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Sample records for calcretes

  1. Isotopic geochemistry of calcretes

    International Nuclear Information System (INIS)

    Sr, C, O, U and Th isotopes have been studied in calcium carbonates accumulated in soils of semi-arid regions (calcretes). We have investigated 1) the role of in-situ weathering and climatic conditions in the genesis of calcretes from Central Spain (Toledo) and Atlantic Morocco (Sidi Ifni), 2) the origin of Ca, and 3) the age of these accumulations. Our results show that calcium carbonates replace the parent rock (granite) and preserve the bulk-volume. Sr isotopic data suggest that 90 % of Ca in the spanish calcretes is allochthonous and related to atmospheric input. O and C isotopic compositions of the carbonates are compatible with soil temperatures and respiration rates during the beginning of the summer season. U-series disequilibrium in the carbonates suggests ages ranging between 40 to 270 ky, commensurate with the climatic cycle. The Sr isotopic signatures of spanish and moroccan calcretes are similar to those of the Quaternary marine carbonates. Assuming that only Ca-rich aerosols have been the source for calcretes of the studied regions, we propose that the wide continental plateaus exposed during glacial periods (low sea level) provided a major part of the calcic input to the soils. Semi-arid conditions of Spain and Morocco allowed the percolation and precipitation in the soil profiles to form calcretes. (author)

  2. Isotopic geochemistry of calcretes; Geochimie isotopique des calcretes

    Energy Technology Data Exchange (ETDEWEB)

    Chiquet, A

    1999-04-23

    Sr, C, O, U and Th isotopes have been studied in calcium carbonates accumulated in soils of semi-arid regions (calcretes). We have investigated 1) the role of in-situ weathering and climatic conditions in the genesis of calcretes from Central Spain (Toledo) and Atlantic Morocco (Sidi Ifni), 2) the origin of Ca, and 3) the age of these accumulations. Our results show that calcium carbonates replace the parent rock (granite) and preserve the bulk-volume. Sr isotopic data suggest that 90 % of Ca in the spanish calcretes is allochthonous and related to atmospheric input. O and C isotopic compositions of the carbonates are compatible with soil temperatures and respiration rates during the beginning of the summer season. U-series disequilibrium in the carbonates suggests ages ranging between 40 to 270 ky, commensurate with the climatic cycle. The Sr isotopic signatures of spanish and moroccan calcretes are similar to those of the Quaternary marine carbonates. Assuming that only Ca-rich aerosols have been the source for calcretes of the studied regions, we propose that the wide continental plateaus exposed during glacial periods (low sea level) provided a major part of the calcic input to the soils. Semi-arid conditions of Spain and Morocco allowed the percolation and precipitation in the soil profiles to form calcretes. (author)

  3. 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

  4. 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

  5. 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

  6. Geochemical exploration techniques applicable to calcrete-covered areas

    International Nuclear Information System (INIS)

    In order to gain a better understanding of dispersion processes within, and beneath calcrete, two base-metal prospects in the north-western Cape Province of South Africa were examined in some detail. The results show that some elements penetrate the calcrete more readily than others, with cadmium showing the least depletion while copper is reduced by the greatest amount. Techniques used included the sampling of the top of the calcrete, which gives greater contrast between the background and the anomaly when compared with the overlaying soils. The samples were digested in a hot mixture of perchloric, nitric, and hydrofluoric acids, and were then analysed by atomic-absorption spectrophotometry for copper, lead, zinc, nickel, cobalt, manganese, cadmium, silver, barium, and chromium, background correction being used where necessary

  7. 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)

  8. 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

  9. Hydrology of uranium deposits in calcretes of western Australia

    International Nuclear Information System (INIS)

    Carnotite is the principal uranium mineral occurring in the calcreted trunk valleys of the ancient drainage system which extends over 400,000 sq km of south-western Australia. The calcretes, accumulations of calcium and magnesium carbonates up to 100 km long, 5 km wide, and 20 m thick, are discontinuous in character but act as aquifers for groundwaters of relatively low salinity that flow sluggishly to playa lakes. Catchment basins draining large areas of Precambrian granitic rocks can yield up to 200 parts per billion of uranium in the oxidizing environment of the water at shallow depth near the base of the calcretes. Where the product of the concentrations of active ion species of uranium, vanadium, and potassium exceeds the solubility product of carnotite, this mineral precipitates in fissures or between the carbonate and clay particles. Vanadium appears to be generally deficient in the upper levels of the aquifers; however, where it has been supplied at the required concentration from deeper reduced waters, forced up, for example, by a bar of resistant bedrock, carnotite mineralization has occurred. The incongruent dissolution of carnotite liberates vanadium preferentially. Some carnotite deposits currently are being leached and redeposited downstream. Where calcrete channels reach salt lakes, great increases in the activity of calcium and potassium promote further carnotite deposition by the decomplexing of uranyl carbonate complexes carried down the aquifers. Many areas of carnotite mineralization are now known. The largest, at Yeelirre, contains 46,000 MT of U3O8 at an average grade of 0.15%. Extraction from the ore is hampered by the carbonate content and the presence of illite-montmorillonite clay phases, but alkaline leach techniques are practicable. An appreciable proportion of the carnotite, in an extremely fine-grained form, can be associated with the clay fraction

  10. 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)

  11. 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)

  12. 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.

  13. 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

  14. Cenozoic calcretes from the Teruel Graben, Spain: microstructure, stable isotope geochemistry and environmental significance

    Science.gov (United States)

    Alonso-Zarza, A. M.; Arenas, C.

    2004-05-01

    In the Teruel Graben (northeast Spain), laminar and nodular calcretes formed in a variety of Cenozoic deposits, ranging in age from Palaeogene to Pleistocene. These calcretes developed in a relatively small area under the influence of the same highlands. Consequently, differences in their microstructure and isotopic composition (C and O) must be related to differences in host rock, climate, vegetation and duration of development. Nine profiles developed in different sedimentary settings, from proximal areas to lacustrine environments, were studied to determine whether the microstructure and stable isotope composition changed during the Cenozoic. These characteristics might be used as indicators of the prevailing climate and vegetation, and reveal any changes that occurred during this time. Most of the laminar calcretes studied are compound profiles that formed on hard substrates (e.g., Jurassic limestones) or coarse detrital deposits (e.g., Palaeogene, Pliocene and Plio-Pleistocene sandstones and conglomerates). These profiles formed in proximal areas of the basin and also in fluvial terraces. Microstructures include biogenic features such as alveolar septal structures, root tubes, calcified root cells and calcified organic filaments. Underside coatings of micrite and fibrous vadose cements are common around gravel clasts. On the other side, spherulites are only preserved at the very top of the youngest calcretes. Nodular calcretes developed on fine detrital substrates (e.g., on Palaeogene, Miocene and Pliocene red mudstones and sandy mudstones of distal alluvial and floodplain environments), and in some places grade vertically into palustrine limestones. The nodules consist of micrite and were elongated vertically, show desiccation cracks and mottling, micritic coatings, some alveolar septal structures, and root traces. Microcodium of type 1 occurs in both laminar and nodular calcretes, but only in those of Palaeogene age, while calcified root cells ( Microcodium

  15. Polygenetic development and paleoenvironmental implications of a Pleistocene calcrete at Tongoy, central northern Chile.

    OpenAIRE

    M. Pfeiffer; J. Le Roux; H. Kemnitz

    2011-01-01

    The Norte Chico Region, in central northern Chile, is a particularly sensitive area to Quaternary climate changes because of its extreme climatic gradients. However, very little has been done to determine the late Pleistocene climatic conditions of the area. Calcretes are known to be important repositories of information on past ecosystems and environments. In the Tongoy paleobay, a series of four marine beach terraces have developed over a Mio-Pliocene calcareous formation since MIS 11 to th...

