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Sample records for arenites

  1. Detrital zircon provenance of Mesoproterozoic to Cambrian arenites in the Western United States and Northwestern Mexico

    Science.gov (United States)

    Stewart, John H.; Gehrels, G.E.; Barth, A.P.; Link, P.K.; Christie-Blick, N.; Wrucke, C.T.

    2001-01-01

    U-Pb isotopic dating of detrital zircon from supracrustal Proterozoic and Cambrian arenites from the western United States and northern Mexico reveal three main age groups, 1.90 to 1.62 Ga, 1.45 to 1.40 Ga, and 1.2 to 1.0 Ga. Small amounts of zircons with ages of 3.1 to 2.5 Ga, 1.57 Ga, 1.32 Ga, 1.26 Ga, 0.7 Ga, and 0.5 Ga are also present. Detrital zircons ranging in age from 1.90 to 1.62 Ga and from 1.45 to 1.40 Ga are considered to have been derived from Proterozoic crystalline basement rocks of these known ages, and probably in part from reworked Proterozoic supracrustal sedimentary rocks, of the western United States. The 1.2 to 1.0 Ga detrital zircon ages from California, Arizona, and Sonora are characterized by distinct spikes (1.11 Ga, in particular) in the age-probability plots. These spikes are interpreted to indicate the influx of zircon from major silicic volcanic fields. Igneous rocks such as the Pikes Peak Granite (1.093 Ga) of Colorado, and the Aibo Granite (1.110 Ga) of Sonora, Mexico, may represent the deeply eroded roots of such volcanic fields. Samples from farther north along the Cordilleran margin that contain abundant 1.2-1.0 Ga detrital zircons do not show spikes in the age distribution, but rather ages spread out across the entire 1.2-1.0 Ga range. These age spectra resemble those for detrital zircons from the Grenville province, which is considered their source. Less common detrital zircons had a variety of sources. Zircons ranging in age from 3.36 to 2.31 Ga were apparently derived from inland parts of the North American continent from Wyoming to Canada. Zircons of about 1.577 Ga are highly unusual and may have had an exotic source; they may have come from Australia and been deposited in North America when Australia and North America were juxtaposed as part of the hypothetical Rodinian supercontinent. Detrital zircon of ??1.320 Ga apparently had the same source as that for tuff (1.320 Ga) in the Pioneer Shale of the Apache Group in Arizona

  2. Geochemistry of Barapani Arenites in Umphyrnai-Mawkynrew-Mawryngkneng Area, East Khasi Hills, Meghalaya: implications on provenance, palaeoweathering, K-metasomatism and uranium mineralisation

    International Nuclear Information System (INIS)

    Geochemical studies on Barapani arenites of Shillong Basin, Meghalaya Plateau, around Umphyrnai-Mawkynrew-Mawryngkneng area, East Khasi Hills, Meghalaya were carried out to understand provenance, palaeoweathering and uranium mineralisation along unconformity contact between Tyrsad and Barapani Formations of Shillong Group. The studies reveal higher concentration of SiO2 (Avg. 82.7%) in Barapani arenites. Antipathic relationship of SiO2 with Al2O3, K2O and CaO indicates that Barapani arenites are highly matured. Positive correlation between K2O and Al2O3, Ba and Rb indicates presence of clay minerals which is further substantiated by positive association of Al2O3 with K2O, Na2O, TiO2 and MgO. Higher ratios of SiO2/Al2O3 and K2O/Na2O indicates felsic provenance with dominance of K-feldspar (K2O up to 2.2%). Higher amount of Cr (58 ppm), Ni (41 ppm), Cr/Ni (1.5 ppm) and Th/Cr (Avg. 0.98) and Cr/Th (Avg. 5.18) ratios further suggest the felsic nature of source rocks. The A-CN-K plot shows that Barapani arenites scatter above feldspar join along A-K line due to lowering of CIA values and related K-enrichment. The discriminate diagram between K2O/Al2O3 vs MgO/Al2O3 ratios reveals illitisation in these arenites. Lowering of chemical index of alteration values and presence of illite also indicate K-metasomatism in Barapani arenites. Barapani arenites along alteration zones have U (total) and U (leachable) values up to 8 ppm and 5 ppm respectively in comparison to average uranium content 0.5 ppm in quartzite. The K-metasomatism and highly oxidised nature of Barapani arenites suggest migration of uranium and probable uranium enrichment at unconformity surface. (author)

  3. On the interaction between fluid turbulence and particle loading: numerical simulation of turbidity currents and prediction of deep-sea arenites

    Science.gov (United States)

    Doronzo, D. M.; Dufek, J.

    2012-04-01

    Turbidity currents are water-particle flows able to move large distance over the seafloor, and the deep-sea arenitic facies of their deposits often represents an important class of hydrocarbon reservoirs. Coupling flow behavior and the resulting deposits may thus help finding new reservoirs, as well as reconstructing the sediment transport mechanisms from the continental shelf to the abyssal plain. There is a broad literature of turbidity currents, which includes field, theoretical, experimental, and numerical studies on flow dynamics and associated deposits. Generally, the field and theoretical approaches focus on the scale of actual deposits and currents, respectively, whereas experimental and numerical approaches are often restricted to the laboratory scale and relatively low-Reynolds number, respectively. Fully resolved simulations that incorporate complex bathymetry, large-scale flow, multiphase and 3D effects, are computationally expensive and require closure schemes. Here, a 2D numerical model of turbidity current is proposed, which is based on the Euler-Lagrange formulation of multiphase physics, and on the Reynolds-averaged Navier-Stokes closure of turbulence. This strategy has been recently used in volcanology to simulate the gas-particle flow of pyroclastic density currents, in order to predict their deposits. The incompressible conservation equations of mass and momentum are solved for the water, and the equation of particle motion is solved for the sediment, which for this example, has an initial concentration of 1 % of 0.5 mm sand particles. The equations are solved numerically with the finite-volume method of Ansys Fluent software, and particle and fluid motion are two-way coupled during calculation, which means that the particles are tracked on the basis of water solution, then are allowed to affect the liquid turbulence through a momentum exchange. The Reynolds (turbulent) stresses, which dominate over the viscous ones in the turbidity current, are

  4. Sandstone caves on Venezuelan tepuis: Return to pseudokarst?

    Science.gov (United States)

    Aubrecht, R.; Lánczos, T.; Gregor, M.; Schlögl, J.; Šmída, B.; Liščák, P.; Brewer-Carías, Ch.; Vlček, L.

    2011-09-01

    Venezuelan table mountains (tepuis) host the largest arenite caves in the world. The most frequently used explanation of their origin so far was the "arenization" theory, involving dissolution of quartz cement around the sand grains and subsequent removing of the released grains by water. New research in the two largest arenite cave systems - Churi-Tepui System in Chimanta Massif and Ojos de Cristal System in Roraima Tepui showed that quartz dissolution plays only a minor role in their speleogenesis. Arenites forming the tepuis are not only quartzites but they display a wide range of lithification and breakdown, including also loose sands and sandstones. Speleogenetic processes are mostly concentrated on the beds of unlithified sands which escaped from diagenesis by being sealed by the surrounding perfectly lithified quartzites. Only the so-called "finger-flow" pillars testify to confined diagenetic fluids which flowed in narrow channels, leaving the surrounding arenite uncemented. Another factor which influenced the cave-forming processes by about 30% was lateritization. It affects beds formed of arkosic sandstones and greywackes which show strong dissolution of micas, feldspars and clay minerals, turning then to laterite ("Barro Rojo"). The main prerequisite to rank caves among karst phenomena is dissolution. As the dissolution of silicate minerals other than quartz appears to play not only a volumetrically important role but even a trigger role, these arenitic caves may be ranked as karst.

  5. Connaissances stratigraphiques sur la base du Mésozoique portugais

    OpenAIRE

    Palain, C.

    2008-01-01

    In Portugal, the Mesozoic lower part is principally composed of conglomeratic, arenitic and pelitic deposits, which are here and there associated with carbonates rocks and evaporites. The Germanic Triassic succession is not observed. The Muschelkalk facies do not exist. Carbonates formation, and some thick evaporites deposits (Keuper facies) are of early Jurassic in age. The thick red beds accumulations deposited in a continental environment are Triassic. In Coimbra area the oldest paly...

  6. Modal analysis and geochemistry of two sandstones of the Bhander Group (Late Neoproterozoic) in parts of the Central Indian Vindhyan basin and their bearing on the provenance and tectonics

    Indian Academy of Sciences (India)

    Apurba Banerjee; D M Banerjee

    2010-12-01

    The Neoproterozoic Bhander Group in the Son Valley, central India conformably overlying the Rewa Group, is the uppermost subdivision of the Vindhyan Supergroup dominantly composed of arenites, carbonates and shales. In Maihar –Nagod area, a thick pile of unmetamorphosed clastic sedimentary rocks of Bhander Group is exposed, which provides a unique opportunity to study Neoproterozoic basin development through provenance and tectonic interpretations. The provenance discrimination and tectonic setting interpretations are based on modal analysis and whole rock geochemistry. The average framework composition of the detrital sediments composed of quartz and sedimentary lithic fragments are classified as quartz arenite to sublitharenite. The sandstone geochemically re flects high SiO2 moderate Al2O3 and low CaO and Na2O type arenite. The high concentration of HFSE such as Zr, Hf , and Th/Sc, Th/U ratios in these sandstones indicate a mixed provenance. The chondrite normalized REE pattern shows moderate to strong negative Eu anomaly which suggests that major part of the sediments were derived from the granitic source area. The sandstone tectonic discrimination diagrams and various geochemical plots suggest that the provenance of the lower and upper Bhander sandstone formations was continental interior to recycled orogen.

  7. Crossbedded nature of Proterozoic Witwatersrand placers in distal environments and a paleocurrent analysis of the Vaal Reef placer

    International Nuclear Information System (INIS)

    The Proterozoic placers in South Africa that were deposited in distal environments are referred to as carbon-seam reefs. They are pebbly quartz-arenite units with a characteristic pi-crossbedded internal geometry. Their external geometry, which is sheetlike, was produced by the braiding of shallow channels in a dendroidal belt. Low-variance, unimodal, paleocurrent data from the Vaal Reef are used to illustrate a transgressing, braided, fluvial environment followed by longshore drift in a deepening water environment. The total variance, evident in detrital heavy-mineral concentrations of carbon-seam placers, is related to the internal geometry, external geometry, and areal position within the deposit

  8. Age determination and provenance of sandy sediments possibly hosting gas hydrate in the eastern margin of Japan Sea

    Science.gov (United States)

    Uchida, T.; Takashima, I.; Sasaki, S.; Matsumoto, R.

    2012-12-01

    In 2010 the MD179 project was undertaken by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments in order to develop the geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles. Sediment samples below the seafloor were obtained in the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas by the cruise. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene silty layers, where trace fossils and strong bioturbations are commonly observed. Those sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these arenite sands were carried out, which indicates that porosities of silty sediments are around 50 % but those of arenites range from 42 to 52 %, of which mean pore sizes and permeabilities are larger than those of silty sediments. These coarser sediments might have been transported approximately around 3 to 30 ka according to the tephra ages, where supplying sediments might have not been abundant due to sea level fluctuation during the Pleistocene ice age. While the presence of gas hydrate in intergranular pores of arenite sands has not been confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands that is called pore-space hydrates. They have been recognized till now in the Mallik as well as in the Nankai Trough areas, which are considered to be common even in the subsurface sandy sediments at the eastern margin of Japan Sea. Time of deposition of coarse-grained sediments can be recognized by the thermoluminescence (TL) dating method. The TL dating works on the principle that materials containing naturally

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

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    A. Müjdat ÖZKAN

    2000-03-01

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

  10. Low porosity/high permeability, deeply-buried reservoirs of the Cusiana Field, Llanos foothills, Eastern Colombia: Controls on reservoir quality

    Energy Technology Data Exchange (ETDEWEB)

    Pulham, A. [Univ. of Colorado, Boulder, CO (United States); Warren, E. [BP Exploration Research, Sunbury (United Kingdom); Naar, J. [BP Exploration, Bogota (Colombia)

    1996-08-01

    The Cusiana Field is a thrust-related anticline located on the eastern edge of the Eastern Cordillera of the Colombian Andes. It comprises three clastic reservoirs: lower Tertiary Mirador and Barco Formations and the Santonian-Campanian Guadalupe Formation. Sandstone porosity is generally low, averaging approximately 8% in the Mirador and Barco; and approximately 15% in the Guadalupe. Despite such low porosities, permeabilities are excellent and can exceed 1000mD. Detailed petrographic, sedimentological and biostratigraphic analyses have been used to identify the controls and distribution of porosity within the Cusiana Field. The majority of the reservoir sandstones in Cusiana are near pure quartz arenites cemented by blocky, euhedral quartz overgrowths. Other cement phases, including kaolinite, are minor. The low porosity values throughout the reservoirs can be simply explained by compactional loss and relatively hot cementation by quartz during deep burial (>20,000 ft) The exception to the pure quartz arenites are zones in the Guadalupe reservoir that contain significant quantities (up to 20%) of detrital phosphate. These phosphatic sandstones lack the blocky quartz cements, contain pore lining microcrystalline quartz cement, minor calcite and clays (kaolinite and chlorite). They also have the best porosities (up to 22%). There is a direct relationship between presence and quantity of phosphate in the Guadalupe reservoir and increased reservoir quality. The Cusiana reservoirs provide a good case study of porosity evolution in deeply buried, quartz-rich sandstones and the contrasts that can occur when a non-quartz component to the sandstones is introduced.

  11. Comparaison de diverses méthodes de dosage des argiles d'un sable de gisement. Dosage des argiles Comparison of Different Methods of Determining Clays in a Reservoir Sand. Quantitative Analysis of Clays

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    Yvon J.

    2006-11-01

    Full Text Available Les argiles d'un sable de gisement, concentrées dans la fraction de diamètre Phi Oil, gas and geothermal reservoirs all contain clayey fractions no matter how small they may be. This has been blamed whenever operating or producing problems arise. It may be revealed by phenomena of mechanical resistance, permeability or interfacial properties (ion exchange, adsorption, etc. . Tests to understand such phenomena then go via the quantitative mineralogical analysis of the clays present. This analysis must also be looked at in terms of methods. It is subjected to constraints of cost, instrumentation, competence or deadlines. This article proposes:(a A so-called conventional route (Dejou et al, 1977 based on chemical and weighted analyses. (b An overall assessment method of the clay phase by difference (determination of two nonclay species. (c A method based on the statistical processing of microanalytic data obtained by an electronic microprobe. The material examined was a quartzose arenite made up mainly of quartz, jarosite, orthoclase, plagioclases, calcite, dolomite, muscovite, kaolinite, illite, montmorillonite, interstratified illite-montmorillionite, iron oxyhydroxides and accessory minerals such as rutile, zircon, garnet, tourmaline and hydroxylapatite. The arenite was subjected to an ultrasonic treatment (Letelier, 1986 to recover pellicular or weakly cemented clays. After this treatment, all the free clays were found in the < 40 m fraction which were used for the measurements. The so-called conventionalmethod is based on the associating of multiple techniques that are normally used for analyzing clays. They include X-ray diffraction, TDA, TGA, selective dissolution, CEC, adsorption of various reagents and gravimetric separations. They have been reviewed by Dejou et al (1977. The results they give depend on the grain size, chrystallochemistry, presence of amorphous elements and especially the typical chemical compositions assigned to the

  12. Petrophysical Properties Of Sandy Sediments Possibly Hosting Gas Hydrate In The Eastern Margin Of Japan Sea

    Science.gov (United States)

    Uchida, T.; Takashima, I.; Sunaga, H.; Sasaki, S.; Matsumoto, R.

    2011-12-01

    In 2010 the MD179 project was undertaken by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments older than 300 ka in order to develop geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles. Sediment samples below the seafloor were obtained in the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas by the MD179 cruise. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene silty layers, where trace fossils and strong bioturbations are commonly observed. Those sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these arenite sands were undertaken, which indicatesd that porosities of muddy sediments are around 50 % but those of arenites range from 42 to 52 %, of which mean pore sizes and permeabilities are larger than those of siltstones and mudstones. These coarser sediments might have been transported approximately around 3 to 30 ka, where supplying sediments may not be abundant due to sea level fluctuation during the Pleistocene ice age. While the presence of gas hydrate in intergranular pores of arenite sands has not been confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands that is called pore-space hydrates. They have been recognized till now in the Mallik as well as in the Nankai Trough areas, which are considered to be very common even in the subsurface sandy sediments at the eastern margin of Japan Sea. Concentration of gas hydrate may need primary intergranular pores large enough to occur within a host sediment that may be arenite sand without matrix grains deposited in the sedimentary

  13. Provenance and Paleoenvironment of Sandy Sediments Possibly Hosting Gas Hydrate in the Eastern Margin of Japan Sea

    Science.gov (United States)

    Uchida, T.; Takashima, I.; Ito, T.; Matsumoto, R.

