WorldWideScience

Sample records for calcretes

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

    International Nuclear Information System (INIS)

    Briot, P.

    1978-12-01

    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 [fr

  2. Uranium occurences in calcrete and associated sediments in Western Australia

    International Nuclear Information System (INIS)

    Butt, C.R.M.; Horwitz, R.C.; Mann, A.W.

    1977-10-01

    The report is a compilation of data pertaining to the occurence and distribution of uranium mineralization in calcretes and associated sediments in Western Australia and contains brief descriptions of many of the calcrete-uranium occurences, including some of the most minor. Virtually all calcretes in the region are liable to contain traces of uranium mineralization, visible as coatings of carnotite. The locations of the uranium occurences are shown on a map which features the distribution of calcrete

  3. The Yeelirrie calcrete uranium deposit, Western Australia

    International Nuclear Information System (INIS)

    Cameron, E.

    1984-01-01

    The Yeelirrie deposit, between Wiluna and Sandstone, lies in the Yilgarn block, in a catchment area of deeply weathered granites and greenstones. The host calcretes are a 1 to 1.5 km wide valley-fill in a long established drainage system, and are developed over a 85 km long distance. The calcretes are either earthy or procellaneous with voids. The deposit is sheetlike, some 9 km long and 5 to 1.5 km wide, averaging 3 m thick and is 4 to 8 meters below the surface, and immediately below the water table. The deposit has 52,500 tonnes of U 3 O 8 at an average grade of 0.15% U 3 O 8 . Carnotite is the only uranium mineral. Water movement in the area is largely subsurface in the calcrete, which is a good aquifer. Uranium concentrations of 100 to 450 ppb are found in the calcrete ground waters compared to background values of 5 to 10 ppb. (author)

  4. Possible variations on the calcrete-gypcrete uranium model

    International Nuclear Information System (INIS)

    Carlisle, D.

    1980-01-01

    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. Possible variations on the calcrete-gypcrete uranium model

    Energy Technology Data Exchange (ETDEWEB)

    Carlisle, D.

    1980-01-01

    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.

  6. Calcic soils and calcretes in the southwestern United States

    Science.gov (United States)

    Bachman, George Odell; Machette, Michael N.

    1977-01-01

    Secondary calcium carbonate of diverse origins, 'caliche' of many authors, is widespread in the southwestern United States. 'Caliche' includes various carbonates such as calcic soils and products of groundwater cementation. The term 'caliche' is generally avoided in this report in favor of such terms as calcrete, calcic soils, and pervasively cemented deposits. Criteria for the recognition of various types of calcrete of diverse origins include field relations and laboratory data. Calcic soils provide a comprehensive set of characteristics that aid in their recognition in the field. These characteristics include a distinctive morphology that is zoned horizontally and can frequently be traced over tens to hundreds of square kilometers. The major process in the formation of pedogenic calcrete and calic soils is the leaching of calcium carbonate from upper soil horizons by downward percolating soil solutions and reprecipitation of the carbonate in alluvial horizons near the base of the soil profile. The formation of pedogenic calcrete involves many factors including climate, source of carbonate, and tectonic stability of the geomorphic surface on which the calcrete is deposited. Most of the carbonate in pedogenic calcrete is probably derived from windblown sand, dust, and rain. Calcic soils and pedogenic calcretes follow a six-stage sequence morphologic development and is based on a classification devised by Gile, Peterson and Grossman in 1966. The .six morphologic stages of carbonate deposition in soils are related to the relative age of the soil and are as follows: I. The first or youngest stage includes filamentous or faint coatings of carbonate on detrital grains. II. The second stage includes pebble coatings which are continuous; firm carbonate nodules are few to common. III. The third stage includes coalesced nodules which occur in a friable or disseminated carbonate matrix. IV. The fourth stage includes platy, firmly cemented matrix which engulfs nodules

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

    International Nuclear Information System (INIS)

    Hema, A.; Navin, S.

    2004-06-01

    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 CaCO 3 . 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)

    Gaskin, A.J.; Butt, C.R.M.; Deutscher, R.L.; Horwitz, R.C.; Mann, A.W.

    1981-01-01

    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 U 3 O 8 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. Comparative analysis of the calcretization process in the Marilia formations (Bauru group - Brasil) and Mercedes ( Paysandu group - Uruguay), Upper Cretaceous of the Parana basin

    International Nuclear Information System (INIS)

    Veroslavsky, G.; Etchebehere, M.; Sad, A.; Fulfaro, J.

    1998-01-01

    Pedogenic and non-pedogenic calcrete facies are very common feature of Marilia (Brazil) and Mercedes (Uruguay) formations in the Parana Basin. The non-pedogenic ones constitute massive limestone facies that have been recently interpreted as groundwater calcretes. These limestones are exploited in both countries to supply raw materials to Portland cement and soil conditioner in origin and age of calcretization phenomena. In Uruguay, the calcretization process seens to be band formation. Field relationships and fossil assemblage point to a Paleocene (or later) age for the calcretization. In Brazilian territory, the groundwater calcretes aresupposed to be of Upper Cretaceous age due to the presence of dinosaurs scattered through the Bauru Group, including siliciclastic beds below and above the calcretes. The authors assume that calcretization processes are similar in both countries (host rocks, intensity, size, textures, geometries and economic potential). The main difference is in age of the calcretization. (author)

  11. Fake age hiatus in a loess section revealed by OSL dating of calcrete nodules

    Science.gov (United States)

    Zhang, Junjie; Li, Sheng-Hua; Sun, Jimin; Hao, Qingzhen

    2018-04-01

    Optically stimulated luminescence (OSL) dating on potassium feldspar has been performed with high resolution in the Luochuan section in the Chinese Loess Plateau. An age hiatus of ∼ 15 ka is found at the top of L2 layer within the loess/paleosol sequences. The age of the potassium feldspar from the calcrete nodules along the S1/L2 boundary is significantly older than those of the paleosol and loess samples lying above and below the boundary. The age overestimation of the potassium feldspar from calcrete nodules is caused by the underestimation of the dose rate, because accretion of carbonates could dilute the radioactivity. The age hiatus at the top of L2 also resulted from the underestimation of the dose rates of four loess samples beneath this hiatus. These four loess samples have high CaO concentrations. Ages of these samples are overestimated in the similar way as the nodules, but with smaller degrees. All results suggest that the accretion of carbonates happened after the loess deposition. The carbonate accretion process of the calcrete nodules has been simulated with accumulation models. The accretion can be as young as 46 ka, assuming the calcrete nodules formed rapidly at a certain time point. For slow and gradual accretion models, the carbonate started to accumulate slowly since the dust deposition and the accumulation became faster afterwards. The transition of the accretion rate may relate to the climate change or a change in the carbonate leaching and re-precipitation system.

  12. Inferences of paleoenvironment from petrographic, chemical and stable-isotope studies of calcretes and fracture calcites

    International Nuclear Information System (INIS)

    Vaniman, D.T.; Whelan, J.F.

    1994-01-01

    Past research has indicated a genetic connection between calcite formed in calcretes at the surface of Yucca Mountain, Nevada, and calcites deposited in underlying fractures of the unsaturated zone. This common genesis suggests that paleoenvironmental information, as well as the timing and pathways of past recharge episodes, might be obtained from studies of the deposits in both the calcretes and the unsaturated fractures. Chemical and isotopic modification of calcite-precipitating fluids appears to begin at the surface, largely under the influence of plant roots and their decay products. Chemical characteristics of the deeper calcites are either initiated or largely defined within the first few meters of fluid migration into the unsaturated tuffs beneath the calcretes. However, petrographic and isotopic data indicate a very unique low-δ 13 C microenvironment that is localized at the upper surfaces of the calcretes. These surfaces form an interface in the soil horizon where infiltration may pond above the underlying carbonate ''plug.'' In order to decipher the chemistry and petrology of past recharge events, it is important to first understand microenvironments such as this that contribute to mineral precipitation/dissolution events in the pedogenic environment

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

    International Nuclear Information System (INIS)

    Achyuthan, Hema; Shankar, Navin; Braida, Martina; Ahmed, S. Masood

    2010-12-01

    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, SiO 2 , Al 2 O 3 and Fe 2 O 3 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 (δ 18 O -3.39 to -5.84 per mille and δ 13 C -3.01 to -6.64 per mille), compared to the hardpan calcretes (δ 18 O -2.91 to -12.98 per mille ) and δ 13 C (-0.05 to -7.4 per mille). The palaeoenvironment during the formation of the calcretes nodules was dominated by the C 4 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)

  14. Mineralogy and origin of surficial uranium deposits hosted in travertine and calcrete from central Jordan

    International Nuclear Information System (INIS)

    Khoury, H.N.; Salameh, E.M.; Clark, I.D.

    2014-01-01

    Highlights: • Surficial uranium deposits are hosted in thick travertine and calcrete. • Tyuyamunite–strelkinite are the major components in central Jordan. • The leached water was enriched in redox sensitive U and V. • Deposition is related to unusual highly alkaline circulating water. - Abstract: Secondary uranium encrustations are hosted in thick travertine and calcrete deposits of Pleistocene–Recent age in central Jordan. The central Jordan varicolored marble and travertine are equivalent to the active metamorphic area in Maqarin, north Jordan. More than 100 samples were collected from the outcrops of the varicolored marble, travertine, calcrete, and the yellow uranium encrustations. The secondary yellow encrustations are mainly composed of uranyl vanadate complexes. Tyuyamunite Ca(UO 2 ) 2 V 2 5+ O 8 ·3(H 2 O)–strelkinite Na 2 (UO 2 ) 2 V 2 O 8 ·6(H 2 O) solid solution series are the major components and their composition reflects changes in the Ca/Na ratio in solution. Potentially, new vanadium free calcium uranate phases (restricted to the varicolored marble) were identified with CaO:UO 3 ratios different from the known mineral vorlanite (CaU 6+ )O 4 . Carbon and oxygen isotope data from calcite in the varicolored marble are characterized by Rayleigh-type enrichment in light isotopes associated with release of 13 C and 18 O enriched CO 2 by high temperature decarbonation during combustion of the bituminous marl. Stable isotope results from uranium hosted travertine and calcrete varieties exhibit a wide range in isotopic values, between decarbonated and normal sedimentary carbonate rocks. The depleted δ 13 C and δ 18 O values in the travertine are related to the kinetic reaction of atmospheric CO 2 with hyperalkaline Ca(OH) 2 water. The gradual enrichment of δ 13 C and δ 18 O values in the calcrete towards equilibrium with the surrounding environment is related to continuous evaporation during seasonal dry periods. Uranium mineralization in

  15. Chemical ore genesis models for the precipitation of carnotite in calcrete

    International Nuclear Information System (INIS)

    Mann, A.W.

