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Sample records for calcretes

  1. Uranium concentration phenomena in continental evaporitic environment: Australian Ylgarn calcretes. Comparison with Mauritanian and Namibian calcretes

    International Nuclear Information System (INIS)

    The Ylgarn calcretes are described and their formation is studied. Uranium migration and trapping in the hydrologic cycle is examined. These calcretes are compared with those from Mauritania and Namibia as a guide for uranium prospection

  2. Possible variations on the calcrete-gypcrete uranium model

    International Nuclear Information System (INIS)

    Genetic models and favorability criteria for calcrete and gypcrete uranium deposits based upon Yeelirrie and other occurrences in Western Australia and upon Langer Henirich and others in Namibia-South West Africa are summarized. Viable analogues of these world-class deposits have not yet been found in USA even though several of the favorable conditions occur in the southwest. A principal deterrent to economic concentration has been tectonic instability. But even in the most favorable areas it is not clear that climates have ever been sufficiently similar to that of the valley-calcrete region of Western Australia. Extensive, thick valley (nonpedogenic) calcretes such as those which host the carnotite in Australia and in Namibia have not been documented here. Nevertheless, submarginal occurrances of carnotite have been found in southwestern United States in small bodies of nonpedogenic and mixed pedogenic-nonpedogenic calcrete. Much of the study is based upon occurrences of carnotite-bearing calcrete and calcrete-gypcrete in the Republic of South Africa. Several of these are described briefly. Some reference is also made to new occurrences and to new data on previously described occurrences on the Namib Desert. Possible variations on the Western Australian and Namibia-South West Africa models which are considered are capillary rise of U in solution, addition of new uraniferous sediment over a calcrete, lateral access of U into a pedogenic calcrete, reworking of U from a weekly mineralized pedogenic calcrete or gypcrete into a new or reconstituted calcrete, or into an unrelated environment for fixation of U

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

    Indian Academy of Sciences (India)

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

    2004-09-01

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

  4. Pedogenic calcretes from Coimbatore area, Tamil Nadu: Micromorphology, geochemistry and palaeoclimate significance

    International Nuclear Information System (INIS)

    In this paper we present geochemistry and micromorphology (petrography and SEM data) study of Quaternary calcretes formed in association with the vertisol and hardpan calcretes-dolocretes formed on bedrock occurring in Coimbatore area, Tamil Nadu. Coimbatore receives an annual average rainfall of 400-500 mm year-1. Understanding the formation of calcretes is important as this region falls in the rain shadow region receiving both the south west as well as northeast monsoon. In the study area the calcretes formed within the vertisols representing the Bk horizon occur as thick profiles (∼3m) in the foothill zone while the laminar hardpan calcretes are found in the topographic lows on the bedrock (0.80-1m). Calcretes occurring in association with the vertisols are powdery calcrete, nodular calcrete and rhizoliths with 95.22% to 64.5% of CaCO3. Nficromorphology study (thin section and SEM study) of the calcretes in vertisols show the occurrence of features such as alveolar septal structures, calcified filaments, coated grains, spherulites, calcified root cells and calcispheres that indicate the biogenic origin of the calcretes, mainly induced by plant root related microbial activity. They consist of quartzose sand grains cemented by fine crystalline, glaebular, grain-coating and pore-filling micrite. Micro fabrics of hardpan calcretes with detritus hosts show evidence of replacement, displacement and shrinkage, indicating that the calcretes formed under relatively ad conditions. These characteristics reflect that the calcretes formed in a relatively near-surface environment with relatively high rates of evaporation. Development of the calcretes in the vertisol profiles took place in phases of soil formation, erosion and reworking. The relationships between these processes caused the formation of different accrete profiles in the foothill region. (author)

  5. Anthropo-Calcretisation: Human Effects on Calcrete Formation

    Science.gov (United States)

    Itkin, Danny

    2014-05-01

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

  6. Uranium-bearing magnesian-calcrete in surficial environment from Khemasar, Churu district, Rajasthan, India

    International Nuclear Information System (INIS)

    Magnesium-bearing calcretes of soft-gritty and hard pan varieties containing uranium concentrations from 16 to 74 ppm with < 10 ppm of thorium are located along the Saraswati palaeochannel at Khemasar village, Churu district, Rajasthan. The uranium-bearing calcretes are exposed over an areal extent of 300 m x 200 m with thickness of up to 2 m in an interdunal depression. The silty sand layer occurring below the calcrete horizon suggests that it is a valley-fill calcrete, deposited along a palaeochannel. This occurrence of uraniferous Mg-calcrete in the Saraswati river palaeochannel opens up a large area for uranium exploration in the calcrete environment of Thar Desert. These calcretes are composed of 15.94% to 25.39% CaO, 7.15% to 22.39% MgO and Sr/Ba ratio up to 66.98. There is a positive correlation of U with Sr/Ba and MgO. The high Sr/Ba ratio and MgO indicate water of saline nature and high rate of evaporation. Ephemeral centripetal drainage mixing with the dissected palaeochannel waters and groundwaters, under arid climatic conditions might have resulted in the formation of this kind of uranium-bearing calcrete in fluvio-lacustrine environment. (author)

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

    Science.gov (United States)

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

    2011-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-02-15

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

  9. Geochemistry of Calcretes (Calcic Palaeosols and Hardpan), Coimbatore, Southern India: Formation and Paleoenvironment

    International Nuclear Information System (INIS)

    This paper deals with the late Quaternary calcic nodules formed within vertisols in the foot-hill regions, and hardpan calcretes (greater than 200 ka) formed over the Precambrian substrate that occur as duricrust horizons in the plains around Coimbatore region, Tamil Nadu, India. The bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in CaO, SiO2, Al2O3 and Fe2O3 content. The trend of trace metal content in calcic nodules and in the hardpan calcrete is Mn>Zn>Ni>Cr>Pb>Co>Cu and Zn>Mn>Ni>Co>Pb>Cu>Cr respectively. PAAS- normalised REE data of the calcretes (calcic nodules and the hardpan) demonstrate a positive Eu anomaly. This could be attributed to feldspar, apatite mineral alteration and soil digenetic processes, differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in Eu. The stable isotope values of the calcic nodules do not exhibit a wide range (δ18O -3.39 to -5.84 per mille and δ13C -3.01 to -6.64 per mille), compared to the hardpan calcretes (δ18O -2.91 to -12.98 per mille ) and δ13C (-0.05 to -7.4 per mille). The palaeoenvironment during the formation of the calcretes nodules was dominated by the C4 plants with sparse vegetation cover and that the parent material/bedrock supported a thin veneer of soil column as present day. Calcic nodule accumulations in the soils has resulted from differential weathering and chemical histories within the soil profiles while the hardpan calcretes formed by complex pedogenic and chemical - groundwater processes in arid - semi arid conditions over a long geological period. During the late MIS3 to the LGM period the south west monsoon was weak with mean annual rainfall (MAR) between 300- 500 mm/yr., the sea level was low and the rainfall at the time of carbonate formation would have remained damp enough to allow silicate weathering of the soil sediments. (author)

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

    Science.gov (United States)

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

    2016-07-01

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

  11. An assessment of the use of hydrogeochemistry in exploration for calcrete uranium in Australia

    International Nuclear Information System (INIS)

    The role of hydrogeochemistry in exploration for calcrete uranium deposits in Australia is reviewed and the sampling and analytical procedures used are described. The concept of carnotite solubility index (CSI) is introduced and a simplified derivation is given for field use. The various interpretation schemes are reviewed and compared. On the basis of experience in Australia, the uranium content of the aquifer was found to provide a guide to the fertility of the system, and anomalous vanadium concentrations in the groundwater could be related to carnotite mineralization. Using the simplified CSI function, values of -3 to zero and upwards were found to be indicative of prospective drainages. It is concluded that water sampling surveys carried out in conjunction with shallow drilling programs make for the most efficient use of hydrogeochemistry in calcrete exploration

  12. Geochemical and C, O, Sr, and U-series isotopic evidence for the meteoric origin of calcrete at Solitario Wash, Crater Flat, Nevada, USA

    Science.gov (United States)

    Neymark, L. A.; Paces, J. B.; Marshall, B. D.; Peterman, Z. E.; Whelan, J. F.

    2005-08-01

    Calcite-rich soils (calcrete) in alluvium and colluvium at Solitario Wash, Crater Flat, Nevada, USA, contain pedogenic calcite and opaline silica similar to soils present elsewhere in the semi-arid southwestern United States. Nevertheless, a ground-water discharge origin for the Solitario Wash soil deposits was proposed in a series of publications proposing elevation-dependent variations of carbon and oxygen isotopes in calcrete samples. Discharge of ground water in the past would raise the possibility of future flooding in the unsaturated zone at Yucca Mountain, Nevada, site of a proposed high-level nuclear waste repository. New geochemical and carbon, oxygen, strontium, and uranium-series isotopic data disprove the presence of systematic elevation-isotopic composition relations, which are the main justification given for a proposed ground-water discharge origin of the calcrete deposits at Solitario Wash. Values of δ13C (-4.1 to -7.8 per mil [‰]), δ18O (23.8-17.2‰), 87Sr/86Sr (0.71270-0.71146), and initial 234U/238U activity ratios of about 1.6 in the new calcrete samples are within ranges previously observed in pedogenic carbonate deposits at Yucca Mountain and are incompatible with a ground-water origin for the calcrete. Variations in carbon and oxygen isotopes in Solitario Wash calcrete likely are caused by pedogenic deposition from meteoric water under varying Quaternary climatic conditions over hundreds of thousands of years.