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

    Science.gov (United States)

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

    2015-04-01

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

  17. Ionic gold in calcrete revealed by LA-ICP-MS, SXRF and XANES

    Energy Technology Data Exchange (ETDEWEB)

    Lintern, Melvyn J.; Hough, Robert M.; Ryan, Chris G.; Watling, John; Verrall, Michael; (CSIRO/EM); (W. Sydney)

    2009-04-02

    Highly anomalous Au concentrations in calcrete were discovered in 1987 at the Bounty Gold Deposit, Western Australia. A strong correlation was noted between the Ca, Mg, Sr and Au in soil profiles which have not only attracted the interest of mineral explorers but also chemists, soil scientists, metallurgists and climatologists. Gold has been considered an inert element and so its strong association with the alkaline earth group of relatively mobile elements is both remarkable and intriguing. Despite widespread interest, there have been few published papers on the Au-calcrete phenomenon. Here, we present work conducted on calcareous soil samples from above the Bounty mineralization in Western Australia, prior to mining. Using SXRF (synchrotron X-ray fluorescence) and XANES (micro-X-ray absorption near-edge structure), we have shown for the first time the distribution of Au in calcrete and that it occurs in both particulate and ionic form. Much of the ionic Au associated with Br is found in a root tubule. The observations are consistent with an evapotranspiration model for the formation of Au in the calcrete; Au has been mobilized then precipitated as vadose water has been removed from the soil by trees and shrubs. While the association between Au and Ca is very strong in bulk sample analyses down the soil profile, other detailed analyses on sub-samples using wet chemical, LA-ICP-MS (laser ablation inductively coupled mass spectrometry) and SXRF techniques show that it is not apparent at the sub-millimeter scale. This suggests that the Au and Ca are behaving similarly but independently and they do not (at the {micro}m scale) co-precipitate with carbonate minerals. These results corroborate other studies that suggest biotic influences can affect the mobilization and distribution of Au in surficial materials. Water-extractable Au in calcrete has been reported previously and the ionic Au described in this study likely represents that soluble component. The presence of

  18. Uraniferous calcretes of Thar Desert from Kanji Ki Sird and Jodhsingh Ki Sird Areas, Jodhpur District, Rajasthan

    International Nuclear Information System (INIS)

    Secondary uranium mineral-bearing calcrete formations have been located for the first time in India at Kanji Ki Sird (27°29 min 30 secN, 72°28min 06 secE) and Jodhsingh Ki Sird (27°29 min17 sec N, 72°29 min 04 secE) areas in Thar Desert environs of the Jodhpur district of Rajasthan. Seven zones of uraniferous calcretes in varying dimensions from 25 m x 25 m to 500 m x 200 m have been delineated by pitting and trenching over an area of 2 sq. km. The thickness of the uraniferous (assayed up to 0.047% U3O8 and chemical up to 0.024% U3O8) calcrete horizon varies from 30 cm to about a meter. These zones fall within a half-kilometer wide WNW-ESE trending low gradient drainage channel. Greenish to yellowish coloured secondary uranium minerals occur along cavities, vugs and fractures in calcretes and along rock fragment boundaries. Uranium minerals identified by X-ray diffraction technique are tyuyamunite (Ca(UO2)2(VO4)2.5-8H2O), wyartite (Ca3U (UO2)6(CO3)2(OH)163-5 H2O) and meta-autunite (Ca(UO2)2(PO4)2.10-12H2O). The Bap Boulder Bed and Badhaura sandstone exposed in the catchment area are the provenance rocks for uranium. (author)

  19. Paleoclimatic implications (Late Cretaceous-Paleogene) from micromorphology of calcretes, palustrine limestones and silcretes, southern Paraná Basin, Uruguay

    Science.gov (United States)

    Tófalo, Ofelia R.; Pazos, Pablo J.

    2010-04-01

    Sedimentologic and petrographic analyses of outcroping and subsurface calcretes, palustrine carbonates, and silcretes were carried out in the southern Paraná Basin (Uruguay). The aim of this work is to describe the microfabric and interpret the genesis of these rocks through detailed analyses, since they contain significant paleoenvironmental and paleoclimatic evolution information. The main calcrete and silcrete host rock (Mercedes Formation) is represented by a fluvial thinning upward succession of conglomerate and sandstone deposits, with isolated pelitic intervals and paleosoils. Most of the studied calcretes are macroscopically massive with micromorphological features of alpha fabric, originated by displacive growth of calcite in the host clastic material due to evaporation, evapotranspiration and degassing. Micromorphologically, calcretes indicate an origin in the vadose and phreatic diagenetic environments. Micrite is the principal component, and speaks of rapid precipitation in the vadose zone from supersaturated solutions. The abundance of microsparite and secondary sparite is regarded as the result of dissolution and reprecipitation processes. Although present, brecciated calcretes are less common. They are frequent in vadose diagenetic environments, where the alternation between cementation and non-tectonic fracturing conditions take place. These processes generated episodes of fragmentation, brecciation and cementation. Fissures are filled with clear primary sparitic calcite, formed by precipitation of extremely supersaturated solutions in a phreatic diagenetic environment. The micromorphological characteristics indicate that calcretes resulted from carbonate precipitation in the upper part of the groundwater table and the vadose zone, continuously nourished by lateral migration of groundwater. The scarcity of biogenic structures suggests that they were either formed in zones of little biological activity or that the overimposed processes related to

  20. 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.

  1. Multi-storey calcrete profiles developed during the initial stages of the configuration of the Ebro Basin's exorrheic fluvial network

    Science.gov (United States)

    Meléndez, Alfonso; Alonso-Zarza, Ana M.; Sancho, Carlos

    2011-11-01

    Multi-storey calcrete profiles developed in the Quaternary on strath terraces of the Cinca and Alcanadre rivers, tributaries of the Ebro River in NE Spain. Two calcrete profiles (Tor 1 and Tor 2) near the village of El Tormillo show horizons with an arrangement that differs from that of commonly described calcrete profiles. Significant lateral changes occur in these profiles within a distance of less than 200 m, reflecting their pedofacies relationship. The Tor 1 profile on terrace Qt1 (the highest and oldest) consists of six horizons (from bottom to top): 1) coarse fluvial gravels; 2) mudstones with carbonate nodules; 3) a chalky horizon; 4) laminar horizons, including one peloidal horizon; 5) a multi-storey horizon formed of at least six minor sequences, each of which includes a lower detrital layer, a pisolithic horizon, and a thin discontinuous laminar horizon (these sequences indicate several cycles of brecciation and/or reworking); and 6) a topmost laminar and brecciated horizon also including reworked pisoliths. Some 200 m to the north of Tor 1, horizon 5 undergoes a lateral change to channel fill-deposits. The infill of the channels shows a fining-upwards sequence ranging from clasts of about 10 cm in diameter to red silts with sparse pebbles. All the clasts come from the underlying calcrete horizons. Laminar horizons are interbedded with the clastic channel deposits. The youngest calcrete profiles developed on terrace Qt3 of the Cinca River and on the Qp4 and Qp6 mantled pediment levels. All show relatively simple profiles composed mostly of lower horizons of coated gravels, with thin laminar horizons at the top. Most of the horizons, especially the laminar ones, show biogenic features such as alveolar septal structures, calcified filaments, biofilms, spherulites, micropores and needle-like calcite crystals. These features indicate the important role of vegetation in the formation of all the above profiles. The interbedding of clastic sediments and

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

    Directory of Open Access Journals (Sweden)

    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

  3. 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

  4. 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)

  5. 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

  6. Deciphering the history of hydrologic and climatic changes on carbonate lowstand surfaces: calcrete and organic-matter/evaporite facies association on a palimpsest Middle Jurassic landscape from Portugal

    Science.gov (United States)

    Azerêdo, Ana C.; Paul Wright, V.; Mendonça-Filho, João; Cristina Cabral, M.; Duarte, Luís V.