    1974-10-01

    An investigation was carried out on the chemical mechanism responsible for the precipitation of carnotite in calcrete. The correct interpretation of uranium and vanadium movement in groundwater may only be possible after a careful and detailed evaluation of the occurrence (or non-occurrence) of many other uranium-vanadium complex salts, particularly those of calcium. It is concluded that a redox controlled mechanism for the precipitation of carnotite from groundwaters seem most likely. (R.L.)

  16. A non-pedological hypothesis for the processes of uranium mineralization in calcrete

    International Nuclear Information System (INIS)

    Briot, P.; Fuchs, Y.

    1984-01-01

    The non-pedological hypothesis presented for the origin of the uraniferous calcrete deposits in Western Australia is based on the premise that alluvial and calcareous lacustrine sediments were initially formed during earlier wet periods, evidence for which has been found in the fossil records. These were followed by subsequent epigenetic alteration accompanied by the precipitation of uranium mineralization during drier semi-arid periods. Typical examples of the processes involved were found in the Yeelirrie uranium deposit. During the latter semi-arid period, the limited surface flow which consisted of periodic flash flood conditions probably contributed marginally to the recharge of the groundwater, and consequently, semi-stagnant groundwater conditions evolved, particularly where the hydraulic gradient was extremely small, for example, for the Yeelirrie channel it is approximately 0.001. In addition, ponding of water behind a natural barrier caused the groundwater to evolve along the following geochemical sequence: mild alkalinity, weak oxidizing conditions, and oversaturation in dissolved elements. These hydrological and hydrogeochemical conditions induced the epigenetic alteration of the palustral/lacustrine limestone, bringing about dolomite neogenesis and the precipitation of carnotite. The source of the uranium in the calcretes and the groundwater of the Yeelirrie channel is considered to be the weathered outcrops of the breakaways along its margins. The genetic hypothesis proposed in this paper, although somewhat different from those described previously and elsewhere in this volume, could be applied to the other uranium-bearing calcretes in Mauritania, Namibia, and Somalia

  17. Assessment of undiscovered resources in calcrete uranium deposits, Southern High Plains region of Texas, New Mexico, and Oklahoma, 2017

    Science.gov (United States)

    Hall, Susan M.; Mihalasky, Mark J.; Van Gosen, Bradley S.

    2017-11-14

    The U.S. Geological Survey estimates a mean of 40 million pounds of in-place uranium oxide (U3O8) remaining as potential undiscovered resources in the Southern High Plains region of Texas, New Mexico, and Oklahoma. This estimate used a geology-based assessment method specific to calcrete uranium deposits.

  18. The discovery and character of Pleistocene calcrete uranium deposits in the Southern High Plains of west Texas, United States

    Science.gov (United States)

    Van Gosen, Bradley S.; Hall, Susan M.

    2017-12-18

    This report describes the discovery and geology of two near-surface uranium deposits within calcareous lacustrine strata of Pleistocene age in west Texas, United States. Calcrete uranium deposits have not been previously reported in the United States. The west Texas uranium deposits share characteristics with some calcrete uranium deposits in Western Australia—uranium-vanadium minerals hosted by nonpedogenic calcretes deposited in saline lacustrine environments.In the mid-1970s, Kerr-McGee Corporation conducted a regional uranium exploration program in the Southern High Plains province of the United States, which led to the discovery of two shallow uranium deposits (that were not publicly reported). With extensive drilling, Kerr-McGee delineated one deposit of about 2.1 million metric tons of ore with an average grade of 0.037 percent U3O8 and another deposit of about 0.93 million metric tons of ore averaging 0.047 percent U3O8.The west-Texas calcrete uranium-vanadium deposits occur in calcareous, fine-grained sediments interpreted to be deposited in saline lakes formed during dry interglacial periods of the Pleistocene. The lakes were associated with drainages upstream of a large Pleistocene lake. Age determinations of tephra in strata adjacent to one deposit indicate the host strata is middle Pleistocene in age.Examination of the uranium-vanadium mineralization by scanning-electron microscopy indicated at least two generations of uranium-vanadium deposition in the lacustrine strata identified as carnotite and a strontium-uranium-vanadium mineral. Preliminary uranium-series results indicate a two-component system in the host calcrete, with early lacustrine carbonate that was deposited (or recrystallized) about 190 kilo-annum, followed much later by carnotite-rich crusts and strontium-uranium-vanadium mineralization in the Holocene (about 5 kilo-annum). Differences in initial 234U/238U activity ratios indicate two separate, distinct fluid sources.

  19. Genesis principles for the precipitation of carnotite in calcrete drainages in western Australia

    International Nuclear Information System (INIS)

    Mann, A.W.; Deutscher, R.L.

    1978-01-01

    Carnotite, K;sub 2;(UO;sub 2;);sub 2;V;sub 2;O;sub 8;*3H;sub 2;O, is a potassium uranyl-vanadate which commonly occurs as a secondary accessory mineral around reduced uranium ore deposits. In recent years, however, carnotite has been recognized to be an important primary ore mineral in the calcreted drainage systems of the arid and semiarid portions of the Yilgarn Block in Western Australia. This paper describes some of the genetic principles which have been derived from a combined drainage-catchment and laboratory experimental study of the solution geochemistry of uranium and vanadium as it applies in particular to the drainage systems of semiarid and arid Western Australia

  20. Comparative analysis of the calcretization process in the Marilia formations (Bauru group - Brasil) and Mercedes ( Paysandu group - Uruguay), Upper Cretaceous of the Parana basin; Analisis comparativo de los procesos de calcretizacion en las Formaciones Marilia (Grupo Bauru-Brasil) y Mercedes (Grupo Paysandu-Uruguay), Cretacico Superior de la cuenca de Parana

    Energy Technology Data Exchange (ETDEWEB)

    Veroslavsky, G; Etchebehere, M; Sad, A; Fulfaro, J

    1998-07-01

    Pedogenic and non-pedogenic calcrete facies are very common feature of Marilia (Brazil) and Mercedes (Uruguay) formations in the Parana Basin. The non-pedogenic ones constitute massive limestone facies that have been recently interpreted as groundwater calcretes. These limestones are exploited in both countries to supply raw materials to Portland cement and soil conditioner in origin and age of calcretization phenomena. In Uruguay, the calcretization process seens to be band formation. Field relationships and fossil assemblage point to a Paleocene (or later) age for the calcretization. In Brazilian territory, the groundwater calcretes aresupposed to be of Upper Cretaceous age due to the presence of dinosaurs scattered through the Bauru Group, including siliciclastic beds below and above the calcretes. The authors assume that calcretization processes are similar in both countries (host rocks, intensity, size, textures, geometries and economic potential). The main difference is in age of the calcretization. (author)

  1. Silica and carbonate relationships in silcrete-calcrete intergrade duricrusts from the Kalahari of Botswana and Namibia

    Science.gov (United States)

    Nash, David J.; Shaw, Paul A.

    1998-07-01

    Silcrete-calcrete intergrade duricrusts (surface or near-surface chemically precipitated crusts with a cement comprising a mixture of silica and CaCO 3) have been widely identified in the geological, geomorphological and pedological literature, but have not, to date, been systematically described or classified. This paper presents a review of previous definitions of the end members of the silcrete-calcrete spectrum and subsequently identifies the major silica-carbonate relationships within intergrade types are identified on the the Kalahari of Botswana and Namibia. Three main intergrade types are identified on the basis of silica-carbonate associations: duricrusts where secondary silica occurs within a calcareous matrix; varieties where secondary carbonate occurs within a siliceous matrix; and materials where silica and carbonate matrix cements appear to have been precipitated contemporaneously or in close succession. Within each of these three groups, sub-types are identified dependent upon whether secondary materials have replaced or been emplaced within a pre-existing duricrust. Finally, a practical procedure for the simple definition of silcrete-calcrete intergrade duricrusts is suggested based upon a combination of bulk chemical and thin-section analyses.

  2. 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)

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

    1978-01-01

    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

  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)

    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)

  4. Regional setting, distribution and genesis of surficial uranium deposits in calcretes and associated sediments in Western Australia

    International Nuclear Information System (INIS)

    Butt, C.R.M.; Mann, A.W.; Horwitz, R.C.

    1984-01-01

    Surficial uranium deposits in Western Australia are largely in the Yilgarn Block in areas of Archean granitoids and greenstones, and in the Gascoyne Province in Proterozoic granites and gneisses. The region has had a long weathering history marked by continuous planation developing a regolith up to 100 metres thick. The distribution of calcrete type uranium deposits is controlled by geologic as well as weathering, erosion and climatic factors. Valley, playa and terrace deposits are recognized. The principal known surficial uranium deposit, Yeelirrie, occurs in the Yilgarn block as a valley deposit. (author)

  5. Stable isotope and 14C study of biogenic calcrete in a termite mound, Western Cape, South Africa, and its palaeoenvironmental significance

    Science.gov (United States)

    Potts, Alastair J.; Midgley, Jeremy J.; Harris, Chris

    2009-09-01

    Late Quaternary terrestrial climate records from the semi-arid zone of the Western Cape of South Africa are rare. However, palaeoenvironmental information may be inferred from ancient termite mounds of the region. Calcrete lenses in these mounds have δ 13C and δ 18O values that show systematic changes with radiocarbon dates, which range from 33,629-36,709 to 21,676-23,256 cal yr BP. These dates confirm that these heuweltjies had been present in the landscape since the last glacial period. The decrease in δ 13C and δ 18O from 33,629-36,709 to 21,676-23,256 cal yr BP indicates that climate information is recorded by the calcretes. It is suggested that a progressive decline in air temperature and an increase in moisture availability, and a decline in abundance of C 4 or CAM plants, occurred in the region during the time heuweltjie calcite precipitated.