  13. Mineralogical, geochemical and micromorphological evaluation of the Plio-Quaternary paleosols and calcretes from Karahamzall, Ankara (Central Turkey

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    Küçükuysal Ceren

    2014-06-01

    Full Text Available We present the mineralogical, micromorphological, and geochemical characteristics of the paleosols and their carbonates from Karahamzall, Ankara (Central Turkey. The paleosols include calcretes of powdery to nodular forms and alternate with channel deposits. The presence of pedofeatures, such as clay cutans, floating grains, circumgranular cracks, MnO linings, secondary carbonate rims, traces of past bioturbation and remnants of root fragments are all the evidence of pedogenesis. Bw is the most common soil horizon showing subangular-angular blocky to granular or prismatic microstructures. Calcretes, on the other hand, are evaluated as semi-mature massive, nodular, tubular or powdery forms. The probable faunal and floral passages may also imply the traces of life from when these alluvial deposits were soil. The presence of early diagenetic palygorskite and dolomite together with high salinization, high calcification and low chemical index of alteration values are evidence of the formation of calcretes under arid and dry conditions. δ13C compositions of the carbonates ranging from -7.11 ‰ to -7.74 ‰ VPDB are comformable with the world pedogenic carbonates favouring the C4 vegetation; likely δ18O compositions of the carbonates are between -3.97 ‰ and -4.91 ‰ which are compatible with the paleosols formed under the influence of meteroic water in the vadose zone

  14. Mineralogical, geochemical and micromorphological evaluation of the Plio-Quaternary paleosols and calcretes from Karahamzall, Ankara (Central Turkey)

    Science.gov (United States)

    Küçükuysal, Ceren; Kapur, Selim

    2014-06-01

    We present the mineralogical, micromorphological, and geochemical characteristics of the paleosols and their carbonates from Karahamzall, Ankara (Central Turkey). The paleosols include calcretes of powdery to nodular forms and alternate with channel deposits. The presence of pedofeatures, such as clay cutans, floating grains, circumgranular cracks, MnO linings, secondary carbonate rims, traces of past bioturbation and remnants of root fragments are all the evidence of pedogenesis. Bw is the most common soil horizon showing subangular-angular blocky to granular or prismatic microstructures. Calcretes, on the other hand, are evaluated as semi-mature massive, nodular, tubular or powdery forms. The probable faunal and floral passages may also imply the traces of life from when these alluvial deposits were soil. The presence of early diagenetic palygorskite and dolomite together with high salinization, high calcification and low chemical index of alteration values are evidence of the formation of calcretes under arid and dry conditions. δ13C compositions of the carbonates ranging from -7.11 ‰ to -7.74 ‰ VPDB are comformable with the world pedogenic carbonates favouring the C4 vegetation; likely δ18O compositions of the carbonates are between -3.97 ‰ and -4.91 ‰ which are compatible with the paleosols formed under the influence of meteroic water in the vadose zone

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1978-01-06

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

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

    Science.gov (United States)

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

    2011-01-01

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

  18. Early Cretaceous pCO2 changes estimated from a calcrete succession in the North American foreland basin, Utah, USA

    Science.gov (United States)

    Ludvigson, G. A.; Murphy, L. R.; Gonzalez, L. A.; Joeckel, R. M.

    2011-12-01

    Using the Aptian-Albian carbon isotope record from a calcrete succession in the Cedar Mountain Fm (CMF; Ludvigson et al., 2010, JSR 80:955-974), we calculate a baseline Aptian atmospheric pCO2 of 1,000 ppm by applying the equation of Ekart et al. (1999, AJS 299:805-827). Isotopic analyses of pedogenic and palustrine carbonates from eight correlated chemostratigraphic positions from the Ap7 feature of Herrle et al. (2004, EPSL 218:149-161) to the C15 feature of Bralower et al. (1999, JFR 29:418-437) are compiled from two sections in the CMF. These sections encompass the Aptian-Albian Ap7-C15 (~125-100 Ma) interval. Significantly, our results indicate a build-up of ~350 ppm above baseline values during the C9-C11 positive carbon isotope excursion. The excursion corresponds with our reported shifts in δ13C values determined from coordinated carbonate and sedimentary organic carbon. We directly compare our pCO2 estimates to compiled estimates from the same interval determined on pedogenic carbonates, stomata, and liverworts previously published by Royer (2010, PNAS 107:517-518). Using a uniform S(z), the soil-derived component of the total soil at depth z, we found our estimates to be generally higher than those previously reported for pedogenic carbonates. Thus, we adjust our reported pCO2 estimates using a range of S(z), to avoid overestimations of S(z) and to account for variations with season, depth, soil type, and paleolatitude between the two data sets. Finally, our pCO2 estimates are correlated with marine chemostratigraphic records (δ13C of marine carbonate and organic matter; strontium isotopes), and magma flux output from the Kergulean Plateau (Indian Ocean). The 116 to 111 Ma rise and fall in pCO2 during the C9-C11 carbon isotope excursion, for which we have identified a pCO2 buildup, coincides with the mid-Cretaceous strontium isotope low, and a peak in magma production at the Kerguelan Large Igneous Province. Therefore, we interpret a tectonic driver for

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

    Institute of Scientific and Technical Information of China (English)

    车永飞; 张云龙; 赵英俊; 林子瑜

    2015-01-01

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

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

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Thamban, M.

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

  1. Depth dependence of soil carbonate accumulation based on cosmogenic 36Cl dating

    Science.gov (United States)

    Liu, Beiling; Phillips, Fred M.; Elmore, David; Sharma, Pankaj

    1994-12-01

    Indurated pedogenic carbonate layers (calcretes) are common in soils on stable surfaces in arid to semiarid climates. The morphology and composition of calcretes provide important information on the geomorphic and climatic histories of the regions where they are formed, but they have proved difficult to date with conventional radiometric methods. We report cosmogenic 36Cl-buildup ages from three fractions (leachable Cl, carbonate, silicate) of a calcrete from the surface of an alluvial slope below the Ajo Mountains in southern Arizona. All three fractions give reasonably concordant ages, ranging from 700 ka at the base of the calcrete horizon to 200 ka at its top. These ages are in good agreement both with estimates of age based on correlation with similar, independently dated, soils in the region and with 36Cl-buildup ages on surficial boulders. These results support the ideas that calcretes accumulate upward with time and that water movement through the carbonate matrix is very limited after induration.

  2. Large lake basins of the southern High Plains: ground-water control of their origin?

    Science.gov (United States)

    Wood, W.W.; Sanford, W.E.; Reeves, C.C., Jr.

    1992-01-01

    We modify the deflation hypothesis by proposing that the calcrete caprock may never have been deposited in the areas now occupied by the basins. The absence of calcrete deposition is proposed to have resulted from high water tables caused by an increase in hydraulic gradient where aquifers thinned above bedrock highs. A high water table close to and/or intersecting the surface prevents deposition of calcrete, and thus, the uncemented surface would be more susceptible to deflation than the surrounding calcrete-covered areas after decline of the water table. The rise in water table associated with bedrock highs is documented by numerical simulation using boundary conditions and hydrologic parameters representative of the southern High Plains. -from Authors

  3. Definition and classification of surficial uranium deposits

    International Nuclear Information System (INIS)

    Uraniferous surficial deposits may be broadly defined as uraniferous sediments or soils, usually of Tertiary to Recent age, that have not been subjected to deep burial and may or may not have been cemented to some degree. Evaluation of the available literature shows that confusion has arisen as to the use of the term ''calcrete'' when describing fluviatile sediments that have been calcified to a greater or lesser degree. It is felt that a useful purpose would be served by proposing a classification system which may go some way towards a redefinition of the applicable terminology. Unfortunately the terms ''calcrete'' or ''valley calcrete'' have been used to define Tertiary to Recent sediments ranging from boulder beds to silts which, in some Namibian examples, contain between 5 and 50% CaCO3 and as much as 90% total carbonate in some Australian surficial uranium deposits. It is proposed that the detrital material constituting the sediments be prefixed with the terms calcareous, dolomitic, gypsiferous, halitiferous or ferruginous (e.g. calcareous grit) rather than the terms calcrete, dolocrete, gypcrete, and ferricrete, all of which have genetic connotations. The latter group of terms are preferably used for the pedogenic uranium deposits only. This will have the effect of placing these deposits in categories of their own and not confusing the issue with the overprint of pedogenic calcrete or duricrustal deposits which may or may not be present. This view is not shared by some authorities notably Butt and Carlisle (see this volume). (author)

  4. Large lake basins of the southern High Plains: Ground-water control of their origin

    Energy Technology Data Exchange (ETDEWEB)