    2015-06-01

    The unusual occurrence of calcretes and prominent organic matter in the Middle Jurassic (Lower Bathonian, Serra de Aire Formation) of the Lusitanian Basin of western Portugal (Western Iberian Margin) revealed a complex palimpsest exposure record, here interpreted as reflecting hydrological changes caused by phases of emergence and immersion. It serves as a potential model for understanding stratigraphic development at lowstand surfaces in carbonate successions. The exposure-dominated facies association grades upwards into peritidal and lagoonal limestones, and the interval is assigned to the regressive peak of a Transgressive-Regressive Facies Cycle (2nd order) of the thick Middle Jurassic carbonate ramp succession. The Galinha Quarry, Fátima region, NE of Lisbon, a type section for this lowstand assemblage, exhibits varied calcretes, with black-clasts, interbedded with, and grading into: organic-rich marly/clayey seams and lenses, locally with carbonate nodules; carbonates with evaporite traces; microbial laminites; black-clast and fenestral limestones; some lithofacies are dolomitized. The palynofacies contains phytoclasts associated with less refractory, more prone to degradation components, which suggests natural combustion/pyrolysis (wild fires). The lowstand surface represents a low relief landscape with small depressions/ponds bordering a more distal marginal-littoral setting; the partly subaerial and partly subaqueous settings were subjected to lengthy exposure and to fluctuating, very shallow water bodies and water table. Coeval climatic regime was a seasonally dry/wet one, with dry/semi-arid phases dominating over the sub-humid, as shown by the combined record of intense calcrete development, rhizogenic structures, microbial mats, brecciation, desiccation, evaporites and wild fire evidence. However, sea level rise caused changes to shallow, sea-water influenced restricted lagoonal-peritidal settings. Comparisons and differences with modern and ancient

  7. 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

  8. 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.

    The calcareous deposits on the western continental shelf of India, off Bhatkal (water depths 50 to 58 m) occur as crusts, sheets, cylinders and reddish brown mudstones. The outer layers of the crusts are micrite-dominated and beneath this layer...

  9. 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.

  10. 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

  11. 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)

  12. 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.

  13. 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.

  14. 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

  15. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Qatar

    International Nuclear Information System (INIS)

    Most of the country is covered either by sand dunes or salt flats. Although there might be a theoretical possibility of calcrete type deposits there is no actual evidence to support this idea. The Speculative Potential must be placed in the category of less than 1000 tonnes uranium. (author)

  16. Handbook on surficial uranium deposits. Chapter 3. World distribution relative to climate and physical setting

    International Nuclear Information System (INIS)

    This chapter discusses regional controls which affect the world distribution of surficial chemogenic uranium deposits. The most important of these are (1) climate, (2) geomorphology, including physiographic and climatic stability, and (3) provenance, i.e., the weathering terrain from which uranium and associated substances are derived. The three economically important environments are the calcrete environment, simple evaporative environments and paludal environments. Of these three categories, the calcrete uranium environment is probably the most uniquely constrained in terms of regional climate, geomorphic setting, provenance (vanadium as well as uranium) and especially the need for long term stability of both climate and physiography. Purely evaporative deposits, though subject to some of the same kinds of constraints, can also reflect local circumstances and a wider range of climates, physiographic settings, and source terrains. The third category encompassing bogs, marshes and organic-rich playas can form under an even wider range of climates and settings provided only that organic materials accumulate in abundance and are contacted by uranium-bearing waters. For all of these reasons and also because of the great economic importance of the calcrete environment as well as its relative novelty and complexity the discussion in this chapter is focused on calcrete, dolocrete and gypcrete uranium deposits. Objective data are reviewed first follwed by inferences and suggestions. 13 figures

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

    International Nuclear Information System (INIS)

    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

  18. 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.

  19. 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

  20. Preliminary data on dinosaurs habitat during the Upper Maastrichtian, Hateg Basin, Romania

    International Nuclear Information System (INIS)

    The Hateg basin is located in the south-western part of the Transylvanian Depression and it is filled with sediments that overly the crystalline rocks of the Getic nappe. The basin show multiple stage of Mesozoic evolution. The Latest Cretaceous (Middle and Upper Maastrichtian) with continuous transition to Paleocene is represented by two continental lithostratigraphic units: the Densus-Ciula and the Sinpetru Formations. The Upper Maastrichtian of Densus-Ciula Formation at Tustea Quarry is represented by a pebbly alluvium with massive, matrix supported conglomerates, cross bedded sandstones and mudstones, the last one containing calcretes and dinosaur remains, including eggs and hatchlings of the hadrosaurid Telmatosaurus transsylvanicus. In order to constrain the paleoenvironment in which dinosaurs lived, calcretes and dinosaur eggshells were analyzed for carbon and oxygen isotopic composition

  1. 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

  2. Geology and mineralogy of the radioactive Quaternary sediments of the North Fayium depression, Western Desert, Egypt

    OpenAIRE

    Fahmy Raslan, Mohamed; Sayed Haroun, Yehia

    2010-01-01

    Quaternary sediments of the North Fayium depression, are mainly represented by residual soil and calcrete, and have been found to be anomalously radioactive. These sediments are deposited on the irregular surface of the carbonaceous shale of the middle member of the Oligocene Qatrani Formation in the northern part of the Fayium depression. A mineralogical investigation involving a preliminary microscopic examination and detailed Environmental Scanning Electron Microscope (ESEM) has revealed t...

  3. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Yemen Arab Republic

    International Nuclear Information System (INIS)

    The Yemen Arab Republic occupies a part of the southern Arabian Shield and has been subject to considerable faulting and movement. As far as is known no uranium exploration has ever been undertaken or is presently contemplated in the country. Uranium could occur in the Shield rocks and conditions are right for calcrete type uranium deposits. The Speculative Potential may be in category 2, i.e. between 1000 and 10,000 tonnes uranium. (author)

  4. Correlation and origin of carnotite occurrences in the southern Nevada region

    International Nuclear Information System (INIS)

    Carnotite [K2(UO2)2(VO4)2.3H2O] is recognized at seven localities in the southern Nevada region. These general areas of occurrence are the Jean-Sloan Calcrete, Hidden Valley Calcrete, Hualapai Limestone, Boulder City ''fossil water table'', Horse Spring Formation type locality, Mormon Mesa Caliche, and exposures of the Willow Tank thrust fault. The carnotite occurrences pre-date the 3.80 MY (million years before present) basalt at Sandy Pint, post-date an 8.66 MY tuff that underlies the Hualapai Limestone, and are approximately coeval with the 5.84 MY Fortification Basalt. Analysis of the Th/U ratios from 2045 dry stream sediment samples collected during the National Uranium Resource Evaluation (NURE) Program indicates uranium depletion in Precambrian terrain of the region and enrichment in areas where carnotite is observed. Anomalous vanadium in dry stream sediment samples is associated with intermediate and mafic Cenozoic volcanic rocks of pre-Colorado River age, and to a lesser extent with uratic Precambrian rocks. Correlation of the Jean-Sloan Calcrete, Hidden Valley Calcrete, Mormon Mesa Caliche, Hualapai Limestone, and Boulder City ''fossil water table'' is proposed based on elevation, relief, and inferred common age and origin. Carnotite studies have provided recognition criteria for facies of a regional geomorphic surface that formed in association with sluggish shallow groundwater flow in axial drainage systems in the Late Miocene. Carnotite and gypsum were deposited in disrupted by normal faulting and climatic conditions become increasingly arid 5-6 MY ago. Major geologic events that approximately coincide with the formation of the carnotite occurrences include the Messinian Crisis, opening of the Gulf of California, and uplift of the Sierra Nevada

  5. Brief communication: beyond the South African cave paradigm--Australopithecus africanus from Plio-Pleistocene paleosol deposits at Taung.

