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Sample records for calcretes

  1. Calcretes in the Thar desert: Genesis, chronology and palaeoenvironment

    Indian Academy of Sciences (India)

    R P Dhir; S K Tandon; B K Sareen; R Ramesh; T K G Rao; A J Kailath; N Sharma

    2004-09-01

    The calcretes in the Thar desert occur in a variety of settings, including the piedmonts, sheet-wash aggraded plains; and this study adds calcretes in regolith and colluvio-alluvial plains to the group of settings in which calcretes occur in the region. Field logs, morphological details and analytical data such as petrographic, cathodoluminescence and geochemical characteristics are described along with a discussion on their implications. Sand dunes and sandy plains dating to > 20 ka have weakly developed calcretes. The better-developed calcrete horizons occur in pied- monts, interdunes or in areas that have sufficient groundwater. Deep sections in the region show phases of calcrete development in aeolian sand aggradation at ∼150, ∼100, ∼60 and 27-14 ka. The extensive sheetwash plains have mature calcretes and date to mid-Pleistocene. Our studies indicate that these calcretes represent a hybrid process, where carbonate enrichment of the originally calcareous host occurred due to periodically raised groundwaters, and its differentiation into nodules occurred under subaerial environment i.e., after recession of groundwater. Deep sections also show a stack of discrete calcretes that developed in individual aggradation episodes with hiatuses as indicated by ESR dating results. Nodules display a multiplicity of carbonate precipitation events and internal reorganization of calcitic groundmass. The process is accompanied by degradation and transformation of unstable minerals, particularly clays and with a neosynthesis of palygorskite. The ancient calcretes are dated from the beginning of the Quaternary to ∼600 ka and show more evolved morphologies marked by brecciation, dissolution, laminar growth on brecciated surfaces, pisolites and several generations of re-cementation. Mica/chlorite schists and such other rocks are particularly vulnerable to replacement by carbonate. In an extreme case, replacement of quart-zose sandstone was observed also. The presence of

  2. Anthropo-Calcretisation: Human Effects on Calcrete Formation

    Science.gov (United States)

    Itkin, Danny

    2014-05-01

    Calcretes are near-surface terrestrial accumulations of secondary calcium carbonate (CaCO3) that form in soils and permeable rocks in regions of arid to dry-summer subtropical climates. While the formation of calcrete under natural conditions has been extensively studied, no reports of anthropogenically induced calcretisation exist in current literature. Following a detailed study of soil micromorphology at the Binyanei Ha-Uma site (Jerusalem) (Itkin, submitted), it becomes evident that a natural Nari-calcrete (Wieder et al. 1993; Itkin et al. 2012) has been overprinted by a secondary calcretisation, specifically arising from human activity ~2 ka ago (related to the production centre of the Tenth Roman Legion in Jerusalem). I hereby introduce the concept of 'Anthropo-Calcretisation', as the sum of processes, by which human actions lead to the accumulation of pedogenic calcium carbonate. Based on soil micromorphological analysis of the Binyanei Ha-Uma site (Itkin, submitted), and other archaeological sites, two characteristic Anthropo-Calcretisation modes can be discerned. The first pathway, termed 'biogeochemical', is dominated by pedogenic chemical reactions, resulting from soil liming, agriculture, and an unintentional soil contamination by calcined lime. The second pathway, termed 'hydropedological', arises from modified soil-water relations due to man-made reshaping of geomorphological units (e.g., agricultural terraces). Anthropo-Calcretisation can follow either of the pathways, and even include both. The study of Anthropo-Calcrete can be applicable (i) to quantify the extent by which (pre)historic human beings have utilised and affected their environment; (ii) to reconstruct paleoclimate, and (iii) to constrain soil development in time by dating associated archaeological artefacts. Furthermore, Anthropo-Calcrete can be also used as a diagnostic tool for evaluating modern human actions (e.g. soil liming, intentional enrichment of soil biomass, or soil

  3. ESR dating of calcrete nodules from Bala, Ankara (Turkey): preliminary results.

    Science.gov (United States)

    Küçükuysal, Ceren; Engin, Birol; Türkmenoğlu, Asuman G; Aydaş, Canan

    2011-02-01

    The age of two calcrete nodules (C1 and C2) from the Bala section in the region of Ankara, Turkey, is determined by the Electron Spin Resonance (ESR) method. Three radiation-induced ESR signals at g=2.0056 (A signal), g=2.0006 (C signal) and g=2.0038 (broad signal, BL) were observed. The broad signal (BL) intensity was used as a dating signal. The properties of this dating signal are described in this manuscript. The calcrete nodules were irradiated with a (60)Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve and fitted well with the single exponential saturation functions. Based on this model, accumulated dose (D(E)) values for dating are obtained using the multiple-aliquot additive dose method. The D(E) values of C1 and C2 calcretes are 1880±207 and 671±67 Gy, respectively. The ESR ages of the two calcrete samples are obtained by assessing the annual dose rate (D) from the content of (238)U, (232)Th and K(2)O determined by wavelength dispersive X-ray fluorescence (XRF) spectrometry. The results are 761±120 and 419±64 ka, respectively, falling into the Middle Pleistocene Epoch in the geological time scale in agreement with the positions of the stratigraphical record.

  4. ESR dating of calcrete nodules from Bala, Ankara (Turkey): Preliminary results

    Energy Technology Data Exchange (ETDEWEB)

    Kuecuekuysal, Ceren [General Directorate of Mineral Research and Exploration, Geological Research Department, 06800 Ankara (Turkey); Engin, Birol, E-mail: birol_engin65@yahoo.co [Turkish Atomic Energy Authority, Saraykoey Nuclear Research and Training Center, 06983 Ankara (Turkey); Tuerkmenoglu, Asuman G. [Middle East Technical University, Geological Engineering Department, 06531 Ankara (Turkey); Aydas, Canan [Turkish Atomic Energy Authority, Saraykoey Nuclear Research and Training Center, 06983 Ankara (Turkey)

    2011-02-15

    The age of two calcrete nodules (C1 and C2) from the Bala section in the region of Ankara, Turkey, is determined by the Electron Spin Resonance (ESR) method. Three radiation-induced ESR signals at g=2.0056 (A signal), g=2.0006 (C signal) and g=2.0038 (broad signal, BL) were observed. The broad signal (BL) intensity was used as a dating signal. The properties of this dating signal are described in this manuscript. The calcrete nodules were irradiated with a {sup 60}Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve and fitted well with the single exponential saturation functions. Based on this model, accumulated dose (D{sub E}) values for dating are obtained using the multiple-aliquot additive dose method. The D{sub E} values of C1 and C2 calcretes are 1880{+-}207 and 671{+-}67 Gy, respectively. The ESR ages of the two calcrete samples are obtained by assessing the annual dose rate (D) from the content of {sup 238}U, {sup 232}Th and K{sub 2}O determined by wavelength dispersive X-ray fluorescence (XRF) spectrometry. The results are 761{+-}120 and 419{+-}64 ka, respectively, falling into the Middle Pleistocene Epoch in the geological time scale in agreement with the positions of the stratigraphical record.

  5. Pedogenic calcretes within fracture systems and beddings in Neoproterozoic limestones of the Irecê Basin, northeastern Brazil

    Science.gov (United States)

    Borges, S. V. F.; Balsamo, F.; Vieira, M. M.; Iacumin, P.; Srivastava, N. K.; Storti, F.; Bezerra, F. H. R.

    2016-07-01

    Calcretes or caliches are continental limestones developed by surficial weathering process that takes place mostly in arid and semi-arid regions. In the Irecê Basin, northeastern Brazil, in addition to the regular occurrence of pedogenic calcretes, a peculiar type of structurally controlled calcretes occurs on Neoproterozoic limestones. These peculiar calcretes developed near the surface and occur (1) between layers, (2) inside fractures and (3) within major thrust faults. Fieldwork on selected outcrops was integrated with petrographic, mineralogic, geochemical, density and mercury intrusion porosity analyses to constrain the environment of formation and their petrophysical properties. The results revealed that this type of calcrete is the product of multiepisodic events of dissolution and precipitation occurring during the wet and dry seasons in the region along fractures and beddings. Based on the petrophysical results, we suggest that these calcretes may have an important role in the migration of fluids through the impermeable host carbonate rock and that they act as a conduit for fluid flow, as revealed by their high porosity (mean value = 26%) and remarkable pore connectivity.

  6. Can calcretes be used to date pedogenic processes in soil profiles under semi arid climate ? An example from U-Th isochrons in calcretes from South India.

    Science.gov (United States)

    Durand, Nicolas; Hamelin, Bruno; Deschamps, Deschamps; Gunnel, Yanni; Curmi, Pierre

    2015-04-01

    Pedogenic carbonates, such as calcretes, have often been questioned as possible markers of the pedogenetic evolution of soil profiles under semi-arid climate. However, providing precise chronological constraints on their formation is a perequisite to determine the climatic and paleo-environmental conditions prevailing during and after their formation, and to improve our understanding of the physical and chemical conditions that promoted their development and preservation. On the other hand, these authigenic calcium carbonate precipitates provide us with an interesting test of the U-Th radioactive disequilibrium dating method, the reliability of which has been demonstrated extensively in aragonitic marine formations, and calcitic continental speleothems, but remain much more questionable in highly porous and chemically complex media such as soil profiles. In this study, we combined U-Th systematics with detailed micromorphologic observations of calcretes from South India, investigated at different spatial scales, from the landscape to the soil profile, down to the micro-fabrics of the samples. The U-Th analyses were performed by Thermo-Ionization Mass Spectrometry. Since calcretes are impure carbonates, mixed with various amounts of parent rock and weathered minerals, all ages had to be computed using the isochron technique to correct for the detrital component. This method involves the extraction of several coeval subsamples from a single soil horizon and their U-Th analyses after total dissolution (TDS method). The isochron age is derived from the slope of the mixing line between the pure authigenic carbonate and the detrital phase, and the precision established statistically using the probability of fit and weighted mean deviations (MSWD). Our results show that each set of samples taken from decimetric blocks is characterized by a well defined isochron line, clearly distinct from each other in the 3D Osmond diagram (232Th/238U; 230Th/238U ; 234U/238U). The

  7. Development and lithogenesis of the palustrine and calcrete deposits of the Dibdibba Alluvial Fan, Kuwait

    Science.gov (United States)

    AlShuaibi, Arafat A.; Khalaf, Fikry I.

    2011-08-01

    A model is proposed for the development of the Quaternary palustrine carbonate-calcrete association, which occurs as hard crust capping low hills at a distal flood plain of Al Dibdibba alluvial fan located at southwestern Kuwait. Field occurrence, detailed petrographic investigation and geochemical analysis revealed that a single cycle of groundwater calcrete with vertical gradational maturity pattern was developed. This represents a continuous sedimentological cycle during which flood sheet conditions prevailed with intermittent periods of humid and arid conditions. Subsequently, calcitic micrite was continuously precipitated from small, shallow, local, isolated and short lived ponds fringed by freshwater marshes with abundant charophyte meadows. The latter were developed as a result of flooding scattered depressions by groundwater supersaturated with respect to calcite due to rise of groundwater table. The deposition of two facies of carbonate muds, namely; biomicrite and pelintraclasts skeletal micrites was followed by a drought phase which witnessed desiccation of the fresh water ponds and significant drop in groundwater level. A sequence of pedogenic and diagenetic processes acted on the deposited carbonate muds are manifested by: (a) desiccation cracks, (b) micrite neomorphism, (c) infilling of root burrows and some cracks by aeolian siliciclastics, (d) karstification, (e) marmorization, (f) calcretization of root burrow infill and development of pseudo-rhizocrete, (g) calcite cementation and mineral authigenesis, and (h) silcretization. These processes are responsible for the development of hard palustrine carbonate crust. At the advent of aridity, the whole system of Al Dibdibba alluvial fan was subjected to deflation. This resulted in reversing the paleotopography of the hard crusted palustrine depressions into carbonate capped domal hills.

  8. Stable isotope geochemistry of calcrete nodules and septarian concretions in a Quaternary 'red clay' paleovertisol from Hungary.

    Science.gov (United States)

    Bajnóczi, Bernadett; Horváth, Zoltán; Demény, Attila; Mindszenty, Andrea

    2006-12-01

    Calcrete nodules and concretions in unusually large amounts are embedded in the Quaternary clay-rich (Vertisol-type) 'red clay' soil-sedimentary complex at the pediment of the Mátra Mountains (Hungary). Stable isotope signatures were studied in nodules and septarian concretions, uncommon due to their several millimeter sized calcite crystals filling voids and fractures, to reveal their origin. The isotope composition of calcrete covers a wide range: delta18O=-5.9 to-10.4 per thousand and delta13C=-8.9 to-12.3 per thousand (vs. V-PDB). Isotope compositions support pedogenic (sensu stricto) and/or shallow groundwater origin for the calcrete nodules and concretions, the role of 'evolved' (isotopically modified) groundwaters in the formation of secondary carbonate was possibly subordinate. Late-stage, large, Mn-rich euhedral calcite crystals in concretions have the lowest delta13C values, which are interpreted as a result of larger contribution of isotopically light organic carbon due to decomposition of organic matter under reducing conditions. Precipitation of late calcite crystals in concretions occurred in early diagenetic environment after shallow burial of the 'red clay' paleovertisol.

  9. Distribution of calcretes and gypcretes in southwestern United States and their uranium favorability, based on a study of deposits in Western Australia and South West Africa (Namibia)

    Energy Technology Data Exchange (ETDEWEB)

    Carlisle, D.; Merifield, P.M.; Orme, A.R.; Kohl, M.S.; Kolker, O.; Lunt, O.R.