    Wood, W.W.; Sanford, W.E. (Geological Survey, Reston, VA (United States)); Reeves, C.C. Jr (Texas Tech. Univ., Lubbock (United States))

    1992-06-01

    The origin of the {approximately}40-50 topographically large lake basins on the southern High Plains of Texas and New Mexico has been an enigma. Previous workers have considered deflation or evaporite dissolution at depth and subsequent collapse as the most probable mechanisms. However, the eolian hypotheses have been unable to provide convincing arguments as to how the wind selectively erodes the thick, deflation-resistant calcrete 'caprock' that is persistent over much of the southern High Plains. Furthermore, recent detailed studies on some of the basins show no significant evaporite dissolution at depth, and neither mechanism offers a satisfactory explanation as to why the basins are almost universally associated with subsurface topographic highs, or why they are absent where the High Plains aquifer thickness exceeds 60 m. The authors address these latter concerns and modify the deflation hypothesis by proposing that the calcrete caprock may never have been deposited in the areas now occupied by the basins. The absence of calcrete deposition is proposed to have resulted from high water tables caused by an increase in hydraulic gradient where aquifers thinned above bedrock highs. A high water table close to an/or intersecting the surface prevents deposition of calcrete, and, thus, the uncemented surface would be more susceptible to deflation than the surrounding calcrete-covered areas after decline of the water table. The rise in water table associated with bedrock highs is documented by numerical simulation using boundary conditions and hydrologic parameters representative of the southern High Plains.

  5. A brief account of coast vegetation near Port Elizabeth

    Directory of Open Access Journals (Sweden)

    H. C. Taylor

    1981-12-01

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

  6. Geological aspects of foreign and domestic uranium deposits and their bearing on exploration

    International Nuclear Information System (INIS)

    Some geological aspects of the major uranium deposits of the world, the prevailing genetic concepts and their possible bearing on exploration, and the questions and problems they pose are examined briefly. The types of geological deposits discussed are domestic sandstone-type, foreign sandstone-type, conglomerate-type, vein-type, and calcrete deposits and disseminated deposits in igneous rocks

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

    Science.gov (United States)

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

    2012-10-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-12-01

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

  9. International Uranium Resources Evaluation Project (IUREP) orientation phase mission report: Somalia

    International Nuclear Information System (INIS)

    The IUREP Orientation Phase Mission to Somalia suggests that in addition to the reasonably assured resources (RAR) of 5 000 t uranium and estimated additional resources (EAR) of 11 000 t uranium in calcrete deposits, the speculative resources (SR) could be within the wide range of 0 - 150 000 t uranium. The majority of these speculative resources are related to sandstone and calcrete deposits. The potential for magmatic hydrothermal deposits is relatively small. The Mission recommends an exploration programme of about US $ 22 000 000 to test the uranium potential of the country which is thought to be excellent. The Mission also suggests a reorganization of the Somalia Geological Survey in order to improve its efficiency. Recommended methods include geological mapping, Landsat Imagery Interpretation, airborne and ground scintillometer surveys, and geochemistry. Follow-up radiometric surveys, exploration geophysics, mineralogical studies, trenching and drilling are proposed in favourable areas

  10. Abanicos aluviales cuaternarios del Baix Camp (provincia de Tarragona): resultados de dataciones radiométricas

    OpenAIRE

    Villamarín, J. A.; Masana, E; Calderón, T.; Julià, Ramón; Santanach, P.

    1998-01-01

    The Quaternary fans which cover the southernmost part of the El Camp Basin belong to three generations. Noticeable calcrete levels developed on the top of fans from the first and second generation. Radiometric dating by means of U/Th and termolumiscence techniques of the mentioned caliche levels allow us to attribute a minimal age of ca. 300000 years to the top of the first generation fans, and ca. 100000 years to the top of the second generation alluvial fans

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

    Science.gov (United States)

    Fernette, Gregory

    2015-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1994-12-31

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Archambeau, C.

    1994-08-01

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

  15. Study of uranium mobilization from Himalayan Siwaliks to the Malwa region of Punjab state in India

    International Nuclear Information System (INIS)

    Fossils, palaeosols and associated sedimentary rock samples from well-dated Siwalik sediments have been measured for their uranium content by low background gamma ray spectrometry with a view to study the role of geo-genic mobilization in enhancing the levels of uranium in ground water bodies of Malwa region in Punjab state, North Western India. Uranium activity in pure palaeosol and palaeosol associated samples i.e. calcrete and nodules varied between 46 and 214 Bq/kg whereas the same in pure fossil samples varied between 208 and 4837 Bq/kg. The data indicates a geo-genic contribution in the enhancement of uranium concentration in groundwater of the region. (author)

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

    Science.gov (United States)

    Jones, Blair F.; Conko, Kathryn M.

    2011-01-01

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

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

    International Nuclear Information System (INIS)

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

  18. A rapid method for the determination of uranium, thorium and vanadium in calcareous samples by ICP-AES

    International Nuclear Information System (INIS)

    A rapid method for the determination of uranium, thorium and vanadium in calcareous samples of western Rajasthan by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) after HNO3 leaching and ammonia precipitation was developed. Analytes were quantitatively leached out and pre-concentrated by ammonia precipitation reaction. The effect of various experimental parameters such as acidity, sample amounts and leaching time on the recovery and determination of these elements were investigated in detail. A number of calcareous samples were analysed by the present method. Results were found in good agreement with 5-10% RSD variation with the pre-analysed calcrete samples prepared by usual method of sample preparation using HF and HNO3. (author)

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

    Directory of Open Access Journals (Sweden)

    Ofelia Rita Tófalo

    2008-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Szymanski, J.S.

    1992-04-01

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

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

    Institute of Scientific and Technical Information of China (English)

    Alsu Kuznetsova; Olga Khokhlova

    2015-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Ofelia Rita Tófalo

    2008-09-01

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

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

    Science.gov (United States)

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

    1996-05-01

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

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

    Science.gov (United States)

    Sulli, A.; Interbartolo, F.

    2016-01-01

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

  5. Stable isotope distribution in continental Maastrichtian vertebrates from the Haţeg Basin, South Carpathians

    Science.gov (United States)

    Bojar, Ana-Voica; Csiki, Zoltan; Grigorescu, Dan

    2010-05-01

    The oxygen isotopic compositions of biogenic apatite from crocodiles, turtles and dinosaurs, and their relationship to climate and physiology have been evidenced by several studies (Barrick and Showers, 1995; Kolodny et al., 1996; Barrick et al., 1999; Fricke and Rogers, 2000; Stoskopf et al., 2001; Straight et al., 2004; Amiot et al., 2007). To date, few attempts have been made to correlate the enamel d13C to dietary resources of dinosaurs (Bocherens et al., 1988; Stanton Thomas and Carlson, 2004; Fricke and Pearson, 2008; Fricke, et al., 2008). One additional complication is that for dinosaurs, the d18O of enamel phosphate depends on both body water and variations in body temperature. Several studies addressed the issue of endothermy vs. ectothermy of fossil vertebrates by studying inter- and intra-bone and enamel isotopic variability (Barrick and Showers, 1994, 1995; Barrick et al., 1996; 1998; Fricke and Rogers, 2000). More recent investigations provided evidence for inter-tooth temporal variations and related them to seasonality and/or changes in physiology (Straight et al., 2004; Stanton Thomas and Carlson, 2004). The main objectives of this study are to extract palaeoclimatic information considering, beside lithofacial characteristics and the isotopic distribution of carbonates formed in paleosols, the stable isotope composition of vertebrate remains from the Haţeg Basin. We also sampled several teeth along their growth axis in order to get further information about growth rates and the amplitude of isotopic variation. Located in the South Carpathians in Romania, the Haţeg Basin contains a thick sequence of Maastrichtian continental deposits yielding a rich dinosaur and mammalian fauna. Stable isotope analyses of both calcretes and dinosaur, crocodilian and turtle remains from two localities (Tuştea and Sibişel) were integrated in order to reconstruct environmental conditions during the Maastrichtian time and to gain further insights into the metabolism

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

    Science.gov (United States)

    Oldknow, Chris; Hooke, Janet; Lang, Andreas

    2016-04-01

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

  7. Hydrochemistry on the Yilgarn Block, Western Australia: Ferrolysis and mineralisation in acid brines

    Energy Technology Data Exchange (ETDEWEB)

    McArthur, J.M.; Osborn, A.O. (University College, London (England)); Turner, J.V. (Commonwealth Scientific and Industrial Research Organization, Wembley (Australia)); Lyons, W.B. (Univ. of Nevada, Reno (United States)); Thirlwall, M.F. (Royal Holloway and Bedford New College, Egham (England))

    1991-05-01

    In the southeastern part of Western Australia internal drainage and a semi-arid climate have resulted in extensive development of playas. The brines beneath the playas wedge outwards and force local infiltration to crop out at playa margins as discharge zones. The discharging water contains dissolved Fe{sup 2+}, oxidation and hydrolysis (ferrolysis) of which generates very acidic water (pH {ge}2.8). At least some of the alkalinity generated by the original reduction of Fe{sup 3+} has been sequestered as subsurface calcrete within local soils. The acidity causes the dissolution of kaolinite, which is abundant in playa sediments and as a thick capping on weathered bedrock, giving water with a low pH and high concentrations of dissolved Al and Si. Evaporation, and mixing with playa brines containing high concentrations of K and SO{sub 4}, causes alunite to precipitate as pH rises from a minimum of 2.8, at chlorinites of 1 to 2 M, to > 6 at chlorinites of 4.8 M. The alunite deposits formed by this process are many orders of magnitude larger than occurrences elsewhere in the world. The large-scale mobilization of Si during the process may be one mechanism for the formation of silica-cemented rocks (silcrete) that are widespread in the Australian regolith.

