Structural pattern in the Precambrian rocks of Sonua-Lotapahar region, North Singhbhum, eastern India

    Science.gov (United States)

    Mukhopadhyay, Dhruba; Bhattacharya, Tapas; Chakraborty, Tapan; Dey, Arun Kanti

    1990-06-01

    In the western part of the North Singhbhum fold belt near Lotapahar and Sonua the remobilized basement block of Chakradharpur Gneiss is overlain by a metasedimentary assemblage consisting of quartz arenite, conglomerate, slate-phyllite, greywacke with volcanogenic material, volcaniclastic rocks and chert. The rock assemblage suggests an association of volcanism, turbidite deposition and debris flow in the basin. The grade of metamorphism is very low, the common metamorphic minerals being muscovite, chlorite, biotite and stilpnomelane. Three phases of deformation have affected the rocks. The principal D1 structure is a penetrative planar fabric, parallel to or at low angle to bedding. No D1 major fold is observed and the regional importance of this deformation is uncertain. The D2 deformation has given rise to a number of northerly plunging major folds on E-W axial planes. These have nearly reclined geometry and the L 2lineation is mostly downdip on the S 2surface, though some variation in pitch is observed. The morphology of D2 planar fabric varies from slaty cleavage/schistosity to crenulation cleavage and solution cleavage. D3 deformation is weak and has given rise to puckers and broad warps on schistosity and bedding. The D2 major folds south of Lotapahar are second order folds in the core of the Ongarbira syncline whose easterly closure is exposed east of the mapped area. Photogeological study suggests that the easterly and westerly closing folds together form a large synclinal sheath fold. There is a continuity of structures from north to south and no mylonite belt is present, though there is attenuation and disruption along the fold limbs. Therefore, the Singhbhum shear zone cannot be extended westwards in the present area. There is no evidence that in this area a discontinuity surface separates two orogenic belts of Archaean and Proterozoic age.

  18. Three-dimensional morphological and textural complexity of Archean putative microfossils from the Northeastern Pilbara Craton: indications of biogenicity of large (>15 microm) spheroidal and spindle-like structures.

    Science.gov (United States)

    Sugitani, Kenichiro; Grey, Kathleen; Nagaoka, Tsutomu; Mimura, Koichi

    2009-09-01

    We recently reported a diverse assemblage of carbonaceous structures (thread-like, film-like, spheroidal, and spindle-like) from chert in the ca. 3.0 Ga Farrel Quartzite of the Gorge Creek Group in the Pilbara Craton, Western Australia. Results from a rigorous examination of occurrence, composition, morphological complexity, size distributions, and taphonomy provided presumptive evidence for biogenicity. In this study, we present new data of morphological and textural complexity of large (>15 microm) spheroidal and spindle-like structures, using an in-focus, 3-D image reconstruction system, which further raises the scale of credibility that these structures are microfossils. While many of the large spheroids are single-walled, and the wall is irregularly folded, a few specimens are partially blistered, double walled, or have a dimpled wall. The wall-surface texture varies from smooth and homogeneous (hyaline) to patchy, granular or reticulate. Such variation is best explained as resulting from taphonomic processes. Additionally, an inner solitary body, present in some large spheroids, is hollow and partially broken, which indicates a primary origin for this substructure. Spindle-like structures have two types of flange-like appendage; one is attached at the equatorial plane of the body, whereas the other appears to be attached peripherally. In both cases, the appendage tends to have a flat geometry, a tapering thickness, and constancy in shape, proportions, and dimensions. Spindle-wall surfaces are variously textured and heterogeneous. These morphological and textural complexities and heterogeneity refute potential abiogenic formation models for these structures, such as crystals coated with organic matter, fenestrae, and the diagenetic redistribution of carbonaceous matter. When coupled with other data from Raman spectroscopy, NanoSIMS analysis, and palynology, the evidence that these large carbonaceous structures are biogenic appears compelling, though it is

  19. Examining early-diagenetic processes as a chief sink for carbonate in the aftermath of the Triassic-Jurassic crisis: Hettangian concretions of Muller Canyon, NV, USA

    Science.gov (United States)

    Ritterbush, K. A.; Loyd, S. J.; Corsetti, F. A.; Bottjer, D. J.; Berelson, W.

    2015-12-01

    Tectonic, climate, and biotic changes across the Triassic-Jurassic transition appear to have resulted in a "carbonate gap" in the rock record of many shallow marine environments. Ecological state changes documented in near-shore settings in both Tethys and Panthassa show an earliest Jurassic switch to sponge-dominated biosiliceous sedimentation regimes. The Sunrise Formation exposed in the Gabbs Valley Range of Nevada (USA) records a peculiar juxtaposition of Hettangian carbonate-rich strata that contain demosponge spicules as the primary bioclast. It is unclear 1) why biocalcifiers were not recorded in higher abundance in this near-shore back-arc basin setting; 2) why carbonates formed following a biosiliceous regime; and 3) what the lithology indicates about post-extinction marine geochemical dynamics. Detailed sedimentological, paleontological, and geochemical analyses were applied to a 20-m thick sequence of limestone and chert in the Muller Canyon area, which is the Auxiliary Stratotype for the Triassic/Jurassic boundary. Concretion anatomy, bioclast microfacies, and oxygen and carbon isotopic signatures all indicate the Hettangian limestones are chiefly diagenetic concretions that all formed very shallowly, some essentially at the sediment-water interface. We infer that local bottom waters and/or pore waters were supersaturated with respect to calcium carbonate and that this contributed to widespread concretion sedimentation independent of biomineralization. Ecological incumbency of the demosponge meadows may have been supported by concurrent augmentation of marine silica concentration and this apparently proved inhospitable to re-colonization of benthic biocalcifying macrofauna. Together the biotic and lithologic consequences of the extinction represent million-year scale ecological restructuring and highlight early diagenetic precipitation as a major sink in long-term regional carbonate cycling. Perhaps the widespread 'carbonate gap' is actually a gap in

  20. Nanoscale petrographic and geochemical insights on the origin of Paleoproterozoic stromatolitic phosphorites from Aravalli, India

    Science.gov (United States)

    Papineau, Dominic; De Gregorio, Bradley; Purohit, Ritesh; Fogel, Marilyn

    2015-04-01

    Stromatolites occur throughout the rock record starting at ca. 3.5 Ga, but their abundance and morphological and mineralogical diversity significantly expanded during the Paleoproterozoic Great Oxygenation Event. In particular, columnar-branching and multifurcate stromatolites composed of jasper or apatite begin to occur in post-Lomagundi-Jatuli successions around 1.9 Ga and suggest the emergence of novel types of biomineralization at that time. The microscopic and nanoscopic petrology of organic matter in stromatolitic phosphorites might provide insights into the suite of diagenetic processes of these types of stromatolites and/or into the role of specific microorganisms in these communities. Here, we report on the occurrence of nanoscopic disseminated organic matter in Paleoproterozoic stromatolitic phosphorite from Rajasthan, India. Microscopic spheroidal grains of apatite occur in both microbial mats in stromatolite columns and in the chert core of microscopic apatite rosettes. Organic petrography by Raman imaging demonstrates syngeneity of the organic matter. Our observations point to a microfossil origin for the microscopic spheroids of organo-apatite, which are cemented to calcite micro-spar by later diagenetic dolomite. Apatite rosettes also likely have a diagenetic origin. Total organic carbon of these stromatolitic phosphorite columns is between 0.05 and 3.0 wt% and has a large range of d13C values with an average of -18.5permil (1sigma = 4.5permil). Whole rock d15N values are between -1.2 to +2.7permil. Nitrogen and carbon isotope compositions suggest that high phosphate abundance caused these cyanobacteria to bloom, thereby enhancing fixing nitrogen to sustain community growth. Synchronous early diagenetic formation of calcite micro-spar, resulted in the growth of centimeter size columns from the seafloor and occasionally branching or multifurcate stromatolites. Finally, our findings suggest that these stromatolites accreted pelagic cyanobacterial

  1. The architecture of an incipient oceanic basin: a tentative reconstruction of the Jurassic Liguria-Piemonte basin along the Northern Apennines-Alpine Corsica transect

    Science.gov (United States)

    Marroni, Michele; Pandolfi, Luca

    2007-11-01

    In this paper, a scenario for the early evolution of the Jurassic oceanic Liguria-Piemonte basin is sketched. For this purpose, four selected examples of ophiolite sequences from the Northern Apennines and Corsica are described and analyzed. In the External Ligurian units (Northern Apennines), the ocean-continent transition of the Adria plate was characterized by a basement made up of subcontinental mantle and lower continental crust, covered by extensional allochthons of upper crust. Both, the basement rocks and the extensional allochthons are cut by basaltic dikes and covered by basalts and pelagic deposits. The conjugate ocean-continent transition of the Corsica margin, represented by the Balagne nappe (Corsica), was composed of mantle peridotites and gabbros covered by basaltic flows and minor breccias, that in addition include continent-derived clasts. By contrast, the innermost (i.e., closest to the ocean) preserved area observed in the Internal Ligurian (Northern Apennines) and Inzecca (Corsica) units consists of former morphological highs of mantle peridotites and gabbros, bordered by small basins where the basement is covered by a volcano-sedimentary complex, characterized by ophiolitic breccias and cherts interlayered with basaltic flows. The overall picture resulting from our reconstructions suggests an asymmetric architecture for the Liguria-Piemonte basin with a central area bounded by two different transition zones toward the continental margins. This architecture can be interpreted as the result of a rifting process whose development includes a final stage characterized by passive, asymmetric extension of the lithosphere along an east-dipping detachment fault system.

  2. Ironstone deposits hosted in Eocene carbonates from Bahariya (Egypt)-New perspective on cherty ironstone occurrences

    Science.gov (United States)

    Afify, A. M.; Sanz-Montero, M. E.; Calvo, J. P.

    2015-11-01

    This paper gives new insight into the genesis of cherty ironstone deposits. The research was centered on well-exposed, unique cherty ironstone mineralization associated with Eocene carbonates from the northern part of the Bahariya Depression (Egypt). The economically important ironstones occur in the Naqb Formation (Early Eocene), which is mainly formed of shallow marine carbonate deposits. Periods of lowstand sea-level caused extensive early dissolution (karstification) of the depositional carbonates and dolomitization associated with mixing zones of fresh and marine pore-water. In faulted areas, the Eocene carbonate deposits were transformed into cherty ironstone with preservation of the precursor carbonate sedimentary features, i.e. skeletal and non-skeletal grain types, thickness, bedding, lateral and vertical sequential arrangement, and karst profiles. The ore deposits are composed of iron oxyhydroxides, mainly hematite and goethite, chert in the form of micro- to macro-quartz and chalcedony, various manganese minerals, barite, and a number of subordinate sulfate and clay minerals. Detailed petrographic analysis shows that quartz and iron oxides were coetaneous and selectively replaced carbonates, the coarse dolomite crystals having been preferentially transformed into quartz whereas the micro-crystalline carbonates were replaced by the iron oxyhydroxides. A number of petrographic, sedimentological and structural features including the presence of hydrothermal-mediated minerals (e.g., jacobsite), the geochemistry of the ore minerals as well as the structure-controlled location of the mineralization suggest a hydrothermal source for the ore-bearing fluids circulating through major faults and reflect their proximity to centers of magmatism. The proposed formation model can contribute to better understanding of the genetic mechanisms of formation of banded iron formations (BIFs) that were abundant during the Precambrian.

  3. Reconstruction of ocean plate stratigraphy in the Gwna Group, NW Wales: Implications for the subduction-accretion process of a latest Proterozoic trench-forearc

    Science.gov (United States)

    Asanuma, Hisashi; Okada, Yoshihiro; Fujisaki, Wataru; Suzuki, Kazue; Sato, Tomohiko; Sawaki, Yusuke; Sakata, Shuhei; Yamamoto, Shinji; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.

    2015-11-01

    The Gwna Group in Anglesey island and Lleyn peninsula, Wales consists of a latest Proterozoic volcano-sedimentary trench mélange, which has a complicated accretionary structure, and is poorly constrained by isotopic ages. The mélange contains oceanic-trench rocks including pillow basalts, cherts, mudstones and sandstones, which have not previously been interpreted as ocean plate stratigraphy (OPS). We reconstructed imbricated OPS at 5 localities in the coastal Lleyn peninsula. In order to constrain the depositional U-Pb age of the upper clastic sediments, detrital zircons, separated from 9 clastic sediments, were analyzed with a Nu AttoM single-collector inductively-coupled plasma-mass spectrometer. The ages indicate that there are two Gwna Groups (maximum depositional ages of: 1 at 608-601 Ma, and 2 at 564-539 Ma) that were deposited between the late Neoproterozoic and the Middle Cambrian contemporaneously with dated calc-alkaline arc magmatism and regional metamorphism in the Anglesey-Lleyn complex. The age spectra of the detrital zircons show a prominent peak at ca. 650-600 Ma, and several Proterozoic and Archean ages. To account for the older ages, we integrated our new isotopic data with published radiometric and fossil ages, and conclude that the clastic sediments at the top of the OPS were deposited in a trench on the western active margin of Avalonia when it was close to the Amazonian craton, and that the Gwna Group OPS began to be incorporated into an accretionary wedge in an active subduction zone in the latest Proterozoic.

  4. Xenon isotopic constraints on the timing of atmospheric volatile recycling

    Science.gov (United States)

    Parai, R.; Mukhopadhyay, S.

    2015-12-01

    Constraints on the recycling of atmospheric volatiles into the deep Earth provide important insights into mantle temperature, cooling rate, structure and style of convection over Earth history. Studies of ancient atmospheric gases trapped in Archean cherts show that the Xe isotopic composition of the atmosphere at ~3.5 Ga differed from the modern atmosphere [1]. This suggests the atmosphere evolved in isotopic composition until it reached its present-day composition at some time after 3.5 Ga. The evolution of the atmospheric Xe isotopic composition presents an opportunity to constrain the timing of Xe recycling into the Earth's mantle. Xe isotopes measured in mid-ocean ridge basalts [MORBs; 2,3] and plume-related basalts [4,5] indicate that both the upper mantle and plume source Xe isotopic compositions are dominated by recycled Xe [e.g., 3]. We find that the mantle source Xe isotopic compositions cannot be explained by recycling ancient atmospheric Xe alone; rather, subduction and incorporation of material bearing the modern atmospheric Xe composition must dominate. We note that our findings are consistent with a number of physical reasons that recently-subducted volatiles should be more prevalent than ancient subducted volatiles. First, a higher Archean mantle potential temperature should inhibit early Xe recycling to the deep Earth. Second, since the mantle turnover time scale is estimated to be between a few hundreds of Myr and 1 Gyr, the mantle recycled atmospheric Xe budget should be primarily composed of Xe subducted after ~2.5 Ga, at which point the atmosphere approaches the modern Xe composition [1]. Therefore, even if ancient atmospheric Xe were recycled efficiently to the mantle early in Earth history, the recycled atmospheric Xe budget of the mantle should still be dominated by the modern atmospheric Xe composition. [1] Pujol et al., 2011, EPSL; [2] Tucker et al., 2012, EPSL; [3] Parai and Mukhopadhyay, 2015, G-cubed; [4] Mukhopadhyay, 2012, Nature; [5

  5. Tectonic evolution of the Brooks Range ophiolite, Alaska

    Energy Technology Data Exchange (ETDEWEB)

    Harris, R.A. (West Virginia Univ., Morgantown, WV (United States). Dept. of Geology)

    1993-04-01

    Detailed studies of the composition, internal structure, and age of the Brooks Range ophiolite (BRO) and its metamorphic sole reveal new constraints for its tectonic evolution. The BRO consists of six separate thrust masses of consanguineous composition, internal organization, structure and age. Subophiolite metamorphic rocks are locally preserved along its structural base, which is well exposed in several places. The metamorphic sole is locally transitional with mafic volcanic sequences, chert, tuffs, and minor clastic sedimentary material of the Copter Peak Complex, which is correlative with the Angayucham terrane. This terrane is much older than, and chemically distinct from the BRO. The internal structure of the BRO is characterized by NE-SW trending igneous layers that expose the transition zone from crust to mantle. Residual mantle material consists of tectonized peridotite in abrupt contact with dunite pods up to 4 km thick. Ductile and brittle structures of the BRO preserve various phases of its dynamic evolution from a magma body to a fragmented thrust sheet. The earliest deformational effects are recorded by ductile lattice and shape fabrics in dunites and the layered series of the BRO. Magmatic flow planes generally parallel the petrologic moho, and dip 40[degree]--70[degree] to the NW and SE. Flow lineations consistently plunge ESE-ENE from 39[degree]--54[degree]. Igneous laminations and compositional layers represent patterns of magmatic flow in, and plastic deformation of, a cumulate sequence -- not the deposition pattern of cumulate layers. In the upper layered series, amphiboles with a shape-preferred orientation yield Ar/Ar plateau ages of 163--169 Ma. These ages overlap with plateau ages of the same kind from amphibolite of the metamorphic sole. This concordance in age indicates that cooling of the BRO coincided with its tectonic emplacement.

  6. Petrology, Magnetic susceptibility, Tectonic setting and mineralization associated with Plutonic and Volcanic Rocks, Eastern Bajestan and Taherabad, Iran

    Directory of Open Access Journals (Sweden)

    Malihe Ghoorchi

    2009-09-01

    Full Text Available Study area is located in district of Bajestan and Ferdows cities, NE of Iran. Structurally, this area is part of Lut block. The oldest exposed rocks, to the north of intrusive rocks and in Eastern Bajestan, are meta-chert, slate, quartzite, thin-bedded crystalline limestone and meta-argillite. The sedimentary units are: Sardar Formation (Carboniferous, Jamal Formation (Permian, Sorkh Shale and Shotori Formations (Triassic, carbonateous rocks (Cretaceous and lithostratigraphically equivalent to Kerman conglomerate (Cretaceous-Paleocene are exposed in this area. Based on relative age, magmatism in eastern Bajestan and Taherabad started after Late Cretaceous and it has been active and repeated during Tertiary time. At least, three episodes of volcanic activities are recognized in this area. The first stage was mainly volcanic flow with mafic composition and minor intermediate. The second episode was mainly intermediate in composition. The third stage was changed to acid-intermediate in composition. Since the plutonic rocks intruded the volcanic rocks, therefore they may be Oligo-Miocene age. Bajestan intrusive rocks are granite-granodiorite-quartz monzonite. Taherabad intrusive rocks are diorite-quartz diorite- monzonite-latite. Bajestan intrusive rocks are reduced type (ilmenite series and Taherabad intrusive rocks are oxidized type (magnetite series.Based on geochemical analysis including trace elements, REE and isotopic data, Bajestan intrusive rocks formed in continental collision zone and the magma has crustal origin. Taherabad intrusive rocks were formed in subduction zone and magma originated from oceanic crust. Taherabad intrusive rock has exploration potential for Cu-Au and pb.

  7. A Middle Permian-Middle Triassic accretionary complex and a Late Triassic foredeep basin: Forerunners of an Indosinian (Late Triassic) thrust complex in the Thailand-Malaysia border area

    Science.gov (United States)

    Ridd, Michael F.

    2013-10-01

    The Semanggol Formation of NW Peninsular Malaysia is a Middle Permian-Late Triassic sequence of predominantly radiolarian chert, sandstone and mudstone (including turbidites), and conglomerate. The belt of country occupied by this unit extends into Thailand where various names including Na Thawi formation have been applied to its correlatives. Fossil evidence, particularly radiolarian, has established its age but also revealed that it is tectonically complex, with numerous out-of-sequence slices interpreted here to be caused by thrusting. The model proposed here involves, initially, in the Middle Permian, accumulation in the oceanward part of an accretionary complex as Palaeotethys began subducting beneath Indochina/East Malaya. This regime, it is proposed, continued until about the end of the Middle Triassic when Sibumasu collided with Indochina/East Malaya bringing an end to subduction. But as crustal shortening continued into the Late Triassic a foredeep basin formed in front of the now-inactive subduction zone and accretionary complex, and the youngest part of the Semanggol Formation was deposited. During this final stage the whole package of rocks comprising those in the accretionary complex and those deposited in the foredeep basin underwent lateral compression resulting in a thrust complex. The Semanggol Formation and its Thailand correlatives occupy part of a N-S belt of imbricately-thrust, deeper-water, sediments which include slope-deposited Carboniferous and Lower Permian beds. That belt is interpreted as a series of thrust slices juxtaposing rocks of different ages, referred to here as the Songkhla-Semanggol terrane. Its western boundary is a N-S line of inferred thrusting which coincides with a major westward facies change to platform carbonates of Middle Permian to Late Triassic age, called here the Rattaphum-Kodiang tectonic line.

  8. Alteration geochemistry of the volcanic-hosted Dedeninyurdu, Yergen and Fındıklıyar Cu-Fe mineralization, Northern part of Gökçedoǧan Village, Çorum-Kargi Region, Turkey: Implications for the rare earth elements geochemical characteristics

    Science.gov (United States)

    Ozturk, Sercan; Gumus, Lokman; Abdelnasser, Amr; Yalçin, Cihan; Kumral, Mustafa; Hanilçi, Nurullah

    2016-04-01

    This study deals with the rare earth element (REE) geochemical behavior the alteration zonesassociated with the volcanic-hosted Cu-Femineralization at the northern part of Gökçedoǧan village, Çorum-Kargi region (N Turkey) which are Dedeninyurdu, Yergen and Fındıklıyar mineralization. The study areacomprises Bekirli Formation, Saraycık Formation, Beşpınar Formation, and Ilgaz Formation. Saraycık Formation consists ofUpper Cretaceous KargıOphiolites, pelagic limestone, siltstone, chert and spilitic volcanic rocks. Fe-Cu mineralization occurred in the spiliticvolcanic rocks of Saraycık Formation representing the host rockand is related with the silicification and sericitizationalteration zones. Dedeninyurdu and Yergen mineralization zone directed nearly N75-80oEis following structural a line but Fındıklıyar mineralization zone has nearly NW direction. The ore mineralogy in these zonesinclude pyrite, chalcopyrite, covellite, hematite with malachite, goethite and a limonite as a result of oxidation. The geochemical characteristics of REE of the least altered spiliticbasalt show flat light and heavy REE with slight positive Eu- and Sr-anomalies according to their chondrite-, N-type MORB, and primitive mantle-normalized REE patterns. While the REE geochemical features of the altered rocks collected from the different alteration zones show that there are negative Eu and Sr anomalies as a result of leaching during the alteration processes.There are positive and negative correlations between K2O index with LREE and HREE, respectively. This is due to the additions of K and La during the alteration processes referring to the pervasive sericitization alteration is the responsible for the Cu-Fe mineralization at the study area. Keywords: Cu-Fe mineralization, Spilitic volcanic rocks, alteration, Rare earth elements (REE) geochemistry.

  9. Origin of Hadean 146Sm-142Nd signatures in supracrustal enclaves of the Innuksuac complex (Quebec)

    Science.gov (United States)

    Caro, G.; Morino, P.; Mojzsis, S. J.; Cates, N.; Bleeker, W.

    2015-12-01

    The discovery of negative 142Nd anomalies produced by the decay of now extinct 146Sm (T1/2=103 Ma) in mafic rocks from the Nuvvuagittuq supracrustal belt (NSB) has fueled a debate on the presence of a 4.2-4.3 Ga old component within the Archean Innuksuac complex (Northeastern Superior Province, Canada). Despite the uniqueness of these Hadean signatures, the NSB remains so far the only studied supracrustal belt in an otherwise largely unexplored terrane. This study investigates the 146,147Sm-142,143Nd record of newly discovered supracrustals located ca. 2 km northeast of Nuvvuagittuq. Petrologically, the Ukalik supracrustal belt (USB) comprises mafic and ultramafic rocks associated with chemical sediments (BIFs, chert). The metabasalts yield near-concordant 147Sm-143Nd and 146Sm-142Nd ages at 4.07±0.22 Ga and 4.22±0.04 Ga, respectively. The negative 142Nd effects, however, are restricted to Low-Ti ("boninite-like") metabasalts, whereas High-Ti ("MORB-like") metabasalts have μ142Nd=0. Neither group shows any internal relationship between Sm/Nd and μ142Nd. Furthermore, chemical sediments interleaved with the metabasalts display no resolvable 142Nd effect despite their very low Sm/Nd ratios. These observations suggest that Hadean 146,147Sm-142,143Nd signatures characterizing Ukalik mafic lithologies were generated, possibly in an Eoarchean supra-subduction zone environment, by addition of a metasomatic fluid with μ142Nd<-15 ppm to a normal mantle with μ142Nd=0.

  10. Late Paleozoic tectonics of the Solonker Zone in the Wuliji area, Inner Mongolia, China: Insights from stratigraphic sequence, chronology, and sandstone geochemistry

    Science.gov (United States)

    Shi, Guanzhong; Song, Guangzeng; Wang, Hua; Huang, Chuanyan; Zhang, Lidong; Tang, Jianrong

    2016-09-01

    The geology in the Wuliji area (including the Enger Us and Quagan Qulu areas) is important for understanding the Late Paleozoic tectonics of the Solonker Zone. Ultramafic/mafic rocks in the Enger Us area, previously interpreted as an ophiolitic suture, are actually lava flows and sills in a Permian turbiditic sequence and a small body of fault breccia containing serpentinite. Subduction zone features, such as accretionary complexes, magmatic arc volcanics or LP/HP metamorphism are absent. Early Permian N-MORB mafic rocks and Late Permian radiolarian cherts accompanied by turbidites and tuffeous rocks indicate a deep water setting. In the Quagan Qulu area, outcrops of the Late Carboniferous to Permian Amushan Formation are composed of volcano-sedimenary rocks and guyot-like reef limestone along with a Late Permian volcano-sedimentary unit. A dacite lava in the Late Permian volcano-sedimentary unit yields a zircon U-Pb age of 254 Ma. The gabbros in the Quagan Qulu area are intruded into the Amushan Formation and caused contact metamorphism of country rocks. Sandstones in the Upper Member of the Amushan Formation contain detrital clasts of volcanic fragments and mineral clasts of crystalline basement rocks (i.e. biotite, muscovite and garnet). Geochemical analysis of volcaniclastic sandstones shows a magmatic affinity to both continental island arc (CIA) and active continental margin (ACM) tectonic settings. A Late Permian incipient rift setting is suggested by analyzing the lithostratigraphic sequence and related magmatism in the Wuliji area. The volcano-sedimentary rocks in the Wuliji area experienced a nearly N-S shortening that was probably related to the Early Mesozoic nearly N-S compression well developed in other areas close to the Wuliji area.

  11. Rare earth elements in Hamersley BIF minerals

    Science.gov (United States)

    Alibert, Chantal

    2016-07-01

    Minerals from the Hamersley banded iron formation, Western Australia, were analyzed for Y and rare earth elements (YREEs) by laser ablation ICP-MS to investigate diagenetic pathways, from precursor phases to BIF minerals. One group of apatites carries the seawater REE signature, giving evidence that P and REEs, thoroughly scavenged from the water column by Si-ferrihydrite particles, were released upon microbial Fe3+ reductive dissolution of Si-ferrihydrite in pore-water and finally sequestered mainly in authigenic apatite. The absence of fractionation between apatite and seawater suggests that REE were first incorporated into an amorphous calcium phosphate as fully hydrated cations, i.e. as outer-sphere complexes. The iron oxides and carbonates carry only a small fraction of the whole-rock REE budget. Their REE patterns are distinctly enriched in Yb and show some M-type tetrad effect consistent with experimental Kd(REE) between solid and saline solution with low carbonate ion concentrations. It is deduced that hematite formed at an incipient stage of Fe2+-catalyzed dissolution of Si-ferrihydrite, via a dissolution-reprecipitation pathway. The REE pattern of greenalite, found as sub-micron particles in quartz in a chert-siderite sample, is consistent with its authigenic origin by precipitation in pore-water after dissolution of a small amount of Si-ferrihydrite. Magnetite carries very low YREEs (ppb-level), has an homogeneous pattern distinctly enriched in the mid-REEs compared to hematite, and includes a late population depleted in light-REEs, Ba and As. Magnetite forming aggregates and massive laminae is tentatively interpreted as reflecting some fluid-aided hematite-magnetite re-equilibration or transformation at low-grade metamorphic temperatures.

  12. STRATIGRAPHY OF THE PB-1 WELL, NOPAL I URANIUM DEPOSIT, SIERRA PENA BLANCA, CHIHUAHUA, MEXICO

    Energy Technology Data Exchange (ETDEWEB)

    NA

    2005-06-25

    Three wells, PB-1, PB-2, and PB-3, were drilled in 2003 at the Nopal I uranium deposit as part of a natural analogue study to evaluate radionuclide transport processes. The wells penetrate through the Tertiary volcanic section down to the Cretaceous limestone basement, and intersect the top of the regional aquifer system. The PB-1 well, drilled immediately adjacent to the Nopal I ore body, was cored to a depth of 250 m, thus providing an opportunity to document the local stratigraphy. The uppermost unit encountered in the PB-1 well is the Nopal Formation, a densely welded, crystal-rich rhyolitic ash-flow tuff. The cored section is highly altered and devitrified, with kaolinite, quartz, chlorite, and montmorillonite replacing feldspars and much of the groundmass. Breccia zones within the tuff contain fracture fillings of hematite, limonite, and goethite. A zone of intense clay alteration encountered in the depth interval 17.45-22.30 m was interpreted to represent the basal vitrophyre of this unit. Underlying the basal vitrophyre is the Coloradas Formation, which consists of a welded, lithic-rich rhyolitic ash-flow tuff. The cored section of this unit has undergone devitrification and oxidation, and has a similar alteration mineralogy to that observed in the Nopal tuff. The Nopal I ore body is restricted to a brecciated zone that intersects these two volcanic units. A sharp contact between the Coloradas tuff and the underlying Pozos Formation was observed at a depth of 136.38 m. The Pozos Formation in the PB-1 core consists of interbedded, poorly sorted sandstone and conglomerate layers. The conglomeratic clasts consist of subangular to subrounded fragments of volcanic rocks, limestone, and chert. Thin (2-6 m) intervals of intercalated pumiceous tuffs were observed within this unit. The contact between the Pozos Formation and the underlying Cretaceous limestone basement was observed at a depth of 244.4 m.

  13. STRATIGRAPHY OF THE PB-1 WELL, NOPAL I URANIUM DEPOSIT, SIERRA PENA BLANCA, CHIHUAHUA, MEXICO

    International Nuclear Information System (INIS)

    Three wells, PB-1, PB-2, and PB-3, were drilled in 2003 at the Nopal I uranium deposit as part of a natural analogue study to evaluate radionuclide transport processes. The wells penetrate through the Tertiary volcanic section down to the Cretaceous limestone basement, and intersect the top of the regional aquifer system. The PB-1 well, drilled immediately adjacent to the Nopal I ore body, was cored to a depth of 250 m, thus providing an opportunity to document the local stratigraphy. The uppermost unit encountered in the PB-1 well is the Nopal Formation, a densely welded, crystal-rich rhyolitic ash-flow tuff. The cored section is highly altered and devitrified, with kaolinite, quartz, chlorite, and montmorillonite replacing feldspars and much of the groundmass. Breccia zones within the tuff contain fracture fillings of hematite, limonite, and goethite. A zone of intense clay alteration encountered in the depth interval 17.45-22.30 m was interpreted to represent the basal vitrophyre of this unit. Underlying the basal vitrophyre is the Coloradas Formation, which consists of a welded, lithic-rich rhyolitic ash-flow tuff. The cored section of this unit has undergone devitrification and oxidation, and has a similar alteration mineralogy to that observed in the Nopal tuff. The Nopal I ore body is restricted to a brecciated zone that intersects these two volcanic units. A sharp contact between the Coloradas tuff and the underlying Pozos Formation was observed at a depth of 136.38 m. The Pozos Formation in the PB-1 core consists of interbedded, poorly sorted sandstone and conglomerate layers. The conglomeratic clasts consist of subangular to subrounded fragments of volcanic rocks, limestone, and chert. Thin (2-6 m) intervals of intercalated pumiceous tuffs were observed within this unit. The contact between the Pozos Formation and the underlying Cretaceous limestone basement was observed at a depth of 244.4 m

  14. Mineralogical characterization of West Chestnut Ridge soils

    International Nuclear Information System (INIS)

    The morphological, physicochemical, and mineralogical properties of the soils and residua from the proposed site of the Central Waste Disposal Facility were characterized. The proposed site is underlain by cherty dolostones, limestones, and shales of the Knox Group covered by a thick residuum. Three diagnostic horizons from four soil profiles and six samples from residuum cores were selected for mineralogical analysis. The coarse fractions (gravel and sand) of the samples included different types of chert, iron-manganese oxide nodules, and quartz. The samples were high in clay content (except those from the A and E horizons) and low in pH and base saturation. The clay fractions were composed of varying amounts of kaolinite, mica, vermiculite, aluminum hydroxy-interlayered vermiculite, amorphous iron and aluminum oxides, gibbsite, and quartz. Aluminum hydroxy-interlayered vermiculite is the major component in surface horizons, but kaolinite becomes dominant in subsurface horizons of the soils. Degradation of kaolinite and formation of aluminum hydroxy-interlayered vermiculite and iron and aluminum oxides are pronounced chemical weathering processes in the surface soils. The aluminum hydroxy interlayering of vermiculite reduces cation exchange and selective sorption capacities of soils. In the residua, micaceous minerals free of aluminum hydroxy interlayering, kaolinite, and amorphous iron and aluminum oxides are major components in the clay fraction. The sorption ratios of 137Cs, 90Sr, 60Co, and the uranium isotopes expected to be in the radioactive wastes should be very high for the clays having such mineralogical composition. The low acid-buffering capacity (base saturation) of the residua suggest that the fragile chemical and mineralogical equilibria can be easily broken if an extreme chemical condition is imposed on the residua

  15. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

    Science.gov (United States)

    Saikia, Ashima; Gogoi, Bibhuti; Ahmad, Mansoor; Ahmad, Talat

    2014-06-01

    The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, cross-cutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

  16. Orbital control on the timing of oceanic anoxia in the Late Cretaceous

    Science.gov (United States)

    Batenburg, Sietske; De Vleeschouwer, David; Sprovieri, Mario; Hilgen, Frederik; Gale, Andrew; Singer, Brad; Koeberl, Christian; Cocioni, Rodolfo; Claeys, Philippe; Montanari, Alessandro

    2015-04-01

    The oceans of the Cenomanian-Turonian transition, at the height of the Cretaceous greenhouse, were abruptly disturbed by a period of oceanic anoxia. This led to the brief but widespread deposition of black organic-rich shales in the world's oceans, such as the Livello Bonarelli in the Umbria-Marche Basin (Italy). However, the origin and exact timing of the onset of oceanic anoxia are debated. We present a 6-Myr-long astronomically-tuned timescale across the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2), obtained from the Furlo and Bottaccione sections in the Umbria-Marche Basin. The cyclic climatic imprint on lithological, geophysical and stable isotope records allows us to decipher the relationship between orbital forcing and the Late Cretaceous carbon cycle. The deposition of black shales and cherts, as well as the onset of oceanic anoxia, is related to maxima in the 405-thousand year cycle of eccentricity modulated precession. In this study, we also present a new radioisotopic Ar/Ar age for the Thatcher bentonite occurring within the mid-Cenomanian carbon isotope event in the Western Interior of the USA. We correlate our astrochronology from the Umbria-Marche Basin to this new and recent radioisotopic ages, and we come to an unprecedented age control for European successions. The most likely tuned age for the Livello Bonarelli base is 94.22 Ma, however a 405-kyr older age cannot be excluded due to increasing uncertainties in stratigraphic correlation, radioisotopic dating, and orbital configuration. Although volcanism was probably the ultimate driver of OAE2, the cyclicity of the Umbria-Marche successions reveals that the exact timing of carbon cycle perturbations in the Late Cretaceous was determined by orbital periodicities.

  17. Effect of grain-coating mineralogy on nitrate and sulfate storage in the unsaturated zone

    Science.gov (United States)

    Reilly, T.J.; Fishman, N.S.; Baehr, A.L.