    2010-12-01

    The MD179 project was undertaken by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments older than 300 ka in order to develop geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles. It has been inferred that methane forming gas hydrate and methane plumes are of thermogenic origin in the study area, which form gas hydrates as mounds, nodules, veins, pore fillings etc. in sediments below seafloor. Permeable intergranular pore systems of arenite sand, fractures, faults as well as gas chimneys may have played an important role as conduits for deep thermogenic hydrocarbon gas migration. Sediment samples below the seafloor were obtained in the Umitaka Spur, the Joetsu Channel, the Toyama Trough, the Japan Basin, the Nishi Tsugaru and the Okushiri Ridge areas by the UT09 and KY09-05 cruises in 2009 as well as this MD179 cruise. They have been mainly composed of muddy sediments with small amount of sandy sediments. Thin sandy layers are intercalated with thick muddy sediments, which are often strongly bioturbated with burrows and pellets. Those sandy sediments consist of fine- to medium-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of fine- to very fine-grained arenite sands are undertaken, which indicate that porosities of muddy sediments are around 50 % but those of arenites range from 42 to 52 % of which mean pore sizes and permeabilities are larger than those of siltstones and mudstones. While the presence of gas hydrate in intergranular pores of arenite sands is not confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands. The geological modeling of the gas hydrate formation and evolution system is concerned for energy resource potential in

  14. Petrology of late Paleozoic-early Mesozoic Pyeongan Group sandstones, Gohan area, South Korea and its provenance and tectonic implications

    Science.gov (United States)

    Yu, Kang-Min; Lee, Gie-Hyeon; Boggs, Sam

    1997-04-01

    Carboniferous to Triassic strata of the Pyeongan Group crop out in the Gohan area, northeastern South Korea. These strata consist, in ascending order, of the Hongjeom, Sadong, Gobangsan, and Nogam formations. Sandstones in these formations comprise three distinct framework-mineral suites. Suite 1 sandstones (Hongjeom Formation through the Middle Member of Gobangsan Formation) are quartz and quartzose arenites/wackes that contain abundant quartz, little or no feldspar, and few acid volcanic clasts. Heavy minerals are mainly tourmaline, rutile, and zircon. Suite 2 sandstones (Upper Member of Gobangsan Formation) are lithic arenites/wackes characterized by moderate quartz content, low amounts of feldspar, and moderate to abundant volcanic clasts. Sphene is the predominant heavy mineral. Suite 3 sandstones (Nogam Formation) are feldspathic arenites/wackes distinguished by low quartz content, moderate to abundant feldspar, and low amounts of acid volcanic clasts. The heavy-mineral assemblage of the Nogam Formation is characterized particularly by epidote and sphene. Feldspar-poor Suite 1 sandstones were derived from a source terrain rich in quartzite and quartzose sandstone. Abundant quartz and stable heavy minerals were supplied initially during Late Carboniferous time to a shallow-marine shelf, which changed gradually near the end of Carboniferous time to a nonmarine, paralic platform setting. Electron probe microanalysis shows that Suite 1 tourmaline was derived originally from Li-poor granitoids, pegmatites, and Ca-poor aplite and metapsammite. Petrographic evidence demonstrates that the scarcity of feldspars in Suite 1 sandstones is not the result of diagenetic intrastratal solution. Major changes in mineralogy from Suite 1 into Suite 2 and Suite 3 sandstone indicate changes in provenance. Suite 2 sandstones were derived from diorite, granodiorite, acid volcanic rocks, and possibly some metamorphic rocks, which furnished feldspars and sphene. The appearance of

  15. NEW BIOSTRATIGRAPHIC DATA FROM THE REITANO FLYSCH AUCT. (SICILY, ITALY: A KEY TO A REVISED STRATIGRAPHY OF THE SICILIDE UNITS

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    STEFANO TORRICELLI

    2010-07-01

    Full Text Available The study of palynomorphs and calcareous nannofossils recovered from the volcano-arenitic succession outcropping at Troina and Cerami (Sicily documents Rupelian assemblages comparable to those published for the Tusa Tuffite. This new evidence, combined with petrographic, geochemical and sedimentological affinities documented in the literature, eventually proves the genetic relationships between these units. Accordingly, the new name Troina-Tusa Formation is proposed to include all these lower Oligocene volcano-sedimentary units and to replace inappropriate names formerly used. The Troina-Tusa Formation conformably lies on a mixed siliciclastic-carbonate turbidite succession, lacking volcanic detritus, reported in the literature with different names (Polizzi Formation, Varicoloured Shales, Troina-Tusa Flysch and different ages (ranging from Eocene to Early Miocene. Palynomorphs and nannofossils recovered from its uppermost part, indicate an earliest Oligocene age. The denomination Polizzi Formation is recommended for this unit that includes also the Varicoloured Shales (Eocene-basal Oligocene. The appearance of conglomerates and volcano-arenites in the basal portion of the Troina-Tusa Formation, immediately above the top of the Polizzi Formation, marks a sudden reorganization of the Rupelian depositional systems related to the rise and erosion of a volcanic belt. Apparently, no biostratigraphically detectable hiatus is associated to this boundary. Differences in the composition of sandstones, sedimentary features and relationships with the substratum do exist between the ‘internal’ Reitano Flysch, outcropping in the type-area on the northern slope of the Nebrodi Mountains, and the volcano-arenitic successions of Cerami and Troina, reported by some authors as ‘external’ Reitano Flysch. These differences are widely documented in the literature, where the ‘internal’ Reitano Flysch is shown to lack volcanic detritus and to rest

  16. Relation between grain size and modal composition in deep-sea gravity-flow deposits. Example from the Voirons Flysch (Gurnigel nappe, Chablais Prealps, France)

    Science.gov (United States)

    Ragusa, Jérémy; Kindler, Pascal

    2016-04-01

    categorized following Mutti's turbiditic facies scheme. Cluster analysis on the composition of major grains discriminated 10 clusters which are merged into seven petrofacies (P1 - P7) following optical observations under the microscope: P1: poorly cemented porous arenite; P2: all porosity are filled by calcitic cement; P3: well-cemented volcano-clastic arenite; P4: red algae-rich highly cemented arenite to calcarenite; P5: highly cemented arenite; P6: globigerina-rich laminated calcarenite and P7: glauconitic quartzarenite. Grain-size distribution is grouped following the petrofacies. They provide a homogeneous distribution within each petrofacies with a gradual fining and progressively increasing sorting from P1 to P7. Moreover, Mutti's facies distribution indicates a progressive change towards more distal environments: from channel facies (F2 to F5) in P1-P3 to lobe facies (F8 to F9) in P4-P6. The washed composition of the P7 petrofacies is interpreted as distal turbidites that were reworked by bottom currents. The results presented here reveal a link between sand composition, grain size and gravity-flow facies. They highlight that composition of gravity flows is modified during their basinward transport. Consequently, coarse proximal deposits are more siliciclastic with limited filling of voids due to low carbonate contents. On the contrary, carbonate content increases significantly in the fine-grained calcarenites of the distal petrofacies. In distal settings, the segregation of light and porous foraminifera from the heavier siliciclastic fraction occurs under the increasing importance of traction currents.

  17. Unusually well preserved casts of halite crystals: A case from the Upper Frasnian of northern Lithuania

    Science.gov (United States)

    Rychliński, Tomasz; Jaglarz, Piotr; Uchman, Alfred; Vainorius, Julius

    2014-07-01

    Upper Frasnian carbonate-siliciclastics of the Stipinai Formation (northern Lithuania) comprise a bed of calcareous silty arenite with casts of halite crystals, including hopper crystals. Unusually well-preserved casts occur on the lower surface of the bed, while poorly-preserved casts are present on the upper bedding surface. The casts originated as the result of the dissolution of halite crystals which grew in the sediment. The dissolution took place during early stages of diagenesis, when host sediment was soft. Unstable cavities after crystal dissolution were filled by overlying sediment forming their casts. The collapsing sediment form sink-hole deformation structures which disturb wave-ripple cross lamination from the upper part of the bed. Dewatering pipe structures are also present. The casts and accompanying sink-hole and dewatering pipes are classified as the postdepositional deformation structures caused by haloturbation.

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

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    A. Müjdat Özkan

    2002-03-01

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

  19. Effect Of Hot Water Injection On Sandstone Permeability

    DEFF Research Database (Denmark)

    Rosenbrand, Esther; Fabricius, Ida Lykke

    2012-01-01

    of published results regarding the effect of temperature on sandstone permeability. These tests are performed with mineral oil, nitrogen gas, distilled water and solutions of NaCl, KCl, CaCl2 as well as brines that contain a mixture of salts. Thirteen sandstone formations, ranging from quartz arenites....... Heating causes thermal expansion, which results in porosity reduction if the sandstone is confined. The maximum effect of porosity reduction as a result of thermal expansion on permeability is modelled and compared the change in specific surface that is computed from the reported data. This does...... not account for all the permeability reductions observed. Permeablity reduction occurs both when distilled water is the saturating fluid as well as in tests with NaCl, KCl or CaCl2 solutions, however, this is not the case in tests with mineral oil or nitrogen gas. The formation of a filter cake or influx...

  20. Geochemical and Mineralogical Composition of Bima Sandstone Deposit, Yola Area, NE Nigeria

    Directory of Open Access Journals (Sweden)

    D.M. Orazulike

    2011-03-01

    Full Text Available The aim of this study is to determine the geochemical and mineralogical composition of Bima Sandstone deposite of northeastern Nigeria. A total number of sixteen (16 sandstone samples were collected in Yola area inorder to classify the deposit of the Bima Sandstone exposed in this area on the basis of its chemical and mineralogical make-up. All the samples were selected randomly and subjected to both geochemical and petrographic studies. Relative concentration of the major oxide groups such as silica and alumina alkali oxides, iron oxide and magnesia has been used to classify the deposit. The results of the log of ratio of the m ajor oxide groups indicate that Bima Sandstone of the study area can be classified as greywackes, arkoses and lithic arenites including sub-greywackes and protoquartzites. The abundant alkali values as shown by the relatively high log K2O/Na2O ratio in most of the samples indicated immature sandstones whereas low alkali values in sam ples F, H and M revealed mature sandstones. The enrichment of silica (quartz over Al2O3 (log SiO2/Al2O3<1.5 indicate that Bima Sandstone has undergone long period of transportation and have been subjected to intense weathering resulting in the destruction of other minerals especially plagioclase and potassium feldspars during transportation. Microscopic examination of about sixteen slides (16 of Bima Sandstone under both plane and cross polars revealed the following average mineralogical composition: quartz (65% feldspars (14%, mica (9%, iron oxide (5%, calcite (3% further confirms quartz/lithic arenites and greywackes as some of the predominant sedimentary rocks in the study area.

  1. Differential Hydrogeological Effects of Draining Tunnels Through the Northern Apennines, Italy

    Science.gov (United States)

    Vincenzi, Valentina; Gargini, Alessandro; Goldscheider, Nico; Piccinini, Leonardo

    2014-05-01

    Water inflows are a major challenge in tunnelling and particularly difficult to predict in geological settings consisting of heterogeneous sedimentary rock formations with complex tectonic structure. For a high-speed railway line between Bologna and Florence (Italy), a series of seven railway tunnels was drilled through turbiditic formations, ranging from pelitic rocks with thin arenitic layers over sequences including thick-bedded sandstone to calcareous rocks showing chemical dissolution phenomena (karstification). The tunnels were built as draining tunnels and caused significant impacts, such as drying of springs and base-flow losses at mountain streams. A comprehensive hydrological monitoring programme and four multi-tracer test were done, focusing on four sections of the tunnel system. The tracer tests delivered unprecedented data on groundwater flow and transport in turbiditic aquifers and made it possible to better characterize the differential impacts of tunnel drainage along a geological gradient. The impact radius is 200 m in the thin-bedded sequences but reaches 2.3-4.0 km in calcareous and thick-bedded arenitic turbidites. Linear flow velocities, as determined from the peaks of the tracer breakthrough curves, range from 3.6 m/day in the thin-bedded turbidites to 39 m/day in the calcareous rocks (average values from the four test sites). At several places, discrete fault zones were identified as main hydraulic pathways between impacted streams and draining tunnels. This case shows that ignoring the hydrogeological conditions in construction projects can cause terrible damage, and the study presents an approach to better predict hydraulic impacts of draining tunnels in complex sedimentary rock settings.

  2. Paleocurrent and lithological facies control of uranium and gold mineralisation in the Witwatersrand Carbon Leader Placer, Carletonville Goldfield, South Africa

    International Nuclear Information System (INIS)

    The Carbon Leader placer in the Carletonville goldfield is a pebbly quartz-arenite that occupies numerous low-sinuosity channelways which trend down a southerly paleoslope. The placer sediment is distinctively grey and siliceous in comparison with the bounding lithologies both above and below the orebody. The most common facies sequence established by Markov analysis consists of an irregular scoured base overlain by oligomictic lag conglomerates, which grade upward into quartz-arenites, quartz-wackes, and finally into shales. The sites of uranium and gold concentration correlate well with each other and are associated with linear zones of thick placer accumulations in channelways. Mineral concentrations associated with thin placer accumulations indicate areas where higher stream-power prevailed. Besides being geographically separate, various channels may have been active at different times when conditions affecting mineral supply and concentration were not the same. The differences noted indicate that deeper, more active channels, probably occupied by perennial streams, deposited more, coarser, and better mineralised placer sediment down the eastern part of the detailed study area. In contrast to this, channelways down the western part of the detailed study area were probably occupied by more ephemeral streams that deposited less gravel, more sand, and more immature, poorly mineralised, sediment. The same conclusion is reached by analysing the uranium-gold ratio pattern across the detailed study area. In this instance, ratios exceeding 12 demarcate the immature western part of this area. High ratios also define distal facies and these clearly indicate that the data in the southwestern part of the detailed study area are on the margin of a distal environment in which the uranium content will be higher than that encountered further upslope. Such positive correlation between sedimentary and mineralisation trends clearly illustrates the detrital nature of the deposit

  3. Provenance, diagenesis, tectonic setting and geochemistry of Rudies sandstone (Lower Miocene), Warda Field, Gulf of Suez, Egypt

    Science.gov (United States)

    Zaid, Samir M.

    2012-05-01

    The Lower Miocene Rudies sandstones are important oil reservoirs in the southeastern part, Gulf of Suez basin, Egypt. However, their provenance and diagenesis and their impact in reservoir quality, are virtually unknown. Samples from the Warda field, representing the Lower and Middle Rudies, were studied using a combination of petrographic, mineralogical and geochemical techniques. The Lower Rudies sandstones have an average framework composition of Q85F7.2R7.8, and 83% of the quartz grains are monocrystalline. By contrast, the Middle Rudies sandstones are only slightly more quartzose with an average framework composition of Q90F7R3 and 86% of the quartz grains are monocrystalline. Rudies sandstones are mostly quartz arenite with subordinate subarkose and sublithic arenites and their bulk-rock geochemistry support the petrographic results. The modal analysis data of studied samples suggest influence of granitic and metamorphic terrains as the main source rock with a subordinate quartzose recycled sedimentary rocks. The geochemical data interpretation on the basis of discriminate function diagrams reveal the source material was deposited on a passive margin. Textural attributes possibly suggest long-distance transport of grains from the source region and indicates a cratonic or a recycled source. Tectonic setting of Rudies Formation reveals that the lower Rudies sandstones are typically rift sandstone and their deposition constrained the beginning of the faulting, while the middle Rudies sandstones were transported from the far along the rift. Diagenetic features include compaction; dolomite, silica and anhydrite cementation with minor iron-oxide, illite, kaolinite and pyrite cements; dissolution of feldspars, rock fragments. Silica dissolution, grain replacement and carbonate dissolution greatly enhance the petrophysical properties of many sandstone samples.

  4. COMPOSITION AND PROVENANCE OF GRÖDEN SANDSTONE FROM THE VELEBIT MTS.

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    Vedran Sudar

    2016-02-01

    Full Text Available Six samples of Gröden sandstones (Middle Permian were analysed: Five of them were from Pikovac Creek valley (in the vicinity of Brušane village at Velebit Mts., Croatia and one was from the locus typicus Gröden/Val Gardena (Italy. Based on the micropetrographical characteristics of sandstones, as well as on the modal composition and heavy mineral association, origin of material, weathering index of source rocks, climate and relief in the period of deposition have been supposed. Four samples from Pikovac Creek were petrographicaly determined as lithic greywackes, one as densely packed lithic arenite, while a specimen from Gröden locus typicus represents feldspar greywacke. Lithic greywackes/arenites imply very low maturity and suggest a close proximity of source rocks as well as the active tectonics in the hinterland of the depositional basin. Heavy mineral association in the samples from Pikovac Creek valley, with a large amount of fairly rounded stable grains (zircon, tourmaline and rutile, indicate that clastic material was derived from recycled orogen, and probably from reworked sedimentary rocks. The presence of kyanite and chlorite in the heavy mineral assemblage suggest their origin is from metamorphic rocks. This data assumes that Gröden sandstones from Pikovac Creek were possibly deposited in the fan delta or braided delta depositional environment as a part of a rift system (recycled orogen. The composition of the sample Gröden s. locus typicus (light and heavy mineral fractions suggests the vicinity of magmatic rocks in the source area. All analysed samples are red coloured and have a large amount of limonitized grains in the heavy mineral assemblage, that point to the arid climate at the time of deposition. A weathering index diagram for Pikovac sandstones implies an arid/semiarid climate and high relief of the source area where metamorphic or sedimentary rocks dominate, while an arid/semiarid climate and high relief with

  5. Geohydrology of the High Energy Laser System Test Facility site, White Sands Missile Range, Tularosa Basin, south-central New Mexico

    Science.gov (United States)

    Basabilvazo, G.T.; Nickerson, E.L.; Myers, R.G.

    1994-01-01

    The Yesum-HoHoman and Gypsum land (hummocky) soils at the High Energy Laser System Test Facility (HELSTF) represent wind deposits from recently desiccated lacustrine deposits and deposits from the ancestral Lake Otero. The upper 15-20 feet of the subsurface consists of varved gypsiferous clay and silt. Below these surfidai deposits the lithology consists of interbedded clay units, silty-clay units, and fine- to medium-grained quartz arenite units in continuous and discontinuous horizons. Clay horizons can cause perched water above the water table. Analyses of selected clay samples indicate that clay units are composed chiefly of kaolinire and mixed-layer illite/ smectite. The main aquifer is representative of a leaky-confined aquifer. Estimated aquifer properties are: transmissivity (T) = 780 feet squared per day, storage coefficient (S) = 3.1 x 10-3, and hydraulic conductivity (K) = 6.0 feet per day. Ground water flows south and southwest; the estimated hydraulic gradient is 5.3 feet per mile. Analyses of water samples indicate that ground water at the HELSTF site is brackish to slightly saline at the top of the main aquifer. Dissolved-solids concentration near the top of the main aquifer ranges from 5,940 to 11,800 milligrams per liter. Predominant ions are sodium and sulfate. At 815 feet below land surface, the largest dissolved-solids concentration measured is 111,000 milligrams per liter, which indicates increasing salinity with depth. Predominant ions are sodium and chloride.