  8. On the formations of the Pampas inthe footsteps of Darwin: south of the Salado

    Directory of Open Access Journals (Sweden)

    Marcelo Zárate

    2009-04-01

    Full Text Available In1833 during his journey across the Buenos Aires Pampas, Charles Darwin madeobservations that reflected his thoughts on two major landscape units, Pampa interserrana and Pampa deprimida, later identified byother authors. Darwin grouped the Pampean sediments into a single unit, the PampeanFormation, based upon the lithological homogeneity and the large extensionof the deposits; the unit was thought to be of estuarine-marine origin andattributed to the Recent Epoch considering the paleontological content(vertebrates and mollusks. At present, the Pampean sedimentary succession,which accumulated approximately during the last 11-12 Ma, is interpreted as a pedosedimentarysequence due to the ubiquity of pedogenetic features throughout the deposits.Four main subcycles of sedimentation are identified related to reactivations ofthe Pampean landscape. At a regional scale, the outcrop distribution of Pampeansediments of different ages suggests the dominance of more stable conditionssince the late Miocene-Pliocene in a vast area of Pampa interserrana, documented by theformation of calcretes. However, sedimentation during the latePliocene-Pleistocene was active within the domain of the Salado tectonic basin andSierras de Tandil. The regional disparity shown by the Pampean stratigraphicrecord reveals the major morphostructural differences of its basement.

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

    Directory of Open Access Journals (Sweden)

    Adrian D. Werner

    2014-11-01

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

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

    Science.gov (United States)

    Howari, Fares; Goodell, Philip; Salman, Abdulaty

    2016-02-01

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

  11. Carboniferous paleogeographic and paleoclimatic reconstructions

    Energy Technology Data Exchange (ETDEWEB)

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

    1992-01-01

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

  12. Geology of the Vaalputs radioactive waste disposal site in the Republic of South Africa

    International Nuclear Information System (INIS)

    The Vaalputs site is underlain by an extensive veneer of Tertiary and Quaternary deposits covering a crystalline basement of Precambrian age. The geological history of the area, from the oldest to the youngest event, may be summarized as follows: 1. Polyphasic ductile/ductile-brittle deformation and 1 100 Ma old granulite facies metamorphism of a (volcano) sedimentary sequence, and of associated syntectonic to late-tectonic granitic and basic intrusions. 2. Deposition of glacial tillite after a long erosional hiatus in Karoo (Permian) times. The preservation of these rocks is limited to down-faulted structural blocks within the area investigated. 3. Lower Tertiary rejuvenation of older faults and shear zones, accompanied by kimberlitic volcanism, resulted in the uplift of the Kamiesberge mountain range west of the site. Intense erosion of these mountains shed abundant detritus, which accumulated in tectonically controlled troughs and fans. 4. From ca. 25 Ma ago to the Present, tectonic stability and (semi)arid conditions have generally prevailed, leading to an extensive thin cover of calcrete and wind-blown Kalahari sands. The unfaulted, highly impermeable nature of the Vaalputs formation renders it very suitable for the safe disposal of low- to medium-level radioactive waste in the area selected. However, the numerous faults and shear zones in the granitic and gneissic basement will need in-depth investigations should a high-level radwaste repository be required

  13. Ichnofabrics and Their Environmental Interpretation from the Fluvial Deposits of the Middle Triassic Youfangzhuang Formation in Western Henan, Central China

    Institute of Scientific and Technical Information of China (English)

    Min Wang; Yongan Qi; Da Li; Mingyue Dai; Yuguang Chang

    2014-01-01

    Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre-serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up-per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa-tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri-odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com-monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace ichnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.

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

    Science.gov (United States)

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

    2016-06-01

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

  15. International Uranium Resources Evaluation Project (IUREP) orientation phase mission summary report: Morocco

    International Nuclear Information System (INIS)

    A report has recently been published on the findings of the mission to Morocco under the International Uranium Resources Evaluation Project (IUREP) Orientation Phase. The IUREP Orientation Phase Mission estimates that the speculative resources of Morocco range from 70 000 to 180 000 tonnes of uranium, half of which could be expected to occur in the Northern Provinces, which are relatively well explored, and the other half in the little explored Southern Provinces. In the north, speculative resources are fairly evenly distributed among the various types of deposit, in particular vein deposits (intragranitic and contact) linked with Hercynian and Precambrian blocks, the sandstone type deposits linked with Mesozoic strata and the volcanogenic deposits, especially of Precambrian age. The potential for large high-grade deposits, especially for those linked with unconformities and linear albitites, has been little investigated in Morocco and is chiefly thought to lie in the Precambrian in the Anti-Atlas and Southern Provinces. Here, the presence of acid volcanic rock reinforces the uranium potential, and there is also some potential for calcrete-related deposits. Phosphate-related uranium, to be recovered shortly, constitutes by far the largest reserves in Morocco, estimated at about 7 million tonnes of recoverable uranium. Recommendations have been made for further study of known occurrences and identification of new ones, such as unconformity and albitite-related deposits. (author)

  16. The geology of the Kalahari Gemsbok National Park

    Directory of Open Access Journals (Sweden)

    S. J Malherbe

    1984-12-01

    Full Text Available The floor rocks of the Kalahari Group are only known from boreholes. It consists of rocks of the Karoo Sequence with its associated intrusions of dolerite. The pre-Kalahari topography was dissected by rivers which drained in the direction of the present Botswana. The distribution of the oldest formation of the Kalahari Group, the Wessels Formation (clayey gravel, and the overlying Budin Formation (clay was also determined from borehole records. The Karoo Sequence was probably the source of these rocks. The overlying Eden Formation (sandstone, grit and conglomerate had a source which could yield much sand. All these formations were deposited under fluviatile conditions. The Mokalanen Formation (calcrete and the Gordonia Formation (sand indicate a change from a humid to an arid environment. The Lonely Formation (clayey diatomaceous limestone was deposited in a lacustrine environment. It also indicates a higher rainfall in an otherwise arid period. The Goeboe Goeboe Formation consists of clay and sand in the pans and rivers.

  17. Distribution, Mineralogy, Petrography, Provenance and Significance of Permian Ash-Carrying Deposits in the Paraná Basin

    Directory of Open Access Journals (Sweden)

    José Moacyr Vianna Coutinho

    Full Text Available The study of thin sections taken from drill core samples and outcrops in southern Brazil has demonstrated the occurrenceof repeated ash fall episodes during the Permian period between 280 and 245 Ma. Scattered or concentrated altered volcanicglass shards were detected in strata of Permian sedimentary rocks of the Rio Bonito and Tatui Formations. The shardcarryingsediment is usually a silty or cherty mudstone with variable amounts of calcrete calcite. Burial and alteration ofunstable glass debris led to the development of analcite and less commonly, calcite, silica minerals, zeolites or montmorillonite.Sources of explosive Permian volcanism, responsible for ample ash falls have been sought in South Africa, in the AndeanCordillera and along the Paraná Basin margin. A swarm of rhyolitic centers described in the Cordillera Frontal and in theCentral Argentinian Provincia de La Pampa (Patagonia is here proposed as the most adequate Permian source. In that area,volcanoes must have expelled ashes that traveled thousands of kilometers before settling in deltaic or shallow marineenvironments. Twenty-three occurrences of Permian shard-carrying sediments have been plotted in a Paraná Basin map. Thenumber of ash-carrying sediments decreases northeastward. The authors envisage dense clouds originated in Patagoniatraveling NE, depositing progressively smaller quantities of ashes but reaching Australia in pre-drift Gondwana. Shardcarrying sediments must be distinguished from “tonstein”, ash fall or ash flow tuffs, also recorded in the Permian Gondwana,which would indicate closer ash source area.

  18. Génesis y evolución de los caliches miocenos del sureste de la depresión del Duero

    Directory of Open Access Journals (Sweden)

    Armenteros, I.

    1984-08-01

    Full Text Available The aim of this paper is to describe and to study the genesis of the fossil calcretes (caliches interbedded in Miocene alluvial-fan sediments bordering the pre-Tertiary basament in the North of Segovia Province. Four types of crusts have been distinguished: brechic, massive, vertically laminated and horizontally laminated, the two later types being differentiated by their position relative to the bedding surfaces. Massive crusts show a variety of discrete carbonate components (pisoids, ooids and peloids embedded in a fine-grained matrix. Erosion of crusts and incorporation of the newly-formed fragments into a different horizon undergoing caliche-forming processes are common. "In situ" rosette like colonies and disengaged prisms of MICROCODIUM have been found. Many features, including basal elongation of the accretion laminae of pisoids and existence vadose cements, suggest that calcretes formed in vadose zones of calcimorph soil profiles under a warm climate with well-marked dry season, X-ray analysis show the existence of diagenetic pali,gorskite that, presumibly, formed before the intense precipitation of calcite in the soil profile that resulted in mature crusts, Afterwards, partial silicification as well as dolomitization to pseudosparite took place.