    2009-01-01

    Unsaturated-zone sediments and the chemistry of shallow groundwater underlying a small (???8-km2) watershed were studied to identify the mechanisms responsible for anion storage within the Miocene Bridgeton Formation and weathered Coastal Plain deposits in southern New Jersey. Lower unsaturated-zone sediments and shallow groundwater samples were collected and concentrations of selected ions (including NO3- and SO42-) from 11 locations were determined. Grain size, sorting, and color of the lower unsaturated-zone sediments were determined and the mineralogy of these grains and the composition of coatings were analyzed by petrographic examination, scanning electron microscopy and energy dispersive analysis of x-rays, and quantitative whole-rock x-ray diffraction. The sediment grains, largely quartz and chert (80-94% w/w), are coated with a very fine-grained (coatings are present as an open fabric, resulting in a large surface area in contact with pore water. Significant correlations between the amount of goethite in the grain coatings and the concentration of sediment-bound SO42- were observed, indicative of anion sorption. Other mineral-chemical relations indicate that negatively charged surfaces and competition with SO 42- results in exclusion of NO3- from inner sphere exchange sites. The observed NO3- storage may be a result of matrix forces within the grain coatings and outer sphere complexation. The results of this study indicate that the mineralogy of grain coatings can have demonstrable effects on the storage of NO 3- and SO42- in the unsaturated zone. ?? Soil Science Society of America. All rights reserved.

  18. The western transverse ranges microplate as a native terrane

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, M.D.; Reed, W.E. (Univ. of California, Los Angeles, CA (United States))

    1994-04-01

    Palocurrent measurements from the entire Cretaceous section of the western Transverse Ranges microplate (WTRM) yield a northerly flow direction. Point count data indicate a mixed provenance for both conglomerates and associated sandstones. The dominant provenance was mixed magmatic arc/recycled orogen and disected/transitional arc terranes. Petrographic, quantitative SEM and microprobe analysis also indicate the presence of diagnostic Franciscan mineralogy in these sediments, including glaucophane, riebeckite, lawsonite, and serpentine, suggesting derivation from a subduction complex. Olistoclasts of chert, jadeitic graywacke, serpentine and blueschist are found intermixed within the arc-derived sediments. Olistoclasts range in size from sub-millimeter to centimeter scale and olistoliths range up to 150 m. Well preserved internal bedding in some of the olistoliths suggest emplacement by landsliding indicating very short transport distance. This Franciscan material represents the oldest melange-derived material reported from this part of California and documents uplift and erosion of the subduction complex earlier than previously suggested. These data are consistent with deposition in a Cretaceous fore-arc basin located west or south of the San Diego area. The allochthonous WTRM of southern California can be reconstructed to an originally north-south oriented fore-arc basin. After deposition of the Sespe Formation (22 Ma [+-]) the microplate was slivered by strike-slip faults and rotated clockwise approximately 90[degrees], after which, the block again accreted against the continental margin. Our reconstruction suggest that depositional and structural trends for Eocene and Cretaceous sediments is likely to be different from that in the Miocene Monterey pay zones in the Santa Barbara channel region. If our reconstruction is correct, exploration strategy for Eocene and Cretaceous petroleum in the southern California Bight should take this tectonic model into account.

  19. Franciscan olistoliths in Upper Cretaceous conglomerate deposits, Western Transverse Ranges, California: Implications for basin morphology and tectonic history

    Energy Technology Data Exchange (ETDEWEB)

    Reed, W.E.; Campbell, M.D. (Univ. of California, Los Angeles, CA (United States). Dept. of Earth and Space Sciences)

    1993-04-01

    Compositional analyses reveal that Upper Cretaceous sediments exposed in the Western Transverse Ranges of CA were deposited in submarine fan systems in a forearc basin. Point count data suggest a magmatic arc/recycled orogen as the dominant provenance for these sediments. Paleocurrent measurements from conglomerates in these sediments yield a northerly transport direction. Removal of ca. 90[degree] of clockwise rotation and 70 km of right-lateral slip restore this section to a position west of the San Diego area. The forearc basin would have had a N-S orientation, with the bulk of sediments supplied by the Peninsular Ranges to the east. Evidence of the erosion of the accretionary wedge is provided by the presence of large, internally stratified olistoliths of Franciscan material interbedded with and surrounded by upper Cretaceous conglomerate. Petrographic, quantitative SEM, and microprobe analyses indicate the presence of diagnostic Franciscan mineralogy, including glaucophane, riebeckite, lawsonite, and serpentine. Olistoclasts of chert, jadeitic graywacke, serpentine, and blueschist are found intermixed with the conglomerates in close association with the olistoliths. This association provides strong field evidence that recirculation of melange material within the subduction zone was active and well-established by late Cretaceous time. Inferences regarding the forearc system morphology can be drawn from these observations. The occurrence of coarse, easterly-derived conglomerates surrounded by large, stratified, but sheared, westerly-derived Franciscan debris, suggests a narrow, relatively steep-sided basin. Paleocurrent measurements gave no indication of axial transport within the basin. This morphology suggests that, in late Cretaceous time, the forearc basin was youthful, with a narrow arc-trench gap. Thus, relative convergence rates between the North American and Pacific plates were possibly slower than Tertiary convergence rates.

  20. Occurrence and significance of blueschist in the southern Lachlan Orogen

    International Nuclear Information System (INIS)

    Serpentinite/talc-matrix melanges, bearing blocks of blueschist metavolcanics, occur within the Heathcote and Governor Fault Zones of the southern Lachlan Orogen. In the Heathcote Fault Zone, serpentinite-matrix melange consists of blocks or small pods of boninite, andesite, ultramafic rocks, chert and volcanogenic sandstone variably metamorphosed to prehnite-pumpellyite, greenschist, or greenschist to blueschist facies. In the Governor Fault Zone, blueschist metavolcanics occur as blocks within serpentinite/talc matrix that is interleaved with prehnite-pumpellyite to greenschist facies, intermediate pressure slate and phyllite. Ar/Ar dating of white mica from slaty mud-matrix (broken formation) indicates that the main fabric development occurred at 446 ± 2 Ma. U-Pb (SHRIMP) dating of titanite from blueschists in the Governor Fault Zone indicates that metamorphism occurred at approximately 450 Ma, close to the time of melange formation. Previously published, Ar/Ar dating of white mica from phyllite and biotite from metadiorite in the Heathcote Fault Zone suggest that blueschist metamorphism occurred at a similar time. These ages are supported by field relationships. Illite crystallinity and b0 data from white mica, and the preservation of blueschist blocks indicate that these fault zones maintained low temperatures both during and after intermediate- to high-pressure metamorphism. Occurrences of blueschists in the Arthur Lineament of the Tyennan (Delamerian) Orogen in Tasmania, and in the New England Orogen, have different ages, and in conjunction with the occurrences described here, suggest that subduction-accretion processes contributed significantly to the development of the Tasmanides from Cambrian through to Carboniferous times. Copyright (2002) Geological Society of Australia

  1. Petrology and structure of greenstone blocks encased in mud-matrix melange of the Franciscan complex near San Simeon, California

    Energy Technology Data Exchange (ETDEWEB)

    Davidsen, R.K.; Cloos, M.

    1985-01-01

    Greenstones comprise about 20% of all mappable (>1 m) blocks encased in blueschist-block-bearing mud-matrix melange exposed in a 10 km-length of sea cliffs near San Simeon. Field and petrographic analysis of 25 blocks show they vary from finely crystalline (<1 mm) locally porphyritic or amygdaloidal, volcanics to coarsely crystalline (1 to 5 mm) diabase. Some are in contact with bedded chert and two have relict pillows. However, most blocks are intensely deformed. Pinch-and-swell and boundinage are recognized on scales from cm to about 10 m. Distortion was accommodated by cataclasis to an aggregate of pieces from mm to m across. Generally, m-sized blocks are pervasively cataclastic whereas larger blocks are crosscut by cataclastic zones that emanate from pervasively cataclastic margins or necked regions of boudins. Discontinuous, cm-thick veins and cavities that are lined by quartz and clacite and rarely, laumontite, prehnite and aragonite locally crosscut all other structures. Relict igneous textures show the primary minerals are plagioclase and clinopyroxene. Abundant secondary minerals, particularly in cataclastic zones, are albite, chlorite, pumpellyite (some have high Al), and calcite. The metamorphic parageneses indicate relatively minor greenschist-facies, sea-floor-type alterations under static conditions followed by lower-temperature alterations synchronous with cataclasis and the development of boudinage. If the blocks are fragments of disrupted ophiolites, only the uppermost section of the suite are present within the mud-matrix melange near San Simeon. The simplest explanation for their crystallization, metamorphism and incorporation into the melange is that they are fragments of seamounts dismembered during subduction.

  2. Evolution of the northern Sierra Nevada metamorphic belt: Petrological, structural, and Ar/Ar constraints

    Energy Technology Data Exchange (ETDEWEB)

    Hacker, B.R. [Stanford Univ., CA (United States)

    1993-05-01

    The Sierra Nevada metamorphic belt constitutes an important record of the growth of continental crust from essentially oceanic materials. In the northern Sierra, the central part of the belt is made up of volcanoplutonic arcs and sediment-dominated units inferred to be accretionary wedges or closed ocean basins. The latter are broken formation and melange composed of radiolarian chert, lava, and volcanogenic and continental turbidites. Sedimentary detritus in the largest of these units can be plausibly linked to sources farther east in the Sierra, suggesting that deposition occurred near the eastern Sierran arc. Isoclinal folds, steeply dipping foliations, and steeply plunging down-dip lineations are characteristics structures. The westernmost unit is only feebly recrystallized, and deformation was accomplished principally by stress solution and local redeposition in veins. More easterly, inboard units are compositionally similar, but they recrystallized at pumpellyite-actinolite-and blueschist-facies conditions and deformed via solution-transfer and dislocation creep. Phengite silica contents, the degree of quartz veining, and the locations of pseudo-isograds support an eastward increase in metamorphic pressure and temperature. Metamorphic conditions during the growth of pumpellyite and actinolite ranged from {approximately}150-350 {degrees}C and 200-400 MPa, compatible with recrystallization and deformation in subduction zones or the deeper levels of magmatic arcs. Ar/Ar ages of volcanisclastic rocks and crosscutting plutons constrain the age of deformation and metamorphism in the western part of the region to 174-165 Ma. Deformation and recrystallization in more easterly units may have been coeval or begun as early as Triassic time. 58 refs., 14 figs., 4 tabs.

  3. Field evidence for fault controlled intrusion of blue-schist-bearing melange into an accretionary wedge, Island Mountain, California

    Energy Technology Data Exchange (ETDEWEB)

    Lamons, R.

    1985-01-01

    Two lithologic units of the Franciscan are well exposed along a loop of the Eel River at Island Mountain. They are 1) zeolite or lower grade lithic graywackes, and 2) a 0.5 km wide band of black shaly melange containing blueschist, chert, greenstone, metagraywacke, and a graywacke-hosted copper deposit. Sedimentary features were not observed in the melange. The graywacke was subdivided on the basis of presence or absence of sodium-cobaltonitrate stained K-spar. Field relationships suggest that the blueschist-bearing melange was emplaced along steep NW-dipping faults in an accretionary wedge. Mapping of S. Jewett Rock and SW Lake Mountain quadrangles show narrow anastomosing bands of the melange following NW-trending faults. East of this band, graywackes without K-spar are folded along NW/SE axes. No folds were found to the west. Other Melange bands pinch out into faults which juxtapose graywackes of different facies. The sheared melange bands are not folded and shale beds in the graywacke show little shear so the melange bands are unlikely to be sheared olistostromes. The areal extent of graywacke is about ten times that of melange shales. Assuming this pattern continues laterally and at depth, the amount of ductile material in the melange is far less than that assumed by Cloos (1982) in his flow model for melange. The ductile melange may have been forced upward by metamorphically produced volatiles, or as a result of relative plate motion. It originated at depth, moved up along the top of a subducting slab, plucking clasts, then splayed upward into pre-existing faults in the accretionary wedge.

  4. Subduction-related metamorphism beneath ophiolites (Oman) and during early stages of continental collision (Himalaya)

    Science.gov (United States)

    Searle, Mike; Waters, David; Cowan, Robert; Cherry, Alan; Cooper, Charles

    2014-05-01

    Subduction-related metamorphism occurs beneath ophiolites (Oman), beneath island arcs (Kohistan) and during the early stages of continental collision (Kaghan, Tso Morari; Himalaya). Ophiolite obduction necessarily involves subduction of first oceanic, then continental crust to mantle depths beneath the ophiolite. In Oman an inverted pressure and temperature profile is exposed beneath the Semail ophiolite from garnet+clinopyroxene-bearing granulite to hornblende+plagioclase amphibolite down through epidote amphibolite and a variety of greenschist facies meta-sediments, dominantly cherts, marbles and quartzites. Thermobarometry on Grt+Cpx-bearing amphibolites immediately beneath the contact with mantle sequence harzburgites shows that the upper sole rocks formed at PT conditions of 770-900°C and 11-13 kbar, equivalent to depths of 30-40 km in oceanic lithosphere. Heat for metamorphism can only have been derived from the overlying mantle peridotites. Pressures are higher than can be accounted for by the thickness of the preserved ophiolite (15-20 km). Timing of peak metamorphism was synchronous with formation of the ophiolite gabbroic - trondhjemite crustal sequence and eruption of the pillow lavas (Cenomanian; 96-95 Ma). During the later stages of obduction the continental margin was dragged down to depths of nearly 100 km and basaltic sills within calc-schists were converted to eclogites (20-25 kbar; 500-560oC; 79.1 Ma), then exhumed back up the same subduction channel. Apparent 'extensional' fabrics throughout the HP units are related to upward flow of deeply buried rocks in a wholly compressional environment. Eclogites in a similar structural position occur along the Himalaya in the northernmost exposures of Indian plate rocks. These eclogites formed either during the latest stage of ophiolite obduction or the earliest stage of continental collision.

  5. 莱河矿稳定性的热力学分析

    Institute of Scientific and Technical Information of China (English)

    王声远

    1980-01-01

    Laihunite, a mineral of ferric and ferrous iron silicate discovered in China in recent years, occurs in high grade metamorphic BIF coexisting with magnetite, quartz,fayaiite, ferrosilite and almandine. Complete nets based on Sehreinemakers bundles and partial nets with maximum closure after the method described by H. W. Day have been constructed by taking into account the existance of this minertl in order to illustrate phase relations for the (n+3) multisystem in the system of Fe2O3-FeO-SiO2. Judging from Lindsley's experimental data on ferrosilits, laihunite is expected to be stable at pressures probably higher than 15 Kb. Two-pyroxene and olivine-clinopyroxene geothermometere give temperatures of formation between 600--700℃. Free energy of laihunite calcultted according to the method of Chert and estimated values of heat capacity allow oxygen fugacity to be plotted against temperature at different total pressures with respect to a number of univariant reactions in which lailunite is involved. The log fo2 -T diagram demonstrates that to a first approximation the stability flels of laihunite overlaps the upper part of the magnetite field, but its upper limit is a little beyond the hematite-magnetite equilibrium. The three major requirements for laihunite stability, i.e., an unusual high pressure, a temperature in the order of 600--700℃ and a relatively higher oxygen fugacity are mutually, exclusive in common geological environment, which may probably account for the rare occurrence of this mineral in nature. For the BIF in which laihunite occurs, the pressure caused by the weight of overlying strata is not high enough to give rise to its formation even in the extreme case of geothermal gradient.So it is suggested that additional tectonic pressure in response to plate activity might have been involved.

  6. Characterization of chlorinated solvent contamination in limestone using innovative FLUTe® technologies in combination with other methods in a line of evidence approach.

    Science.gov (United States)

    Broholm, Mette M; Janniche, Gry S; Mosthaf, Klaus; Fjordbøge, Annika S; Binning, Philip J; Christensen, Anders G; Grosen, Bernt; Jørgensen, Torben H; Keller, Carl; Wealthall, Gary; Kerrn-Jespersen, Henriette

    2016-06-01

    Characterization of dense non-aqueous phase liquid (DNAPL) source zones in limestone aquifers/bedrock is essential to develop accurate site-specific conceptual models and perform risk assessment. Here innovative field methods were combined to improve determination of source zone architecture, hydrogeology and contaminant distribution. The FACT™ is a new technology and it was applied and tested at a contaminated site with a limestone aquifer, together with a number of existing methods including wire-line coring with core subsampling, FLUTe® transmissivity profiling and multilevel water sampling. Laboratory sorption studies were combined with a model of contaminant uptake on the FACT™ for data interpretation. Limestone aquifers were found particularly difficult to sample with existing methods because of core loss, particularly from soft zones in contact with chert beds. Water FLUTe™ multilevel groundwater sampling (under two flow conditions) and FACT™ sampling and analysis combined with FLUTe® transmissivity profiling and modeling were used to provide a line of evidence for the presence of DNAPL, dissolved and sorbed phase contamination in the limestone fractures and matrix. The combined methods were able to provide detailed vertical profiles of DNAPL and contaminant distributions, water flows and fracture zones in the aquifer and are therefore a powerful tool for site investigation. For the limestone aquifer the results indicate horizontal spreading in the upper crushed zone, vertical migration through fractures in the bryozoan limestone down to about 16-18m depth with some horizontal migrations along horizontal fractures within the limestone. Documentation of the DNAPL source in the limestone aquifer was significantly improved by the use of FACT™ and Water FLUTe™ data. PMID:27116640

  7. Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey-Lleyn, NW Wales, U.K.: MORB and OIB in the Iapetus Ocean

    Science.gov (United States)

    Saito, Takuya; Uno, Masaoki; Sato, Tomohiko; Fujisaki, Wataru; Haraguchi, Satoru; Li, Yi-bing; Sawaki, Yusuke; Yamamoto, Shinji; Maruyama, Shigenori

    2015-11-01

    The Gwna Group in Anglesey-Lleyn, NW Wales, UK, is a Neoproterozoic accretionary complex that consists of basalt, bedded chert, red claystone, and trench turbidite that have been intercalated in coherent and incoherent mélanges that are considered typical Ocean plate stratigraphy (OPS). The sediments in the OPS can be useful for constraining the geological environment in the Iapetus Ocean. Most basalts in this area have undergone hydrothermal alteration, greenschist facies regional metamorphism, and surface oxidation. This indicates that immobile elements such as Al2O3 and TiO2, Rare Earth Elements (REE) and High Field Strength Elements (HSFE) are appropriate for discriminating the origin of the basalts in the Gwna Group. Most basalts showing light REE-enriched pattern in CI chondrite-normalized spider diagrams in within-plate basalt (WPB) fields, and some have flat patterns in spider diagrams in mid-oceanic ridge basalt (MORB) fields. In view of these relations, we conclude that the former erupted in an oceanic island. Oceanic island basalts (OIB) are common in Phanerozoic accretionary complexes, and this study presents the first evidence of OIB in a Neoproterozoic accretionary complex of the Gwna Group in Anglesey-Llyen and Llyen area. The OIB-like basalts are locally capped by red hematite-rich claystones. This indicates that a fully oxic pelagic condition was present around the oceanic island in the Iapetus Ocean in the Neoproterozoic, which is consistent with the redox condition estimated from contemporaneous shallow marine sediments. On the other hand, the presence of black mudstones on top of MORB-like meta-basalts suggests that deep-sea anoxia conditions were prevalent during the end-Proterozoic.

  8. Lunar and Planetary Science XXXV: Astrobiology

    Science.gov (United States)

    2004-01-01

    The presentations in this session are: 1. A Prototype Life Detection Chip 2. The Geology of Atlantis Basin, Mars, and Its Astrobiological Interest 3. Collecting Bacteria Together with Aerosols in the Martian Atmosphere by the FOELDIX Experimental Instrument Developed with a Nutrient Detector Pattern: Model Measurements of Effectivity 4. 2D and 3D X-ray Imaging of Microorganisms in Meteorites Using Complexity Analysis to Distinguish Field Images of Stromatoloids from Surrounding Rock Matrix in 3.45 Ga Strelley Pool Chert, Western Australia 4. Characterization of Two Isolates from Andean Lakes in Bolivia Short Time Scale Evolution of Microbiolites in Rapidly Receding Altiplanic Lakes: Learning How to Recognize Changing Signatures of Life 5. The Effect of Salts on Electrospray Ionization of Amino Acids in the Negative Mode 6. Determination of Aromatic Ring Number Using Multi-Channel Deep UV Native Fluorescence 7. Microbial D/H Fractionation in Extraterrestrial Materials: Application to Micrometeorites and Mars 8. Carbon Isotope Characteristics of Spring-fed Iron-precipitating Microbial Mats 9. Amino Acid Survival Under Ambient Martian Surface UV Lighting Extraction of Organic Molecules from Terrestrial Material: Quantitative Yields from Heat and Water Extractions 10. Laboratory Detection and Analysis of Organic Compounds in Rocks Using HPLC and XRD Methods 11. Thermal Decomposition of Siderite-Pyrite Assemblages: Implications for Sulfide Mineralogy in Martian Meteorite ALH84001 Carbonate Globules 12. Determination of the Three-Dimensional Morphology of ALH84001 and Biogenic MV-1 Magnetite: Comparison of Results from Electron Tomography and Classical Transmission Electron Microscopy 13. On the Possibility of a Crypto-Biotic Crust on Mars Based on Northern and Southern Ringed Polar Dune Spots 14. Comparative Planetology of the Terrestrial Inner Planets: Implications for Astrobiology 15. A Possible Europa Exobiology 16. A Possible Biogeochemical Model for Titan

  9. Bedded jaspers of the Ordovician Løkken ophiolite, Norway: seafloor deposition and diagenetic maturation of hydrothermal plume-derived silica-iron gels

    Science.gov (United States)

    Grenne, Tor; Slack, John F.

    2003-01-01

    Sedimentary beds of jasper (red hematitic chert) in the Ordovician Løkken ophiolite of Norway are closely associated with volcanogenic massive sulphide (VMS) deposits. The jaspers occur in the immediate hangingwall and laterally peripheral to the large Løkken (25–30 Mt) and small Høydal (0.1 Mt) VMS deposits, and are exposed discontinuously for several kilometres along strike. Massive or laminated types predominate; jasper-sulphide debris-flow deposits are also abundant near VMS deposits. The jaspers contain hematite-rich laminae showing soft-sediment deformation structures and microtextural evidence that record the presence of a colloidal precursor and an origin as gels. Early textures include: (1) straight or curved chains of hematitic filaments 3–10 µm in diameter and 20–100 µm long; (2) branching networks of 15–25 µm-thick, tubular structures surrounded by cryptocrystalline hematite and filled with quartz and euhedral hematite; (3) small (up to 10 µm) spherules composed of cryptocrystalline hematite and silica; and (4) up to 50 µm silica spherules with hematitic cores. The small filaments seem to have been deposited in varying proportions in the primary laminae, possibly together with hematitic and siliceous microspheroids. Diagenetic changes are represented by polygonal syneresis cracks, and the presence of cryptocrystalline (originally opaline) silica, chalcedony, quartz, carbonate and cryptocrystalline hematite and/or goethite forming botryoidal masses and spheroids silica-rich jaspers preserve only small relics of fine-grained hematite-rich domains, and locally contain sparse pockets composed of coarse euhedral hematite±epidote.

  10. Climate modeling - a tool for the assessment of the paleodistribution of source and reservoir rocks

    Energy Technology Data Exchange (ETDEWEB)

    Roscher, M.; Schneider, J.W. [Technische Univ. Bergakademie Freiberg (Germany). Inst. fuer Geologie; Berner, U. [Bundesanstalt fuer Geowissenschaften und Rohstoffe, Hannover (Germany). Referat Organische Geochemie/Kohlenwasserstoff-Forschung

    2008-10-23

    In an on-going project of BGR and TU Bergakademie Freiberg, numeric paleo-climate modeling is used as a tool for the assessment of the paleo-distribution of organic rich deposits as well as of reservoir rocks. This modeling approach is based on new ideas concerning the formation of the Pangea supercontinent. The new plate tectonic concept is supported by paleo- magnetic data as it fits the 95% confidence interval of published data. Six Permocarboniferous time slices (340, 320, 300, 290, 270, 255 Ma) were chosen within a first paleo-climate modeling approach as they represent the most important changes of the Late Paleozoic climate development. The digital maps have a resolution of 2.8 x 2.8 (T42), suitable for high-resolution climate modeling, using the PLASIM model. CO{sub 2} concentrations of the paleo-atmosphere and paleo-insolation values have been estimated by published methods. For the purpose of validation, quantitative model output, had to be transformed into qualitative parameters in order to be able to compare digital data with qualitative data of geologic indicators. The model output of surface temperatures and precipitation was therefore converted into climate zones. The reconstructed occurrences of geological indicators like aeolian sands, evaporites, reefs, coals, oil source rocks, tillites, phosphorites and cherts were then compared to the computed paleo-climate zones. Examples of the Permian Pangea show a very good agreement between model results and geological indicators. From the modeling approach we are able to identify climatic processes which lead to the deposition of hydrocarbon source and reservoir rocks. The regional assessment of such atmospheric processes may be used for the identification of the paleo-distribution of organic rich deposits or rock types suitable to form hydrocarbon reservoirs. (orig.)

  11. THE VEGETATION OF LAMBUSANGO FOREST, BUTON, INDONESIA

    Directory of Open Access Journals (Sweden)

    ANDREW POWLING

    2016-01-01

    Full Text Available POWLING, A., PHILLIPS, A., PRITCHETT, R., SEGAR, S. T., WHEELER, R. & MARDIASTUTI, A. 2015. Thevegetation of Lambusango Forest, Buton, Indonesia. Reinwardtia 14(2: 265 – 286. ― Lambusango Forest is a tropicalrainforest on the island of Buton, which lies close to south east Sulawesi. The forest covers an area of about 95.000 ha,with different parts of the forest having different levels of conservation protection. It lies on rocks of both calcareous(limestone and non-calcareous (sandstone, conglomerate, peridotite and chert nature, which give rise to soils withvarying pH values, nutrient levels and water-holding capacities. The climate is seasonal, with a dry season of threemonths and considerable year-to-year variability due to El Niño and La Niña events. The vegetation on the differentsoils and in different habitats has been studied. Over 300 species of vascular plants found in the forest and surroundingareas are listed, including trees and shrubs, herbs, climbers, epiphytes, ferns and club-mosses. Two genera, Calamuswith 18 species and Ficus with 29 species, are particularly species-rich, apparently due to their ability to occupy numerousedaphic and ecological niches. Species of these two genera are also good colonists and so better able to reachButon in the recent past than other species. The plants of the forest indicate that Buton is floristically very similar toSulawesi, with at least 83% of the species found in the forest also being known from Sulawesi. Most of the plant familiesand genera present on Buton are common in SE Asia, indicating colonisation primarily from that continent. Manyfewer families and genera have colonised from the Australasian continent. The conservation of plant diversity is necessaryfor the forest to continue as a functioning ecosystem, to the benefit of the animals of the forest and also the localpeople.

  12. Trachyhystrichosphaera: An age-marker acanthomorph from the Bhander group, upper Vindhyan, Rajasthan

    Indian Academy of Sciences (India)

    Purnima Srivastava

    2009-10-01

    A highly diversified, advanced and exceptionally well preserved microfossil assemblage, dominated by a planktic community,has been recorded from petrographic thin sections of chert belonging to the Sirbu Shale Formation,Bhander group,upper Vindhyans,Rajasthan.Recently, it was noticed that the assemblage also contains well preserved,large-sized acanthomorphic acritarchs, Trachyhystrichosphaera considered to be an age-marker microfossil of the Cryogenian (850 –630 Ma).It is reported for the first time from any Indian microfossil assemblage of Proterozoic succession.The other microfossils of the Sirbu Shale Formation are:well preserved simple,small and large-sized sphaeromorphs;complex acanthomorphs,cyanobacterial community;especially a very small-sized but exceptionally well preserved Obruchevella ,a form resembling Volvox colonies; cf.vase-shaped microfossils and morphologies,possibly inclining towards fungal affinity,or lichen- like symbiotic associations of algae and fungi.Till date, Trachyhystrichosphaera has so far not been reported from successions older than the Tonian (1000 –850 Ma).It is believed that acanthomorphs attained maximum size in Ediacaran (630 –542 Ma),and further decreased in size in the Cambrian.The global paleontological literature indicates that Trachyhystrichosphaera ranges in age from Tonian –Ediacaran (1000 –542 Ma). The present record of Trachyhystrichosphaera as well as the earlier studies of micro and megascopic life of the Bhander Group in general and the Sirbu Shale in particular (aided by the absence of any Cambrian fossil record)indicate that in all possibilities,age of the Sirbu Shale should lie near Cryogenian (850 –630 Ma)and the uppermost Bhander group,may incline towards the Ediacaran (630 –542 Ma).

  13. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

    Indian Academy of Sciences (India)

    Ashima Saikia; Bibhuti Gogoi; Mansoor Ahmad; Talat Ahmad

    2014-07-01

    The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, crosscutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

  14. Rujevac Sb-Pb-Zn-As polymetallic deposit, Boranja orefield, Western Serbia: native arsenic and arsenic mineralization

    Science.gov (United States)

    Radosavljević, Slobodan A.; Stojanović, Jovica N.; Radosavljević-Mihajlović, Ana S.; Vuković, Nikola S.

    2014-02-01

    Rujevac is a low-temperature hydrothermal polymetallic Sb-Pb-Zn-As vein-type ore deposit, hosted within a volcanogenic-sedimentary zone situated in the Rujevac-Crvene Stene-Brezovica Diabase-Chert Formation (DCF) of the Podrinje Metallogenic District (PMD), Serbia. It is located several kilometers SE from the Boranja contact aureole, which is an integral part of the PMD in Western Serbia. Genetically related to the Tertiary granodioritic magma, the mineral assemblages are characterized by specific features. The mineral association of this deposit consists of sulfides, Pb-Sb(As) sulfosalts, native metals, oxides, hydroxides and gangue minerals. Chemical composition of the ore is very complex, where contents of valuable metals range as follows: Sb (0.17-24.31 wt.%), Zn (0.21-6.29 wt.%), Pb (0.15-6.33 wt.%), As (0.06-1.28 wt.%), Cd (25-747 ppm), Ag (7-408 ppm), Hg (13-473 ppm), and Tl (<1-29 ppm). Electron Probe Microanalyses (EPMA) of native arsenic from both the Rujevac and Stragari deposits showed contents of As up to 98.8 and 97.1 wt.%, with impurity contents of Sb up to 1.3 and 6.6 wt.%, and Tl up to 2 and 1.3 wt.%, respectively. Rhombohedral unit-cell parameters for native arsenic from Rujevac and Stragari deposits amount to: a = 3.760(2), c = 10.555(3) Å, V = 129.23(7) Å3 and a = 3.763(1), c = 10.560(5) Å, V = 129.48(8) Å3, respectively. Mineral assemblages, deposition order and genesis of the Rujevac polymetallic deposit were also discussed in detail. Native arsenic mineralization here has been additionally compared with similar well-known global deposits.

  15. Study of Diagenetic Features in Rudist Buildups of Cretaceous Edwards Formation Using Ground Based Hyperspectral Scanning and Terrestrial LiDAR

    Science.gov (United States)

    Krupnik, D.; Khan, S.; Okyay, U.; Hartzell, P. J.; Biber, K.

    2015-12-01

    Ground based remote sensing is a novel technique for development of digital outcrop models which can be instrumental in performing detailed qualitative and quantitative sedimentological analysis for the study of depositional environment, diagenetic processes, and hydrocarbon reservoir characterization. For this investigation, ground-based hyperspectral data collection is combined with terrestrial LiDAR to study outcrops of Late Albian rudist buildups of the Edwards formation in the Lake Georgetown Spillway in Williamson County, Texas. The Edwards formation consists of shallow water deposits of reef and associated inter-reef facies, including rudist bioherms and biostromes. It is a significant aquifer and was investigated as a hydrocarbon play in south central Texas. Hyperspectral data were used to map compositional variation in the outcrop by distinguishing spectral properties unique to each material. Lithological variation was mapped in detail to investigate the structure and composition of rudist buildups. Hyperspectral imagery was registered to a 3D model produced from the LiDAR point cloud with an accuracy of up to one pixel. Flat-topped toucasid-rich bioherm facies were distinguished from overlying toucasid-rich biostrome facies containing chert nodules, overlying sucrosic dolostones, and uppermost peloid wackestones and packstones of back-reef facies. Ground truth was established by petrographic study of samples from this area and has validated classification products of remote sensing data. Several types of porosity were observed and have been associated with increased dolomitization. This ongoing research involves integration of remotely sensed datasets to analyze geometrical and compositional properties of this carbonate formation at a finer scale than traditional methods have achieved and seeks to develop a workflow for quick and efficient ground based remote sensing-assisted outcrop studies.

  16. Lava and Life: New investigations into the Carson Volcanics, lower Kimberley Basin, north Western Australia

    Science.gov (United States)

    Orth, Karin; Phillips, Chris; Hollis, Julie

    2014-05-01

    The Carson Volcanics are the only volcanic unit in the Paleoproterozoic Kimberley Basin and are part of a poorly studied Large Igneous Province (LIP) that was active at 1790 Ma. New work focussing on this LIP in 2012 and 2013 involved helicopter-supported traverses and sampling of the Carson Volcanics in remote areas near Kalumburu in far north Western Australia's Kimberley region. The succession is widespread and flat lying to gently dipping. It consists of three to six basalt units with intercalated sandstone and siltstone. The basalts are 20-40 m thick, but can be traced up to 60 km along strike. The basalt can be massive or amygdaloidal and commonly display polygonal to subhorizontal and rare vertical columnar jointing. Features of the basalt include ropy lava tops and basal pipe vesicles consistent with pahoehoe lavas. The intercalated cross-bedded quartzofeldspathic sandstone and siltstone vary in thickness up to 40 m and can be traced up to 40 km along strike. Peperite is common and indicates interaction between wet, unconsolidated sediment and hot lava. Stromatolitic chert at the top of the formation represents the oldest life found within the Kimberley region. Mud cracks evident in the sedimentary rocks, and stromatolites suggest an emergent broad tidal flat environment. The volcanics were extruded onto a wide marginal margin setting subject to frequent flooding events. Thickening of the volcanic succession south and the palaeocurrents in the underlying King Leopold Sandstone and the overlying Warton Sandstone suggest that this shelf sloped to the south. The type of basalt and the basalt morphology indicate a low slope gradient of about 1°.

  17. Impact of Cretaceous Climate on Upwelling and Erosive Capacity of Transequatorial Current in the Tethys Seaway - Tales from Deep-Sea Sediments

    Science.gov (United States)

    Weissert, H.; Wohlwend, S.

    2014-12-01

    Early Cretaceous sedimentary archives from the Atlantic and Tethys Ocean record a reorganization of ocean circulation triggered by a further opening and deepening oft the Hispanic corridor. Nannofossil ooze, deposited in Atlantic and Tethys Oceans during earliest Cretaceous mirrors a stable equatorial circulation pattern with oligotrophic surface water conditions. Tethyan limestone-marlstone deposits and dark clays in the western North Atlantic mark reorganization of circulation pattern dominating Valanginian-Albian oceanography and favoring episodic black shale formation in Atlantic and Tethys Ocean. An east-west directed trans-equatorial current (TEC), coupled with equatorial upwelling and with varying erosive capacity was established (Hotinski and Toggweiler, Paleoceanography, 2003). Aptian sedimentary records from Tethys and Atlantic Oceans provide information on the sensitivity of the TEC to changing climate at times of perturbed carbon cycling as registered in the carbon isotope record. A greenhouse pulse defines the base of Aptian Oceanic Anoxic Event (OAE) 1a, while available temperature and pCO2 records point at post-OAE1a cooling of climate. In the eastern Tethys (Oman Mts), the Aptian greenhouse pulse coincides with onset of chert deposits at a time of a shallowing CCD and of increased upwelling. Well-ventilated Pacific-type deep-water conditions prevented the formation of black shales in the deep Hawasina Basin (Oman Mts). Low oxygen or anoxic conditions, however, favored black shale formation in basinal settings of the Western Tethys and Atlantic Ocean. Frequent sedimentary gaps in basinal successions and erosive surfaces, sometimes phosphatized, on alpine Tethyan submarine highs and along the Northern Tethyan shelf provide evidence for increased erosive power of the TEC, reaching depths of up to 1000m or more. If increased erosive power of TEC was triggered by the greenhouse pulse or by post-OAE1a cooling remains to be tested.