  6. Petroleum systems of the Upper Magdalena Valley, Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Sarmiento, L.F.; Rangel, A. [Instituto Colombiano del Petroleo, Bucaramanga (Colombia). ECOPETROL

    2004-03-01

    In the Upper Magdalena Valley, Colombia, four petroleum systems were identified. Two petroleum systems are located in the Girardot sub-basin and the other two in the Neiva sub- basin. Limestones laterally changing to shales of the lower part of the Villeta Gp, deposited during Albian and Turonian marine flooding events, constitutes the main source rocks of the oil families. These rocks contain 1-4% TOC and type II kerogen. The littoral quartz arenites of the Caballos (Albian) and Monserrate (Maastrichtian) Fms. are the main reservoir rocks. Seal rocks are Cretaceous and Paleocene shales. Overburden includes the Cretaceous rocks and the Tertiary molasse deposited simultaneously with development of two opposite verging thrust systems during Cenozoic time. These deformation events were responsible for trap creation. Except for the Villarrica area, where the source rock reached maturity during the Paleocene, generation occurred during Miocene. Two oil families are identified, each in both sub-basins: One derived from a clay-rich source and the second from a carbonate-rich source rock lithofacies of the lower part of Villeta Gp. Geochemical source-rock to oil correlations are demonstrated for the three of the petroleum systems. Up-dip lateral migration distances are relatively short and faults served as vertical migration pathways. A huge amount of oil was probably degraded at surface, as a result of Miocene deformation and erosion. (author)

  7. Were the hydraulic parameters of Precambrian rivers different?

    Science.gov (United States)

    Mukhopadhyay, Soumik; Choudhuri, Adrita; Samanta, Pradip; Sarkar, Subir; Bose, Pradip K.

    2014-09-01

    Palaeohydraulic estimates have been made using time-tested standard empirical formula involving channel dimensions, especially channel depth, in four Indian Proterozoic fluvial formations. These are the Mesoproterozoic Ramdurg, younger Mesoproterozoic Muchkundi and Neoproterozoic Cave Temple Arenite in Karnataka, and Upper Rewa Sandstone in central India. The basic data came from direct measurement of decompacted thicknesses of completely preserved channel-fills or bedforms, and more commonly of cross-sets. The result, in combination with data derived by others in a similar way from a few other Precambrian fluvial formations helps to provide a new insight into the palaeohydraulics of Precambrian rivers. River gradients appear to have been steeper during the Precambrian; the possibly continuous range of variation in river gradients from alluvial fans to the plains, as a whole shifted to higher values during the Precambrian epoch. The likely reason is a greater possibility of sediment bypassing on vegetation-free land. Concomitant downstream increase in discharge was enhanced in Precambrian rivers due to lack of withdrawal of groundwater through biogenic activity. Precambrian rivers were commonly ephemeral, but downstream the ephemerality index was reduced and some rivers might have been perennial where they debouched into standing bodies of water. The Precambrian river deposits studied generally had smaller width and depth with respect to Phanerozoic and modern rivers, possibly due to unstable substratum causing surface run-off tended to be impelled along multiple independent minor channels.

  8. Heavy mineral distribution and geochemistry related to sedimentary facies variation within the uraniferous intermediate reefs placers, Witwatersrand Supergroup, South Africa

    International Nuclear Information System (INIS)

    The Intermediate Reefs placers of the Precambrian Central Rand Group, Welkom goldfield, comprise interbedded quartz arenites, quartz wackes, and pyritic U-Au bearing quartz pebble conglomerates which currently are of subeconomic potential. On lithological grounds the Intermediate Reefs are subdivided into two members. The present investigations showed that the lower member is developed as a mature placer which accumulated in a perennial braided stream environment, and the upper one as immature sedimentary deposits which were accumulated under ephemeral conditions. Geochemical and mineragraphic studies reveal that for the Intermediate Reefs zone, brannerite is the principal uranium carrier and that the gold/uranium ratio is low when compared to other reefs of the Welkom goldfield. The studies, furthermore, show that the two members of the Intermediate Reefs differ in the relative abundance of their detrital minerals. It is suggested that these differences are caused by differing lithologies in the respective provenance terranes rather than by variations of the prevailing sedimentary processes. The subeconomic ore grade of the Intermediate Reefs is attributed to: (i) lack of economic minerals in their sedimentary source, (ii) absence of reworkable well mineralized placers in their footwall, and (iii) inadequate hydraulic conditions preventing the efficient accumulation of uraninite and gold. (author). 28 refs, 9 figs, 3 tabs

  9. Hydrothermal Synthesis of Hematite-Rich Spherules: Implications for Diagenesis and Hematite Spherule Formation in Outcrops at Meridiani Planum, Mars

    Science.gov (United States)

    Golden, D. C.; Ming, D. W.; Morris, R. V.; Graff, T. G.

    2007-01-01

    The Athena science payload onboard the Opportunity rover identified hematite-rich spherules (mean diameter of 4.2 +/- 0.8 mm) embedded in outcrops and occurring as lag deposits at Meridiani Planum. They have formed as diagenetic concretions from the rapid breakdown of pre-existing jarosite and other iron sulfates when chemically distinct groundwater passed through the sediments. Diagenetic, Fe-cemented concretions found in the Jurassic Navajo Formation, Utah and hematite-rich spherules found within sulfate-rich volcanic breccia on Mauna Kea volcano, Hawaii are possible terrestrial analogues for Meridiani spherules. The Navajo Formation concretions form in porous quartz arenite from the dissolution of iron oxides by reducing fluids and subsequent Fe precipitation to form spherical Fe- and Si-rich concretions. The Mauna Kea spherules form by hydrothermal, acid-sulfate alteration of basaltic tephra. The formation of hematite-rich spherules with similar chemical, mineralogical, and morphological properties to the Meridiani spherules is rare on Earth, so little is known about their formation conditions. In this study, we have synthesized in the laboratory hematite-rich spherules that are analogous in nearly all respects to the Meridiani spherules.

  10. Faunistic survey of sandstone caves from Altinópolis region, São Paulo State, Brazil

    Directory of Open Access Journals (Sweden)

    Douglas Zeppelini Filho

    2003-01-01

    Full Text Available The fauna of eight sandstone caves of the region of Altinópolis, (Serra Geral Arenitic Speleological province, São Paulo State, Southeastern Brazil was surveyed. Our results improve the previous faunistic knowledge of the region, recording 15 new occurrences for Brazilian caves and 26 for Brazilian sandstone caves. The fauna is characterized by a large number of detritivores/omnivores such as crickets and cockroaches, and several predators like spiders and heteropterans in bat guano.A fauna de oito cavernas areníticas da região de Altinópolis (província espeleológica arenítica da Serra Geral, Estado de São Paulo, Sudeste do Brasil foi amostrada. Nossos resultados aumentaram o conhecimento faunístico prévio da região, com o registro de 15 novas ocorrências para cavernas brasileiras e 26 para cavernas brasileiras em arenito. A fauna é caracterizada por um grande número de detritívoros/carnívoros tais como grilos e baratas, diversos predadores tais como aranhas e heterópteros no guano de morcego.

  11. Acid-gas injection in the Long Coulee Glauconite F Pool, Alberta : implications for enhanced gas recovery and acid-gas disposal

    International Nuclear Information System (INIS)

    Acid gas disposal in depleted oil and gas reservoirs is now being used as a means of safely and economically reducing acid gas emissions into the environment. Acid gas is currently being disposed into the Long Coulee Glauconite F pool in southern Alberta. The pool consists of a small oil leg and a large gas cap trapped in quartz arenite. In this study, reservoir mapping and permeability and porosity measurements were used to model the acid gas flow of a 98 per cent carbon dioxide (CO2) and 2 per cent hydrogen sulfide (H2S) mixture in order to determine the effects of acid gas injection on reservoir performance and recovery rates. The study demonstrated that acid gas injection resulted in increased gas recovery even with rapid CO2 breakthrough at offsetting gas producers. CO2 breakthrough occurred faster than H2S breakthrough. Gas partitioning occurred as a result of the preferential solubility of H2S in the formation brine. It was concluded that acid gas injection results in the partial re-pressurization of the gap cap.

  12. Weathering behavior investigations and treatment of Kom Ombo temple sandstone, Egypt - Based on their sedimentological and petrogaphical information

    Science.gov (United States)

    Temraz, Mostafa Gouda; Khallaf, Mohamed K.

    2016-01-01

    The Temple of Kom Ombo is a huge ancient Egyptian temple in Upper Egypt. It was built by Ptolemy VI Philometor (180-145 BC) and added to by subsequent Ptolemys. The structure of the temple is built of local sandstone attributed to the Quseir Formation of "Nubian Sandstone" group at Gebel el-Silsila. Sandstone samples from Kom Ombo temple were taken to verify the source rock of the quarried material. Optical Polarizing Microscope (OPM) and Scanning Electron Microscope (SEM) were used to determine the microstructure and physical properties of the sandstone. X-Ray diffraction (XRD) was carried out for the Sandstone samples to identify its mineralogical composition. The sandstone samples were treated with six polymeric products to determine changes in their physical and mechanical properties after penetration, consolidation of polymers within them. This sandstone is composed mainly of three quartz arenite microfacies (feldspathic, sublithic and calcareous) that are interpreted to have been deposited in fluvial to fluvial-marine environment. Silane polymers is showing a good penetration and filling pores between grains and recommended for treatment and conservation of the sandstone. Acrylic polymer shows random penetration of polymer and formation of a film of polymer on the surface of sandstone. Silo11 gave the best result in consolidation of sandstone samples then primal AC33. Wacker BS29 gave the best result in isolating process of sandstone samples, then wacker BS 290.

  13. Microrrelieve costero vs. icnitas humanas en la localidad El Caracolero (Claromecó, Argentina

    Directory of Open Access Journals (Sweden)

    Mariano Bonomo

    2016-05-01

    Full Text Available The aim of this paper is to discuss the origin of a series of cavities from an area of the Atlantic coast in the Pampean Region known as the Caracolero from Claromecó (Tres Arroyos County, Buenos Aires Province, Argentina which, have been interpreted as human footprints. They are located on a rock that outcrops on the littoral abrasion platform. The discovery of the footprints and their ascription of a high antiquity ca. 30.000 years 14C BP was initially disclosed to the media, where they first had an impact. The lithological studies carried out allowed to establish that the features of rocky substratum consist of an arenite with carbonate cement linked to deposits from the Pleistocene transgression dating back to 120.000 years BP. The morphological features of the abrasion platform’s cavities match those produced by natural carbonate dissolution and are mainly defined as “pans” and “pits” in the geological literature. Finally, according to the available information, it is concluded that the cavities from Claromecó do not have a clear anthropic origin. Therefore, they cannot be taken into account in the archaeological debate about the early peopling of the Americas.

  14. Developing conceptual hydrogeological model for Potsdam sandstones in southwestern Quebec, Canada

    Science.gov (United States)

    Nastev, Miroslav; Morin, R.; Godin, Rejean; Rouleau, Alain

    2008-01-01

    A hydrogeological study was conducted in Potsdam sandstones on the international border between Canada (Quebec) and the USA (New York). Two sandstone formations, arkose and conglomerate (base) and well-cemented quartz arenite (upper), underlie the study area and form the major regional aquifer unit. Glacial till, littoral sand and gravel, and marine silt and clay discontinuously overlie the aquifer. In both sandstone formations, sub-horizontal bedding planes are ubiquitous and display significant hydraulic conductivities that are orders of magnitude more permeable than the intact rock matrix. Aquifer tests demonstrate that the two formations have similar bulk hydrologic properties, with average hydraulic conductivities ranging from 2 ?? 10-5 to 4 ?? 10-5 m/s. However, due to their different lithologic and structural characteristics, these two sandstones impose rather different controls on groundwater flow patterns in the study area. Flow is sustained through two types of fracture networks: sub-horizontal, laterally extensive fractures in the basal sandstone, where hydraulic connectivity is very good horizontally but very poor vertically and each of the water-bearing bedding planes can be considered as a separate planar two-dimensional aquifer unit; and the more fractured and vertically jointed system found in the upper sandstone that promotes a more dispersed, three-dimensional movement of groundwater. ?? Springer-Verlag 2007.

  15. Impact of depositional facies on the distribution of diagenetic alterations in the Devonian shoreface sandstone reservoirs, Southern Ghadamis Basin, Libya

    Science.gov (United States)

    Khalifa, Muftah Ahmid; Morad, Sadoon

    2015-11-01

    The middle Devonian, shoreface quartz arenites (present-day burial depths 2833-2786 m) are important oil and gas reservoirs in the Ghadamis Basin, western Libya. This integrated petrographic and geochemical study aims to unravel the impact of depositional facies on distribution of diagenetic alterations and, consequently, related reservoir quality and heterogeneity of the sandstones. Eogenetic alterations include the formation of kaolinite, pseudomatrix, and pyrite. The mesogenetic alterations include cementation by quartz overgrowths, Fe-dolomite/ankerite, and illite, transformation of kaolinite to dickite, illitization of smectite, intergranular quartz dissolution, and stylolitization, and albitization of feldspar. The higher energy of deposition of the coarser-grained upper shoreface sandstones combined with less extensive chemical compaction and smaller amounts of quartz overgrowths account for their better primary reservoir quality compared to the finer-grained, middle-lower shoreface sandstones. The formation of kaolin in the upper and middle shoreface sandstones is attributed to a greater flux of meteoric water. More abundant quartz overgrowths in the middle and lower shoreface is attributed to a greater extent of stylolitization, which was promoted by more abundant illitic clays. This study demonstrated that linking the distribution of diagenetic alterations to depositional facies of shoreface sandstones leads to a better understanding of the impact of these alterations on the spatial and temporal variation in quality and heterogeneity of the reservoirs.

  16. Late Pleistocene cryogenic calcite spherolites from the Malachitdom Cave (NE Rhenish Slate Mountains, Germany: Origin, unusual internal structure and stable C-O isotope composition.

    Directory of Open Access Journals (Sweden)

    Detlev Konrad Richter

    2008-07-01

    Full Text Available Cryogenic calcites yielded U-series ages in the range from 15.61±0.20 ka to 14.48±0.12 ka, which is the youngest age obtained so far for this type of cryogenic cave carbonates in Europe. Most of these particles of the Malachitdom Cave (NE Brilon, Sauerland, North Rhine-Westphalia are complex spherolites usually smaller than 1 cm. They show δ13C-values between –1 and –5 ‰ VPDB and δ18O-values ranging from –7 to –16 ‰ VPDB, the δ13C-values increase and the δ18O-values decrease from centre to border. The complex spherolites are interpreted to be formed in slowly freezing pools of residual water on ice, a situation that repeatedly occurred during the change of glacial to interglacial periods in the periglacial areas of Central Europe. After the melting of the cave-ice, the complex spherolites make up one type of cryogenic calcite particles in the arenitic to ruditic sediment.

  17. Thermoluminescence dating of the Kamil impact crater (Egypt)

    Science.gov (United States)

    Sighinolfi, Gian Paolo; Sibilia, Emanuela; Contini, Gabriele; Martini, Marco

    2015-02-01

    Thermoluminescence (TL) dating has been used to determine the age of the meteorite impact crater at Gebel Kamil (Egyptian Sahara). Previous studies suggested that the 45 m diameter structure was produced by a fall in recent times (less than 5000 years ago) of an iron meteorite impactor into quartz-arenites and siltstones belonging to the Lower Cretaceous Gilf Kebir Formation. The impact caused the complete fragmentation of the impactor, and the formation of a variety of impactites (e.g., partially vitrified dark and light materials) present as ejecta within the crater and in the surrounding area. After a series of tests to evaluate the TL properties of different materials including shocked intra-crater target rocks and different types of ejecta, we selected a suite of light-colored ejecta that showed evidence of strong thermal shock effects (e.g., partial vitrification and the presence of high-temperature and -pressure silica phases). The abundance of quartz in the target rocks, including the vitrified impactites, allowed TL dating to be undertaken. The variability of radioactivity of the intracrateric target rocks and the lack of direct in situ dosimetric evaluations prevented precise dating; it was, however, possible to constrain the impact in the 2000 BC-500 AD range. If, as we believe, the radioactivity measured in the fallback deposits is a reliable estimate of the mean radioactivity of the site, the narrower range 1600-400 BC (at the 2σ confidence level) can be realistically proposed.

  18. Acid-gas injection in the Long Coulee Glauconite F Pool, Alberta : implications for enhanced gas recovery and acid-gas disposal

    Energy Technology Data Exchange (ETDEWEB)

    Dashtgard, S. [Simon Fraser Univ., Burnaby, BC (Canada); Pooladi-Darvish, M; Hong, H.; Theys, S.; Stocker, R. [Fekete Associates Inc., Calgary, AB (Canada); Bachu, S. [Energy Resources Conservation Board, Calgary, AB (Canada)

    2008-07-01

    Acid gas disposal in depleted oil and gas reservoirs is now being used as a means of safely and economically reducing acid gas emissions into the environment. Acid gas is currently being disposed into the Long Coulee Glauconite F pool in southern Alberta. The pool consists of a small oil leg and a large gas cap trapped in quartz arenite. In this study, reservoir mapping and permeability and porosity measurements were used to model the acid gas flow of a 98 per cent carbon dioxide (CO{sub 2}) and 2 per cent hydrogen sulfide (H{sub 2}S) mixture in order to determine the effects of acid gas injection on reservoir performance and recovery rates. The study demonstrated that acid gas injection resulted in increased gas recovery even with rapid CO{sub 2} breakthrough at offsetting gas producers. CO{sub 2} breakthrough occurred faster than H{sub 2}S breakthrough. Gas partitioning occurred as a result of the preferential solubility of H{sub 2}S in the formation brine. It was concluded that acid gas injection results in the partial re-pressurization of the gap cap.

  19. Quantifying the Micromechanical Effects of Variable Cement in Granular Porous Media

    Energy Technology Data Exchange (ETDEWEB)

    Goodwin, Laurel B.; Boutt David F.