  6. Paleosoils and pedogenic calcretes formations in Fray Bentos (Oligocene - early miocene) Raigon (late pliocene and middle pleistocene) and Libertad (early - middle pleistocene)

    International Nuclear Information System (INIS)

    Tofalo, O.; Morras, H.; Sanchez-Bettucci, L.

    2012-01-01

    The Fray Bentos formation is composed by loessic deposits based on paleosoils and pedogenic calcretes (Oligocene - early miocene). In this deposits are tubular and lamellar formations which would have been formed in arid climates.The fluvial origen of Raigon Formation, (late pliocene and middle pleistocene) presents a paleosoil roof which is generated under a subhumid climate.The Libertad Formation during the glacial intervals consisted of loess deposits

  7. Calcretes in the Thar desert: Genesis, chronology and ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    to Yaalon (1988) soils with secondary carbonate accumulations ..... The fraction over 500 µm constituted 6 to 8% of the sample and its absolute carbonate was less than 1%. .... However, if we take note of the uncertainty level of the estimate, an ...

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

    OpenAIRE

    TIWARI, DESIKAN RAMAKRISHNAN & KRISHNA CHANDRA

    2006-01-01

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

  9. 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.

    detrital/carbonate sands with thin heavy mineral laminations are found. Textural studies indicate that the detrital sands are derived from dunes. Drusy calcite and neomorphic calcite cements are associated with the sands. Sheet deposits contain coarse...

  10. Reguibat calcrete uranium project, Mauritania: Beneficiation upgrades and rapid leaching. A new paradigm for “calcrete” uranium projects?

    International Nuclear Information System (INIS)

    Beeson, Bob; Clifford, Neil; Goodall, Will

    2014-01-01

    Future of the project: • Scoping Study completed in the next two weeks; • Moving into Feasibility Studies: – Measured and Indicated resources; – Detailed beneficiation testing; – Leach testing of uranium concentrates; – Water drilling; – Commence process for Exploitation Permit. • Decision to mine in 12-18 months subject to funding; • Target production early 2017; • Convert known anomalies to achieve a 100Mlb uranium resource

  11. Surficial uranium occurrences in relation to climate and physical setting

    International Nuclear Information System (INIS)

    Carlisle, D.

    1984-01-01

    Important surficial chemogenic uranium deposits develop within 1) calcretes, 2) simple evaporative environments and 3) bogs or similar organic environments (''young'' uranium). Calcrete occurrences are the largest, most novel and most dependent upon extreme aridity and geomorphic stability. Economic calcrete deposits are nonpedogenic, resulting from near-surface groundwater transport and lateral concentration of uranium, vanadium, potassium, calcium, and magnesium rather than from ordinary soil-forming processes. Their genesis is essentially observable in Western Australia where carnotite-bearing nonpedogenic calcrete is currently forming under a unique aridic soil moisture regime and where major deposits have formed under similar climates during the last few thousand years. Rainfall is less than 250mm annually, only 1/12 to 1/20 of potential evaporation and concentrated almost entirely in episodic late summer storms. Outside this region, under less arid conditions, only pedogenic calcretes form and they do not contain economic uranium. In southern Africa, calcrete and gypcrete uranium deposits, although Late Tertiary to Quaternary in age, are also nonpedogenic and appear to have formed under similar climatic constraints with local variations in geomorphology and calcrete morphology. (author)

  12. Palaeopedogenic features and their palaeoclimatological significance for the nevremont formation (Lower Givetian), the Northern Ardennes, Belgium

    NARCIS (Netherlands)

    Molenaar, N.

    1984-01-01

    The lower member of the Nèvremont Formation is characterized by the frequent occurrence of pedogenic features, which suggest intermittent exposure of the fluvial depositional environment. The evidence for pedogenesis comprises horizons of calcite glaebules and nodular calcrete, haematite

  13. Definition and classification of surficial uranium deposits

    International Nuclear Information System (INIS)

    Toens, P.D.; Hambleton-Jones, B.B.

    1984-01-01

    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% CaCO 3 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)

  14. Lake Austin uranium deposit, Western Australia

    International Nuclear Information System (INIS)

    Heath, A.G.; Deutscher, R.L.; Butt, C.R.M.

    1984-01-01

    The Lake Austin uranium deposit is a calcrete type deposit in the Yilgarn Block, near Cue, in a catchment area of granitoids and greenstones. The uranium is in valley fill and the sediments of the Lake Austin playa. The mineralization occurs over 1 to 6 meter thickness close to the water table in calcrete overlying clays and/or weathered bedrock. The principal uranium mineral is carnotite. Waters in nearby channels have an uranium content of over 30 ppb. The chloride content of the water increases downstream in the nearby drainages, as does the uranium and vanadium content. (author)

  15. Growth form and seasonal variation in leaf gas exchange of Colophospermum mopane savanna trees in northwest Botswana

    NARCIS (Netherlands)

    Veenendaal, E.M.; Mantlana, K.B.; Pammenter, N.W.; Weber, P.; Huntsman-Mapila, P.; Lloyd, J.

    2008-01-01

    We investigated differences in physiological and morphological traits between the tall and short forms of mopane (Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Leonard) trees growing near Maun, Botswana on a Kalahari sandveld overlying an impermeable calcrete duricrust. We sought to determine if

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

    Science.gov (United States)

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

    2000-01-01

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

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

    International Nuclear Information System (INIS)

    Carlisle, D.

    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

  18. Bone-collecting habits of spotted hyaenas Crocuta crocuta in the ...

    African Journals Online (AJOL)

    An examination of 18 Crocuta crocuta dens in the Kruger. National Park, showed that this species can be responsible for bone assemblages at dens, more so at permanent sites such as granite or calcrete caves than at temporarily occupied aardvark holes or road culverts. Because of the facultative nature of ...

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

    NARCIS (Netherlands)

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

    2015-01-01

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

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

    International Nuclear Information System (INIS)

    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

  1. The Quaternary Environmental Change in the Northeast of Quintana Roo, Mexico:The Paleopedological Proxies

    Science.gov (United States)

    Cabadas Báez, H. V.; Sedov, S.; Solleiro Rebolledo, E.

    2010-03-01

    The Yucatán Peninsula, located in the southeast part of Mexico, is characterized to be an extended and low altitude platform constituted by calcareous rocks. These rocks are mainly limestones formed since Cretaceous under a marine shelf environment. In the northeast coast, the youngest sediments are found, as products of Quaternary sea level changes. We studied various profiles in quarries, following north-south transect in the Yucatan coast, near Cancún. In such profiles a sequence consisting of different kind of calcareous sediments and a soil in the surface were analyzed. The base of the sequence is constituted by a petrocalcic horizon (calcrete) that was formed during the last interglacial, 125,000 yrs. ago. Under the calcrete, a transgressive sequence appears with calcareous sediments of lagoon and reef facies. The uppermost part consists of dune-like sediments with crossed stratification overlied by another petrocalcic horizon, maybe formed during the Pleistocene-Holocene transition. Soils of the Yucatan Peninsula are very thin, rich in organic matter, neutral and well structured, and their image do not correspond to that found in tropical soils (deep, strongly weathered, leached). They are directly associated with the dune sediment dissolution because are infilling the "space" generated by rock dissolution. Calcrete is always in the uppermost part, but is broken and crossed by soil. This sequence reveals some aspects of the environmental dynamic during Late Pleistocene-Holocene. First, a dryer environment is assumed due to the presence of the calcrete in the base. During the glacial period, a transgressive environment prevailed and marine calcareous sedimentation started. During Last Glacial Maximum a regression occurred, the climate was drier and the formation of dune sediments and another calcrete occurred. In the Holocene climate changed shifting toward more humid conditions that produced the modern soil cover, under tropical conditions.

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

    International Nuclear Information System (INIS)

    Grigorescu, D.; Klarik, L.; Bojar, A.-V.

    2002-01-01

    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

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

    International Nuclear Information System (INIS)

    Levich, Robert A.; Muller-Kahle, Eberhard

    1983-04-01

    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

  4. Pe do sedimentary sequence in late Quaternary section in Zarate, Argentina

    International Nuclear Information System (INIS)

    Tofalo, O.; Orgeira, M.; Alonso, M.; Ramos, A.

    2007-01-01

    Field geological features, grain-size, sand, silt and clay mineralogy, micromorphology, optically simulated luminiscence (OSL) ages have been used to reconstruct the pedosedimentary sequence in a late Quaternary section in Zarate, Buenos Aires province. Paleosols were developed on loess and four clear discontinuities in sedimentation and paleosols generation were observed. These discontinuities have determinated four units with different types of calcrete. The welded paleosols developed on unit C can be 1correlated and linked to the other ones outcropped in Baradero (Buenos Aires province) and Lozada (Cordoba province). These records probably span the equivalent of marine oxygen isotope stage (OIS) 5, the last interglacial stage before the present. The ground water and pedogenic calcretes and their association with smectite, illite and ferric oxide suggest dried climate than present one and strongly seasonality. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Grigorescu, D; Klarik, L [University of Bucharest, Faculty of Geology and Geophysics (Romania); Bojar, A -V [Department of Geology and Paleontology, Graz (Austria)

    2002-10-01

    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.