    Science.gov (United States)

    Hopley, Philip J; Herries, Andy I R; Baker, Stephanie Edwards; Kuhn, Brian F; Menter, Colin G

    2013-06-01

    Following the discovery of the "Taung Child" (Australopithecus africanus) in 1924 in the Buxton-Norlim Limeworks near Taung, the fossil-bearing deposits associated with the Dart and Hrdlička pinnacles have been interpreted as the mined remnants of cave sediments that formed within the Plio-Pleistocene Thabaseek Tufa: either as a younger cave-fill or as contemporaneous carapace caves. When combined with the Plio-Pleistocene dolomitic cave deposits from the "Cradle of Humankind," a rather restricted view emerges that South African early hominins derived from cave deposits, whereas those of east and central Africa are derived from fluvio-lacustrine and paleosol deposits. We undertook a sedimentological and paleomagnetic analysis of the pink-colored deposit (PCS) from which the "Taung Child" is purported to have derived and demonstrate that it is a calcrete, a carbonate-rich pedogenic sediment, which formed on the paleo-land surface. The deposit extends 100 s of meters laterally beyond the Dart and Hrdlička Pinnacles where it is interbedded with the Thabaseek Tufa, indicating multiple episodes of calcrete development and tufa growth. The presence of in situ rhizoconcretions and insect trace fossils (Celliforma sp. and Coprinisphaera sp.) and the distinctive carbonate microfabric confirm that the pink deposit is a pedogenic calcrete, not a calcified cave sediment. Paleomagnetic and stratigraphic evidence indicates that a second, reversed polarity, fossil-bearing deposit (YRSS) is a younger fissure-fill formed within a solutional cavity of the normal polarity tufa and pink calcrete (PCS). These observations have implications for the dating, environment, and taphonomy of the site, and increase the likelihood of future fossil discoveries within the Buxton-Norlim Limeworks. PMID:23633001

  6. Soil carbon in the arid and semi-arid tropics

    International Nuclear Information System (INIS)

    Soils in the arid and semi-arid tropics are often poor in soil organic matter (SOM) contents. On the other hand, calcretes and soils with calcic or petrocalcic horizons have a world-wide distribution and are regarded as important carbon reservoirs. For this reason, knowledge on their formation processes and the carbon source-sink relationship is necessary. An evaluation is made of the major models of calcrete formation using stable isotope techniques, especially on Tunisian soils. Normally, calcretes do not act as carbon sinks unless at least part of the calcium originates from weathering. However, in some cases they can change to carbon sources under anthropogenically altered environmental conditions when acids are precipitated. Desert losses are quite rich in carbonates and can form fertile soils, but good management practices and conservation efforts are required. These soils are usually poor in SOM contents and their carbon source-sink relationship depends on the way in which the soil is managed. Vertisols play an important role in soils of the semi-arid tropics. Despite their dark colour, they generally contain little organic carbon. Using stable isotope and radiocarbon methods it has been shown that carbon fixation takes place even over a few decades. Research experiments carried out on Vertisols in India have shown that the SOM decomposition rates can be influenced by the soil management practices. (author). 3 figs

  7. Evolution of subterranean diving beetles (Coleoptera: Dytiscidae: Hydroporini, Bidessini) in the arid zone of Australia.

    Science.gov (United States)

    Leys, Remko; Watts, Chris H S; Cooper, Steve J B; Humphreys, William F

    2003-12-01

    Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification. PMID:14761060

  8. Uraniferous surficial deposits

    International Nuclear Information System (INIS)

    As a result of the discovery of uranium in surficial deposits of Tertiary to Recent age, in Australia and Southern Africa, increasing attention is being paid to the location and understanding of the genesis of these deposits. The paper discusses the definitions and terminology currently in use and a classification of these deposits is presented. It is concluded that in order to obtain a measure of clarity, the terms calcrete, gypcrete and dolocrete should not be used to describe the uraniferous valley-fill deposits of Southern Africa and Australia

  9. International Uranium Resources Evaluation Project (IUREP) national favourability studies: People's Republic of Mongolia

    International Nuclear Information System (INIS)

    Mongolia, a country of 1,525,000 square kilometers, and a population of almost the same number of people is land locked between China and USSR. Historically it's closest ties have been with China, but it is now more closely associated with USSR. Geologically it's complex - most exposed formations are younger than PreCambrian although old exist. Potential for uranium is considered fairly good because the fairly complex geology appears to be favourable both for continental sandstone type deposits and calcretes (less than 50%) and vein type, and other deposits (more than 50$). Considerable effort should be made to obtain additional information related to Mongolian geology. (author)

  10. 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.

  11. Uranium ore deposits

    International Nuclear Information System (INIS)

    The main uranium deposits and occurrences in the Argentine Republic are described, considering, in principle, their geologic setting, the kind of 'model' of the mineralization and its possible origin, and describing the ore species present in each case. The main uraniferous accumulations of the country include the models of 'sandstong type', veintype and impregnation type. There are also other kinds of accumulations, as in calcrete, etc. The main uranium production has been registered in the provinces of Mendoza, Salta, La Rioja, Chubut, Cordoba and San Luis. In each case, the minerals present are mentioned, having been recognized 37 different species all over the country (M.E.L.)

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

    International Nuclear Information System (INIS)

    A full report has been compiled describing the findings of the International Uranium Resources Evaluation Project (IUREP) Orientation Phase Mission to Somalia. The Mission 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. (author)

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

    International Nuclear Information System (INIS)

    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

  14. U-Th-Pb systematics of some granitoids from the northeastern Yilgarn Block, Western Australia and implications for uranium source rock potential

    International Nuclear Information System (INIS)

    The Mount Boreas-type granite and spatially associated syenitic granitoid of Western Australia yield Pb-Pb ages of 2370 +- 100 Ma and 2760 +- 210 Ma, respectively. Th-Pb ages, although less precise, are concordant with these ages, and therefore the apparent ages are interpreted to be the crystallisation ages for these two units. U-Pb ages are variable and for the most part anomalously old, which suggests a Cainozoic uranium loss. However, this loss is generally small (3μg/g); therefore, neither granitoid in its fresh state provides a good source for nearby calcrete-hosted uranium deposits. The possibility remains that the Mount Boreas-type granite that has been completely weathered during the Tertiary could have been a source for the calcrete-type uranium deposits in W.A. Although the Mount Boreas-type granite is highly fractionated, it does not bear a strong geochemical imprint of a sedimentary precursor. This feature contrasts it with apparently fresh granitoids from other parts of the world that have lost large amounts of uranium (approx. 20μg/g) and are associated with large roll-type and other low temperature-type uranium deposits

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

    International Nuclear Information System (INIS)

    A report has recently been made public which describes the findings of the International Uranium Resources Evaluation Project (IUREP) Mission to Madagascar. The IUREP Orientation Phase Mission to Madagascar estimates the Speculative Resources of that country to be within the wide range of 4 000 to 38 000 tonnes uranium. Such resources could lie in areas with known occurrences (uranothorianite, Ft. Dauphin up to 5 000 t U, i.e. 'pegmatoids'; uranocircite, Antsirabe up to 3 000 t U in Neogene sediments; carnotiteautonite, Karoo area up to 30 000 t U in sandstones and in areas with as yet untested environments (e.g. related to unconformities and calcretes). Modifications to existing uranium exploration programmes are suggested and policy alternatives reviewed. No specific budget is proposed. (author)

  16. 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.

  17. 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)

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

    International Nuclear Information System (INIS)

    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

  19. 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

  20. International Uranium Resources Evaluation Project (IUREP) orientation phase mission summary report: Peru

    International Nuclear Information System (INIS)

    A report has recently been published which describes the findings of the International Uranium Resources Evaluation Project (TUREP) Mission to Peru. The IUREP Orientation Phase Mission to Peru estimates that the Speculative Resources of that country fall within the range of 6 000 to 11 000 tonnes uranium. The majority of this potential is expected to be located in Late Tertiary ignimbrites and associated sediments in the high Andes of southern Peru. Other favourable geological environments include calcretes, developed from Tertiary volcanogenic sources over the Precambrian in the Pacific Coastal desert in southern Peru, and Hercynian subvolcanic granites in the eastern Cordillera of southern Peru. The Mission recommends that over a period of five years approximately U.S. $10 million be spent on exploration in Peru. The majority of this would be spent on drilling ($5 million) and tunnelling ($2 million) with an additional $3 million on surface and airborne radiometric surveys. (author)

  1. 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)

  2. 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

  3. 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.