    2010-02-18

    The mechanical and hydrologic behavior of clastic rocks and sediments is fundamentally controlled by variables such as grain size and shape, sorting, grain and cement mineralogy, porosity, and %cement - parameters that are not used directly in field-scale models of coupled flow and deformation. To improve our understanding of the relationship between these micromechanical properties and bulk behavior we focused on (1) relating detailed, quantitative characterization of the grain-pore systems to both hydrologic and mechanical properties of a suite of variably quartz-cemented quartz arenite samples and (2) the use of a combination of discrete element method (DEM) and poroelastic models parameterized by data from the natural samples to isolate and compare the influence of changes in the mechanical and hydrologic properties of granular porous media due to changes in degree of cementation. Quartz overgrowths, the most common form of authigenic cements in sandstones, are responsible for significant porosity and permeability reduction. The distribution of quartz overgrowths is controlled by available pore space and the crystallographic orientations of individual quartz grains. Study of the St. Peter Sandstone allowed evaluation of the relative effects of quartz cementation and compaction on final grain and pore morphology, showing that progressive quartz cementation modifies the grain framework in consistent, predictable ways. Detailed microstructural characterization and multiple regression analyses show that with progressive diagenesis, the number and length of grain contacts increases as the number of pores increases, the number of large, well-connected pores decreases, and pores become rounder. These changes cause a decrease in pore size variability that leads to a decrease in bulk permeability and both stiffening and strengthening of the grain framework. The consistent nature of these changes allows us to predict variations in hydrologic and mechanical properties

  20. Cryptic indicators of provenance from the geochemistry of the Okavango Delta sediments, Botswana

    Science.gov (United States)

    Huntsman-Mapila, P.; Kampunzu, A. B.; Vink, B.; Ringrose, S.

    2005-01-01

    The siliciclastic sediments of the Okavango inland Delta of northwest Botswana have a modal composition of quartz arenites and result from a complex history, including transport by river and deposition in a nascent rift basin located in a desert environment with input of aeolian sands. The geochemical composition of sediments from the Okavango Delta was determined in order to constrain the role of weathering at the source and the composition of the source rocks. The chemical analyses and the interelement ratios show a broad compositional range usually encompassing the PAAS composition. The chemical index of alteration (CIA) values and the A-CN-K diagram define an evolution trend which can be interpreted using a mixing model involving a strongly weathered component which corresponds to the sedimentary fraction transported by the Okavango River and a relatively immature component which corresponds to the aeolian sand component of the Okavango sediments. Field geological data supported by geochemical ratios involving elements with affinity for mafic-ultramafic and felsic rocks such as Th/Cr, Th/Sc, La/Sc, La/Co and Eu/Eu* support a source area including mafic-ultramafic and felsic rocks, with or without intermediate rocks. The relationships between certain elements (Cr-Ni, Na 2O-Al 2O 3, K 2O-Al 2O 3) refine the interpretation by pointing to the existence of at least three source rock end-members, including a felsic rock source and pyroxene-rich and olivine-rich mafic-ultramafic source rocks. Proterozoic granitoid-gabbro and related volcanic and ortho-metamorphic rock complexes exposed in NW Botswana and adjacent Angola and Namibia are the source rocks of the sediment component which was mixed with aeolian sand and interacted with a variable proportion of diagenetic carbonates to produce the Okavango sediments.

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

    Science.gov (United States)

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

    1990-06-01

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

  2. Proterozoic sequences and their implications for precamorian and cambrian geologic evolution of Western Kentucky: Evidence from seismic-reflection data

    Science.gov (United States)

    Drahovzal, J.A.

    1997-01-01

    Analyses of two seismic-reflection lines in western Kentucky indicate the presence of two Proterozoic, unconformity-bounded sequences. One is autochthonous and of probable Late Proterozoic age; the other is allochthonous and of probable Middle Proterozoic age. Reflector patterns and apparent relationships to similar sequences elsewhere in the region suggest that the two sequences are of continental-rift origin. The two Proterozoic sequences lie beneath and adjacent to rocks of the Cambrian rift sequence in the Rough Creek Graben. The oldest sequence, the pre-Grenville sequence, was apparently folded and thrust faulted by the Grenville compressional event, implying that it is older than ???0.975 Ga (Middle Proterozoic). Two seismic-reflection pattern types are present in the western Kentucky data that may relate to the Middle Run (lithic arenite) and volcanic sequences defined farther east near the Grenville Front. The presence of imbricate, thrust-belt geometries in the pre-Grenville sequence extends the known westward limit of Grenville compressional structures into western Kentucky. The younger, post-Grenville sequence is less deformed and was apparently formed after the Grenville compressional event; several lines of evidence indicate that it is Late Proterozoic (0.7 to 0.6 Ga) in age. This probable siliciclastic and volcanic-rift sequence is represented by only thin remnants in western Kentucky and has no equivalent near the Grenville Front in southwestern Ohio and central Kentucky. Rocks of the better documented Cambrian rifting event belong to the thick, pre-Knox sequence in the Rough Creek Graben of western Kentucky and lie unconformably above these earlier sequences. A previously undocumented, northward-thickening interval within the lower part of the Cambrian pre-Knox sequence is recognized north of the Rough Creek Graben.

  3. Water pollution in relation to mineral exploration: a case study from Alayi-Ovim area of southeastern Nigeria.

    Science.gov (United States)

    Ibe, Kalu K; Akaolisa, Casmir C Zanders

    2012-05-01

    Water samples from rivers, streams, springs, and shallow wells in Alayi-Ovim area of southeast Nigeria have been analyzed for Pb, Ca, Mg, Fe, Mg, PO(4), NO(3), CO(3), SO(4), Cl, and pH. The analyses were carried out using atomic absorption spectrometer and Hach Direct Reading Equipment. Results of the analyses from the area conform to the WHO (1995) standards for drinking water. However, the results show relative enrichment of Ca, pH, Mg, CO(3), and Cl. Low values were obtained for Fe, SO(4), and NO(3). While the Cl and Pb enrichment in the area north of Alayi-Ovim axis is attributed to proximity to the lead-zinc and chloride-rich formations of the Turonian Eze-Aku and the Albian Asu River; the Ca, Mg, SO(4), and CO(3) enrichment in Southern part of Alayi-Ovim is due to the limestone-bearing Late Maastrichtian Nsukka Formation. Furthermore, the very low values of less than 5 ppm for these characters in water in the central region correlate well with the relatively clean Maastrichtian quartz arenite Ajali Sandstone Formation. The Pb-Zn and Cl incursions into the water system from the Older Albian Asu River/Turonian Eze-Aku Formations in the northern part of Alayi-Ovim area and the leaching of Mg, and Ca into the water system in the Maastrichtian limestone area in the south thus constitute geochemical indices for chemical pollution and mineral exploration for brine and dolomitic limestone in the area. PMID:21713493

  4. Palaeomagnetic constraints on formation of the Mianwali reentrant, Trans-Indus and western Salt Range, Pakistan

    Science.gov (United States)

    Klootwijk, Chris T.; Nazirullah, Russell; de Jong, Kees A.

    1986-11-01

    Successions of Lower to lower Middle Cambrian, Upper Permian to Upper Triassic and Lower Tertiary carbonates and arenites have been sampled in five sections, representative of the three main segments of the Mianwali reentrant in the (Trans-Indus) Salt Range (northern Pakistan), i.e.: the southern Khisor Range, the northern Surghar Range and the western Salt Range. Comparison of primary and secondary magnetization directions with the Indian APWP demonstrates the secondary origin of the Mianwali reentrant and shows a pattern of rotations which varies in sense and magnitude along the reentrant with the main structural trends. Data from the Trans-Indus and western Salt Range and published Early Cambrian, Early Permian and Late Tertiary palaeomagnetic results from the southern Salt Range and the Potwar Plateau show that the Hazara Arc underwent a 20-45° counterclockwise rotation relative to the Indian Shield. A contrasting clockwise rotation over about 45° has recently been established for thrust sheets in the opposing eastern limb of the Western Himalayan Syntaxis, i.e. for the Panjal Nappe [1] and the Riasi thrust sheet [2]. These palaeomagnetically established rotations conform with the about 75° azimuthal change in structural trend along the Syntaxis, and support Crawford's [3] suggestion that the Salt Range was originally in line with the northwestern Himalaya. The Salt Range front prograded and moved southwards as part of the Hazara Arc thrust sheet, detached from basement along the evaporitic Salt Range Formation. The Mianwali reentrant originated through obstruction of the southwards advancing thrust sheet by moulding around basement topography of the northwest oriented Sarghoda Ridge.

  5. Evaluation of bacterial diversity recovered from petroleum samples using different physical matrices.

    Science.gov (United States)

    Dellagnezze, Bruna Martins; Vasconcellos, Suzan Pantaroto de; Melo, Itamar Soares de; Santos Neto, Eugênio Vaz Dos; Oliveira, Valéria Maia de

    2016-01-01

    Unraveling the microbial diversity and its complexity in petroleum reservoir environments has been a challenge throughout the years. Despite the techniques developed in order to improve methodologies involving DNA extraction from crude oil, microbial enrichments using different culture conditions can be applied as a way to increase the recovery of DNA from environments with low cellular density for further microbiological analyses. This work aimed at the evaluation of different matrices (arenite, shale and polyurethane foam) as support materials for microbial growth and biofilm formation in enrichments using a biodegraded petroleum sample as inoculum in sulfate reducing condition. Subsequent microbial diversity characterization was carried out using Scanning Electronic Microscopy (SEM), Denaturing Gradient Gel Electrophoresis (DGGE) and 16S rRNA gene libraries in order to compare the microbial biomass yield, DNA recovery efficiency and diversity among the enrichments. The DNA from microbial communities in petroleum enrichments was purified according to a protocol established in this work and used for 16S rRNA amplification with bacterial generic primers. The PCR products were cloned, and positive clones were screened by Amplified Ribosomal DNA Restriction Analysis (ARDRA). Sequencing and phylogenetic analyses revealed that the bacterial community was mostly represented by members of the genera Petrotoga, Bacillus, Pseudomonas, Geobacillus and Rahnella. The use of different support materials in the enrichments yielded an increase in microbial biomass and biofilm formation, indicating that these materials may be employed for efficient biomass recovery from petroleum reservoir samples. Nonetheless, the most diverse microbiota were recovered from the biodegraded petroleum sample using polyurethane foam cubes as support material. PMID:27282730

  6. Electric field effects in RUS measurements.

    Science.gov (United States)

    Darling, Timothy W; Allured, Bradley; Tencate, James A; Carpenter, Michael A

    2010-02-01

    Much of the power of the Resonant Ultrasound Spectroscopy (RUS) technique is the ability to make mechanical resonance measurements while the environment of the sample is changed. Temperature and magnetic field are important examples. Due to the common use of piezoelectric transducers near the sample, applied electric fields introduce complications, but many materials have technologically interesting responses to applied static and RF electric fields. Non-contact optical, buffered, or shielded transducers permit the application of charge and externally applied electric fields while making RUS measurements. For conducting samples, in vacuum, charging produces a small negative pressure in the volume of the material--a state rarely explored. At very high charges we influence the electron density near the surface so the propagation of surface waves and their resonances may give us a handle on the relationship of electron density to bond strength and elasticity. Our preliminary results indicate a charge sign dependent effect, but we are studying a number of possible other effects induced by charging. In dielectric materials, external electric fields influence the strain response, particularly in ferroelectrics. Experiments to study this connection at phase transformations are planned. The fact that many geological samples contain single crystal quartz suggests a possible use of the piezoelectric response to drive vibrations using applied RF fields. In polycrystals, averaging of strains in randomly oriented crystals implies using the "statistical residual" strain as the drive. The ability to excite vibrations in quartzite polycrystals and arenites is explored. We present results of experimental and theoretical approaches to electric field effects using RUS methods. PMID:19850314

  7. An extraordinary example of photokarren in a sandstone cave, Cueva Charles Brewer, Chimantá Plateau, Venezuela: Biogeomorphology on a small scale

    Science.gov (United States)

    Lundberg, J.; McFarlane, D. A.; Brewer-Carias, C.

    2010-09-01

    A distinctive suite of small-scale erosional forms that are oriented towards the light occur close to the entrance of Cueva Charles Brewer, a large cave in a sandstone tepui, in SE Venezuela. These are the third example of photokarren ever studied in the world, the other two being from Borneo and Ireland. They are the only photokarren ever described from sandstone, and the only example from a non-carbonate environment. The host rock is a poorly-lithified unit of the Precambrian quartz arenite of the Roraima Supergroup. The forms are all oriented towards the light at 30° regardless of rock surface orientation. The primary (negative) erosional form is the tube. Coalescence of tubes results in the positive remnant forms of rods, pinnacles, and cones. The final stage is a bumpy, wavy surface of degraded cones. The size of the features varies with erosion rate, and details of the form vary with development stage. The main population averages 4.4 cm in depth, with 55% of the surface eroded. This is divided into 10% tubes, 70% rods, 10% cones, 5% linear valley and 5% wavy lowland. The micro-ecosystem includes many bacteria, diatoms, red algae, green algae, liverworts, and oribatid mites, but, surprisingly, no cyanobacteria. The presence of a surface biofilm inside the forms but not on the remnant rock surface and, in the non-degraded forms, the direct relationship of biomass with depth suggests that biological activity is the dominant control on development. In addition, direct bacterial corrosion was noted. These same features occur to varying extents in the photokarren of Borneo and Ireland, and the model for development that we present provides a unifying theory for all photokarren. (This study also includes the first published petrographic analysis of uppermost unit of the Mataui Formation).

  8. Provenance analysis of the Guaritas Group (RS conglomeratic sandstones: implications for the paleoclimate and paleogeography of the Eocambrian Central Camaquã sub-basin

    Directory of Open Access Journals (Sweden)

    Antonio Romalino Santos Fragoso-Cesar

    2013-06-01

    Full Text Available The Camaquã Supergroup, located in the central-south region of Rio Grande do Sul, Brazil, constitutes a rift-type post-orogenicsedimentary basin, whose deposition occurred in a continental environment between the Ediacaran and the Eocambrian.The upper succession of the Camaquã Supergroup is represented by the Guaritas Group, a unit formed by fluvial, eolian andalluvial fan deposits that keeps important records of the sedimentation right after the end of the neoproterozoic orogenesis thatgave rise to the Gondwana supercontinent. The objective of the present work was to apply sedimentary provenance analysis inconglomeratic arenites and conglomerates of the Guaritas Group, in order to explore the climatic and tectonic evolution historyof this unit. Based on the pebble compositional data, two main source areas were recognized for the deposits of this unit,a more distal one located to the north, related with a trunk river system parallel to the basin main axis, and a more proximalone located to the east, related to transversal fluvial systems and alluvial fans at the border of the basin. The comparison of theprovenance data with previous studies on facies and paleocurrents suggests that, during the entire evolution of the east borderof the basin, there was a same transversal fluvial system, whose catchment area suffered significative reductions due to thereactivation of the east border fault during the deposition of the Varzinha and Pedra Pintada Formations. The Serra do ApertadoFormation, the upper unit of Guaritas Group, shows a high correlation between the variation of quartzose and non quartzosepebbles composition, and it was attributed to a variation between more humid and more arid climatic conditions.

  9. Electric Field Effects in RUS Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Darling, Timothy W [Los Alamos National Laboratory; Ten Cate, James A [Los Alamos National Laboratory; Allured, Bradley [UNIV NEVADA, RENO; Carpenter, Michael A [CAMBRIDGE UNIV. UK

    2009-09-21

    Much of the power of the Resonant Ultrasound Spectroscopy (RUS) technique is the ability to make mechanical resonance measurements while the environment of the sample is changed. Temperature and magnetic field are important examples. Due to the common use of piezoelectric transducers near the sample, applied electric fields introduce complications, but many materials have technologically interesting responses to applied static and RF electric fields. Non-contact optical, buffered, or shielded transducers permit the application of charge and externally applied electric fields while making RUS measurements. For conducting samples, in vacuum, charging produces a small negative pressure in the volume of the material - a state rarely explored. At very high charges we influence the electron density near the surface so the propagation of surface waves and their resonances may give us a handle on the relationship of electron density to bond strength and elasticity. Our preliminary results indicate a charge sign dependent effect, but we are studying a number of possible other effects induced by charging. In dielectric materials, external electric fields influence the strain response, particularly in ferroelectrics. Experiments to study this connection at phase transformations are planned. The fact that many geological samples contain single crystal quartz suggests a possible use of the piezoelectric response to drive vibrations using applied RF fields. In polycrystals, averaging of strains in randomly oriented crystals implies using the 'statistical residual' strain as the drive. The ability to excite vibrations in quartzite polycrystals and arenites is explored. We present results of experimental and theoretical approaches to electric field effects using RUS methods.

  10. Petrographic and geochemical characteristics of the ignimbritic units containing uranium mineralization of the Sierra Pena Blanca, Mexico

    International Nuclear Information System (INIS)

    The Sierra Pena Blanca, which is characterized by Miocene-Plioquaternary Basin and Range tectonics, is a mountain range 70 km long oriented NNW-SSE and located 50 km to the north of the city of Chihuahua. This range is divided into two parts: a southern one with outcrops of old Palaeozoic and Mesozoic series and a northern one in which the Eocene ignimbritic sequence lies in unconformity over the folded Mesozoic series. The Eocene volcanic sequence consists of five cooling units locally separated by levels of calcareous breccias, conglomerates or arenites; the first two units were deposited at 43.5+-1 MA and the other three at 37.8+-0.5 MA. The uranium mineralization is found in the oldest ignimbritic units with the exception of the El Nopal I deposit which is of the breccia pipe type and is situated in the second cooling unit (Nopal ''rhyolite'' - Escuadra ''rhyolite''); the El Nopal deposit is either on the border between the lava flows (El Nopal III) or is well disseminated (El Puerto III and Las Margaritas). The Nopal and Escuadra ''rhyolites'', which are rich in silicon (75+-0.5%) and in alkalines (>8%) are noted for their K2O contents of above 6%; this is a primary characteristic confirmed by the composition of the vitreous inclusions of quartz phenocrysts (Na2O+K2O>10%-K2O=6.3+-0.1%) predating post-depositional processes which, on the other hand, have influenced the percentage of Na2O, causing the chemical compositions to move in the direction of hyperaluminosity. Developed rhyolites are enriched in Th (35 ppm) and U (10 ppm); this continuous background is sufficient to permit in situ remobilization as a result of the circulation of fluids linked with the escape of gases

  11. Lithologic characteristics and diagenesis of the Devonian Jauf sandstone at Ghawar Field, Eastern Saudi Arabia

    Energy Technology Data Exchange (ETDEWEB)

    Al Ramadan, K.A.; Hussain, M. [King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia). Dept. of Earth Sciences; Imam, B. [Dhaka Univ. (Bangladesh). Dept. of Geology; Saner, S. [King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia). Research Inst.