  6. Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

    Science.gov (United States)

    Ringrose, S.; Harris, C.; Huntsman-Mapila, P.; Vink, B. W.; Diskins, S.; Vanderpost, C.; Matheson, W.

    2009-07-01

    Trace elements together with some O and C isotope analysis were undertaken on duricrust strandline deposits in the palaeo-Makgadikgadi sub-basin (PMSB) to provide insight into palaeo-climatic conditions through the interpretation of calcrete, silcrete-calcrete intergrade and silcrete deposits. Trace element content and relative abundance suggest that the duricrust origins are associated with the long-term weathering of the Karoo Large Igneous Province which underlies the PMSB. This work shows that duricrust origins are related to Ca 2+ and Si (and associated trace elements) being transported mainly through the groundwater and then subsequently precipitated at different strandline elevations over time. Local groundwater feeding in towards the pan margin and accumulating in near-neutral pan-marginal pools, appears to facilitate Si concentration and permeation of pre-existing calcretes. The silica precipitates as the pH drops when renewed freshwater enters the pools. Hence the inferred palaeo-climatic regime for silcretisation may be similar to that occurring in Botswana at present being dry semi-arid with low seasonal rainfall. In contrast the extensive calcrete precipitation in the strandlines results from abundant Ca 2+ in adjacent waters which appear to be derived from both local and regional sources. The arrival of Ca 2+ from regional sources (shown by trace element evidence) infers heavy rainfall in the upper catchment suggesting a major humid event followed by regional drying. Palaeo-climatic inferences suggest the juxtaposition of major humid events interspersed with more normal semi-arid palaeo-climates with an exception obtained from isotope data, of drier and cooler conditions than usual for the region around 80-90 000 years ago. Whereas trace element data can greatly assist in the interpretation of complex deposits such as duricrusts, care should be taken over the use of particular ratios (such as Yb/Gd ratio) which may produce spurious results.

  7. Theater of Operations Construction in the Desert. A Handbook of Lessons Learned in the Middle East. Phase I.

    Science.gov (United States)

    1981-01-01

    pavements (calcrete duricrusts ) for coarse aggregate sources, discard the top 1 ft because it is most highly contaminated by chlorides and sulfates. Most...The basic cross " sabkhas, sa/inas, salt playas and some sectional profile comprises a mountain duricrusts , unsuitable construction and a piedmont plain...various forms of metres below the surface, where for stops when sand and silts are damp: " duricrust ". The latter is often, but not example :,vers of

  8. Theater of Operations Construction in the Desert: A Handbook of Lessons Learned in the Middle East

    Science.gov (United States)

    1981-01-01

    concentration. 7. When using natural desert or beach pavements (calcrete duricrusts ) for coarse aggregate sources, discard the top 1 ft because it is most...profile comprises a mountain duricrusts ; unsuitable construction and a piedmont plain. Although such a P.G. Fookes materials - e.g. some silts, sands...surface, where for stops when sand and silts are damp; " duricrust ". The latter is often, but not example layers of fibrous gypsum can capillary moisture

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

    International Nuclear Information System (INIS)

    Johnson, C.L.

    1982-01-01

    Carnotite [K 2 (UO 2 ) 2 (VO 4 ) 2 .3H 2 O] 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

  10. Paleosols of the upper Paleozoic Sangre de Cristo Formation, north-central New Mexico: Record of early Permian palaeoclimate in tropical Pangaea

    Directory of Open Access Journals (Sweden)

    Lawrence H. Tanner

    2017-04-01

    During the early Permian, northern New Mexico was situated in a near equatorial position (ca. 4° N. The overall character of the paleosols suggests a persistent warm, semi-humid, seasonal climate throughout most of the interval of deposition during the Wolfcampian, but with episodically increased aridity during formation of the more mature calcretes. No long-term trend of climate change is evident in the stratigraphic section examined for this study.

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

    International Nuclear Information System (INIS)

    1977-11-01

    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)

  12. Uranium-thorium dating of quaternary carbonate accumulations in the Nevada Test Site region, southern Nevada

    International Nuclear Information System (INIS)

    Szabo, B.J.; Carr, W.J.; Gottschall, W.C.

    1981-01-01

    A useful way to approach the problem of tectonic activity in an arid region is through study of the history of movement of faults and fractures and of the young alluvial material they displace. Easily datable materials are scarce in these deposits, but carbonates such as caliche, calcrete, travertine, calcite vein, and tufa are common. Several types of these carbonates from the Nevada Test Site area in the southern Great Basin have been collected and dated by the uranium-series method. A variety of geologic settings are represented. The carbonate samples were subjected to a complex treatment process, and the resulting preparations were counted on an alpha spectrometer. Some of the samples from obviously closed systems yielded reasonable ages; others gave only a minimum age for a material or event. Many of the ages obtained agree well with estimates of age determined from dated volcanic units, fault-scarp morphology, and displaced alluvial units. Among the significant ages obtained were three dates of greater than 400,000 years on calcite-filling fractures above and below the water table in an exploratory drill hole for a possible candidate nuclear waste repository site at Yucca Mountain. Another date on calcrete from immediately below the youngest basalt in the region gave an age of 345,000 years, which agrees extremely well with the K-Ar age determined for the basalt of about 300,000 years. Undisturbed travertine that fills faults in several areas gave ages from about 75,000 years to greater than 700,000 years. Soil caliche and calcretes slightly displaced or broken by repeated movement on faults gave minimum ages in the range from more than 5000 to more than about 25,000 years

  13. Preliminary study of lead isotopes in the carbonate-silica veins of Trench 14, Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Zartman, R.E.; Kwak, L.M.

    1993-01-01

    The sub-vertical carbonate-silica veins filling the Bow Ridge Fault, where exposed in Trench 14 on the east side of Yucca Mountain, carry a lead isotopic signature that can be explained in terms of local sources. Two isotopically distinguishable--silicate and carbonate--fractions of lead are recognized within the vein system as well as in overlying surficial calcrete deposits. The acid-insoluble silicate fraction is contributed largely from the decomposing Miocene volcanic tuff, which forms the wall rock of the fault zone and is a ubiquitous component of the overlying soil. Lead contained in the silicate fraction approaches in isotopic composition that of the Miocene volcanic rocks of Yucca Mountain, but diverges from it in some samples by being more enriched in uranogenic isotopes. The carbonate fraction of lead in both vein and calcrete samples resides dominantly in the HCl- and CH 3 COOH-soluble calcite. HCl evidently also attacks and removes lead from silicate phases, but the milder CH 3 COOH dissolution procedure oftentimes identifies a significantly more radiogenic lead in the calcite. Wind-blown particulate matter brought to the area from Paleozoic and Late Proterozoic limestones in surrounding mountains may be the ultimate source of the calcite. Isotopically more uniform samples suggest that locally the basaltic ash and other volcanic rock have contributed most of the lead to both fractions of the vein system. An important finding of this study is that the data does not require the more exotic mechanisms or origins that have been proposed for the veins. Instead, the remarkably similar lead isotopic properties of the veins to those of the soil calcretes support their interpretation as a surficial, pedogenic phenomenon

  14. Evidencias paleoclimáticas en duricostras, paleosuelos y sedimentitas silicoclásticas del Cenozoico de Uruguay Paleoclimatic evidence in duricrust, paleosoils and siliciclastic deposit of the Cenozonic of Uruguay

    OpenAIRE

    Ofelia Rita Tófalo; Héctor J. M. Morrás

    2009-01-01

    Las sedimentitas continentales del oeste y sur de Uruguay permiten inferir importantes cambios climáticos ocurridos durante el Cenozoico, que se inicia con calizas palustres paleocenas denominadas Formación Queguay y relacionadas con calcretes freáticos que afectan principalmente a sedimentitas fluviales de la Formación Mercedes (Cretácico Tardío). La presencia de estas rocas carbonáticas indica clima semiárido, marcadamente estacional. La Formación Asencio (Eoceno temprano) está separada de ...

  15. 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.

  16. Development of uranium processing at Wiluna

    Energy Technology Data Exchange (ETDEWEB)

    Kenny, D., E-mail: dayle.kenny@toroenergy.com.au [Toro Energy Ltd., West Perth, WA (Australia); Dombrose, E. [Metallurgical Support Pty Ltd., Shelley, WA (Australia)

    2010-07-01

    Toro Energy Ltd. has identified a resource of 20.2 million tonnes at a grade of 548 ppm U{sub 3}O{sub 8} at Wiluna, Western Australia. Calcrete and clay delta formations host the uranium mineral carnotite. Initial studies indicate a mining operation is technically, environmentally and commercially viable. Increase in demand for uranium and a change in State Government policy on uranium mining have lead Toro to proceed with a bankable feasibility study and commence approvals with State and Federal Governments. This paper discusses how Toro arrived at the decision to utilise alkaline heap leach, a process not widely used, and how it is being developed. (author)

  17. Effect of prolonged mixing time on concrete properties

    International Nuclear Information System (INIS)

    Mohd Noorul Ikhsan Mohamed; Sidek, H.A.A.; Wahab, Z.A.

    2009-01-01

    The correlation between workability, compressive strength and mixing time of fresh concrete has been studied. The concrete samples used in the study are normal concrete of grade 30. The mix design of the concrete samples was estimated using software called Calcrete. Three concrete cubes of 150 mm size were cast immediately after mixing. The same grade of concrete was prepared with the mixing time of 30 minutes to 5 hours. All of the concrete samples were cured for 28 days under room temperature before they were compressed using a compression machine. Result shows that the compressive strength of concrete decreases when mixing time is increased. (author)

  18. The electrodeposition of thorium in natural materials for alpha spectrometry

    International Nuclear Information System (INIS)

    Roman, D.