  18. Der Glaube als Erkenntnisquelle Belief as the source of knowledge

    Directory of Open Access Journals (Sweden)

    Andrea Hartwig

    2004-03-01

    Full Text Available Seit ihrer Kanonisation 1998 und Ernennung zur Mit-Patronin Europas 1999 steht die 1942 in Auschwitz ermordete Phänomenologin Edith Stein, 1922 vom jüdischen zum christlichen Glauben konvertiert und 1933 als Benedicta vom Kreuz in den Kölner Karmel eingetreten, mehr denn je im Blickfeld der Öffentlichkeit. Die Bedeutung ihrer wissenschaftlichen Arbeit u. a. als Assistentin von Edmund Husserl in Freiburg und als Dozentin am Deutschen Institut für wissenschaftliche Pädagogik in Münster, aber auch in privaten Studien wurden im Juli 2000 im Rahmen eines Symposiums des Internationalen Edith Stein Instituts in Würzburg diskutiert. Die Beiträge der vorliegenden Publikation beleuchten breit gefächert Aspekte des Werks und seiner Interpretation mit dem Ziel, die Philosophin neu zu entdecken und die bisherige Forschung zu intensivieren.Since her canonisation and her appointment as Martyr and Co-Patroness of Europe in 1999, Edith Stein has, more than ever, been in the public eye. Murdered in Auschwitz in 1942, the phenomenologist converted from Judaism to Catholicism in 1922 and entered the Carmel of Cologne in 1933 as Teresa Benedicta of the Cross. In July 2000, at a symposium of the International Edith Stein Institute in Wurzburg, the significance of her academic work (among other things as an assistant to Edmund Husserl in Freiburg and as a lecturer at the German Institute for Pedagogy in Munster was discussed. The wide-ranging contributions in this publication highlight aspects of this work and its interpretation with the aim of rediscovering the philosopher and of intensifying research conducted to date.

  19. Extensional tectonics during the igneous emplacement of the mafic-ultramafic rocks of the Barberton greenstone belt

    Science.gov (United States)

    Dewit, M. J.

    1986-01-01

    The simatic rocks (Onverwacht Group) of the Barberton greenstone belt are part of the Jamestown ophiolite complex. This ophiolite, together with its thick sedimentary cover occupies a complex thrust belt. Field studies have identified two types of early faults which are entirely confined to the simatic rocks and are deformed by the later thrusts and associated folds. The first type of fault (F1a) is regional and always occurs in the simatic rocks along and parallel to the lower contacts of the ophiolite-related cherts (Middle Marker and equivalent layers). These fault zones have previously been referred to both as flaser-banded gneisses and as weathering horizons. In general the zones range between 1-30m in thickness. Displacements along these zones are difficult to estimate, but may be in the order of 1-100 km. The structures indicate that the faults formed close to horizontal, during extensional shear and were therefore low angle normal faults. F1a zones overlap in age with the formation of the ophiolite complex. The second type of faults (F1b) are vertical brittle-ductile shear zones, which crosscut the complex at variable angles and cannot always be traced from plutonic to overlying extrusive (pillowed) simatic rocks. F1b zones are also apparently of penecontemporaneous origin with the intrusive-extrusive igneous processs. F1b zones may either represent transform fault-type activity or represent root zones (steepened extensions) of F1a zones. Both fault types indicate extensive deformation in the rocks of the greenstone belt prior to compressional overthrust tectonics.

  20. Late Triassic rifting and Jurassic-Cretaceous passive margin development of the Southern Neotethys: evidence from the Adıyaman area, SE Turkey

    Science.gov (United States)

    Robertson, A. H. F.; Parlak, O.; Yıldırım, N.; Dumitrica, P.; Taslı, K.

    2016-01-01

    Evidence of rifting and continental break-up to form the S Neotethys is found within the volcanic-sedimentary Koçali Complex. This is a folded, thrust-imbricated succession that includes lavas, volcaniclastic sediments, pelagic carbonates, radiolarites and manganiferous deposits. Interbedded ribbon cherts contain radiolarians of Late Triassic to Late Jurassic age. The lower part of the succession of Mid?-Late Triassic age (Tarasa Formation) is dominated by enriched mid-ocean ridge basalt (E-MORB). The overlying Late Triassic to Mid-Jurassic interval (Konak Formation) is characterised by intercalations of ocean island basalt and E-MORB. Taking account of structural position, the basalts erupted within the outer part of a continent-ocean transition zone. Continental break-up probably occurred during the Late Triassic (Carnian-Norian). Early to Mid-Jurassic lavas and volcaniclastic sediments record volcanism probably after continental break-up. In addition, the Karadut Complex is a broken formation that is located at a relatively low structural position just above the Arabian foreland. Pelagic carbonates, redeposited carbonates and radiolarites predominate. Radiolarians are dated as Early to Mid-Jurassic and Late Cretaceous in age. The pelagic carbonates include planktic foraminifera of Late Cretaceous age. The Karadut Complex resulted from the accumulation of calcareous gravity flows, pelagic carbonate and radiolarites in a relatively proximal, base-of-slope setting. After continental break-up, MORB and ophiolitic rocks formed within the S Neotethys further north. Tectonic emplacement onto the Arabian platform took place by earliest Maastrichtian time. Regional interpretation is facilitated by comparisons with examples of Triassic rifting and continental break-up in the eastern Mediterranean region and elsewhere.

  1. An anoxic, Fe(II)-rich, U-poor ocean 3.46 billion years ago

    Science.gov (United States)

    Li, Weiqiang; Czaja, Andrew D.; Van Kranendonk, Martin J.; Beard, Brian L.; Roden, Eric E.; Johnson, Clark M.

    2013-11-01

    The oxidation state of the atmosphere and oceans on the early Earth remains controversial. Although it is accepted by many workers that the Archean atmosphere and ocean were anoxic, hematite in the 3.46 billion-year-old (Ga) Marble Bar Chert (MBC) from Pilbara Craton, NW Australia has figured prominently in arguments that the Paleoarchean atmosphere and ocean was fully oxygenated. In this study, we report the Fe isotope compositions and U concentrations of the MBC, and show that the samples have extreme heavy Fe isotope enrichment, where δ56Fe values range between +1.5‰ and +2.6‰, the highest δ56Fe values for bulk samples yet reported. The high δ56Fe values of the MBC require very low levels of oxidation and, in addition, point to a Paleoarchean ocean that had high aqueous Fe(II) contents. A dispersion/reaction model indicates that O2 contents in the photic zone of the ocean were less than 10-3 μM, which suggests that the ocean was essentially anoxic. An independent test of anoxic conditions is provided by U-Th-Pb isotope systematics, which show that U contents in the Paleoarchean ocean were likely below 0.02 ppb, two orders-of-magnitude lower than the modern ocean. Collectively, the Fe and U data indicate a reduced, Fe(II)-rich, U-poor environment in the Archean oceans at 3.46 billion years ago. Given the evidence for photosynthetic communities provided by broadly coeval stromatolites, these results suggests that an important photosynthetic pathway in the Paleoarchean oceans may have been anoxygenic photosynthetic Fe(II) oxidation.

  2. Uranium minerals and radioactive equilibrium in the Jordan phosphate deposit of Ruseifa

    International Nuclear Information System (INIS)

    In the open pit of Ruseifa (Jordan) a marine sedimentary succession is mined, which belongs to the Maastrichian stage (Upper Cretacious). This up to 28 m thick succession is composed of an alternated stratification of phosphorites, limestones, clay marls and cherts with gradations between these main rock types. As all these rocks contain apatite in varying amounts the whole succession is designed by the term 'phoshate layer'. In the 'phosphate layer' 4 workable phosphorite bearing beds with thicknesses between 1.15 and 3.45 m are present, giving an eminent economical importance to the deposit. Especially the stratigraphically youngest, the fourth phosphorite bed, shows remarkably increased gamma-activities. In the phoshorite the average uranium content amounts up to 110 ppm U. The mineral apatite has been identified to be the main carrier of the uranium. In veins and fissures yellow secondary uranium minerals occur, which have been determined as carnotite and metatuyamunite. The discovery, that uranium is in a state of preponderant radioactive equilibrium with its daughter products, is important for the genesis of the uranium enrichments as well as for practical means of mining. The detected radioactive disequilibria are restricted to the formation of secondary uranium minerals on fissures and joints demonstrating distinct migration of uranium and its daughter product in the last 800 000 years (quaternary until recent weathering). These young geochemical weathering processes did not essentially change the syngenetic distribution of uranium in the phosphorite. With the determined mean uranium content of 110 ppm the whole uranium reserves of Ruseifa evaluates approximately 8580 t of uranium metal out of total phosphate reserves of 78 mio. t. (orig.)

  3. An open ocean record of the Toarcian oceanic anoxic event

    Directory of Open Access Journals (Sweden)

    D. R. Gröcke

    2011-11-01

    Full Text Available Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic matter-rich sediments (black shales and significant perturbations in the global carbon cycle. These perturbations are globally recorded in sediments as carbon isotope excursions irrespective of lithology and depositional environment. During the early Toarcian, black shales were deposited on the epi- and pericontinental shelves of Pangaea, and these sedimentary rocks are associated with a pronounced (ca. 7 ‰ negative (organic carbon isotope excursion (CIE which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the lower Toarcian is thought to represent an oceanic anoxic event (the T-OAE. If the T-OAE was indeed a global event, an isotopic expression of this event should be found beyond the epi- and pericontinental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg of lower Toarcian organic matter-rich cherts from Japan, deposited in the open Panthalassa Ocean, was analysed. The results show the presence of a major (>6 ‰ negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the lower Toarcian negative CIE known from Pangaean epi- and pericontinental strata. A smaller negative excursion in δ13Corg (ca. 2 ‰ is recognized lower in the studied succession. This excursion may, within the current biostratigraphic resolution, represent the excursion recorded in European epicontinental successions close to the Pliensbachian/Toarcian boundary. These results from the open ocean realm suggest, in conjunction with other previously published datasets, that these Early Jurassic carbon cycle perturbations affected the active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric.

  4. THE JURASSIC SEDIMENTARY EVOLUTION OF A CARBONATE PLATFORM INTO A DEEP-WATER BASIN, MT. MANGART (SLOVENIAN-ITALIAN BORDER

    Directory of Open Access Journals (Sweden)

    ANDREJ SMUC

    2005-03-01

    Full Text Available A complete Jurassic succession, recording the evolution from platform margin to a deep-water basin, is exposed at Mt. Mangart in the Julian Alps. The succession is a part of the Julian Nappe, where the Southern Alps overlap with the Dinarides. In the Jurassic, the area comprised part of the south Tethyan passive continental margin. The section was studied sedimentologically in detail and dated with radiolarians. It is divided into five lithostratigraphic units: Unit 1: Lower Jurassic shallow-water peloidal and oncoidal limestones; Unit 2: Pliensbachian distal shelf limestones rich in juvenile ammonites and sponge spicules topped by an Fe-Mn hardground; Unit 3: lower to possibly middle Toarcian sequence of black shales with interbedded siliceous limestone; Unit 4: upper Bajocian/Bathonian to lower Tithonian cherts, cherty limestones, and carbonate gravity-flow deposits; Unit 5: upper Tithonian red nodular cherty limestones with abundant calpionellids and aptychi. A stratigraphic gap, comprising the late Toarcian to early Bajocian, separates Unit 4 from Unit 3. In general, the succession correlates well with known Tethyan transgressive/regressive facies cycles. In addition, two periods of accelerated subsidence were recognized, the first, in the Pliensbachian, drowned the platform, the second, prior to the late Bajocian, created accommodation space for resedimented carbonate deposits from the adjacent Friuli Carbonate Platform. The present day position of the succession is between the Belluno Basin to the west and the Slovenian Basin to the south. The hitherto described successions of these two basins were located more distally from the Friuli Carbonate Platform than the Mt. Mangart succession. 

  5. Characterization of chlorinated solvent contamination in limestone using innovative FLUTe® technologies in combination with other methods in a line of evidence approach

    Science.gov (United States)

    Broholm, Mette M.; Janniche, Gry S.; Mosthaf, Klaus; Fjordbøge, Annika S.; Binning, Philip J.; Christensen, Anders G.; Grosen, Bernt; Jørgensen, Torben H.; Keller, Carl; Wealthall, Gary; Kerrn-Jespersen, Henriette

    2016-06-01

    Characterization of dense non-aqueous phase liquid (DNAPL) source zones in limestone aquifers/bedrock is essential to develop accurate site-specific conceptual models and perform risk assessment. Here innovative field methods were combined to improve determination of source zone architecture, hydrogeology and contaminant distribution. The FACT™ is a new technology and it was applied and tested at a contaminated site with a limestone aquifer, together with a number of existing methods including wire-line coring with core subsampling, FLUTe® transmissivity profiling and multilevel water sampling. Laboratory sorption studies were combined with a model of contaminant uptake on the FACT™ for data interpretation. Limestone aquifers were found particularly difficult to sample with existing methods because of core loss, particularly from soft zones in contact with chert beds. Water FLUTe™ multilevel groundwater sampling (under two flow conditions) and FACT™ sampling and analysis combined with FLUTe® transmissivity profiling and modeling were used to provide a line of evidence for the presence of DNAPL, dissolved and sorbed phase contamination in the limestone fractures and matrix. The combined methods were able to provide detailed vertical profiles of DNAPL and contaminant distributions, water flows and fracture zones in the aquifer and are therefore a powerful tool for site investigation. For the limestone aquifer the results indicate horizontal spreading in the upper crushed zone, vertical migration through fractures in the bryozoan limestone down to about 16-18 m depth with some horizontal migrations along horizontal fractures within the limestone. Documentation of the DNAPL source in the limestone aquifer was significantly improved by the use of FACT™ and Water FLUTe™ data.

  6. Terrestrial evidence of a nuclear catastrophe in paleoindian times

    International Nuclear Information System (INIS)

    A common problem at paleoindian sites in the northeastern region of North America is the recovery of radiocarbon dates that are much younger than their western counterparts, sometimes by as much as 10,000 years. Other methods like thermoluminescence, geoarchaeology, and sedimentation suggest that the dates are incorrect. Evidence has been mounting that the peopling of the Americas occurred much earlier than 12,000 bp. The discovery of tracks and micrometeorite-like particles in paleoindian artifacts across North America demonstrates they were bombarded during a cosmic event. Measurements of Uranium 235 (235U), depleted by 17-77%, and enhanced concentrations of Plutonium 239 (239Pu), from neutron capture on Uranium 238 (238U), in artifacts, associated chert types, and sediments at depth indicates that the entire prehistoric North American landscape was bombarded by thermal neutrons. Radiocarbon dating assumes that there is no substantial change in isotopic composition over time. A large thermal neutron event would convert residual Nitrogen 14 (14N) in charcoal to Carbon 14 (14C) thus resetting the radiocarbon date to a younger value and pushing back the date that paleoindians occupied the Americas by thousands of years. Analysis of data from 11 locations across North America indicates there were episodes of cosmic ray bombardments of the prehistoric landscape in Late Glacial times. Examination of the radiocarbon record suggests these events were coupled with geomagnetic excursions at 41,000, 33,000, and 12,500 bp and irradiated the landscape with massive thermal neutron fluxes of the order of approximately1015 neutrons/cm2. These data provide a clear body of terrestrial evidence supporting either one of two longstanding hypotheses for catastrophe in paleoindian times: (1) a giant solar flare during a geomagnetic excursion as explored by Wolfendale and Zook, and (2) a supernova shockwave as forwarded by Brackenridge, Clarke, and Dar. The evidence is reviewed, and

  7. Timing and evolution of ocean anoxic event during Early Cambrian in south China

    Science.gov (United States)

    Yang, J.; Jiang, S.; Pi, D.; Ling, H.

    2008-12-01

    The Precambrian/Cambrian (PC-C) interval is one of the most interesting intervals in the evolution of life because of the sudden diversification of animals with mineralized skeletons, known as "Cambrian Explosion". The Yangtze Platform in south China is one of the best occurrences that can provide excellent insights into the palaeo-environmental and biological changes across the PC-C boundary. Our study show that the ocean anoxia were widespread during the Early Cambrian period, however, the start of this anoxic event was not from the PC-C boundary (i.e., 542 Ma), but some 7 Ma later (~535 Ma) when the Niutitang Formation black rock series (black phosphorite, chert, and black shale) deposited along a thousand kilometer long NEE zone in the transitional facies in the Yangtze Platform, while the major Cambrian radiation (Changjiang fauna) took place during 521-511 Ma. During the Niutitang period, the depositional environment of the Early Cambrian sedimentary sequence in south China have evolved from an initial oxic/dysoxic to a major anoxic/euxinic environment, and then back to dysoxic/oxic environment. A Ni-Mo sulfide layer occurred in the lower part of the Niutitang black shales which contains extremely enrichments of many metals, and can serve as a marker layer in south China when the depositional environment turned into euxinic condition. Re-Os isotope study of the sulfide ores and host black shales show an age of 535 Ma. Initial Os isotopic compositions, Mo isotopic compositions, and rare earth elements and Pt group element geochemistry suggest involvement of submarine hydrothermal fluids during the metal enrichments in black shale.

  8. Isotopic compositions of small shelly fossil Anabarites from Lower Cambrian in Yangtze Platform of South China: Implications for palaeocean temperature

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Anabarites belong to small shelly fossils (SSF), which occur widely in the Lower Cambrian strata of Yangtze Platform in South China. They are phosphate shell in composition and represent the earliest stage of the Cambrian bioradiation of Bilateria, the socalled "Cambrian Explosion". In this study, we attempted to separate Anabarites fossils from Lower Cambrian dolostones, and we obtained samples of both the fossils (SSF) and the granular phosphates (GP). Isotopic analyses were performed on samples of SSF, GP, and matrix dolostone (DH-23). The results showed that the δ30 Si values of the quartz filling in fossils celoms, and the siliceous materials in granular phosphates are -0.6‰ and -0.7‰, which is different from normal sedimentary siliceous rocks from the Lower Cambrian strata (0-0.7‰) as reported by Li et al., but is consistent with the data for siliceous rocks and cherts of submarine hydrothermal origin. It is likely that a later hydrothermal replacement could have taken place in the SSF-bearing sedimentary rocks. The oxygen isotope values of the phosphate of SSF and GP are 16.8‰ and 17.0‰, respectively. These are significantly higher than the Neoproterozoic phosphate ores (10.9‰-13.9‰) as reported by Ling et al., hence, late diagenesis and hydrothermal replacement may not have caused a significant change in the oxygen isotope compositions of the small shelly fossils, and the calculated temperatures (25.4-26.3 ℃ ) for palaeo-seawater using a SSF phosphate oxygen isotope thermometer are therefore considered here as the upper limit of seawater temperature in the Early Cambrian ocean of the Yangtze Platform.

  9. Paleogeographic significance of Upper Triassic basinal succession of the Tamar Valley, northern Julian Alps (Slovenia

    Directory of Open Access Journals (Sweden)

    Gale Luka

    2015-08-01

    Full Text Available The Julian Alps (western Slovenia structurally belong to the eastern Southern Alps. The Upper Triassic succession mostly consists of shallow water platform carbonates of the Dolomia Principale-Dachstein Limestone system and a deep water succession of the Slovenian Basin outcropping in the southern foothills of the Julian Alps. In addition to the Slovenian Basin, a few other intraplatform basins were present, but they remain poorly researched and virtually ignored in the existing paleogeographic reconstructions of the eastern Southern Alps. Herein, we describe a deepening-upward succession from the Tamar Valley (north-western Slovenia, belonging to the Upper Triassic Tarvisio Basin. The lower, Julian-Tuvalian part of the section comprises peritidal to shallow subtidal carbonates (Conzen Dolomite and Portella Dolomite, and an intermediate carbonate-siliciclastic unit, reflecting increased terrigenous input and storm-influenced deposition (Julian-lowermost Tuvalian shallow-water marlstone and marly limestone of the Tor Formation. Above the drowning unconformity at the top of the Portella Dolomite, Tuvalian well-bedded dolomite with claystone intercalations follows (Carnitza Formation. The latter gradually passes into the uppermost Tuvalian–lowermost Rhaetian bedded dolomite with chert and slump breccias, deposited on a slope and/or at the toe-of-slope (Bača Dolomite. Finally, basinal thin-bedded bituminous limestone and marlstone of Rhaetian age follow (Frauenkogel Formation. The upper part of the Frauenkogel Formation contains meter-scale platform-derived limestone blocks, which are signs of platform progradation. The Tarvisio Basin may have extended as far as the present Santo Stefano di Cadore area, representing a notable paleogeographic unit at the western Neotethys margin.

  10. Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Guba, Chukotka (NE Russia): Significance for interregional correlations

    Science.gov (United States)

    Ledneva, G. V.; Pease, V. L.; Sokolov, S. D.

    2008-12-01

    In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska-Chukotka microplate prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Guba, eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments, minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U-Pb zircon age of 252+/-4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal mafic rocks of the Kolyuchinskaya Guba region have major and trace element compositions identical the tholeiitic flood basalts of the main plateau stage of the Siberian LIP. They are strongly differentiated, the result of high-pressure equilibrium crystallization of a low-Ti/Y tholeiitic melt, and contaminated. The compositional variations in these rocks, however, neither proves nor disproves a correlation between the Permo-Triassic tholeiitic flood basalts of eastern Chukotka and the Siberian LIP. Thus, two alternative geodynamic interpretations are possible: 1) The hypabyssal mafic rocks and associated tholeiitic flows crystallized from a plume-derived melt; 2) The rocks are not related to plume activity, consequently eastern Chukotka was probably part of a passive rifted or extensional continental margin in the Permo-Triassic. Nonetheless, we prefer the first of these two possibilities. Funding for this work is gratefully acknowledged from the Swedish Polar Research Secretariat ("Beringia-2005"), the Swedish Research Council, the Russian Foundation for Basic Research (grant No 08-05-00547), Leading Scientific School (NSH-3172.2008.5) and ONZ RAS. Thanks are also extended to M.J. Whitehouse and the Nordsim facility - the Nordsim facility is funded by the research councils of Denmark, Norway, Sweden, the Geological Survey of Finland, and the Swedish Museum of

  11. Tectono-depositional patterns and palaeogeography in the Middle Yangtze River region during the Early Cambrian%中扬子地区早寒武世构造—沉积样式与古地理格局

    Institute of Scientific and Technical Information of China (English)

    陈代钊; 汪建国; 严德天; 韦恒叶

    2012-01-01

    地除外).从第四构造幕热液活动后,盆地基底热衰减迅速,深部硅输入通量大幅减少,并在扬子地块发生大范围均匀挠曲沉降和快速海平面上升,造成碳酸盐台地淹没,形成了牛蹄塘组(或同期)富有机质黑色岩系.从此后,中扬子地区进入了一个新的构造—沉积演化时期.%The Precambrian-Cambrian transition is a key interval in Earth's history, as it records the advent,extinction and accelerated diversification of metazoans ('Cambrian explosion') and co-evolution of tectonic re-organization of global plates, a prolonged global oceanic anoxia and swift shifts in ocean geochemistry. To understand better the fundamental environmental changes on Earth's surface system, detailed analyses on depositional facies and sequences of the Lower Cambrian (Stages 1 and 2) were carried out across the western Hubei and northwestern Hunan in the Middle Yangtze River region, South China, and 16 types of lithofacies in three main lithological categories of carbonate, chert and fine-grained clastic mudrock were identified, which can be grouped into four depositional sequences (SI ~ S4 ) in terms of tempo-spatial facies variations. Just at the onset of Cambrian, the carbonate platform in northwestern Hunan was subject to subaerial exposure, its southern margin, however, underwent rapid subsidence , forming the perched terrace; the northern flank also suffered large-scale subsidence, plunging down to the basin in the northwestern Hunan ( Yangjiaping) , where the basement relief begun to rise once again to the north and evolved into carbonate platform in Three Gorges area in western Hubei. The vast lateral topographic differences shaped by the two uplift-depressions point toblock tilting in the context of extensional tectonism, which could have episodically occurred and thereby controlled the deposition, facies patterns and distributions in the Early Cambrian as recorded by the depositional sequences. A depositional

  12. 蓟县中元古界高于庄组沉积岩系及地质意义%Sedimentary Rocks of Gaoyuzhuang Formation of Mesoproterozoic in Jixian County and Its Geological Significance

    Institute of Scientific and Technical Information of China (English)

    杨云祥; 郭峰; 杨友运

    2011-01-01

    天津蓟县元古界剖面具有极高的综合研究价值,而髙于庄组在该剖面中居于承上启下的位置.高于庄组在整个中、新元古界剖面中厚度较大,岩石类型多样且成因特殊,主要岩石类型包括碳酸盐岩、泥岩、硅质岩和石英砂岩.碳酸盐岩主要为泥晶灰岩、瘤状灰岩、砂屑灰岩、臼齿灰岩及粉细晶白云岩等,硅质岩包括燧石和沉积石英岩,沉积石英岩具鲕状或砾状结构.仅在本组底部见石英砂岩.上述岩石特征表明,蓟县地区在中元古代长城纪晚期的高于庄期以浅海中深缓坡沉积为主,有短期的潮坪碳酸盐沉积环境,沉积作用受大红峪时期火山物质的影响.臼齿灰岩的存在可能提供华北地区中元古代年代地层学和构造沉积演化研究的新证据.%The Proterczoic section in Jixian, Tianjin, is highly worthy of an integrated research.The Gaoyuzhuang formation plays a the key role of linking the old and new strata · Gaoyuzhuang formation is rather thick compared with the whole Proterczoic section, and it has multiple types of rocks with special origins.The main kinds of rocks include carbonate rocks, mudstone, silicalite, and quartz sandstone.The carbonate rocks are predominantly composed of pelsparite, nodular limestone, calcarenite, Molar-tooth carbonates, and other fine-grained dolomite.Silicalite includes chert and depositional quartz with textures of oolite and pebble.The quartz sandstone appears at the bottom of Gaoyuzhuang formation.The petrology shows that the depositional environment of the study area is carbonate tide-flat and shallow sea,which is also strongly affected by the volcanic materials and wind brought clastics from Gaoyuzhuang formation.Molar-tooth carbonates are expected to propel the study of the Proterczoic chronology and tectono-sedimentary evolution of North China.

  13. Bioessential element-depleted ocean following the euxinic maximum of the end-Permian mass extinction

    Science.gov (United States)

    Takahashi, Satoshi; Yamasaki, Shin-ichi; Ogawa, Yasumasa; Kimura, Kazuhiko; Kaiho, Kunio; Yoshida, Takeyoshi; Tsuchiya, Noriyoshi

    2014-05-01

    We describe variations in trace element compositions that occurred on the deep seafloor of palaeo-superocean Panthalassa during the end-Permian mass extinction based on samples of sedimentary rock from one of the most continuous Permian-Triassic boundary sections of the pelagic deep sea exposed in north-eastern Japan. Our measurements revealed low manganese (Mn) enrichment factor (normalised by the composition of the average upper continental crust) and high cerium anomaly values throughout the section, suggesting that a reducing condition already existed in the depositional environment in the Changhsingian (Late Permian). Other redox-sensitive trace-element (vanadium [V], chromium [Cr], molybdenum [Mo], and uranium [U]) enrichment factors provide a detailed redox history ranging from the upper Permian to the end of the Permian. A single V increase (representing the first reduction state of a two-step V reduction process) detected in uppermost Changhsingian chert beds suggests development into a mildly reducing deep-sea condition less than 1 million years before the end-Permian mass extinction. Subsequently, a more reducing condition, inferred from increases in Cr, V, and Mo, developed in overlying Changhsingian grey siliceous claystone beds. The most reducing sulphidic condition is recognised by the highest peaks of Mo and V (second reduction state) in the uppermost siliceous claystone and overlying lowermost black claystone beds, in accordance with the end-Permian mass extinction event. This significant increase in Mo in the upper Changhsingian led to a high Mo/U ratio, much larger than that of modern sulphidic ocean regions. This trend suggests that sulphidic water conditions developed both at the sediment-water interface and in the water column. Above the end-Permian mass extinction horizon, Mo, V and Cr decrease significantly. On this trend, we provide an interpretation of drawdown of these elements in seawater after the massive element precipitation event

  14. Nanoscale petrographic and geochemical insights on the origin of the Palaeoproterozoic stromatolitic phosphorites from Aravalli Supergroup, India.

    Science.gov (United States)

    Papineau, D; De Gregorio, B; Fearn, S; Kilcoyne, D; McMahon, G; Purohit, R; Fogel, M

    2016-01-01

    Stromatolites composed of apatite occur in post-Lomagundi-Jatuli successions (late Palaeoproterozoic) and suggest the emergence of novel types of biomineralization at that time. The microscopic and nanoscopic petrology of organic matter in stromatolitic phosphorites might provide insights into the suite of diagenetic processes that formed these types of stromatolites. Correlated geochemical micro-analyses of the organic matter could also yield molecular, elemental and isotopic compositions and thus insights into the role of specific micro-organisms among these communities. Here, we report on the occurrence of nanoscopic disseminated organic matter in the Palaeoproterozoic stromatolitic phosphorite from the Aravalli Supergroup of north-west India. Organic petrography by micro-Raman and Transmission Electron Microscopy demonstrates syngeneity of the organic matter. Total organic carbon contents of these stromatolitic phosphorite columns are between 0.05 and 3.0 wt% and have a large range of δ(13) Corg values with an average of -18.5‰ (1σ = 4.5‰). δ(15) N values of decarbonated rock powders are between -1.2 and +2.7‰. These isotopic compositions point to the important role of biological N2 -fixation and CO2 -fixation by the pentose phosphate pathway consistent with a population of cyanobacteria. Microscopic spheroidal grains of apatite (MSGA) occur in association with calcite microspar in microbial mats from stromatolite columns and with chert in the core of diagenetic apatite rosettes. Organic matter extracted from the stromatolitic phosphorites contains a range of molecular functional group (e.g. carboxylic acid, alcohol, and aliphatic hydrocarbons) as well as nitrile and nitro groups as determined from C- and N-XANES spectra. The presence of organic nitrogen was independently confirmed by a CN(-) peak detected by ToF-SIMS. Nanoscale petrography and geochemistry allow for a refinement of the formation model for the accretion and phototrophic growth of

  15. Analysis of the Younger Dryas Impact Layer

    Energy Technology Data Exchange (ETDEWEB)

    Firestone, Richard B.; West, Allen; Revay, Zsolt; Hagstrum, Jonathon T,; Belgya, Thomas; Hee, Shane S. Que; Smith, Alan R.

    2010-02-27

    We have uncovered a thin layer of magnetic grains and microspherules, carbon spherules, and glass-like carbon at nine sites across North America, a site in Belgium, and throughout the rims of 16 Carolina Bays. It is consistent with the ejecta layer from an impact event and has been dated to 12.9 ka BP coinciding with the onset of Younger Dryas (YD) cooling and widespread megafaunal extinctions in North America. At many locations the impact layer is directly below a black mat marking the sudden disappearance of the megafauna and Clovis people. The distribution pattern of the Younger Dryas boundary (YDB) ejecta layer is consistent with an impact near the Great Lakes that deposited terrestrial-like ejecta near the impact site and unusual, titanium-rich projectile-like ejecta further away. High water content associated with the ejecta, up to 28 at. percent hydrogen (H), suggests the impact occurred over the Laurentide Ice Sheet. YDB microspherules and magnetic grains are highly enriched in TiO{sub 2}. Magnetic grains from several sites are enriched in iridium (Ir), up to 117 ppb. The TiO{sub 2}/FeO, K/Th, TiO{sub 2}/Zr, Al{sub 2}O{sub 3}/FeO+MgO, CaO/Al{sub 2}O{sub 3}, REE/ chondrite, FeO/MnO ratios and SiO{sub 2}, Na{sub 2}O, K{sub 2}O, Cr{sub 2}O{sub 3}, Ni, Co, U, Th and other trace element abundances are inconsistent with all terrestrial and extraterrestrial (ET) sources except for KREEP, a lunar igneous rock rich in potassium (K), rare-earth elements (REE), phosphorus (P), and other incompatible elements including U and Th. Normal Fe, Ti, and {sup 238}U/{sup 235}U isotopic abundances were found in the magnetic grains, but {sup 234}U was enriched over equilibrium values by 50 percent in Murray Springs and by 130 percent in Belgium. 40K abundance is enriched by up to 100 percent in YDB sediments and Clovis chert artifacts. Highly vesicular carbon spherules containing nanodiamonds, glass-like carbon, charcoal and soot found in large quantities in the YDB layer are

  16. Oil shales, evaporites and ore deposits

    Science.gov (United States)

    Eugster, Hans P.

    1985-03-01

    elevated temperatures and with carbonates as principal host rocks. The Pine Point deposits are cited for their close association with evaporites. Alkaline, metal-rich brines are postulated for the HYC deposit of McArthur River, Australia. Such brines are known from the Green River Formation and deposits formed from such brines constitute the GRT class. They can be recognized by the presence of Magadi-type cherts and zeolite-analcime-K-spar tuffs. The Cu-Co ore bodies of Outokumpu, Finland, might also belong to this type. A new classification of sedimentary ore deposits is proposed, based on their geochemical environment. KST and MVT are formed from acid ore fluids, while GRT and CT (Creede type) are derived from basic ore fluids. pH of the fluids is best evaluated not from the ores themselves, but from their effect on the host-rocks.

  17. A Sr-Nd isotopic study of sand-sized sediment provenance and transport for the San Francisco Bay coastal system

    Science.gov (United States)

    Rosenbauer, Robert J.; Foxgrover, Amy C.; Hein, James R.; Swarzenski, Peter W.

    2013-01-01

    A diverse suite of geochemical tracers, including 87Sr/86Sr and 143Nd/144Nd isotope ratios, the rare earth elements (REEs), and select trace elements were used to determine sand-sized sediment provenance and transport pathways within the San Francisco Bay coastal system. This study complements a large interdisciplinary effort (Barnard et al., 2012) that seeks to better understand recent geomorphic change in a highly urbanized and dynamic estuarine-coastal setting. Sand-sized sediment provenance in this geologically complex system is important to estuarine resource managers and was assessed by examining the geographic distribution of this suite of geochemical tracers from the primary sources (fluvial and rock) throughout the bay, adjacent coast, and beaches. Due to their intrinsic geochemical nature, 143Nd/144Nd isotopic ratios provide the most resolved picture of where sediment in this system is likely sourced and how it moves through this estuarine system into the Pacific Ocean. For example, Nd isotopes confirm that the predominant source of sand-sized sediment to Suisun Bay, San Pablo Bay, and Central Bay is the Sierra Nevada Batholith via the Sacramento River, with lesser contributions from the Napa and San Joaquin Rivers. Isotopic ratios also reveal hot-spots of local sediment accumulation, such as the basalt and chert deposits around the Golden Gate Bridge and the high magnetite deposits of Ocean Beach. Sand-sized sediment that exits San Francisco Bay accumulates on the ebb-tidal delta and is in part conveyed southward by long-shore currents. Broadly, the geochemical tracers reveal a complex story of multiple sediment sources, dynamic intra-bay sediment mixing and reworking, and eventual dilution and transport by energetic marine processes. Combined geochemical results provide information on sediment movement into and through San Francisco Bay and further our understanding of how sustained anthropogenic activities which limit sediment inputs to the system (e

  18. Xenon Fractionation, Hydrogen Escape, and the Oxidation of the Earth

    Science.gov (United States)

    Zahnle, K. J.; Catling, D. C.

    2014-12-01

    Xenon in Earth's atmosphere is severely mass fractionated and depleted compared to any plausible solar system source material, yet Kr is unfractionated. These observations seem to imply that Xe has escaped from Earth. Vigorous hydrodynamic hydrogen escape can produce mass fractionation in heavy gases. The required hydrogen flux is very high but within the range permitted by solar EUV heating when Earth was 100 Myrs old or younger. However this model cannot explain why Xe escapes but Kr does not. Recently, what appears to be ancient atmospheric xenon has been recovered from several very ancient (3-3.5 Ga) terrestrial hydrothermal barites and cherts (Pujol 2011, 2013). What is eye-catching about this ancient Xe is that it is less fractionated that Xe in modern air. In other words, it appears that a process was active on Earth some 3 to 3.5 billion years ago that caused xenon to fractionate. By this time the Sun was no longer the EUV source that it used to be. If xenon was being fractionated by escape — currently the only viable hypothesis — it had to be in Earth's Archean atmosphere and under rather modest levels of EUV forcing. It should be possible for Xe, but not Kr, to escape from Earth as an ion. In a hydrodynamically escaping hydrogen wind the hydrogen is partially ionized. The key concepts are that ions are much more strongly coupled to the escaping flow than are neutrals (so that a relatively modest flow of H and H+ to space could carry Xe+ along with it, the flux can be small enough to be consistent with diffusion-limited flux), and that Xe alone among the noble gases is more easily ionized than hydrogen. This sort of escape is possible along the polar field lines, although a weak or absent magnetic field would likely work as well. The extended history of hydrogen escape implicit in Xe escape in the Archean is consistent with other suggestions that hydrogen escape in the Archean was considerable. Hydrogen escape plausibly played the key role in creating

  19. A Mossbauer investigation of iron-rich terrestrial hydrothermal vent systems: lessons for Mars exploration

    Science.gov (United States)

    Wade, M. L.; Agresti, D. G.; Wdowiak, T. J.; Armendarez, L. P.; Farmer, J. D.

    1999-01-01

    -rich chert stromatolite. Our research demonstrates that in situ Mossbauer spectroscopy can help determine whether hydrothermal mineral deposits exist on Mars, which is significant for exobiology because of the issue of whether that world ever had conditions conductive to the origin of life. As a useful tool for selection of samples suitable for transport to Earth, Mossbauer spectroscopy will not only serve geological interests but will also have potential for exopaleontology.