    2004-12-01

    The Lower Devonian Jauf Formation in Saudi Arabia is an important hydrocarbon reservoir. However, in spite of its importance as a reservoir, published studies on the Jauf Formation more specifically on the reservoir quality (including diagenesis), are very few. This study, which is based on core samples from two wells in the Ghawar Field, northeastern Saudi Arabia, reports the lithologic and diagenetic characteristics of this reservoir. The Jauf reservoir is a fine to medium-grained, moderate to well-sorted quartz arenite. The diagenetic processes recognized include compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of the calcite cements and of feldspar grains. The widespread occurrences of early calcite cement suggest that the Jauf reservoir lost a significant amount of primary porosity at a very early stage of its diagenetic history. Early calcite cement, however, prevented the later compaction of the sandstone, thus preserving an unfilled part of the primary porosity. Based on the framework grain-cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-bridging clay cement. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late calcite cement occurs as isolated patches, and has little impact on reservoir quality of the sandstones. In addition to calcite, several different clay minerals including illite and chlorite occur as pore-filling and pore-lining cements. While the pore-filling illite and chlorite resulted in a considerable loss of porosity, the pore-lining chlorite may have helped in retaining the porosity by preventing the precipitation of syntaxial quartz overgrowths. Illite, which largely occurs as hair-like rims around the grains and bridges on the pore throats, caused a substantial deterioration to permeability of the

  12. Geochemistry of a tropical lake (Lake Leopoldo) on pseudo-karst topography within the Roraima Group, Guayana Shield, Venezuela

    International Nuclear Information System (INIS)

    A geochemical assessment was performed on Lake Leopoldo, a tropical lake located on the Guayana Shield, Venezuela. The lake water was characterized (Ca2+, Mg2+, Na+, K+, Cl-, NO3-, NO2-, SO42-, NH4+, Fe, and P), lacustrine setting the origin, transport and fate of sedimentary material in this highly unusual lacustrine setting. Lake sediments were analyzed for textural, mineralogical and chemical composition, including the rare earth element (REE) contents. In addition to %TOC, δ13C, δ15N and elemental C/N ratios, the molecular distributions of several biomarker compounds were determined and used to assess organic matter source and transport to the lake. Lake Leopoldo developed on a sequence of quartz arenites of the Precambrian Roraima Group. The area conforms to the definition of pseudo-karst morphology. The results show that the lake is oligotrophic where primary production seems to be limited by nutrients. In the sediments, organic matter shows an overwhelming higher plant-derived origin. Certain elements (K, V, Cu, Th, Ba, Hg, and LREE) displayed enrichments with organic matter, while others (Zr, Hf, Si, Sn, Pb, and Ta) displayed an association with the mineral fraction. The results obtained in this study suggest that the lake water characteristics and the affinities of trace elements for sediment organic fractions are controlled by biogeochemical processes within the surrounding forest soil environment, prior to the transport of the terrestrially-derived organic matter to the lake. The most significant geochemical finding is that organic matter can play an important role in the distribution of trace metals in such highly oligotrophic terrains of humid, tropical environments. vironments

  13. Paleoproterozoic mojaveprovince in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

    Science.gov (United States)

    Lang, Farmer G.; Bowring, S.A.; Matzel, J.; Maldonado, G.E.; Fedo, C.; Wooden, J.

    2005-01-01

    Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the ??? 1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleo- proterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, "A-type" granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States ?? 2005 Geological Society of America.

  14. Petroliferous basin analysis in Taegu area (II)

    Energy Technology Data Exchange (ETDEWEB)

    Cheong, T.J.; Oh, J.H.; Son, J.D.; Bong, P.Y.; Lee, H.Y.; Ryu, B.J.; Son, B.K.; Kwon, Y.I.; Hwang, I.G.; Lee, Y.J.; Kim, H.J. [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)

    1997-12-01

    Sandstones of the Sindong and Hayang groups belong to the arkose-feldspar arenite. In the Sindong Group, sandstones are dominated by quartz. In the Hayang Group, however, feldspar and tuffaceous sandstones are abundant. Sand grains are subangular to subrounded and moderately-sorted, in which the sand grains show point- and long-contact. Primary pores are filled with diagenetic minerals such as calcite, silica and authigenic clay minerals. Replacement and dissolution of calcite, and alternation of feldspar form the minor secondary pores. Reservoir quality of the sandstones is poor with less than 5% of porosity. In the study area, illite crystallinity is strongly affected by the post depositional intrusion, regardless of stratigraphic position. The burial temperature of the study area could be estimated at about 150-180 deg.C based on illite crystallinity data. In the Sindong Group, vitrinite reflectance ranges from 2.51% to 3.85% Ro and Rock-Eval Tmax ranges from 613 deg. to 711 deg.C, indicating that thermal maturity of the organic matter reached at the last stage of dry gas generation. These data also indicate that all of the transformable organic matter has been transformed into hydrocarbon and that considerable hydrocarbons could have been generated. Geophysical study on the Jinju Formation suggests that P-wave velocity of the sediments is very high and high frequency seismic source should be used to identify main depositional units. In this case, some depositional units can not be recognized, using ordinary seismic data acquisition method. In summary, the Nakdong and Jinju formations contain abundant black shales, and thermal maturity of the organic matter reached at the final stage of dry gas generation. These formations also contain thick sandstones which can act as a petroleum reservoir. However, reservoir quality of the sandstones is poor (porosity: < 5%; permeability: < 0.001 md). In these sandstones, secondary pores such as dissolution pores and

  15. Uranium in lower Proterozoic conglomerates of the Koli area, eastern Finland

    International Nuclear Information System (INIS)

    Jatulian meta-arenites form an extensive part of the Karelian Supergroup (middle to lower Proterozoic) in the Baltic Shield. In North Karelia, eastern Finland, the middle and lower Karelian supracrustal rocks (Jatulian an Sariolian; 2,000-2,500 Ma) trend northwesterly for 150 km along the margin of the Archean basement in the east. The thickness of this sequence varies from less than 500 m to 2,000 m. Already in the late 1950's, near Koli in North Karelia small uranium deposits were discovered. Uranium and, in places, thorium occur in the lower Jatulian Quartzite Member as lenses along a horizon that bears spotty pigmentation of hematite. Interbeds of quartz-pebble conglomerate are typical of this horizon. Uranium is also enriched at the contacts of Jatulian diabases where they cut across the uraniferous horizon. Small uranium bodies also lie in the middle Jatulian Arkosite Member. Ipatti, a well-exposed occurrence of uranium at Koli (71,000 tons of mineralized rock averaging 0.083% U) is situated in the Arkosite Member 200-300 m above the hematite-stained horizon. The Ipatti arsenites are predominantly pebbly and clayey subarkoses indicating poor sorting and, hence, rapid burial. The maximum dimensions of the uraniferous body are 6x50x300 m. Colloform low-thorium pitchblende forms part of the cement material between the quartz clasts in the mineralized grit. Secondary uranium minerals envelop the pitchblende mineralization as a network of fracture fillings. Systematic lithogeochemical study across the Ipatti deposit and the lower Jatulian Quartzite Member at Koli did not reveal anomalous contents of gold. The uranium mineralization at Ipatti is suggested to have originated from pore fluids in at least three stages of epigenetic precipitation. The Prejatulian weathering crust and Archean granitoids are considered to be the most probable sources of uranium. Sedimentological, mineralogical, and geochemical evidence for syngenetic conglomerate-type mineralization of

  16. Silica Transport and Cementation in Quartz Aggregates

    Science.gov (United States)

    Pebble, C.; Farver, J.; Onasch, C.; Winslow, D.

    2008-12-01

    Silica transport and cementation in quartz aggregates have been experimentally investigated. Starting materials include a natural quartz arenite (Pocono sandstone), sized clasts of synthetic quartz, and sized grains of disaggregated natural sandstones. Experimental charges consisted of amorphous silica powder (~25 mg), AlCl3 powder (~3 mg), 25 wt% NaCl brine solution (~20 mg), and the starting material (~150 mg). The charges were weld-sealed in gold capsules and run in cold-seal pressure vessels at 300°C to 600°C at 150 MPa confining pressure for up to 4 weeks. Detailed calibrations of the furnaces indicate the maximum temperature variation across the length of the sample charges (3-7mm) was vacuum impregnated with epoxy containing a blue dye and sawn in half along the long axis of the sample charge. The nature and amount of silica transport and cementation in the samples was determined by a combination of Cathodoluminescence (CL), Light Microscopy (LM), and Scanning Electron Microscopy (SEM). Photomosaics of the samples were collected and the amount of cement, porosity, and average grain sizes were determined by point-counting. The cement was easily recognized from the quartz grains by the difference in luminescence. The experiments indicate that the presence of amorphous silica results in rapid silica cementation in quartz aggregates (e.g., up to 12% cement by volume in 4 weeks at 450°C). The amount of cementation is a function of substrate type, time, temperature, and ionic strength of the brine. The rate of silica transport through the length of the experimental charge appears to be limited by the silica solubility and its rapid depletion by cementation. Although most of the cement was derived from the amorphous silica, evidence for local dissolution-precipitation was observed. The experiments demonstrate that the mobility of silica, and consequent precipitation of cement, does not require a temperature or pressure gradient as is commonly assumed. Rather

  17. Deformation of Aztec Sandstone at Valley of Fire of Nevada: failure modes, sequence of deformation, structural products and their interplay with paleo fluids

    Science.gov (United States)

    Aydin, A.

    2014-12-01

    The Valley of Fire State Park, 60 km NE of Las Vegas, is a beacon of knowledge for deformation of Aztec Sandstone, a cross-bedded quartz arenite deposited in the Aztec-Navajo-Nugget erg in early Jurassic. It displays great diversity of physical properties, different localization types and micromechanics. The two deformation episodes, the Sevier folding & thrusting and the Basin & Range extension affected the area. The appearance of compaction bands marks the earliest deformation structure and their distribution, orientation, and dimension are controlled by the depositional architecture and loading. The earliest shear structures in the area are the Muddy Mountain, Summit, and Willow Tank thrusts and numerous small-scale bed-parallel faults. They altogether produced several kilometers of E-SE transport and shortening in the late Cretaceous and display numerous shear bands in its damage zone within the Aztec Sandstone. Shear bands also occur along dune boundaries and cross-bed interfaces. These observations indicate that the early deformation of the sandstone was accommodated by strain localization with various kinematics. The younger generation of faults in the area is of mid-Miocene age, and crops out pervasively. It includes a series of small offset normal faults (less than a few ten meters) which can be identified at steep cliff faces. These faults are highly segmented and are surrounded by a dense population of splay fractures. A large number of these splays were later sheared sequentially resulting in a well-defined network of left- and right-lateral strike-slip faults with slip magnitudes up to a few kilometers in the Park. The formation mechanisms of both the normal and strike-slip faults can be characterized as the sliding along planes of initial weaknesses and the accompanying cataclastic deformation. Some of the initial weak planes are associated with the depositional elements such as interdune boundaries and cross-bed interfaces while others are joint

  18. Open-System Alkaline Magmatism in the Caledonides of North-Central Norway

    Science.gov (United States)

    Barnes, C. G.; Prestvik, T.; Barnes, M. A.

    2002-12-01

    The Caledonian-age Hortavaer intrusion is exposed on small islands and skerries off the coast of north-central Norway. It was emplaced into a range of host rocks that includes calcitic and dolomitic marble to migmatitic gneiss to quartz-rich meta-arenite. The intrusion is unusual relative to Caledonian plutons on the mainland because of its alkaline nature and its possible circa 460-470 Ma age (based on imprecise Sr and Nd isochrones). The intrusion is broadly zoned, with central diorite and outer syenite. Dike-like bodies of monzonite and syenite are also present and are elongate in a NNE-SSW direction. Each lithologic unit is characterized by evidence for magma mingling, particularly by synplutonic dikes and enclaves. In the syenitic zone, mingled magmas ranged from monzonitic (syenitic) to dioritic. In the diorite zone, mingling was dominated by diorite-in-diorite, but composite diorite-syenite dikes are present. The contact between the syenite and diorite units is marked by an approximately 500-m-wide zone of sheeted diorite/syenite dikes that are mutually intrusive. In addition to magma mingling, the complex shows a variety of types of interaction with screens of its host rocks, which are typically subparallel to foliation in the pluton. Some screens were apparently unreactive with the surrounding magma, whereas others resulted in intense reaction and formation of garnet melasyenite, pyroxene-rich monzodiorite, and rare nepheline-bearing rocks. A trend toward Fe enrichment among the dioritic rocks, the low Mg/(Mg+Fe) and Sr contents of the evolved syenites, and curvilinear composition trends for many elements in the suite suggest fractional crystallization was a major control on magma evolution. However, low epsilon Nd (465 Ma) (-3 to -10), moderate initial 87Sr/86Sr (0.705 to 0.710), and high delta18O (+8.3 to +14.0 %) suggest either a crustal source or intense contamination. The presence of primary calcite with delta13C typical of host carbonate rocks

  19. LITHOSTRATIGRAPHY, CONODONT BIOSTRATIGRAPHY AND DEPOSITIONAL ENVIRONMENT OF THE MIDDLE DEVONIAN (GIVETIAN TO EARLY CARBONIFEROUS (TOURNAISIAN LIPAK FORMATION IN THE PIN VALLEY OF SPITI (NW INDIA

    Directory of Open Access Journals (Sweden)

    ERICH DRAGANITS

    2002-03-01

    Full Text Available Bed-by-bed lithostratigraphic sections combined with sequence stratigraphy and conodont biostratigraphy provide new information on the depositional environment and age of the Lipak Formation in the Pin Valley (Spiti. The formation comprises mixed siliciclastic and calcareous sediments at lower levels, richly fossiliferous limestones with two distinct sandstone incursions at higher levels, and dark mudstones followed by a thin siltstone interval. The upper limit of the Lipak Formation is defined by the angular unconformity below the sandstones of the Permian Gechang Formation. Lithologic correlation with sections in upper Lahaul indicates that, in the Pin Valley, the formation has been truncated just below its characteristic gypsum horizon. The lower boundary of the Lipak Formation is gradational from coastal arenites of the Muth Formation; the mappable boundary is drawn at the first appearance of dark carbonaceous, argillaceous siltstone and shale.Sedimentary structures, microfacies and conodont faunas indicate a general shallow marine depositional environment of the Lipak Formation in the Pin Valley; five sequence stratigraphic units have been distinguished. Conodont data demonstrate that the lowest 33 m of the Lipak Formation of the Pin Valley is mid to late Early varcus Subzone with characteristic species of Icriodus and Bipennatus. A previously unrecognised hiatus at c. 33 m above the base, at the boundary of sequence stratigraphic units S1 and S2, represents the interval Middle varcus Subzone to at least the end of the late Famennian Early expansa Zone. Because this hiatus does not correspond to a mappable boundary, no division of the Lipak Formation into named stratigraphic units is suggested, but we refer informally to the sediments represented by cycle S1 as Lipak A, and the sediments represented by cycles S2-S5 as Lipak B. Determination of S1 as Early varcus Subzone provides a maximum age for the gradationally underlying Muth Formation

  20. Petrographic, mineralogical and geochemical characterization of the Serrinha coal waste pile (Douro Coalfield, Portugal) and the potential environmental impacts on soil, sediments and surface waters

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, J. [Centro de Geologia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Ferreira da Silva, E. [GeoBioTec, Geobiosciences, Geotechnologies and Geoengineering Research Center, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro (Portugal); Li, Z.; Ward, C. [School of Biological, Earth and Environmental Sciences, University of New South Wales. Sydney, NSW 2052 (Australia); Flores, D. [Departamento de Geociencias, Ambiente e Ordenamento do Territorio, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal)

    2010-09-01

    Serrinha is the largest coal waste pile resulting from mining activities in the Douro Coalfield, Portugal. The exploitation of anthracite in tens of small mines caused some environmental impacts, as is the case of the coal waste piles that exist in old mines and adjacent areas. The Serrinha waste pile is essentially made up of 2 million tonnes of shales and carbonaceous shales, deposited in a topographical depression over about 30 years. Despite the environmental restoration accomplished in the Serrinha waste pile, some environmental problems seem to persist. In this study a petrographic, mineralogical and geochemical characterization was done in order to recognize and understand these problems. The materials studied were coal waste, sediments and waters from the drainage system and decanting basins, soils from the surrounding areas, leachates from waste material and neoformed minerals formed at the bottom of the waste pile. The main lithologies (carbonaceous shale and lithic arenite) and coal from the Douro Coalfield were also analyzed. Petrographic analysis shows some evidence of weathering (on organic and inorganic matter) related to the time of exposure to the weathering agents and the easy access of air within the waste pile (due to both the poor compaction and the heterogeneity of the material). Mineralogically, the composition of coal waste material has contributions from both the coal and the associated lithologies. R-type cluster analysis of the waste pile material allows two distinct clusters to be identified. In the first cluster a sulfide fraction is represented by the association of As, Cd, Cu, Pb, Ni and Zn, while Fe clustered with Al, Co, and Ti indicates that some of the Fe and the other elements are likely associated with silicate minerals such as clays. The second cluster, represented by Cr, V, Zr, Rb, REE, Mn, Li and Ba, probably represent a silicate fraction, perhaps detrital accessory minerals. The waste pile material, leachates, soils

  1. The Jurassic of Denmark and Greenland: The use of spectral natural gamma-ray analysis in reservoir evaluation of siliciclastic sediments: a case study from the Middle Jurassic of the Harald Field, Danish Central Graben

    Directory of Open Access Journals (Sweden)

    Fabricius, Ida L.