    1980-01-01

    A technique has been developed for the electrodeposition of thorium on stainless steel planchettes following standard radiochemical separation and uptake in acetate buffer. The method has been used on over 130 samples including calcrete, clay, granite and shell matrices. To assess the efficiency at ultra low levels, three solutions of carrier free 228 Th ( -7 μg in 5 ml electrolyte) and four solutions of 229 Th (4.4x10 -4 μg in 5 ml) were studied. The efficiencies of the former averaged 66 per cent; those of the 229 Th varied from 41 to 91%. (author)

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

    International Nuclear Information System (INIS)

    1977-12-01

    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)

  20. Uranium ore deposits

    International Nuclear Information System (INIS)

    Angelelli, Victorio.

    1984-01-01

    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.) [es

  1. Uraniferous surficial deposits

    International Nuclear Information System (INIS)

    Toens, P.D.; Hambleton-Jones, B.B.

    1980-10-01

    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 [af

  2. Hinkler Well - Centipede uranium deposits

    International Nuclear Information System (INIS)

    Crabb, D.; Dudley, R.; Mann, A.W.

    1984-01-01

    The Hinkler Well - Centipede deposits are near the northeastern margin of the Archean Yilgarn Block on a drainage system entering Lake Way. Basement rocks are granitoids and greenstones. The rocks are deeply weathered and overlain by alluvism. Granitoids, the probable uranium source, currently contain up to 25 ppm uranium, in spite of the weathering. The host calcrete body is 33 km long and 2 km wide. Uranium up to 1000 ppm occurs in carnotite over a 15 km by 2.5 km area. (author)

  3. Geohydrological investigation of an uranium anomaly near Vanzylsrus in the Northern Cape Province

    International Nuclear Information System (INIS)

    Levin, M.; Talma, A.S.; Vogel, J.C.

    1982-01-01

    An anomaly, caused by low-grade uranium accumulations in organic-rich diatomaceous earth deposits, was located by an airborne radiometric survey near Vanzylsrus in the Northern Cape. Low-grade uraniferous calcrete also occurs in the vicinity of the anomaly. A significant uranium anomaly was found along the whole course of the palaeodrainage with the highest values occuring behind a dolerite dyke a few kilometres south of the confluence. A multidisciplinary approach in corporating geohydrology, water geochemistry, isotopic data and radiometric borehole logging studies was used to evaluate its potential

  4. Late quaternary hillslope evolution recorded in eastern South African colluvial badlands

    CSIR Research Space (South Africa)

    Clarke, ML

    2003-09-01

    Full Text Available -8-03 Palaeogeography, Palaeoclimatology, Palaeoecology 197 (2003) 199^212 www.elsevier.com/locate/palaeo dates for calcrete nodules which formed post-dep- ositionally within the sequences and which could not constrain individual depositional or pedogenic events. As a..., the earlier ones of which correlate with the calculated changes in latitudinal insolation. As identi?ed by Thomas and Thorp (1995), the PALAEO 3146 4-8-03 M.L. Clarke et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 197 (2003) 199^212 timing...

  5. Spectral pathways for exploration of secondary uranium: An investigation in the desertic tracts of Rajasthan and Gujarat, India

    Science.gov (United States)

    Bharti, Rishikesh; Kalimuthu, R.; Ramakrishnan, D.

    2015-10-01

    This study aims at identifying potential zones of secondary uranium enrichment using hyperspectral remote sensing, γ-ray spectrometry, fluorimetry and geochemical techniques in the western Rajasthan and northern Gujarat, India. The investigated area has suitable source rocks, conducive past-, and present-climate that can facilitate such enrichment. This enrichment process involves extensive weathering of uranium bearing source rocks, leaching of uranyl compounds in groundwater, and their precipitation in chemical deltas along with duricrusts like calcretes and gypcretes. Spatial distribution of groundwater calcretes (that are rich in Mg-calcite) and gypcretes (that are rich in gypsum) along palaeochannels and chemical deltas were mapped using hyperspectral remote sensing data based on spectral absorptions in 1.70 μm, 2.16 μm, 2.21 μm, 2.33 μm, 2.44 μm wavelength regions. Subsequently based on field radiometric survey, zones of U anomalies were identified and samples of duricrusts and groundwater were collected for geochemical analyses. Anomalous concentration of U (2345.7 Bq/kg) and Th (142.3 Bq/kg) are observed in both duricrusts and groundwater (U-1791 μg/l, Th-34 μg/l) within the palaeo-delta and river confluence. The estimated carnotite Solubility Index also indicates the secondary enrichment of U and the likelihood of occurrence of an unconventional deposit.

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

    Energy Technology Data Exchange (ETDEWEB)

    Stuckless, J S; Nkomo, I T [Geological Survey, Denver, CO (USA); Bunting, J A [Geological Survey of Western Australia, Perth

    1981-11-01

    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 (3..mu..g/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. 20..mu..g/g) and are associated with large roll-type and other low temperature-type uranium deposits.

  7. Role of neotectonics and climate in development of the Holocene geomorphology and soils of the Gangetic Plains between the Ramganga and Rapti rivers

    Science.gov (United States)

    Srivastava, Pankaj; Parkash, B.; Sehgal, J. L.; Kumar, Sudhir

    1994-12-01

    Fifteen soil-geomorphic units have been delineated from the Gangetic Plains between the Ramganga and Rapti rivers. They were identified by remote sensing and field checks. On the basis of degree of profile development, their soils are grouped into five members (QGH1 to QGH5, QGH5 being the oldest) of a soil chrono-association. Tentative ages assigned to QGH1 to QGH5 are 500, > 2500, 8000 and 13,5000 yr B.P., respectively. From the early Holocene to about 6500 yr. B.P. a cold, arid to semi-arid climate prevailed and pedogenic calcrete developed over large areas in the Gangetic Plains. Later, a warm and humid climate and improved drainage resulted in complete removal of calcrete from soil profiles in some areas or its dissolution and re-precipitation in lower horizons in other areas. Neotectonics seems to have played a significant role in the evolution of the geomorphology and soils of the area. It determined areas of active sedimentation, pedogenesis and erosion (in upland regions). It led to tilting and sagging of large blocks resulting in shifting and increase in sinuosity of the rivers. Tectonic slopes/faults determined the courses of large rivers.

  8. Geology and climatic indicators in the Westphalian A New Glasgow formation, Nova Scotia, Canada: implications for the genesis of coal and of sandstone-hosted lead deposits

    Energy Technology Data Exchange (ETDEWEB)

    Chandler, F.W. [Geological Survey of Canada, Ottawa, ON (Canada)

    1998-03-01

    Disagreement exists on whether the early Pennsylvanian climate of the Euramerican coal province was everwet or seasonal. Abundant paleopedological evidence, including calcrete-bearing vertisols, shows that during formation of Westphalian C to Stephanian coals in Nova Scotia, the climate was tropical and seasonal with a pronounced by dry season; but interpretation of Westphalian A-B coal-bearing sequences lacks this form of evidence. Development of calcrete-bearing vertisols in alluvial fan deposits of the Westphalian A New Glasgow formation indicate that a tropical climate with a pronounced dry season was already in force by early Westphalian time. During the dry season, the coal swamps of the early Westphalian Joggins and Springhill Mines formations were fed by groundwater from coeval alluvial fan deposits of the Polly Brook Formation at the basin margin. Sedimentological evidence indicates that, similarly, groundwater flowed northward from the toe of the New Glasgow alluvial fan, but correlative palustrine sediments have not been found on land in the New Glasgow area. The possibility remains of an early Westphalian coalfield associated with the New Glasgow formation to the north under the Northumberland Strait and Gulf of St. Lawrence. Formation of the Yava sandstone-hosted lead deposit in the fluvial Silver Mine Formation of Cape Breton Island, a stratigraphic equivalent of the Cumberland Basin coal swamps, indicates that such deposits can form in fluvial strata deposited under a tropical seasonal climate with a pronounced dry season.

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

    International Nuclear Information System (INIS)

    1985-01-01

    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)

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

    International Nuclear Information System (INIS)

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

    1994-01-01

    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

  11. Provenance analysis and thermo-dynamic studies of multi-type Holocene duricrusts (1700 BC) in the Sua Salt Pan, NE Botswana

    Science.gov (United States)

    Dill, Harald G.; Dohrmann, R.; Kaufhold, S.; Techmer, A.

    2014-08-01

    Multi-type duricrusts, composed of silcretes, calcretes, halcretes and sulcretes developed during the Holocene at the northern rim of the Sua Salt Pan, NE Botswana. They were investigated for their light (quartz/chalcedony, feldspar, analcime, clinoptilolite, calcite, kaolinite/halloysite, illite-smectite mixed-layers, halite) and heavy minerals (baryte, clinozoisite-epidote s.s.s., amphibole, corundum, tourmaline, ilmenite, rutile, sphene, kyanite, andalusite, staurolite, garnet, zircon, apatite, monazite, cassiterite, garnet, biotite) using petrographic microscopy, X-ray fluorescence and diffraction analyses, radio-carbon dating, scanning electron microscopy equipped with an EDX-system, cation exchange capacity and infrared spectroscopy. Detrital minerals predominantly derived from the erosion of rocks belonging to the Archaean Basement Complex, the Stormberg Volcanites and the Kalahari sediments. Of particular interest to exploration geologists, geikielite-enriched ilmenite fragments are a hint to kimberlitic pipes. Biodetritus was derived from invertebrates and from vertebrates (fish bones?). A man-made impact on the heavy mineral suite has to be invoked from small fragments of cassiterite fragments that derived from processing of sulfidic and pegmatitic Sn-bearing ore. In the salt-pan-derived duricrusts mainly the aeolian and to a lesser degree fluvial inputs were responsible for the concentration of clasts in these multi-type duricrusts. Moreover, their variegated mineralogy enables us to constrain the physical-chemical regime, prevalently as to the pH and the chemical composition of the major constituents. All duricrusts developed in a self-sufficient chemically closed system where quartz and feldspar provided the elements Si, Na, K, Ca, and Ba to produce the encrustations. The spatial and temporal trend in the Sua Salt Pan rim encrustations may be described as follows: (1) sulcrete-silcretes, (2) silcretes with kaolinite-group minerals towards more recent

  12. Importance of Surface Texture to Infrared Remote Sensing Interpretations

    Science.gov (United States)

    Kirkland, L. E.; Adams, P. M.; Herr, K. C.; Salisbury, J. W.