    El objeto de este trabajo es el estudio descriptivo y genético de los caliches fósiles situados en sedimentos de abanicos aluviales miocenos que orlan el zócalo preterciario de Honrubia Pradales (norte de la provincia de Segovia. Se reconocen cuatro tipos de costras: bréchica, masiva, laminada vertical y laminada horizontal, y las dos últimas se diferencian por su posición respecto al plano de estratificación. La costra masiva presenta una serie de elementos formados "in situ" (pisoides, ooides y peloides destacados en una matriz. Es frecuente la erosión de una costra y la inclusión de los fragmentos resultantes a un nuevo nivel que va a sufrir el proceso de costrificación, Se

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

    Science.gov (United States)

    Mader, Detlef

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

  20. Recovery of uranium low grade ores by froth flotation: study of the texture and synergetic effects of flotation reagents

    International Nuclear Information System (INIS)

    Due to the energy growing demand, uranium low grade ores may be those exploited in the future. Uranium ores conventional treatment does not often use mineral processing such as concentration methods for reducing leaching reagent consumption. The aim of this work is to develop an upgrading process to improve the operating process (alkaline heap leaching) taking into account the mineralogical and textural variability of the ore. The Trekkopje deposit is composed of calcrete and a gypscrete. The uranium bearing mineral is carnotite (K2(UO2)2 [VO4]2.3H2O). The gangue minerals are composed by silicates, such as quartz, feldspars, micas and Ca-minerals, calcite and gypsum (XRD and ICP-MS analysis). A SEM image processing was used to study the textural properties and the exposed free surface of mineral inclusions in clay clusters. In calcrete milled to -200 μm, 50 % of all carnotite is associated with clay clusters, which are composed by 98 % of palygorskite, 2 % of illite, montmorillonite, and interbedded clays (XRD and microprobe analysis). The carnotite grain size is 95 % less than 70 μm. Calcite is the main inclusion in clay clusters. Indeed, the calcite inclusions average rate in the clay clusters is 12 % and 5 % for carnotite inclusion. And the free exposed surface percentage of these minerals in clay clusters is 3 % and 6 %, thus indicating that the inclusions should not affect the behavior of mixed clay particles. However, ore flotation essays did not verify this hypothesis. Three minerals separation have been proposed based on the mineral ability to consume leaching reagents: separating Ca-minerals from silicates, palygorskite from gangue minerals and carnotite from gangue minerals. A study of silicates and Ca-minerals electrokinetic properties (electrophoresis) was carried out to select the collectors and the optimum pH range for selective flotation. Basic pH near neutral was proved to be optimal for the separation of gangue minerals with cationic or anionic

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

    Science.gov (United States)

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

    2016-06-01

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

  2. The genesis of solution pipes: Evidence from the Middle-Late Pleistocene Bridgewater Formation calcarenite, southeastern Australia

    Science.gov (United States)

    Lipar, Matej; Webb, John A.; White, Susan Q.; Grimes, Ken G.

    2015-10-01

    Solution pipes are abundant in Late Pleistocene aeolian calcarenites at Cape Bridgewater in southwestern Victoria, and were studied using field work, morphometric analysis, thin sections, mineralogical and chemical analyses, and OSL dating. The solution pipes are vertical tubes formed in aeolian limestone with matrix porosity. They are typically 0.1-1 m wide and 1-5 m deep, with rounded terminations and cemented rims up to 10 cm thick. They are overlain by palaeosols and filled mostly with palaeosol material; rhizoliths are commonly present in the solution pipe fills and the surrounding calcarenite. The solution pipes have formed by focused dissolution of aeolianite, relatively quickly after the sand deposition, and concurrently filled with soil as they developed. They most likely formed beneath trees (as a result of focused infiltration due to stemflow) or due to fingered flow (unstable wetting front that breaks into fingers as it moves downwards). Solution pipe formation was strongly dependent on climate; periods of solution pipe formation followed the deposition of aeolianites at the end of interglacials MIS 7, 9 and 11, when the dunes were stabilised by vegetation and there was sufficient rainfall for substantial subsoil dissolution. The cemented rims formed in the following drier glacial climates. Solution pipes are most abundant in the youngest aeolianite, probably reflecting the wetter climate at the end of MIS 7 that allowed a dense forest to cover the dunes. From MIS 5 to MIS 2 no deposition of calcareous sand occurred on Cape Bridgewater, and combined with a very wet interglacial period MIS 5e, resulted in additional karstification, allowing the pipes in the MIS 7 aeolianite to extend deeper and drill down into the underlying member. A well-developed calcrete layer drapes over these solution pipes, and probably formed during the dry, windy climate of the Last Glacial Maximum.

  3. A low diversity, seasonal tropical landscape dominated by conifers and peltasperms: Early Permian Abo Formation, New Mexico

    Science.gov (United States)

    DiMichele, W.A.; Chaney, D.S.; Nelson, W.J.; Lucas, S.G.; Looy, C.V.; Quick, K.; Jun, W.

    2007-01-01

    ], calcrete in paleosols, and abundant mud cracks evidencing ephemeral flow in streams) and biology (low floristic diversity, xeromorphic plant physiognomies). ?? 2006 Elsevier B.V. All rights reserved.

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

    Science.gov (United States)

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

    2016-03-01

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

  5. Phytosociology of the farm Haribes in the Nama-Karoo biome of southern Namibia

    Directory of Open Access Journals (Sweden)

    Ben J. Strohbach

    2012-01-01

    Full Text Available Limited historic vegetation data (prior to the 1980s are available for Namibia. Finding such historic data at Haribes prompted a follow-up survey of the vegetation. We present a classification of the recent data in this paper as a first step towards comparing the two data sets. Six new associations (three with two subassociations each are formally described. The landscape at Haribes is dominated by a pan with surrounding hummock dunes. The pan supports the Lycio cinereum – Salsoletum, whilst on the hummock dunes the Salsolo – Tetragonietum schenckii can be found. The surrounding plains and escarpment can be divided into three landforms: the torras with the Monsonio umbellatae – Boscietum foetidae, the ranteveld with the Acacio senegal – Catophractetum alexandri (and two subassociations and calcrete ridges with the Zygophylo pubescentis – Leucosphaeretum bainesii. Dry river beds on the farm support two subassociations of Anthephoro pubescentis – Ziziphodetum mucronatae. The area covered by each dominant landform has been calculated after being mapped. The composition and diversity of the associations are briefly compared to other known vegetation descriptions within the Nama-Karoo. Since November 2011, Haribes has been used as a resettlement farm. This may result in the overutilisation of the limited grazing resources, to the extent that the present, fairly dense Acacio senegal – Catophractetum alexandri of the ranteveld is feared to become degraded to resemble the Monsonio umbellatae – Boscietum foetidae of the torras.Conservation implications: This paper describes six plant associations of the Nama-Karoo biome in arid southern Namibia. The information presented forms a baseline description, which can be used for future monitoring of the vegetation under altered land use.

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

    Science.gov (United States)

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

    2016-03-01

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

  7. Rasgos morfologicos y petrologicos del paleokarst de la unidad superior del mioceno de la cuenca de Madrid

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    Cañaveras, J. C.

    2003-08-01

    Full Text Available In the Madrid Basin, especially in the Southem part (Mesa de Ocaña, the Miocene- Pliocene stratigraphic boundary is defined by a paleokarst sculpted on the Miocene limestones. The development of the paleokarst was completed in three main successive stages. The first one was initiated when the lacustrine sedimentary complex, settled in the basin during the Turolian, dried out. Although the water table dropped, it was still close to the surface, as indicated by the location of sub-horizontal caves in the limestone formation. The proximity of the water table favored an encroachment of vegetation into the unlithified sediment. Conduits related to the plant roots, together with the horizontal caves, represent the most prominent dissolution features of the resulting «uncovered» karst. The second stage of karstification took place after the limestones folded. It was characterized by the formation of calcretes, which exhibit typical fabrics (laminar, pisoliths, etc., on the previous profiles, providing evidence of a dry climatic stage. Karstic profiles scovered by calcretes~w ere buried by a Pliocene river system. In the south zone of the Mesa de Ocaña, far away of the fluvial complex, a third episode of karstification has been verified. This episode is defined by the accumulation of soils, basically in the synclines, which caused the dissolution and brecciation of the substrate, as it is reflected in a third type of profiles, called «brechoides». These features are consistent with a humid climate. Finally, al1 types of karst were buried by a laminar calcrete formed at the latest Pliocene. Therefore, the polyphase development of the paleokarstic surface lasted almost al1 the Pliocene. Nevertheless, figures on the order of lo5 years are envisaged as reliable to assess the duration of the first phase, the only one evenly affecting the limestone formations.En la Cuenca de Madrid y, especialmente, en la zona sur (Mesa de Ocaña, la