  4. 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

  5. Ore-processing technology and the uranium supply outlook

    International Nuclear Information System (INIS)

    The subject is covered in sections, as follows: the resource base (uranium content of rocks, regional distribution of Western World uranium); ore types (distribution of Western World uranium, by ore types, response to ore-processing); constraints on expansion in traditional uranium areas (defined for this paper as the sandstone deposits of the U.S.A. and the quartz-pebble conglomerates of the Witwatersrand and Elliot Bay areas, all other deposits being referred to as new uranium areas). Sections then follow dealing in detail with the processing of deposits in U.S.A., South Africa, Canada, Niger, Australia, South West Africa, Greenland. More general sections follow on: shale, lignite and coal deposits, calcrete deposits. Finally, there are sections on: uranium as a by-product; uranium from very low-grade resources; constraints on expansion rate for production facilities. (U.K.)

  6. Uranium occurrences in the Gordonia and Kuruman districts

    International Nuclear Information System (INIS)

    This report highlights uranium occurrences discovered by the author in the Kuruman and Gordonia Districts. These discoveries are the result of follow-up work of the regional geological, hydrological and hydrochemical studies of the area, undertaken by the Geology Division of the Atomic Energy Board since 1974. A surficial uranium deposit was discovered on the farm Rus en Vrede in the Kuruman District, at the junction of a palaeo-river with the Kuruman River. Uranium occurs in carbonaceous diatomaceous earth, with surface samples assaying up to 308 ppm U3O8. As uranium is also present in calcrete 18 km south of this deposit, there is a distinct possibility that significant surficial deposits may occur under the Kalahari sand cover in this area. In the Gordonia District an interesting discovery was made on the farm Tsongnapan where four boreholes, drilled for water, intersected radioactive bands in the Dwyka Tillite Formation. These rocks, which outcrop in the northeast corner of the Tsongnapan, also proved to be radioactive. Some 35 km to the east of this occurrence, borehole logging indicated the existence of an anomalous zone near the base of the Dwyka. In some of these boreholes uranium anomalies were also found in the calcrete and gravel of the Kalahari Formation. It is evident, therefore, that the Gordonia District has the potential of becoming an economically important uranium province. A radiometric ground survey of one of the pans indicated that wind and water action is possibly responsible for the local dispersion and segregation of radioactive minerals

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. Formación de sepiolita-paligorskita en litofacies lutítico-carbonáticas en el sector de Borox-Esquivias (cuenca de Madrid

    Directory of Open Access Journals (Sweden)

    Leguey, S.

    1988-04-01

    Full Text Available According to lithological composition three units were stablished in the area studied: a Clayey unit. Green and pinkish clays with sandy beds and early formation of calcretes. Clay minerals association: smectite-mixed-layers (kerolite-stevensite sepiolite-illite-kaolinite. b Clayey calcareous unit Green clays with calcretes and a sandy level at bottom of the unit. Clay minerals association: smectite-illite-palygorskite-sepiolite-kaolinite. c Clayey-dolomitic unit. Green clays with dolomicrites. Clay minerals association: smectiteillite-palygorskite-sepiolite. Results let us to stablish a sepiolite and palygorskite genesis related to lacustrine paludine environments where pedodiagenetic processes (v.s. carbonation, dolomitization, silicification, vertic features were responsible of smectite instability, with development of palygorskite or sepiolite, according to their respectively di or triocthedral character.En el área estudiada, desde un punto de vista litológico se han diferenciado tres tramos: a Lutítico. Lutitas verdes y rosáceas con intercalaciones samíticas e incipiente desarrollo de calcretas. la asociación de minerales de la arcilla es: esmectita-interestratificados (kerolitaestevensita-sepiolita-illita-caolinita. b Lutítico-calcáreo. Lutitas verdes y calcretas con un nivel samítico en la base del tramo. La asociación de minerales de la arcil1a es: esmectita-illita-paligorskita-sepiolita-eaolinita. c Lutítico-dolomítico. Lutitas verdes y dolomicritas. La asociación de minerales de la arcilla es: esmectita-illita-paligorskita-sepiolita. Los resultados permiten establecer una génesis de sepiolita y paligorskita en relación con ambientes lacustres-palustres, donde los procesos edafodiagenéticos (carbonatación, dolomitización, silicificación, vertisolización provocan la desestabilización de fases esmectíticas precursoras. De acuerdo con el carácter di o trioctaédrico de la esmectita se propicia la formación de

  12. 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.

  13. 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.

  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. On the Sources of Salinity in Groundwater under Plain Areas. Insights from δ18O, δ2H and Hydrochemistry in the Azul River Basin, Argentina

    International Nuclear Information System (INIS)

    The Azul River basin, with some 6200 km2, is located in the plains of Buenos Aires Province, Argentina. The Azul River flows along 160 km from the Tandilia Range, in the SW, to the Channel 11, in the NE. Average annual precipitation is 1005 mm (1988-2000); mean reference evapotranspiration is 1090 mm. The geology consists of Miocene to recent sediments, mostly sands and silts with some clay and calcrete layers, overlying crystalline rocks and marine sediments. The water table is shallow and groundwater in the aquifer upper 30 m displays an increasing salinity from SW to NE. The previous hypothesis to explain the salinity was infiltration of evapo-concentrated surface water, as the small soil slope in the northern basin (< 0.2%) induces rainfall accumulation in lowlands, where water evaporates prior to infiltration. But recent chemical and isotopic data reveal two salinity sources: evaporation of recent recharge water, and mixing with old saline groundwater of yet unknown origin. (author)

  16. The geology of the Kalahari Gemsbok National Park

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    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. 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.

  18. 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)

  19. 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.

  20. 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

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

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    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.

  2. 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

  3. Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits

    Science.gov (United States)

    Uvarova, Yulia A.; Kyser, T. Kurt; Geagea, Majdi Lahd; Chipley, Don

    2014-12-01

    Variations in 238U/235U and 234U/238U ratios were measured in uranium minerals from a spectrum of uranium deposit types, as well as diagenetic phosphates in uranium-rich basins and peraluminous rhyolites and associated autunite mineralisation from Macusani Meseta, Peru. Mean δ238U values of uranium minerals relative to NBL CRM 112-A are 0.02‰ for metasomatic deposits, 0.16‰ for intrusive, 0.18‰ for calcrete, 0.18‰ for volcanic, 0.29‰ for quartz-pebble conglomerate, 0.29‰ for sandstone-hosted, 0.44‰ for unconformity-type, and 0.56‰ for vein, with a total range in δ238U values from -0.30‰ to 1.52‰. Uranium mineralisation associated with igneous systems, including low-temperature calcretes that are sourced from U-rich minerals in igneous systems, have low δ238U values of ca. 0.1‰, near those of their igneous sources, whereas uranium minerals in basin-hosted deposits have higher and more variable values. High-grade unconformity-related deposits have δ238U values around 0.2‰, whereas lower grade unconformity-type deposits in the Athabasca, Kombolgie and Otish basins have higher δ238U values. The δ234U values for most samples are around 0‰, in secular equilibrium, but some samples have δ234U values much lower or higher than 0‰ associated with addition or removal of 234U during the past 2.5 Ma. These δ238U and δ234U values suggest that there are at least two different mechanisms responsible for 238U/235U and 234U/238U variations. The 234U/238U disequilibria ratios indicate recent fluid interaction with the uranium minerals and preferential migration of 234U. Fractionation between 235U and 238U is a result of nuclear-field effects with enrichment of 238U in the reduced insoluble species (mostly UO2) and 235U in oxidised mobile species as uranyl ion, UO22+, and its complexes. Therefore, isotopic fractionation effects should be reflected in 238U/235U ratios in uranium ore minerals formed either by reduction of uranium to UO2 or chemical

  4. Estratigrafía y paleoambientes de la Formación Los Llanos (La Rioja: una secuencia condensada Miocena en el antepaís fragmentado andino central Stratigraphy and paleoenvironments of Los Lanos Formation (La Rioja: A condensed sequence in the broken foreland of the Central Andes

    Directory of Open Access Journals (Sweden)

    M. Ezpeleta

    2006-06-01

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

  5. 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

  6. 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

  7. 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.