    1978-01-06

    Calcrete, dolocrete, and gypcrete carnotite are abundant in western Australia and Namib Desert, although only a few are of ore grade. The geology of these deposits are described. A genetic classification of calcretes emphasizing uranium favorability was developed, based on the distinction between pedogenic and nonpedogenic processes. Similarities between western Australia and South West Africa give support for the conclusions that lateral transport of U in groundwater is essential to ore deposition and that bedrock barriers or constrictions which narrow the channel of subsurface flow or force the water close to the land surface, greatly favor the formation of uraniferous calcretes. Criteria for uranium favorability deduced from the Australian and South West African studies were applied in a preliminary way to the southern Basin and Range Province of U.S. The procedure is to search for areas in which nonpedogenic calcrete or gypcrete may have developed. A caliche distribution map was compiled from soil survey and field data. Many areas were visited and some of the more interesting are described briefly, including parts of Clark County, Nevada, with occurrences of carnotite in calcrete. (DLC)

  10. Formation of Titan's Lakes by Episodic Dissolution and Precipitation of a Surface Layer Under Semi-Arid Conditions: Comparison with the Pans and Calcretes of Etosha (Namibia)

    Science.gov (United States)

    Bourgeois, O.; Lopez, T.; Le Mouélic, S.; Fleurant, C.; Tobie, G.; Cornet, T.

    2009-12-01

    Radar images from the Cassini spacecraft reveal closed, smooth and flat depressions above northern and southern latitudes of 60° on Titan, Saturn’s largest moon. These depressions have been interpreted as lakes of liquid hydro-carbons and dissolved nitrogen, resting on the icy crust that covers this moon. The depressions include large (over 100,000 square kilometers) seas with dendritic or poorly defined contours, small (1-10 km wide) circular steep-sided depressions, and medium-sized (20-50 km wide) depressions, the contours of which are composed of adjacent circular segments. Some depressions are completely filled with radar-dark material, while others are partially filled and some are empty. Most of these depressions lie in flat plains. By comparison with a terrestrial analogue located in the Etosha Basin (Namibia), we introduce here a dissolution-precipitation model for the formation of these lakes at the expense of a superficial soluble layer. The Etosha Basin is a flat sedimentary basin located at the western border of the Kalahari desert. The climate is semi-arid, with an average annual precipitation rate of 400 mm/yr and an average annual potential evaporation rate of 2200 mm/yr. Sediments in the basin include clays and silts; they are covered by a layer of soluble calcrete a few meters in thickness. The calcrete has formed by precipitation, in the subsurface, of calcium carbonate dissolved in groundwater. Precipitation of calcium carbonate from groundwater is due to the average annual dominance of groundwater evaporation over precipitation. The calcrete layer is dotted with dozens of so-called pans: these are closed, steep-sided, flat and smooth depressions, 1 to 200 km wide and a few meters deep. Relict boulders of calcrete rest on the silty, clayey and evaporitic floors of the pans and provide evidence that the pans grow by radial regressive dissolution of the calcrete layer. By comparison with the development of pans at the expense of the calcrete

  11. Ant-nest ichnofossils in honeycomb calcretes, Neogene Ogallala Formation, High Plains region of western Kansas, U.S.A.

    Science.gov (United States)

    Smith, J.J.; Platt, B.F.; Ludvigson, Greg A.; Thomasson, J.R.

    2011-01-01

    Two new ant-nest trace fossils are described from calcic sandy paleosols of the Neogene Ogallala Formation in western Kansas. The ichnofossils are preserved within and below calcrete beds weathering in positive relief as carbonate-filled casts or as cavities in negative relief. Daimoniobarax ichnogenus nov. is established for burrow systems composed of vertically tiered, horizontally oriented pancake-shaped chambers connected by predominantly vertical and cylindrical shafts ~. 0.8. cm in diameter. Ichnospecies of Daimoniobarax are differentiated based on differences in the plan view outline of chambers, shaft orientation, and junctions between chambers and shafts.Daimoniobarax nephroides ichnospecies nov. is composed of an ~. 24-76. cm long vertical sequence of distinctly lobed chambers (~. 2-20. cm wide and ~. 1. cm high) arranged along sinuous to helical shafts. Chamber shape in plan view ranges from small teardrops to larger kidney- and U-shaped forms. Shafts intersect at chamber edges such that chambers appear to bud from the central shafts. Daimoniobarax nephroides is most similar to the nests of extant seed-harvester ants of the New World genus Pogonomyrmex. Such ants are specialized granivores and prefer sandy soils in arid to semi-arid grassland and desert regions.Daimoniobarax tschinkeli ichnospecies nov. is ~. 30-80. cm in vertical extent. Chambers (~. 2-30. cm wide and ~. 1. cm high) are circular to elongate or pseudopodial in plan view. Vertical shafts are straight to slightly sinuous and intersect most often toward the center of the chambers. The generalized architecture of D. tschinkeli is similar to that of the nests or nest portions of several extant ant genera, though it does not closely resemble any known modern nest.Ant ichnofossils provide valuable information on hidden biodiversity, paleohydrologic regimes, paleopedogenic processes, and paleoclimate during the time of nest occupation. Depth-related changes in chamber size and vertical spacing

  12. 航空γ能谱测量数据在西澳伊尔岗地区钙结岩型铀矿勘查中的应用%Application of Airborne Spectrometry Data to the Exploration of Calcrete hosted Uranium Deposit in Yilgarn Area Western Australia

    Institute of Scientific and Technical Information of China (English)

    车永飞; 张云龙; 赵英俊; 林子瑜

    2015-01-01

    The calcrete distribution in Yilgarn area of western Australia was studied by analyzing the re-gional uranium ore prediction factors,multi parameter combination and supervised classification was used to process and analyze the airborne spectroscopy data and to predict the calcrete hosted uranium metallization.According to the geochemical characteristics differences between airborne uranium, thorium and potassium spectrum data,space modeling tool in ERDAS software was used to calculate the ancient uranium enrichment factors and identify the area of uranium enrichment source.Bayesian decision criterion and supervised classification technology of feature space domain were used to extract multi level aero radiometric anomaly in the study area,and comprehensive analysis methods was used to select calcrete hosted uranium mineralization prospects.%以西澳伊尔岗钙结岩分布区为例,在分析区域铀矿预测要素的基础上,利用多参数组合和监督分类2种方法对航空γ能谱测量数据进行处理和分析,开展钙结岩型铀矿的成矿预测研究。根据航空γ能谱数据铀、钍、钾元素之间的地球化学特征差异,利用 ERDAS软件空间建模工具计算古铀量、铀富集系数,识别铀源区和铀后生富集区。利用特征空间域的贝叶斯决策准则监督分类技术,提取研究区多级航放示矿信息,经过综合分析,最终圈定7片钙结岩型铀成矿远景区。

  13. Dune associated calcretes, Rhizoliths and Paleosols from the western continental shelf of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Thamban, M.

    diameter, interpreted as vascular cylinders of the root tissues are typical. Radial fibrous calcite and spar calcite with inclusions indicate neomorphic cements. Reddish brown mudstones contain calcified root-hair sheaths, micrite glaebules and reworked...

  14. Calcretized Ferricretes Around the Jaisalmer Area, Thar Desert, India: Their Chemistry, Mineralogy, Micromorphology and Genesis

    OpenAIRE

    TIWARI, DESIKAN RAMAKRISHNAN & KRISHNA CHANDRA

    2006-01-01

    Ferricrete, an iron duricrust, caps Tertiary and Mesozoic rocks around Jaisalmer in the Indian desert. These ferricretes are associated with two distinct present-day landforms. The upper unit is a high-level dissected, rocky structural plain and the lower one a colluvial flat with soft ferricrete gravels. This study pertains to the first situation wherein field observations, micromorphological features and regolith chemistry suggest an in situ origin for the ferricretes, as in the case of the...

  15. Study on the diagenetic calcareous accumulations in a soil profile from Floresti (Cluj County, Romania

    Directory of Open Access Journals (Sweden)

    Horea Bedelean

    2004-04-01

    Full Text Available The studied calcretes developed in two different levels (horizons in the soil profile from Floreşti (Cluj County. The deposits outcropping in the area are represented by Bartonian-Priabonian sedimentary rocks (Ciuleni Member, Viştea Limestone and the Quaternary horizon (terrace of Someşul Mic River, consisting of pebbles of different origin, which represent the parent rock of the soil. A detailed petrographical and mineralogical description of the calcretes is given below, based on macroscopic, microscopic and X-ray diffraction analysis. It led to the conclusion that the calcretes from the studied profile have a pedogenic origin. The calcretes consist of distinctive subhorizons within the host horizon of the soil. According to their microstructure, the studied calcretes belong to the alpha-type and may be considered as “nodular calcretes” or “glaebular calcretes”. The source of carbonate was variable: from the parent material of the soil including fragments of carbonate rocks, bioclasts, vegetal rests, eolian dust.

  16. A brief account of coast vegetation near Port Elizabeth

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    H. C. Taylor

    1981-12-01

    Full Text Available The environment and vegetation of an area of coast north-east of Port Elizabeth, South Africa, are briefly described. Five major vegetation categories are recognized. These are: 1.  Scaevola thunbergii Pioneer Vegetation of  littoral dunes and  Ficinia lateralis Sedgeland of calcrete gravel; 2.  Olea exasperata Bush,  Pterocelastrus tricuspidatus Bushclumps and Dune Woodland; 3. Sundays River Scrub; 4. Fynbos of calcrete areas; and 5.  Themeda triandra Grassland. Invasion of the area by Acacia cyclops (Australian W'attle is described. A recommendation for the conservation of the area as a nature reserve is made.

  17. Microtextures in recent and fossil caliche

    NARCIS (Netherlands)

    Nagtegaal, Peter J.C.

    1969-01-01

    Microtextures of calcite in recent caliche are similar to those of authigenic calcite in Upper Carboniferous, Permian and Lower Triassic continental sandstones and mudstones in the South-Central Pyrenees, Spain. Except for one profile in the Permian, no complete caliche profiles containing calcrete

  18. Reconstructing Early Pleistocene (1.3 Ma) terrestrial environmental change in western Anatolia: Did it drive fluvial terrace formation?

    NARCIS (Netherlands)

    Veldkamp, A.; Candy, I.; Jongmans, A.G.; Maddy, D.; Demir, T.; Schoorl, J.M.; Schreve, D.; Stemerdink, C.; Schriek, van der T.

    2015-01-01

    A terrestrial environmental reconstruction of an Early Pleistocene landscape from western Anatolia is presented. The basis of this reconstruction is a sedimentary stack comprising fluvial and colluvial slope deposits. Contained within this stack is a sequence comprising two massive laminar calcretes

  19. Orbital radar studies of paleodrainages in the central Namib Desert

    Science.gov (United States)

    Lancaster, N.; Schaber, G.G.; Teller, J.T.

    2000-01-01

    Orbital radar images of the central Namib Desert show clearly the extent of relict fluvial deposits associated with former courses of the Tsondab and Kuiseb rivers. South of the Kuiseb River, radar data show the existence of a drainage network developed in calcrete-cemented late Tertiary fluvial deposits. The sand-filled paleovalleys are imaged as radar-dark tones in contrast to the radar-bright interfluves where the calcreted gravels occur. The drainage network developed as a result of local runoff from indurated gravels and channeled surface and subsurface flow to the sites of the many interdune lacustrine deposits found in the area. (C) Elsevier Science Inc., 2000.Orbital radar images of the central Namib Desert show clearly the extent of relict fluvial deposits associated with former courses of the Tsondab and Kuiseb rivers. South of the Kuiseb River, radar data show the existence of a drainage network developed in calcrete-cemented late Tertiary fluvial deposits. The sand-filled paleovalleys are imaged as radar-dark tones in contrast to the radar-bright interfluves where the calcreted gravels occur. The drainage network developed as a result of local runoff from indurated gravels and channeled surface and subsurface flow to the sites of the many interdune lacustrine deposits found in the area.

  20. Reply to comment by J.L. Díaz-Hernández and R. Julià on “Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix-Baza basin, SE Spain)”

    Science.gov (United States)

    Pérez-Peña, José Vicente; Azañón, José Miguel; Azor, Antonio; Sánchez-Almazo, Isabel María; Tuccimei, Paola; Della Seta, Marta; Soligo, Michele

    2012-10-01

    We demonstrate that the age of 43 ka obtained for the topmost calcrete layer in the Guadix-Baza remains the only reliable numerical dating of the flat geomorphic surface that marks the end of the sedimentation in the basin. Consequently, the late Pleistocene to Holocene erosion rates derived from the incision of the present-day drainage network into the flat geomorphic surface remain valid. The calcrete radiometric ages reported by Díaz-Hernández and Julià (2012) in their comment are untenable due to the contamination with detrital 230Th (not corrected with the applied U/Th technique) and the possible mix of textural elements with different ages (older inherited grains and newly formed grains). Díaz-Hernández and Julià also quote U/Th ages for travertine terraces formed later than the calcrete layer. These ages lack internal consistency probably due to systematic contamination and/or weathering of the samples. The archaeological ages reported by Díaz-Hernández and Julià are subjected to great uncertainties, but independently of the age assumed as most realistic, they are completely compatible with the age of 43 ka that we obtained for the topmost calcrete layer in the Guadix-Baza basin.

  1. Petrography, mineralogy, and chemistry of calcite-silica deposits at Exile Hill, Nevada, compared with local spring deposits

    Energy Technology Data Exchange (ETDEWEB)

    Vaniman, D.T.; Chipera, S.J.; Bish, D.L.