  8. Accelerated weathering of carbonate rocks following the 2010 forest wildfire on Mt. Carmel, Israel

    Science.gov (United States)

    Shtober-Zisu, Nurit; Tessler, Naama; Tsatskin, Alexander; Greenbaum, Noam

    2015-04-01

    Massive destruction of carbonate rocks occurred on the slopes of Mt. Carmel, during the severe forest fire in 2010. The bedrock surfaces exhibited extensive exfoliation into flakes and spalls covering up to 80%-100% of the exposed rocks; detached boulders were totally fractured or disintegrated. The fire affected six carbonate units -- various types of chalk, limestone, and dolomite. The burned flakes show a consistent tendency towards flatness, in all lithologies, as 85%-95% of the flakes were detached in the form of blades, plates, and slabs. The effects of the fire depend to a large extent on the rocks' physical properties and vary with lithology: the most severe response was found in the chalk formations which are covered by calcrete (Nari crusts). These rocks reacted by extreme exfoliation, at an average depth of 7.7 to 9.6 cm and a maximum depth of 20 cm. The flakes formed in chalk were thicker, longer, and wider than those of limestone or dolomite formations. Moreover, the chalk outcrops were exfoliated in a laminar structure, one above the other, to a depth of 10 cm and more. Their shape also tended to be blockier or rod-like. In contrast, the limestone flakes were the thinnest, with 99% of them shaped like blades and plates. Scorched and blackened faces under the upper layer of spalls provided strong evidence that chalk breakdown took place at an early stage of the fire. The extreme response of the chalks can be explained by the laminar structure of the Nari, which served as planes of weakness for the rock destruction. Three years after the fire, the rocks continue to exfoliate and break down internally. As the harder surface of the Nari was removed, the more brittle underlying chalk is exposed to erosion. If fires can obliterate boulders in a single wildfire event, it follows that wildfires may serve as limiting agents in the geomorphic evolution of slopes. However, it is difficult to estimate the frequency of high-intensity fires in the Carmel region

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

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    M. Ezpeleta

    2006-06-01

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

  10. The III working days of the Cenozoic

    International Nuclear Information System (INIS)

    The third working days in geology were organized by the Uruguayan Society of geology and took place in DINAMIGE in June - 2012. The lectures were given by national and foreign professionals and included important topics such as mineral raw materials used in the archaeological artifacts in Guayacas - Dayman - Paysandu . The Holocene in the coastal zone of Uruguay. Aspect of the early human occupation in Uruguay. Change effects in the land use about the mineral clay (eucalyptus forestation, illite). Paleoclimatic and paleoenvironmental reconstruction for middle and late holocene (Rocha). Gas hydrate resource quantification in Uruguay. Application of the geophysical techniques in the environmental pollution in Montevideo - Piriapolis. Environmental evolution and builders of small hills in India Muerta zone. Human or natural forcing in the geomorphological processes in Pocitos and Ramirez beaches (80 years of aerophotographic records).Tipology and nomenclature proposal for technological soil. Quarries reconditioning methodology. Hydraulic conductivity in sugar cane cultivated in soils previous vinaza application. Paleosoils and pedogenic calcretes formations in Fray Bentos (Oligocene - early miocene) Raigon (late pliocene and Middle pleistocene) and Libertad (early - middle pleistocene). Tectonics and sedimentary process in the continental talud in Uruguay. Rio de la Plata as paleoenvironmental focus using diatomos as proxies. Oleistocene mammals in the late-early Holocene in Santa Lucia river basin (Uruguay southern). Anthropization in Montevideo Bay during the Holocene. Paleocene stratigraphic plays in Uruguay offshore. Continental Influence versus marine transition in Rio de la Plata zone - internal continental shelf of the South Atlantic - a multiproxy study. Macrofossils vegetable in Palmar formation (later pleistocene) in Entre Rios - Argentina. Phytolith analysis in quaternary fluvial sediment (plio-pleistocene) in San Salvador and Palmar formation - Uruguay

  11. The time has changed: Middle Triassic climate changes revealed by carbon isotopes

    Science.gov (United States)

    Schmid, S.; Worden, R.; Fisher, Q.

    2003-04-01

    The Middle Triassic stratigraphy in Europe can be subdivided into a marine section of the Germanic and Paris Basin and a continental red-bed succession of Western Europe (Irish Basin, Wessex Basin). The link between the marine and continental is uncertain due to a lack of biostratigraphic information but recent palaeomagnetic studies have given a better understanding of the two environments (Hounslow et. al, 2001). In this study we have produced geochemical evidence which emphasize the implications of the palaeomagnetic data. We show that the marine and continental strata can be correlated using carbon isotopes. Throughout Europe the Middle Triassic is characterized by limestone deposits of the Muschelkalk Formation that contain evidence of a hiatus in sedimentation due to sea-level fall in the Middle Muschelkalk with the consequent deposition of evaporites. The Sherwood Sandstone Group (SSG) characterizes the Middle Triassic of Western Europe. The SSG is dominated by fluvial deposits with intercalated floodplain deposits, sand-flats and playas, which are penetrated by dolocretes and calcretes. The abundance of fluvial channels and sandflats are dependent on the fluvial activity and the water table height. In both depositional environments water plays a major role in the type of sediment. The volume of water is controlled by the prevalent climate. Climate signals are stored in carbon isotopes in both the marine Muschelkalk and the continental SSG. Carbon isotopes from the SSG from the Corrib Field, Slyne Basin, west of Ireland and from the Muschelkalk of the Germanic Basin have thus been interpreted in terms of climate change linked to stratigraphy. The continental sediments show a distinct positive carbon isotope excursion (taken from dolocretes), which is interpreted to present a more arid climate. In contrast the marine limestones exhibit a negative carbon isotopes excursion from a sea level low stand for the same time interval. The plot of both carbon isotopes

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

    Science.gov (United States)

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

    2010-01-01

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

  13. Lower Eocene alluvial paleosols (Willwood Formation, Northwest Wyoming, U.S.A.) and their significance for paleoecology, paleoclimatology, and basin analysis

    Science.gov (United States)

    Bown, T.M.; Kraus, M.J.

    1981-01-01

    of gley mottles, increase in numerical proportion and thickness of red versus orange coloration, and increase in abundance of calcrete glaebules indicate better drained soils and probably drier climate in late Willwood time. This drying is believed to be related to creation of rain shadows and spacing of rainfall (but not necessarily decrease in absolute rainfall) due to progressive tectonic structural elevation of the mountainous margins of the Bighorn Basin. ?? 1981.

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

    Science.gov (United States)

    Williams, Martin

    2014-05-01

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

  15. Long-term effect of land use change on soil quality: Afforestation and land abandonment in semi-arid Spain

    Science.gov (United States)

    Zethof, Jeroen; Cammeraat, Erik; Nadal-Romero, Estela

    2016-04-01

    Soils under the Mediterranean climate are vulnerable for degradation, especially after land abandonment. Abandonment is an important factor in the Mediterranean landscape as vegetation regeneration is hampered due to the characteristic semi-arid and sub-humid Mediterranean climate regime. During the past 70 year extensive afforestation projects have been conducted with the aim to protect landscapes and soils against degradation. While large investments are still being made, little is known about the impact of afforestation on soil quality on a longer time scale. During the past decade, there is a growing interest in qualifying and quantifying the carbon storage in soils by such afforestation projects, to get a better understanding of the carbon cycle and look for possibilities to fixate atmospheric CO2 in the soil. It is generally accepted that afforestation projects will increase the soil carbon pool, but data on this process is scarce. Therefore an intensive fieldwork has been carried out in Murcia, southeastern Spain to study the effects of land abandonment and afforestation on soil quality along a chronosequence and included two afforested areas (from the early '70s and 1993). The Pinus halepensis trees were planted in rows, for which the underlying calcrete was broken. Samples were taken to study changes in soil quality (Aggregate stability, Corg, N, P, K, Na), Soil Organic Carbon (SOC) stocks and soil hydraulic properties, such as infiltration and water retention, between the afforestation projects, abandoned agricultural plots of similar age, semi-natural vegetation, cereal crop fields and almond orchards. As the natural vegetation is characterized by a spotted pattern of bare areas and trees, forming so-called "islands of fertility", both bare and vegetation covered sub-sites were sampled. First results showed a positive effect of both land abandonment and afforestation on the soil aggregation. Especially the 40-year-old plots showed underneath trees

  16. The Agoudal (High Atlas Mountains, Morocco) shatter cone conundrum: A recent meteorite fall onto the remnant of an impact site

    Science.gov (United States)

    Chennaoui Aoudjehane, Hasnaa; El Kerni, Houda; Reimold, Wolf Uwe; Baratoux, David; Koeberl, Christian; Bouley, Sylvain; Aoudjehane, Mohamed