    2003-10-01

    Full Text Available A cored sandstone interval from the Middle Jurassic Harald Field of the Danish North Sea was chosen for an investigation of the mineralogical sources for the gamma-ray activity, and with the purpose of determining how the Spectral Natural Gamma (SNG log could be used as an indicator of reservoir quality. Core intervals of quartz arenites and quartz wackes were selected. Although no linear relationship was found between clay content and potassium (K, thorium (Th, or uranium (U, the K content characterises three discrete lithofacies. Lithofacies I has a grain-supported texture, with a predominance of quartz grains; only minor fine-grained matrix is present. Sandstones of lithofacies I have a low K content and most of the K is hosted in feldspar. Porosity varies between 23% and 28% and permeability is in the range 200-2000 mD. Lithofacies II sandstones have a grain-supported texture, with a predominance of quartz grains; fine-grained matrix fills the intergranular volume. Sandstones of lithofacies II have an intermediate K content, with K-feldspar, mica, and illite as the main sources. Porosity varies between 11% and 17% and permeability is in the range 0.4-25 mD. Lithofacies III has a matrix-supported texture with quartz grains floating in a clay-rich matrix. Samples from lithofacies III have the highest K signal. Illite and illitised kaolinite are roughly equal in importance as sources of K. Porosity is up to 11% and permeability up to 0.5 mD. The Th and U content of all lithofacies is governed primarily by the presence of heavy minerals; no apparent general relationship between U and Total Organic Carbon (TOC was found. Comparisons between the core measurements of K, Th, and U, and the SNG log disclosed a discrepancy between the calibrations of laboratory and borehole measurements. For U the discrepancy contains an erratic element, whereas the difference for K and Th can be eliminated by correction factors. Thus, the conclusions based on

  2. Petrographic, mineralogical and geochemical characterization of the Serrinha coal waste pile (Douro Coalfield, Portugal) and the potential environmental impacts on soil, sediments and surface waters

    International Nuclear Information System (INIS)

    Serrinha is the largest coal waste pile resulting from mining activities in the Douro Coalfield, Portugal. The exploitation of anthracite in tens of small mines caused some environmental impacts, as is the case of the coal waste piles that exist in old mines and adjacent areas. The Serrinha waste pile is essentially made up of 2 million tonnes of shales and carbonaceous shales, deposited in a topographical depression over about 30 years. Despite the environmental restoration accomplished in the Serrinha waste pile, some environmental problems seem to persist. In this study a petrographic, mineralogical and geochemical characterization was done in order to recognize and understand these problems. The materials studied were coal waste, sediments and waters from the drainage system and decanting basins, soils from the surrounding areas, leachates from waste material and neoformed minerals formed at the bottom of the waste pile. The main lithologies (carbonaceous shale and lithic arenite) and coal from the Douro Coalfield were also analyzed. Petrographic analysis shows some evidence of weathering (on organic and inorganic matter) related to the time of exposure to the weathering agents and the easy access of air within the waste pile (due to both the poor compaction and the heterogeneity of the material). Mineralogically, the composition of coal waste material has contributions from both the coal and the associated lithologies. R-type cluster analysis of the waste pile material allows two distinct clusters to be identified. In the first cluster a sulfide fraction is represented by the association of As, Cd, Cu, Pb, Ni and Zn, while Fe clustered with Al, Co, and Ti indicates that some of the Fe and the other elements are likely associated with silicate minerals such as clays. The second cluster, represented by Cr, V, Zr, Rb, REE, Mn, Li and Ba, probably represent a silicate fraction, perhaps detrital accessory minerals. The waste pile material, leachates, soils

  3. Physical and Chemical Effects of Two-Phase Brine/Supercritical-CO2 Fluid Flow on Clastic Rocks: Real-Time Monitoring and NMR Imaging of Flow-Through Core Experiments

    Science.gov (United States)

    Shaw, C. A.; Vogt, S.; Maneval, J. E.; Brox, T.; Skidmore, M. L.; Codd, S. L.; Seymour, J. D.

    2010-12-01

    Sandstone core samples were challenged with a supercritical CO2-saturated brine mixture in a laboratory flow-through core reactor system over a range of temperatures and brine strengths. Cores of quartz arenite from the Berea formation were selected to represent ideal ‘clean’ sandstone These laboratory experiments potentially provide an analog for the acidification of pore fluids near the brine/CO2 interface during CO2 flooding of depleted clastic hydrocarbon reservoirs for carbon sequestration. Flow in the reactor was perpendicular to bedding. Initial experiments were run at 50°C and 100°C with brine concentrations of 1g/L and 10g/L (TDS) to test effects of different temperatures and brine compositions. Real-time monitoring of fluid pH and conductivity provided a measure of reaction rates. Introduction of supercritical CO2 into the brine-saturated cores initiated a reduction in pH accompanied by an increase in conductivity. NMR images of fresh cores were compared with images of challenged cores using a protocol for pixel-by-pixel comparison to determine the effects on bulk pore volume and geometry. Two types of imaging experiments were conducted: multi-slice spin echo and 3-D spin echo images. Multi-slice experiments had a slice thickness of 1.5 mm and an in-plane resolution of 0.27 mm x 0.27 mm, and 3-D experiments had a resolution of 0.47 mm x 0.55 mm x 0.55mm. Imaging results reflected the observed changes in the physical and chemical structure post-challenge. Two-dimensional relaxation correlation experiments were also conducted to probe the pore sizes, connectivity and fluid saturation of the rock cores before and after challenging. Chemical analyses and microscopic examination of the challenged cores will provide a better understanding of alteration in the cores and the changes in the volume, geometry and connectivity of pore space.

  4. Acoustic Emission and Ultrasonic Characterization of Jurassic Navajo Formation Deformation During Axisymmetric Compression Testing

    Science.gov (United States)

    Rinehart, A. J.; Dewers, T. A.; Holcomb, D. J.; Broome, S. T.

    2011-12-01

    Linking continuum-scale and microscale brittle damage in rock remains a challenge impacting CO2 sequestration, secondary recovery, structural monitoring, and other geotechnical engineering applications. We examine if the mode of micromechanical failure scales directly up to continuum-scale damage-induced velocity anisotropy. Axisymmetric drained lab-dry compression experiments are performed on facies of moderately cemented finely laminated quartz arenite from the Jurassic Navajo Formation, a target reservoir rock for CO2 sequestration in Utah. The tests are 1 unconfined uniaxial compression test, 1 hydrostatic compression test, and 3 triaxial compression tests. Microscale damage is monitored using acoustic emissions (AE) and continuum scale damage is monitored with ultrasonic velocity scans. During the non-hydrostatic tests, three to five unload loops are performed pre-failure, with one unload loop performed post-failure. While stresses are increasing, AEs are monitored continuously using 1.6-mm diameter, 0.5-mm thick PZT-5A pins attached circumferentially around the cylindrical sample, and with 6-mm diameter, 2-mm thick PZT-5A discs at the ends of the sample. Before and after each unload loop, the test is paused and the AE transducers sequentially emit an ultrasonic pulse to measure wave speeds. The resulting elastic wave is detected by the other AE transducers. Post-test, the changing anisotropic velocity structure of the rock during compression and failure is compared to the locations, frequency, and relative moment tensors of the AEs measured between ultrasonic scans. Pre- and post-test visual and x-ray CT scan observations of the sample are compared to the acoustic metrics. These tiered observations of rock damage will further elucidate the scaling of microscale brittle failure to the continuum-scale This work was supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of

  5. Detrital zircons from samples of five Neo proterozoic sandstone units deposited on Uruguay and Argentina: about evolution of paleographic Rio de la Plata craton

    International Nuclear Information System (INIS)

    We report U-Pb ages of detrital zircons from samples of five Neoproterozoic sandstone units deposited on the Rio de la Plata Craton (RPC) in Uruguay and Argentina. Quartz-arenites of the Piedras de Afilar Formation show typical Transamazonian ages, with peaks at 2.00-2.07, 1.87 and 1.78 Ga. However, the most important zircon population is Mesoproterozoic, showing maxima at 1.49, 1.35, 1.25 and 1.0 Ga. Zircons recovered from two sandstone levels in the Arroyo del Soldado Group (Yerbal and Cerros San Francisco formations) are mostly Archean in age, with maxima at 3.2 and 2.7 Ga. Palaeoproterozoic zircons are also prominent in this unit, with peaks at 2.45 and 2.18, with the latter a typical Transamazonian age. Two samples from the Sierras Bayas Group in Tandilia (Argentina) show different age spectra. Sandstones of the Villa Monica Formation show a unimodal zircon population of Transamazonian age (peak at 2.13 Ga). Sandstones of the Cerro Largo Formation are characterized by a dominant Transamazonian zircon population (peaks at 2.15, 2.0 and 1.79), but also important Archean-lowermost Palaeoproterozoic (3.33, 2.99, 2.7, 2.47 Ga) and Mesoproterozoic peaks (1.55, 1.23 and 1.06). The abundance of Mesoproterozoic detrital zircons is surprising. A proto-Andean, Mesoproterozoic belt is suggested as the source of the Mesoproterozoic detritus. Archean rocks of the RPC crop out only in the Nico Perez Terrane in Uruguay, suggesting that the Nico Perez Terrane was much closer to Tandilia than it is today. The sinistral reactivation of the Sarandi del Yi Shear Zone in the Cambrian, as a result of tangential collision of the Cuchilla Dionisio-Pelotas Terrane, may explain this observations. The absence of Neoproterozoic zircons shows that the studied units were deposited in a stable continental margin opening to the East and South. These Neoproterozoic basins had obviously no contribution whatsoever from Brasiliano-Pan African belts, supporting the idea of Cambrian terrane

  6. Formation of the Archean crust of the ancient Vodlozero domain (Baltic shield)

    Science.gov (United States)

    Arestova, N. A.; Chekulaev, V. P.; Lobach-Zhuchenko, S. B.; Kucherovskii, G. A.

    2015-03-01

    .8 Ga, which includes arenite quartzite and graywackes and polymictic conglomerates developed in the Lake Oster area in addition to volcanics. These rocks indicate a stable tectonic regime, which resulted in deep erosion of the crust. The emplacement of sanukitoids (2.73-2.74 Ga) as well as subsequent two-feldspar granites (2.68-2.70 Ga) and basite dikes (2.61-2.65 Ga) may be considered as resulting from the plume influence on the relatively stabilized sialic crust of the Baltic shield.

  7. On the formation, growth, and shapes of solution pipes - insights from numerical modeling

    Science.gov (United States)

    Szymczak, Piotr; Tredak, Hanna; Upadhyay, Virat; Kondratiuk, Paweł; Ladd, Anthony J. C.

    2015-04-01

    distances between the pipes as well as their growth rates. The most interesting result is the existence of two different regimes of the piped growth, depending on the flow rate. At high flow rates, well-separated, cyllindrical shafts are formed, of a nearly uniform diameter all along their lengths. They advance quickly into the matrix, with velocities several times larger than that of a unperturbed, planar dissolution front. Conversely, for small flow rates, the pipes are funnel-shaped with parabolic tips and their advancement velocity is of the same order as that of a planar front. The transition between the two forms is abrupt, with no intermediate forms observed. The simulation results are compared with field evidence from limestone quarries in Smerdyna, Poland, where several hundred of solution pipes have been exposed. Interestingly, both forms (shaft-like and tunnel-like) are found in the field, sometimes in close proximity to each other. [1] P. Walsh and I. Morawiecka-Zacharz, A dissolution pipe palaeokarst of mid-Pleistocene age preserved in Miocene limestones near Staszow, Poland, Palaeogeogr. Palaeoclimatol. Palaeoecol., 174 (2001), pp. 327-350. [2] K. G. Grimes, Solution pipes and pinnacles in syngenetic karst. In: Gines A., Knez M., Slabe T., Dreybrodt W. (Eds.), Karst Rock Features: Karren Sculpturing. Ljubljana, ZRC Publishing, (2009), pp. 513-523. [3] J. De Waele, S. E. Lauritzen and M. Parise On the formation of dissolution pipes in Quaternary coastal calcareous arenites in Mediterranean settings. Earth. Surf. Proc. Land" 36, (2011), pp. 143-157.

  8. Migmatites and migmatite-like rocks of Olkiluoto

    Energy Technology Data Exchange (ETDEWEB)

    Kaerki, A. [Kivitieto Oy, Oulu (Finland)

    2015-02-15

    Bedrock of the Olkiluoto Island in the western end of the Palaeoproterozoic Svecofennian Accretionary Arc Complex, SW Finland is composed of high-grade metamorphic pelites, arenites and intermediate, arc type metavolcanic rocks intruded by granodioritic to tonalitic plutonic rocks. Regional metamorphism culminated with voluminous migmatization in the temperature of 660 - 700 deg C and relatively low pressure of about 3.5 - 4 kbar. The end result of polyphase metamorphism and deformation is a metamorphic rock succession composed of diverse migmatite rocks, metatexites and diatexites. Metatexites are migmatites in which several, discrete components can be detected, and in which the paleosome with some pre-partial-melting textures is identifiable. Diatexites are more advanced migmatites in which the pre-migmatization structures are often totally destroyed and the rock is dominated by different neosome components meaning leucosome, melanosome or mesosome. Based on the migmatite structures the metatexites of Olkiluoto have been classified into six subgroups. Dike-structured metatexites are composed of well preserved paleosome intruded by one single set of narrow, subparallel leucosome dikes which cover ca. 5 - 10 % of the whole rock volume. Net-structure is composed of a network of narrow leucosome dikes which show a reticulated structure in a plane section and cover less than 30 % of the whole rock volume. Breccia-structure is composed of angular or rounded paleosome blocks surrounded by moderate amount of leucosome. Patch-structure is composed of irregular leucosome patches which intruded the well preserved paleosome and compose typically 20 - 70 % of the rock volume. Layer-structure is characterized by more or less regular leucosome dikes sub-parallel to the foliation of the well preserved paleosome. Vein-structured metatexites and also diatexites include a set of pipe-like, longish leucosome veins most probably generated by synchronous melting and deformation

  9. Mineralogía de arenas y limos en suelos, sedimentos fluviales y eólicos actuales del sector austral de la cuenca Chacoparanense: Regionalización y áreas de aporte Sands and clay mineralogy in soils, fluvial and eolian Present sediments in the southern sector of the Chacoparanense basin: Different regions and source areas

    Directory of Open Access Journals (Sweden)

    M. C. Etchichury

    2004-06-01

    Corrientes provinces allowed to define two zones characterized by two genetically different mineralogical associations. Minerals of volcanic - pyroclastic origin (heavy: green, basaltic and brown hornblende, hypersthene, enstatite, augite, magnetite, hematite, ilmenite, leucoxene, epidote, zoicite, and light: plagioclase, volcanic fragments, pumice and glass shards, quartz, orthoclase are observed over a broad area including whole Buenos Aires and Cordoba provinces, northwestern regions of La Pampa, central and southern Santa Fe and southern Entre Ríos. The provenence of these minerals included the pampean and post-pampean sediments and scarce contribution from volcanic Mesozoic rocks of north Patagonia, Sierras Pampeanas and also Quaternary pyroclastic eruptions. Conversely, a heavy suite of metamorphic provenence (staurolite, kyanite, sillimanite, andalusite, hornblende, epidote, opaques and a light association composed of igneous and metamorphic clast (monocrystalline and polycrystalline quartz, orthoclase,microcline, schists and others of sedimentary origin (quartz arenites is recorded in Corrientes and northern Santa Fe and Entre Ríos provinces. These minerals are coming from older basement rocks outcropping in Brazil and Uruguay and the younger overlain sedimentary succession. The peculiar material distribution is related to the drainage systems and wind pattern. Quartz 30% frecuency isoplet points out the limit between both mineralogical associations.