  20. Petrología y geoquímica de una ritmita marga-caliza del Hemisferio Austral: El Miembro Los Catutos (Formación Vaca Muerta, Tithoniano medio de la Cuenca Neuquina

    Directory of Open Access Journals (Sweden)

    R. A. Scasso

    2002-06-01

    Full Text Available Una secuencia rítmica de margas y calizas de 25 m de espesor, correspondiente al Miembro Los Catutos (Formación Vaca Muerta, Jurásico superior de la Cuenca Neuquina, fue estudiada capa por capa en varias canteras cercanas a Zapala. Estratos de hasta un metro de espesor de calizas litográficas, masivas o laminadas, fosilíferas, a veces moteadas o débilmente bioturbadas (?Chondrites, se intercalan con bancos más delgados de margas. Las calizas y margas pueden clasificarse como pelbiomicritas y biopelmicritas, mayormente compuestas por pellets, radiolarios, foraminíferos, ostrácodos, equinoideos, espículas de esponjas y gastrópodos, con cantidades menores de peloides, feldespato, chert, muscovita, glauconita y colofano. Los valores de δ;;18O son muy probablemente resultado de modificaciones diagenéticas del sedimento original, pero el δ;;13C muestra buena coincidencia con los valores de las curvas de "agua de mar" publicadas para el Tithoniano y con el registro sedimentario en calizas del Tethys. Un análisis preliminar de las excursiones negativas de δ;;13C indican que pueden responder a crisis en la productividad del sistema con una periodicidad de 400 ka, acorde con cambios en la excentricidad de la órbita terrestre. La esmectita y los interestratificados componen principalmente la fracción menor de 2 micrones, como reflejo de procesos pedogenéticos desarrollados sobre rocas-madre volcanogénicas. La mayor abundancia de caolinita en las margas sería resultado de condiciones más húmedas en el continente. Las rocas muestran hasta un 1,95% de COT y configuran una roca madre de hidrocarburos regular a buena, aunque térmicamente inmadura. Se infiere un ambiente sedimentario de mar abierto, baja energía, disaeróbico, con altas tasas de sedimentación resultado de una alta productividad en la superficie sumada al aporte de plumas de material suspendido desde la zona litoral. Se propone una acumulación en forma de amplios

  1. Pseudomorphs of Neotethyan Evaporites in Anatolia's HP/LT belts - Aptian basin-wide pelagic gypsum deposits

    Science.gov (United States)

    Scheffler, Franziska; Oberhänsli, Roland; Pourteau, Amaury; Immenhauser, Adrian; Candan, Osman

    2015-04-01

    Rosetta Marble was defined in SW Anatolia as 3D-radiating textures of dm-to-m-long calcite rods in the HP/LT metamorphosed Mid-Cretaceous pelagic carbonate sequence of the Ören Unit. Rosetta Marble in the type locality are interbedded with meta-chert beds, and may constitute entire carbonate beds. Rare aragonite relicts and Sr-rich, fibrous calcite pseudomorphs after aragonite witness the HP metamorphic imprint of this sequence during the closure of a Neotethyan oceanic domain during latest Cretaceous-Palaeocene times. We investigated the Rosetta Marble of the Ören Unit, as well as other known and newly found localities in the Tavşanlı and Afyon zones, and the Alanya Massif and Malatya area, to decipher the metamorphic, diagenetic and sedimentologic significance of these uncommon textures. Based on field, petrographic and geochemical investigations, we document a wide variety of Rosetta-type textures. A striking resemblance with well-known gypsum morphologies (e.g. shallow-tail, palm-tree textures) leads us to argue that Rosetta Marble was initially composed of giant gypsum crystals (selenite). The absence of anhydrite relicts of pseudomorphs indicate that gypsum transformed into calcite soon after the deposition by the mean of a sulphate reduction reaction. The gypsum-to-calcite transformation requires that organic matter intervened as a reactant phase. Mid Cretaceous oceanic domains in the Tethyan realm are characterised by overall anoxic conditions that allowed the preservation of organic material. Rosetta Marble exposures are widely distributed over 600 km along the Neotethyan suture zone. During deepening of the Neotethyan ocean in Mid Cretaceous times, basin-wide and cyclic sedimentation of gypsum and radiolarite occurred. The origin of high-salinity waters needed for gypsum precipitation was located at shelf levels. Density and gravity effects forced the brines to cascade downwards into the deep ocean. Favorable climatic conditions trigger the formation

  2. Epithermal paleosurfaces

    Science.gov (United States)

    Sillitoe, Richard H.

    2015-10-01

    Many active volcanic-hydrothermal and geothermal systems are characterized by distinctive surface and near-surface landforms and products, which are generated during discharge of a spectrum of fluid types under varied conditions. Remnants of most of these products are preserved in some of their less-eroded, extinct equivalents: epithermal deposits of high-sulfidation (HS), intermediate-sulfidation (IS), and low-sulfidation (LS) types. Steam-heated alteration occupying vadose zones and any underlying silicified horizons formed at paleogroundwater tables characterize HS, IS, and LS deposits as do hydrothermal eruption craters and their subaerial or shallow sub-lacustrine breccia aprons and laminated infill. Although rarely recognized, HS, IS, and LS systems can also contain finely laminated, amorphous silica sediments that accumulated in acidic lakes and mud pots and, exclusive to HS systems, in hyperacidic crater lakes. In contrast, silica sinter and more distal carbonate travertine are hot spring discharge products confined mainly to LS and IS settings, as both form from near-neutral-pH liquids. Hydrothermal chert deposition and sediment silicification can take place in shallow, lacustrine rift settings, also largely restricted to LS and IS deposits. These surface and near-surface hydrothermal products are typically metal deficient, although mercury concentrations are relatively commonplace and were formerly exploited in places. Nonetheless, sinters, hydrothermal eruption craters, and silicified lacustrine sediments may contain anomalously high precious metal values; indeed, the last of these locally constitutes low-grade, bulk-tonnage orebodies. The dynamic nature of epithermal paleosurfaces, caused by either syn-hydrothermal aggradation or degradation, can profoundly affect deposit evolution, leading to either eventual burial or telescoping of shallower over deeper alteration ± precious metal mineralization. Formational age, tectonic and climatic regime

  3. Architecture and dynamic of lower Cretaceous carbonate platform in sultanate of Oman: correlations between seismic data and outcrop; Architecture et dynamique des systemes carbonates de la plate-forme Cretace inferieur du Sultanat d'Oman: correlations entre donnees de sismique et d'affleurement

    Energy Technology Data Exchange (ETDEWEB)

    Le Bec, A.

    2004-12-15

    The Rayda Basin, located in northern Oman at the south-eastern passive margin of the Arabian plate, has been filled in by a pro-grading carbonate system during the Lower Cretaceous. The filling up basin realized to carbonate platform pro-gradation on 300 km. Pelagic facies represented with radiolarian chert and shallowing facies with erosive surface, mud-cracks and lagoonal mud, and displaying on seismic lines an alternation of high angle and low angle clinoforms at the 10's of kilometers scale. Detailed study of these two types of clinoforms in the nearby outcrops shows that the high angle system is dominated by high-energy, grainy facies (ooliths, rudists, stromatoporoids), while the low angle system is dominated by a low-energy, carbonate mud facies. Based on the subsurface (geometries) and outcrop (facies) data a regional depositional model is proposed for this system. The outcrop study is based on 14 measured sections (6764 meters), completed with photo panoramas, thin section analysis and geochemical analyses (carbonate and organic matter content). The subsurface dataset consists of several regional seismic lines, two high resolution 3D blocs, and is supported by core material The regional seismic lines allow to map out the position of the high and low angle clinoform belts. One high angle belt and two low angle belts are identified in the profiles. In outcrop at least one more high angle belt and one more low angle belt are present. These overall geometries probably define the large scale sequence organisation. At a smaller scale, the 3D blocs allow to show the detailed geometrical organisation of the clinoform belts. The outcrop sections provide critical sub-seismic scale data on the facies composition and depositional geometries. The high energy system of the steep clinoforms (angle estimated at several degrees), is probably a wave controlled barrier coastline system, while the muddy low angle clinoforms (angle < 0.5 degree) shows large convex and

  4. Regional Fluid Flow and Basin Modeling in Northern Alaska

    Science.gov (United States)

    Kelley, Karen D., (Edited By)

    2007-01-01

    INTRODUCTION The foothills of the Brooks Range contain an enormous accumulation of zinc (Zn) in the form of zinc sulfide and barium (Ba) in the form of barite in Carboniferous shale, chert, and mudstone. Most of the resources and reserves of Zn occur in the Red Dog deposit and others in the Red Dog district; these resources and reserves surpass those of most deposits worldwide in terms of size and grade. In addition to zinc and lead sulfides (which contain silver, Ag) and barite, correlative strata host phosphate deposits. Furthermore, prolific hydrocarbon source rocks of Carboniferous and Triassic to Early Jurassic age generated considerable amounts of petroleum that may have contributed to the world-class petroleum resources of the North Slope. Deposits of Zn-Pb-Ag or barite as large as those in the Brooks Range are very rare on a global basis and, accordingly, multiple coincident favorable factors must be invoked to explain their origins. To improve our understanding of these factors and to contribute to more effective assessments of resources in sedimentary basins of northern Alaska and throughout the world, the Mineral Resources Program and the Energy Resources Program of the U.S. Geological Survey (USGS) initiated a project that was aimed at understanding the petroleum maturation and mineralization history of parts of the Brooks Range that were previously poorly characterized. The project, titled ?Regional Fluid Flow and Basin Modeling in Northern Alaska,? was undertaken in collaboration with industry, academia, and other government agencies. This Circular contains papers that describe the results of the recently completed project. The studies that are highlighted in these papers have led to a better understanding of the following: *The complex sedimentary facies relationships and depositional settings and the geochemistry of the sedimentary rocks that host the deposits (sections 2 and 3). *The factors responsible for formation of the barite and zinc deposits

  5. Principal stages in evolution of precambrian organic world: Communication 2. The late proterozoic

    Science.gov (United States)

    Sergeev, V. N.; Semikhatov, M. A.; Fedonkin, M. A.; Vorob'eva, N. G.

    2010-12-01

    A new suggested model outlining the evolution of the organic world from the mid-Early Proterozoic (˜2.0 Ga) to the Early Cambrian is based on data characterizing the relevant chert-embedded and compression-preserved organic-walled microbiotas, impressions of soft-bodied multicellular organisms, and biomarkers. Critical analysis of overall paleontological data resulted in the distinguishing of seven successive assemblages of Proterozoic micro- and macrofossils. Being of global geographic range, the assemblages correspond to the major stages in evolution of the organic world and typify global units which are termed the Labradorian (˜2.0-1.65 Ga), Anabarian (1.65-1.2 Ga), Turukhanian (1.2-1.03 Ga), Uchuromayan (1.03-0.85 Ga), Yuzhnouralian (0.85-0.635 Ga), Amadeusian (0.635-0.56 Ga), and Belomorian (0.56-0.535 Ga). Characteristic of the Labradorian unit are microfossil assemblages of the Gunflint type including remains of morphologically bizarre prokaryotic microorganisms: star-like Eoastrion, umbrella-shaped Kakabekia, dumbbell-shaped Xenothrix, and some others. Fine-grained siliciclastic deposits of the same age yield the oldest remains of millimeter-sized eukaryotes: spherical to ribbon-like Chuaria and Tawuia. Microfossils prevailing in shallow-water carbonate facies of the Anabarian unit are akinetes of nostocalean cyanophyceae Archaeoellipsoides and entophysalidacean cyanobacteria Eoentophysalis, whereas acanthomorphic acritarchs Tappania and Shuiyousphaeridium dominate the assemblages of open-shelf facies, where they are associated with the first-found rare macroscopic multicellular fossils Horodyskia. The distinguishing feature of the next Turukhanian unit is the first occurrence of filamentous red alga Bangiomorpha and the stalked cyanobacterium Polybessurus. The Uchuromayan unit is characterized by the appearance and worldwide radiation of structurally complicated eukaryotic microorganisms, primarily of acanthomorphic acritarchs Trachyhystrichosphaera and

  6. Study of flint properties for artefacts raw material sources detection in the future

    Science.gov (United States)

    Zarina, Liga; Seglins, Valdis

    2014-05-01

    The natural diversity of flint and chert is extremely high and their changes in hypergenesis zone are relevant, as well the processes speed is high, which makes these natural silicates problematic in modern scientific studies. This is also evidenced by the numerous attempts to determine precise the flint chemical and physical properties that still are recognized only as indicative. At the same time, flint is one of the few natural raw materials, what people have used for making tools through thousands of years. Despite the many advances in ancient material culture studies, the raw material in relation to the development of these cultures can be localised sufficiently accurate only in some cases, but others have to be limited to the assumption that the raw material was obtained through an exchange. In the study was assessed the natural diversity of the flint in northern Europe and its characteristic properties. It was found that only a part of them are associated with secondary changes and relate mainly to the low purity of the flint, as well as to an external layer formation, less - to the individual layers of the nodules. Those cannot always be macroscopically evaluated, particularly in circumstances when the samples cover patina and the objects may be investigated only by non-destructive methods. The studies in ultraviolet light partially solved before mentioned. The internal structure of the objects is recognizable, and at the same time are evident also various inclusions, squares and diffuse, hidden cracks and other disparities, which often cover most of the research objects. This explains why so far determined flint properties are so very different and enable to mark the specific locations for the further composition research. These characteristic locations were studied under UV light and it is optimal apply excitation filters 340-380nm, 450-490nm and 515-560nm with corresponding emission zones from 425nm, 515nm and 590nm. The results show that it is possible

  7. Recycling of quartz-poor/lithic-rich foreland-basin sediments in arid climate (Euphrates-Tigris-Karun river system)

    Science.gov (United States)

    Garzanti, Eduardo; Juboury, Ali Ismail Al; Zoleikhaei, Yousef; Vermeesch, Pieter; Hamzah Abdulhussein Jotheri, Jaafar; Akkoca, Dicle Bal; Allen, Mark; Andò, Sergio; Limonta, Mara; Padoan, Marta; Resentini, Alberto; Vezzoli, Giovanni

    2016-04-01

    In this detailed petrological analysis of a large source-to-sink sediment-routing system (catchment area > 1 million km2) we document its several peculiarities, and illustrate a rich petrographic and heavy-mineral dataset integrated by bulk-sediment geochemistry and detrital-zircon U-Pb geochronological data that widens the spectrum of compositions generally assumed as paradigmatic for orogenic settings. We test traditional versus upgraded sedimentary-petrology models in the endeavor to derive a more refined conceptual model of reference, in order to enhance the power of provenance analysis but also to define its limitations and understand which secret of nature is likely to remain beyond reach in our efforts to reconstruct orogenic landscapes of the past. Sands derived from the Zagros-Southeast Anatolian fold-thrust belt contain an abundance of lithic grains derived not only first-cycle from carbonates, cherts, mudrocks, arc volcanics, and obducted mantle serpentinites representing the exposed shallow structural level of the orogen, but also recycled from Neogene molassic strata exposed in the foothills. Quartz, K-feldspar and mica are equally scarce in first-cycle and recycled sediments. This quartz-poor petrographic signature, characterizing the broad undissected tectonic domain of the Anatolia-Iranian plateau, is markedly distinct from that of sands shed by highly elevated and dissected collision orogens of the same mountain system such as the Himalaya or the Alps. Arid climate in the region allows full preservation of chemically unstable grains including carbonate and mafic/ultramafic rock fragments even through more than a single sedimentary cycle. Also, it reduces transport capacity of fluvial systems, which dump most of their load in Mesopotamian marshlands upstream of the Arabian/Persian Gulf allochemical carbonate factory. Quartz-poor orogenic sediments from the Zagros-Southeast Anatolian range mix with quartz-rich recycled sands ultimately derived from

  8. ALVIN-SeaBeam studies of the Sumisu Rift, Izu-Bonin arc

    Science.gov (United States)

    Taylor, B.; Brown, G.; Fryer, P.; Gill, J. B.; Hochstaedter, A. G.; Hotta, H.; Langmuir, C. H.; Leinen, M.; Nishimura, A.; Urabe, T.

    1990-10-01

    Bimodal volcanism, normal faulting, rapid sedimentation, and hydrothermal circulation characterize the rifting of the Izu-Bonin arc at 31°N. Analysis of the zigzag pattern, in plan view, of the normal faults that bound Sumisu Rift indicates that the extension direction (080° ± 10°) is orthogonal to the regional trend of the volcanic front. Normal faults divide the rift into an inner rift on the arc side, which is the locus for maximum subsidence and sedimentation, and an outer rift further west. Transfer zones that link opposing master faults and/or rift flank uplifts further subdivide the rift into three segments along strike. Volcanism is concentrated along the ENE-trending transfer zone which separates the northern and central rift segments. The differential motion across the zone is accommodated by interdigitating north-trending normal faults rather than by ENE-trending oblique-slip faults. Volcanism in the outer rift has built 50-700 m high edifices without summit craters whereas in the inner rift it has formed two multi-vent en echelon ridges (the largest is 600 m high and 16 km long). The volcanism is dominantly basaltic, with compositions reflecting mantle sources little influenced by arc components. An elongate rhyolite dome and low-temperature hydrothermal deposits occur at the en echelon step in the larger ridge, which is located at the intersection of the transfer zone with the inner rift. The chimneys, veins, and crusts are composed of silica, barite and iron oxide, and are of similar composition to the ferruginous chert that mantles the Kuroko deposits. A 1.2-km transect of seven ALVIN heat flow measurements at 30°48.5'N showed that the inner-rift-bounding faults may serve as water recharge zones, but that they are not necessarily areas of focussed hydrothermal outflow, which instead occurs through the thick basin sediments. The rift basin and arc margin sediments are probably dominated by permeable rhyolitic pumice and ash erupted from submarine

  9. Compositional Grading in an Impact-produced Spherule Bed, Barberton Greenstone Belt, South Africa: A Key to Condensation History of Rock Vapor Clouds

    Science.gov (United States)

    Krull, A. E.; Lowe, D. R.; Byerly, G. R.

    2003-01-01

    The chemical and physical processes by which spherules form during the condensation of impact-produced rock vapor clouds are poorly understood. Although efforts have been made to model the processes of spherule formation, there is presently a paucity of field data to constrain the resulting theoretical models. The present study examines the vertical compositional variability in a single early Archean spherule bed in the Barberton Greenstone Belt (BGB), South Africa, in order to better identify the process by which impact vapor clouds condense and spherules form and accumulate. The BGB spherule beds are suitable for this type of study because of their great thickness, often exceeding 25cm of pure spherules, due to the massive sizes of the impactors. Two main problems complicate analysis of vertical compositional variability of graded spherule beds: (1) differential settling of particles in both the vapor and water column due to density and size differences and (2) turbulence within the vapor cloud. The present study compares sections of spherule bed S3 from four different depositional environments in the Barberton Greenstone Belt: (1) The Sheba Mine section (SAF-381) was deposited under fairly low energy conditions in deep water, providing a nice fallout sequence, and also has abundant Ni-rich spinels; (2) Jay's Chert section (SAF-380) was deposited in subaerial to shallow-water conditions with extensive post-depositional reworking by currents. The spherules also have preserved spinels; (3) the Loop Road section (loc. SAF-295; samp. KSA-7) was moderately reworked and has only rare preservation of spinels; and (4) the shallow-water Barite Syncline section (loc. SAF-206; samp KSA-1) has few to no spinels preserved and is not reworked. Although all of the spherule beds have been altered by silica diagenesis and K-metasomatism, most of the compositional differences between these sections appear to reflect their diagenetic histories, possibly related to their differing

  10. Accretionary Complexes: Recorders of Plate Tectonism and Environmental Conditions Through Time on Earth and Possibly Those Early Noachian (Hadean-equivalent) in Age on Mars

    Science.gov (United States)

    Dohm, J. M.; Maruyama, S.; Miyamoto, H.; Viviano-Beck, C. E.; Anderson, R. C.

    2014-12-01

    On Earth, highlighted in Japan, North America, Europe, and Greenland, accretionary complexes comprehensively record information compiled while the oceanic crust is en route from the mid-oceanic ridge to the subduction zone, spanning hundreds of millions of years. At the zone, oceanic crustal materials are stacked along thrust faults and/or subducted to be eventually recycled into the mantle. The surviving accretionary-complex materials include Ocean Plate Stratigraphy (OPS). The ideal succession of the OPS (from oldest to youngest) is mid-ocean ridge basalt, pelagic sediment including radiolarian chert, hemipelagic sediment including siliceous shale, and trench turbidite deposits. Therefore, accretionary complexes often record diverse environmental conditions from deep- to shallow-marine environments, including those perturbed by magmatic, impact, and possibly extrasolar events. Stratigraphic, impact-crater, paleotectonic, and magnetic-anomaly information point to Early Noachian (Hadean-equivalent) Martian geologic terrains; they are extremely ancient environmental records compared to those destroyed on Earth due to differences in planetary mass and evolutional states. Such record a dynamic phase of the evolution of Mars, including interacting ocean, landmass, and atmosphere, as well as possible plate tectonism during an operating dynamo. A candidate accretionary complex and nearby outcrops of steeply dipping beds comprising olistostrome-like blocks, nearby and in the Claritas rise, respectively, may be key evidence of major crustal shortening related to plate tectonism, in addition to being extremely ancient environmental records. Claritas rise is a rugged promontory about 250 km across, which forms the northwest part of an extremely ancient and large mountain range, Thaumasia highlands, with a length nearing 2,400 km, or approximating that of the Himalayas. Future investigation of the ancient Martian basement, which includes geochemical analyses for possible OPS

  11. Investigation on primary and secondary processes in Nasirabad manganese deposit, south of Neyriz: using mineralogy and Pb isotope geochemistry

    Directory of Open Access Journals (Sweden)

    Ali Reza Zarasvandi

    2013-04-01

    Full Text Available The Nasirabad manganese deposit is located 5 km south of Nasirabad, 8 km SW of Neyriz in the Fars province. Structurally, the area is placed in the southeastern part of Zagros thrust belt. In this area, the manganese mineralization occurred as ore layers and nodules, interlayered with Pichakun radiolarite chert deposits. In this study, mineralogy and geochemistry of uranium, thorium and lead isotopes were used to investigate the primary and secondary processes. In this way, in addition to petrographic and XRD studies, ICP-MS analysis was carried out in order to measure the U, Th and Pb isotopes. The strong fractionation of Fe and Mn phases and also the absence of Fe-bearing minerals in the XRD results, presence of syngenetic todorokite and quartz crystals, high U/Th ratios in some samples and Th versus U diagrams, all indicate entrance of Mn-bearing hydrothermal fluids into the sedimentary basin of the Nasirabad manganese deposit. The pyrolusites in radiolarites tests as replacement textures, host rock space filling and fracture filling pyrolusites, indicates the influence of secondary exogenic processes on primary hydrothermal mineralization. Non-homogenous 206Pb/Pb204, 207Pb/Pb204 and 208Pb/Pb204 values show non-steady hydrothermal processes in the sedimentary basin and indicate mixing of hydrothermal lead isotopes with another secondary source. Strong positive correlation between absolute values of radiogenic lead isotopes and insoluble High Field Strength Elements (HFSE such as 207Pb vs Nb (r=0.81, 207Pb vs TiO2 (r=0.93, 207Pb vs Th (r=0.79 and strong correlation between these elements and some mafic components like 208Pb vs Fe2O3 (r=0.94 and Th vs MgO (r=0.86 represent entrance of radiogenic lead with mafic detrital materials into the sedimentary basin. Similar linear trend among 206Pb/Pb204 vs 208Pb/Pb204 and 207Pb/Pb204 ratios in nodules and manganese layers show the same geochemical condition in Mn-nodules and layers formation and

  12. Blueschist Blocks in the Shale-matrix Melange of the Franciscan Complex of California: Metamorphic Aureoles and Subduction Channel Upwelling

    Science.gov (United States)

    Cloos, Mark; Ukar, Estibalitz

    2014-05-01

    The subduction channel concept postulates that where oceanic lithosphere converges faster than ~2 cm/yr, the plate boundary is best approximated as a viscous shear zone. Channel capacity can abruptly decrease where there is a sharp increase in the pressure gradient along the top of the shear zone. Where this occurs, subducted sediment can upwell and flow back towards the inlet. The Central Belt of the Franciscan Complex is up to tens of km wide and extends from where subduction continues in Oregon southwards to the Nacimiento Block, west of the San Andreas fault. The scaly shale matrix outcrops poorly along the 1500+ km belt because it is weakly metamorphosed (blueschists (e.g., Tiburon, Jenner Beach). How these high-T blocks, the oldest metamorphics in the Franciscan and the more voluminous lower-T blueschists became rounded fragments encased in shale-matrix has been the subject of much discussion. Uplift in serpentine diapirs is widely invoked, but the scarcity of these blocks in serpentinite where exposures are good is problematic. Explaining the blocks as sedimentary olistoliths requires both a phantom source terrane and exhumation mechanism. The simplest explanation is that the coarse blueschists are fragments of a metamorphic aureole formed during subduction initiation that were later detached from the base of the ophiolitic leading edge of the North American plate. Later, tectonic melange was generated by subduction-driven shearing that caused upwelling of shale-rich sediment. Slabs of blueschist were boudinaged and mixed with fragments of greenstone and chert detached from seamounts. Blueschist block incorporation into upwelling mélange is a kind of subduction erosion akin to plucking by glaciers. The exposure of the blueschist along the roof of the subduction channel may have been mostly localized to near where normal faults formed in the overriding block as Farallon plate dip flattened from 80 to 40 Ma. Only blocks of the appropriate size and density can

  13. Magmatic origin of low-T mafic blueschist and greenstone blocks from the Franciscan mélange, San Simeon, California

    Science.gov (United States)

    Ukar, Estibalitz; Cloos, Mark

    2015-08-01

    The Franciscan mélange exposure near San Simeon contains abundant greenstone and minor blueschist blocks that were tectonically boudinaged while encased in the shale-matrix. Tectonic deformation of the blueschists is evident from variable amounts of cataclastic flow along their margins and in pinched tails. Major, trace, and rare earth elemental analyses indicate that blueschist and greenstone blocks in this area of the mélange were derived from sources with MORB-like composition along with some having trace element and REE patterns similar to OIB compositions. Most blocks are low LREE basalts that probably formed in an open ocean ridge setting, but some blocks have high LREE contents similar to off-axis seamounts. Linear trends of incompatible elements for both blueschist and greenstone blocks indicate that both lithologies were probably derived from a similar, variably fractionated, tholeiitic magma. Blueschist blocks with sodic amphibole + lawsonite ± epidote were pervasively recrystallized at 300-350 °C and foliated during ductile deformation that included folding. Their protolith can only be identified as mafic. A few blocks contain very small amounts of metasedimentary materials indicating some were probably seafloor basalts, but some may have been diabase or even gabbro. Where interlayered sediment was present, the mafic protolith was enriched in K, Rb, and Na. Greenstones, on the other hand, contain abundant pseudomorphic evidence of magmatic textures. Alteration to albite, chlorite and pumpellyite at temperatures of 100-200 °C is intense, especially in cataclastic margins and pinched tails. Some of the basaltic greenstones have attached radiolarian chert, and a few have relict diabasic textures. The mafic blueschists and greenstones in the mélange near San Simeon are probably fragments from the uppermost part of the Farallon plate. The blueschists may be mostly mafic slabs uprooted from the subducting crust, underplated to the base of the North

  14. Internal P-T-t Structure of Subduction Complexes — Insights from Lu-Hf Geochronology on Garnet and Lawsonite (Halilbağı, Central Anatolia)

    Science.gov (United States)

    Pourteau, A.; Scherer, E. E.; Schmidt, A.; Bast, R.

    2014-12-01

    The subduction complex near Halilbağı (Central Anatolia) is among the best sites to investigate deep-seated tectonic, petrologic, and geochemical processes taking place in subduction zones. The Halilbağı Unit comprises slices of lawsonite- and/or epidote-bearing blueschist and eclogite, as well as meta-chert and marble. The unit is overlain by an ophiolitic slab and underlain by a HP/LT metamorphosed carbonate platform. Previous studies of the Halilbağı Unit suggested tectonic blocks were metamorphosed under diverse peak conditions, but shared a common exhumation P-T path marked by syn-decompression cooling (Davis and Whitney, 2006; Çetinkaplan et al., 2008). To better understand the internal structure and dynamics of this subduction complex, we carried out Lu-Hf geochronology on garnet (grt) and lawsonite (lws) from a variety of HP oceanic rocks, as well as the sub-ophiolitic metamorphic sole. Our results suggest that intra-oceanic subduction started at ~110 Ma (grt-amph isochron from a grt amphibolite). Less than 23 Myr later, the subduction interface was refrigerated enough to allow clockwise P-T loops (~87 Ma peak grt-matrix isochron for a lws+grt-bearing eclogitic blueschist) and syn-decompression cooling (~79 Ma retrograde lws-matrix isochron) of subducted oceanic rocks. We will present further results for several HP metamorphic sub-facies (e.g., epidote (ep) eclogite, lws+ep blueschist, lws blueschist, lws eclogite). Such data may allow unraveling whether the co-occurrence of "warm" (i.e., ep-bearing), and "cold" (i.e., lws-bearing) HP rocks in the same locality results from (a) sampling of distinct levels of the subduction slab, (b) thermal maturation of the juvenile subduction zone, or (c) inaccurate P-T estimates. Novel natural constraints are thus expected on the dynamics of the Halilbağı Unit and of subduction complexes in general. Çetinkaplan M., Candan O., Oberhänsli R. and Bousquet R., 2008. Pressure-Temperature Evolution of Lawsonite

  15. Petrologic Evolution of Palau; A Nascent Island Arc

    Science.gov (United States)

    Hawkins, J. W.; Ishizuka, O.

    2008-12-01

    Initiation of subduction in intra-oceanic settings requires relative differences in plate thickness and density (i.e., age difference); a major zone of weakness separating the plates, e.g., a fracture zone; and a change in relative vectors of movement to cause convergence. These factors help explain the origin of the southern- most part of the > 2500 km long Kyushu - Palau Ridge (KPR). Palau Islands, at 7 deg 30 ' N, are the only significant emergent feature on KPR. Small islands are mainly uplifted Pliocene and younger reef carbonate. Large islands are mainly volcanic comprising rare boninite; major basalt, basaltic andesite and andesite; and minor dacite. Polymict breccia is abundant; sills, flows, dikes are common; pillows are rare. The same rock types, as well as high-Mg basalt, were dredged from the Palau Trench. Volcanism on Palau began in late Eocene and ended by early Miocene. Rocks are low-K primitive island arc- tholeiite series. None are MORB. REE and HFSE require a depleted mantle source. Zr* and Ti* suggest that melts interacted with OL-PX rocks of upper mantle or deep crust cumulates. Moderate enrichment of LILE and LREE indicate influx of "dehydration fluid." Ce/Ce* and Eu/Eu* show no evidence for subducted sediments or recycling of arc- derived clastics yet there is no accreted sedimentary prism. This paradox may be owing to lack of arc or terrigenous clastics on seafloor formed in open ocean "sterile" equatorial latitudes. Plate reconstructions and paleomagnetic data suggest that the "arc" probably formed on the trace of a transform fault that has migrated northward and rotated clockwise up to 90 deg. since Oligocene time. Episodes of transtension allowed upwelling of relatively fertile hot mantle into depleted mantle and sheared, altered, rocks of the transform. Episodes of transpression may have initiated subduction of seafloor having a thin cover of pelagic sediments (calcareous and radiolarian ooze, chert, chalk, limestone) deposited far from

  16. Gemmological and Mineralogical Characteristics of Nephrite from Luodian,Guizhou Province%贵州罗甸软玉的宝石矿物学特征

    Institute of Scientific and Technical Information of China (English)

    支颖雪; 廖冠琳; 陈琼; 李英哲; 周征宇

    2011-01-01

    近期,中国贵州省罗甸县发现了一种新的软玉矿。为了验证贵州罗甸软玉的矿物组成,采用ICP-MS,XRD及FTIR等测试仪器对该软玉样品进行了测试与研究。结果表明,贵州罗甸软玉主要由透闪石组成,含少量的方解石细脉及燧石团块;其折射率、密度与标准的透闪石接近,但普遍略低于新疆和田玉的。为了进一步评估贵州罗甸软玉的质地,运用SEM观测其显微结构,揭示其透闪石主要呈纤维状、柱状和片状变晶结构,晶粒(片)粒度小,结构细腻,具有较好的加工性能。XRD慢速扫描结果显示,贵州罗甸软玉中透闪石矿物的结晶度相对较高,推测可能与其相对稳定的结晶环境有关。%A new kind of nephrite deposit has been discovered in Luodian County,Guizhou Province recently.In order to verify the mineral components of the nephrite from Luodian,Guizhou Province,this paper investigates this kind of nephrite samples by using the ICP-MS,XRD and FTIR.The results show that the nephrite from Luodian,Guizhou Province is mainly composed of tremolite with minor calcite veins and glaebule chert.The refractive index and density of the nephrite samples,quite close to those of the standard tremolite,are generally lower than those of the nephrite from Hetian,Xinjiang.Based on the SEM observation,the tremolite in the nephrite samples from Luodian,Guizhou Province has fibrous texture,columnar texture and sheet-like texture.The characteristics of fine grains and compact structure make the nephrite samples have good process properties.The result of XRD slow scanning shows that the crystallinity of the tremolite in the nephrite samples from Luodian,Guizhou Province is comparatively high,which are probably related with a stable crystalline environment.

  17. Seepage carbonate mounds in Cenozoic sedimentary sequences from the Las Minas Basin, SE Spain

    Science.gov (United States)

    Pozo, M.; Calvo, J. P.; Scopelliti, G.; González-Acebrón, L.

    2016-04-01

    A number of carbonate mounds composed of indurate, strongly folded and/or brecciated calcite and dolomite beds occur interstratified in Cenozoic sedimentary sequences from the Las Minas Basin. Part of the fabric of the rock forming the carbonate mounds is composed of laminated to banded dolostone similar to the host rock but showing contrasted lithification. Moreover, the carbonate deposits of the mounds display aggrading neomorphism of dolomite, partial replacement of dolomite by calcite, calcite cementation, and extensive silicification, locally resulting in box-work fabric. Eight main lithofacies were distinguished in the carbonate mound deposits. In some lithofacies, chert is present as both microcrystalline to fibro-radial quartz and opal, the latter occurring mainly as cement whereas the former replace the carbonate and infill voids. Yet one of the carbonate mounds shows distinctive petrography and geochemical features thus suggesting a distinctive growth pattern. The carbon isotope compositions of calcite from the mound samples range from - 11.56 to - 5.15 δ‰ whilst dolomite is depleted in 13C, with values of - 12.38 to 3.02 δ‰. Oxygen isotopic compositions vary from - 9.42 to - 4.64 δ‰ for calcite and between - 6.68 and 8.19 δ‰ for dolomite. Carbonate in the mounds shows significant enrichment in Co, Cr, Ni and Pb content, especially in the strongly deformed (F-2-2 lithofacies) and brecciated carbonate (F-4). The carbonate deposits show depletion in REE and Y in contrast to that determined in lutite. The formation of the carbonate mounds was related to local artesian seepage thermal water flows of moderate to relative high temperatures. Pressure differences between the low permeability host rock and the circulating fluids accounted for dilational fracturing and brecciation of the host sediment packages, which combined with precipitation of new carbonate and silica mineral phases. Locally, some carbonate mounds developed where groundwater

  18. Hydrogeological assessment based on ground water flow modeling around Atbara town

    International Nuclear Information System (INIS)

    Study area lies in the River Nile state North Central of Sudan between latitudes 17o 34 - 18o 00 N and longitudes 33o 55 - 34o 43 E. The geological settings of the study area are composed of pre-Cambrian Basement Complex, upper Cretaceous Nubian sandstone formation, Oligocene Hudi Chert, and quaternary superficial deposits in ascending order. Generally there are two main aquifers: shallow or upper aquifer in the alluvial deposits (5 - 37 m thick) and deep or lower aquifer in cretaceous Nubian sand stone (17 - 60 m). The upper aquifer is semi confined, whereas, the lower aquifer is almost confined except in the area around Atbara Town. Hydraulic conductivities of the aquifer varies between 1.89 x 10-1 to 8.95 x 10-1 m/min. Most of the water quality in the study area is suitable for domestic, agriculture, and industrial used with the exception of small pockets at Atbara town and some village in West of study area where salinity and contaminations were detected. Generally most of water quality in the study area is fit for human consumption. The ground water flow model of the study area was constricted using 40 column, 50 rows and 3 layers, forming 6000 cells covering the model domain. The model was calibrated using 3D Finite difference visual MODFLOW. The model calibration criteria such as mean absolute error (MAE), root mean square error (RMS) and mass balance error of water into and of out of the system were adjusted to less 1.3, 1.6 m, and 2.5% respectively. The contour maps of the simulated heads produced by visual MODFLOW show fair similarity with the contour map drawn using initial heads which confirm the reliability of Visual MODFLOW application and acceptable model calibration for the problem. As the result of model prediction, the calibration seemed to be more acceptable with average (RMS) of 2.5 m and average absolute mean error (AM) of 1.38 m and average normalized root mean square (NRMS) of (2.02%). Prediction results reflect the increasing of drawdown

  19. The Alta Stock, Utah: An Exemplar Rock Suite for Learning Metamorphic Concepts

    Science.gov (United States)

    Davidson, C.; Haileab, B.