    1995-12-01

    Chemical, mineralogic, and petrographic analyses of siliceous calcretes from Exile Hill east of Yucca Mountain, Nevada, indicate that pedogenic processes alone account for the formation of the calcretes. These calcretes have been interpreted by some observers as evidence of seismically triggered eruptions of deep water. Such an origin could have important consequences if Yucca Mountain is developed as an unsaturated site for the disposal of high-level nuclear waste. At odds with this hypothesis are the absence of features that should be present at fault-fed springs (e.g., fissure-ridge mounds with microterraces) and the preservation within root casts of delicate pedogenic microfossils, such as calcified filaments and needle-fiber calcites. Mineral-chemical evidence of pedogenic origin is found in heavy-mineral concentrations, reflected in Fe and Sc enrichments. These concentrations, which occur in the most massive of the vein calcretes, require derivation of detritus from a mixture of weathered and eolian materials that occur in the overlying B soil horizons, as opposed to direct incorporation of adjacent unweathered bedrock. Carbonate and silica abundances and accumulation rates are well within the scope of pedogenic processes. Calcium is derived from rainwater or eolian sources, whereas silica is derived in part by dissolution of local volcanic glasses or from dissolution of unstable silica minerals that are abundant in the local tuffs. In contrast with local deposits that are of spring or seep origin, the siliceous calcretes at Yucca Mountain are pedogenic in origin as well as evolution and provide no evidence in support of conjectured spring activity.

  2. Paleosols, types and their characteristics in the Shurijeh Formation, Kopet- Dagh basin, NE Iran

    Directory of Open Access Journals (Sweden)

    Asadolah Mahbobi

    2012-01-01

    Full Text Available The Shurijeh Formation (Late Jurassic- Early Cretaceous consists of siliciclastic facies in the southeastern and eastern parts of the Kopet- Dagh basin, whereas evaporate and carbonate strata are present in its facies succession toward central and western parts of the basin. In addition, various paleosols are identified in this formation that based on relative preference of pedogenic procecces, are classified into three classes including histosols, oxisols and calcisols. The Shurijeh Formation calcisols, based on mineralogical composition, are divided into calcretes and dolocretes and contain special macromorphology and micromorphology features. Based on macroscopic- microscopic properties (alpha and beta microfabrics, the Shurijeh calcretes are divided into pedogenic and non- pedogenic (ground water types that are formed under different conditions. The Shurijeh Formation dolocretes, only found in one section (Esfidan section, and the mudstone host rocks, are probably non- pedogenic (ground water. Water table fluctuations with arid to semiarid climatic conditions are caused calsisols creation in the Shurijeh Formation.

  3. Arsenic concentrations in soils and sediments of the southern Pampean Plain, within Claromecó River Basin (Argentina)

    Science.gov (United States)

    Sosa, N. N.; Datta, S.; Zarate, M.

    2015-12-01

    The Pampean plain is an extensive flatland covering ~1000000 km2 of central and northern Argentina. The region, dominated by Neogene and quaternary volcanoclastic loess and loess-like deposits, shows one of the highest groundwater As concentrations of the world which cause serious problems to human health. The oxidising and high pH conditions of the Pampean groundwater leads to the dissolution of volcanic glass and Fe oxy-hydroxides and the release of As to water. Variation of As content related to lithogenic factors is evident from our study in Claromecó River Basin (Southern Pampean plain): the Mio-Pliocene fluvial facies (MPFF) show low As content (2.6mg/kg) compared to the Late Pleistocene fluvial facies (11.6mg/kg; LPFF). Furthermore, the pedogenic calcrete and the paleosols developed in fluvial facies present significantly different As content: 3.9 mg/Kg in MPFF pedogenic calcrete and 16.5 mg/Kg in LPFF paleosols. Modern soils show the highest As content, especially in the illuvial horizons (23.3 mg/Kg) controlled by grain size and clay mineralogy constituents. Preliminary results demonstrate a sedimentological control embarking differences in As concentrations. These differences are probably attributed to a major hydraulic gradient during the MPFF, which is reflected in grain size and in fluvial structures, which probably was followed by washed out sediments. A geomorphological control was observed through an increase of As concentrations from the interfluves (MPFF) to the valleys (LPFF) as well as from the upper to the lower basin zone within the LPFF. Pedogenic calcrete and paleosols developed in MPFF and LPFF respectively reflect the different geomorphological conditions showing high As content in LPFF paleosols (attributed to Fe oxy-hydroxides). This study relates mineralogy and sedimentological environment to groundwater, surface water from wetlands to understand the hydrochemical processes in controlling As within the Claromecó basin.

  4. Uranium in the Islamic Republic of Mauritania (phase V, deliverable 81): Chapter N in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

    Science.gov (United States)

    Fernette, Gregory

    2015-01-01

    Mauritania has 80 known uranium mineral occurrences and is the current focus of active exploration for uranium by a number of private companies. Seventeen occurrences have had resource estimates published and can be considered as mineral deposits. Fourteen of these are calcrete-type deposits with a total resource of 138.3 million tonnes at an average grade of 331 ppm U3O8. The three bedrock-hosted deposits are granite hosted vein/shear zone type deposits with a total resource of 46.5 million tonnes at a grade of 248 ppm U3O8.

  5. Evidencias paleoclimáticas en duricostras, paleosuelos y sedimentitas silicoclásticas del Cenozoico de Uruguay

    Directory of Open Access Journals (Sweden)

    Ofelia Rita Tófalo

    2009-12-01

    Full Text Available Las sedimentitas continentales del oeste y sur de Uruguay permiten inferir importantes cambios climáticos ocurridos durante el Cenozoico, que se inicia con calizas palustres paleocenas denominadas Formación Queguay y relacionadas con calcretes freáticos que afectan principalmente a sedimentitas fluviales de la Formación Mercedes (Cretácico Tardío. La presencia de estas rocas carbonáticas indica clima semiárido, marcadamente estacional. La Formación Asencio (Eoceno temprano está separada de la Formación Mercedes por una discontinuidad, la paleosuperficie Yapeyú, que limita dos ciclos sedimentarios. Sobre ella se disponen depósitos fluviales que en clima cálido, húmedo y estacional generaron Ultisoles; estos durante lapsos de desecamiento prolongado habrían originado ferricretes, cuyos niveles superiores fueron desmantelados por rehidratación debido a incremento de las precipitaciones. Suprayace en discordancia la Formación Fray Bentos (Oligoceno-Mioceno temprano, integrada por loess depositados bajo clima semiárido, a partir de los cuales se desarrollan paleosuelos y calcretes pedogénicos, entre los que se describe una nueva variedad: calcretes tubulares. Su morfología en planta correspondería a la de un microrrelieve gilgai típico de Vertisoles, igual que la estructura prismática derivada de procesos de expansión-contracción de arcillas esmectíticas en climas estacionales. La presencia de calcretes pedogénicos sugiere condiciones de clima semiárido estacional. La Formación Raigón (Plioceno tardío-Pleistoceno medio de origen fluvial, se formó en un período húmedo y presenta en el techo un paleosuelo generado bajo clima estacional. La Formación Libertad (Pleistoceno temprano a medio, apoya en discordancia y está integrada por loess depositados durante intervalos glaciales y modificados por pedogénesis durante períodos interglaciales o interestadiales.

  6. Strontium isotope geochemistry of soil and playa deposits near Yucca Mountain, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, B.D.; Mahan, S.A.

    1994-12-31

    The isotopic composition of strontium contained in the carbonate fractions of soils provides an excellent tracer which can be used to test models for their origin. This paper reports data on surface coatings and cements, eolian sediments, playas and alluvial fan soils which help to constrain a model for formation of the extensive calcretes and fault infilling in the Yucca Mountain region. The playas contain carbonate with a wide range of strontium compositions; further work will be required to fully understand their possible contributions to the pedogenic carbonate system. Soils from an alluvial fan to the west of Yucca Mountain show that only small amounts of strontium are derived from weathering of silicate detritus. However, calcretes from a fan draining a carbonate terrane have strontium compositions dominated locally by the limestone strontium component. Although much evidence points to an eolian source for at least some of the strontium in the pedogenic carbonates near Yucca Mountain, an additional component or past variation of strontium composition in the eolian source is required to model the pedogenic carbonate system.

  7. Comparative uranium-thorium and thermoluminescence dating of weathered quaternary alluvium in the tropics of Northern Australia

    Science.gov (United States)

    Nanson, Gerald C.; Price, David M.; Short, Stephen A.; Young, Robert W.; Jones, Brian G.

    1991-05-01

    Thermoluminescence (TL) age determinations of alluvial sediments in the tropics are evaluated by comparison with U/Th age determinations of pedogenic accumulations in the alluvium of the lower Gilbert River, a large fan delta in the wet-dry tropics of northern Queensland, Australia. This study extends U/Th dating by applying it not only to calcretes, but also to Fe/Mn oxyhydroxide/oxide accumulations. While a direct correlation cannot be made between U/Th dates from secondary minerals and TL dates from the host sediments, both sets of data show broad consistency. In addition to providing a minima for acceptable TL ages, U/Th dates are useful for determining the chronology of pedogenesis/diagenesis. They show that calcretes and ferricretes have formed under similar climatic conditions in the wet-dry tropics of northern Australia during the late pleistocene. Beneath about 5-12 m the Gilbert fan delta consists of an extensive sand body older than 85,000 yr and probably about 120,000 yr in age, representative of a period of major fluvial activity not repeated since this time. Above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that TL dates at 40,000-50,000 yr B.P. A system of sandy distributary channels over the fan surface represents an early Holocene fluvial phase probably more active than at present.

  8. Sedimentological characteristics of the surficial deposits of the Jal Az-Zor area, Kuwait

    Science.gov (United States)

    Al-Bakri, D.; Kittaneh, W.; Shublaq, W.

    1988-10-01

    The purpose of this article is to discuss the nature and characteristics of the surface geology of the Jal Az-Zor escarpment and the adjacent area, to better understand the sedimentology of desert landforms, and the main factors controlling depositional and diagenetic processes active in this environment. The oldest outcrops along the face of the escarpment are the sand and sandstone sequences of the Mutla and Jal Az-Zor Formations of the Kuwait Group (Neogene). Gravelly deposits of the upper member of the Kuwait Group, Dibdibba Formation (Pleistocene) are restricted to a few hillocks and ridges in the summit area of the escarpment. The Neogene deposits in most of the study area are overlain by a veneer of unconsolidated Holocene sediments. These were classified, according to their morphological setting and field occurrence, into: coastal deposits (intertidal mud, sabkha deposits, and sand dunes) and inland deposits (sand drifts, slope deposits, wadi fills, residual deposits and playa deposits). Wind-born quartzitic sand is the most common Holocene sediment in the study area indicating the dominance of the aeolian processes. Gypsum and carbonate present as cementing materials or in the form of gypcrete and calcrete, respectively, are characteristic sedimentological features of the pre-Holocene deposits. Gypcrete and gypsum cement are abundant in the upper section of the escarpment and decreases downward, whereas the carbonate (calcrete) shows a reverse pattern, i.e., it becomes more dominant in the lower section of the escarpment. The source of sulphate ions in the groundwater that is responsible for the development of gypcrete is believed to be the evaporites in the lower section of the Neogene sequence. The source of ions for the formation of calcrete and calcite cement is less understood due to the lack of significant primary carbonates in the near-surface deposits. It is believed that the nature and distribution of the chemically precipitated material (gypsum

  9. Dialogs by Jerry Szymanski regarding the Yucca Mountain controversy from December, 1990 to March, 1991: Volume 3. Special report number 9, Contract number 92/94.0004

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1993-07-01

    This report is a critical review of a US Geological Survey (USGS) paper regarding the origin of the Yucca Mountain calcite-opaline silica deposits. The report is in the form of a letter to the original authors in the USGS detailing the criticism regarding the origin of calcitic veins in the Yucca Mountain region. The USGS paper contributed most of these calcrete deposits to meteoric dissolution and precipitation mechanisms while the author presents his case for hydrothermal and magmatic origins. The paper presents strong isotopic characterization of these deposits to demonstrate a volcanic influence or source of this mineralization. Strontium, uranium, and carbon isotopes are graphed and compared from the numerous geologic and ground water samples available.

  10. Commentary on the state of knowledge of the origins of the Yucca Mountain calcite veins. Special report number 17, Contract number 94/96.0003

    Energy Technology Data Exchange (ETDEWEB)

    Archambeau, C.

    1994-08-01

    This report is a compilation of papers and a letter providing technical information on the origin and geochemistry of calcite veins and calcretes in the vicinity of the Yucca Mountain repository. The information is presented to demonstrate that these deposits may be ``thermogenic`` in origin with some alteration by pedogenic processes. The papers present isotope ratios of uranium, strontium, and carbon to support the claims for a hydrothermal source. The letter provides a critical review of a previous paper presented at the 64th Advisory Committee on Nuclear Waste. The report makes an attempt to emphasize the need to review this possible origin because it has dramatic implications on the geologic history, paleo-ground water levels, and integrity of the repository.

  11. Environmental influences on the occurrences of sepiolite and palygorskite: a brief review

    Science.gov (United States)

    Jones, Blair F.; Conko, Kathryn M.