  10. The oldest sediments of Greece revealed by detrital zircon LA-ICP-MS U-Pb dating: Cambro-Ordovician sandstones from northern Gondwana in the External Hellenides - implications on the evolution of the eastern Mediterranean

    Science.gov (United States)

    Kydonakis, Konstantinos; Kostopoulos, Dimitrios; Poujol, Marc; Brun, Jean-Pierre; Papanikolaou, Dimitrios; Paquette, Jean-Louis

    2013-04-01

    Detrital zircon U-Pb ages of a quartzite from the Feneos locality of Peloponnesus, S. Greece, were determined by LA-ICPMS. The rock classifies as a mature quartz arenite and belongs to an original shale-sandstone succession now metamorphosed into a phyllite-quartzite unit. The latter chiefly represents the External Blueschist Belt of the Hellenides widely known as the Arna or Phyllite - Quartzite (PQ) Unit. Zircon age clusters at 0.5-0.75, 0.85, 0.95-1.1, 1.75-2 and 2.4-3 Ga point at the Saharan Metacraton and the Transgondwanan Supermountain as contributing sources; the youngest concordant grain is 522 Ma old. Based on great similarities in lithology, zircon age-distribution patterns and depositional setting between the Feneos quartzite and intact Cambro-Ordovician sandstone-shale sequences of Libya (Murzuq and Kufrah basins) we propose that the protolith of the former was deposited in an epeiric sea north of Libya during the Cambro-Ordovician. Feneos, as part of the Cimmerian block, had become detached from the NE Gondwanan margin during Late Carboniferous - Early Permian times and drifted northward. In central Crete, similar-looking sequences (Galinos beds) were originally deposited in an accretionary/fore-arc complex outboard of the south Laurussian active margin (Pelagonia) between ~297-230 Ma. The southern Pelagonian margin eventually collided (mild docking) with the northward drifting Cimmerian block signaling the closure of Palaeotethys by early Late Triassic. The Gondwanan affinity of the Feneos quartzite strongly contrasts the European one of the Galinos beds; the suture of Palaeotethys can thus be traced in S. Greece within the pre-Triassic sedimentary sequences of Peloponnesus and Crete. In the eastern Mediterranean realm, rocks with similar age clusters crop out in Greece (Peloponnesus, this study; eastern Crete, Sfaka locality; north-central Macedonia, Vertiskos terrane), NW Turkey (central Sakarya terrane), Libya (Murzuq and Kufrah basins), Israel

  11. Sedimentological and geochimical features of chaotic deposits in the Ventimiglia Flysch (Roya-Argentina valley- NW Italy)

    Science.gov (United States)

    Perotti, Elena; Bertok, Carlo; D'Atri, Anna; Martire, Luca; Musso, Alessia; Piana, Fabrizio; Varrone, Dario

    2010-05-01

    The Ventimiglia Flysch is a Upper Eocene turbidite succession deposited in the SE part of the Eocene Alpine foreland basin, truncated at the top by the basal thrust of the Helminthoides Flysch, a Ligurian tectonic unit that presently covers part of the Dauphinois and Briançonnais successions of Western Ligurian Alps. The Ventimiglia Flysch is made of alternations of sandstones and shales. The upper part is characterized by chaotic deposits. The chaotic deposits are constituted by: - km to hm-sized intrabasinal blocks (Ventimiglia Flysch) and extrabasinal blocks (Cretaceous sediments of Dauphinois Domain, Nummulite Limestone of the Alpine foreland basin and Helminthoides Flysch ); - conglomerates with block-in-matrix fabric interpreted as debris flow deposits. They occur as m-thick beds interbedded with the normal turbidite succession or locally as matrix of the larger blocks. Debris flow clasts show: - different sizes, ranging from metre to centimetre; - different shapes, from rounded to subangular; - different lithologies, such as fine-grained quartz-arenites, marls, dark shales and fine-grained calcisiltites. They may be referred to both coeval, intrabasinal lithologies (Ventimiglia Flysch), and extrabasinal formations (Nummulite Limestone, Globigerina Marl and Helminthoides Flysch). The clasts are disposed randomly into a chaotic matrix that consists of a dark mudstone in which submillimetre- to millimetre-sized lithic grains, with the same compositions of larger clasts, are present. Locally matrix consists of sandstones with quartz and feldspar grains and fragments of nummulitids that suggest reworking of unlithified Eocene sediments. Cathodoluminescence observations allow the distinction of two kinds of clasts: dull clasts that underwent a cementation before the formation of conglomerates, and clasts with the same orange luminescence as the matrix that may be interpreted as soft mud clasts that were cemented together with the matrix. Debris flow deposits are

  12. Geology of the Blue Mountains region of Oregon, Idaho, and Washington; stratigraphy, physiography, and mineral resources of the Blue Mountains region

    Science.gov (United States)

    Vallier, T. L., (Edited By); Brooks, H.C.

    1994-01-01

    island-arc terrane. PART 2: Mesozoic rocks exposed along the Snake River in the northern Wallowa terrane represent a volcanic island and its associated sedimentary basins within the Blue Mountains island arc of Washington, Oregon, and Idaho. In the northern part of the Wallowa terrane, rock units include the Wild Sheep Creek, Doyle Creek, and Coon Hollow Formations, the (informal) Imnaha intrusion, and the (informal) Dry Creek stock. The volcanic rocks of the Ladinian to Karnian Wild Sheep Creek Formation show two stages of evolution-an early dacitic phase Gower volcanic faciesY and a late mafic phase (upper volcanic facies). The two volcanic facies are separated by eruption-generated turbidites of siliceous argillites and arkosic arenites (argillitesandstone facies). The two magmatic phases of the Wild Sheep Creek Formation may be recorded by the compositional zoning from older quartz diorite and diorite to younger gabbro in the Imnaha intrusion. Although the Late Triassic Imnaha intrusion is in fault contact with the Wild Sheep Creek Formation, it may be a subduction-related pluton and was the likely magma source for the Wild Sheep Creek Formation. Interbedded with the upper volcanic facies are eruption-generated turbidite and debris flow deposits (sandstone-breccia facies) and thick carbonate units (limestone facies). The limestone facies consists of two marker units, which may represent carbonate platform environments. Clast imbrication, fossil orientation, and cross-stratification in the Wild Sheep Creek Formation indicate a shoaling to subaerial volcanic island to the south and southeast; sediment was transported to the north and northwest. The Karnian Doyle Creek Formation consists largely of epiclastic conglomerate, sandstone, and shale that were deposited in welloxygenated basins. Vitric tuffs interbedded with these sediments suggest shallow or subaerial pyroclastic eruptions. Quartz diorite clasts in this formation may indicate uplift

  13. Análise multivariada de atributos pedológicos e fitossociológicos aplicada na caracterização de ambientes de cerrado no norte de Minas Gerais Multivariate analysis of pedological and phytosociogical attributes applied to characterization of cerrado environments in north of Minas Gerais State, Brazil

    Directory of Open Access Journals (Sweden)

    Luciano de Oliveira Toledo

    2009-10-01

    , in order to correlate the spatial distribution of groups of species with soil attributes. The results showed the classification of the environments into two groups, based on the nature of parent materials: arenitic-quartzitic and sandy-clayey and clayey sediments. The selection of variables using the multivariate analysis was able to discriminate the environments represented in the phytosociological plots. The patterns identified by the local farmers corresponded, in general, to the variations in the floristic and phytosociological parameters and edaphic attributes. The absolute density, basal area, Shannon index and the granulometric fractions were the determinant parameters in the differentiation of the environments.

  14. Relationship between Mineralogy and Porosity in Subsurface Formations Relevant to Geologic CO2 Sequestration

    Science.gov (United States)

    Cole, D. R.; Swift, A.; Sheets, J.; Welch, S.; Anovitz, L. M.; Rother, G.; Vlcek, L.

    2013-12-01

    Porosity and permeability are the key variables that link the thermal, hydrological, geochemical and geomechanical processes that redistribute mass and energy in response to injection of CO2 into the subsurface. The size, shape, distribution and connectivity of rock pores dictate how fluids migrate into and through these micro- and nanoenvironments, wet and react with the solid. The link between pore size distribution and connectivity and pore-wall mineralogy is still poorly constrained for both reservoir and caprocks.. The objectives of this effort are to characterize the nano- to macropore features, quantify mineral-specific reactive surface areas in both pore and fracture networks, and determine how pores and fractures evolve in reacted systems at temperature-pressure-composition conditions relevant to CO2 injection. Representative caprocks and reservoir rocks associated with CO2 injection activities (e.g. shallow buried quartz arenites from the St. Peter Sandstone and the deeper Mt. Simon sandstone in Ohio as well as the Eau Claire Formation shale and mudrocks) are being interrogated with an array of complementary methods - e.g. SEM, TEM, neutron scattering, X-ray CT, neutron tomography as well as conventional petrophysics. (Ultra)small-angle neutron scattering and autocorrelations derived from BSE imaging provide a powerful method of quantifying pore structures in a statistically significant manner from the nanometer to the centimeter scale. Results will be described comparing shale and mudrocks that indicate there are significant variations not only in terms of total nano- to micro-porosity and pore interconnectivity, but also in terms of pore surface fractal (roughness) and mass fractal (pore distributions) dimensions as well as size distributions. For tight formations we have observed that: (a) total porosity exhibiting bimodality may be typical of shale and mudstones, (b) connected porosity exhibiting bimodal tendencies may not be uncommon in shale and

  15. Metamorphic belts of Anatolia

    Science.gov (United States)

    Oberhänsli, Roland; Prouteau, Amaury; Candan, Osman; Bousquet, Romain

    2015-04-01

    Investigating metamorphic rocks from high-pressure/low-temperature (HP/LT) belts that formed during the closure of several oceanic branches, building up the present Anatolia continental micro-plate gives insight to the palaeogeography of the Neotethys Ocean in Anatolia. Two coherent HP/LT metamorphic belts, the Tavşanlı Zone (distal Gondwana margin) and the Ören-Afyon-Bolkardağ Zone (proximal Gondwana margin), parallel their non-metamorphosed equivalent (the Tauride Carbonate Platform) from the Aegean coast in NW Anatolia to southern Central Anatolia. P-T conditions and timing of metamorphism in the Ören-Afyon-Bolkardağ Zone (>70?-65 Ma; 0.8-1.2 GPa/330-420°C) contrast those published for the overlying Tavşanlı Zone (88-78 Ma; 2.4 GPa/500 °C). These belts trace the southern Neotethys suture connecting the Vardar suture in the Hellenides to the Inner Tauride suture along the southern border of the Kirşehir Complex in Central Anatolia. Eastwards, these belts are capped by the Oligo-Miocene Sivas Basin. Another HP/LT metamorphic belt, in the Alanya and Bitlis regions, outlines the southern flank of the Tauride Carbonate Platform. In the Alanya Nappes, south of the Taurides, eclogites and blueschists yielded metamorphic ages around 82-80 Ma (zircon U-Pb and phengite Ar-Ar data). The Alanya-Bitlis HP belt testifies an additional suture not comparable to the northerly Tavşanlı and Ören-Afyon belts, thus implying an additional oceanic branch of the Neotethys. The most likely eastern lateral continuation of this HP belt is the Bitlis Massif, in SE Turkey. There, eclogites (1.9-2.4 GPa/480-540°C) occur within calc-arenitic meta-sediments and in gneisses of the metamorphic (Barrovian-type) basement. Zircon U-Pb ages revealed 84.4-82.4 Ma for peak metamorphism. Carpholite-bearing HP/LT metasediments representing the stratigraphic cover of the Bitlis Massif underwent 0.8-1.2 GPa/340-400°C at 79-74 Ma (Ar-Ar on white mica). These conditions compares to the Tav

  16. Uranium mineralization in late cretaceous sandstones in parts of Meghalaya, India

    International Nuclear Information System (INIS)

    Full text: Late Cretaceous Lower Mahadek sandstone of Meghalaya has been established as the potential host rock for sandstone type of uranium mineralization in India. Till date nearly 16 000 tonnes of U3O8 reserves have been estimated in four locations viz., Domiasiat, Wahkyn, Tyrnai and Lostoin, in the southern part of Meghalaya plateau. The uranium investigations are primarily confined to in the areas where the Lower Mahadek sandstones are exposed either on the surface or along deep river cuttings, otherwise concealed by thick cover of Tertiary sediments. The area poses major logistic challenge due to thick forest and remoteness. Out of nearly 1 800 km2 of extent of the Mahadek Basin, only 28% of the area exposes Lower Mahadek sediments. Survey in recent years has also established few more occurrences at Umthongkut, Wahkut and Rongcheng Plateau in Balphakram area. Systematic study of available surface and subsurface data has revealed that mineralization is controlled by palaeo channel configuration of Mahadek sediments and also the typical geochemical interface. Regional and local tectonics also have played an important role in distribution and concentration of uranium mineralization in the area. It is observed that the deposits and the very promising occurrences described above fall strikingly along an E-W lineament. Lithostructural studies indicate that the southern block appears to have gone upwards relative to the northern block in contrast to other such signatures in the area. This might have influenced ground hydrodynamic flow pattern and helped in concentration of uranium. The Lower Mahadek sandstones, host rock of these deposits are mostly sub-arkosic to arkosic, grading sometimes to felspathic arenite. The main uranium minerals are pitchblende, coffinite and organouranyl complex. Uranium mineralization is associated with bituminous organic matter occurring as dense inclusions, isolated clusters and lumps of various sizes and as clayey - dusty organic

  17. Uranium mineralization in late Cretaceous sandstones in parts of Meghalaya, India

    International Nuclear Information System (INIS)

    deposits are mostly sub-arkosic to arkosic, grading sometimes to felspathic arenite. The main uranium minerals are pitchblende, coffinite and organo-uranyl complex. Uranium mineralization is associated with bituminous organic matter occurring as dense inclusions, isolated clusters and lumps of various sizes and as clayey – dusty organic matter associated with cementing material. The work so far has been confined to the shallower part of the basin (28% of the total area). There is no reason not to believe that many more concealed deposits in the remaining 72% of unexposed Lower Mahadek sediments may be present. Multidisciplinary investigations have been initiated to locate such concealed occurrences. Geophysical investigations, mainly magnetic survey is in progress in some identified blocks in the area between Wahkyn and Umthongkut which are otherwise covered by 300-400 m thick Tertiary sediments. Such surveys would help in delineating magnetic lows which indirectly points to the presence of buried palaeochannel. Integrated Remote Sensing studies using high resolution satellite data of IRS LISS-III and LISS– IV are being undertaken to delineate broad lithological and structural patterns between Umthongkut and Wahkyn. The role of neo-tectonics in disposition of Lower Mahadek sandstone is being evaluated prior to taking up deeper subsurface exploration. Thus, the Lower Mahadek sandstones covered by thick Tertiary sediments in the larger part of the Mahadek basin are being probed by indirect techniques in order to discover more sandstone type of uranium deposits in Meghalaya. (author)

  18. A detrital zircon provenance study of the Lower Carboniferous sequences in the East Fife section of the Midland Valley of Scotland

    Science.gov (United States)

    Murchie, Sean; Robinson, Ruth, ,, Dr; Lancaster, Penelope, ,, Dr

    2014-05-01

    Detrital zircons from the Lower Carboniferous clastic rocks of the Midland Valley of Scotland have been dated using U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to determine which source areas contributed sediment to the basin during its development, and to investigate whether provenance changed during deposition of these units. Specific provenance detection using U/Pb dating of zircons has never been attempted in these rocks, and there are uncertainties remaining about the regional paleogeographic setting for the Midland Valley. Four samples from the Dinantian Strathclyde Group have been analysed, and the units are locally known as the Fife Ness, Anstruther, Pittenweem, Sandy Craig, and Pathhead formations. The formations are composed of shallow marine, deltaic, fluvial and floodplain deposits and these predominantly siliciclastic sedimentary rocks are interbedded with thin fossiliferous carbonate bands. The samples are quartz arenitic, sub-arkosic and lithic arkosic medium-grained sandstones, predominantly from a fluvial origin. The British Geological Survey developed a lithostratigraphy which is the most used framework for the Strathclyde Group (Browne et al., 1997), but a different biostratigraphical framework based on palynology has been proposed by Owens et al. (2005). In addition to identifying provenance, the zircon age populations for each formation are compared to test which stratigraphic framework is correct. More broadly, the provenance data provides a way to improve the regional palaeogeographic setting for the Midland Valley. Zircon ages in the Strathclyde Group are dominated by Late Mesoproterozoic to Late Palaeoproterozoic (0.9 - 2.0 Ga) and Early Palaeozoic (350 - 450 Ma) ages which reflect Caledonide (Laurentian-Baltica margin including Scotland, Scandinavia, Greenland, Newfoundland), Grampian and internal Midland Valley source areas. Notable peaks occur at 400 Ma, 1.0 --1.1 Ga, 1.3 Ga, 1.6 - 1.7 Ga, and 2.7 Ga, and

  19. Characteristics and main controlling factors of porous carbonate reservoirs: A case from the Jia 5 Member of the Jialingjiang Formation, southwest Sichuan Basin%孔隙型碳酸盐岩储集层特征及主控因素——以川西南嘉陵江组嘉5段为例

    Institute of Scientific and Technical Information of China (English)

    刘宏; 谭秀成; 李凌; 罗冰; 马昌林; 杨立根

    2011-01-01

    With the help of core observation, conventional and cast slices, physical property analysis and mercury penetration, this paper studies the reservoir characteristics and main controlling factors of the Jia 5 Member, Triassic Jialingjiang Formation, and identifies two types of reservoir rocks, silt-sized crystalline dolomite and calcarenite, which are different in forming environment, reservoir space,poroperm characteristics, and pore throat structure. The silt-sized crystalline dolomite reservoir developed in the dolomite-flat microfacies has a good pore/throat configuration with intercrystalline pores and dissolved pores as reservoir space. It has excellent permeability and is the best reservoir in thc region of interest. The calcarenite reservoir developed in the microfacies of arenite bank has the reservoir space of isolated intragranular dissolved pores and moldic pores; the mesoporosity and micro-throat configuration makes the reservoir characterized by high porosity and low permeability. Research on the main controlling factors of the reservoirs indicated that they are typically facies-controlled reservoirs. Microreliefs inside the carbonate platform lead to high heterogeneity of the reservoirs.Dolomitization and the leaching of syngenesis meteoric water are the key factors for forming good porous carbonate reservoirs.%利用岩心、常规及铸体薄片、物性分析、压汞等资料研究四川盆地西南部三叠系嘉陵江组嘉段储集层基本特征及主控因素.识别出两种不同类型的储集层:粉晶云岩储集层和砂屑灰岩储集层,两类储集层的形成环境、储集空间、孔渗性能、孔喉结构等均不相同.云坪微相内发育的粉晶云岩储集层以晶间孔和晶间溶孔为主要储集空间,具有良好的孔喉配置关系,储渗性能极好,为本区最优质储集层;砂屑滩微相内发育的砂屑灰岩储集层主要储集空间为较孤立的粒内溶孔及铸模孔,中孔微喉的配置关系导致

  20. New quantitative, in-situ characterization of weathering in geomaterials.

    Science.gov (United States)

    Scrivano, Simona; Gaggero, Laura; Gisbert Aguilar, Josep; Yus Gonzalez, Adrian

    2016-04-01

    The mineralogical and microtextural analyses of weathered rocks and mortars are the main diagnostic tools to address the materials exposed under different environmental conditions in order to enucleate and mitigate the decay factors. The characterization of weathering intensity is mostly descriptive and non-quantitative (ICOMOS Glossary, 2008); the Fitzner indexes in arenites (Fitzner et al., 2002) and more recently applied to marbles (Scrivano et al., 2013) provide an operator dependent method. The current diagnostic of decay (Drdàcky & Slìzkovà, 2014) based on a scotch tape tearing off the surface was improved by a specifically adapted pocket penetrometer, and a joint gravimetric + minero-chemical analysis under SEM of ablational decay products. The steps are the following: i) Preparation of stubs for SEM with adherent conductive carbon tape (surface area 1.3 cm2) ii) Weighing of stub + tape + its plastic envelope at 0.001 g precision iii) Connecting the stub to a pocket penetrometer iv) Non invasive sampling of the incoherent dust applying a constant pressure of 2 kgf for 1 minute, and then packing away the stub without loosing grains v) Weighing of stub + tape + weathering products + their plastic envelope at 0.001 g precision vi) Recast the weight of removed material vii) Addressing the weathering products to SEM - EDS. Our quantitative peeling test was applied on a 96m long cladded wall in the Staglieno Monumental Cemetery in Genoa. The wall shows weathering gradients due to a neighbouring interred stream and to different insulation. Slabs of ophicalcite marble were tested from three different areas (5 samples were collected to the E, 5 samples at the centre, 5 samples to the W). The results highlighted capillary rise up to 2 meters height and a more weathered central area. On the whole, our protocol allows a delicate, virtually not impacting and reproducible factual sampling. Moreover, if carried out on a statistically significant population, the decay