    2003-12-01

    Using rock suites in a discovery-based setting is a terrific way to learn important petrologic processes and concepts such as the role of fluids during metamorphism, phase equilibrium, and metastability to name just a few. A particularly effective rock suite we use in our petrology course is from the contact aureole of the Tertiary Alta stock in Utah. The intrusion of the Alta stock into Paleozoic dolostone containing chert nodules produced a well-defined contact metamorphic aureole that includes talc-, tremolite-, forsterite-, and periclase-in field isograds (Cook and Bowman, 2000). Students work in free-form groups with collaboration between groups to define the mineral assemblages using hand samples and thin sections from throughout the areole and then work out what they think are the important petrologic processes that worked together to form what they see. The main goals of the exercise include: 1) learning to identify mineral assemblages common to metamorphosed siliceous dolostones; 2) learning to infer metamorphic reactions from progressive changes in mineral assemblages; 3) being able to identify balanced metamorphic reactions responsible for isograds mapped in the field; 4) begin to develop an understanding of how bulk composition and fluid composition controls mineral assemblages; and 5) learning how to infer the temperature and fluid composition evolution of the Alta stock aureole based on published T-X(CO2)diagrams. This suite is particularly effective because all the important minerals the students observe in thin section can be defined by the easy to plot and understand CaO-MgO-SiO2 system. This offers the opportunity to introduce (or reinforce) the concept of plotting minerals in composition space, using the phase rule to define the variance of your system, using tie lines to define stable mineral assemblages, and the flipping of tie lines to produce univariant reactions. In addition, the students work out the topology of these reactions in P-T space

  20. Jurassic metabasic rocks in the Kızılırmak accretionary complex (Kargı region, Central Pontides, Northern Turkey)

    Science.gov (United States)

    Çelik, Ömer Faruk; Chiaradia, Massimo; Marzoli, Andrea; Özkan, Mutlu; Billor, Zeki; Topuz, Gültekin

    2016-03-01

    The Kızılırmak accretionary complex near Kargı is tectonically bounded by the Jurassic and Early Cretaceous metamorphic massives of the Central Pontides. It consists mainly of serpentinite, serpentinized peridotite, gabbro, basalt, metabasite and deep-marine sedimentary rocks. The metabasites in the Kızılırmak accretionary complex are tectonically located within a serpentinite, radiolarian chert, spilitized basalt, gabbro association and commonly display a steep contact with serpentinites. Amphiboles from metabasites yielded robust 40Ar/39Ar plateau ages ranging between 159.4 ± 0.4 Ma and 163.5 ± 0.8 Ma. These are interpreted as cooling ages of the metabasites. The metabasites have 87Sr/86Sr(i) between 0.7035 and 0.7044 and 206Pb/204Pb(i) ranging between 18.18 and 18.92. The gabbros have higher 87Sr/86Sr(i) between 0.7044 and 0.7060 and 206Pb/204Pb(i) ranging between 17.98 and 18.43. Three basalt samples display 87Sr/86Sr(i) between 0.7040 and 0.7059. Their 206Pb/204Pb(i) are unrealistically low (15.42 and 15.62), suggesting, most likely, Pb loss which results in over-corrected values for decay through time. Pb-Sr-Nd isotopic compositions for all samples consistently plot between the fields of MORB or the Depleted MORB Mantle reservoirs and enriched mantle reservoirs (EMII rather than EMI). All the samples (except one dolerite dike) have negative ɛNdDM(t = 160 Ma) values, suggesting derivation from a reservoir more enriched than the depleted mantle. The protoliths of metabasites correspond to diverse sources (N-MORB, E-MORB, OIB and IAT) based on whole rock major and trace element composition. An IAT-like protolith for the metabasites indicates that the İzmir-Ankara-Erzincan ocean domain was subducting and the tectonic regime was compressional during Late Jurassic and before. The protoliths of these rocks were metamorphosed during the subduction/accretion processes, as observed in the metamorphic rocks located along the Balkan, Northern Turkey and

  1. Evolution of the African continental crust as recorded by U-Pb, Lu-Hf and O isotopes in detrital zircons from modern rivers

    Science.gov (United States)

    Iizuka, Tsuyoshi; Campbell, Ian H.; Allen, Charlotte M.; Gill, James B.; Maruyama, Shigenori; Makoka, Frédéric

    2013-04-01

    To better understand the evolutionary history of the African continental crust, a combined U-Pb, Lu-Hf and O isotopic study has been carried out by in situ analyses of approximately 450 detrital zircon grains from the Niger, Nile, Congo, Zambezi and Orange Rivers. The U-Pb isotopic data show age peaks at ca. 2.7, 2.1-1.8, 1.2-1.0, ca. 0.8, 0.7-0.5 and ca. 0.3 Ga. These peaks, with the exception of the one at ca. 0.8 Ga, correspond with the assembly of supercontinents. Furthermore, the detrital zircons that crystallized during these periods of supercontinent assembly have dominantly non-mantle-like O and Hf isotopic signatures, in contrast to the ca. 0.8 Ga detrital zircons which have juvenile characteristics. These data can be interpreted as showing that continental collisions during supercontinent assembly resulted in supermountain building accompanied by remelting of older continental crust, which in turn led to significant erosion of young igneous rocks with non-mantle-like isotopic signatures. Alternatively, the data may indicate that the major mode of crustal development changed during the supercontinent cycle: the generation of juvenile crust in extensional settings was dominant during supercontinent fragmentation, whereas the stabilization of the generated crust via crustal accretion and reworking was important during supercontinent assembly. The Lu-Hf and O isotope systematics indicate that terreigneous sediments could attain elevated 18O/16O via prolonged sediment-sediment recycling over long crustal residence time, and also that reworking of carbonate and chert which generally have elevated 18O/16O and low Hf contents is minor in granitoid magmatism. The highest 18O/16O in detrital zircon abruptly increased at ca. 2.1 Ga and became nearly constant thereafter. This indicates that reworking of mature sediments increased abruptly at that time, probably as a result of a transition in the dynamics of either granitoid crust formation or sedimentary evolution

  2. Controls on accretion of flysch and melange belts at convergent margins: evidence from the Chugach Bay thrust and Iceworm melange, Chugach accretionary wedge, Alaska

    Science.gov (United States)

    Kusky, T.M.; Bradley, D.C.; Haeussler, P.J.; Karl, S.

    1997-01-01

    Controls on accretion of flysch and melange terranes at convergent margins are poorly understood. Southern Alaska's Chugach terrane forms the outboard accretionary margin of the Wrangellia composite terrane, and consists of two major lithotectonic units, including Triassic-Cretaceous melange of the McHugh Complex and Late Cretaceous flysch of the Valdez Group. The contact between the McHugh Complex and the Valdez Group on the Kenai Peninsula is a tectonic boundary between chaotically deformed melange of argillite, chert, greenstone, and graywacke of the McHugh Complex and a less chaotically deformed melange of argillite and graywacke of the Valdez Group. We assign the latter to a new, informal unit of formational rank, the Iceworm melange, and interpret it as a contractional fault zone (Chugach Bay thrust) along which the Valdez Group was emplaced beneath the McHugh Complex. The McHugh Complex had already been deformed and metamorphosed to prehnite-pumpellyite facies prior to formation of the Iceworm melange. The Chugach Bay thrust formed between 75 and 55 Ma, as shown by Campanian-Maastrichtian depositional ages of the Valdez Group, and fault-related fabrics in the Iceworm melange that are cut by Paleocene dikes. Motion along the Chugach Bay thrust thus followed Middle to Late Cretaceous collision (circa 90-100 Ma) of the Wrangellia composite terrane with North America. Collision related uplift and erosion of mountains in British Columbia formed a submarine fan on the Farallon plate, and we suggest that attempted subduction of this fan dramatically changed the subduction/accretion style within the Chugach accretionary wedge. We propose a model in which subduction of thinly sedimented plates concentrates shear strains in a narrow zone, generating melanges like the McHugh in accretionary complexes. Subduction of thickly sedimented plates allows wider distribution of shear strains to accommodate plate convergence, generating a more coherent accretionary style

  3. A calibration of the triple oxygen isotope fractionation in the SiO2-H2O system and applications to natural samples

    Science.gov (United States)

    Sharp, Z. D.; Gibbons, J. A.; Maltsev, O.; Atudorei, V.; Pack, A.; Sengupta, S.; Shock, E. L.; Knauth, L. P.

    2016-08-01

    It is now recognized that variations in the Δ17O of terrestrial materials resulting from purely mass dependent fractionations, though small, have geological significance. In this study, the δ18O and δ17O values of selected low temperature quartz and silica samples were measured in order to derive the quartz-water fractionation-temperature relationship for the three oxygen isotope system. A 18O/16O quartz-water fractionation equation valid for all temperatures was generated from published high temperature exchange experiments and low temperature empirical estimates and is given by 1000ln αqz-H2O18O /16O = 4.20 (0.11) ×106/T2 - 3.3 (0.2) × 1000/T (T in Kelvins). The equilibrium δ17O-δ18O relationship is given by the equation lnα17O/16O = θlnα18O/16O . The variation of θ with temperature for the quartz-water system was determined empirically using low temperature marine diatoms, microcrystalline quartz and a modern sinter sample. A best fit to the data give the equation θSiO2 - H2O = -(1.85 ± 0.04)/T + 0.5305 , indistinguishable from an earlier theoretical estimate. Application of the quartz-water triple isotope system to low temperature samples provides constraints on both temperature and composition of the water with which the silica last equilibrated. Authigenic quartz crystallization temperatures cluster around 50 °C, which are lower than many previous estimates. The combined δ18O and δ17O values of samples considered to be in equilibrium with ocean or meteoric waters can be used to estimate both formation temperatures and the δ18O value of the meteoric water. Unlike other multiple isotopes systems, such as combined H and O isotopes in cherts, the oxygen source and diagenetic potential for both 17O/16O and 18O/16O ratios are identical, simplifying interpretations from ancient samples.

  4. The role of sedimentology, oceanography, and alteration on the δ56Fe value of the Sokoman Iron Formation, Labrador Trough, Canada

    Science.gov (United States)

    Raye, Urmidola; Pufahl, Peir K.; Kyser, T. Kurtis; Ricard, Estelle; Hiatt, Eric E.

    2015-09-01

    The Sokoman Formation is a ca. 100-m-thick succession of interbedded iron formation and fine-grained siliciclastics deposited at 1.88 Ga. Accumulation occurred on a dynamic paleoshelf where oxygen stratification, coastal upwelling of hydrothermally derived Fe and Si, microbial processes, tide and storm currents, diagenesis, and low-grade prehnite-pumpellyite metamorphism controlled lithofacies character and produced complex associations of multigenerational chert, hematite, magnetite, greenalite, stilpnomelane and Fe carbonate. Hematite-rich facies were deposited along suboxic segments of the coastline where photosynthetic oxygen oases impinged on the seafloor. Hematitic, cross-stratified grainstones were formed by winnowing and reworking of freshly precipitated Fe-(oxyhydr)oxide and opal-A by waves and currents into subaqueous dunes. Magnetite-rich facies contain varying proportions of greenalite and stilpnomelane and record deposition in anoxic middle shelf environments beneath an oxygen chemocline. Minor negative Ce anomalies in hematitic facies, but prominent positive Ce and Eu anomalies and high LREE/HREE ratios in magnetite-rich facies imply the existence of a weakly oxygenated surface ocean above anoxic bottom waters. The Fe isotopic composition of 31 whole rock (-0.46 ⩽ δ56Fe ⩽ 0.47‰) and 21 magnetite samples (-0.29 ⩽ δ56Fe ⩽ 0.22‰) from suboxic and anoxic lithofacies was controlled primarily by the physical oceanography of the paleoshelf. Despite low-grade metamorphism recorded by the δ18O values of paragenetically related quartz and magnetite, the Sokoman Formation preserves a robust primary Fe isotopic signal. Coastal upwelling is interpreted to have affected the isotopic equilibria between Fe2+aq and Fe-(oxyhydr)oxide in open marine versus coastal environments, which controlled the Fe isotopic composition of lithofacies. Unlike previous work that focuses on microbial and abiotic fractionation processes with little regard for

  5. Mineralogical controls on surface colonization by sulfur-metabolizing microbial communities

    Science.gov (United States)

    Jones, A. A.; Bennett, P.

    2012-12-01

    When characterizing microbial diversity and the microbial ecosystem of the shallow subsurface the mineral matrix is generally assumed to be homogenous and unreactive. We report here experimental evidence that microorganisms colonize rock surfaces according to the rock's chemistry and the organism's metabolic requirements and tolerances. We investigated this phenomenon using laboratory biofilm reactors with both a pure culture of sulfur-oxidizing Thiothrix unzii and a mixed environmental sulfur-metabolizing community from Lower Kane, Cave, WY, USA. Reactors contained rock and mineral chips (calcite, albite, microcline, quartz, chert, Madison Limestone (ML), Madison Dolostone (MD), and basalt) amended with one of the two inoculants. Biomass of attached microorganisms on each mineral surface was quantified. The 16S rRNA of attached microbial communities were compared using Roche FLX and Titanium 454 next generation pyrosequencing. A primary controlling factor on taxonomy of attached microorganisms in both pure and mixed culture experiments was mineral buffering capacity. In mixed culture experiments acid-buffering carbonates were preferentially colonized by neutrophilic sulfur-oxidizing microorganisms (~18% to ~27% of microorganisms), while acidophilic sulfur-oxidizing microorganisms colonized non-buffering quartz exclusively (~46% of microorganisms). The nutrient content of the rock was a controlling factor on biomass accumulation, with neutrophilic organisms selecting between carbonate surfaces of equivalent buffer capacities according to the availability of phosphate. Dry biomass on ML was 17.8 ± 2.3 mg/cm2 and MD was 20.6 ± 6.8 mg/cm2; while nutrient poor calcite accumulated 2.4 ± 0.3 mg/cm2. Biomass accumulation was minimal on non-buffering nutrient-limited surfaces. These factors are countered by the competitive exclusion of some populations. A pure culture of T. unzii preferentially colonizes carbonates while a very closely related Thiothrix spp is excluded

  6. Authigenic carbonate precipitation at the end-Guadalupian (Middle Permian) in China: Implications for the carbon cycle in ancient anoxic oceans

    Science.gov (United States)

    Saitoh, Masafumi; Ueno, Yuichiro; Isozaki, Yukio; Shibuya, Takazo; Yao, Jianxin; Ji, Zhansheng; Shozugawa, Katsumi; Matsuo, Motoyuki; Yoshida, Naohiro

    2015-12-01

    Carbonate precipitation is a major process in the global carbon cycle. It was recently proposed that authigenic carbonate (carbonate precipitated in situ at the sediment-water interface and/or within the sediment) played a major role in the carbon cycle throughout Earth's history. The carbon isotopic composition of authigenic carbonates in ancient oceans have been assumed to be significantly lower than that of dissolved inorganic carbon (DIC) in seawater, as is observed in the modern oceans. However, the δ13Ccarb values of authigenic carbonates in the past has not been analyzed in detail. Here, we report authigenic carbonates in the uppermost Guadalupian (Middle Permian) rocks at Chaotian, Sichuan, South China. Monocrystalline calcite crystals black mudstone/chert sequence that was deposited on a relatively deep anoxic slope/basin along the continental margin. Textures of the crystals indicate in situ precipitation on the seafloor and/or within the sediments. The calcite precipitation corresponds stratigraphically with denitrification and sulfate reduction in the anoxic deep-water mass, as indicated by previously reported nitrogen and sulfur isotope records, respectively. Relatively high δ13Ccarb values of the authigenic carbonates (largely -1 ‰) compared with those of organic matter in the rocks (ca. -26 ‰) suggest that the main carbon source of the carbonates was DIC in the water column. The calcite crystals precipitated in an open system with respect to carbonate, possibly near the sediment-water interface rather than deep within the sediments. The δ13Ccarb values of the carbonates were close to the δ13CDIC value of seawater due to mixing of 13C-depleted remineralized organic carbon (that was released into the water column by the water-mass anaerobic respiration) with the large DIC pool in the oceans. Our results imply that δ13Ccarb values of authigenic carbonates in the anoxic oceans might have been systematically different from the values in the oxic

  7. A modern vs. Permian black shale - the hydrography, primary productivity, and water-column chemistry of deposition

    Science.gov (United States)

    Piper, D.Z.; Perkins, R.B.

    2004-01-01

    The sediment currently accumulating in the Cariaco Basin, on the continental shelf of Venezuela, has an elevated organic-carbon content of approximately 5%; is accumulating under O2-depleted bottom-water conditions (SO42- reduction); is composed dominantly of foraminiferal calcite, diatomaceous silica, clay, and silt; and is dark greenish gray in color. Upon lithification, it will become a black shale. Recent studies have established the hydrography of the basin and the level of primary productivity and bottom-water redox conditions. These properties are used to model accumulation rates of Cd, Cr, Cu, Mo, Ni, V, and Zn on the seafloor. The model rates agree closely with measured rates for the uppermost surface sediment.The model is applied to the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, a phosphate deposit of Permian age in the northwest United States. It too has all of the requisite properties of a black shale. Although the deposit is a world-class phosphorite, it is composed mostly of phosphatic mudstone and siltstone, chert, limestone, and dolomite. It has organic-carbon concentrations of up to 15%, is strongly enriched in several trace elements above a terrigenous contribution and is black. The trace-element accumulation defines a mean primary productivity in the photic zone of the Phosphoria Basin as moderate, at 500 g m-2 year-1 organic carbon, comparable to primary productivity in the Cariaco Basin. The source of nutrient-enriched water that was imported into the Phosphoria Basin, upwelled into the photic zone, and supported primary productivity was an O2 minimum zone of the open ocean. The depth range over which the water was imported would have been between approximately 100 and 600 m. The mean residence time of bottom water in the basin was approximately 4 years vs. 100 years in the Cariaco Basin. The bottom water was O2 depleted, but it was denitrifying, or NO3- reducing, rather than SO42- reducing. Published by Elsevier B.V.

  8. Biomarkers in Archaean banded iron formations : examples from Pilbara and Dhawar Craton

    Science.gov (United States)

    Orberger, B.; Pinti, D. L.; Cloquet, C.; Hashizume, K.; Soyama, H.; Jayananda, M.; Wirth, R.; Gallien, J. P.; Massault, M.; Rouchon, V.

    The origin of Archeaen banded iron formations (BIF) and the role of biosphere in Fe precipitation is still highly debated. In order to elucidate these processes, detailed mineralogical and textural analyses combined with δ 15 N, δ 56 Fe and δ 13 C data were obtained on Fe-oxide bands from Marble Bar chert Unit (MB, 3.46 Ga, Pilbara craton, W. Australia) and a BIF from the Bababudan Group (BG, 2.7-2.9 Ga, Dhawar Craton, Southern India). Both samples are composed of alternating quartz and Feoxide bands with wavy micro-textures. CI-normalized REE patterns show that MB reflects hydrothermal fluid/basalt interactions, while BG precipitated from a hydrothermal fluid/seawater mixture. In MB, nano-cristalline hematite replaced magnetite, Mgcalcite and Fe-sulfides producing a matlike surface, preserving nanometric N-bearing amorphous carbon nodules. Measured C/N ratios (2.3 to 52) are typical of Precambrian organic matter. The δ 56 Fe of -0.40±0.02% suggests MOR-hydrothermal fluids as a Fe-source, while a δ 15 N of +7.4±0.4% is compatible with nitrification- denitrification processes and δ 13 C of -19.9±0.1% support an organic origin. BG is composed of intergrown magnetite and hematite. Disseminated grunerite and magnetite grew during low T metamorphism. Fe-oxide spherules compose vermicular- filaments that nucleated perpendicular to quartz surfaces. Fe-oxide spherule bunches are perfectly preserved in the silica bands forming micrometric mats, which contain heterogeneously distributed N (˜0.09at.%) and C (0.51 at.%, C/N=5.73). Bulk δ 13 C of -15.35%±0.10 points to an organic origin for C. The ?56 Fe in Fe and Si layers (0.75% to 2.16%) is compatible with a chemical precipitation for BIF. A negative correlation between ?56 Fe and the Th/U ratio suggests that Fe isotopic variations are related to fluid circulation and re-precipitation of Fe-oxides. High ?15 N, on one Feoxide layer, of +21.8±0.7%, corresponds to that observed for Archeaen BIFs and may be related

  9. The Aromatic Carotenoids in the Organic Matter of the Devonian Domanic Formation (on example of Tatarstan territory)

    Science.gov (United States)

    Plotnikova, Irina; Nosova, Fidania; Ostroukhov, Sergey; Pronin, Nikita

    2015-04-01

    This report contains the results of the studies of shale hydrocarbons (HC) from carbonate-siliceous rocks on the territory of Melekess depressoin and South-Tatar arch of Volga-Ural oil and gas province of the East European Platform. Studies were performed in the laboratory of Geochemistry of Combustible Minerals at the Institute of Geology and Petroleum Technology of the Kazan Federal University. The main object of this study is Domanicoid high-TOC rocks of Devonian time. They are mainly represented by dark gray, almost black bituminous limestones that are interbedded with calcareous siliceous shales and cherts. Complex studies include the following: - extraction of bitumen from the rock, - determination of organic carbon content, - determination of the group and elemental composition of the bitumen, - gas chromatographic studies of the alkanoic lube fractions of bitumoid and oil, - gas chromato-mass spectrometry of the naphthenic lube fractions of bitumoid and oil, - isotopic studies of bitumens and oils, - pyrolysis studies of the rock using the Rock -Eval method (before and after extraction), - study of trace-element composition of the rocks and petrologen, comparison in terms of adsorbed gas and studying of the composition of adsorbed gases. Simultaneously with the study of standard and generally accepted biomarkers, deep and detailed study of alkyl toluene, aromatic hydrocarbons (and aromatic carotenoids in particular) were conducted. The comparison and comparative correlation aromatic carotenoids with standard biomarkers (for example, with hopanes C30 and steranes C27:C28:C29). Attitude hopane/aromatic carotenoids is 0.05. This testifies to the dominance of the transformation of carotenoid compounds on bacterial activity in the water column. Bacterial activity in the studied samples is also high. Attitude steranes C29/aromatic carotenoids reaches 10-3. The study of aromatic carotenoids has allowed first in the region of Tatarstan to get a new information on

  10. A calibration of the triple oxygen isotope fractionation in the SiO2-H2O system and applications to natural samples

    Science.gov (United States)

    Sharp, Z. D.; Gibbons, J. A.; Maltsev, O.; Atudorei, V.; Pack, A.; Sengupta, S.; Shock, E. L.; Knauth, L. P.

    2016-08-01

    It is now recognized that variations in the Δ17O of terrestrial materials resulting from purely mass dependent fractionations, though small, have geological significance. In this study, the δ18O and δ17O values of selected low temperature quartz and silica samples were measured in order to derive the quartz-water fractionation-temperature relationship for the three oxygen isotope system. A 18O/16O quartz-water fractionation equation valid for all temperatures was generated from published high temperature exchange experiments and low temperature empirical estimates and is given by 1000ln αqz-H2O 18O /16O =4.20 (0.11) ×106/T2 - 3.3 (0.2) × 1000/T (T in Kelvins). The equilibrium δ17O-δ18O relationship is given by the equation lnα17O/16O = θlnα18O/16O . The variation of θ with temperature for the quartz-water system was determined empirically using low temperature marine diatoms, microcrystalline quartz and a modern sinter sample. A best fit to the data give the equation θSiO2-H2O = -(1.85 ± 0.04)/T + 0.5305 , indistinguishable from an earlier theoretical estimate. Application of the quartz-water triple isotope system to low temperature samples provides constraints on both temperature and composition of the water with which the silica last equilibrated. Authigenic quartz crystallization temperatures cluster around 50 °C, which are lower than many previous estimates. The combined δ18O and δ17O values of samples considered to be in equilibrium with ocean or meteoric waters can be used to estimate both formation temperatures and the δ18O value of the meteoric water. Unlike other multiple isotopes systems, such as combined H and O isotopes in cherts, the oxygen source and diagenetic potential for both 17O/16O and 18O/16O ratios are identical, simplifying interpretations from ancient samples.

  11. Copper Metallogenic Conditions and Prospecting Direction of Zoumadi Ore Block of Wuding County%武定县走马地矿段铜矿成矿条件及找矿方向

    Institute of Scientific and Technical Information of China (English)

    宋禹霖; 范柱国; 宋尚鑫

    2014-01-01

    武定地区区域矿产资源极丰富,矿区经过40多年的勘查,共发现各类矿点百余个,综合研究表明,武定县平地耀左所铜矿床类型以“东川式”铜矿最重要,分布在金钟罩、鸡冠山、油基田、周家箐、走马地、黄龙河、牛德庄等地;次为稀矿山式,主要在蒿枝地,走马地等地。“东川式”铜矿:落雪组底部过渡层,“稀矿山式”铁铜矿:因民组下部,同生断裂旁侧,古火山机构中的火山洼地,火山旋回的中上部,富含Na2O的细碧角斑岩系,硅质岩、萤石岩、钠长岩等喷流岩以及黑云母、绿泥石火山凝灰岩的分布区。%Regional mineral resources of Wuding region are extremely rich, after 40 years of mining exploration, all kinds of hundred mines were found. Comprehensive studies show that, "Dongchuan style" copper mine is the most important mine in Wuding Pingdi-Zuosuo copper deposits, which located in Jinzhongzhao, Jiguanshan, oil-based fields, Zhoujiaqing, Zoumadi, Huanglong River, Niudezhuang etc.;Dilute mine type is the second important, mainly in Artemisia sticks, Zoumadi and other places. "Dongchuan style" copper mine: bottom snow group buffer layer; "dilute mine type" iron-copper: due to the lower part of the public group, contemporaneous faults flanking the ancient volcano volcanic depressions institutions, volcanic cycles in the upper rich Na2O of spilite porphyry system, chert, fluorite rock, rock and other jet albite rock and biotite, chlorite volcanic tuff distribution.

  12. Endeavor research into evolving paradigms around ophiolites: the case of the oceanic igneous complexes of Costa Rica

    International Nuclear Information System (INIS)

    Studies on the radiolarite igneous (ophiolitic) complexes were done for more than one century in Costa Rica that range from Jurassic to Eocene. These studies can be grouped in four stages of knowledge: 1) from 1904 to 1957 were recognized the cherts, and the mafic and ultramafic igneous complexes, the first regional maps were done, and the first time were recognized ellipsoidal basalts, now widely known as pillow lavas. 2) From 1958 to 1978 the complexes were seen under the concept of the association of ophiolites (serpentine, gabbro, diabase, basalts, and related rocks) and interpreted the radiolarites as deep-sea sediments. The stage is characterized by the seminal work of Gabriel Dengo and by the first geochemical analyses in the framework of the plate tectonics. 3) A huge amount of geochemical data, paleontological and K/Ar ages were published from 1979 to 1994 and it was the stage of more controversial papers, their interpretation varied for the same locality (i.e. (Nicoya Peninsula) from relative simple stratigraphic model to a very complex nappe slices, and from a simple tectonic evolution (in situ and formed by a mid oceanic ridge volcanism) to a multistage evolution (terrains, and mid oceanic ridge, aseismic ridge, intraplate and island arc volcanism). The situation was similar in the other Costa Rican oceanic complexes. 4) The outlook for 1995 to the present it has been clarified and mutual agreement between the different groups. The stage is characterized by joint collaboration, the use of modern laboratory techniques as Sr, Nd, and Pb isotopes, major, trace and complete rare earth elements. 40Ar/39Ar dating, and volcanological criteria, together with detailed field mapping. The main new result of these studies was that the radiolarites (164-84 Ma) in the Nicoya Peninsula were significatively older than the basic igneous rocks (140-84 Ma), indicating a complex magmatic event intruding and erupting into the thick sedimentary sequence. For other areas

  13. An open marine record of the Toarcian oceanic anoxic event

    Directory of Open Access Journals (Sweden)

    D. R. Gröcke

    2011-04-01

    Full Text Available Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic-rich sediments (black shales and significant perturbations in the global carbon cycle. The expression of these perturbations is globally recorded in sediments as excursions in the carbon isotope record irrespective of lithology or depositional environment. During the Early Toarcian, black shales were deposited on the epi- and peri-continental shelves of Pangaea and these sedimentary rocks are associated with a pronounced (ca. 7‰ negative (organic carbon isotope excursion (CIE which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the Early Toarcian is thought to represent an oceanic anoxic event (the T-OAE. Associated with this event, there were pronounced perturbations in global weathering rates and seawater temperatures. Although it is commonly asserted that the T-OAE is a global event and that the distribution of black shales is likewise global, an isotopic and/or organic-rich expression of this event has as yet only been recognized on epi- and peri-continental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg of Early Toarcian cherts from Japan that were deposited in the open Panthalassa Ocean was analysed. The results show the presence of a major (>6‰ negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the Early Toarcian negative CIE known from European epicontinental strata. Furthermore, a secondary ca. −2‰ excursion in δ13Corg is also recognized lower in the studied succession that, within the current biostratigraphical resolution, is likely to represent the excursion that occurs close to the Pliensbachian/Toarcian boundary and which is also recorded in European epicontinental successions

  14. Was the Palaeo-Tethys Responsible for Ending the Palaeozoic?

    Science.gov (United States)

    Sengor, A. C.; Atayman, S.

    2008-12-01

    -Tethys) life continued normally, where, for example, no chert gap developed. Most nectonic organisms (for example the fishes) escaped the great killing most likely by migrating to Panthalassa. The analysis of the Permian conditions indicate that regional geology must form the basis of the studies of the history of the biosphere and any hypothesis based on few stratigraphic sections or on few taxa is unlikely to yield a correct picture of life at any given time in the past of the earth.

  15. Geochemical Features of Shale Hydrocarbons of the Central Part of Volga-Ural Oil and Gas Province

    Science.gov (United States)

    Nosova, Fidania F.; Pronin, Nikita V.; Plotnikova, Irina N.; Nosova, Julia G.

    2014-05-01

    This report contains the results of the studies of shale hydrocarbons from carbonate-siliceous rocks on the territory of South-Tatar arch of Volga-Ural oil and gas province of the East European Platform. The assessment of the prospects of shale hydrocarbon in Tatarstan primarily involves finding of low permeable, poor-porous shale strata that would be rich in organic matter. Basing on the analysis of the geological structure of the sedimentary cover, we can distinguish three main objects that can be considered as promising targets for the study from the point of the possible presence of shale hydrocarbons: sedimentary deposits Riphean- Vendian; Domanicoid high-carbon rocks of Devonian time; sedimentary strata in central and side areas of Kama-Kinel deflection system. The main object of this study is Domanicoid high-carbon rocks of Devonian time. They are mainly represented by dark gray, almost black bituminous limestones that are interbedded with calcareous siliceous shales and cherts. Complex studies include the following: extraction of bitumen from the rock, determination of organic carbon content, determination of the group and elemental composition of the bitumen, gas chromatographic studies of the alkanoic lube fractions of bitumoid and oil, gas chromato-mass spectrometry of the naphthenic lube fractions of bitumoid and oil, pyrolysis studies of the rock using the Rock -Eval method (before and after extraction), study of trace-element composition of the rocks and petrologen, comparison in terms of adsorbed gas and studying of the composition of adsorbed gases. Group and elemental analyses showed that hydrocarbons scattered in the samples contain mainly resinous- and asphaltene components, the share lube fraction is smaller. The terms sediment genesis changed from weakly to strongly reducing. According to the results of gas chromatography, no biodegradation processes were observed. According to biomarker indicators in the samples studied there is some certain

  16. Selenium in Paleozoic stone coal (carbonaceous shale) as a significant source of environmental contamination in rural southern China

    Science.gov (United States)

    Belkin, H. E.; Luo, K.