    2011-01-01

    Sepiolite is a hydrous magnesium silicate formed by precipitation of near-surface brackish or saline waters, under semi-arid climatic conditions. Four major influences on the distribution of sepiolite are source materials, climate, physical parameters and associated phase relations. Two major pathways governing the occurrence of sepiolite and palygorskite are direct precipitation from solution, and the transformation of precursor phases by dissolution–precipitation. Sepiolite is most commonly found as a result of the former process, whereas palygorskite is often characterized as a product of the latter. Thus, sepiolite typically occurs in lacustrine, often saline, strata, while palygorskite is commonly found in conjunction with soils, alluvium, or most abundantly, calcretes. Here, we review briefly some examples of sepiolite deposits in Spain, Turkey, Argentina, USA, and the African countries of Kenya, Morocco, Tunisia, Senegal, Somalia and South Africa.

  12. Sucesión sedimento-pedológica del Cenozoico Tardío de Zárate (Buenos Aires: registro continental del MIS 5 e intervalos interglaciales más antiguos A pedosedimentary succession of the Late Cenozoic of Zárate (Buenos Aires: continental record of the MIS5 and older inter glacial intervals

    Directory of Open Access Journals (Sweden)

    Ofelia Rita Tófalo

    2008-09-01

    Full Text Available Se presenta la reconstrucción de una secuencia de procesos pedosedimentarios de una sección del Cuaternario Tardío en las proximidades de la localidad de Zárate con el fin de contribuir al conocimiento de la evolución del paisaje en el sector norte de la provincia de Buenos Aires. Para ello se integraron observaciones de campo con estudios de laboratorio: tamaño de grano, mineralogía de las fracciones arena, limo y arcilla, micromorfología, concentraciones de Rb y Sr, análisis por luminiscencia óptica (OSL y un estudio paleomagnético preliminar. Los paleosuelos se desarrollaron en loess y se observaron cuatro claras interrupciones en la sedimentación y generación de los mismos, que determinaron cuatro unidades con distintos tipos de calcretes. Los paleosuelos soldados desarrollados en la unidad C pueden correlacionarse con los observados en Baradero (provincia de Buenos Aires y Lozada (provincia de Córdoba y corresponderían al estadío isotópico 5 (MIS 5, último intervalo interglacial antes del presente, determinado en testigos marinos. El aumento de la relación Rb/Sr indica alteraciones ocurridas durante los procesos de meteorización química y en general se incrementa en los niveles de paleosuelos. Los niveles de calcretes de aguas subterráneas y pedogénicos y su asociación con esmectita, illita y óxido férrico indican que el clima habría sido más seco que el actual y marcadamente estacional. Finalmente, se sugiere la posible correlación de uno de los paleosuelos estudiados con el estadío isotópico 11 (MIS 11.Pedosedimentary processes, recorded in a late Quaternary section near Zarate city, north Buenos Aires province are reconstructed in this study. Both field features and laboratory results were analyzed as a whole. Grain size, sand, silt and clay mineralogy, micromorphology, Rb and Sr concentrations, optical stimulated luminescence (OSL ages as well as preliminary paleomagnetic analysis were performed in order

  13. The origin and history of alteration and carbonatization of the Yucca Mountain ignimbrites. Volume I

    Energy Technology Data Exchange (ETDEWEB)

    Szymanski, J.S.

    1992-04-01

    This document contains Volume I of the report entitled The Origin and History of Alteration and Carbonatization of the Yucca Mountain Ignimbrites by Jerry S. Szymanski and a related correspondence with comments by Donald E. Livingston. In the Great Basin, the flow of terrestrial heat through the crust is affected in part by the flow of fluids. At Yucca Mountain, the role of fluids in crustal heat transport is manifested at the surface by youthful calcretes, sinters, bedrock veins, hydrothermal eruption breccias and hydrothermal alteration. This report discusses evidence for recent metasomatism high in the stratigraphic section at Yucca Mountain. Over the last several hundred years, episodes of calcite emplacement contemporaneous with local mafic volcanism have occurred at intervals that are not long in comparison with the isolation time required for a High-Level Radioactive Waste repository.

  14. Dynamics and genesis of calcic accumulations in soils and sediments of the Argentinean Pampa

    Institute of Scientific and Technical Information of China (English)

    Alsu Kuznetsova; Olga Khokhlova

    2015-01-01

    abstract Micromorphology of calcic accumulations (calcite, whewellite and gypsum) and geochemical indices were considered as indicators of genesis and evolution of pedogenic accumulations in soils and paleosediments of the Argentinean Pampa. Two groups of separate and independent calcic accumula-tions were studied using scanning electron microscopy:(i) in situ Argiudolls, reflecting the current soil formation; (ii) in the layers of calcrete (locally named tosca), reflecting the past environments and conditions of these layers sedimentation. New pedogenic gypsum accumulations in Argiudolls were described and possible ways of their formation were suggested. Combined analyses of morphology of carbonate accumulations and geochemical indices in different horizons of Argiudolls and layers of tosca showed that the tosca is paleopedocomplex with complicated formation history. Influence of current environment on tosca morphology is absent, so it is possible to use these pedofeatures for paleor-econstructions in further studying.

  15. Groundwater ferricretes from the Silurian of Ireland and Permian of the Spanish Pyrenees

    Science.gov (United States)

    Wright, V. P.; Sloan, R. J.; Valero Garcés, B.; Garvie, L. A. J.

    1992-04-01

    Haematite nodule horizons occur in alluvial-lacustrine deposits from the Mill Cove Formation (Silurian) of Dingle, Ireland and the Unidad Roja Superior (Permian) of the Spanish Pyrenees. These horizons, generally less than 1 m thick, are not associated with palaeosol profiles but are hosted by laminated or structureless, bioturbated mudstones to sandstones. The sequences contain weakly developed calcrete profiles. The haematite nodules are interpreted as having formed around fluctuating water-tables and are analogous to present-day groundwater ferricretes (laterites or plinthites). Fe 2+, mobilised during periods of reducing groundwaters, was segregated into ferric oxide nodules during falls in the water-table or during influxes of oxygenated meteoric waters. The prevailing climate during deposition of both sequences was probably semi-arid and the presence of ferricrete-like horizons is not evidence of humid climates. The horizons represent early "diagenetic" effects, not related to prevailing soil moisture regime.

  16. Sucesión sedimento-pedológica del Cenozoico Tardío de Zárate (Buenos Aires: registro continental del MIS 5 e intervalos interglaciales más antiguos

    Directory of Open Access Journals (Sweden)

    Ofelia Rita Tófalo

    2008-09-01

    Full Text Available Se presenta la reconstrucción de una secuencia de procesos pedosedimentarios de una sección del Cuaternario Tardío en las proximidades de la localidad de Zárate con el fin de contribuir al conocimiento de la evolución del paisaje en el sector norte de la provincia de Buenos Aires. Para ello se integraron observaciones de campo con estudios de laboratorio: tamaño de grano, mineralogía de las fracciones arena, limo y arcilla, micromorfología, concentraciones de Rb y Sr, análisis por luminiscencia óptica (OSL y un estudio paleomagnético preliminar. Los paleosuelos se desarrollaron en loess y se observaron cuatro claras interrupciones en la sedimentación y generación de los mismos, que determinaron cuatro unidades con distintos tipos de calcretes. Los paleosuelos soldados desarrollados en la unidad C pueden correlacionarse con los observados en Baradero (provincia de Buenos Aires y Lozada (provincia de Córdoba y corresponderían al estadío isotópico 5 (MIS 5, último intervalo interglacial antes del presente, determinado en testigos marinos. El aumento de la relación Rb/Sr indica alteraciones ocurridas durante los procesos de meteorización química y en general se incrementa en los niveles de paleosuelos. Los niveles de calcretes de aguas subterráneas y pedogénicos y su asociación con esmectita, illita y óxido férrico indican que el clima habría sido más seco que el actual y marcadamente estacional. Finalmente, se sugiere la posible correlación de uno de los paleosuelos estudiados con el estadío isotópico 11 (MIS 11.

  17. Late Pleistocene stratigraphy of a carbonate platform margin, Exumas, Bahamas

    Science.gov (United States)

    Aalto, K. R.; Dill, Robert F.

    1996-05-01

    Detailed field studies of the southern Exuma Cays on the eastern margin of the Great Bahama Bank show a complex history of late Pleistocene island construction. Pleistocene rocks include island core eolianites, overlain at island margins by fossil patch reefs and reef sands, which in turn are overlain by, and/or grade laterally into, talus breccia cones derived from the erosion of island core eolianite at paleo-seacliffs situated at approximately 5-6 m above present mean high tide. Laminated pedogenic calcrete widely caps Pleistocene rocks. Minor zones of penetrative subsurface calcretization, developed in association with root growth, occur along permeable horizons, including: contacts between talus units or crossbed sets, along tension joints, and (possibly) at the Pleistocene reef-eolianite contact. Among Pleistocene eolianite samples studied in thin-section, the relative proportions of ooids-intraclasts+grapestones-skeletal grains-peloids are approximately 48:39:6:7. Marginal to the Exuma Sound and on the Brigantine Cays, a greater proportion of ooids have peloidal nuclei and cortices with numerous laminae, which may reflect ooid derivation from shelf margin and broad platform interior regions that were characterized by high wave energy during ooid formation. Between these two areas, ooids are more commonly superficial and have cortices with few laminae and nuclei composed of subrounded micrite or pelmicrite intraclasts. Such ooid nuclei are most likely derived from storm erosion of partially cemented seafloor muds. Some skeletal-rich eolianite in this region may reflect local sediment input from platform margin reefs, or may be part of an older(?) stratigraphic unit.

  18. Subaerial exposure and drowning processes in a carbonate platform during the Mesozoic Tethyan rifting: The case of the Jurassic succession of Western Sicily (central Mediterranean)

    Science.gov (United States)

    Sulli, A.; Interbartolo, F.

    2016-01-01

    The Liassic carbonate platform succession outcropping at Monte Maranfusa (central Western Sicily) consists of a shallowing-upward sequence of peritidal carbonates, with Jurassic to Paleogene pelagic limestone and siliciclastic Tertiary covers above. The cyclic sequences of subtidal wackestones/packstones, intertidal microcrystalline carbonates with bird's-eye pores, and supratidal bioclastic grainstones are interbedded with dark layers of the following composition: 1) dark-gray, compact, and well-cemented limestone with blackish clasts, interpreted as calcretes (a type of carbonate soil) and 2) reddish calcite laminae, deformed by elongated cavities, filled with vadose silt, interpreted as paleokarst. This succession is crossed by almost vertical faults, of the Late Liassic to Miocene, which often coincides with neptunian dykes, filled by several generations of Toarcian-Early Miocene pelagic sediments. Another system of dykes, known as neptunian sills, filled by injected Upper Lias-Dogger pelagic sediments, lies parallel to the stratification. The parallel dykes were caused by the flexure of the platform during the Jurassic and presumably by a planar slip in the carbonate rocks, whereas neptunian dykes are caused by faulting episodes. Here, we present evidence that the dark layers in the Liassic succession of Monte Maranfusa, previously described by many authors only as parallel dykes, can actually be interpreted as a) neptunian sills, b) pedogenic calcretes, and c) paleospeleothems. Therefore, we found evidence of exposure/flooding intervals in the evolution of the carbonate platform during the Liassic, linked to different pulses in both the subsidence/tectonic activity and the sea-level oscillations. At the top, Fe-Mn crusts (hardgrounds) seal the carbonate platform succession, which is in turn overlain by condensed pelagic deposits, confirming its drowning during rifting processes.

  19. Late Quaternary landscape evolution in the Great Karoo, South Africa: Processes and drivers.

    Science.gov (United States)

    Oldknow, Chris; Hooke, Janet; Lang, Andreas

    2016-04-01

    major increase in the palaeo-water table, enhanced vegetation productivity and led to the formation of extensive calcified root-mats. Soil micromorphological evidence from this calcrete unit and burial of T2 by up to 1.5 m of alluvium (T3) indicates subsequent aridification, but depth of channel entrenchment was retarded by the blanketing effect of the underlying calcrete. The final terrace (T4) is much younger (Late Holocene), reflecting slow aggradation in a wetland setting. Wider segments of valley preserve a 'cut and fill' phase intermediate in age between regional T3 and T4 which appears to be a function of varying alluvial preservation potential. The research demonstrates that phases of alluviation and pedogenesis in these valleys reflect a complex interplay between Late Quaternary climate change and autogenic-feedbacks relating to abrupt changes in sediment supply and connectivity.

  20. Moessbauer and magnetic studies of parent material from argentine pampas soils

    Energy Technology Data Exchange (ETDEWEB)

    Bidegain, J. C. [Laboratorio de Entrenamiento Multidisciplinario para la Investigacion Tecnologica (Argentina); Bartel, A. A. [Universidad Nacional de La Pampa, Facultad de Ciencias Exactas y Naturales (Argentina); Sives, F. R.; Mercader, R. C., E-mail: mercader@fisica.unlp.edu.ar [Universidad Nacional de La Plata, Departamento de Fisica, Facultad de Ciencias Exactas (Argentina)

    2007-02-15

    In order to establish a correlation between the different types of soils using hyperfine and magnetic parameters as climatic and environmental proxies, we have studied the differentiation of soil developed around 38.5{sup o} south latitude, in the central Pampas of Argentina, by means of Moessbauer spectroscopy and environmental magnetism. The soils transect (climosequence) investigated stretches from the drier west (around 64{sup o} W) to the more humid east (at around 59{sup o} W) in the Buenos Aires Province, covering a distance of 600 km. The soils studied developed during recent Holocene geologic times in a landscape characterized by small relict plateaus, slopes and depressions, dunes and prairies. The parent material consists of eolian sandy silts overlying calcrete layers. The low mean annual precipitation in the western parts of the region gives rise to soils without B-horizons, which limits the agricultural use of land. The preliminary results show an increase of the paramagnetic Fe{sup 3+} relative concentration from west to east in the soils investigated. Magnetite is probably mainly responsible for the observed enhancement in the susceptibility values. The magnetic response of the parent material is similar to that of the loess part of the previously investigated loess-paleosol sequences of the Argentine loess plateau.