    2001-11-01

    Thermal infrared remote sensing may be used to identify minerals present on the surface using diagnostic spectral bands. As band depth (spectral contrast) exhibited by the mineral increases, the mineral is easier to detect. In order to determine the expected spectral contrast, thermal infrared spectra of typical mineral endmembers are commonly measured in the laboratory. For example, for calcite, well-crystalline limestone is commonly studied. However, carbonates occur in several forms, including thin coatings, indurated carbonate (calcrete), and hot springs deposits. Different formation pathways may cause different microstructures and surface textures. This in turn can also affect the surface texture of the weathered material. Different surface textures can affect the measured band contrast, through roughness that causes a cavity (hohlraum) effect, and particle size and roughness on a scale that causes volume scattering. Thus since detection limits vary with the spectral contrast, surface texture can be an important variable in how detectable a mineral is. To study these issues, we have examined limestone and calcrete deposits at Mormon Mesa, Nevada that have two distinctly different microstructures and surface texture [Kirkland et al., 2001]. The limestone studied has larger grains and the grains frequently have flat, smooth surfaces on the order of 10-50 microns in cross-section length. The calcrete has smaller, more angular calcite grains, which exhibit almost no flat surfaces longer than 5 microns in cross-section length. We will show scanning electron microscope images to compare the different microstructures and surface textures of both the fresh and weathered surfaces, and we will show corresponding thermal infrared spectra to illustrate the different spectral signatures. The results demonstrate the importance of understanding the microstructure of mineral deposits to accurately interpret infrared remote sensing data, especially for studies that lack ground

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

    International Nuclear Information System (INIS)

    1985-01-01

    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)

  14. Surficial uranium deposits in Somalia

    International Nuclear Information System (INIS)

    Briot, P.

    1984-01-01

    Surficial uranium deposits in Somalia are of the valley-fill calcrete type and occur in the arid Mudugh Province of the Dusa Mareb-El Bur region. They are located in a belt about 240 km in length which is orientated parallel to the north-south regional tectonic framework. The uranium resources of the region amount to about 5,000 t U 3 O 8 at an average grade of 0.1% U 3 O 8 . Basement rocks constitute a 7,000 m thick succession of Jurassic to Quaternary sediments of the Somalian Basin. Uranium mineralization in the form of carnotite occurs in the uppermost Mercia Series. The origin of the uranium and vanadium is unclear due to a shortage of the favourable source rocks. (author)

  15. Uranium ore deposits: geology and processing implications

    International Nuclear Information System (INIS)

    Belyk, C.L.

    2010-01-01

    There are fifteen accepted types of uranium ore deposits and at least forty subtypes readily identified around the world. Each deposit type has a unique set of geological characteristics which may also result in unique processing implications. Primary uranium production in the past decade has predominantly come from only a few of these deposit types including: unconformity, sandstone, calcrete, intrusive, breccia complex and volcanic ones. Processing implications can vary widely between and within the different geological models. Some key characteristics of uranium deposits that may have processing implications include: ore grade, uranium and gangue mineralogy, ore hardness, porosity, uranium mineral morphology and carbon content. Processing difficulties may occur as a result of one or more of these characteristics. In order to meet future uranium demand, it is imperative that innovative processing approaches and new technological advances be developed in order that many of the marginally economic traditional and uneconomic non-traditional uranium ore deposits can be exploited. (author)

  16. Geophysical features of uranium mineralization in Wadi Bahiya area, southern Jordan

    International Nuclear Information System (INIS)

    Zhao Xigang; Liang Shanming; Deng Xiaowei; Li Shengxiang; Wang Jinping

    2010-01-01

    Based on comprehensive study of geologic survey, sample analysis and ground gamma spectral survey, it is concluded that the uranium mineralization in Wadi Bahiya area, southern Jordan occurs near surface and is mostly hosted in weathered gray-brown chalk marl of Muwaqqar Chalk Marl Formation of the Upper Cretaceous and Paleocene, and belongs to surficial calcrete-type which is related to modern oxidation. The ground gamma spectral survey shows that surface anomaly area is small and big gradient change of the anomalies. The trenches reveal that uranium content of the anomalies falls down from near-surface to the deep. The analytical results of the samples from the area correspond with the gamma spectral measurements, demonstrating that uranium mineralization is mainly located within the depth between 0.5 and 1.5 m. (authors)

  17. 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)

    Archambeau, C.

    1994-08-01

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

  18. National uranium resource evaluation, Las Vegas Quadrangle, Nevada, Arizona, and California

    International Nuclear Information System (INIS)

    Johnson, C.; Glynn, J.

    1982-03-01

    The Las Vegas 1 0 x 2 0 quadrangle, Nevada, Arizona, and California, contains rocks and structures from Precambrian through Holocene in age. It lies within the Basin and Range physiographic province adjacent to the westernmost portion of the Colorado Plateau. Miocene nonmarine sedimentary rocks of the Horse Spring Formation contain in excess of 100 tons U 3 O 8 in deposits at a grade of 0.01% or greater, and therefore meet National Uranium Resource Evaluation base criteria for uranium favorability. One favorable area lies in the South Virgin Mountains at the type locality of the Horse Spring Formation, although the favorable environment extends into the unevaluated Lake Mead National Recreation Area and Desert National Wildlife Range. Environments within the Las Vegas Quadrangle considered unfavorable for uranium include the Shinarump Conglomerate member of the Triassic Chinle Formation, Mesozoic sediments of the Glen Canyon Group, Precambrian pegmatites, Pliocene and Quaternary calcrete, Laramide thrust faults, and a late Precambrian unconformity

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

    International Nuclear Information System (INIS)

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

    1994-01-01

    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 infillings 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 a fan draining a carbonate terrane have 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

  20. Classification of Uranium deposits

    International Nuclear Information System (INIS)

    Dahlkamp, F.J.

    1978-01-01

    A listing of the recognized types of uranium mineralization shows nineteen determinable types out of which only six can be classified as of economic significance at present: Oligomiitic quartz pebble conglomerates, sandstone types, calcretes, intra-intrusive types, hydrothermal veins, veinlike types. The different types can be genetically related to prevalent geological environments, i.e. 1. the primary uranium occurrences formed by endogenic processes, 2. the secondary derived from the primary by subsequent exogenic processes, 3. the tertiary occurrences are assumed to be formed by endogenic metamorphic processes, although little is known about the behaviour of the uranium during the metamorphosis and therefore the metallogenesis of this tertiary uranium generation is still vague. A metallotectonic-geochronologic correlation of the uranium deposits shows a distinct affinity of the uranium to certain geological epochs: The Upper Archean, Lower Proterozoic, the Hercynian and, in a less established stage, the Upper Proterozoic. (orig.) 891 HP/orig. 892 MKO [de

  1. 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)

    1993-07-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Archambeau, C.

    1994-08-01

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

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

    International Nuclear Information System (INIS)

    1984-01-01

    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)

  4. Soil stabilization by a prokaryotic desert crust - Implications for Precambrian land biota

    Science.gov (United States)

    Campbell, S. E.

    1979-01-01

    The ecology of the cyanophyte-dominated stromatolitic mat forming the ground cover over desert areas of Utah and Colorado is investigated and implications for the formation of mature Precambrian soils are discussed. The activation of the growth of the two species of filamentous cyanophyte identified and the mobility of their multiple trichromes upon wetting are observed, accompanied by the production and deposition of a sheath capable of accreting and stabilizing sand and clay particles. The formation of calcium carbonate precipitates upon the repeated wetting and drying of desert crust is noted, and it is suggested that the desert crust community may appear in fossil calcrete deposits as lithified microscopic tubes and cellular remains of algal trichromes. The invasion of dry land by both marine and freshwater algae on the model of the desert crust is proposed to be responsible for the accumulation, stabilization and biogenic modification of mature Precambrian soils.

  5. Ore-processing technology and the uranium supply outlook

    International Nuclear Information System (INIS)

    James, H.E.; Simonsen, H.A.

    1978-01-01

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

    International Nuclear Information System (INIS)

    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

  7. Kuwaiti dolocrete: petrology, geochemistry and groundwater origin

    Science.gov (United States)

    El-Sayed, M. I.; Fairchild, I. J.; Spiro, B.

    1991-09-01

    Near-surface sediments in southern Kuwait show extensive development of duricrusts. The host materials are siliciclastic sandstones of the post-Eocene Kuwait Group. Inland, the duricrusts are dominantly pedogenic calcrete (with some silcrete and gypcrete), whereas within 10-20 km of the coast, dolomite is the dominant duricrust mineral. Both these dolocretes and the inland calcretes display a similar maturation sequence in which carbonate-rich nodules develop and coalesce, carbonate progressively replacing and displacing detrital grains. The dolomite of the dolocretes forms mosaics of crystals typically 10-70 μm in size, varying from simple rhombs to spherulites. An intermediate morphology, named artichoke dolomite from its appearance in SEM, is particularly abundant. Authigenic palygorskite is associated with the dolomite. Dissolution of cores or zones within dolomite crystals has occurred. Calcite is present as sparry crystals (always post-dating dolomite) and is the expected precipitate from present-day soil and groundwaters. Chemical analyses of dolomite show highly negative values of δ13C (- to - 10.7‰ PDB) and δ18O varying from + 0.6 to + 3.3‰ PDB. The oxygen isotope values are interpreted as reflecting evaporation of a marine-based fluid. Manganese values of around 1000 ppm show that this fluid was reducing. Strontium data show variability reflecting mineral-fluid reactions. The general absence of metastable carbonates and presence of zoning in dolomite crystals suggests that meteoric dilution of seawater also occurred. Given that the duricrusts lack biogenic features, the light carbon isotope values are taken to indicate oxidation of seeping hydrocarbons. The dolocretes are interpreted as groundwater precipitates near the water table of a brackish water body formed at a time of higher relative sea level than today.