    2012-04-01

    Selenium occurs in high concentrations (typically > 10 and up to 700 ppm) in organic-rich Paleozoic shales and cherts (called "stone coal" - shíméi), in southern China. Stone coals are black shales that formed in anoxic to euxinic environments and typically contain high concentrations of organic carbon, are enriched in various metals such as V, Mo, Pb, As, Cr, Ni, Se, etc., and are distinguished from "humic" coal in the Chinese literature. We have examined stone coal from Shaanxi, Hubei, and Guizhou Provinces, People's Republic of China and have focused our study on the mode of occurrence of Se and other elements (e.g. As, Pb, etc.) hazardous to human health. Scanning electron microscope, energy-dispersive analysis and electron microprobe wave-length dispersive spectroscopy were used to identify and determine the composition of host phases observed in the stone coals. Native selenium, Se-bearing pyrite and other sulfides are the hosts for Se, although we cannot preclude an organic or clay-mineral association. Stone coals are an important source of fuel (reserves over 1 billion tonnes), both domestically and in small industry, in some rural parts of southern China and present significant environmental problems for the indigenous population. The stone coals create three main environmental problems related to Se pollution. First, the residual soils formed on stone coal are enriched in Se and other metals contained in the stone coals and, depending on the speciation and bioavailability of the metals, may enrich crops and vegetation grown on them. Second, weathering and leaching of the stone coal contaminates the local ground water and/or surface waters with Se and other metals. Third, the local population uses the stone coal as a source of fuel, which releases the more volatile elements (Se and As) into the atmosphere in the homes. The ash will be extremely enriched with the balance of the heavy metal suite. Disposal of the ash on agricultural lands or near water

  17. Petrography and mineral chemistry of wehrlites in contact zone of gabbro intrusions and mantle peridotites of the Naein ophiolite

    Directory of Open Access Journals (Sweden)

    Farhad Ghaseminejad

    2014-10-01

    Full Text Available Introduction Geological background Ophiolites have played a major role in our understanding of Earth’s processes ranging from seafloor spreading, melt evolution and magma transport in oceanic spreading centers, and hydrothermal alteration and mineralization of oceanic crust to collision tectonics, mountain building processes, and orogeny. They provide the essential structural, petrological, geochemical, and geochronological evidence to document the evolutionary history of ancient continental margins and ocean basin. Ophiolites include a peridotitic mantle sequence, generally characterized by high-temperature plastic deformation and residual chemistry, and a comagmatic crustal sequence (gabbros, diabase dikes, and submarine basalts, weakly or not deformed. According to this interpretation, ophiolites were allochthonous with respect to their country rocks. They were assembled during a primary accretion stage at an oceanic spreading center, and later tectonically emplaced on a continental margin or island arc (Dilek, 2003. The indigenous dikes of pyroxenites and gabbros that were injected into a melting peridotite, or intrusive dikes of pyroxenite and gabbro that injected when the peridotite was fresh and well below its solidus, are discussed in different ophiolite papers. Pyroxenite formation and contact of gabbro and mantle peridotite are discussed in different articles (Dilek, 2003. When a gabbro intrude a fresh mantle peridotite could not significantly react with it, but if intrusion occurs during the serpentinization, the gabbro will change to rodingite. Geological setting The Naein ophiolitic melanges comprise the following rock units: mantle peridotites (harzburgite, lherzolite, dunite, with associated chromitite, gabbro, pyroxenite, sheeted and swarm dikes, massive basalts, pillow lava, plagiogranite, radiolarian chert, glaubotruncana limestone, rodingite, listvenite, and metamorphic rocks (foliated amphibolitic dike, amphibolite, skarn

  18. Petrología y geoquímica de una ritmita marga-caliza del Hemisferio Austral: El Miembro Los Catutos (Formación Vaca Muerta, Tithoniano medio de la Cuenca Neuquina Petrology and geochemistry of a limestone-marl rhythmite from the Southern Hemisphere: the Los Catutos Member (Vaca Muerta Formation, Middle Tithonian of Neuquén Basin

    Directory of Open Access Journals (Sweden)

    R. A. Scasso

    2002-06-01

    Full Text Available Una secuencia rítmica de margas y calizas de 25 m de espesor, correspondiente al Miembro Los Catutos (Formación Vaca Muerta, Jurásico superior de la Cuenca Neuquina, fue estudiada capa por capa en varias canteras cercanas a Zapala. Estratos de hasta un metro de espesor de calizas litográficas, masivas o laminadas, fosilíferas, a veces moteadas o débilmente bioturbadas (?Chondrites, se intercalan con bancos más delgados de margas. Las calizas y margas pueden clasificarse como pelbiomicritas y biopelmicritas, mayormente compuestas por pellets, radiolarios, foraminíferos, ostrácodos, equinoideos, espículas de esponjas y gastrópodos, con cantidades menores de peloides, feldespato, chert, muscovita, glauconita y colofano. Los valores de δ;;18O son muy probablemente resultado de modificaciones diagenéticas del sedimento original, pero el δ;;13C muestra buena coincidencia con los valores de las curvas de "agua de mar" publicadas para el Tithoniano y con el registro sedimentario en calizas del Tethys. Un análisis preliminar de las excursiones negativas de δ;;13C indican que pueden responder a crisis en la productividad del sistema con una periodicidad de 400 ka, acorde con cambios en la excentricidad de la órbita terrestre. La esmectita y los interestratificados componen principalmente la fracción menor de 2 micrones, como reflejo de procesos pedogenéticos desarrollados sobre rocas-madre volcanogénicas. La mayor abundancia de caolinita en las margas sería resultado de condiciones más húmedas en el continente. Las rocas muestran hasta un 1,95% de COT y configuran una roca madre de hidrocarburos regular a buena, aunque térmicamente inmadura. Se infiere un ambiente sedimentario de mar abierto, baja energía, disaeróbico, con altas tasas de sedimentación resultado de una alta productividad en la superficie sumada al aporte de plumas de material suspendido desde la zona litoral. Se propone una acumulación en forma de amplios

  19. The 3.26-3.24 Ga Barberton asteroid impact cluster: Tests of tectonic and magmatic consequences, Pilbara Craton, Western Australia

    Science.gov (United States)

    Glikson, Andrew; Vickers, John

    2006-01-01

    The location in the Barberton Greenstone Belt (Kaapvaal Craton) of ∼3.26-3.24 Ga asteroid impact ejecta units at, and immediately above, a sharp break between a > 12 km-thick mafic-ultramafic volcanic crust (Onverwacht Group ∼3.55-3.26 Ga, including the ∼3.298 > 3.258 Ga Mendon Formation) and a turbidite-felsic volcanic rift-facies association (Fig Tree Group ∼3.258-3.225 Ga), potentially represents the first documented example of cause-effect relations between extraterrestrial bombardment and major tectonic and igneous events [D.R. Lowe, G.R. Byerly, F. Asaro, F.T. Kyte, Geological and geochemical record of 3400 Ma old terrestrial meteorite impacts, Science 245 (1989) 959-962; D.R. Lowe, G.R. Byerly, F.T. Kyte, A. Shukolyukov, F. Asaro, A. Krull, Spherule beds 3.47-3.34 Ga-old in the Barberton greenstone belt, South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution, Astrobiology 3 (2003) 7-48; A.Y. Glikson, The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2 ± 0.1 Ga bombardment of the Earth-Moon system, J. Geodyn. 32 (2001) 205-229]. Here we correlate this boundary with a contemporaneous break and peak magmatic and faulting events in the Pilbara Craton, represented by the truncation of a 3.255-3.235 Ga-old volcanic sequence (Sulphur Springs Group-SSG) by a turbidite-banded iron formation-felsic volcanic association (Pincunah Hill Formation, basal Gorge Creek Group). These events are accompanied by ∼3.252-3.235 Ga granitoids (Cleland plutonic suite). The top of the komatiite-tholeiite-rhyolite sequence of the SSG is associated with a marker chert defined at 3.238 ± 3-3.235 ± 3 Ga, abruptly overlain by an olistostrome consisting of mega-clasts of felsic volcanics, chert and siltstone up to 250 × 150 m-large, intercalated with siliciclastic sedimentary rocks and felsic volcanics (Pincunah Hill Formation-basal Gorge

  20. Existencia de estructuras nodulosas de celestina afectadas por silicificación en el Valle de Losa (N. de Burgos

    Directory of Open Access Journals (Sweden)

    Elorza, J.

    1984-04-01

    Full Text Available The present work describes sorne nodules of celestite, which appear in a marly clay level of the Upper Cretaceous (Santonian in Losa Valley (North of Burgos. A great number of nodules have been in some extent, or totally pseudomorphized by quartzine and lutecite (length-slow chalcedony. These nodules have not been mentioned up to now in the research works carried out in the Basque Cantabric Basin; some nodules present elongated shapes, while some others are subspherical, In the inside, the radial arrangement shows pyramidal shapes with rhombic sections, emerging from a compact nucleus. These nodules are diagenetic structures growing expansively from the nucleus towards the periphery. In this action echinoid spines, pelecypods fragments, bryozoans, etc., are enclosed. Celestite here is highly pure; there is no barite at all. For the celestite ions the following origin in proposed. The sulphate was supplied by fluids which laterally migrate from the Triassic gypsum (Keuper. Sr seems to have been released along the transformation process of aragonite sediments to calcite. Although it can't be forgotten the amount of Sr furnished in the parcial dolomitization process suffered by the sedimentary sequence, In the same level, irregular cherts appear associated to celestite nodules. These cherts have a considerable amount of siliceous sponge spicules (litisteids? replaced by sparry carbonate what doubtless shows the biogenic origin of the silica. The silicification process has allowed the preservation of the nodules, in spite of the strong celestite solution which afterwards originated a great loss celestite.

    En el presente trabajo se describen unos nódulos de celestina que aparecen concentrados en un nivel de margas arcillosas pertenecientes al Cretácico superior (Santoniense del Valle de Losa (N. de Burgos. Gran parte de los nódulos se encuentran parcial o totalmente sustituidos por cuarzo en las formas fibrosas de cuarcina y lutecita

  1. Tracing source terranes using U-Pb-Hf isotopic analysis of detrital zircons: provenance of the Orhanlar Unit of the Palaeotethyan Karakaya subduction-accretion complex, NW Turkey

    Science.gov (United States)

    Ustaömer, Timur; Ayda Ustaömer, Petek; Robertson, Alastair; Gerdes, Axel

    2016-04-01

    Sandstones of the Late Palaeozoic-Early Mesozoic Karakaya Complex are interpreted to have accumulated along an active continental margin related to northward subduction of Palaeotethys. The age of deposition and provenance of the sandstones are currently being determined using radiometric dating of detrital zircons, coupled with dating of potential source terranes. Our previous work shows that the U-Pb-Hf isotopic characteristics of the sandstones of all but one of the main tectonostratigraphic units of the Karakaya Complex are compatible with a provenance that was dominated by Triassic and Permo-Carboniferous magmatic arc-type rocks, together with a minor contribution from Lower to Mid-Devonian igneous rocks (Ustaömer et al. 2015). However, one of the tectono-stratigraphic units, the Orhanlar Unit, which occurs in a structurally high position, differs in sedimentary facies and composition from the other units of the Karakaya Complex. Here, we report new isotopic age data for the sandstones of the Orhanlar Unit and also from an extensive, associated tectonic slice of continental metamorphic rocks (part of the regional Sakarya Terrane). Our main aim is to assess the provenance of the Orhanlar Unit sandstones in relation to the tectonic development of the Karakaya Complex as a whole. The Orhanlar Unit is composed of shales, sandstone turbidites and debris-flow deposits, which include blocks of Devonian radiolarian chert and Carboniferous and Permian neritic limestones. The sandstones are dominated by rock fragments, principally volcanic and plutonic rocks of basic-to-intermediate composition, metamorphic rocks and chert, together with common quartz, feldspar and mica. This modal composition contrasts significantly with the dominantly arkosic composition of the other Karakaya Complex sandstones. The detrital zircons were dated by the U-Pb method, coupled with determination of Lu-Hf isotopic compositions using a laser ablation microprobe attached to a multicollector

  2. Geologic history of the Neogene “Qena Lake” developed during the evolution of the Nile Valley: A sedimentological, mineralogical and geochemical approach

    Science.gov (United States)

    Philobbos, Emad R.; Essa, Mahmoud A.; Ismail, Mustafa M.

    2015-01-01

    Siliciclastic and carbonate sediments were laid down in southern Wadi Qena and around the Qena Nile bend (Middle Egypt) in a lacustrine-alluvial environment which dominated a relatively wide lake, the "Qena Lake" that interrupted the Nile course during the Neogene time. These sediments are represented mainly by the oldest dominantly lacustrine chocolate brown mudstones of the Khuzam Formation that accumulated nearer to the center of that lake (now forming a 185 m terrace above sea level), overlain by the dominantly lacustrine carbonates and marls of the Durri Formation which accumulated during semi-arid conditions, mainly nearer to the periphery of the lake (now forming 170, 180 and 185 m terraces a.s.l. in the studied sections). The water level of the "Qena Lake" reached 240 m. above sea level, as indicated by the maximum carbonate elevation reached in the region. Finally fanglomerates of the Higaza Formation with its chert and limestone conglomerates accumulated during torrential periods at higher elevations (forming 240, 300 and 400 m terraces a.s.l.). These three formations accumulated in this particular area before and during the unroofing of the basement rocks of the Eastern Desert, west of the watershed. According to the known Early Miocene initial development of the Nile Valley, beside the occurrence of similar deposits of Oligocene age along the eastern side of the basement range, the earlier known Pliocene age given for these sediments in the Qena area is here questioned. It might belong to earlier Miocene?-Pliocene times. As the basement rocks of the Eastern Desert were still covered by Cretaceous-Paleogene sedimentary rocks while the Khuzam, Durri and Higaza Formations were accumulating in the Qena Lake region, it is believed, contrary to the belief of some authors, that the basement rocks of the Eastern Desert were not the source of these sediments. The carbonate petrographic study, beside the X-ray, and the11 major oxides and 22 trace elements

  3. New geological data of New Siberian Archipelago

    Science.gov (United States)

    Sobolev, Nikolay; Petrov, Evgeniy

    2014-05-01

    -bearing unconformably overlies folded basement. The latter encompasses two sedimentary units: the Middle Devonian shallow-marine carbonate and Late-Devonian-Permian olistostrome - flysch deposited in transitional environment from carbonate platform to passive margin. Dating of detrital zircons suggests the Siberian Platform and Taimyr-Severnaya Zemlya areas as the most possible provenance. The magmatic activity on Belkovsky Island resulted in formation of Early Triassic gabbro-dolerite similar to the Siberian Platform traps. Proximity of Belkovsky Island to the north of Verkhoyansk foldbelt allows continuation of the latter into the Laptev Sea shelf. The geology of Bolshoy Lyakhovsky Island is discrepant from the rest of the NSA. In the south of Bolshoy Lyakhovsky Island the ophiolite crops complex out: it is composed of tectonic melange of serpentinized peridotite, bandedf gabbro, pillow-basalt, and pelagic sediments (black shales and cherts). All the rocks underwent epidot - amphibolite, glaucophane and greenschist facies metamorphism. The ophiolite is intruded by various in composition igneous massifs - from gabbro-diorite to leuco-granite, which occurred at 110-120 Ma. The Bolshoy Lyakhovsky Island structure is thought to be a westerly continuation of the South Anui suture of Chukchi.

  4. Geologic Evolution of the eastern Panama Isthmus from biostratigraphic, tectonic and geophysical data

    Science.gov (United States)

    Barat, F.; Mercier de Lépinay, B.; Sosson, M.; Müller, C.

    2012-04-01

    Panama is located at the junction of Nazca, Cocos, Caribbean and South America Plates, and reflects a complex geological history: the isthmus is mainly an island arc, formed by the convergence between the oceanic Farallon and Caribbean Plates during Late Cretaceous-Paleogene, deformed by extension from the beginning of the Miocene, and shortened during the Middle Miocene collision of the Panama-Choco block with the South America Plate. We focused our researches on the eastern part of Panama, mainly in the Darien province, the least explored territory of the country, combining field work data, remote sensing analyses (SAR images) and geophysical data in order to better constrain the geological history of Panama since the Late Cretaceous. New field observations and detailed biostratigraphic data (nannoflora) allow us to precise the stratigraphic units of eastern Panama. We recognize from bottom to top: (1) the Upper Cretaceous basement of the Caribbean plate consists of basalts, pillow basalts, with minor intercalations of radiolarian cherts, outcropping in the Gulf of San Miguel, San Blas Massif and Sapo Massif; (2) an early volcanic arc, Upper Cretaceous in age, composed by breccias, basalts, intrusive volcanic rocks, limestones and siliceous tuffs, outcropping in the Portobelo Peninsula and San Blas-Darien Massif, attributed to the Ocù formation; (3) a Paleocene-Middle Eocene island-arc magmatic rock suite, outcropping in the Massifs of San Blas-Darien, Mahé and Sapo, attributed to the San Blas Formation; (4) a thick package of Lower-Middle Eocene-Oligocene epiclastic volcanosedimentary rocks, tuffs, with few basaltic lavas, observed in the Mahé Massif, attributed to the Darien Formation; (5) Several sedimentary formations, composed by carbonated and siliceous fine sediments and conglomerates, Upper Middle Eocene to Upper Miocene in age, which outcrop in the basins of Chucunaque-Tuira and Sambu (Porcona, Clarita, Tapaliza, Tuira, Chucunaque formations). We also

  5. Internal-wave and internal-tide deposits of the Middle Ordovician Xiangshan Group Xujiajuan Formation, Ningxia%宁夏中奥陶统香山群徐家圈组内波和内潮汐沉积

    Institute of Scientific and Technical Information of China (English)

    李向东; 何幼斌; 王丹; 高振中; 郑昭昌

    2009-01-01

    宁夏中奥陶统香山群为一套遭受轻微区域变质的陆源碎屑岩,并夹有少量碳酸盐岩和硅质岩,主要为深水浊流沉积.其中,徐家圈组主要由灰绿色、黄绿色轻变质细砂岩、钙质砂岩及粉砂岩和页岩组成,顶部发育有薄层石灰岩.在该组的中-薄层钙质粉-细砂岩、细粉屑质石灰岩和粉砂质页岩中发现了双向交错层理及纹层倾向与区域斜坡倾向相反或有较大夹角的单向交错层理,其中双向交错层理形态丰富、纹层清晰,其纹层倾向有沿斜坡向上的,有沿斜坡向下的.在深水环境中,这些交错层理不应是等深流沉积或浊流沉积的产物,而应为内波产生的沿斜坡上下水流交替流动所形成的.从沉积背景、沉积构造和古水流等方面对徐家圈组的内波、内潮汐沉积进行了详细的研究,认为其形成于水道不发育的深水斜坡环境,并对斜坡环境中内波、内潮汐沉积中不发育脉状、波状和透镜状层理的现象进行了解释.%The Xiangshan Group of the Middle Ordovician in Ningxia is dominated by deep water turbidity current deposits which are mainly a set of lightly metamorphic terrigenous clastic rocks with lower content of carbonate rocks and chert interbeds.The Xujiajuan Formation of the Lower Xiangshan Group is composed of grayish green, yellowish green, fine- to medium-grained lightly metamorphic sandstone, calcareous sandstone, siltstone and shale(slate), and thin bedded limestone at the top.Cross laminations including bi-directional cross bedding with abundant shapes and clear lamina and unidirectional ones with dipping up-slope or large angle between them are found in thin- to medium-bedded and very fine- to fine-grained sandstones, silty micrite and silty shale.Those lamina of bi-directional cross bedding are also inclined bi-directionally up- and down-slope.These cross beddings in deep water environment may not be formed by contour currents or turbidity

  6. Meeting of the French geological society - Uranium: geology, geophysics, chemistry. Book of abstracts

    International Nuclear Information System (INIS)

    -temperature, and metallogenic provinces; 21 - Magmatic-hydrothermal transition in the Roessing pegmatite: implications for uranium mineralisation; 22 - Deformation and partial fusion of a Archean-paleo-Proterozoic crust: implication on uraniferous ores mobilization and deposition, Torngats orogenesis, Ungava bay; 23 - Black chert pebbles of the Pongola basin conglomerates (∼2, 9 Ga - South Africa): a potential uranium source?; 24 - origin and evolution of detrital pyrites in meso-Archean conglomerates (3.08-2.64 Ga) of South Africa: uranium source or trap?; 25 - Experimental study of U(VI) carbonates with respect to 3 parameters: pH, carbonate concentration, temperature, using vibrational (Raman, FTIR, ATR) and optical (UV-visible) spectroscopy; 26 - Nature and significance of the contact between the Abbabis gneiss complex and the meta-sedimentary sequences of the Damara orogenic belt; 27 - Metallogenic potentialities of Proterozoic orogenic belts accreted to Archean basements: the Damara/Lufilien orogen - Namibia and Zambia; 28 - Contribution of the Geological Exploration to the development of the KATCO ISR mine - Chu-Sarysu basin, Kazakhstan; 29 - Remarks about some remarkable events which occurred during the Francevillien formation; 30 - Geochemical signature of different mineral phases obtained by ICP-MS laser ablation (trace elements and rare earths): Application Uranium deposits; 31 - Role of fluids and irradiation in complex pegmatite euxenite/zircon assemblies from Norway and their U-Pb geochronological consequences; 32 - Mechanical modeling of rupture around metamictic minerals; 33 - Helium diffusion in apatite: Effect alpha recoil-linked damages; 34 - Rare earth spectra in uranium oxides: a marker of the uranium deposit type; 35 - Rare earths: tracers of uranium behaviour during acid sulphated hydrothermal weathering - the Guadeloupe example; 36 - What metallogenic model for the Kiggavik-Andrew Lake trend? Nunavut, Canada; 37 - Uranium mobility in the Southern

  7. Modeling CO2 Sequestration in Saline Aquifer and Depleted Oil Reservoirs to Evaluate Regional CO2 Sequestration Potential of Ozark Plateau Aquifer System, South-Central Kansas

    Science.gov (United States)

    Watney, W. L.; Rush, J.

    2011-12-01

    The Paleozoic-age Ozark Plateau Aquifer System (OPAS) in southern Kansas consists of a thick (>450 m) and deeply buried (>1 km) succession of Cambro-Ordovician Arbuckle Group strata (dolomite) overlain by Lower Ordovician to Lower Carboniferous-age carbonate, chert, and shale. The Arbuckle Group is a thick widespread saline aquifer in southern Kansas. A 500 meter core of the OPAS interval and immediate overlying Pennsylvanian shale caprock were cored in early 2011 in the BEREXCO Wellington KGS #1-32 well in Wellington Field, a nearly depleted oil field in Sumner County, in south-central Kansas. An exhaustive set of modern logs were run in the KGS #1-32 well including chemical, microresistivity imaging, dipole sonic, nuclear magnetic resonance, and standard porosity and resistivity wireline logs. In addition, routine and special core analyses provide vital means to calibrate these logs. Core also provide vital chemical analyses and rock samples to run flow experiments, including in situ conditions, to establish reaction kinetics of rock and connate brines with CO2. Core and logs also provide the means to calibrate a 26 km2 multicomponent 3D seismic survey that was acquired in Wellington Field in 2010. Studies of four oil fields, also part of this project, are underway in southwestern Kansas to provide additional calibration points for the western part of the regional study that covers 65,000 km2 where CO2 sequestration capacity will be measured. Several hundred deep wells have been identified to serve as type wells in the regional study area. Well logs and sample descriptions are being digitized, correlated, and mapped to define distribution of aquifers, oil reservoirs, and caprocks. Drill stem test data have been analyzed for deep wells to establish that the Arbuckle is an open aquifer connected to surface exposures 100s of km to east in central Missouri. Over 500 km2 of 3D seismic have been donated by industrial partners to aid in understanding fault and fracture

  8. Petrophysical, Lithological and Mineralogical Characteristics of the Shale Strata of the Volga- Ural Region

    Science.gov (United States)

    Morozov, Vladimir P.; Plotnikova, Irina N.; Pronin, Nikita V.; Nosova, Fidania F.; Pronina, Nailya R.

    2014-05-01

    The objects of the study are Upper Devonian carbonate rocks in the territory of South-Tatar arch and Melekess basin in the Volga- Urals region. We studied core material of Domanicoid facies from the sediments of Mendymski and Domanik horizons of middle substage of Frasnian stage of the Upper Devonian. Basic analytical research methods included the following: study of the composition, structural and textural features of the rocks, the structure of their voids, filter and reservoir properties and composition of the fluid. The complex research consisted of macroscopic description of the core material, optical microscopy analysis, radiographical analysis, thermal analysis, x-ray tomography, electron microscopy, gas-liquid chromatography, chromate-mass spectrometry, light hydrocarbons analysis using paraphase assay, adsorbed gases analysis, and thermal vacuum degassing method. In addition, we performed isotopic studies of hydrocarbons saturating shale rocks. Shale strata are mainly represented by carbonate-chert rocks. They consist mainly of calcite and quartz. The ratio of these rock-forming minerals varies widely - from 25 to 75 percent. Pyrite, muscovite, albite, and microcline are the most common inclusions. Calcareous and ferruginous dolomite (ankerite), as well as magnesian calcite are tracked down as secondary minerals. While performing the tests we found out that the walls of open fractures filled with oil are stacked by secondary dolomite, which should be considered as an indication moveable oil presence in the open-cut. Electron microscopy data indicate that all the studied samples have porosity - both carbonates and carbonate-siliceous rocks. Idiomorphism of the rock-forming grains and pores that are visible under a microscope bring us to that conclusion. The analysis of the images indicates that the type of reservoir is either porous or granular. The pores are distributed evenly in the volume of rock. Their size is very unstable and varies from 0.5 microns

  9. Characteristics and Origin of Sedimentary-Related Manganese Layers in Timor Island, Indonesia

    Directory of Open Access Journals (Sweden)

    Arifudin Idrus

    2014-07-01

    Full Text Available DOI: 10.17014/ijog.v8i4.169Sedimentary-related manganese layers have been discovered in South Central Timor Regency, Timor Island, Indonesia, which is tectonically active and being uplifted due to north-trending tectonic collision between Timor Island arc and Australian continental crust. The manganese layers of 2 to 10 cm-wide interbed with deep sea sedimentary rocks including reddish - reddish brown claystone, radiolarian chert, slate, marl as well as white and pinkish calcilutite of Nakfunu Formations. Stratigraphically, the rock formations are underlain by Bobonaro Formation. Two types of manganese ores found comprise manganese layers and manganese nodule. The manganese layers strongly deformed, lenticular, and segmented, are composed of manganite [MnO(OH], groutite [MnO(OH], pyrolusite (MnO2, lithioporite (Al,Li MnO2(OH2, and hollandite [Ba (Mn4+, Mn2+8O16] associated with gangue minerals including calcite, quartz, limonite [FeO(OH], hematite (Fe2O3, and barite (BaSO4. Whilst the nodule type is only composed of manganite and less limonite. Geochemically, the manganese layers have grade of 63 - 72 wt.% MnO, whereas the nodule one has grade of 63 - 69 wt.% MnO. Generally, iron in Mn ore is very low ranging from 0.2 to 1.54 wt.% Fe2O3, averaged 0.76 wt.%. Hence, Fe/Mn ratio which is very low (0.003 - 0.069, typically indicates a sedimentary origin, which is also supported by petrologic and petrographic data showing layering structure of manganite and lithioporite crystal/grain. Trace element geochemistry indicates that manganese ore was precipitated in a reduction condition. Rare earth element (REE analysis of manganese ore shows an enrichment of cerium (Ce suggesting that the ore is basically originated in a marine environment. The manganese nodule is interpreted to be formed by chemical concretion process of unsoluble metals (i.e. mangan, iron in seawater (hydrogenous and precipitated on deep sea bottom. On the other hand, the manganese

  10. Soils of Walker Branch Watershed

    Energy Technology Data Exchange (ETDEWEB)

    Lietzke, D.A.

    1994-01-01

    indicates that most of this silty material is the result of slope wash processed during the Holocene Age. Residual soils of the watershed were related to the underlying geologic formations by their morphology and types of chert. Colluvial soils were identified and mapped whenever the colluvium thickness exceeded 20 in. (50 cm). Except for the ancient colluvial soils (colluvium without a present-day source area), colluvial soils were not separated according to their geologic age, but stacked colluvial deposits are located in low footslope landforms. Colluvial soils in the watershed were identified and mapped according to their morphologic properties that would influence the perching and subsurface movement of water. Alluvial soils were restricted to present floodplains, low fan terraces, and low fan deltas. Nearly all alluvial soils contained very young surficial sediments derived from slopewash resulting from land clearing and subsequent agricultural activities.

  11. Graphite as a Biomarker in Rocks of the 3.8 Ga Isua Supracrustal Belt

    Science.gov (United States)

    Lepland, A.; van Zuilen, M.; Layne, G. D.; Arrhenius, G.

    2002-12-01

    Recent petrographic and isotopic studies of graphite and apatite in supracrustal rocks from the 3.8 Ga Isua belt (ISB) in southern West Greenland [1, 2] have shown inconsistencies in interpreting traces of life in the earliest terrestrial sediment record. Isotopically light graphitic carbon, suggestive of a bioorganic origin, has been previously reported from the carbonate-rich Isua rocks [3, 4] that at the time were recognized as sedimentary deposits. However, these carbonate-rich rocks, that provided the basis for original biologic interpretations, have been shown to have a metasomatic origin [5] not sedimentary as previously believed. This protolith reinterpretation has highlighted the need for assessment of graphite genesis and related isotopic systematics when using graphite as an ancient biomarker. We have, for this purpose, studied graphite in a suite of samples from the ISB including metacarbonates, turbidites, cherts and banded iron formations (BIFs). Graphite is relatively abundant (0.1-2 wt. %) in metacarbonate samples, while the abundances of reduced carbon in metasedimentary BIFs and metacherts are below 100 ppm. Petrographic analyses show that graphite in metacarbonates typically associates with Fe-bearing carbonate and magnetite. This mineral association indicates graphite formation in Isua metacarbonates by thermal-metamorphic reduction of carbonate ion, in which the carbonate ion is reduced to form graphite and ferrous iron is oxidized to form magnetite. Carbon isotopic compositions of graphite (δ13C ca. -2 per mil) and associated Fe-carbonate (δ13C ca. -6 per mil) indicate isotopic equilibrium between these two phases at ca. 500 C, consistent with the metamorphic history of the ISB. Stepped-combustion experiments undertaken on Isua BIFs and metacherts reveal that these sediments contain virtually no graphite, and the small amount of reduced carbon found there represents recent organic contamination. Our stepped-combustion-mass-spectrometry data

  12. Biological Effects of the Great Oxidation Event

    Science.gov (United States)

    Schopf, J.

    2012-12-01

    are the new discoveries of fossil sulfuretums of the ~2,300 Ma Kazput Fm. and ~1,800 Ma Duck Creek Fm., both of Western Australia. Both assemblages are cellularly permineralized in deepwater, evidently sub-photic zone cherts, and both are essentially identical in sub-seafloor setting, cobweb-like community fabric, and dominant microbial components to a modern sulfuretum known from anoxic sediments off the coast of Chile. These new findings indicate that not only did life respond to the GOE, but that in a unchanging stable environment -- such as that of the deepwater, evidently sub-photic zone, 2 degrees C, quiescent subsurface anoxic mud inhabited by anaerobic sulfuretums, an ecologic setting that has persisted over billions of years -- the inhabiting microbes remain similarly unchanged, in this instance from 2,300 Ma (Kazput Fm.) to 1,800 Ma (Duck Creek Fm.) to the present (Chilean sulfuretum). To Precambrian paleobiology, these findings are significant, providing biology-based data consistent with the GOE and a new deepwater facies in which to search for evidence of ancient life. But their greatest importance is to Evolutionary Biology, providing firm evidence of the null hypothesis to Darwin's theory of evolution: life evolves as is adapts to changing conditions but, as shown here, there is no evolution if an environment remains constant.

  13. Spectral gamma-ray evaluation of Lower Jurassic basalts and lacustrine sediments from the Fundy Basin (Nova Scotia, Canada)

    Science.gov (United States)

    Silva, Ricardo L.; Wach, Grant; Wong, Carlos

    2014-05-01

    In the Fundy Basin (Nova Scotia, Canada), the McCoy Brook Formation corresponds to the first sedimentary unit of Early Jurassic (Hettangian-Pliensbachian) age deposited after the North Mountain basalts, part of the Central Atlantic Magmatic Province (CAMP). The McCoy Brook Formation includes at its base the Scots Bay Member, comprising red and green lutites, silicified limestones, cherts, stromatolites and sandstones. Deposition of the Scots Bay Member occurred in a shallow and oxygenated lake, where the trophic state varied from oligotrophic to eutrophic. The McCoy Brook Formation is less than 100ky younger than the end-Triassic extinction event (Olsen and Et-Touhami, 2008 and references therein). We analysed the spectral gamma-ray (GR) response of the top of the North Mountain basalts and base of the Scots Bay member at Broad Cove (Kings County, Nova Scotia, Canada) in order to calibrate outcrop with borehole wireline data and test uranium as a proxy for organic matter richness. The North Mountain basalts have a constant and low GR profile, varying from 58-92 cts. Potassium varies from 0.5-1.3%, U from 0-3.1ppm and Th from 0-5.1ppm. Average content of these elements are 1.0 %, 1.9ppm and 2.5ppm, respectively. The Scots Bay Member presents more variation, from 162 cts at the base to 68 cts at the top. Potassium varies from 0.4-2.3%, U from 0-6.4ppm and Th from 0-10.0ppm. Average content of these elements are 1.2%, 3.4ppm and 4.1ppm, respectively. The use of U contents to estimate TOC (see for example, Correia et al., 2012) generates non-significant results, where limestones have TOC of 11wt%. Olsen and Et-Touhami (2008) report that these outcrops are organically lean, with TOC lower that 1wt%. It is apparent that the high U contents and the overestimation of authigenic U is linked with U mineralization due the stromatolites and microbial activity, highlighting that lithological and mineralogical components are critical to accurate petrophysical interpretation of

  14. Miocene magmatism and tectonics within the Peri-Alboran orogen (western Mediterranean)

    Science.gov (United States)

    El Azzouzi, M.; Bellon, H.; Coutelle, A.; Réhault, J.-P.

    2014-07-01

    volcanic edifice, major calc-alkaline to shoshonitic volcanoes were built between 9.0 ± 0.5 and 4.8 ± 0.5 Ma, in particular the large Gourougou volcanic complex. Near Oujda, volcanic activity of alkaline affinity leads to multiple emissions of basalts throughout Pliocene times until the beginning of Pleistocene, between 6.2 ± 0.3 and 1.5 ± 0.1 Ma. In the Alboran domain, an age of 19.7 ± 0.8 Ma is reported (this study) for the andesitic tuffites that form the emergent part of the Alboran Island. This age is comparable to that of the Algerian tuffites and cherts “silexites” and the Malaga ones in Spain. Younger activity, completely separated from the previous one, forms the low-K basaltic andesitic dikes from Alboran Island, dated between 9.1 ± 0.5 and 7.5 ± 0.3 Ma. Along the Alboran Ridge both low-K and high-K andesites to dacites were emitted in the estimated range of 10.7-8.7 Ma. Low-K and high-K andesites to dacites sampled at ODP sites 977 and 978 into the East Alboran Basin, are dated between 12.1 ± 0.2 and 9.3 ± 0.1 Ma.

  15. The genome of the diatom Thalassiosira pseudonana: Ecology,evolution, and metabolism

    Energy Technology Data Exchange (ETDEWEB)

    Ambrust, E.V.; Berges, J.; Bowler, C.; Green, B.; Martinez, D.; Putnam, N.; Zhou, S.; Allen, A.; Apt, K.; Bechner, M.; Brzezinski, M.; Chaal, B.; Chiovitti, A.; Davis, A.; Goodstein, D.; Hadi, M.; Hellsten,U.; Hildebrand, M.; Jenkins, B.; Jurka, J.; Kapitonov, V.; Kroger, N.; Lau, W.; Lane, T.; Larimer, F.; Lippmeier, J.; Lucas, S.; Medina, M.; Montsant, A.; Obornik, M.; Parker, M. Schnitzler; Palenik, B.; Pazour,G.; Richardson, P.; Rynearson, T.; Saito, M.; Schwartz, D.; Thamatrakoln,K.; Valentin, K.; Vardi, A.; Wilkerson, F.; Rokhsar, D.; Vardi, A.; Wilkerson, F.P.; Rokhsar, D.S.

    2004-09-01

    Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for {approx}20% of global carbon fixation. We report the 34 Mbp draft nuclear genome of the marine diatom, Thalassiosira pseudonana and its 129 Kbp plastid and 44 Kbp mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, utilization of a range of nitrogenous compounds and a complete urea cycle, all attributes that allow diatoms to prosper in the marine environment. Diatoms are unicellular, photosynthetic, eukaryotic algae found throughout the world's oceans and freshwater systems. They form the base of short, energetically-efficient food webs that support large-scale coastal fisheries. Photosynthesis by marine diatoms generates as much as 40% of the 45-50 billion tonnes of organic carbon produced each year in the sea (1), and their role in global carbon cycling is predicted to be comparable to that of all terrestrial rainforests combined (2, 3). Over geological time, diatoms may have influenced global climate by changing the flux of atmospheric carbon dioxide into the oceans (4). A defining feature of diatoms is their ornately patterned silicified cell wall or frustule, which displays species-specific nano-structures of such fine detail that diatoms have long been used to test the resolution of optical microscopes. Recent attention has focused on biosynthesis of these nano-structures as a paradigm for future silica nanotechnology (5). The long history (over 180 million years) and dominance of diatoms in the oceans is reflected by their contributions to vast deposits of diatomite, most cherts and a significant fraction of current petroleum reserves (6). As photosynthetic heterokonts, diatoms reflect a fundamentally

  16. The Genome of the Diatom Thalassiosira Pseudonana: Ecology, Evolution and Metabolism

    Energy Technology Data Exchange (ETDEWEB)

    Armbrust, E V; Berges, J A; Bowler, C; Green, B R; Martinez, D; Putnam, N H; Zhou, S; Allen, A E; Apt, K E; Bechner, M; Brzezinski, M A; Chaal, B K; Chiovitti, A; Davis, A K; Demarest, M S; Detter, J C; del Rio, T G; Goodstein, D; Hadi, M Z; Hellsten, U; Hildebrand, M; Jenkins, B D; Jurka, J; Kapitonov, V V; Kroger, N; Lau, W Y; Lane, T W; Larimer, F W; Lippmeier, J C; Lucas, S; Medina, M; Montsant, A; Obornik, M; Parker, M S; Palenik, B; Pazour, G J; Richardson, P M; Rynearson, T A; Saito, M A; Schwartz, D C; Thamatrakoln, K; Valentin, K; Vardi, A; Wilkerson, F P; Rokhsar, D S

    2005-11-14

    Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for {approx}20% of global carbon fixation. We report the 34 Mbp draft nuclear genome of the marine diatom, Thalassiosira pseudonana and its 129 Kbp plastid and 44 Kbp mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, utilization of a range of nitrogenous compounds and a complete urea cycle, all attributes that allow diatoms to prosper in the marine environment. Diatoms are unicellular, photosynthetic, eukaryotic algae found throughout the world's oceans and freshwater systems. They form the base of short, energetically-efficient food webs that support large-scale coastal fisheries. Photosynthesis by marine diatoms generates as much as 40% of the 45-50 billion tonnes of organic carbon produced each year in the sea (1), and their role in global carbon cycling is predicted to be comparable to that of all terrestrial rainforests combined (2, 3). Over geological time, diatoms may have influenced global climate by changing the flux of atmospheric carbon dioxide into the oceans (4). A defining feature of diatoms is their ornately patterned silicified cell wall or frustule, which displays species-specific nano-structures of such fine detail that diatoms have long been used to test the resolution of optical microscopes. Recent attention has focused on biosynthesis of these nano-structures as a paradigm for future silica nanotechnology (5). The long history (over 180 million years) and dominance of diatoms in the oceans is reflected by their contributions to vast deposits of diatomite, most cherts and a significant fraction of current petroleum reserves (6). As photosynthetic heterokonts, diatoms reflect a fundamentally

  17. Sulfur isotope study of the Velardeña skarn (Zn-Pb), Durango, Mexico

    Science.gov (United States)

    Jimenez, A.