  8. Metre-scale cyclicity in Permian ramp carbonates of equatorial Pangea (Venezuelan Andes): Implications for sedimentation under tropical Pangea conditions

    Science.gov (United States)

    Laya, Juan Carlos; Tucker, Maurice E.; Perez-Huerta, Alberto

    2013-06-01

    Palmarito strata in the mid-Permian of the Venezuelan Andes show three different types of metre-scale cycle: Type A cycles are mixed clastic-carbonate, shallowing-upward peritidal cycles. The upper boundaries of the cycles are exposure surfaces with calcrete. This kind of cycle shows a significant degree of randomness in its thickness pattern and this is attributed to an autocyclic origin through tidal-flat progradation, and variations in carbonate productivity and clastic input to the depositional area. Type B cycles consist entirely of shallow subtidal facies with a shallowing-upward arrangement and an alternation between heterozoan and photozoan assemblages. Type C cycles were deposited in a middle to outer ramp setting and are characterized by a heterozoan assemblage and shallowing-upward trends that includes spiculitic wackestone-packstone passing up into neomorphic bioclastic wackestone or bioclastic crinoidal-bryozoan wackestone-packstone. All cycles are interpreted as 4th-5th order (104 to 105 years duration) and some can be linked to Milankovitch orbital rhythms, notably short eccentricity (~ 100,000 years). Overall, the origin of the Palmarito cycles was a complex combination of autocyclic and allocyclic controls; however, the evidence suggests that cycles in the lower part of the succession were dominated more by autocyclic processes whereas those in the upper part were more the result of allocyclic controls. Climate-driven processes, such as migration of the intertropical convergence one and the waxing and waning of polar ice-caps, had significant effects on deposition of the Palmarito succession and the cycles therein, controlling the clastic sediment supply, nutrient availability and thus carbonate production, and sea-level change, and these factors determined the vertical stacking pattern of the cycles.

  9. 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.

  10. 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.

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

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    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.

  12. 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

  13. 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

  14. Palaeoclimate reconstructions from lacustrine terraces and lake-balance modeling in the southern central Andes: New insights from Salar de Pocitos (Salta Province, Argentina)

    Science.gov (United States)

    Bekeschus, Benjamin; Bookhagen, Bodo; Strecker, Manfred R.; Freymark, Jessica; Eckelmann, Felix; Alonso, Ricardo

    2013-04-01

    The arid Puna Plateau in the southern central Andes of NW-Argentina constitutes the southern part of Earth's second largest orogenic plateau. Numerous internally drained basins are restricted by ranges that peak 5-6 km above sea level, creating a compressional basin and range morphology. The conspiring effects of this structurally controlled topography and the high degree of aridity have resulted in low stream power of the fluvial network and internally drained basins. A steep rainfall gradient exists across this area ranging from a humid Andean foreland (>1m/yr annual rainfall) to progressively drier areas westwards. At the present-day, the interior of the plateau is widely characterized by Salar de Pocitos (24.5°S, 67°W, 3650 m asl) records repeated former lake highstands. This intermontane basin has existed since the late Tertiary, constituting a 435 km² salt flat in the region of Salta, NW Argentina. Comparison with palaeoclimate records from the neighboring Salar de Atacama suggests that the terrace systems at Salar de Pocitos were formed during the Late Pleistocene and early Holocene. Here we report on our preliminary results of the extent of several terrace generations in this region. We mapped terraces in the field and on satellite images and determined their elevations during a high-resolution DGPS field survey. Our analysis reveals 3-4 distinct terrace levels associated with individual lake-level highstands. However, basin-wide correlation is difficult due to ongoing tectonism and differential tilting of the basin. The highest lake terrace, ca. 25 m above modern base level, locally comprises a calcrete horizon, which provided a 14C age of 40.180 (+1420/-1200) yr BP, which may coincide with a protracted highstand in other basins in the Puna and the Bolivian Altiplano. If the extent of this pronounced terrace is used for volumetric calculations, the corresponding former water body involved 8 km³. To reconstruct palaeoenvironmental conditions and the

  15. 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.

  16. A probable martian analogue in muttom in southern india

    Science.gov (United States)

    Wankhede, Tushar; Rajesh, V. J.; Charri, Abhishek

    2012-07-01

    Mars, a terrestrial planet fourth from the Sun in the solar system, is widely known as the red planet. The iron oxide sand/dust is predominant on its surface and gives the reddish appearance. Recent explorations have exposed abundance of haematite-rich loose materials in the surface of Mars especially at Meridiani Planum. Sedimentary structures like bedding, cross-bedding, ripple marks, gullies, mud cracks etc. are identified in this area. It is essential to look for some terrestrial analogues for the iron oxide rich sand/dust in order to explore their genetic mechanisms in Martian surface. Red sand beds occur above the crystalline basement or younger calcareous sandstone/limestone as isolated patches of partly indurated or unindurated dunes and sheets fringing the south western coastal lands of Tamil Nadu. Calcretes, source of carbonates, also occur at places within these red sand beds. Muttom soils are dark red in color on fresh surfaces. The red sand beds are dominated by iron-bearing minerals such as hematite and ilmenite. Local patches of heavy mineral deposition by the action of wind and water were also observed in the Muttom area. Preliminary spectral analyses confirmed the presence of iron bearing minerals like hematite and ilmenite which are also present in Mars. Many sedimentary structures like gullies, channels, polygonal mud cracks, erosion pits and dunes were present in Muttom area similar to those observed on Martian surface. Meridiani planum outcrops are composed of some siliciclastics grains, and hematite, and only few deposits on Earth match this description. The siliciclastics grains are primarily quartz grain coated with hematite. Quartz is also found in Muttom which, may have been transported by the action of wind while in the Mars siliciclastics is the alteration product of basalt. The structures are more or less similar to those observed at Meridiani Planum. Previous workers interpreted these red sands as `unique' formed either by a mixed

  17. 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

  18. 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

  19. 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

  20. 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 (High 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

  1. 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

  2. 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

  3. 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.

  4. Diagenetic origin of ironstone crusts in the Lower Cenomanian Bahariya Formation, Bahariya Depression, Western Desert, Egypt

    Science.gov (United States)

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

    2015-01-01

    In this paper, a new interpretation of the ironstone crusts of the Bahariya Formation as late diagenetic products is provided. The siliciclastic Lower Cenomanian Bahariya Formation outcropping in the northern part of the Bahariya Depression (Western Desert, Egypt) is subdivided into three informal units that are mainly composed of thinly laminated siltstone, cross-bedded and massive sandstone, fossiliferous sandstone/sandy limestone and variegated shale. Abundant ironstone crusts occur preferentially within its lower and upper units but are absent in the middle unit. The ironstone crusts show selective replacement of carbonate components, including calcretes, by iron oxyhydroxides. More permeable parts of the terrigenous beds such as burrow traces, subaerial exposure surfaces, concretionary features and soft-sediment deformation structures led to heterogeneous distribution of the iron oxyhydroxides. A variety of diagenetic minerals, where goethite and hematite are the main end-products, were characterized by mineralogical analysis (XRD), petrography and SEM observation, and geochemical determinations (EMPA). Other diagenetic minerals include Fe-dolomite/ankerite, siderite, manganese minerals, barite, silica, illite/smectite mixed-layer, and bitumen. These minerals are interpreted to be formed in different diagenetic stages. Some minerals, especially those formed during eodiagenesis, show features indicative of biogenic activity. During burial, dolomite and ankerite replaced preferentially the depositional carbonates and infilled secondary porosity as well. Also during mesodiagenesis, the decomposition of organic matter resulted in the formation of bitumen and created reducing conditions favorable for the mobilization of iron-rich fluids in divalent stage. Telodiagenesis of the Cenomanian Bahariya deposits took place during the Turonian-Santonian uplift of the region. This resulted in partial or total dissolution of Fe-dolomite and ankerite which was concomitant to

  5. Discovery of kimberlite in a magnetically noisy environment: a case study of the Syferfontein and Goedgevonden kimberlites (Invited)

    Science.gov (United States)

    Webb, S. J.; Van Buren, R.