  1. Latest extension of the Laujar fault in a convergence setting (Sierra Nevada, Betic Cordillera)

    Science.gov (United States)

    Martínez-Martos, Manuel; Galindo-Zaldívar, Jesus; Sanz de Galdeano, Carlos; García-Tortosa, Francisco Juan; Martínez-Moreno, Francisco José; Ruano, Patricia; González-Castillo, Lourdes; Azañón, José Miguel

    2017-02-01

    The present-day relief of the Betic Cordillera formed since the Late Miocene through the regional N-S to NW-SE Africa-Eurasia convergence that developed large folds. The Laujar Fault Zone is a south-dipping E-W oriented structure located at the northern boundary of the Alpujarran Corridor Neogene intramontane basin, which separates Sierra Nevada and Sierra de Gador antiforms, in the Internal Zones of the Betic Cordillera. The fault zone acted in a first stage as a dextral strike-slip fault. Currently it moves as a normal fault evidenced by striated calcretes, also in agreement with regional continuous GPS (CGPS) data that support the hypothesis of an active N-S extension in the fault area. In order to analyse the deep geometry of the Laujar Fault Zone, we combined several geophysical techniques (gravity, magnetic, electric resistivity tomography and audio-magnetotelluric data) with field geological observations. Fault surfaces seem to join at a southward-dipping shallow detachment level, including faults covered by the sedimentary infill. The fault zone was developed in a previously weakened area by wrench faults parallel to the Alpujarran Corridor. The recent normal activity of this fault zone may be a consequence of a change in the Africa-Eurasia convergence orientation, which implies a decrease in the N-S compression component. This structure along the southern limb of Sierra Nevada antiform evidences the gravitational collapse of previously thickened crust in a regional compressional context simultaneous to metamorphic core uplift.

  2. Metallogenic evolution of uranium deposits in the Middle East and North Africa deposits

    Science.gov (United States)

    Howari, Fares; Goodell, Philip; Salman, Abdulaty

    2016-02-01

    This paper is briefly involved in classification and distributions of the Middle East and North Africa (MENA) uranium deposits. The study of these mineral systems can significantly contribute to our further understanding of the metallogeny of known and poorly explored deposits. This provides contribution to, and further enhancement of, current classifications and metallogenic models of uranium systems, allowing researchers to emphasize on unknown or poorly studied mineral systems found in MENA. The present study identified eight metallogenic types of uranium associated with: 1) the Archean rocks and intra-cratonic basins, 2) the Pan-African granites and rhyolites which are characterized by igneous activity, 3) Phanerozoic (Paleozoic) clastics, these deposits are the sedimentological response to Pan African magmatism, 4) Mesozoic (basal) clastics type e.g. Nubia sandstones which are characterized by uranium minerals, 5) regional sedimentary phosphate deposits which are categorized as geosynclinal, or continental margin deposits, on the shelf of the Tethys Ocean, 6) Cenozoic Intracratonic Felsic Magmatism of the Tibesti and Hoggar, and the sandstone U deposits of adjoining Niger. These are similar to the Pan-African magmatism metallogenic, 7) Calcretes, and 8) Resistate minerals which are often enriched in rare earth elements, sometimes including uranium. They are thus sometimes considered as U resources but poorly explored in the MENA region. These metallogenic types are described and discussed in the current paper.

  3. Eolian deposits of the southwestern margin of the Botucatú paleoerg: Reconstruction of the Gondwana landscape in Central Northern Argentina

    Science.gov (United States)

    Peri, V. Gisel; Naipauer, Maximiliano; Pimentel, Marcio; Barcelona, Hernan

    2016-06-01

    The Mesozoic Botucatú paleoerg at the southwestern margin of Gondwana includes a succession of eolian dunes cross-strata which are presently exposed in Otumpa Hills (Central Northern Argentina). Here, the architectural facies, petrology, and provenance of those rocks were studied in order to investigate depositional environments and paleoclimates. The stratigraphic sequence included basal eolian two-dimensional crescentic dunes (Slp) overlain by three-dimensional crescentic dunes of smaller scale (Smt). These were correlated with the Upper Member Rivera of the Tacuarembó Formation (Uruguay), or its equivalent in Brazil, the Botucatú Formation. These outcrops partially mark the southwestern margin of the Botucatú paleoerg along the Chaco-Paraná Basin boundary. The paleocurrents from the W, NW, and SW and the U-Pb ages of detrital zircons indicate a main Pampean cratonic and secondary Andean magmatic arc (180 Ma) source. A detrital zircon of 180 Ma by U-Pb limits a maximum depositional age at 180 Ma (Toarcian) for facies Slp. Upwards, the phreatic silcrete and calcrete indicate semiarid conditions during the Paleocene, which are correlated with the Queguay Formation of Uruguay. A saprolite paleoweathering profile, recording wet tropical-hyper-tropical climate at the Early Eocene and representing the Gondwana landscape and climate conditions, crowns the sequence. This study represents the first provenance and surface texture analysis of minerals from the Botucatú paleoerg and was instrumental to unravel past environmental and sedimentary conditions.

  4. Karst Aquifer Recharge: Comments on Somaratne, N. Characteristics of Point Recharge in Karst Aquifers. Water 2014, 6, 2782–2807

    Directory of Open Access Journals (Sweden)

    Adrian D. Werner

    2014-11-01

    Full Text Available The article “Characteristics of Point Recharge in Karst Aquifers, Water 6: 2782–2807” by N. Somaratne evaluates various recharge estimation techniques applied to four limestone aquifers in South Australia. Somaratne [1] concludes that methods based on watertable fluctuations, groundwater modelling and water budgets are independent of recharge processes, and are therefore superior to the chloride mass balance (CMB approach for karst aquifers. The current comment offers alternative interpretations from existing field measurements and previous literature, in particular for the Uley South aquifer, which is the focus of much of the article by Somaratne [1]. Conclusions regarding this system are revised, partly to account for the misrepresentation of previous studies. The aeolianite sediments of Uley South are mostly unconsolidated or poorly consolidated, and dissolution features in the calcrete capping provide point infiltration into a predominantly unconsolidated vadose zone, whereas Somaratne’s [1] findings require that the system comprises well-developed conduits in otherwise low-conductivity limestone. Somaratne’s [1] assertion that the basic premise of CMB is violated in Uley South is disputable, given strong evidence of relatively well-mixed groundwater arising from mostly diffuse recharge. The characterization of karst aquifer recharge should continue to rely on multiple techniques, including environmental tracers such as chloride.

  5. Carboniferous paleogeographic and paleoclimatic reconstructions

    Energy Technology Data Exchange (ETDEWEB)

    Scotese, C.R. (Univ. of Texas, Arlington, TX (United States). Dept. of Geology); Raymond, A. (Texas A and M Univ., College Station, TX (United States). Dept. Geology)

    1992-01-01

    The Carboniferous was an important transitional period in earth history. The Paleozoic oceans separating the continents of Gondwana, Laurentia, Baltica, Kazakhstan, and Siberia had closed by the late Carboniferous forming the late Paleozoic supercontinent of Pangea. Plate motions which appear to have been rapid during the Early Carboniferous (6--10 cm/yr), slowed to a temperature gradient increased as the Earth's climate changed from hot-house to ice-house conditions. Sea level, which stood high during the Early Carboniferous, fell as a result of continental collision and mountain-building, and then began to rise and fall rhythmically as the South Polar ice-cap waxed and waned. These environmental changes intersected important evolutionary events, namely, the explosive colonization of the emergent land areas by plants and the rise of terrestrial vertebrates. In this paper the authors present paleogeographic reconstructions for 6 intervals during the Carboniferous. These maps illustrate the latitudinal position of the continents deduced from paleomagnetic data and the distribution of climatically restricted lithofacies (coal, bauxite, evaporite, calcrete, and tillite), the inferred location of active plate boundaries, and the changing configuration of mountains, land, shallow seas, and deep ocean basins. For each of these paleogeographic maps a climatic simulation was run using the Parametric Climate Model. These simulations predict the distribution of high and low pressure cells, prevailing wind directions, pole-to-equator temperature gradient, relative wetness/dryness, as well as zones of coastal upwelling.

  6. The contributions of Donald Lee Johnson to understanding the Quaternary geologic and biogeographic history of the California Channel Islands

    Science.gov (United States)

    Muhs, Daniel R.

    2013-01-01

    Over a span of 50 years, native Californian Donald Lee Johnson made a number of memorable contributions to our understanding of the California Channel Islands. Among these are (1) recognizing that carbonate dunes, often cemented into eolianite and derived from offshore shelf sediments during lowered sea level, are markers of glacial periods on the Channel Islands; (2) identifying beach rock on the Channel Islands as the northernmost occurrence of this feature on the Pacific Coast of North America; (3) recognizing of the role of human activities in historic landscape modification; (4) identifying both the biogenic and pedogenic origins of caliche “ghost forests” and laminar calcrete forms on the Channel Islands; (5) providing the first soil maps of several of the islands, showing diverse pathways of pedogenesis; (6) pointing out the importance of fire in Quaternary landscape history on the Channel Islands, based on detailed stratigraphic studies; and (7), perhaps his greatest contribution, clarifying the origin of Pleistocene pygmy mammoths on the Channel Islands, due not to imagined ancient land bridges, but rather the superb swimming abilities of proboscideans combined with lowered sea level, favorable paleowinds, and an attractive paleovegetation on the Channel Islands. Don was a classic natural historian in the great tradition of Charles Darwin and George Gaylord Simpson, his role models. Don’s work will remain important and useful for many years and is an inspiration to those researching the California Channel Islands today.

  7. Paleosols in laterite and silcrete profiles Evidence from the South East Margin of the Australian Precambrian Shield

    Science.gov (United States)

    Firman, J. B.

    1994-08-01

    Laterite and silcrete profiles are common in the arid and semi-arid areas of the Australian Precambrian Shield - a vast planar surface masked by the regolith. Much of the geological history of the shield subsequent to its early development is recorded in ancient cover rocks and younger basin sediments which occur in important stratigraphic sequences, particularly on the margins of the shield. Within these sequences, stratigraphically associated or as companion materials, weathering zones and paleosols were developed which individually and as assemblages of layers and horizons record the history of weathering and of soil formation since the Proterozoic. Laterite and silcrete profiles are seen to be assemblages of paleosols, stratigraphically associated deposits and companion materials which were formed in response to changes in groundwater conditions at particular times in the past. The paleosols record the evolution of the regolith: Older weathering zones and bleached rocks were features of successive landscapes after the early Palaeozoic; ferruginous mottling, ferricrete and silcrete pans were formed after the early Cainozoic; ferricretes and mottled clay paleosols - some of which have been described as "laterite" - were formed during and after the Pliocene. Materials in laterite and silcrete profiles are overlain in places by calcretes formed after the early Pleistocene and by younger soils. The assemblages are distinctive and are characteristic of particular morpholithogical provinces.

  8. Overland flow generation on deep soils in Ethiopia (Lake Tana basin): role of soil texture and plough pan

    Science.gov (United States)

    Nyssen, Jan; Dessie, Mekete; Monsieurs, Elise; Poesen, Jean; Admasu, Teshager; Verhoest, Niko; Adgo, Enyew; Deckers, Jozef

    2014-05-01

    Different applications of rainfall/runoff models in Lake Tana basin (Ethiopia) tend to show that on hill slopes there are vast areas that yield a high runoff response and that behave as if the soil would be nearly impervious (up to 20 % of the hilly catchments). This is well beyond the area occupied by rock outcrops. Duricrusts or hardpans of pedogenetic origin are absent in this environment on basaltic rock with mild tropical climate: no silcretes, calcretes or even ferricretes are known to occur in the basin. Field observations show that runoff response from tilled farmlands can however be unexpectedly high, even when deep theoretically well drained Nitisols occur. In the rainy season, rills and ephemeral gullies are created and these often expose a rock-hard plough pan at some 15 cm depth. Due to repeated tillage at constant depth, the downward pressure of the tip of the ox-drawn ard plough compacts the soil aggregates that are located just below the tilled horizon. In this poster we will discuss the need to not only evaluate the effect of soil texture when interpreting rainfall-runoff relations, but also to investigate the structural and hydrological characteristics of such plough pans.