    2012-04-01

    Sulfur isotope study of the Velardeña skarn (Zn-Pb), Durango, Mexico Abigail Jimenez-Franco1*, Pura Alfonso Abella2, Carles Canet3, Eduardo González-Partida4 1 Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México D.F., Mexico 2 Departament d'Enginyeria Minera i Recursos Naturals, Universitat Politècnica de Catalunya, Av de Les Bases de Manresa 61-73, 08242 Manresa. 3Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México D.F., Mexico 4Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Boulevard Juriquilla 3001, 76230 Santiago de Querétaro, Qro., Mexico The Velardeña mining district is located in north-eastern part of the state of Durango, in northern of Mexico. The ore deposit is a lead-zinc, garnet-rich skarn developed at the contact between granite porphyry dikes (Eocene) and well-laminated limestones with interbedded chert (Albian-Cenomanian). A study of sulfur isotopes has been carried out in various sulfide minerals of the ores of Velardeña, in order to: (a) constrain the possible sources of sulfur and, therefore, better understand the sulfide mineralizing processes, and (b) to estimate the temperature of the ore-forming stage of the skarn. Sulfur isotope analyses were performed in 21 pure fractions of sulfide minerals of the ore mineralization (pyrite, chalcopyrite, sphalerite and galena). The mineral separation was performed using a series of sieves, and the purity of the samples was verified under a binocular microscope. Isotopic analyses were done on a Finnigan MAT Delta C flow elemental analyzer coupled to a TC-EA, according with the method of Giesemann et al. (1974). The δ34S values of the analyzed sulfides range mostly between -0.6 and +2.6 ‰ (relative to the CDT standard). These values are indicative of a magmatic source of sulfur. A single analysis falls

  18. Geology of the Blue Mountains region of Oregon, Idaho, and Washington; stratigraphy, physiography, and mineral resources of the Blue Mountains region

    Science.gov (United States)

    Vallier, T. L., (Edited By); Brooks, H.C.

    1994-01-01

    PART 1: Stratigraphic and sedimentological analysis of sedimentary sequences from the Wallowa terrane of northeastern Oregon has provided a unique insight into the paleogeography and depositional history of the terrane, as well as establishing important constraints on its tectonic evolution and accretionary history. Its Late Triassic history is considered here by examining the two most important sedimentary units in the Wallowa terrane-the Martin Bridge Limestone and the Hurwal Formation. Conformably overlying epiclastic volcanic rocks of the Seven Devils Group, the Martin Bridge Limestone comprises shallow-water platform carbonate rocks and deeper water, off-platform slope and basin facies. Regional stratigraphic and tectonic relations suggest that the Martin Bridge was deposited in a narrow, carbonate-dominated (forearc?) basin during a lull in volcanic activity. The northern Wallowa platform was a narrow, rimmed shelf delineated by carbonate sand shoals. Interior parts of the shelf were characterized by supratidal to shallow subtidal carbonates and evaporites, which were deposited in a restricted basin. In the southern Wallowa Mountains, lithofacies of the Martin Bridge are primarily carbonate turbidites and debris flow deposits, which accumulated on a carbonate slope apron adjacent to the northern Wallowa rimmed shelf from which they were derived. Drowning of the platform in the latest Triassic, coupled with a renewed influx of volcanically derived sediments, resulted in the progradation of fine-grained turbidites of the Hurwal Formation over the carbonate platform. Within the Hurwal, Norian conglomerates of the Excelsior Gulch unit contain exotic clasts of radiolarian chert, which were probably derived from the Bakei terrane. Such a provenance provides evidence of a tectonic link between the Baker and Wallowa terranes as early as the Late Triassic, and offers support for the theory that both terranes were part of a more extensive and complex Blue Mountains

  19. Sedimentología y petrología de los abanicos aluviales y facies adyacentes en el Neogeno de Paracuellos de Jarama (Madrid

    Directory of Open Access Journals (Sweden)

    Alonso, M.

    1986-06-01

    Full Text Available Lateral and vertical variations of middle Miocene lithofacies (Lower and Intermediate Units of the Miocene of the Madrid Basin have been analyzed in the Paracuellos de Jarama area, near Madrid. A complete transition from medial to distal alluvial fan facies and palustrinelshaltow 1acustrine deposits can be observed. This sedimentary evolution is inferred from the detailed sedimentological. analysis carried out in each of the previously defined lithostratigraphic units: a1 Green shale and dolomite Unit, a2 Brown clays, arkosic and carbonate Unit; these two units are linked together into a Lower Group. b Coarse Arkosic Unit (Upper Group. Facies relationsbips within the Lower Group show a lateral change pattern between alluvial fan deposits, and palustrine deposits. Also the former ones gradually prograde over the palustrine deposits, as deduced from vertical evolution in the southernmost parts of the area. Upper Group represents a sudden progradation of the alluvial fan systems, that extensively overlie the distal facies observed in the Lower Group.
    Wide development of calcretes, sepiolite deposits, and nodular chert is an outstanding feature in the most distal parts of the alluvial fan bodies. They are studied in some detail provided the scarcity of well described examples of facies relationships in the kinds of deposits.

    Se estudia en este trabajo la variación lateral y vertical de las litofacies del Mioceno medio (Unidades Inferior e Intermedia en el área de Paracuellos de Jarama, próxima a Madrid, quedando representada en este área una transición completa entre depósitos de facies medias de abenícos aluviales y depósitos de ámbitos palustres. Estas conclusiones se extraen a partir del análisis sedimentológico realizado en cada una de las unidades previamente definidas: a Unidad de arcillas verdes y carbonatos y Unidad de arcillas pardas, arcillas y carbonatos en el Conjunto Inferior; b Unidad de

  20. A Systems Approach to Identifying Exploration and Development Opportunities in the Illinois Basin: Digital Portifolio of Plays in Underexplored Lower Paleozoic Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Beverly Seyler; David Harris; Brian Keith; Bryan Huff; Yaghoob Lasemi

    2008-06-30

    Albany Shale is regarded as the source rock for petroleum in Silurian and younger strata in the Illinois Basin and has potential as a petroleum reservoir. Field studies of reservoirs in Devonian strata such as the Geneva Dolomite, Dutch Creek Sandstone and Grassy knob Chert suggest that there is much additional potential for expanding these plays beyond their current limits. These studies also suggest the potential for the discovery of additional plays using stratigraphic concepts to develop a subcrop play on the subkaskaskia unconformity boundary that separates lower Devonian strata from middle Devonian strata in portions of the basin. The lateral transition from Geneva Dolomite to Dutch Creek Sandstone also offers an avenue for developing exploration strategies in middle Devonian strata. Study of lower Devonian strata in the Sesser Oil Field and the region surrounding the field shows opportunities for development of a subcrop play where lower Devonian strata unconformably overlie Silurian strata. Field studies of Silurian reservoirs along the Sangamon Arch show that opportunities exist for overlooked pays in areas where wells do not penetrate deep enough to test all reservoir intervals in Niagaran rocks. Mapping of Silurian reservoirs in the Mt. Auburn trend along the Sangamon Arch shows that porous reservoir rock grades laterally to non-reservoir facies and several reservoir intervals may be encountered in the Silurian with numerous exploration wells testing only the uppermost reservoir intervals. Mapping of the Ordovician Trenton and shallower strata at Centralia Field show that the crest of the anticline shifted through geologic time. This study illustrates that the axes of anticlines may shift with depth and shallow structure maps may not accurately predict structurally favorable reservoir locations at depth.

  1. NanoSIMS opens a New Window for Deciphering Organic Matter in Terrestrial and Extraterrestrial Samples

    Science.gov (United States)

    Oehler, Dorothy ZS.; Robert, Francois; Mostefaoui, Smail; Meibom, Anders; Selo, Madeleine; McKay, David S.; Gibson, Everett K.

    2007-01-01

    combine NanoSIMS element maps with optical microscopic imagery in an effort to develop a new method for assessing biogenicity. They showed that the ability to simultaneously map the distribution of organic elements [such as carbon (C), nitrogen (N), and sulfur (S)] and compare those element distributions with optically recognizable, cellularly preserved fossils could provide significant new insights into the origin of organic materials in ancient sediments. This chapter details a recent NanoSIMS study which was designed to acquire new data relevant to establishing critical biosignatures (Oehler et al., 2006a-c). In this study, NanoSIMS was used to characterize element distributions of spheroidal and filamentous microfossils and associated organic laminae in chert from the approx. 0.85 billion year old (Ga) Bitter Springs Formation of Australia. Previous work established preservation of a diverse microbiota in the Bitter Springs Formation (Schopf, 1968; Schopf and Blacic, 1971), and there is no dispute within the scientific community regarding the biogenicity of any of the Bitter Springs structures evaluated in this new study. Thus, the NanoSIMS results described below provide new insight into - and can be used as a guide for assessing - the origin of less well understood organic materials that may occur in early Archean samples and in meteorites or other extraterrestrial samples.

  2. Stratigraphy of the PB-1 well, Nopal I uranium deposit, Sierra Pena Blanca, Chihuahua, Mexico

    International Nuclear Information System (INIS)

    The Nopal I site in the Pena Blanca uranium district has a number of geologic and hydrologic similarities to the proposed high-level radioactive waste repository at Yucca Mountain, making it a useful analogue to evaluate process models for radionuclide transport. The PB-1 well was drilled in 2003 at the Nopal I uranium deposit as part of a DOE-sponsored natural analogue study to constrain processes affecting radionuclide transport. The well penetrates through the Tertiary volcanic section down to Cretaceous limestone and intersects the regional aquifer system. The well, drilled along the margin of the Nopal I ore body, was continuously cored to a depth of 250 m, thus providing an opportunity to document the local stratigraphy. Detailed observations of these units were afforded through petrographic description and rock-property measurements of the core, together with geophysical logs of the well. The uppermost unit encountered in the PB-1 well is the Nopal Formation, a densely welded, crystal-rich, rhyolitic ash-flow tuff. This cored section is highly altered and devitrified, with kaolinite, quartz, chlorite, and montmorillonite replacing feldspars and much of the groundmass. Breccia zones within the tuff contain fracture fillings of hematite, limonite, goethite, jarosite, and opal. A zone of intense clay alteration encountered in the depth interval 17.45-22.30 m was interpreted to represent the basal vitrophyre of this unit. Underlying the Nopal Formation is the Coloradas Formation, which consists of a welded lithic-rich rhyolitic ash-flow tuff. The cored section of this unit has undergone devitrification and oxidation, and has a similar alteration mineralogy to that observed in the Nopal tuff. A sharp contact between the Coloradas tuff and the underlying Pozos Formation was observed at a depth of 136.38 m. The Pozos Formation consists of poorly sorted conglomerate containing clasts of subangular to subrounded fragments of volcanic rocks, limestone, and chert

  3. Structural analysis and shape-preferred orientation determination of the mélange facies in the Chañaral mélange, Las Tórtolas Formation, Coastal Cordillera, northern Chile

    Science.gov (United States)

    Fuentes, Paulina; Díaz-Alvarado, Juan; Fernández, Carlos; Díaz-Azpiroz, Manuel; Rodríguez, Natalia

    2016-04-01

    This study sheds light on the tectonic and structural knowledge of the mélange facies located to the south of Chañaral city, Chile. The Chañaral mélange has been related to an accretionary prism at the western active continental margin of Gondwana. Based on the fossil content, the original turbidite sequence would have been deposited during Devonian to Carboniferous times. The Chañaral mélange is included in the Las Tórtolas Formation, which corresponds to the Paleozoic metasedimentary basement located in the Coastal Range in northern Chile. It consists of a monotonous sequence of more than 90% of interbedded sandstones and shales, with a few limestones, pelagic chert, conglomerates and basic volcanic rocks, metamorphosed to the greenschist facies. In the study area, the Las Tórtolas Formation is divided into two structural domains separated by a major reverse dextral structure, called here the Infieles fault. To the east, the Las Tórtolas Formation is characterized by a brittle-ductile deformation, defined by the original sedimentary contacts in the turbiditic sequence. Besides, thrust faults and associated thrust propagation folds promotes a penetrative axial plane foliation. Mélange facies are located to the west of the Infieles fault. Although lithologies comprising this domain are similar to the rest of the Las Tórtolas Formation, mélange facies (ductile domain) are characterized by the complete disruption of the original architecture of the turbidite succession. The most significant structures in the mélange are the ubiquitous boudinage and pinch and swell structures, asymmetric objects, S-C structures and tight to isoclinal folds. This deformation is partitioned in the Chañaral mélange between linear fabric domains (L), characterized by quartzite blocks with prolate shape in a phyllite matrix with pencil structures, and linear-planar fabric domains (L-S), where quartzite objects show oblate shape and phyllites present a penetrative foliation

  4. Hochschuldidaktische Qualifizierung in der Medizin: I. Bestandsaufnahme [Faculty Development Initiatives in Medical Education in German-Speaking Countries: I. State of Affairs

    Directory of Open Access Journals (Sweden)

    Lammerding-Köppel, Maria

    2006-11-01

    gewonnen. Im Rahmen der Professionalisierung der medizinischen Aus-, Fort- und Weiterbildung ist eine pädagogisch-didaktische Ausbildung der Lehrenden unumgänglich. Um Orientierung und Argumentationshilfe zu geben, werden in einer dreiteiligen Artikelfolge Stellenwert der Medizindidaktik, Anforderungsprofil der Angebote und Konzepte zur Implementierung und zur Erfolgsmessung für den deutschsprachigen Raum beleuchtet. In Teil I geben wir eine Bestandsaufnahme zur Medizindidaktik. Aktuell gibt es bundesweit ein breit gefächertes Qualifizierungsangebot. Es reicht von einfachen unstrukturierten Kurzfortbildungen wie zum Beispiel Vorträgen und Seminaren, die inhaltlich, formal und qualitativ eine große Beliebigkeit zeigen, bis hin zu umfassenden mehrjährigen (Aufbau-Studiengängen mit "Master-Degree". Im internationalen Vergleich fehlt in Deutschland ein allgemein verbindliches "Basis-Programm", das die täglich Lehrenden systematisch auf ihre Ausbildungsaufgaben vorbereitet. Dies ist bisher nur lokal umgesetzt wie zum Beispiel in Baden-Württemberg mit dem ministeriell zertifizierten Programm der Medizindidaktischen Qualifikation I und II. Vergleichbares ist in Nordrhein-Westfalen und Bayern im Aufbau.

  5. Provenance and sediment fluxes in the Irrawaddy (Ayeyarwadi) River

    Science.gov (United States)

    Garzanti, Eduardo; Wang, Jiangang; Vezzoli, Giovanni; Limonta, Mara

    2016-04-01

    The Irrawaddy (Ayeyarwadi) River, still a natural system scarcely affected by human activities, ranks among the five major rivers in the world for its annual suspended load, estimated as 364±60 million tons (Robinson et al., 2007). Sourced in Himalayan glaciers southeast of the eastern Himalayan syntaxis at ca. 28°N, the Irrawaddy originates from the confluence of the Nmai and Mali Rivers, flows southward to receive its major Chindwin tributary in the middle of the central Myanmar Basin, and eventually empties through a nine-armed delta into the Andaman Sea. The compositional fingerprint of bedload sand in the upper Irrawaddy is characterized by common feldspars, medium/high rank of metamorphic rock fragments and high heavy-mineral concentration, reflecting provenance from mid-crustal granitoids, amphibolite-facies and subordinately greenschist-facies rocks widely exposed in the Mogok Belt and Lohit Plutonic Complex. Minor volcanic/metavolcanic and serpentinite grains indicate additional supply from volcanic-arc remnants and the Neotethyan ophiolitic suture. Sand of the Chindwin River has much higher quartz/feldspar ratio and much lower metamorphic indices and heavy-mineral concentration, reflecting provenance mainly from upper crustal sedimentary and very low-grade metasedimentary rocks exposed in the Indo-Burman Ranges (Garzanti et al., 2013). Feldspatho-litho-quartzose to litho-feldspatho-quartzose composition in the lower Irrawaddy is intermediate between that of Chindwin and upper Irrawaddy sand. The slight progressive downstream increase in volcanic rock fragments and chert, and decrease in metamorphic indices, point to additional local supply from volcanic and sedimentary cover rocks. U-Pb age spectra of detrital zircons are characterized by a major cluster between 30 and 150 Ma, corresponding to the long-lasting magmatic activity of the Western Myanmar Arc (Wang et al., 2014), with other clusters at 500-600 Ma and 800-1200 Ma, and a few ages between 1

  6. A Preliminary Geological and Geochemical Study of the Sharebabak-Baft Ophiloites, South of Kahduiyeh, Central Iran.

    Science.gov (United States)

    Khalatbari Jafari, Morteza; Sepehr, Hadi

    2010-05-01

    The Kahduiyeh tectonized Ophiolite of the northern part of Sharebabak-Baft Ophiolite belt is located in the southern margin of the central Iran micro-plate at 53o 45' to 54o 00' E latitude and 31o 00' to 31o 25'N longitude. The mantle sequence of this ophiolite comprised of lherzholite and cpx-bearing harzburgite that are highly serpentinized and are cut across with individual diabase and plagiogranite- tronjemite dikes and pods. The crustal section comprises extensively of high level isotropic and cumulate gabbro with the olivine gabbro, pyroxene gabbro and foliated hornblende- bearing gabbrodiorite compositions. There is no layered gabbro in the crustal sequence. This section is normally and not tectonically transitioned to the diabasic sheeted dikes complex on top of the sequence. These sheeted dikes are oriented in N-S direction with a couple of degrees of inclinations towards either the East or the West and are cut across with wherlitic dikes and intrusions, the small intrusions of quartz diorite to quartz monzodiorite, packets of pegmatitic gabbro, and individual diabase and tronjemite dikes. The microscopic studies of the scarce and fresh peridotites, show kink bands in olivine and deformed pyroxenes which is the characteristics of the mantle peridotites. The sporadic distribution of undeformed pyroxenes as well as the presence of the deformed minerals mentioned above and the crystallization of neoformed olivine in the rim and inside of the deformed orthopyroxenes probably indicates the effect of transiting fluids and their reactions with the primitive peridotites. The extrusive sequence comprises of chert and radiolarite with intercalation of pelagic limestones at base of sequence and hyaloclastic breccia, hyaloclastite, tuff, sheet flow and pillow lava on top of the sequence. In some cases, pelagic limestone and radiolarite have the Upper Cretaceous micro faunas. Rodingite and listvenite are among the metasomatic rocks of this tectonized assemblage. A few

  7. Jurassic Oceanic Remnants In The Siuna Area (NE-Nicaragua) - Tracing The Chortis- Caribbean Paleo-plate Boundary

    Science.gov (United States)

    Flores, K.; Baumgartner, P. O.; Skora, S.; Baumgartner, L.; Baumgartner-Mora, C.; Rodriguez, D.

    2006-12-01

    The southern limit of the Chortis Block has been commonly placed along a line between the Santa Elena Peninsula (Costa Rica) and the Hess Escarpment (Eastern Caribbean). However, we have mapped extensive occurrences of ultramafic and mafic rocks, associated with Jurassic radiolarites in the Siuna area. These are in conflict with the current plate tectonic schemes. In the area S and NE of Siuna, we observe three tectono-stratigraphic units: 1. A pre-Cretaceous, subduction-related melange outcropping in a 30 x 5 km sized erosional window. Serpentinite is a (tectonic) matrix for a variety of mappable blocks grouped into the following categories: Gabbros and peridotites preserving original cumulate textures, greenstones, epidote-bearing greenschists, barroisite-bearing metamafics that partially contain garnet+clinopyroxene inclusions, phengite-schists, blue- green amphibole-rich metacherts, detrital quartzites, radiolarian cherts, black shales and Mn-radiolarites- bearing Middle and Late Jurassic Radiolaria. Blocks with greenschists and higher pressure metamorphic facies appear to be concentrated in the central part of the window. In some blocks, greenstones (mainly altered metabasalts) are associated with ribbon-bedded radiolarites and siliceous shales suggesting an original sedimentary contact of sediments on the oceanic crust. This melange resembles (though more polymict) the subduction melanges of the Franciscan and indicates that the Siuna area exposes part of a major suture zone between the Chortis Block and the Caribbean Large Igneous Province (CLIP). 2. Thin-bedded calcareous hemipelagites yielding Aptian/Albian planktonic Foraminifera rest unconformably on the oceanic melange. Distal volcaniclastic turbitites are interbedded. The sequence contains shallow upsections into thick bedded limestones, in which andesitic flows may be intercalated. Well rounded/sorted and imbricated volcanic pebble conglomerates sometimes intervene between the andesites and

  8. Geochemistry and Geochronology of Oceanic Rock Assemblages in the Izmir-Ankara-Erzincan Suture Zone, Turkey

    Science.gov (United States)

    Sarifakioglu, Ender; Dilek, Yildirim; Sevin, Mustafa

    2013-04-01

    We report here new data from the Izmir-Ankara-Erzincan Suture Zone (IAESZ), which connects the Vardar Suture Zone in the west with the Sevan-Akera Suture Zone in the east. It occurs between the Sakarya Continent and the Anatolide-Tauride ribbon continent in Turkey, and consists mainly of ophiolitic thrust sheets emplaced into a subduction-accretion mélange. The ophiolites include upper mantle peridotites, cumulate to massive gabbros, sheeted doleritic dykes, plagiogranite dykes and stocks, and basalt-chert-radiolarite as in a complete Penrose-type ophiolite pseudostratigraphy. They display a geochemical progression in their magmatic evolution from initially MORB-like to island arc tholeiites (IAT) to boninites, similar to many other Tethyan ophiolites in the eastern Mediterranean region. Boninitic dykes and volcanic rocks have very low TiO2 (0.03-0.50 wt.%), Nb (0.03-1.9 ppm), Y (1,9-10.7ppm) and Zr (4.10-42 ppm) values. IAT-type doleritic dykes and basaltic lavas contain low TiO2 (0.42-1.04 wt.%), Nb (0.90-2.7 wt.%), Y (9.7-33.3 ppm) and Zr (12.7-85 ppm). The TiO2 (0.81-2.60 wt.%), Nb (3.30-4.8 ppm), Y (22.6-63.8 ppm) and Zr (36.01-179.33 ppm) contents of the MORB-like basaltic rocks are higher than those in the IAT and boninitic lavas. The subduction-accretion mélange (Ankara Mélange) in the central part of the IAESZ, includes volcanic mega-blocks derived from seamounts and/or an oceanic plateau that have OIB and P-MORB geochemical characteristics. This subduction-accretion complex also contains blocks of MORB- and/or IAT-like ophiolite fragments within a matrix composed of serpentinite, altered volcanics-volcaniclastics and/or pelitic sedimentary rocks. Pegmatitic gabbros in the ophiolites in the western and eastern IAESZ reveal 40Ar-39Ar hornblende ages of 168.9Ma and 195.7±2.7Ma, respectively. Plagiogranite dykes in the central and eastern parts of the IAESZ are 180 Ma and 179±2 Ma to 180.1±2.4 Ma in age as determined from U-Pb from zircon dates. The

  9. Meeting of the French geological society - Uranium: geology, geophysics, chemistry. Book of abstracts; Reunion de la Societe Geologique de France - Uranium: geologie, geophysique, chimie. Recueil des resumes

    Energy Technology Data Exchange (ETDEWEB)

    Zakari, A.A.; Mima, S.; Bidaud, A.; Criqui, P.; Menanteau, P.; David, S.; Pagel, M.; Chagnes, A.; Cote, G.; Courtaud, B.; Thiry, J.; Miehe, J.M.; Gilbert, F.; Cuney, M.; Bruneton, P.; Ewington, D.; Vautrin-Ul, C.; Cannizzo, C.; Betelu, S.; Chausse, A.; Ly, J.; Bourgeois, D.; Maynadie, J.; Meyer, D.; Clavier, N.; Costin, D.T.; Cretaz, F.; Szenknect, S.; Ravaux, J.; Poinssot, C.; Dacheux, N.; Durupt, N.; Blanvillain, J.J.; Geffroy, F.; Aparicio, B.; Dubessy, J.; Nguyen-Trung, C.; Robert, P.; Uri, F.; Beaufort, D.; Lescuyer, J.L.; Morichon, E.; Allard, T.; Milesi, J.P.; Richard, A.; Rozsypal, C.; Mercadier, J.; Banks, D.A.; Boiron, M.C.; Cathelineau, M.; Dardel, J.; Billon, S.; Patrier, P.; Wattinne, A.; Vanderhaeghe, O.; Fabre, C.; Castillo, M.; Salvi, S.; Beziat, D.; Williams-Jones, A.E.; Trap, P.; Durand, C.; Goncalves, P.; Marquer, D.; Feybesse, J.L.; Richard, Y.; Orberger, B.; Hofmann, A.; Megneng, M.; Orberger, B.; Bouttemy, M.; Vigneron, J.; Etcheberry, A.; Perdicakis, M.; Prignon, N.; Toe, W.; Andre-Mayer, A.S.; Eglinger, A.; Jordaan, T.; Hocquet, S.; Ledru, P.; Selezneva, V.; Vendryes, G.; Lach, P.; Cuney, M.; Mercadier, J.; Brouand, M.; Duran, C.; Seydoux-Guillaume, A.M.; Bingen, B.; Parseval, P. de; Guillaume, D.; Bosse, V.; Paquette, J.L.; Ingrin, J.; Montel, J.M.; Giot, R.; Maucotel, F.; Hubert, S.; Gautheron, C.; Tassan-Got, L.; Pagel, M.; Barbarand, J.; Cuney, M.; Lach, P.; Bonhoure, J.; Leisen, M.; Kister, P.; Salaun, A.; Villemant, B.; Gerard, M.; Komorowski, J.C.; Michel, A.; Riegler, T.; Tartese, R.; Boulvais, P.; Poujols, M.; Gloaguen, E.; Mazzanti, M.; Mougel, V.; Nocton, G.; Biswas, B.; Pecaut, J.; Othmane, G.; Menguy, N.; Vercouter, T.; Morin, G.; Galoisy, L.; Calas, G.; Fayek, M.

    2010-11-15

    -temperature, and metallogenic provinces; 21 - Magmatic-hydrothermal transition in the Roessing pegmatite: implications for uranium mineralisation; 22 - Deformation and partial fusion of a Archean-paleo-Proterozoic crust: implication on uraniferous ores mobilization and deposition, Torngats orogenesis, Ungava bay; 23 - Black chert pebbles of the Pongola basin conglomerates ({approx}2, 9 Ga - South Africa): a potential uranium source?; 24 - origin and evolution of detrital pyrites in meso-Archean conglomerates (3.08-2.64 Ga) of South Africa: uranium source or trap?; 25 - Experimental study of U(VI) carbonates with respect to 3 parameters: pH, carbonate concentration, temperature, using vibrational (Raman, FTIR, ATR) and optical (UV-visible) spectroscopy; 26 - Nature and significance of the contact between the Abbabis gneiss complex and the meta-sedimentary sequences of the Damara orogenic belt; 27 - Metallogenic potentialities of Proterozoic orogenic belts accreted to Archean basements: the Damara/Lufilien orogen - Namibia and Zambia; 28 - Contribution of the Geological Exploration to the development of the KATCO ISR mine - Chu-Sarysu basin, Kazakhstan; 29 - Remarks about some remarkable events which occurred during the Francevillien formation; 30 - Geochemical signature of different mineral phases obtained by ICP-MS laser ablation (trace elements and rare earths): Application Uranium deposits; 31 - Role of fluids and irradiation in complex pegmatite euxenite/zircon assemblies from Norway and their U-Pb geochronological consequences; 32 - Mechanical modeling of rupture around metamictic minerals; 33 - Helium diffusion in apatite: Effect alpha recoil-linked damages; 34 - Rare earth spectra in uranium oxides: a marker of the uranium deposit type; 35 - Rare earths: tracers of uranium behaviour during acid sulphated hydrothermal weathering - the Guadeloupe example; 36 - What metallogenic model for the Kiggavik-Andrew Lake trend? Nunavut, Canada; 37 - Uranium mobility in the Southern

  10. Hominin-bearing caves and landscape dynamics in the Cradle of Humankind, South Africa

    Science.gov (United States)

    Dirks, Paul H. G. M.; Berger, Lee R.

    2013-02-01

    This paper provides constraints on the evolution of the landscape in the Cradle of Humankind (CoH), UNESCO World Heritage Site, South Africa, since the Pliocene. The aim is to better understand the distribution of hominin fossils in the CoH, and determine links between tectonic processes controlling the landscape and the evolution and distribution of hominins occupying that landscape. The paper is focused on a detailed reconstruction of the landscape through time in the Grootvleispruit catchment, which contains the highly significant fossil site of Malapa and the remains of the hominin species Australopithicus sediba. In the past 4 My the landscape in the CoH has undergone major changes in its physical appearance as a result of river incision, which degraded older African planation surfaces, and accommodated denudation of cover rocks (including Karoo sediments and various sil- and ferricretes) to expose dolomite with caves in which fossils collected. Differentially weathered chert breccia dykes, calibrated with 10Be exposure ages, are used to estimate erosion patterns of the landscape across the CoH. In this manner it is shown that 2 My ago Malapa cave was ˜50 m deep, and Gladysvale cave was first exposed; i.e. landscape reconstructions can provide estimates for the time of opening of cave systems that trapped hominin and other fossils. Within the region, cave formation was influenced by lithological, layer-parallel controls interacting with cross-cutting fracture systems of Paleoproterozoic origin, and a NW-SE directed extensional far-field stress at a time when the African erosion surface was still intact, and elevations were probably lower. Cave geometries vary in a systematic manner across the landscape, with deep caves on the plateau and cave erosion remnants in valleys. Most caves formed to similar depths of 1400-1420 mamsl across much of the CoH, indicating that caves no longer deepened once Pliocene uplift and incision occurred, but acted as passive

  11. Formation of the Late Palaeozoic Konya Complex and comparable units in southern Turkey by subduction-accretion processes: Implications for the tectonic development of Tethys in the Eastern Mediterranean region

    Science.gov (United States)

    Robertson, Alastair H. F.; Ustaömer, Timur

    2009-07-01

    The southern margin of Eurasia, from the Balkan region eastwards, is widely envisaged as an active continental margin related to northward subduction, at least during Late Carboniferous-Early Cenozoic time. By contrast, the Late Palaeozoic setting of the southern (Gondwana) margin was previously interpreted as an intra-continental marginal basin related to southward subduction beneath the northern margin of Gondwana, or as part of a forearc complex (e.g. forearc basin) related to northward subduction beneath Eurasia. Palaeotethyan evolution is recorded in the Konya Complex (new name), an assemblage of Palaeozoic (Silurian-Carboniferous) meta-sedimentary and meta-igneous rocks that is exposed beneath metamorphosed Upper Permian-Mesozoic shelf-type sediments in central southern Turkey to the north of the Tauride Mountains. The Konya Complex is dominated by large thrust slices of mainly Devonian shallow-water platform carbonates (Bozdağ unit). There is also a melange that is made up of lenticular sheets and blocks of mainly Lower Carboniferous shallow-water limestones, Silurian-Devonian black chert (lydite), pelagic limestones and rare blocks of mid-ocean ridge-type and within plate-type basaltic rocks. The blocks are set in a mainly terrigenous-derived siliciclastic matrix, locally including siliceous tuff. The matrix is interpreted as mainly deep-water turbidites and debris-flow deposits. An overlying, intact volcanic-sedimentary sequence includes chemically enriched extrusives (e.g. trachyandesites) that also exhibit a negative Nb anomaly, suggesting a subduction influence. Dykes crosscutting the carbonate platform units are relatively depleted and also show a subduction influence. Shallow-marine carbonates and terrigenous quartzose sediments of mainly Late Permian age are exposed above the Konya Complex in the west of the area. In contrast, Triassic non-marine, to shallow-marine, clastic sediments unconformably overlie the Konya Complex in the east of the area

  12. Oxygen isotope perspective on crustal evolution on early Earth: A record of Precambrian shales with emphasis on Paleoproterozoic glaciations and Great Oxygenation Event

    Science.gov (United States)

    Bindeman, I. N.; Bekker, A.; Zakharov, D. O.

    2016-03-01

    .4-2.3 Ga. Shales do not show comparable δ18 O rise in the early Phanerozoic as is observed in the coeval δ18 O trends for cherts and carbonates. There is however a sharp increase in the average δ18 O value from the Early Archean to the Late Archean followed by a progressively decelerating increase into the Phanerozoic. This decelerating increase with time likely reflects declining contribution of mantle-extracted, normal-δ18 O crust and lends support to crustal maturation and increasing 18O sequestration into the crust and recycling of high-δ18 O (and 87Sr/86Sr) sedimentary rocks. This secular increase in the δ18 O composition of the continental crust could have also had a mild effect on seawater δ18 O composition.

  13. Early terrestrial impact events: Archean spherule layers in the Barberton Greenstone Belt, South Africa

    Science.gov (United States)

    Ozdemir, Seda; Koeberl, Christian; Schulz, Toni; Reimold, W. Uwe; Hofmann, Axel

    2015-04-01

    In addition to the oldest known impact structure on Earth, the 2.02-billion-year-old Vredefort Structure in South Africa, the evidence of Early Earth impact events are Archean spherule beds in South Africa and Australia. These spherules have been interpreted as condensation products from impact plumes and molten impact ejecta or/and impact ejecta that were melted during atmospheric re-entry [e.g., 1,2]. The 3.2-3.5 Ga spherule layers in the Barberton Greenstone Belt in South Africa currently represent the oldest known remnants of impact deposits on Earth. Aiming at identification of extraterrestrial components and to determine the diagenetic and metamorphic history of spherule layer intersections recently recovered in the CT3 drill core from the northeastern part of the Barberton Greenstone Belt, we have studied samples from these layers in terms of petrography and geochemistry. All samples, including spherule layer intersections and intercalating country rocks, were studied for mineral identification by optical and electron microscopy, as well as electron microprobe analysis (EPMA) at Natural History Museum Vienna and Museum für Naturkunde Berlin (MfN). Major and trace element compositions were determined via X-ray fluorescence spectrometry at MfN and instrumental neutron activation analysis (INAA) at University of Vienna. Os isotopes were measured by thermal ionization mass spectrometry (N-TIMS) at University of Vienna. Eighteen spherule beds are distributed over 150 meter drill core in CT3. Spherules are variably, deformed or undeformed. The high number of these layers may have been caused by tectonic duplication. Spherule beds are intercalated with shale, chert, carbonate, and/or sulfide deposits (country rocks). The size range of spherules is 0.5 to 2 mm, and some layers exhibit gradation. Shapes of spherules differ from spherical to ovoid, as well as teardrops, and spherules commonly show off-center vesicles, which have been interpreted as a primary

  14. Stratigraphy of the PB-1 well, Nopal I uranium deposit, Sierra Pena Blanca, Chihuahua, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Dobson, P.; Fayek, M.; Goodell, P.; Ghezzehei, T.; Melchor, F.; Murrell, M.; Oliver, R.; Reyes-Cortes, I.A.; de la Garza, R.; Simmons, A.