    2013-12-01

    pipes have significant responses on the DIGHEM system. The HELITEM, helicopter borne time domain EM system also clearly mapped both pipes as did the TEMPEST time domain system from a fixed wing platform. Although there are other EM anomalies in the area, these are easily associated with dykes in the area based on joint interpretation with the aeromagnetic data. The lack of kimberlite exploration in this region is likely due to the lack of alluvial diamonds, the magnetically noisy environment, and the well-developed ferricrete and calcrete layers on surface which trap and resorb heavy minerals such as garnet, traditionally used in soil sampling. In this challenging environment, airborne EM combined with magnetic and ground geophysical methods for ground truthing are viable exploration methods.

  6. 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

  7. 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

  8. Quaternary tectonic activity of the Carboneras Fault in the La Serrata range (SE Iberia): Geomorphological and chronological constraints

    Science.gov (United States)

    Moreno, Ximena; Masana, Eulàlia; Pallàs, Raimon; Gràcia, Eulàlia; Rodés, Ángel; Bordonau, Jaume

    2015-11-01

    The Eastern Betic Shear Zone (EBSZ) in Southern Iberia is known to accommodate part of the 4-5 mm/yr convergence between Africa and Iberia, but its seismic hazard is not sufficiently understood for an accurate risk assessment. One of the main structures of the EBSZ, the left-lateral 150 km-long Carboneras Fault, displays no clear instrumental and historical activity despite being morphologically expressive. Detailed geomorphological mapping, geochronological analysis, and structural observation on the La Serrata segment of the Carboneras Fault were designed to investigate its recent evolution. Quaternary sediments and geomorphic features were targeted and 42 new numerical ages were obtained based on 66 samples (thermoluminescence, U-series, 14C, 10Be). The chronological framework of La Serrata was constructed by combining these numerical ages with a conceptual model previously developed in the region, which assumes that alluvial fan aggradation was produced during cold and dry periods (glacials and stadials), whereas stability and phases of calcrete formation were favored during warm and wetter periods (interglacials and interstadials). The spatial distribution of dated alluvial fans suggests an early phase of uplift that probably occurred between 1 Ma and 56.6 ka in the northeastern portion of the study area, whereas in the southwest sector the main uplift phase occurred later than 110.3 ka. A decline in fault activity would have taken place after 30.8 ka. Vertically offset dated units indicate minimum dip-slip rates of 0.05 mm/yr and 0.18 mm/yr, averaged for the last 1 Ma and the last 110.3 ka, respectively. Deflected channels and associated dated units yield a minimum left-lateral strike-slip rate of 1.31 mm/yr, averaged for the last 110.3 ka. The most recent fault movement of the fault could be younger than AD 637. Our results suggest therefore that the Carboneras Fault is among the fastest in Iberia, and should be considered in future hazard analyses.

  9. Los depósitos aluviales del paleógeno basal en el sector suroriental de la Cuenca del Duero (provincia de Segovia: evolución y minerales de la arcilla característicos

    Directory of Open Access Journals (Sweden)

    Garzón, M. G.

    1989-04-01

    Full Text Available This paper deals with the detritic facies which represents the prearcosic cycle and the lowermost part of the arcosic cycle (Paleogene in age outcropping in the southeastern margin of the Duero Basin. On the basis of geological mapping and lithological correlation, four lithostratigraphic units, which also presents different clay minerals associations, have been distinguished: Unit T.1.1., composed by clays and quartzose sands, in which the c1ay mineral association is illite + kaolinite; unit T.1.2., of quartzose sands with ferruginous paleosoils, with smectite as the main clay mineral; unit T.2.1., of polimictic conglomerates, arcosic sands and clays, with frequent calcrete profiles and palygorskite is the most abundant mineral; unit T.2.2., composed by arcosic sands with duricrust levels resembling those of the previous unit, and with smectite and illite as the main clay minerals. The first and second units are transitional and they keep a genetic relationship corresponding lo a «First Depositional Sequence», which is large scale coarsening upwards and represents a prograding evolution from a distal braided system (T.1.1. to a proximal one (T.1.2. of humid alluvial fans. Units T.2.1. and T.2.2. belong to a «Second Depositional Sequence», which is large scale fining and reflects the transition from proximal (T.2.1. to medial (T.2.2. parts of arid to semiarid alluvial fans. From the mineralogical and sedimentological study it may be concluded that, during the deposits of these materials, an important climatic change took place. During the sedimentation of T.1.1., climate was warm and wet producing a clay mineral association (illite + kaolinite tipical of well drained areas. Unit T.1.2. represents a more arid climate with seasonal fluctuations and long dry periods, yielding smectite as the main clay mineral. Nevertheless, the more drastic change towards arid conditions took place during the sedimentation of the «Second Depositional

  10. Late cretaceous continental deposits in Romania: mineralogical and stable isotope investigations

    International Nuclear Information System (INIS)

    values vary from -143 to -166 0/00 (SMOW). Also for the Hateg basin, measurements on the isotopic composition of the rainwater have been started in August 2006. The calcretes show a narrow range of isotopic compositions, with δ8O values between 24.1 and 25 0/00 and δ13C between 8.1 and -8.9 0/00 (PDB) Using appropriate fractionation factors, the isotopic data indicate that the smectite are in equilibrium with the local present meteoric water line. This fact was also put in evidence by early workers. In contrast, the stable isotopic composition of calcretes are preserved reflecting in precipitation regime and/or temperature at the time of late Cretaceous. (author)

  11. 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

  12. 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

  13. 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

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

    International Nuclear Information System (INIS)

    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

  15. Shrub patterns and surface hydrological fluxes in a semiarid hillslope

    Science.gov (United States)

    Svoray, Tal; Sela, Shai; Assouline, Shmuel

    2010-05-01

    Climate-vegetation interactions and feedbacks are the subject of many studies and recently, the rainfall-plant-soil interplay in the hillslope scale is in the foci of ecohydrology. As most of the models in this scale rely on synthetic environments, there is a need for studies that use remotely sensed and in-situ data to examine the effect of hillslope hydrological processes on ecosystem functioning and plant population spread in a more realistic manner. A major problem is the difficulty encountered in simulating water budget and measuring vegetation at the individual level. In this research, a typical hillslope was chosen offering variations in slope decline and orientation, soil depth and vegetation cover, at the LTER Lehavim site in the center of Israel (31020' N, 34045' E). The annual rainfall is 290 mm, the soils are brown lithosols and arid brown loess and the dominant rock formations are Eocenean limestone and chalk with patches of calcrete. The vegetation is characterized by scattered dwarf shrubs (dominant species Sarcopoterium spinosum) and patches of herbaceous vegetation, mostly annuals, are spread between rocks and dwarf shrubs. Eight areal photographs of the slope, between the years 1978-2005, were acquired, georeferenced and shrub cover was estimated based on supervised classification of the airphotos. An extensive spatial database of soil hydraulic and environmental parameters (e.g. slope, radiation, bulk density, soil depth) was measured in the field and interpolated to continuous maps using geostatistical techniques and physically-based modeling. This spatio-temporal database was used to characterize 1187 spatial cells serving as an input to a numeric hydrological model (Hydrus 1D) solving the flow equations to predict soil water content at the single storm and seasonal scales. The model was verified by sampling soil moisture at 63 random locations at the research site, during three consecutive storms in the 2008-09 rainy seasons. The results show

  16. Spatiotemporal evolution of water content at the rainfall-event scale under soil surface sealing conditions

    Science.gov (United States)

    Sela, S.; Svoray, T.; Assouline, S.