  9. Braidplain, floodplain and playa lake, alluvial-fan, aeolian and palaeosol facies composing a diversified lithogenetical sequence in the permian and triassic of South Devon (England)

    Science.gov (United States)

    Mader, Detlef

    The Permian and Triassic of South Devon (England) are a continental red bed sequence of very diversified lithogenetical composition. Within the thick series, the distribution of the main depositional environments being fluvial braidplain, fluvial floodplain and playa lake, alluvial fan, aeolian dune and calcrete palaeosol changes repeatedly in both horizontal and vertical direction. Significant sedimentary milieus such as aeolian dunes and calcrete palaeosols occur repeatedly within the succession, but are also lacking in several parts of the sequence. Fluvial braidplain deposits comprise conglomerates, sandstones, intraformational reworking horizons and mudstones and originate in channels and overbank plains of a braided river system. Conglomerates and sandstones are formed by migration of bars and spreading out of sheets during infilling of streams and aggradation of flats. Gravel is often enriched as lag pockets or veneers within steeper scour holes and kolk pots or on the plane floor of the watercourse. Finer-grained sandstones and mudstones are laid down by suspension settling in stagnant water bodies such as small lakes in the overbank area and residual pools in interbar depressions during low-stage or waning-flow in active channels or in abandoned streams. Spectacular bioturbation features in some sandstones with both horizontal tubes and vertical burrows testify to the colonization of the sediments at the bottom of the rivers with declining discharge and transport capacity. Intraformational reworking horizons with ghost-like remnants of degraded sandstones, mudstones and pedogenic carbonates document partially severe condensation of the sequence by removal of some facies elements from the depositional record. The occasionally occurring gravel-bearing mudstones or silty-clayey sandstones represent products of high-energy water surges overspilling the channel banks and transporting sandy and gravelly bed-load in limited amounts beyond the levee wall. The

  10. Microcodium: An extensive review and a proposed non-rhizogenic biologically induced origin for its formation

    Science.gov (United States)

    Kabanov, Pavel; Anadón, Pere; Krumbein, Wolfgang E.

    2008-04-01

    Microcodium has been previously described as a mainly Cenozoic calcification pattern ascribed to various organisms. A review of the available literature and our data reveal two peaks in Microcodium abundance; the Moscovian-early Permian and the latest Cretaceous-Paleogene. A detailed analysis of late Paleozoic and Cenozoic examples leads to the following new conclusions. Typical Microcodium-forming unilayered 'corn-cob' aggregates of elongated grains and thick multilayered (palisade) replacing structures cannot be linked to smaller-grained intracellular root calcifications, as became widely accepted after the work of Klappa [Klappa, C.F., 1979. Calcified filaments in Quaternary calcretes: organo-mineral interactions in the subaerial vadose environment. J. Sediment. Petrol. 49, 955-968.] Typical Microcodium is recognized from the early Carboniferous (with doubtful Devonian reports) to Quaternary as a biologically induced mineralization formed via dissolution/precipitation processes in various aerobic Ca-rich soil and subsoil terrestrial environments. Morphology and δ13C signatures of Microcodium suggest that neither plants, algae, or roots and root-associated mycorrhiza regulate the formation of these fossil structures. Non-recrystallized Microcodium grains basically consist of slender (1.5-4 μm) curved radiating monocrystalline prisms with occasionally preserved hyphae-like morphology. Thin (0.5-3 μm) hypha-like canals can also be observed. These supposed hyphae may belong to actinobacteria. However, thin fungal mycelia cannot be excluded. We propose a model of Microcodium formation involving a mycelial saprotrophic organism responsible for substrate corrosion and associated bacteria capable of consuming acidic metabolites and CaCO 3 reprecipitation into the Microcodium structures.

  11. Stratigraphy of the Neogene Sahabi units in the Sirt Basin, northeast Libya

    Science.gov (United States)

    El-Shawaihdi, M. H.; Mozley, P. S.; Boaz, N. T.; Salloum, F.; Pavlakis, P.; Muftah, A.; Triantaphyllou, M.

    2016-06-01

    A revision of the nomenclature of lithostratigraphic units of Neogene strata at As Sahabi, northeast Libya, is presented, based on new fieldwork conducted during 2006-2008. The Sahabi units are correlated across the Ajdabya Sheet (NH 34-6) in northeastern Libya. Major conclusions are: (1) Miocene (Langhian through Messinian) strata are predominantly carbonate and should be referred to as formation "M"; (2) A local unconformity of Miocene (early Messinian) age overlies strata of the formation "M"; (3) This unconformity is overlain by Messinian gypsiferous sand and mud (formerly formation "P" and partially member "T"), which are designated as the "lower member" (gypsiferous) of the Sahabi Formation; (4) The "lower member" is overlain by sand and mud of late Messinian age (formerly partially member "T" and members "U1", "UD", and "U2") in a generally fining-upwards sequence, and are designated as the "upper member" (non-gypsiferous) of the Sahabi Formation; (5) The latest Miocene sand and mud of the "upper member" are capped by an unconformity that is correlated with the regression and desiccation of the Mediterranean Sea during the Messinian Salinity Crisis and with Eosahabi Channel cutting; (6) The unconformity is overlain by Pliocene medium, coarse, and pebbly sands, which are referred to as the Qarat Weddah Formation (formerly Garet Uedda Formation); (7) The Pliocene sands of Qarat Weddah Formation are overlain by carbonate soil (calcrete) of Late Pliocene age, which is referred to as formation "Z" (formerly member "Z"). The major outcome of this study is a revised stratigraphic description and nomenclature of the Sahabi units that helps to provide a formal and unified context for understanding paleontological discoveries in northeastern Libya, which will serve to facilitate a broader correlation of the Sahabi units with their equivalents elsewhere in Africa and in Europe and Asia.

  12. Sandstone Diagenesis at Gale Crater, Mars, As Observed By Curiosity

    Science.gov (United States)

    Siebach, K. L.; Grotzinger, J. P.; McLennan, S. M.; Hurowitz, J.; Kah, L. C.; Edgett, K. S.; Williams, R. M. E.; Wiens, R. C.; Schieber, J.

    2014-12-01

    The Mars Science Laboratory rover, Curiosity, has encountered a significant number of poorly-sorted and very well-lithified sandstones along its traverse on the floor of Gale Crater. We use images from the hand-lens imager (MAHLI) and elemental chemistry from the ChemCam laser-induced breakdown spectroscopy instrument (LIBS) and the alpha-particle x-ray spectrometer (APXS) to begin to constrain the diagenetic history of these sandstones, including lithification and possible later dissolution. Investigation of MAHLI images reveals that the sediments are poorly-sorted and show very low apparent porosity, generally less than ~5%. However, in some cases, such as the Gillespie Lake sandstone identified in Yellowknife Bay, this apparent porosity includes a significant fraction of void spaces larger than typical sediment grain sizes (~30% by number or 75% of void spaces by area). One possible explanation of these larger pits is that they represent recent removal of soft intraclasts by eolian abrasion. Another possibility is that later diagenetic fluids caused dissolution of more soluble grains, and production of secondary porosity. Investigation into the elemental chemistry of the sandstones has shown that they have a relatively unaltered basaltic bulk composition in spite of possessing a variety of secondary minerals and amorphous material, indicating isochemical diagenetic processes. The chemistry and mineralogy of the cement is not immediately evident based on the initial analyses; there is not a high percentage of salts or evaporative minerals that may easily cement near-surface sandstones. Furthermore, these sandstones lack textures and compositions consistent with pedogenic processes, such as calcrete, silcrete, or ferricrete. Instead, they may record burial and cementation at depth. Cement composition may be constrained through comparison to terrestrial basaltic sandstones, and studying chemical variations along ChemCam and APXS transects of the rocks.

  13. Deposition and early diagenesis of playa glauberite in the Karinga Creek drainage system, Northern Territory, Australia

    Science.gov (United States)

    Arakel, A. V.; Cohen, A.

    1991-02-01

    Glauberite [Na 2Ca(SO 4) 2], in the form of discrete crystals, nodules and lenses, represents the second most common sulphate mineral type (after gypsum) in the chain of modern playa lakes located in the Karinga Creek drainage system, Northern Territory. These modern glauberite deposits exhibit textures and fabrics which reflect both syndeposition with gypsum within the playa phreatic zone, and early diagenetic replacement of host gypsite in the playa vadose zone. Because the distribution of hydrological zones in individual playa lakes vary significantly, the extent of glauberite facies development is highly irregular. Factors controlling glauberite deposition include the nature and extent of groundwater discharge from local and regional aquifers, playa surface evaporation rates, porewater geochemistry and the depth to basal aquicludes. Geochemical and petrographic evidence indicate that the paragenesis of sulphate minerals in the playa lakes of the study area is primarily dictated by the solubility of gypsum, which in turn reflects the extent of dilution and concentration of playa porewaters. On a regional scale, brine dilution and concentration can be related to seasonal and longer-term groundwater recharge-discharge patterns; but, on a local scale, the proximity to springs and ephemeral seepage creeks emanating from local calcrete aquifers is the dominating influence. Hence, a thorough knowledge of groundwater hydrodynamics, particularly the recharge-discharge pattern in playa-marginal areas, must be an essential part of any detailed assessment of the role of depositional and early diagenetic processes in the genesis of glauberite facies in similar arid drainage basins. The close relationship between glauberite facies development and the playa groundwater level has significant implications for interpretations of variation in the water table and other environmental conditions in the shallowing-upwards sequences of ancient lacustrine deposits. The presence of

  14. Cryptic Species or Inadequate Taxonomy? Implementation of 2D Geometric Morphometrics Based on Integumental Organs as Landmarks for Delimitation and Description of Copepod Taxa.

    Science.gov (United States)

    Karanovic, Tomislav; Djurakic, Marko; Eberhard, Stefan M

    2016-03-01

    Discovery of cryptic species using molecular tools has become common in many animal groups but it is rarely accompanied by morphological revision, creating ongoing problems in taxonomy and conservation. In copepods, cryptic species have been discovered in most groups where fast-evolving molecular markers were employed. In this study at Yeelirrie in Western Australia we investigate a subterranean species complex belonging to the harpacticoid genus Schizopera Sars, 1905, using both the barcoding mitochondrial COI gene and landmark-based two-dimensional geometric morphometrics. Integumental organs (sensilla and pores) are used as landmarks for the first time in any crustacean group. Complete congruence between DNA-based species delimitation and relative position of integumental organs in two independent morphological structures suggests the existence of three distinct evolutionary units. We describe two of them as new species, employing a condensed taxonomic format appropriate for cryptic species. We argue that many supposedly cryptic species might not be cryptic if researchers focus on analyzing morphological structures with multivariate tools that explicitly take into account geometry of the phenotype. A perceived supremacy of molecular methods in detecting cryptic species is in our view a consequence of disparity of investment and unexploited recent advancements in morphometrics among taxonomists. Our study shows that morphometric data alone could be used to find diagnostic morphological traits and gives hope to anyone studying small animals with a hard integument or shell, especially opening the door to assessing fossil diversity and rich museum collections. We expect that simultaneous use of molecular tools with geometry-oriented morphometrics may yield faster formal description of species. Decrypted species in this study are a good example for urgency of formal descriptions, as they display short-range endemism in small groundwater calcrete aquifers in a

  15. Miocene-Pleistocene Paleoclimate and Paleoenvironment in the Meade Basin, Kansas

    Science.gov (United States)

    Snell, K. E.; Uno, K. T.; Fetrow, A. C.; Burgess, C.; Lukens, W. E.; Fox, D. L.; Fox-Dobbs, K.; Polissar, P. J.

    2015-12-01

    The Meade Basin in southwestern Kansas preserves a unique record of paleovegetation and small mammal faunal change from the Miocene to the Pleistocene. Many of the paleosols preserved in this basin contain paleosol carbonate nodules, thick calcretes and abundant organic-rich horizons, which makes it ideally suited for a multiproxy study that explores the role of paleoenvironmental change in driving floral and faunal change. Here we focus on the carbonate samples where we measured carbon and oxygen isotopes (δ13Cc and δ18Oc, respectively); used clumped isotope thermometry (Δ47) to estimate soil temperature and soil water δ18O; and assessed the preservation state and additional paleoenvironmental features of the samples using optical and cathodoluminescence (CL) microscopy. The carbon isotope record matches previous studies from the region and shows an increase in the relative abundance of C4 biomass on the landscape since the late Miocene. The Δ47 temperatures and the δ18O of soil water, while variable, show no significant change in average values through time. The textural and luminescenece characteristics suggest some samples have undergone moderate to extensive diagenetic alteration from groundwater fluids, perhaps causing some of the variability in the geochemical records. Soil depth may also account for some of the variability. Overall, these data suggest that temperature is unlikely to be the dominant factor driving paleovegetation and faunal change in this region from the Miocene to Pleistocene. In addition, these data highlight the importance of assessing preservation for all carbonate samples, regardless of whether or not the samples have been deeply buried.

  16. Typology and Geographic Geotectonic Distribution of Uranium Deposits Typologie et répartition géographique/géotectonique des gisements d'uranium

    Directory of Open Access Journals (Sweden)

    Dahlkamp F. J.