  1. Investigations on alluvial deposits through borehole stratigraphy, radiocarbon dating and passive seismic technique (Carnic Alps, NE Italy)

    Science.gov (United States)

    Viero, Alessia; Marchi, Lorenzo; Cavalli, Marco; Crema, Stefano; Fontana, Alessandro; Mozzi, Paolo; Venturini, Corrado

    2016-04-01

    Alluvial sediment investigations provide fundamental tools to infer the processes that control geomorphological evolution of mountain environments. By analyzing sediment stratigraphy in depth, it is possible to retrieve the source, the geology, the time of deposition, the relative distance travelled by material as well as to distinguish among different type of transport (i.e., gravitational, fluvial or glacial). In this work, we present a combination of log stratigraphy, radiocarbon dating and geophysical surveys carried out on the valley floor of the But River (Carnic Alps, North East Italy). The But River basin drains an area of 326 km2 with a range in elevation from 2769 to 323 m a.s.l.; the bedrock mainly consists of carbonates and quartz arenites with minor inclusions of effusive rocks. After Pleistocene the gravitational deposits from mountain slopes have impounded the But River several times. In particular, we analyzed a sector of the upper portion of the But valley close to the confluence of the Moscardo Torrent, frequently affected by debris flows. A borehole was drilled in the But River floodplain, at the intersection with the Moscardo Torrent alluvial fan, down to a depth of 80 m. The analysis of the core samples allowed discerning three sedimentary levels rich in clay and organic materials, which testify the presence of small dam lakes, originated from the Moscardo debris-flow deposits. Three samples of wood and plant debris were collected from 13, 14 and 23 m of depth, respectively. They were analyzed through radiocarbon dating in order to determine the age of the lakes and, thus, to infer the activity of the debris flows building the Moscardo cone. The calibrated ages of the 3 samples are close to the younger limit of the radiocarbon method indicating a fast aggradation of the valley floor, starting from a period ranging between 1450 - 1632 AD. Historical maps and documents confirm the presence of the lakes until 19th century and they permit to assess

  2. Migmatites and migmatite-like rocks of Olkiluoto

    International Nuclear Information System (INIS)

    Bedrock of the Olkiluoto Island in the western end of the Palaeoproterozoic Svecofennian Accretionary Arc Complex, SW Finland is composed of high-grade metamorphic pelites, arenites and intermediate, arc type metavolcanic rocks intruded by granodioritic to tonalitic plutonic rocks. Regional metamorphism culminated with voluminous migmatization in the temperature of 660 - 700 deg C and relatively low pressure of about 3.5 - 4 kbar. The end result of polyphase metamorphism and deformation is a metamorphic rock succession composed of diverse migmatite rocks, metatexites and diatexites. Metatexites are migmatites in which several, discrete components can be detected, and in which the paleosome with some pre-partial-melting textures is identifiable. Diatexites are more advanced migmatites in which the pre-migmatization structures are often totally destroyed and the rock is dominated by different neosome components meaning leucosome, melanosome or mesosome. Based on the migmatite structures the metatexites of Olkiluoto have been classified into six subgroups. Dike-structured metatexites are composed of well preserved paleosome intruded by one single set of narrow, subparallel leucosome dikes which cover ca. 5 - 10 % of the whole rock volume. Net-structure is composed of a network of narrow leucosome dikes which show a reticulated structure in a plane section and cover less than 30 % of the whole rock volume. Breccia-structure is composed of angular or rounded paleosome blocks surrounded by moderate amount of leucosome. Patch-structure is composed of irregular leucosome patches which intruded the well preserved paleosome and compose typically 20 - 70 % of the rock volume. Layer-structure is characterized by more or less regular leucosome dikes sub-parallel to the foliation of the well preserved paleosome. Vein-structured metatexites and also diatexites include a set of pipe-like, longish leucosome veins most probably generated by synchronous melting and deformation

  3. Tectono-metamorphic evolution and magmatic processes in the thermo-metamorphic aureole of the Monte Capanne pluton (Elba Island, Northern Tyrrhenian Sea, Italy).

    Science.gov (United States)

    Morelli, M.; Pandeli, E.; Principi, G.

    2003-04-01

    Introduction In this work we present new structural and petrographic data collected in the thermo-metamorphic aureole of Monte Capanne (western Elba Island) and its metamorphic evolution. In the western Elba Island the Monte Capanne monzogranitic body (ca. 7 Ma) and its thermo-metamorphic aureole crop out. At least two different tectonic units can be distinguished: the Punta Le Tombe Unit, weak re-crystallized, and the Punta Nera Unit. In the latter one the re-crystallization is strong and a pre-intrusion tectono-metamorphic framework is evident (Morelli et al., 2002). The latter is mainly constituted by thermo-metamorphosed meta-ophiolites and meta-sedimentary successions previously correlated by Barberi et al. (1969) with the un-metamorphic ones (Complex IV and V of Trevisan, 1950) cropping out in the central-eastern Elba. According to Perrin (1975) and Reutter &Spohn (1982) a pre-intrusion tectono-metamorphic framework was recognized into such rocks. As suggested by Daniel &Jolivet (1995) complex relationships between metamorphic evolution and magmatic events are also recognizable. Geological Data The Punta Nera Unit crops out all around the Monte Capanne magmatic body and the primary contact with the underlying granitoid is somewhere preserved. This unit, strongly re-crystallized and locally crosscut by aplitic and porphyritic dikes, is represented by (Coli &Pandeli, 1997; Morelli, 2000) tectonized meta-serpentinites, meta-gabbros with rodingitic dikes, rare meta-basalts and meta-ophicalcites, meta-cherts, marbles, cherty meta-limestones, phyllites and meta-limestones with rare meta-arenites intercalations. A "pre-magmatic" tectono-metamorphic framework of this unit is well evident only in its meta-sedimentary portion. The meta-sediments are deformed by syn-metamorphic isoclinal folds caractherized by N-S trending axes, west dipping axial planes and easternward vergence. A later folding and flattening event clearly post-dated the above said folds and associated

  4. Efficacité comparée de divers procédés physiques de séparation des argiles d'un sable de gisement A Comparison of Different Physical Processes for the Recovery of Clays from an Unconsolidated Sandstone

    Directory of Open Access Journals (Sweden)

    Yvon J.

    2006-11-01

    Full Text Available Divers procédés physiques (mixage, attrition, vibration ultra-sonique ont été utilisés pour désagréger et disperser les argiles d'un sable de gisement. Le traitement aux ultra-sons s'est avéré le plus efficace : après 10 min de vibration on récupère environ 1,5 fois plus de particules fines ( The characterizing of clays is an essential operation for understanding many problems encountered in production. It goes via a preliminary phase in which species are separated quickly and effectively without altering their nature. Chemical processes disperse clays by solubilizing their cements, amorphous compounds and poorly crystallized oxyhydroxides. But they attack fragile species and lead to mistaken results. Therefore, we have chosen various physical processes (mixing, attrition, ultrasonic vibration and compared their efficacy with a reservoir sand. This sand was a quartzose arenite in which 96. 6 % of the grains were between 63 µm and 2 mm. The < 40 µm fine fraction, obtained by wet sieving, represented 2. 44 % of the unprocessed sand, and the clayey fraction (kaolinite, illite, montmorillonite, interstratified illite-montmorillonite was 1. 20%. Mixing was done with a bladed stirer. 40 g of sand and 100 cm³ of demineralized water were stirred for 3 min at a speed of 3000 rpm. Attrition was done by two devices :(1 For attrition by rotation, 400 g of sand and 0. 5 liter of demineralized water were placed in a porcelain jar rotating at a speed of 37 rpm. Tests were performed with water alone and with the adding of a dispersant (0. 3 % sodium hexametaphosphate and a surfactant (0. 6 mole/liter of sodium sulfonate paraoctylphenyl. (2 Attrition by a Turbula TC2 mixer, which gave the jar a complex rotation movement including shaking and rhythmic rocking. 500 g of sand were thus processed in 1 literof 3 % sodium hexametaphosphate solution for varying times. Ultrasonic processing was done with a Sonifer 830 device. The probe was plunged into a

  5. Sediment composition of big Chinese and Indochinese rivers reflects geology of their source, not tectonic setting of their sink.

    Science.gov (United States)

    Garzanti, Eduardo; Andò, Sergio; Limonta, Mara; Nie, Junsheng; Resentini, Alberto; Vezzoli, Giovanni; Wang, Jiangang; Yang, Shouye

    2016-04-01

    continental areas sediment composition reveals the geological character of the orogenic source, rather than the passive-margin or back-arc-basin setting of the sink. The accurate reconstruction of such long and complex sediment-routing systems is thus required for a correct provenance analysis of many large ancient clastic wedges (e.g., Wang et al., 2016). CITED REFERENCES Dickinson W.R. 1985. Interpreting provenance relations from detrital modes of sandstones. In: Zuffa, G.G. (Ed.), Provenance of arenites. Reidel, Dordrecht, NATO ASI Series 148:333-361. Dickinson W.R. 1988. Provenance and sediment dispersal in relation to paleotectonics and paleogeography of sedimentary basins. In: Kleinspehn, K.L., Paola, C. (Eds.), New perspectives in basin analysis. Springer, 3-25. Franzinelli E., Potter P.E. 1983. Petrology, chemistry, and texture of modern river sands, Amazon River system. The Journal of Geology 91:23-39. Garzanti E., Limonta M., Resentini A., Bandopadhyay P. C., Najman Y., Andò S., Vezzoli G. 2013. Sediment recycling at convergent plate margins (Indo-Burman Ranges and Andaman-Nicobar Ridge). Earth-Science Reviews 123:113-132. Nie J., Stevens T., Rittner M., Stockli D., Garzanti E., Limonta M., Bird A., Andò S., Vermeesch P., Saylor J., Lu H., Breecker D., Hu X., Liu S., Resentini A., Vezzoli G., Peng W., Carter A., Ji S., Pan B. 2015. Loess Plateau storage of Northeastern Tibetan Plateau-derived Yellow River sediment. Nature Communications 6:10.1038/ncomms9511. Vezzoli G., Garzanti E., Limonta M., Andò S., Yang S. 2016. Erosion patterns in the Changjiang (Yangtze River) catchment revealed by bulk-sample versus single-mineral provenance budgets. Geomorphology, in review. Wang J.G., Wu F.Y., Garzanti E., Hu X.M., Ji, W.Q., Liu, Z.C., Liu X.C. 2016. Upper Triassic turbidites of the northern Tethyan Himalaya (Langjiexue Group): the terminal of a sediment-routing system sourced in the Gondwanide Orogen. Gondwana Research, in review.

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

    Science.gov (United States)

    Glikson, Andrew; Vickers, John

    2006-01-01

    Creek Group-GCG [R. M. Hill, Stratigraphy, structure and alteration of hanging wall sedimentary rocks at the Sulphur Springs volcanogenic massive sulphide (VMS) prospect, east Pilbara Craton, Western Australia. B.Sc Hon. Thesis, University of Western Australia (1997) 67 pp.; M.J. Van Kranendonk, A.H. Hickman, R.H. Smithies, D.R. Nelson, Geology and tectonic evolution of the Archaean north Pilbara terrain, Pilbara Craton, Western Australia, Econ. Geol. 97 (2002) 695-732; M.J. Van Kranendonk, Geology of the North Shaw 1 : 100 000 Sheet. Geological Survey Western Australia 1 : 100 000 Geological Series (2000) 86 pp., R. Buick, C.A.W. Brauhart, P. Morant, J.R. Thornett, J.G. Maniew, J.G. Archibald, M.G. Doepel, I.R. Fletcher, A.L. Pickard, J.B. Smith, M.B. Barley, N.J. McNaughton, D.I. Groves, Geochronology and stratigraphic relations of the Sulphur Springs Group and Strelley Granite: a temporally distinct igneous province in the Archaean Pilbara Craton, Australia, Precambrian Res. 114 (2002) 87-120]). The structure and scale of the olistostrome, not seen elsewhere in the Pilbara Craton, is interpreted in terms of intense faulting and rifting, supported by topographic relief represented by deep incision of overlying arenites (Corboy Formation) into underlying units [M.J. Van Kranendonk, Geology of the North Shaw 1 : 100 000 Sheet. Geological Survey Western Australia 1 : 100 000 Geological Series (2000) 86 pp.]. The age overlaps between (1) 3.255 ± 4-3.235 ± 3 Ga peak igneous activity represented by the SSG and the Cleland plutonic suite (Pilbara Craton) and the 3.258 ± 3 Ga S2 Barberton impact unit, and (2) 3.235 ± 3 Ga top SSG break and associated faulting and the 3.243 ± 4 S3-S4 Barberton impact units may not be accidental. Should correlations between the Barberton S2-S4 impact units and magmatic and tectonic events in the Pilbara Craton be confirmed, they would imply impact-triggered reactivation of mantle convection, crustal anatexis, faulting and strong vertical

  7. Solos do topo da Serra São José (Minas Gerais e suas relações com o paleoclima no Sudeste do Brasil Soils of the São José Hills (Minas Gerais State, Brazil and their relationship with palaeoclimate in Southeastern Brazil

    Directory of Open Access Journals (Sweden)

    A. C. Silva

    2004-06-01

    Full Text Available A diversidade de ecossistemas do sudeste do Brasil nem sempre pode ser relacionada com fatores edáficos, geomorfológicos ou hidrológicos. Topos de elevações, onde os solos são caracterizados pela unicidade de material de origem, podem constituir ambiente especial para estudos de gênese de solos e datações de eventos cíclicos relacionados com a dinâmica do clima regional. Depois de um levantamento detalhado de solos no topo da Serra São José (Prados - Minas Gerais, dois perfis de solo (P1 e P2, originados de metarenitos da Formação Tiradentes e caracterizados por deposições sucessivas de camadas arenosas alternadas com camadas arenosas enriquecidas com matéria orgânica, foram estudados, com intuito de encontrar testemunhos de paleoambientes. O pequeno platô localiza-se a 1.350 m acima do nível de mar e 350 m acima do nível topográfico regional dominante. No P1, foram identificadas trinta e três camadas enriquecidas com matéria orgânica, alternadas com camadas de areia. Três camadas no P1 (20-30, 70-80 e 100-110 cm, com conteúdo de C orgânico respectivamente de 0.5, 7 e 1 dag kg-1, apresentam idades radiocarbônicas The diversity of ecosystems in southeastern Brazil can not always be related to edaphic, geomorphologic, or hydrologic factors. Mountain summits, where soils are characterized by common parent material, offer a special environment for studies of soil genesis and dating of cyclic events related to regional climate dynamics. After a detailed investigation of soils from the São José Hills (Prados - Minas Gerais State, Brazil, two soil profiles (P1 and P2 originated from arenite of the Tiradentes Formation were studied. They are characterized by successive depositions of sandy layers alternated with layers of sand enriched with organic matter. The study site lies 1,350 m above sea level and 350 m above the dominant topographical level of the region. Thirty-three layers with organic matter, alternated with

  8. 苏北盆地金湖凹陷碳酸盐岩沉积特征及演化模式%Sedimentary characteristics and evolutionary patterns of carbonates in Jinhu depression, Subei Basin

    Institute of Scientific and Technical Information of China (English)

    邵先杰; 王彩凤; 黄伟; 钟思瑛; 刘金华; 廖光明; 陈军

    2013-01-01

    根据对大量薄片和岩心的观察,金湖凹陷西斜坡碳酸盐岩的颗粒类型主要有生物碎屑、鲕粒、球粒、藻叠层石和陆源砂.生物碎屑含量丰富,以蠕虫动物中的环节动物门龙介虫科(Serpulidae)含量最高,占生物碎屑颗粒的70%以上,其他也见藻类、介形虫腕足、腹足、硅藻、有孔虫、苔藓等化石.生物数量虽然比较多,但种属单调,耐盐度比较窄,为半咸水海洋生物组合.微量元素硼的质量分数平均为77.6×10-6,硼与镓的比值(B/Ga)平均为3.6,也显示为半咸水环境.结合沉积物特征、生物组合和特殊矿物分析,认为金湖凹陷在古新统阜宁组二段第Ⅱ油组(E1f22)沉积时期,发生了海侵或与海洋有通道沟通、具有半咸水溺湖环境特征.水体清澈,构造活动相对平静,湖盆沉降和沉积速率缓慢且补偿适中,因此在西斜坡沉积了一套厚度为10~20 m、分布广阔的碳酸盐岩.根据颗粒类型和沉积特征,划分出4种沉积相带,包括陆源碎屑-碳酸盐混合相、鲕粒滩相、生物碎屑滩相、泥晶灰岩相,各相带在纵向和横向出现有规律的交替分布.生物碎屑灰岩溶孔发育,含油气丰富,已作为产能接替区投入了开发,并取得了一定效果.%Based on observations of a large number of cast thin sections and rock cores,grain types of carbonates in the west slope of the Jinhu depression were identified to be mainly composed of bioclast,oolite,spherulite,algal stromatolite and arenite.Of which bioclast is abundant and predominated by Annelida Serpulidae of vermes,which account for over 70 percent of the bioclast.And the other bioclast consists of algal,ostracod,brachiopod,gastropod,diatom,foraminifera and moss fossils.Although the amount of organisms is large,their species,composed mainly of brackish halobios,are relatively monotonous with narrower salt tolerance.The mass fraction of boron in microelements averages 77.6 × 10-6 and the ratio