    2012-04-01

    Surface water content dynamics rules the partitioning between infiltration, runoff, and evaporation fluxes. Extending the knowledge on factors controlling top-soil water content temporal stability (TS) is needed to calibrate and validate various remote sensing technologies. Spatiotemporal evolution of water content is highly non-linear, being affected by various factors at different spatial and temporal scales. In semi-arid climates, this evolution is significantly affected by the formation of surface seals, shown in previous studies to significantly reduce both infiltration and evaporation fluxes from the soil. The drying regime in a natural sealed soil system exerts a sharp contrast in the soil profile - a very dry seal is superimposed on top of a wetter soil layer. One question is thus, whether seal layers contribute to or destroy temporal stability of top soil water content at the hillslope scale. To address this question, a typical hillslope (0.115 km2) was chosen at the LTER Lehavim site in the south of Israel (31020' N, 34045' E) offering different aspects and a classic geomorphologic banding. The annual rainfall is 297 mm, the soils are brown lithosols and arid brown loess and the dominant rock formations are Eocenean limestone and chalk with patches of calcrete. The vegetation is characterised by scattered dwarf shrubs (dominant species Sarcopoterium spinosum) and patches of herbaceous vegetation, mostly annuals, are spread between rocks and dwarf shrubs. An extensive spatial database of soil hydraulic and environmental parameters (e.g. slope, radiation, bulk density) was measured in the field and interpolated to continuous maps using geostatistical techniques and physically based modelling. To explore the effect of soil surface sealing, Mualem and Assouline [1989] model describing the change in hydraulic parameters resulting from soil seal formation were applied. This spatio-temporal database was used to characterise 8240 spatial cells (3X3m2) serving as

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

    Science.gov (United States)

    Sela, Shai; Svoray, Tal; Assouline, Shmuel

    2010-05-01

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

  18. Stable isotopic composition of soil calcite (O, C) and gypsum (S) overlying Cu deposits in the Atacama Desert, Chile: Implications for mineral exploration, salt sources, and paleoenvironmental reconstruction

    International Nuclear Information System (INIS)

    atmospheric CO2. At the Spence deposit, soils only rarely contain sufficient SO4 for S isotope analysis; the SO4-bearing soils occur only above the fracture zones in the gravel. Results are uniform (3.7–4.9‰ δ34SCDT), which is near the middle of the range for SO4 in groundwater (0.9–7.3‰). Sulfur in soils at the Gaby Sur deposit (3.8–6.1‰ δ34SCDT) is dominated by gypsum, which primarily occurs on the flanks and tops of hills, suggesting deposition from SO4-rich fogs. Sulfate in Gaby Sur deposit gypsum is possibly derived by condensation of airborne SO4 from volcanic SO2 from the nearby Andes. At the Gaby Sur deposit and Tamarugal anomaly, pedogenic stable isotopes cannot distinguish between S from porphyry or redeposited SO4 from interior salars. The three sites studied have had different histories of salt accumulation and display variable influence of groundwater, which is interpreted to have been forced to the surface during earthquakes. The clear accumulation of salts associated with fractures at the Spence deposit, and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process. The interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism

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

    Directory of Open Access Journals (Sweden)

    Alonso, M.

    1986-06-01

    Full Text Available Lateral and vertical variations of middle Miocene lithofacies (Lower and Intermediate Units of the Miocene of the Madrid Basin have been analyzed in the Paracuellos de Jarama area, near Madrid. A complete transition from medial to distal alluvial fan facies and palustrinelshaltow 1acustrine deposits can be observed. This sedimentary evolution is inferred from the detailed sedimentological. analysis carried out in each of the previously defined lithostratigraphic units: a1 Green shale and dolomite Unit, a2 Brown clays, arkosic and carbonate Unit; these two units are linked together into a Lower Group. b Coarse Arkosic Unit (Upper Group. Facies relationsbips within the Lower Group show a lateral change pattern between alluvial fan deposits, and palustrine deposits. Also the former ones gradually prograde over the palustrine deposits, as deduced from vertical evolution in the southernmost parts of the area. Upper Group represents a sudden progradation of the alluvial fan systems, that extensively overlie the distal facies observed in the Lower Group.
    Wide development of calcretes, sepiolite deposits, and nodular chert is an outstanding feature in the most distal parts of the alluvial fan bodies. They are studied in some detail provided the scarcity of well described examples of facies relationships in the kinds of deposits.

    Se estudia en este trabajo la variación lateral y vertical de las litofacies del Mioceno medio (Unidades Inferior e Intermedia en el área de Paracuellos de Jarama, próxima a Madrid, quedando representada en este área una transición completa entre depósitos de facies medias de abenícos aluviales y depósitos de ámbitos palustres. Estas conclusiones se extraen a partir del análisis sedimentológico realizado en cada una de las unidades previamente definidas: a Unidad de arcillas verdes y carbonatos y Unidad de arcillas pardas, arcillas y carbonatos en el Conjunto Inferior; b Unidad de

  20. 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)

  1. 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

  2. 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

  3. Mesozoic climates: General circulation models and the rock record

    Science.gov (United States)

    Sellwood, Bruce W.; Valdes, Paul J.

    2006-08-01

    more, giving more atmospheric humidity and a greatly enhanced hydrological cycle. Much of the rainfall was predominantly convective in character, often focused over the oceans and leaving major desert expanses on the continental areas. Polar ice sheets are unlikely to have been present because of the high summer temperatures achieved. The model indicates extensive sea ice in the nearly enclosed Arctic seaway through a large portion of the year during the late Cretaceous, and the possibility of sea ice in adjacent parts of the Midwest Seaway over North America. The Triassic world was a predominantly warm world, the model output for evaporation and precipitation conforming well with the known distributions of evaporites, calcretes and other climatically sensitive facies for that time. The message from the geological record is clear. Through the Phanerozoic, Earth's climate has changed significantly, both on a variety of time scales and over a range of climatic states, usually baldly referred to as "greenhouse" and "icehouse", although these terms disguise more subtle states between these extremes. Any notion that the climate can remain constant for the convenience of one species of anthropoid is a delusion (although the recent rate of climatic change is exceptional).

  4. 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

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

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

    2005-07-01

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

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

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    F.M. Dávila

    2005-03-01

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

  7. Litología y Génesis de los depósitos del Cenozoico tardío del Bajo del Durazno, provincia de La Pampa, Argentina Lithology and Genesis of Late Cenozoic Deposits of Bajo Del Durazno, La Pampa Province, Argentina

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    Adriana E. Mehl

    2007-12-01

    Bajo reproduce en una escala local la dinámica de un sistema de piedemonte, con sistemas de elevaciones de diferente altura relativa resultantes de ciclos de degradación-agradación. Los períodos de agradación, según sugieren los depósitos analizados, habrían estado vinculados con la acción de corrientes efímeras de baja sinuosidad de tipo entrelazado que transportaron sedimentos gravosos, arenosos y limosos desde los depósitos perimetrales del Bajo, producto del retroceso erosivo de los mismos.Bajo del Durazno (65°10' - 65°30'O y 36°33' - 36°45'S, Loventué Departament, Figs. 1 and 2 is a transitional landscape area between two major phisiographic subregions: Subregion of Hills and Meadows (Subregión de las Colinas y Lomas and Subregion of Plateaux and Valleys (Subregión de las Mesetas y Valles, which dominate the central-northeastern and middle-eastern part of La Pampa Province (INTA, 1980. At present Bajo del Durazno is a closed drainage system forming a minor geomorphic unit within a regional longitudinal depression, which together with several other depressions run across an extensive structural plain. These longitudinal depressions are known as Valles transversales (Calmels, 1996. This paper reports the sedimentary characteristics of the deposits outcropping in the western part of Bajo del Durazno (Fig. 1. A lithofacies analysis approach was followed to describe and interpret the sedimentary processes involved in the accumulation of the sediments, the environment and the source area of the deposits. The general purpose is to shed light on the geological evolution of the depression. Bajo del Durazno is excavated in reddish brown sandy silts capped by a calcrete crust (Cerro Azul Formation, late Miocene which outcrop along the southern and western margin of the depression (Figs.3 and 4. The deposits of Bajo del Durazno were studied in three main elevation systems of the western sector and the depression floor (Mehl y Zárate, 2006. The deposits

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

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    Michele Louise Francis

    2012-03-01

    Full Text Available

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