    2006-11-01

    Full Text Available In the last ten years, twenty new uranium deposits have been discovered. They provide nearly 50% of the known and reasonably assured resources. The most important deposits known in the past by size and ore grade were those found in oligomictic quartz pebble conglomerates, sandstones and, to a lesser extent, hydrothermal veins. The types found more recently, which are greater in quantity than the former ones, are of the vein type (Canada, Australia as well as of the intrusive type (Rössing, Namibia and in calcretes (Yeelirrie, Australia and acid volcanic rocks (Mexico. Several classifications have been worked out in the past (E. W. Heinrich, 1958; M. Roubault, 1958; A. Mancher, 1962. More recently new data have enabled these classifications to be extended on a worldwide basis (Ruzicka, 1971; Ziegler, 1974; Dahlkamp, 1974, 1978 or on a regional basis (McMillon for Canada, 1978; Ingram for Australia, 1974. This classification attempt takes all available useful data into consideration to define different types of uranium deposits in as comprehensive and strict a manner as possible. Pendant les dix dernières années 20 nouveaux types de gisements d'uranium ont été découverts. Ils contribuent à assurer près de 50 % des ressources connues raisonnablement assurées. Dans le passé, les gisements les plus importants par la taille et la teneur en minerai étaient ceux des conglomérats à galets de quartz monogéniques, ceux des grès et, dans une plus faible mesure, ceux des filons hydrothermaux. Les nouveaux types connus, qui dépassent les premiers par la quantité, sont classés en gisements filoniens (Canada, Australie aussi bien qu'en intrusifs (Rössing, Namibie, en calcrêtes (Yeelirie, Australie et volcaniques acides (Mexique. Plusieurs classifications furent élaborées dans le passé (E. W. Heinrich, 1958 ; M. Roubault, 1958 ; A. Mancher, 1962. Plus récemment les données recueillies ont permis de les développer sur une base mondiale

  17. Morphogenèse, climat et sociétés dans la plaine de Sfax (Tunisie depuis le Pléistocène supérieur : l'exemple du bassin versant de l'oued Chaâl-Tarfaoui

    Directory of Open Access Journals (Sweden)

    Noômène Fehri

    2007-12-01

    Full Text Available À travers une démarche chronologique et une approche géomorpho-historico-archéologique, cet article est une synthèse sur les rapports entre la morphogenèse, les variations climatiques et les sociétés humaines depuis le Pléistocène supérieur jusqu'à nos jours.Dans le bassin versant de l'oued Chaâl-Tarfaoui, le Pléistocène supérieur est représenté par un niveau sableux à concrétions calcaires. À l'Holocène, le remaniement de ces sables essentiellement éoliens accumulés, selon toute vraisemblance, à la fin du Würm par des vents de secteur Nord, génère deux nappes alluviales majeures : une basse nappe alluviale holocène pré-romaine (préhistorique ? et une très basse nappe alluviale holocène historique post-romaine. Les crues exceptionnelles de 1969 ont édifié une troisième nappe mais d'une épaisseur moins importante que les précédentes.This paper is a synthesis of relations between morphogenetic activity, climatic changes and human societies from Upper Pleistocene up to now, using a chronological and geomorpho-historico-archaeological approach.In wadi Chaâl-Tarfaoui catchment, Upper Pleistocene formations are sandy with nodular calcretes very probably wind blown at the end of Würmian period by southward winds. During Holocene they were removed by runoff into two main alluvial formations. The older one is the low Holocene historic pre-roman (prehistoric ? formation and the younger one is the very low Holocene historic post-roman formation. A third formation has been deposited by 1969 exceptional floods. It is thinner than the previous formations.

  18. Potential impacts of damming the Juba Valley, western Somalia: Insights from geomorphology and alluvial history

    Science.gov (United States)

    Williams, Martin

    2014-05-01

    In 1988 plans were well advanced to dam the Juba River in western Somalia. The aims of the Baardheere Dam Project were to generate hydroelectric power for the capital Mogadishu, and to provide water for irrigation in the Juba Valley. A reconnaissance survey on foot along 500 km of the river upstream of the proposed dam site at Baardheere and detailed geomorphic mapping from air photos provided a basis for reconstructing the late Quaternary alluvial history of the river and for assessing the potential impact of the proposed dam. The Juba River rises in the Ethiopian Highlands and is the only river in Somalia that flows to the sea. Its history reflects climatic events in Ethiopia, where the Rift Valley lakes were very low during the LGM (21±2 ka), and high for about 5, 000 years before and after then. Cave deposits in Somalia indicate wetter conditions at 13, 10, 7.5 and 1.5 ka. Alluvial terraces in the Juba Valley range in age from late Pleistocene to late Holocene but only attain a few metres above the present floodplain. This is because the dry tributary valleys contain limestone caves and fissures that divert any high flows from the parent river underground, a process not known when the project was first approved. The oldest preserved terrace was cemented by calcrete by 40 ka. Alluvial gravels were deposited at the outlet of dry tributary valleys during times of episodic high-energy flow between 26 ka and 28 ka. Finely laminated shelly sands accumulated at 10 ka to form the 5 m terrace. The 2 m terrace was laid down 3.2 ka ago as a slackwater deposit. The lack of high-level alluvial terraces raises doubts over plans to dam the river, since rapid leakage would occur from side valleys and the reservoir would not attain the height needed to generate hydroelectric power. It would submerge all existing arable land along the river. Finally, the presence in the late Holocene alluvium of the sub-fossil gastropods Bulinus truncatus and Biomphalaria pfeifferi, which are

  19. Estratigrafía y paleoambientes de la Formación Los Llanos (La Rioja: una secuencia condensada Miocena en el antepaís fragmentado andino central

    Directory of Open Access Journals (Sweden)

    M. Ezpeleta

    2006-06-01

    Full Text Available En la región central de las Sierras Pampeanas, un conjunto de afloramientos saltuarios conocidos como Formación Los Llanos, se disponen irregularmente a través de las sierras Brava, Los Llanos y Ulapes-Las Minas, formando parte de la cubierta cenozoica. Esta sucesión sedimentaria está dominantemente compuesta por niveles de calcretes y depósitos fluvio-eólicos, y su espesor raramente supera los ~40 m. Desde su definición, existen escasos trabajos de detalle sobre su estratigrafía desde una óptica moderna. El mapeo y análisis detallado de facies permitieron dividir a la unidad en miembros inferior y superior, y caracterizar sus paleoambientes sedimentarios. Para el conjunto se definieron ocho facies: 1 conglomerados clastos soportados, 2 brechas y microbrechas, 3 areniscas con megaestratificación cruzada, 4 conglomerados arenosos calcáreos fuertemente cementados, 5 areniscas y arcilitas con estructura columnar, 6 areniscas conglomerádicas con cemento silícico, 7 limo-arcilitas pardo-rojizas, y 8 brechas fangosas. Estas facies fueron agrupadas en las asociaciones de facies (I fluvio-eólica y (II aluviales con paleosuelos, que parcialmente coinciden con los miembros reconocidos. El conjunto permite deducir un paleoambiente de abanicos aluviales medios a distales periódicamente afectados por formación de paleosuelos. Estos últimos reflejan sectores distales con escasa influencia de relieve indicativos de episodios de condensación. Debido a los escasos registros paleontológicos con procedencia documentada, y hasta tanto se tengan edades geocronológicas precisas, nuestras interpretaciones paleoclimáticas permitirían realizar una correlación con los eventos climáticos del Mioceno Medio- Plioceno ampliamente difundidos en el antepaís andino, que habrían afectado a los depósitos sinorogénicos desarrollados en una zona de domamiento periférico.

  20. Correlation of aptian-albian carbon isotope excursions in continental strata of the cretaceous Foreland Basin, Eastern Utah, U.S.A.

    Science.gov (United States)

    Ludvigson, Greg A.; Joeckel, R.M.; Gonzalez, Luis A.; Gulbranson, E.L.; Rasbury, E.T.; Hunt, G.J.; Kirkland, J.I.; Madsen, S.

    2010-01-01

    Nodular carbonates ("calcretes") in continental foreland-basin strata of the Early Cretaceous Cedar Mountain Formation (CMF) in eastern Utah yield ??13C and ??O records of changes in the exogenic carbon cycle related to oceanic anoxic events (OAEs), and terrestrial paleoclimate. Chemostratigraphic profiles of both forebulge and foredeep sections show two prominent positive ??13C excursions, each with a peak value of -3% VPDB, and having background ??13C values of about -6% VPDB. These excursions correlate with the global early Aptian (Ap7) and late Aptian-early Albian (Apl2-All) carbon isotope excursions. Aptian-Albian positive ??13C excursions in the CMF also correspond to 3-4 per mil increases in carbonate ??18O. These phenomena record local aridification events. The chemostratigraphic profile on the thinner forebulge section of the CMF is calibrated, for the first time, by a radiogenic U-Pb date of 119.4 ?? 2.6 Ma on a carbonate bed, and by detrital zircon U-Pb dates on two bounding sandstone units (maximum depositional ages of 146 Ma and 112 Ma). P??trographie observations and diagenetic analyses of micritic to microsparitic carbonates from nodules indicate palustrine origins and demonstrate that they crystallized in shallow early meteoric phreatic environments. Meteoric calcite lines derived from CMF carbonates have ??18O values ranging between -8.1 to -7.5%o VPDB, supporting an estimate of zonal mean groundwater ??18O of -6% VSMOW for an Aptian-Albian paleolatitude of 34?? N. Furthermore, our two chemostratigraphic profiles exhibit a generally proportionate thinning of correlative strata from the foredeep on to the forebulge, suggesting that there were consistently lower rates of accumulation on the forebulge during the Aptian-Albian. Identification of the global Aptian-Albian ??13C excursions in purely continental strata, as demonstrated in this paper, opens a new avenue of research by identifying specific stratigraphie intervals that record the terrestrial

  1. Radial patterns of bitumen dykes around Quaternary volcanoes, provinces of northern Neuquén and southernmost Mendoza, Argentina

    Science.gov (United States)

    Cobbold, Peter R.; Ruffet, Gilles; Leith, Leslie; Loseth, Helge; Rodrigues, Nuno; Leanza, Hector A.; Zanella, Alain

    2014-12-01

    geochemically of low grade. In contrast, a large crosscutting bitumen dyke is of higher grade and formed later. At other localities, near basement faults, bitumen dykes have cap-rocks of hydrothermal calcrete. Other dykes or their wall rocks contain hydrothermal minerals. Finally, some dykes splay upward towards the current land surface. We conclude that (1) the bitumen dykes formed during volcanic activity in Pliocene-Pleistocene times, and that (2) heat advection by hydrothermal fluids helped to generate oil, which migrated upwards or downwards from the source rock and filled intrusive veins, before solidifying to bitumen, by loss of volatile elements. This unconventional hydrocarbon system may have significant implications for regional exploration in the foothills of the Andes.

  2. Génesis de las acumulaciones de carbonatos en aridisoles nordpatagónicos: su significado paleopedológico Genesis of carbonate accumulations in North Patagonic aridisols: its paleopedological significance

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    Pablo José Bouza

    2012-06-01

    correlate soils and paleosols (chronosequence. The accumulations of pedogenetic carbonates are revealed by the presence of typical morphological features (laminar structure, calcitic nodules, pendants, alpha-type fabric, pellets and ooids and palygorskite and sepiolite formed during calcretización processes. The analysis of the isotopic compositions of d13C and d18O showed an acceptable positive correlation (r2 = 0.5, p <0.001 indicating a correspondence between assemblages of plants with higher proportion of C4, which are tolerant to water stress and high temperatures (values more positive of d13C and d18O respectively. The calcretes present in Caleta Valdés Formation were formed during the culmination of MIS 5 period (5a-c, while the carbonates present in the Rodados Patagónicos would have developed in a warmer and drier interglacial period, presumably during MIS 11.

  3. Analysis of a intra-Carixian clay horizon into carbonate platform of the Ouarsenis (Algeria): composition, dynamic and paleo-climatic implication

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    Benhamou, M.; Salhi, A. [Oran Univ., Faculte des Sciences de la Terre et de l' Amenagement du Territoire, Dpt. de Geologie (Algeria)

    2005-07-01

    During the Late Sinemurian a carbonate platform has developed on the Ouarsenis area (external Tell o f the Algerian Alpine belt) with setting deposits of the Kef Sidi Amar Carbonate Formation. A first maximum flooding materialized by a brachiopods (Zeilleriids) layer, is occurring during the Late Carixian. The Late Carixian deepening has been followed by a sea-level fall documented by several meters incisions filled by transgressive breccia and conglomerates. After this episode, this material was sealed by a pedogenic bed (0,05 to 0,20 m) which corresponds to a yellow clay deposit containing well rounded particles interpreted as pedo-genetic globules. These corpuscles are composed of reddish and hardened clay, corroded quartz grains, rhombic and zoned dolomite crystals and ankerite, monocrystalline and xeno-morphous detrital quartz grains (1-2 mm). The observed characteristics allow to recognize a typical calcrete. They are the result of pedo-genetic diagenesis developed inside the phreatic water-table near the surface: this is an alteration profile. The mineralogic fraction has been analyzed by X-Ray which show results of association clay mineral as a predominance of illite (85%) and mixed-layer illite-montmorillonite (I-M, 10%) associated with a low ration of chlorite (5%) and kaolinite trace (1%). This mineralogic clay association indicates a shallow water (hydro-morphic zone). Among these clay minerals, the illite reveals the precious indications in a source area. In this case, it comes from the decomposition of the schist paleo-relief located in the internal domain. This rock was transformed by acid leaching (action of the sour humus) into kaolinite with the presence of the quartzification. The origin of the mixed-layer clay I-M (10%) is the result of the active pedogenesis. The simultaneous presence of the illite, chlorite, kaolinite and the mixed-layer clay I-M seems to be result from the erosion exercised on the alteration product or arenitisation of the

  4. Genesis of petroduric and petrocalcic horizons in Latinamerica volcanic soils

    Science.gov (United States)

    Quantin, Paul

    2010-05-01

    -arid climate. A complex soil profile of petrocalcic Phaeozem, derived from 4 pyroclastic layers, shows among its successive horizons: in layer 3 the 'upper cangahua' with petrocalcic features and in layer 4 the 'lower cangahua' with hard fragipan properties. The features of the petrocalcic cangahua differ from a Mexican fragipan (Hidalgo & al 1997) by: a hard calcrete, higher alkalinity, stability in water after HCl and NaOH treatment, 2-4% of 'free silica'. The macro and micro-morphology shows: the laminar calcite crust, at the top of cangahua, with alternate micrite-sparite layers; downwards, microcalcite infillings in the voids of a prismatic structure, invading the groundmass by epigenesis of clay sheets, together whith microcrystalline opal. From these data this scenario is inferred: after a former weathering of volcanic glass to form a clayey matrix, as well amorphous silica and microcalcite coatings and infillings, then a second process, perhaps due to drier climate, produced the laminar crust formation, by invasion of microcalcite in the matrix. Conclusion. The petrocalcic horizon in Ecuador was produced by two processes: from a former phase of weathering giving a fragic horizon to a second producing the accumulation of calcite and some opal over and inside the matrix, due to climate change. The petroduric horizon in Mexico, is the product of a very complex soil transformation, from a former clayey Nitisol, through four successive processes: clay eluviation-illuviation, alternate redoximorphy, clay degradation, finally a progressive silicification over and inside the groundmass, probably due to pedoclimate change. References F. Elsass, D. Dubroeucq & M. Thiry. 2000. Clay Minerals, 35, 477-489. C. Hidalgo, P. Quantin & F. Elsass. 1997. Memorias del III Simposio Internacional sobre Suelos volcanicos endurecidos (Quito 1996), p. 65-72. - P. Quantin & C. Zebrowski. 1997. idem, p. 29-47.- J.P. Rossignol & P. Quantin. 1997. idem, p. 73-82.