    2016-08-01

    Associations between impact structures and meteorite occurrences are rare and restricted to very young structures. Meteorite fragments are often disrupted in the atmosphere, and in most cases, meteorite falls that have been decelerated by atmospheric drag do not form a crater. Furthermore, meteorites are rapidly weathered. In this context, the finding of shatter cones in Jurassic marly limestone in the same location as a recent (105 ± 40 ka) iron meteorite fall near the village of Agoudal (High Atlas Mountains, Morocco) is enigmatic. The shatter cones are the only piece of evidence of a meteorite impact in the area. The overlap of a meteorite strewn field with the area of occurrence of shatter cones led previous researchers to consider that the meteorite fall was responsible for the formation of shatter cones in the context of formation of one or several small (Atlas tectonics has been observed, such as a vertical to overturned stratum trending N150-N160. New outcrops with exposures of shatter cones are reported and extend the previously known area of occurrence. The area of in situ shatter cones (~0.15 km2) and the strewn field of meteorites are distinct, although they show some overlap. The alleged impact breccia is revealed as calcrete formations. No evidence for a genetic relationship between the shatter cones and the meteorites can be inferred from field observations. The extent of the area where in situ shatter cones and macrodeformation not corresponding to Atlas tectonic deformation are observed suggest that the original diameter of an impact structure could have been between at least 1-3 km. For typical erosion rates in the Atlas region (~0.08 cm yr-1), the period of time required for the erosion of such a structure (1.25-3.75 Ma) is much larger than the age of the meteorite fall. This line of reasoning excludes a genetic link between the shatter cones and the meteorite fall and indicates that the observed shatter cones belong to an ancient impact

  17. Moving to world's best uranium address

    International Nuclear Information System (INIS)

    Most exploration dollars spent in South Australia are focused on exploiting uranium. This is for good reason as South Australia is the world's best address for uranium. Pressure to cut CO2 emissions and the ballistic growth of the Chinese and Indian economies has heightened expectations that the worldwide use of uranium for power generation will mushroom beyond its current 17% market share. The recent Australia-China deal only seems to confirm this; hence uranium's growing popularity among miners and explorers. Such is the attractiveness of uranium-related floats, when Toro Energy sought $18m in March it was swamped with more than three times share application volume. In the north west, Southern Gold and Hindmarsh Resources are expectantly drilling for commercial uranium deposits all around the acreage that hosts the Challenger gold mine in the Gawler Craton. The first exploration drilling for uranium in quaternary-age river channels will take place in South Australia's far north in May. Red Metal says while older and deeper tertiary river channels in the area that host the Beverley uranium mine were explored for uranium, the younger near-surface channel has not had a single hole drilled for uranium. This is despite the area being one of the 'hottest radiogenic terrains in South Australia'. The company will target calcrete-style uranium mineralisation similar to the Yerrlirrie deposit in Western Australia (52,000t U308). Tasman Resources will start drilling to test seven uranium targets within 30km of Olympic Dam, the world's largest known uranium deposit, later this year. Tasman also holds tenements adjoining the Warrior uranium deposit near Tarcoola that contains known radiometric anomalies within the 40km-long Wynbring paleochannels. They are the fourth largest uranium explorer in South Australia. Alliance Resources and its JV partner Quasar Resources are exploring the Beverley 4 Mile uranium prospect at Arkaroola. Quasar is an affiliate of Heathgate Resources

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

    Directory of Open Access Journals (Sweden)

    Noômène Fehri

    2007-12-01

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

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

    Directory of Open Access Journals (Sweden)

    Dahlkamp F. J.

    2006-11-01

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

  20. Soil organic matter studies and nutrient cycling

    International Nuclear Information System (INIS)

    A short account is given of biomass and soil organic matter (SOM) development in the geological past, from Hadean via Archaean and Proterozoic, to present day Phanerozoic, with its much reduced atmospheric CO2, enriched O2, a stratospheric ozone belt that supports the evolution of terrestrial life and, currently, a carbon sink (by photosynthesis, chemical weathering, precipitation in oceans) that exceeds the carbon source (by respiration, volcanism, ejection from subduction zones). Radiation and isotope use in studies of SOM and nutrient cycling relies mainly on: (1) Scanning the turnover of uniformly 14C or 13C labelled biomass. (2) Measurement of the SOM-C residence time by natural 14C tests. (3) Use of the whole set of labelled plant nutrients, especially 32P, 33P and 42K for tracer studies, e.g. for A or L value tests. (4) Most importantly, use of 15N labelled nitrogen fertilizer and natural 15N to reveal the N dynamics in the soil-plant system as well as to assess, via isotope fractionation, the contribution of atmospheric N in the diazotrophic system's nitrogen collection. (5) Thin layer scanning of soil profiles for natural 14C and 13C, the latter to indicate the changes in photosynthesis resulting from climate or land use changes (C3 forest with a 13C value of -25 per mille → C4 savannah grasses with a 13C value of - 10 per mille). The 13C and 18O measurements in semi-arid calcretes (about 1000 Pg C) reflect the mechanism of formation (ad ascensum-ad descensum-catena). (6) Owing to 13C enrichment in residual SOM, 13C in wetlands is used to indicate emission of methane, which is depleted in 13C to -60 per mille. (7) Nitrogen-15 labelling of nitrification and denitrification is used to reveal the N2O emission from soil related sources, about 7 Tg/a. The NH3-N emission from soil + fertilizer + livestock + motor vehicles amounts to 22-35 Tg N/a. The N release from fires, shifting agriculture, firewood and agricultural wastes is about 15-46 Tg N/a (C:N 100

  1. International Uranium Resources Evaluation Project (IUREP) orientation phase mission report: Sudan. February-March 1981

    International Nuclear Information System (INIS)

    The IUREP Orientation Phase Mission to the Democratic Republic of the Sudan believes that the Speculative Resources of the country might fall between 20,000 and 40,000 tonnes uranium and more. This indicates that the Speculative Resources of the Sudan could be significantly higher than previously estimated (7,500 tonnes uranium) by the NEA/IAEA Steering Group on the Uranium Resources - IUREP Phase I. The Government is willing to consider valid exploration programmes presented by prospective partners as long as they serve the interests of both parties. Within the general six-year (1977/78-1982/83) plan for development of the country's mineral resources, the Ministry of Energy and Mining has set up certain priorities which it would like to see expeditiously implemented: uranium exploration and production stands high on the list of priorities. On the basis of very limited information on regional geology and on previous exploration which was available to the Mission, it is estimated that the greatest potential for the Speculative Resources of possible economic significance will prove to occur in the following geological environments of the Sudan (Red Sea Hills area is not included): precambrian basement complex, palaeozoic-mesozoic-tertiary sedimentary basins and the tertiary to recent calcretes. The IUREP Orientation Phase Mission believes that some 20 Million US$ (very rough estimate) will be needed to (1) check the validity of the basic geological concepts formulated on the uranium potential of the selected areas, (2) accumulate diagnostic geological, geophysical, geochemical data indicative of a true uranium potential there, (3) study the basement complex rocks and the sedimentary formations at least on a broad structural-stratigraphic reconnaissance basis (a tremendous amount of valuable water drilling data has accumulated over the last years for some of the selected sedimentary basins) and (4) determine the most appropriate investigation techniques to be utilized

  2. Stress Patterns Across South Africa: Something Amiss?

    Science.gov (United States)

    Andreoli, Marco; Ben-Avraham, Zvi; Delvaux De Fenffe, Damien; Durrheim, Ray; Fagereng, Ake; Heidbach, Oliver; Van Der Merwe, Nielen; Saalmann, Kerstin; Saunders, Ian; Hodge, Matthew; Logue, Andrew; Malephane, Hlompho; Muaka, Joseph J.

    2013-04-01

    To mitigate the uncertainties in assessing the geohazards and rock conditions that affect the nuclear, mining (including hydrocarbon extraction) and civil engineering activities in South Africa, the authors are working to improve the data coverage concerning the present day stress field. In principle, this implies constraining the principal compressive stresses (σ1>σ2>σ3) or at least the maximum horizontal compressive stress (σH) because knowledge of these parameters may determine the reactivation potential of known faults, or the behaviour of large excavations and wells. By contrast, much of the subcontinent is under-represented in the World Stress Map database. For this reason we have taken a number of steps, firstly by installing a compact Trillium seismic sensor at Stofkloof (Namaqualand; adjacent to the Vaalputs low and intermediate level radioactive waste disposal facility) and 1-sec sensors at Aggeneys and Koffiemeul (Bushmanland). All stations are equipped with Reftek data loggers and powered by solar panels. The data from these stations will be integrated with data from the national network to obtain focal mechanism solutions for seismic events in the Northern Cape - southernmost Namibia region (also known as the Grootvloer cluster). These neotectonic stress tensors are then combined with σH parameters obtained from calliper logs of off-shore wells and from the geometry of joints, faults and sheared fractures in palaeosols (Bushmanland), soils and calcrete (NW Free State) and aeolianites (southern Cape). We also include underground rock engineering phenomenological observations and measurements, and data in the public domain. Our data consistently indicate a NNW-SSE oriented σH (Wegener Stress Anomaly or WSA) that prevails across most of central, southern and western South Africa, Namibia up to the Ruacana hydroelectric power plant at the Angola border. However, in the Congo basin, a few earthquake focal mechanisms suggest rotation of the regional