  8. Estimation of vertical slip rate in an active fault-propagation fold from the analysis of a progressive unconformity at the NE segment of the Carrascoy Fault (SE Iberia)

    Science.gov (United States)

    Martin-Banda, Raquel; Insua-Arevalo, Juan Miguel; Garcia-Mayordomo, Julian

    2017-04-01

    Many studies have dealt with the calculation of fault-propagation fold growth rates considering a variety of kinematics models, from limb rotation to hinge migration models. In most cases, the different geometrical and numeric growth models are based on horizontal pre-growth strata architecture and a constant known slip rate. Here, we present the estimation of the vertical slip rate of the NE Segment of the Carrascoy Fault (SE Iberian Peninsula) from the geometrical modeling of a progressive unconformity developed on alluvial fan sediments with a high depositional slope. The NE Segment of the Carrascoy Fault is a left-lateral strike slip fault with reverse component belonging to the Eastern Betic Shear Zone, a major structure that accommodates most of the convergence between Iberian and Nubian tectonics plates in Southern Spain. The proximity of this major fault to the city of Murcia encourages the importance of carrying out paleosismological studies in order to determinate the Quaternary slip rate of the fault, a key geological parameter for seismic hazard calculations. This segment is formed by a narrow fault zone that articulates abruptly the northern edge of the Carrascoy Range with the Guadalentin Depression through high slope, short alluvial fans Upper-Middle Pleistocene in age. An outcrop in a quarry at the foot of this front reveals a progressive unconformity developed on these alluvial fan deposits, showing the important reverse component of the fault. The architecture of this unconformity is marked by well-developed calcretes on the top some of the alluvial deposits. We have determined the age of several of these calcretes by the Uranium-series disequilibrium dating method. The results obtained are consistent with recent published studies on the SW segment of the Carrascoy Fault that together with offset canals observed at a few locations suggest a net slip rate close to 1 m/ka.

  9. Uranium occurrences in the Gordonia and Kuruman districts

    International Nuclear Information System (INIS)

    Levin, M.

    1978-11-01

    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 U 3 O 8 . 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 [af

  10. Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana

    Science.gov (United States)

    Thomas, Andrew D.

    2012-01-01

    Biological soil crusts (BSCs) are an important source of organic carbon, and affect a range of ecosystem functions in arid and semiarid environments. Yet the impact of grazing disturbance on crust properties and soil CO2 efflux remain poorly studied, particularly in African ecosystems. The effects of burial under wind-blown sand, disaggregation and removal of BSCs on seasonal variations in soil CO2 efflux, soil organic carbon, chlorophyll a and scytonemin were investigated at two sites in the Kalahari of southern Botswana. Field experiments were employed to isolate CO2 efflux originating from BSCs in order to estimate the C exchange within the crust. Organic carbon was not evenly distributed through the soil profile but concentrated in the BSC. Soil CO2 efflux was higher in Kalahari Sand than in calcrete soils, but rates varied significantly with seasonal changes in moisture and temperature. BSCs at both sites were a small net sink of C to the soil. Soil CO2 efflux was significantly higher in sand soils where the BSC was removed, and on calcrete where the BSC was buried under sand. The BSC removal and burial under sand also significantly reduced chlorophyll a, organic carbon and scytonemin. Disaggregation of the soil crust, however, led to increases in chlorophyll a and organic carbon. The data confirm the importance of BSCs for C cycling in drylands and indicate intensive grazing, which destroys BSCs through trampling and burial, will adversely affect C sequestration and storage. Managed grazing, where soil surfaces are only lightly disturbed, would help maintain a positive carbon balance in African drylands. PMID:23045706

  11. Revisiting dirt cracking as a physical weathering process in warm deserts

    Science.gov (United States)

    Dorn, Ronald I.

    2011-12-01

    A half century ago C.D. Ollier proposed that insolation-driven temperature changes expand and contract fill in fissures enough to widen cracks, a process that would permit progressively deeper penetration of fissure fills, that would in turn generate a positive feedback of greater and greater strain until desert boulders and bedrock shatters. Although desert physical weathering by "dirt cracking" has occasionally been cited, this hypothesized process remains without support from subsequent research. Here, field observations, electron microscopy, X-ray powder diffraction, particle-size analysis, and laboratory experiments shed new light on dirt cracking. Little clear evidence supports the original notion of expansive pressures from thermal fluctuations. However, mineralogical, high resolution transmission electron microscopy, back-scattered electron microscopy, and experimental evidence support two alternative processes of widening fractures: wetting and drying of fills inside fissures; and the precipitation and remobilization of calcium carbonate. A re-envisioned dirt-cracking wedging process starts with calcium carbonate precipitating in fissures less than 5 μm wide. First precipitation, and then ongoing dissolution of this laminar calcrete, opens enough space for dust to penetrate into these narrow fractures. Wetting of expansive clays in the fissure fill exerts enough pressure to widen and deepen the fissure, allowing the carbonate precipitation process to penetrate even deeper and allowing even more dust to move into a fracture. As the dust infiltrates, its texture changes from a chaotic mix of particles to an alignment of clays parallel to fissure sides. This parallel alignment could increase the efficiency of fill wedging. Ollier's concept of a positive feedback remains supported; each increment of fracture deepening and widening permits more, even deeper infiltration of laminar calcrete and dust. Field and electron microscope observations of rock spalling

  12. 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

  13. Rivers turned to rock: Late Quaternary alluvial induration influencing the behaviour and morphology of an anabranching river in the Australian monsoon tropics

    Science.gov (United States)

    Nanson, Gerald C.; Jones, Brian G.; Price, David M.; Pietsch, Timothy J.

    2005-09-01

    Late Quaternary alluvial induration has greatly influenced contemporary channel morphology on the anabranching Gilbert River in the monsoon tropics of the Gulf of Carpentaria. The Gilbert, one of a number of rivers in this region, has contributed to an extensive system of coalescing low-gradient and partly indurated riverine plains. Extensive channel sands were deposited by enhanced flow conditions during marine oxygen isotope (OI) Stage 5. Subsequent flow declined, probably associated with increased aridity, however, enhanced runoff recurred again in OI Stages 4-3 (˜65-50 ka). Aridity then capped these plains with 4-7 m of mud. A widespread network of sandy distributary channels was incised into this muddy surface from sometime after the Last Glacial Maximum (LGM) to the mid Holocene during a fluvial episode more active than the present but less so than those of OI Stages 5 and 3. This network is still partly active but with channel avulsion and abandonment now occurring largely proximal to the main Gilbert flow path. A tropical climate and reactive catchment lithology have enhanced chemical weathering and lithification of alluvium along the river resulting in the formation of small rapids, waterfalls and inset gorges, features characteristic more of bedrock than alluvial systems. Thermoluminescence (TL) and comparative optically stimulated luminescence (OSL) ages of the sediments are presented along with U/Th ages of pedogenic calcrete and Fe/Mn oxyhydroxide/ oxide accumulations. They show that calcrete precipitated during the Late Quaternary at times similar to those that favoured ferricrete formation, possibly because of an alternating wet-dry climate. Intense chemical alteration of the alluvium leading to induration appears to have prevailed for much of the Late Quaternary but, probably due to exceptional dryness, not during the LGM. The result has been restricted channel migration and a reduced capacity for the channel to adjust and accommodate sudden

  14. 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.

  15. Sedimentary Evolution of Marginal Ganga Foreland Basin during the Late Pleistocene

    Science.gov (United States)

    Ghosh, R.; Srivastava, P.; Shukla, U. K.

    2017-12-01

    Ganga foreland basin, an asymmetrical basin, was formed as result of plate-plate collision during middle Miocene. A major thrust event occurred during 500 ka when upper Siwalik sediments were uplifted and the modern Ganga foreland basin shifted towards craton, making a more wide and deep basin. The more distal part of this basin, south of axial river Yamuna, records fluvial sedimentary packages that helps to understand dynamics of peripheral bulge during the late Quaternary. Sedimentary architecture in conjunction with chemical index of alteration (CIA), paleocurrent direction and optically stimulated dating (OSL) from 19 stratigraphic sections helped reconstructing the variations in depositional environments vis-à-vis climate change and peripheral bulge tectonics. Three major units (i) paleosol; (ii) cratonic gravel; (iii) interfluve succession were identified. The lower unit-I showing CIA values close to 70-80 and micro-morphological features of moderately well-developed pedogenic unit that shows development of calcrete, rhizoliths, and mineralized organic matter in abundance. This is a regional paleosols unit and OSL age bracketed 200 ka. This is unconformably overlain by unit-II, a channelized gravel composed of sub-angular to sub-rounded clasts of granite, quartz, quartzite, limestone and calcrete. The gravel have low CIA value up to 55, rich in vertebrate fossil assemblages and mean paleocurrent vector direction is NE, which suggesting deposition by a fan of a river draining craton into foreland. This unit is dated between 100 ka and 54 ka. The top unit-III, interfluve succession of 10-15 m thick is composed of dark and light bands of sheet like deposit of silty clay to clayey silt comprises sand lenses of red to grey color and displaying top most OSL age is 12 ka. The basal mature paleosol signifies a humid climate developed under low subsidence rate at >100 ka. After a hiatus represented by pedogenic surface deposition of unit-II (gravel) suggests uplift

  16. Lead isotopic composition of paleozoic and late proterozoic marine carbonate rocks in the vicinity of Yucca Mountains, Nevada

    International Nuclear Information System (INIS)

    Zartman, R.E.; Kwak, L.M.