  5. Modeling spatial and seasonal soil moisture in a semi arid hillslope: The impact of integrating soil surface seal parameters

    Science.gov (United States)

    Sela, Shai; Svoray, Tal; Assouline, Shmuel

    2010-05-01

    Modeling hillslope hydrology and the complex and coupled reaction of runoff processes to rainfall, lies in the focus of a growing number of research studies. The ability to characterize and understand the mechanisms underlying the complex hillslope soil moisture patterns, which trigger spatially variable non linear runoff initiation, still remains a current hydrological challenge especially in ungauged catchments. In humid climates, connectivity of transient moisture patches was suggested as a unifying concept for studying thresholds for subsurface flow and redistribution of soil moisture at the hillslope scale. In semiarid areas, however, transient moisture patches control also the differentiation between evaporation and surface runoff and the ability to identify a unifying concept controlling the large variability of soil moisture at the hillslope scale remains an open research gap. At the LTER Lehavim site in the center of Israel (31020' N, 34045' E) a typical hillslope (0.115 km2) was chosen offering different aspects and a classic geomorphologic banding. The annual rainfall is 290 mm, the soils are brown lithosols and arid brown loess and the dominant rock formations are Eocenean limestone and chalk with patches of calcrete. The vegetation is characterised by scattered dwarf shrubs (dominant species Sarcopoterium spinosum) and patches of herbaceous vegetation, mostly annuals, are spread between rocks and dwarf shrubs. An extensive spatial database of soil hydraulic and environmental parameters (e.g. slope, radiation, bulk density) was measured in the field and interpolated to continuous maps using geostatistical techniques and physically based modelling. To explore the effect of soil surface sealing, Mualem and Assouline (1989) equations describing the change in hydraulic parameters resulting from soil seal formation were applied. Two simple indices were developed to describe local evaporation values and contribution of water from rock outcrops to the soil

  6. Sedimentología y petrología de los abanicos aluviales y facies adyacentes en el Neogeno de Paracuellos de Jarama (Madrid

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    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

  7. Evolution of U fractionation processes through geologic time : consequences for the variation of U deposit types from Early Earth to Present

    Science.gov (United States)

    Cuney, M.

    2009-12-01

    pegmatoids (Charlebois, Canada), (iv) hydrothermal remobilization in veins (Beaverlodge, Canada) at about 1.75 Ga, and (v) U mineralization related to Na-metasomatism (Lagoa Real, Brazil ; Central Ukraine). After 1.75 Ga, a long period of tectonic quiescence occurred on the Earth, and large intracontinental basins, comprising at their base thick oxidized siliciclastic sequences were formed in many parts of the Nuna. In the Athabasca (Canada) and Kombolgie (Australia) basins, the siliciclastic sediments represented huge aquitards for sodic brines derived from overlying evaporites. The brines became calcic when infiltrated into the basement and leached U dominantly from Paleoproterozoic epicontinental sediments, their anatectic derivatives and high-K-U granites, to form the unconformity related U deposits. By the end of Silurian, with the apparition of land plants, deposits hosted by continental to marginal marine sandstone (roll front, tabular, tectono-lithologic, paleovalleys) became widespread. The largest volcanic related U-deposits are mostly known during the Mesozoic and calcrete are only known during late Caenozoic to Quaternary, but this may by due to the non preservation from erosion of such deposits formed at very shallow levels.

  8. Sequestration of Soil Carbon as Secondary Carbonates (Invited)

    Science.gov (United States)

    Lal, R.

    2013-12-01

    Rattan Lal Carbon Management and Sequestration Center The Ohio State University Columbus, OH 43210 USA Abstract World soils, the major carbon (C) reservoir among the terrestrial pools, contain soil organic C (SOC) and soil inorganic C (SIC). The SIC pool is predominant in soils of arid and semi-arid regions. These regions cover a land area of about 4.9x109 ha. The SIC pool in soils containing calcic and petrocalcic horizons is estimated at about 695-748 Pg (Pg = 1015 g = 1 gigaton) to 1-m depth. There are two types of carbonates. Lithogenic or primary carbonates are formed from weathering of carbonaceous rocks. Pedogenic or secondary carbonates are formed by dissolution of CO2 in the soil air to form carbonic acid and precipitation as carbonates of Ca+2 or Mg+2. It is the availability of Ca+2 or Mg+2 from outside the ecosystem that is essential to sequester atmospheric CO2. Common among outside sources of Ca+2 or Mg+2 are irrigation water, aerial deposition, sea breeze, fertilizers, manure and other amendments. The decomposition of SOC and root respiration may increase the partial pressure of CO2 in the soil air and lead to the formation of HCO_3^- upon dissolution in H20. Precipitation of secondary carbonates may result from decreased partial pressure of CO2 in the sub-soil, increased concentration of Ca+2, Mg+2 and HCO_3^- in soil solution, and decreased soil moisture content by evapotranspiration. Transport of bicarbonates in irrigated soils and subsequent precipitation above the ground water (calcrete), activity of termites and other soil fauna, and management of urban soils lead to formation of secondary carbonates. On a geologic time scale, weathering of silicate minerals and transport of the by-products into the ocean is a geological process of sequestration of atmospheric CO2. Factors affecting formation of secondary carbonates include land use, and soil and crop management including application of biosolids, irrigation and the quality of irrigation water

  9. Ediacaran stromatolites and intertidal phosphorite of the Salitre Formation, Brazil: Phosphogenesis during the Neoproterozoic Oxygenation Event

    Science.gov (United States)

    Caird, R. A.; Pufahl, P. K.; Hiatt, E. E.; Abram, M. B.; Rocha, A. J. D.; Kyser, T. K.

    2017-04-01

    of hydrothermal veins range from - 4.7‰ to - 3.0‰ (mean = - 4.2‰) reflecting equilibration with temperatures > 80 °C. δ13C values are between - 7.0‰ and + 5.6‰ (mean = - 1.8‰,). Late lateritic weathering produced calcretes with δ18O values between - 3.3‰ and - 1.3‰, and δ13C values from - 9.2‰ to - 8.0‰ (mean values are - 1.8‰ and - 8.7‰, respectively). Petrographic analysis, generally low δ18O, and high δ13C values suggest hydrothermal dolomitization and remobilization of P led to secondary phosphate mineralization of intertidal stromatolite biostromes to produce economic phosphorite. Collectively, these results suggest that the benthic P-cycle in the Neoproterozoic was more complex than previously surmised and emphasize the multifaceted significance of microbial, paleoenvironmental, and diagenetic processes that allowed phosphorite to accumulate on the São Franciscan craton. Such information further elucidates attributes of the onset of Earth's second major phosphogenic episode, which is roughly coincident with the Neoproterozoic Oxygenation Event (NOE) and the evolution of multicellular animals.

  10. A critique of Phanerozoic climatic models involving changes in the CO 2 content of the atmosphere

    Science.gov (United States)

    Boucot, A. J.; Gray, Jane

    2001-12-01

    Critical consideration of varied Phanerozoic climatic models, and comparison of them against Phanerozoic global climatic gradients revealed by a compilation of Cambrian through Miocene climatically sensitive sediments (evaporites, coals, tillites, lateritic soils, bauxites, calcretes, etc.) suggests that the previously postulated climatic models do not satisfactorily account for the geological information. Nor do many climatic conclusions based on botanical data stand up very well when examined critically. Although this account does not deal directly with global biogeographic information, another powerful source of climatic information, we have tried to incorporate such data into our thinking wherever possible, particularly in the earlier Paleozoic. In view of the excellent correlation between CO 2 present in Antarctic ice cores, going back some hundreds of thousands of years, and global climatic gradient, one wonders whether or not the commonly postulated Phanerozoic connection between atmospheric CO 2 and global climatic gradient is more coincidence than cause and effect. Many models have been proposed that attempt to determine atmospheric composition and global temperature through geological time, particularly for the Phanerozoic or significant portions of it. Many models assume a positive correlation between atmospheric CO 2 and surface temperature, thus viewing changes in atmospheric CO 2 as playing the critical role in regulating climate/temperature, but none agree on the levels of atmospheric CO 2 through time. Prior to the relatively recent interval of time in which atmospheric CO 2 is directly measurable, a variety of biological and geological proxies have been proposed to correlate with atmospheric CO 2 level or with pCO 2/temperature. Atmospheric models may be constructed for the Pre-Cenozoic but the difficulties of assessing variables in their construction are many and complex. None of the modelers have gathered enough biological and geological data to

  11. Revisión estratigráfica y paleoambientes del Grupo Angulos (Neógeno, Sierra de Famatina, La Rioja: Su significado en el relleno del antepaís fragmentado Stratigraphic revision of the Angulos Group (Miocene Famatina Ranges, La Rioja province: Sedimentary environements and its bearing on the Central Andean broken foreland till

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    F.M. Dávila

    2005-03-01

    con otras unidades del oeste argentino permitieron reposicionar a la unidad entre el Mioceno Medio y Plioceno Inferior. El análisis de procedencia sugiere la participación de áreas fuentes distintas e inversión de las paleocorrientes que indican un marcado cambio en la evolución del antepaís, que difiere de interpretaciones previas. Se diferenciaron tres episodios tectosedimentarios, desde una etapa de cuenca extensional con un episodio de sag terminal, seguido de dos etapas de antepaís fragmentado.Thick synorogenic Tertiary strata are exposed on the eastern flank of the Famatina Ranges, largely known as the "Estratos Calchaquenses" and formally named as the Angulos Group (>1500 m thick. This group was originally divided into three Formations: Del Abra, Del Buey and El Durazno. This work carries out a detail revision of the Angulos Group stratigraphy with emphasis on the paleoenvironmental evolution. The El Durazno Formation is emended and subdivided, redefining its lower large-scale cross-stratified section as the Santo Domingo Formation. On the base of its stratigraphic position, together to the paleontological record and regional correlations, the Angulos Group is reassigned between the Middle Miocene and the Early Pliocene. Eleven facies were distinguished that are dominated by epiclastic and volcanoclastic sediments onto the carbonate rocks. The Del Abra Formation facies association allows interpreting a proximal alluvial fan setting which evolved toward more distal fan deposits. Low-efficiency processes dominated the basal section, which are gradually replaced by high-efficiency alluvial facies toward the top of the formation. Transitionally, the Del Buey Formation is characterized by distal alluvial fan facies, and records biolaminated carbonate beds and calcrete horizons, indicating low-gradient environments as well as low sedimentation rates. Alternation of large-scale cross-stratified sandstones and strongly incised sandy conglomerates compound the

  12. Petroduric and 'petrosepiolitic' horizons in soils of Namaqualand, South Africa Horizontes petrodúricos y "petrosepiolíticos" en suelos de Namaqualand, Suráfrica Horizontes petrodúricos e “petrosepiolíticos” em solos de Namaqualand, África do Sul

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    Michele Louise Francis

    2012-03-01

    Full Text Available

    Indurated, light-coloured 'sepiocrete' horizons have been found in Namaqualand Calcisols and Durisols. These horizons resembled calcrete but were non- to only mildly calcareous, resisted slaking in acid and alkali, and often broke with a conchoidal fracture. The presence of elevated quantities of sepiolite in the bulk-soil was confirmed by XRD analysis. The degree of induration in some these horizons suggested cementation by silica, and so in this paper the slaking properties, bulk chemistry, mineralogy and micromorphology of these horizons are compared with the typical silica-cemented, reddish-brown petroduric/duripan (dorbank encountered in the region. 'Sepiocrete' horizons are chemically, mineralogically and morphologically distinct from the petrocalcic and petroduric horizons with which they are commonly associated. Micromorphology of the petroduric horizons revealed prominent illuviation in the form of oriented clay parallel to grains and crescent coatings on voids, a red matrix due to iron oxides, and translucent, isotropic amorphous silica coatings on grains and voids. In the 'sepiocrete' horizons, sepiolite appeared as a matrix of interlocking, sub-parallel fibres while the amorphous material was localised. The amorphous material was silica-rich with prominent aluminium and lesser magnesium; light brown under plane polarised light; not completely isotropic and had a lower birefringence than the sepiolite. The calcite was usually micritic, but also appeared as loose granules and as elongate crystals in a sepiolite matrix. The presence of the laminar Si-Al -rich areas on the sections suggested at the least localised duric properties and so mutual reinforcement of sepiolite and silica is possible. However, the 'sepiocrete' horizons did not meet the slaking requirements of the petroduric (dorbank horizons and are distinct in appearance to the typical petroduric horizons in the region. They contained