  3. International Uranium Resources Evaluation Project (IUREP) orientation phase mission report: Peru. August - October 1981

    International Nuclear Information System (INIS)

    The IUREP Orientation Phase Mission to Peru believes that the Speculative Resources of that country fall between 6,000 and 11,000 tonnes uranium. There has been no uranium production in Peru and there are no official estimates of uranium resources. Past exploration in Peru (dating from about 1952) has indicated a paucity of valid uranium occurrences and radioactive anomalies. Only recently (1980) have anomalous areas been identified, (Macusani-Picotani). The identified Speculative Resources are mainly in Late Tertiary ignimbrites and associated sediments in the high Andes of southern Peru. Geologically, there are direct parallels between these resources and deposits of the Los Frailes areas of neighbouring Bolivia. Other minor Speculative Resources may be present in calcretes developed from Tertiary volcanogenic sources over the Precambrian in the Pacific Coastal desert of southern Peru but no positive indications have been recognised. Hercynian sub-volcanic granites in the eastern cordillera of southern Peru may have some associated Speculative Resources both intra and extra granitic. No Speculative Potential could be identified in Permo-Triassic or Tertiary post tectonic continental sediments anywhere in Peru. Such potential may exist but further reconnaissance of the continental late Tertiary basins, with positive indications would be required before inclusion of potential in this category. Recent discoveries in the volcanogenic environment of southern Peru have been by carborne, helicopter borne and on on-foot reconnaissance of isolated areas. It is recommended that there be a more systematic, integrated study of the entire volcanic district assisted by volcanic petrographic examination. Assessment of the known occurrences requires immediate subsurface study by drilling and exploration audits to assess their continuity, grade variation and thickness. This phase will be significantly more expensive than previous exploration. Non-core drilling should supplement

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

    Science.gov (United States)

    Lal, R.

    2013-12-01

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

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

    Science.gov (United States)

    Quantin, Paul

    2010-05-01

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

  6. On the formations of the Pampas inthe footsteps of Darwin: south of the Salado Sobre las formaciones de las Pampasen los pasos de Darwin: al sur del Salado

    Directory of Open Access Journals (Sweden)

    Marcelo Zárate

    2009-04-01

    Full Text Available In1833 during his journey across the Buenos Aires Pampas, Charles Darwin madeobservations that reflected his thoughts on two major landscape units, Pampa interserrana and Pampa deprimida, later identified byother authors. Darwin grouped the Pampean sediments into a single unit, the PampeanFormation, based upon the lithological homogeneity and the large extensionof the deposits; the unit was thought to be of estuarine-marine origin andattributed to the Recent Epoch considering the paleontological content(vertebrates and mollusks. At present, the Pampean sedimentary succession,which accumulated approximately during the last 11-12 Ma, is interpreted as a pedosedimentarysequence due to the ubiquity of pedogenetic features throughout the deposits.Four main subcycles of sedimentation are identified related to reactivations ofthe Pampean landscape. At a regional scale, the outcrop distribution of Pampeansediments of different ages suggests the dominance of more stable conditionssince the late Miocene-Pliocene in a vast area of Pampa interserrana, documented by theformation of calcretes. However, sedimentation during the latePliocene-Pleistocene was active within the domain of the Salado tectonic basin andSierras de Tandil. The regional disparity shown by the Pampean stratigraphicrecord reveals the major morphostructural differences of its basement.Durante su viaje por la Pampa bonaerense en 1833 CharlesDarwin efectuó observaciones que reflejaban las dos grandes unidades de paisajeposteriormente reconocidas en la región, la Pampa interserrana y la Pampadeprimida. La homogeneidad litológica y la vasta extensión de los depósitosfueron los criterios básicos empleados para agruparlos en una única unidad, la FormaciónPampeano; basado en criterios paleontológicos le atribuyó origenestuárico-marino y la asignó a la época Reciente. Si bien han existido otraspropuestas estratigráficas, Formación Pampeano o simplemente Pampeano, sondenominaciones

  7. Exploration for uranium in Argentina: New policies of reactivation

    International Nuclear Information System (INIS)

    Pintada: prospection stage, volcano-sedimentary environment. Neuquina Basin area: prospection stage. Uranium anomalies hosted by sedimentary deposits. This area is being tested for the application of in-situ leaching techniques (LIS). Regional Patagonia, East Pichinan uranium District: it includes the Cerro Solo, El Ganso, Puesto Alvear, El Molino and Arroyo Perdido deposits hosted by sedimentary rocks. Exploration drilling and reserve evaluation are currently being developed in Cerro Solo, whereas exploration drilling is carried out in the other deposits. Laguna Colorada deposit: Corresponds to a volcano-sedimentary environment: an exploration-drilling program has been planned for this area. Mineralized areas Mirasol Norte, El Cruce, El Picahueso, La Salteada, El Curioso, Meseta Cuadrada, Sierra Cuadrada Norte and Sierra Cuadrada Sur, hosted by sedimentary rocks and Cerro Chivo, hosted by volcano-sedimentary rocks. Different stages of surface exploration are being performed in these areas. Mineralized areas Laguna Sirven and Primavera, calcrete-type of mineralization, are being explored by means of trenches. (author)

  8. Fluvial conglomerates in continental red beds of the Buntsandstein (Lower Triassic) in the Eifel (F.R.G.) and their palaeoenvironmental, palaeogeographical and palaeotectonic significance

    Science.gov (United States)

    Mader, Detlef

    1985-05-01

    during the course of the lateral extension of the basin results in ascension of the fluvial conglomerate wedges into successively younger formations comprising consecutively Middle Buntsandstein, Upper Buntsandstein, Lower Muschelkalk, Middle Muschelkalk and finally Middle Keuper. The extraformational conglomerates mainly delineate the palaeogeographical framework, whereas the intraclastic rudites primarily give evidence of processes operating within the depositional area, reflecting erosion and reworking of overbank sequences with floodplain fines, palaeosols and aeolian dune sands during lateral channel shift. The Bröckelbank intraformational carbonate breccias to conglomerates originating from reworking of calcrete palaeosols are a peculiar facies element with particularly high palaeoenvironmental significance. They document the frequency, spatial extension and temporal persistence of pedogenesis within the alluvial plain. The size of the extraformational clasts gives evidence of the range of current velocities during aggradation of the channels. The distribution of conglomerate type and clast characteristics within cyclothems indicates the presence of stage fluctuations and variations in discharge in parts of the sequence. The preservation of complete cyclothems or the multistoreying of channel bar conglomerates reflects the differential importance of the two main mechanisms controlling accumulation of sediments in the alluvial plain: primary-depositional restriction to suppression of formation and secondary-erosional removal to destruction of finer-grained channel sediments, floodplain deposits and aeolian dune sands or palaeosols. Condensation of a series of depositional events within monotonous stacked conglomerate sequences obliterates the full range of sedimentary processes and mimics periods of long-term stability of conglomerate formation. Waning-flow mud drapes are particularly significant instruments to split up the individual genetical units of formation

  9. Fluvial sedimentary styles and associated depositional environments in the buntsandstein west of river rhine in saar area and pfalz (F.R. Germany) and vosges (France)

    Science.gov (United States)

    Dachroth, Wolfgang

    individual sand storms operating in the erg are recorded in a mm-scale graded grain-size lamination. The desert-type setting is divided into depositional sand ergs where aeolian bedforms migrate, and deflationary gravel serirs where pebbly fluvial sediments are winnowed, resulting in concentration of the gravel to residual lags and in abundant grinding of clasts to ventifacts. During time of flooding of the chotts by atmospheric precipitation, fluvial incursions or rising ground water level, lacustrine playa deposits settle out in shallow stagnant water. The fluvial Felsbänke originate in wadi-type braided river systems intersecting the erg and serir zones and often redepositing aeolian sand which is derived from undercutting during abandonment and displacement of the watercourses. The stream complexes are partially fed at their proximal ends by runoff from local alluvial fans which are aligned along parts of the margins of the basin. The Upper Buntsandstein comprises the third magnacycle which is split into three megacycles that in turn are divided into several phases. A change from generally arid to primarily semi-arid climate along with tectonical up-lift in the source area results in extinction of aeolian deposition and gives rise to formation of Violette Horizonte calcrete palaeosols which are widespread throughout the Upper Buntsandstein, if their origin was not inhibited by the dynamics of the fluvial systems. The palaeosols occur in different evolutionary stages and are mainly characterized by the typical blue-violet colour, presence of root tubes, carbonate nodules and carbonate crusts, destratification and polyedric jointing. The fluvial fining-upwards cyclothems are formed in braided river systems which partially pass into meandering stream complexes. At the top of the Upper Buntsandstein, the alluvial inland plain is converted into a delta complex in the coastal plain along the approaching sea, and with a sequence of alternating progradation and recession events

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-07-01

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

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

    Science.gov (United States)

    Cuney, M.

    2009-12-01

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

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

    Science.gov (United States)

    Boucot, A. J.; Gray, Jane

    2001-12-01

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

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

    Directory of Open Access Journals (Sweden)

    Michele Louise Francis

    2012-03-01

    Full Text Available

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