    2008-08-01

    The Nopal I site in the Pena Blanca uranium district has a number of geologic and hydrologic similarities to the proposed high-level radioactive waste repository at Yucca Mountain, making it a useful analogue to evaluate process models for radionuclide transport. The PB-1 well was drilled in 2003 at the Nopal I uranium deposit as part of a DOE-sponsored natural analogue study to constrain processes affecting radionuclide transport. The well penetrates through the Tertiary volcanic section down to Cretaceous limestone and intersects the regional aquifer system. The well, drilled along the margin of the Nopal I ore body, was continuously cored to a depth of 250 m, thus providing an opportunity to document the local stratigraphy. Detailed observations of these units were afforded through petrographic description and rock-property measurements of the core, together with geophysical logs of the well. The uppermost unit encountered in the PB-1 well is the Nopal Formation, a densely welded, crystal-rich, rhyolitic ash-flow tuff. This cored section is highly altered and devitrified, with kaolinite, quartz, chlorite, and montmorillonite replacing feldspars and much of the groundmass. Breccia zones within the tuff contain fracture fillings of hematite, limonite, goethite, jarosite, and opal. A zone of intense clay alteration encountered in the depth interval 17.45-22.30 m was interpreted to represent the basal vitrophyre of this unit. Underlying the Nopal Formation is the Coloradas Formation, which consists of a welded lithic-rich rhyolitic ash-flow tuff. The cored section of this unit has undergone devitrification and oxidation, and has a similar alteration mineralogy to that observed in the Nopal tuff. A sharp contact between the Coloradas tuff and the underlying Pozos Formation was observed at a depth of 136.38 m. The Pozos Formation consists of poorly sorted conglomerate containing clasts of subangular to subrounded fragments of volcanic rocks, limestone, and chert

  15. Investigation on parenting style to students of senior high schools%流动儿童校园欺负行为的调查研究

    Institute of Scientific and Technical Information of China (English)

    曹薇

    2012-01-01

    Bullying behavior is a deliberate harm bullying action among children, whose main feature is the asymmetry, intent and injury in the power of behavior of both sides. Bullying behavior is prevalent in primary and secondary students, it has brought a negative impact on children' s physical and mental behavior. Objective : To investigate bullying behavior of the migrant children' s in school. Methods: Using the Chinese translation of Chert Shiping and revised version of the Smith children bullying behavior questionnaire for Guiyang City 555 misrant children investigation statistics. Results the floating children bullying prevalence and ratio is quite high; bullying the age difference is not significant, with the increase of age decreased; floating children under direct verbal bullying was the highest, fol- lowed by direct physical bullying, indirect bullying had the lowest incidence; bullying occurs in classmates maximum likelihood; bullying behavior place of study abroad and similar sites, the most is in playground, followed by schools elsewhere, corridors and classrooms.%欺负行为是指儿童之间的一种以强凌弱的故意伤害行为,它的主要特征是行为双方的力量不对等性、故意性和伤害性。已有的研究表明:校园欺负行为在中小学生中普遍存在,给儿童身心带来一定的消极影响。研究目的:探讨流动儿童校园欺负行为的状况。方法:采用我国陈世平翻译并修订的Smith版儿童欺负行为问卷对贵阳市555名流动儿童进行调查统计。结论:流动儿童校园欺负行为普遍存在且比例还相当高;欺负行为年龄差异不显著,随年龄增长而有所降低;流动儿童受直接言语欺负的比例最高,其次是直接身体欺负,而间接欺负的发生率最低;欺负行为发生在同班同学的可能性最大;欺负行为的发生地点与国外研究相似,发生地点最多的是操场,其次是学校其他地方,走廊和教室。

  16. Broken formations, melanges and olistostromes in Puerto Plata area (Northern Dominican Republic) as a record of subduction and collisional processes between the Caribbean and North-American plates

    Science.gov (United States)

    Hernaiz Huerta, Pedro Pablo; Valera Fernando, Pérez; de Los Santos Manuel, Abad; Jacques, Monthel; de Neira Alberto, Díaz

    2010-05-01

    The Northern Cordillera of the Dominican Republic records the (oblique) subduction and collisional processes occurred between the Caribbean and North-American plates during Upper Cretaceous to Lower Paleogene times. The boundary between these two plates can be traced within this range disrupted by an Upper Paleogene to present intense left-lateral strike-slip tectonism, onset after collision. In the western part of the range this boundary might be defined by the Camu fault. In the coastal area of Puerto Plata, located on the northern block of the Camu fault, basement rocks belonging to the subducting plate (the Puerto Plata Basement Complex) and several related units probably formed in an accretionary prism, preserve in a large (300 km2) outcrop of chaotic formations presumably formed (and exhumed) during collision. They include from broken formations and tectonic melanges to olistostromes and other coeval sedimentary deposits. The Puerto Plata Basement Complex (PPBC) consists of highly faulted and dismembered blocks formed by discontinuous but sometimes coherent outcrops of serpentinized or massive peridotite, pods of ultramafic cumulates, massive or banded gabbros and Los Caños Fm, a thick sequence of gross bedded volcaniclastic material with interbedded basaltic (sometimes pillowed) or andesitic flows. All these rocks bear low grade metamorphism and lack a general deformation fabric apart from occasional transformation to mylonites due to localized shearing. The PPBC has been interpreted as a fragment of oceanic crust, belonging to the subducting (North-American) slab that has been exhumed as a tectonic melange or a broken complex. The Imbert Fm, of Palaeocene-Eocene age, is formed by a well bedded succession of white very fine grained porcelaneous tuffs, with eventual intercalations of cherts, limestones and marls that, towards the lower part, is interbedded with volcanic-derived graywackes and limolites, and more occasionally, thick beds of conglomerates and

  17. Glaciation of the Coastal Plain of Northern Alaska

    Science.gov (United States)

    Jorgenson, M. T.; Shur, Y.

    2008-12-01

    Our 15 years of studies of permafrost soils on the coastal plain of northern Alaska show that it was affected by a continental ice sheet during the last glacial maximum. Evidence for this includes: occurrence of buried glacial basal ice at Barter Island; widespread sandy diamicton from Demarcation Bay to Barrow of late Pleistocene age; orientation of surficial deposits; poorly integrated drainage and gentle ridge and swale topography; the continuity of glacial-related deposits from the coast to the Brooks Foothills; and perennially frozen sediments unlike those of unglaciated Arctic regions. We documented a 10-m-high exposure ~1 km long at Barter Island that had abundant basal glacier ice with large-scale deformation structures, complex ice-contact deposits, and highly deformed bedded silt, sand, and gravel inclusions within the basal ice. Similar ice structures were observed at Prudhoe Bay and Cape Halkett. The glacial till is highly unusual in that it is comprised of massive, non-fossiliferous, brackish, slightly pebbly loamy sand with occasional gravel to cobble-sized clasts. In most areas the till is only 2-5 m thick, although at Barter Island the till was up to 10- m thick. Gravel particles, which comprise 1-5% of the deposits, usually are 0.5-2 cm long, mostly durable chert, highly polished, and frequently cracked off at one end, with the broken face faceted and polished. We believe the material mostly originated from marine deposits on the continental shelf, although rocks of Canadian provenance also occur. Prevalent, large (1-5 m) deformation features of discontinuous yellow oxidized and gray reduced sediment suggest deformation of sediment during collapse of the ice sheet. The sandy till is found along most of the Beaufort coast with the exception of deltas and lagoons and is found inland as much as 80 km. The sandy till is easily eroded, causing the morainal margin to be indistinct and the topography subdued. Previous thermoluminescence dating by

  18. Palaeoenvironmental and geochemical approach of Archaeocyath-rich facies from Lower Cambrian of Western Gondwana margin at Central Iberian Zone (Urda, Toledo Mountains, Spain)

    Science.gov (United States)

    Menéndez, Silvia; Rodríguez-Martínez, Marta; Moreno-Eris, Elena; Perejón, Antonio; Reitner, Joachim

    2010-05-01

    Archaeocyath-rich facies are located in a quarry close to Urda village, at Toledo Mountains, Spain. The outcrops belong to the Caliza de los Navalucillos Formation and they record a considerably high diverse archaeocyath assemblage in the Lower Cambrian successions from the Central Iberian Zone (Julivert et al. 1972 [1974]). In fact, it is first time recorded the presence of Agyrekocyathus, Dokidocyathus, and Plicocyathus in the Central Iberian Zone. Therefore Plicocyathus is no longer exclusive to biozone VI in Spain. The presence of Anthomorpha is characteristic for the early Botomian, presently early Stage 4 (ICS, 2009), and the assemblage corresponds to the biozone VII (late Ovetian, following the biozonation of Perejón & Moreno-Eiris, 2006). The fossiliferous part of the succession is formed by seven lithofacies, all of them tectonically folded and with a low grade metamorphic overprint. They are comprised by two main groups of facies: (a) mound-shaped to massive lithofacies (A1, A2, A3, A4) and (b) massive to bedded and nodular lithofacies (B1, B2, B3). Archaeocyaths occur in several facies: (A1) mound-shaped white marble with irregular to stromatactoid cavities; (A2) massive mottled white to grey limestone; (A3) massive grey limestone with slumps levels; (A4) massive archaeocyath-rich orange limestone; as well as in carbonate nodules embedded in siltstones and cherts (B1, B2 and B3). The best preserved assemblage comes from the nodule record, where fossils are partially pyritized. This type of preservation is exceptional and has never been described before. XRD and wavelength-dispersive electron microprobe analyses reveal the presence of pyrite and pyrrotine partially altered to iron oxides and hydroxides (hematite and goethite) surrounding the archaeocyath cups. In Central Iberian Zone, the development of mounds and nodular facies like those described here is unusual, although the Botomian marks the peak for Early Cambrian archaeocyathan-microbial mounds

  19. Geological Fluid Mapping in the Tongling Area: Implications for the Paleozoic Submarine Hydrothermal System in the Middle-Lower Yangtze Metallogenic Belt, East China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    that enveloped no economic stringerstockwork zones beneath massive sulfides. This transgressive zone likely marks an upflow path of highflux fluids from the hydrothermal aquifer. Lateral zonation of the sub-discordant alteration zones and their relationship to overlying massive sulfide lenses suggest lateral flows and diffusive discharging of the hydrothermal fluids in a permeable sandstone sequence. Three large-sized, 14 middle-small massive sulfide deposits, and 40 massive sulfide sites have been mapped in detail. They show regional stratabound characters and two major styles, i.e., the layered sheet plus strata-bound stringer-style and the mound-style. Associated exhalite and chemical sedimentary rock suites include (1) anhydrite-barite, (2) jasper-chert, (3) Mg-rich mudstone-pyrite shale, (4) barite lens, (5) siderite-Fe-bearing dolomite, and (6) Mn-rich shale-mudstone, which usually comprise three sulfide-exhalite cyclic units in the area.The spatial distribution of these alteration zones (minerals) and associated massive sulfides and exhalites, and regional variation in δ34S of hydrothermal pyrite and in δ18O-δ34C of hanging wall carbonates, suggest three WNW-extending domains of fluid flow, controlled by the basement faults and syn-depositional faults. Each fluid domain appears to have at least two upflow zones, with estimated even spacing of about 5-8 km in the mapped area. The repeated appearance of sulfide-sulfate or sulfide-carbonate rhythmic units in the area suggests episodically venting of fluids through the upflow conduits by breaking the overlying seals of the hydrothermal aquifer.

  20. Formación de corrensita en turbiditas calcáreas con silex del Campo de Gibraltar (SW de España

    Directory of Open Access Journals (Sweden)

    Carrasco, F.

    1988-04-01

    Full Text Available In this paper is considered the relationship between the process of silicification in turbiditic limeslones and tbe growth of corrensite. This mineralogy is thought to be a result of two fundamental faetors: a Type of detrital material, and b Diagenetic conditions of the environment. Type of detrital material (in general similar to that found in otber calcareous rocks of the Campo de Gibraltar Units determine tbe presence of illite and mixed-layers illite smectite, limited smectite and scarce kaolinite. Diagenetic environment is responsible for the corrensite and possible zeolite growth, and the carbonate silicification. The paragenesis and cbemical characteristics studied showed that the environment for the formation of these minerals needs a high activity of silica in solutions, a high content of iron (divalent and magnesium, but is not necesarily be in relation with evaporitic deposits and thus alkaline conditions of formations. In this examples, the silicification process of limestone (which shows in the chemical analysis a certain proportion of iron and magnesium is accompanied by iron oxides growth. The release of magnesium did not, as it frequently does, cause dolomite growth but, instead, led lo the corrensite formation. Because of the absence of siliceous organisms (radiolarian, sponge-spicules... in this racles, the silicification process which has conduced lo development of chert nadules probably took place in an early stage of diagenesis, using silica precipitation from the solution. In this case, the volcanic activity cannot be considered as a last source of silica, as there is no evidence for contemporary volcanism with the sedimentation of these materials.Este trabajo tiene como objetivo fundamental el poner de manifiesto las relaciones que existen entre el proceso de silicificación de las calizas turbidíticas y el desarrollo de corrensita. La mineralogía determinada viene condicionada por dos factores: tipo de aportes y

  1. The provenance of clasts deposited on the Surveyor Fan, Gulf of Alaska: First results of IODP Expedition 341

    Science.gov (United States)

    Bahlburg, H.; Childress, L. B.; Cowan, E. A.; Forwick, M.; Moy, C. M.; Müller, J.; Ribeiro, F.; Ridgway, K. D.

    2013-12-01

    present in the Pleistocene sediment are more diverse than at Site U1417. In decreasing order of abundance they are argillite, siltstone, basalt, sandstone and granitoids. Minor lithologies include gabbro, quartzite, metasiltstone, chert, rhyolite, gneiss and diorite. The average clast ratio for Site U1418 is M39I23S38 and demonstrates a relatively even distribution of the three lithology groups with igneous rocks being slightly less abundant. These preliminary results indicate that the sources and oceanographic dispersal mechanisms of clasts delivered to the distal and proximal Surveyor Fan may be different, in space and time. The metamorphic rocks recovered from the distal fan including its Neogene parts were likely derived primarily from the Chugach terrane. The site representing the Quaternary proximal fan displays a wider range of lithologies indicative of both the Chugach terrane as well as more interior parts of the convergent margin.

  2. Change in wedge state with seismic cycle inferred from paleostress analysis in on-land accretioanry complex: Shimanto Belt, Shikoku, Southwest Japan

    Science.gov (United States)

    Eida, M.; Hashimoto, Y.

    2012-12-01

    Great earthquakes occur along subduction interface repeatedly. The states of the plate interfaces and those within accretionary wedges change during the earthquake cycles. It is important to recognize those changes along subduction zones for understand the earthquake cycles. The purposes of this study are to estimate paleostresses related with various deformation structures in an on-land accretioanry complex and to reveal the state on plate interface and that within hanging-wall for each deformation structure. The study area is Yokonami mélange in the Cretaceous Shimanto Belt in Southwest Japan. The Yokonami mélange consists of black shale with blocks of sandstone, mudstone, red shale, chert, limestone and basalt. The Goshikinohama Fault is an upper boundary fault of the Yokonami mélange, having a sharp fault interface with ~100μm in thickness within the cataclastic zone with ~2-3m in thickness. The localized fault interface has a flow texture which might be related to slip weakening processes. Therefore, it can be a seismic fault. We have estimated paleostresses from slip data sets obtained from shear veins which are classified as 1) those distributed throughout the Yokonami mélange and 2) those distributed close to the Goshikinohama Fault. We used MIM (multiple inverse method) by Yamaji et al. (2000), an inversion method to estimate the orientation and ratio of paleostress from fault slip data, where the stress ratio Φ is defined as (σ2 - σ3) / (σ1 - σ3). To recognize ideal stress tensors yielded by MIM, we used k-means clustering (Otsubo et al., 2006). 6 stresses are obtained from each data set. From those stresses, we choose a reasonable stress after some examinations of some parameters such as stress ratio. The chosen stresses are 1) an axial compression with Φ = 0.32 and 2) an axial compression with Φ = 0.22. For each stress, effective frictional coefficients μb' are estimated as suggested by Angelier (1989) and fluid pressure ratios along plate

  3. Integrated “plume winter” scenario for the double-phased extinction during the Paleozoic-Mesozoic transition: The G-LB and P-TB events from a Panthalassan perspective

    Science.gov (United States)

    Isozaki, Yukio

    2009-11-01

    The event across the Paleozoic-Mesozoic transition involved the greatest mass extinction in history together with other unique geologic phenomena of global context, such as the onset of Pangean rifting and the development of superanoxia. The detailed stratigraphic analyses on the Permo-Triassic sedimentary rocks documented a two-stepped nature both of the extinction and relevant global environmental changes at the Guadalupian-Lopingian (Middle and Upper Permian) boundary (G-LB, ca. 260 Ma) and at the Permo-Triassic boundary (P-TB, ca. 252 Ma), suggesting two independent triggers for the global catastrophe. Despite the entire loss of the Permian-Triassic ocean floors by successive subduction, some fragments of mid-oceanic rocks were accreted to and preserved along active continental margins. These provide particularly important dataset for deciphering the Permo-Triassic paleo-environments of the extensive superocean Panthalassa that occupied nearly two thirds of the Earth's surface. The accreted deep-sea pelagic cherts recorded the double-phased remarkable faunal reorganization in radiolarians (major marine plankton in the Paleozoic) both across the G-LB and the P-TB, and the prolonged deep-sea anoxia (superanoxia) from the Late Permian to early Middle Triassic with a peak around the P-TB. In contrast, the accreted mid-oceanic paleo-atoll carbonates deposited on seamounts recorded clear double-phased changes of fusuline (representative Late Paleozoic shallow marine benthos) diversity and of negative shift of stable carbon isotope ratio at the G-LB and the P-TB, in addition to the Paleozoic minimum in 87Sr/ 86Sr isotope ratio in the Capitanian (Late Guadalupian) and the paleomagnetic Illawarra Reversal in the late Guadalupian. These bio-, chemo-, and magneto-stratigraphical signatures are concordant with those reported from the coeval shallow marine shelf sequences around Pangea. The mid-oceanic, deep- and shallow-water Permian records indicate that significant

  4. THE INFLUENCE OF FOLD AND FRACTURE DEVELOPMENT ON RESERVOIR BEHAVIOR OF THE LISBURNE GROUP OF NORTHERN ALASKA

    Energy Technology Data Exchange (ETDEWEB)

    Wesley K. Wallace; Catherine L. Hanks; Jerry Jensen; Michael T. Whalen

    2002-01-01

    increases in resistance upward. The Alapah consists of a lower resistant member (100 m) of alternating limestone and chert, a middle recessive member (100 m), and an upper resistant member (260 m) that is similar to Wahoo in the northeastern Brooks Range. The Wahoo is recessive and is thin (30 m) due either to non-deposition or erosion beneath the sub-Permian unconformity. The Lisburne of the area records two major episodes of transgression and shallowing-upward on a carbonate ramp. Thicknesses and facies vary along depositional strike. Asymmetrical folds, mostly truncated by thrust faults, were studied in and south of the local range front. Fold geometry was documented by surveys of four thrust-truncated folds and two folds not visibly cut by thrusts. A portion of the local range front was mapped to document changes in fold geometry along strike in three dimensions. The folds typically display a long, non-folded gently to moderately dipping backlimbs and steep to overturned forelimbs, commonly including parasitic anticline-syncline pairs. Thrusts commonly cut through the anticlinal forelimb or the forward synclinal hinge. These folds probably originated as detachment folds based on their mechanical stratigraphy and the transition to detachment folds to the north. Their geometry indicates that they were asymmetrical prior to thrust truncation. This asymmetry may have favored accommodation of increasing shortening by thrust breakthrough rather than continued folding. Fracture patterns were documented in the gently dipping panel of Lisburne and the asymmetrical folds within it. Four sets of steeply dipping extension fractures were identified, with strikes to the (1) N, (2) E, (3) N to NW, and (4) NE. The relative timing of these fracture sets is complex and unclear. En echelon sets of fractures are common, and display normal or strike-slip sense. Mesoscopic and penetrative structures are locally well developed, and indicate bed-parallel shear within the flat panel and strain

  5. A Preliminary Investigation of the Development and Hydrocarbon Potential of the the Black Shales in the Upper Permian Dalong Formation, Southern Anhui Province in the Lower Yangze Region, China%下扬子皖南大隆组黑色岩系发育特征及油气资源潜力初探

    Institute of Scientific and Technical Information of China (English)

    廖志伟; 胡文瑄; 曹剑; 姚素平; 许志敏; 张月霞; 万野; 丁海

    2016-01-01

    The upper Permian Dalong Formation in the Lower Yangtze Region with black shales is potential for hydrocarbon source rock. Little attention has been paid to this issue. In order to improve the understanding about it, we conducted a comprehensively combined study of petrology and organic geochemistry based on three recently-discovered Dalong black shales outcrops in the southern Anhui province, with the aim to characterize the development and hydrocarbon potential of the Dalong black shales. The results show that the black shales developed widely in all the three outcrops, including the Niushan (Xuancheng City), Caicun (Jingxian County) and Changqiao (Jingxian County). Lithology of the shales is variable from chert to calcareous shale, as well as siliceous mudstone. Stratigraphic correlation and sedimentology of the shales imply that the study area has been subjected to a complete sequence of marine transgression and regression and the black shales generally developed in the environment of deep seawater under reducing, restricted and undercompensated conditions. The results from the study of petrology and organic geochemistry show that the Dalong black shales are rich in organic with the average total organic carbon content being around 2.0%. In terms of kerogen types, the organic matter is primarily Ⅱ2 and Ⅲ. Combined with the high to over maturation of organic matter, we propose that the regional exploration should be focused on natural gas reservoir. Based on the comparison of the distribution of Mesozoic-Cenozoic igneous rocks and black shales in the study area, we infer that the over maturation of organic matter may be primarily influenced by large-scale magmatism in South China during the Mesozoic to Cenozoic period. Thus, petroleum exploration potential can also be considered in the areas where there was no/little significant influence of magmatism (e.g., the Jingxian-Guangde area). These results and understanding can also provide highlights for the

  6. Mineralogy, geochemistry, genesis, and industrial application of silica in Arefi area, south of Mashhad

    Directory of Open Access Journals (Sweden)

    Mohammad Hassan Karimpour

    2014-10-01

    Full Text Available Introduction Arefi quartz-bearing conglomerate (Middle Jurassic is situated within Binalud structural zone. The unit is trending NW-SE located 25 km south of Mashhad. More than 97% of the pebbles are quartz as mono-crystalline, poly-crystalline, and minor fragments of chert, quartzite, and mica schist. Less that 3% of the remaining minerals are feldspar, mica, chlorite, hornblende, tourmaline, zircon, sphene, and opaque minerals. The cement is mainly silica. Hashemi (Hashemi, 2004 suggested this unit is orthoquartzitic polymictic conglomerate. In this study, we carried out detailed mineralogical studies, geochemical analyses for SiO2 and troublesome elements, determination of quartz pebbles source using geological observations and fluid inclusion microthermometry, and industrial application studies with new insight for porcelain and ceramic factories as the nearest silica-rich reserve to Mashhad. Material and methods 1. Preparing geologic map in 1:10000 scale in the Arefi area. 2. Petrographic study of 65 samples from the quartz-bearing conglomerate unit. 3. Major elements such as SiO2, TFeO, TiO2, and CaO were analyzed at the Maghsoud Porcelain Factories Group, using a Philips PW1480 X-ray spectrometer. 4. Ore dressing analyses in Danesh Faravaran Engineering Company. 5. Fluid-inclusion studies in 4 samples doubly-polished wafers of quartz crystals were studied using standard techniques (Roedder, 1984 and Linkam THM 600 heating-freezing stage (from –190 to 600ºC mounted on a Olympus TH4–200 microscope stage at Ferdowsi University of Mashhad, Iran. Salinities and density of fluid inclusions were calculated using the Microsoft Excel spreadsheet HOKIEFLINCS-H2O-NACL (Steele-MacInnis et al., 2012; Lecumberri-Sanchez et al., 2012 Results and Discussion Fluid Inclusion studies of both mono- and poly- crystalline quartz revealed that the inclusions consist of three phases (LVS with NaCl crystals. Homogenization temperature is between 484 and more

  7. Mineralogy of chromites in Mandaleke ophiolite of South Tianshan Mountains and its geological implications%南天山满大勒克蛇绿岩铬铁矿矿物学特征及其意义

    Institute of Scientific and Technical Information of China (English)

    张炜斌; 张东阳; 张招崇; 黄河; 赵莉

    2011-01-01

    满大勒克蛇绿岩属于南天山晚古生代蛇绿岩带,主要由蛇纹石化橄榄岩、玄武岩和含放射虫硅质岩组成.其中蛇纹岩富含铬铁矿,并具有豆英状特征.显微镜观察和电子探针分析表明,铬铁矿具有明显的环带结构,从核部到边部呈现出由铬尖晶石到铬铁矿到磁铁矿的变化特征,元素组成上具有由富Al和Cr、贫Fe到贫Al和Cr、富Fe的变化趋势.利用铬铁矿(铬尖晶石)核部矿物的化学成分,得出铬尖晶石的结晶温度为1359~1394℃,平均1379℃;压力为2.76~3.00 GPa,平均2.87 GPa;相对于FMQ缓冲剂的地幔氧逸度为FMQ-1.50~FMQ-2.92log单位,平均值为FMQ-2.14 log单位;地幔熔融程度F为16.7%~18.0%.结合已有研究成果,推测满大勒克蛇绿岩的基底橄榄岩单元源区为石榴石二辉橄榄岩,形成于亏损的软流圈地慢,对应的大地构造位置为弧前盆地.研究区铬尖晶石的环带特征显示其经历了温度由高到低、氧逸度由低到高的演变,反映了满大勒克蛇绿岩套的橄榄岩单元经历了高温高压的地幔环境(低氧逸度),之后随构造变动被推覆到地壳,定位之后又经历了区域变质作用的演化过程(高氧逸度).%The Mandaleke ophiolite belongs to the late Paleozoic ophiolite belt in South Tianshan Mountains and is composed of serpentinized peridotites, basalts and radiolarian cherts.The chromite or Cr-spinel occurs in the serpentinized peridotites as a ubiquitous accessory mineral, some of which has the podiform texture.Petrographic observation and electron microprobe analysis indicate that the Cr-spinel grains display obvious composition zoning, suggesting the path of such thermal events as crystallization, upwelling and alteration.The core of the Crspinel crystal represents the provenance where the mineral crystallized.The authors thus chose cores of the Crspinel to trace the nature of the mantle and the whole crystals to deduce the thermal events that the

  8. Interplay between compression and extension and its impact on basins evolution along the Europe-Adria suture in the area of Belgrade, Serbia

    Science.gov (United States)

    Marinko, Toljić; Liviu, Matenco; Uroš, Stojadinović

    2015-04-01

    The segment of the suture zone between units of contrasting Adriatic and European affinities situated in Belgrade area of central Serbia is composed of a complex tectono-sedimentary setting that was amalgamated during Cretaceous to Paleogene closure of the Neothethys Ocean. We have analyzed this Cretaceous sedimentary succession in the context of broader kinematic and depositional evolution of the Europe - Adria collision zone, where the basinal evolution was governed by the enduring processes of subduction. A slice of oceanic lithosphere was obducted during the latest Jurassic times far towards the SW over the Adriatic continental margin creating an underlying ophiolitic mélange. This mélange contains radiolarites deposited over oceanic lithosphere, the youngest being of Early Tithonian in age. These radiolarites and the Cretaceous post-tectonic overlying the ophiolites cover define a Middle-Late Tithonian age of the obduction. The obduction was followed by rapid subsidence affecting the European margin during Cretaceous times, which was unconformably covered by a gradual deepening facies. The base of this overstepping sequence, generally referred as the Lower Cretaceous "para-flysch", is composed of thick layered shallow-water limestones that cemented large fragments of re-deposited Tithonian high-organic limestones. These are overlain by a turbiditic alternation of mudstones and sandstones that are laterally replaced by graded calcareous sandstones and breccias containing Lower Cretaceous microfauna and local large olistostromic fragments of re-deposited Upper Jurassic macrofauna. These deposits are overlain into a deep-water carbonatic succession containing often cherts and radiolarites replaced laterally to the S and SW by turbidites that marks the transition to the Barremian. These gradually deepening deposits with a highly lateral variation in paleo-bathimetry define an Early Cretaceous fore-arc basin system, its sediments being deposited over the European

  9. Uranium geology and chemistry, programme and book of abstracts

    International Nuclear Information System (INIS)

    column in the presence of humic acids; 35 - U speciation and stability factors in the Cominak mining wastes (Niger); 36 - IMOURAREN - leaching tests and analcimes specificity; 37 - Modeling of U ore acid leaching tests, application to in-situ recovery; 38 - Role of detrital pyrites in U concentration in the meso-Archean Pongola basin (2.9 Ga, South Africa); 39 - The role of black chert pebbles in uranium mineralisation in conglomerates of the basal Mozaan Group (Pongola basin, South Africa); 40 - U hydrothermal alteration and leaching in the Questembert granite (Massif Armoricain, France)

  10. Environmental isotope application for determination artificial recharge efficiency, cases from arid and semi-arid areas of Jordan

    International Nuclear Information System (INIS)

    Full text: Jordan is one of the arid and semi arid regions where 90% of the country receives less than 200 mm of annual precipitation. Artificial recharge and surface water harvesting has been given an importance and priorities in the last years. Four dams have been taken under study of environmental isotope hydrology to define the efficiency of the artificial recharge to the groundwater, two dams are located in the highland areas (altitude ∼ 740m above see level) and the other two dams at the main escarpment of the Jordan Valley graben (altitude is around -150m below sea level). Monthly and several sampling campaigns from the dams and the surrounding wells of the stable isotopes oxygen-18 (18O), Deuterium (2H) and radioactive tritium (3H) including complete chemical have been sampled and analyzed within the period 1995-2001. This has existed within the framework of technical cooperation projects with the IAEA, RER/8/002 and RAW/8/007. The aquifer, which is outcropping at upper dams, is formed from chert and limestone of campanian and turonian age as Siwaqa dam and overlies by Basalt at Khlidiya dam (upland areas) where the aquifer is formed from sandstone aquifer at Kafrain and Shueib dams at the Jordan valley. The diagrams of 18O and 2H of Siwaqa and Khadiya dams and some selected surrounding wells indicates that there is significant enrichment of the stable isotopes in the groundwater wells near the dams especially at the first years of dams operation which indicates a natural recharge of the enriched water from both lakes. The significant accumulations of silts and sediments at the bottom of both dams makes clogging and reduce the recharge, unless infiltration to the groundwater could occur through dam's escarpment after flooding and water rising. The regression line of the diagram of 18O and deuterium (2H) of the four wells mentioned above including the dam water for the period 1995-2001 has high correlation coefficient, this is represented by the following

  11. Geology, mineralogy and geochemistry of Ferezneh ferromanganese anomaly, east of Sangan mines complex, NE Iran

    Directory of Open Access Journals (Sweden)

    Nazi Mazhari

    2015-04-01

    ., 2015, there is no evidence of limestone skarnification, skarn minerals and magnetite mineralization in the Ferezneh prospect area. Based on the listed data and interpretations, there is no relationship and similarity between Sangan mineralization and Ferezneh ferromanganese anomaly. This anomaly may be related to a younger mineralization and might be associated with the function of supersion fluid by leaching the sulfide hydrothermal deposits that form in the fault zones. References Crerar, D.A., Namson, J., Chyi, M.S., Williams, L. and Feigenson, M.D., 1982. Manganiferous cherts of the Franciscan Assemblage: I. General geology, ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers. Economic Geology, 77(3: 519-540. Golmohammadi, A., Karimpour, M.H., Malekzadeh Shafaroudi, A. and Mazaheri S.A., 2015. Alteration-mineralization, and radiometric ages of the source pluton at the Sangan iron skarn deposit, northeastern Iran. Ore Geology Reviews, 65(2: 545-563. Karimpour, M.H. and Malekzadeh Shafaroudi, A., 2006. Comparison of the geochemistry of source rocks at Tannurjeh Au-bearing magnetite and Sangan Au-free magnetite deposits, Khorasan Razavi, Iran. Iranian Journal of Crystallography and Mineralogy, 13(1: 3–26. (in Persian with English abstract Karimpour, M.H. and Malekzadeh Shafaroudi, A., 2008. Skarn geochemistry – mineralogy and petrology of source rock, Sangan iron mine, Khorasan Razavi, Iran. Scientific Quarterly Journal of Geosciences, 17(65, 108–125. (in Persian with English abstract Xu Bao, S., Yang Zhou, H., Tong Peng, X., Wu Ji, F. and Qiang Yao, H., 2008. Geochemistry of REE and yttrium in hydrothermal fluids from the Endeavour segment. Juande Fuca Ridge. Geochemical Journal, 42(4: 359–370.

  12. Stratigraphic position, origin and characteristics of manganese mineralization horizons in the Late Cretaceous volcano-sedimentary sequence, south-southwest of Sabzevar

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    Sajjad Maghfouri

    2014-10-01

    Full Text Available Introduction The Mn mineralization occurs in the northeastern segment of the Sabzevar zone (SZ, north of the Central Iranian Microcontinent (CIM. This Zone (SZ is located between the CIM fragmentation in the south and the Kopeh dagh sedimentary sequence in the north. The ore deposits of the northeastern segment of the Sabzevar zone can be divided into three groups, each with different metal association and spatial distribution and each related to a major geodynamic event. The first mineralization with associated Ordovician host rock is characterized by Taknar polymetallic (Fe-rich massive sulfide deposit. The Cretaceous mineralization consists of Cr deposits associated with serpentinized peridotites, Cyprus type VMS, Mn deposit in pillow lava, volcano-sedimentary hosted Besshi type VMS and Mn deposit. Paleogene mineralization in eastern segment of the Sabzevar zone began with porphyry deposits, Cu Red Bed mineralization occurs in the Paleogene sandy red marl. Materials and methods A field study and sampling was performed during the autumn of 2012. To assess the geochemical characteristics of 48 systematic samples (least fractured and altered of ore-bearing layers and host rocks were collected from the deposit for polished thin section examination. In order to correctly characterize their chemical compositions, 15 least-altered and fractured samples were chosen for major elements analysis. Results The Late Cretaceous volcano-sedimentary sequence in south-southwest of Sabzevar hosts numerous manganese mineralization. The sequence based on the stratigraphic position, age and composition of the rocks, can be divided into two lower and upper parts. The lower part or K2tv unit mainly formed from marine sediments interbedded with volcanic rocks. The sedimentary rocks of this part include silicified tuff, chert, shale and sandstone, and the volcanic rocks involve pyroclastic rocks of various composition, rhyolite, dacite and andesitic lava. The upper

  13. Hydrologic and Soil Science in a Mediterranean Critical Zone Observatory: Koiliaris River Basin

    Science.gov (United States)

    Nikolaidis, Nikolaos; Stamati, Fotini; Schnoor, Jerald; Moraetis, Daniel; Kotronakis, Manolis

    2010-05-01

    The Koiliaris River watershed is situated 25km east from the city of Chania, Crete, Greece. The total watershed area is 145km2 and the main supply of water originates in the White Mountains. At high elevations (altitude 2014 m), the maximum slope is 43% while at the lower elevations the slope measures 1-2%. Land use includes heterogeneous agricultural areas (25.4%), olive and orange groves (15.6%), and scrub and/or herbaceous vegetation associations (57.6%). The geology of the Basin consists of 23.8% Plattenkalk (dolomites, marbles, limestone and re-crystallized limestone with cherts); 31% of Trypali units (re-crystallized calcaric breccias); 9.4% limestones with marls in Neogene formations; 13% marls in Neogene formations; 12.8% schists, and 10% quaternary alluvial deposits. Intensive hydrologic and geochemical monitoring has been conducted since 2004 while the site has historical data since the ‘60s. In addition, a telemetric high-frequency hydrologic and water quality monitoring station has been deployed to obtain data for the characterization of the hydrologic and biogeochemical processes with varying process response-times. Hydrologic and geochemical modeling confirms the estimation of characteristic times of these processes. The main type of soil degradation in the basin as well as in other arid and semi-arid regions is water erosion, which is due to the clearing of forests and natural vegetation for cropping and livestock grazing. De-vegetation and inappropriate cultivation practices induces soil organic matter (SOM) losses making soils susceptible to erosion and desertification with global consequences for food security, climate change, biodiversity, water quality, and agricultural economy. Cropland plowing breaks-up water stable aggregates making the bio-available pool bio-accessible; which could be microbially attacked and oxidized resulting in SOM decline. Chronosequence data analysis suggested first-order kinetic rate of decline of the bio

  14. Tectono-metamorphic evolution and magmatic processes in the thermo-metamorphic aureole of the Monte Capanne pluton (Elba Island, Northern Tyrrhenian Sea, Italy).

    Science.gov (United States)

    Morelli, M.; Pandeli, E.; Principi, G.

    2003-04-01

    Introduction In this work we present new structural and petrographic data collected in the thermo-metamorphic aureole of Monte Capanne (western Elba Island) and its metamorphic evolution. In the western Elba Island the Monte Capanne monzogranitic body (ca. 7 Ma) and its thermo-metamorphic aureole crop out. At least two different tectonic units can be distinguished: the Punta Le Tombe Unit, weak re-crystallized, and the Punta Nera Unit. In the latter one the re-crystallization is strong and a pre-intrusion tectono-metamorphic framework is evident (Morelli et al., 2002). The latter is mainly constituted by thermo-metamorphosed meta-ophiolites and meta-sedimentary successions previously correlated by Barberi et al. (1969) with the un-metamorphic ones (Complex IV and V of Trevisan, 1950) cropping out in the central-eastern Elba. According to Perrin (1975) and Reutter &Spohn (1982) a pre-intrusion tectono-metamorphic framework was recognized into such rocks. As suggested by Daniel &Jolivet (1995) complex relationships between metamorphic evolution and magmatic events are also recognizable. Geological Data The Punta Nera Unit crops out all around the Monte Capanne magmatic body and the primary contact with the underlying granitoid is somewhere preserved. This unit, strongly re-crystallized and locally crosscut by aplitic and porphyritic dikes, is represented by (Coli &Pandeli, 1997; Morelli, 2000) tectonized meta-serpentinites, meta-gabbros with rodingitic dikes, rare meta-basalts and meta-ophicalcites, meta-cherts, marbles, cherty meta-limestones, phyllites and meta-limestones with rare meta-arenites intercalations. A "pre-magmatic" tectono-metamorphic framework of this unit is well evident only in its meta-sedimentary portion. The meta-sediments are deformed by syn-metamorphic isoclinal folds caractherized by N-S trending axes, west dipping axial planes and easternward vergence. A later folding and flattening event clearly post-dated the above said folds and associated