    1993-01-01

    Paleozoic and Late Proterozoic marine carbonate rocks (limestones, dolomites, and their metamorphic equivalents) cropping out in the vicinity of Yucca Mountain contain lead with an isotopic composition strongly suggesting them to be a major source of the lead observed at Trench 14 in the carbonate phase of carbonate-silica veins and nearby surficial calcrete deposits. Six whole-rock samples of marine carbonate rocks yield 206 Pb/ 204 Pb = 19.21-29.06, 207 Pb/ 204 Pb = 15.74-16.01, and 208 Pb/ 204 Pb = 37.90-39.25, and leachate and residue fractions of the rocks reveal additional isotopic heterogeneity within individual samples. Two samples of eolian dust also have isotopic compositions lying along a 'carbonate' to 'silicate' mixing trend that appears to arise entirely from pedeogenic processes. The tendency for the marine carbonate rocks to evolve highly uranogenic, but not thorogenic, lead results in a distinctive isotopic composition that serves as a tracer in eolian dust and secondary carbonate minerals derived from the marine carbonate rocks

  17. Diagenesis of Permian alluvial fan deposits of Northern Switzerland

    International Nuclear Information System (INIS)

    Bluem, W.

    1987-01-01

    Fine-grained sandstones of Permian alluvial fan deposits from three Nagra boreholes (Weiach, Riniken, Kaisten) and an exploration well, drilled at Wintersingen are clast supported, moderately sorted arkosic greywackes containing typically 2-20 % clayey matrix. Petrographic studies indicate that the origin of this clayey matrix is postdepositional. Mechanical infiltration of fines and diagenetic reddening of detrital and authigenic iron oxides are the earliest recorded events. Additionally, nodular calcites of calcrete origin and fibrous illitic clays are also ascribed to the eogenetic environment. The present strong compaction fabric results from general lack of eogenetic framework supporting cements. During mesogenesis, secondary porosity was generated through partial removal of early calcite. At the same time, a first generation of syntaxial quartz cementation and a subsequent fibrous illite authigenesis took place. Leaching of detrital K-feldspars post-dating compaction is recorded throughout the studied boreholes. The following burial diagenetic events differ between the various boreholes: in Weiach and Wintersingen kaolinite, illite, prismatic quartz and ankerite/siderite are recorded; in Riniken K-feldspar, illite, prismatic quartz and dolomite developed; whilst in Kaisten K-feldspar and microcrystalline quartz-cement dominate. These differences reflect the chemistry, pH and ionic strength of the pore fluids. Filling of veins by dolomite/ankerite, iron-rich and subsequent iron-poor calcite is the latest recorded event. (author) 21 refs., 10 figs., 1 tab

  18. Geological investigations for the South African nuclear waste repository facility

    International Nuclear Information System (INIS)

    Hambleton-Jones, B.B.; Levin, M.; Andersen, N.J.B.; Brynard, H.J.; Toens, P.D.

    1984-02-01

    The selection of the Vaalputs site on the arid Bushmanland Plateau in the northwestern Cape of the Republic of South Africa for the disposal of low-level radioactive waste was based on a national screening phase program involving socio-economic and geological criteria. Regional geohydrological studies over an area of 27,000 km 2 and a detailed study over 1,300 km 2 indicated that in general the groundwater is saline and that Vaalputs and environs was the most favourable area. The groundwater table lies between 30 and 45 m below the surface, with 14 C ages between 2,500 and 9,000 years old in the immediate vicinity. The geology of Vaalputs consists of Proterozoic granites, gneisses, metasediments, and noritoids of the 1,050 Ma Namaqualand Metamorphic Complex. Upper cretaceous kimberlitic and basaltic intrusions occur locally. Overlying these basement rocks surficial upper Tertiary to Recent argillaceous sediments occur in the Vaalputs basin. The sediments consist of aeolian sand, calcrete, fluvial sandy to gritty clay, white kaolinised clay and very weathered basement rocks. It is in these rocks that the low-level waste trenches will be located. Extensive airborne geophysical surveys, such as aeromagnetics, INPUT, and infrared thermal line scanning, were undertaken to assist in the evaluation of the regional and local subsurface geology. Ground geophysical surveys included refraction seismics, electromagnetics, magnetics, borehole radiometrics and resistivity. Geohydrological modelling of the unsaturated and saturated zones is in progress

  19. Continental cretaceous in well ER-N-1 Nogoya Argentina in order to correlation Guichon and Mercedes formation (Uruguay)

    International Nuclear Information System (INIS)

    Tofalo, O.; Pazos, P.; Etchichury, M. . E mail: rtofalo@gl.fcen.uba.ar

    2004-01-01

    The petrographic al and dia genetical features of cutting samples obtained from the YPF ER.N.1 (Nogoya) log g situated in Entre Rios (Argentina) have been compared with those features documented from the Guichon and Mercedes Formation (Uruguay), in order to propose an stratigraphic al correlation. Two stratigraphic al intervals situated between 516-660 depth and 258-516 depth have been differentiated. The lower one is composed of brown reddish poor consolidated quartz-feldespatic and commonly matrix supported sandstones having abundant clay size matrix, conforming clay and clay-ferrocuttans. The scarce reddish pelitic intervals evidence pedoturbation and edafization features. Taking into account all those features a correlation with the Guichon Formation is suggested. The upper one is constituted by unconsolidated and poor consolidated intervals of sands and sandstones having a dominance of quartz over feldespathic grains, c last-supported fabric, early diagenetic calci tic cement and also silic ious and rare gypsum as late diagenetic pulses. Carbonate precipitation is related to calcretization fenomena responsible of replacement of grains, penetration and displacive growing. All these features are frequently reported from Mercedes Formation and a correlation with that lithostratigraphic units is here favored [es

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

    International Nuclear Information System (INIS)

    Andreoli, M.A.G.; Andersen, N.J.B.; Levin, M.; Niemand, N.

    1987-01-01

    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. Regional exploration for channel and playa uranium deposits in Western Australia using groundwater

    International Nuclear Information System (INIS)

    Noble, R.R.P.; Gray, D.J.; Reid, N.

    2011-01-01

    Shallow calcrete aquifers in the central north of the Yilgarn Craton in Western Australia are the host to numerous secondary carnotite U deposits. Sampling and analysis of approximately 1400 shallow aquifer groundwaters were conducted to test if U mineralisation of this type may be found using a >5 km sample spacing. Results show this can be achieved. All the economic deposits and most of the minor deposits and occurrences are associated with groundwater that has carnotite (KUO 2 VO 4 ) approaching or exceeding saturated conditions. Soluble U concentrations alone identified the largest deposit (Yeelirrie) and several smaller deposits, but this parameter was not as successful as the mineral saturation indices. Palaeodrainage distribution and thickness of cover combined with surface drainage and catchment boundaries provided background information of U primary sources and for areas with the highest exploration potential for channel and playa U deposits. Granites in the SE of the study area are less prospective with regard to secondary U deposits. Groundwater geochemistry in conjunction with palaeodrainage mapping may greatly improve exploration through cover where radiometric geophysics is not effective. The study of regional, shallow groundwater for U shows multiple benefits for mineral exploration, the economy and potable water quality.

  2. On the Sources of Salinity in Groundwater under Plain Areas. Insights from {delta}{sup 18}O, {delta}{sup 2}H and Hydrochemistry in the Azul River Basin, Argentina

    Energy Technology Data Exchange (ETDEWEB)

    Zabala, M. E.; Varni, M.; Weinzettel, P. [Instituto de Hidrologia de llanuras, Azul (Argentina); Manzano, M. [Technical University of Cartagena (Spain)

    2013-07-15

    The Azul River basin, with some 6200 km{sup 2}, 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)

  3. Typology and geographic/geotectonic distribution of uranium deposits

    International Nuclear Information System (INIS)

    Dahlkamp, F.J.

    1980-01-01

    In the last ten years, twenty new uranium deposits have been discovered. They provide nearly 50% of the known and reasonably assured resources. The most important deposits known in the past by size and ore grade were those found in oligomictic quartz pebble conglomerates, sandstones and, to a lesser extent, hydrothermal veins. The type found more recently, which are greater in quantity than the former ones, are of the vein type (Canada, Australia) as well as of the intrusive type (Roessing, Namibia) and in calcretes (Yeelirrie, Australia) and acid volcanic rocks (Mexico). Several classifications have been worked out in the past (E.W. Heinrich, 1958; M. Roubault, 1958; A. Mancher, 1962). More recently new data have enabled these classifications to be extended on a worldwide basis (Ruzicka, 1971; Ziegler, 1974; Dahlkamp, 1974, 1978) or on a regional basis (McMillan for Canada, 1978; Ingram for Australia, 1974). This classification attempt takes all available useful data into consideration to define different types of uranium deposits in as comprehensive and strict a manner as possible

  4. First record of lobed trace fossils in Brazil's Upper Cretaceous paleosols: Rhizoliths or evidence of insects and their social behavior?

    Science.gov (United States)

    Luciano do Nascimento, Diego; Batezelli, Alessandro; Bernardes Ladeira, Francisco Sérgio

    2017-11-01

    This is the first report of trace fossils potentially associated with insect social behavior in sandy and well-drained paleosols of the Upper Cretaceous continental sequence of Brazil. The trace fossils consist of dozens of lobed and vertical structures cemented by CaCO3 and preserved mainly in full relief in paleosols of the Marilia Formation (Bauru Basin) in the state of Minas Gerais. The described ichnofossils are predominantly vertical, up to 2 m long, and are composed of horizontal lobed structures connected by vertical tunnel-like structures that intersect in the center and at the edges. The lobed structures range from 3 to 15 cm long and 2-6 cm thick. Two different hypotheses are analyzed to explain the origin of the trace fossils; the less probable one is that the structures are laminar calcretes associated with rhizoliths and rhizoconcretions. The hypothesis involving social insects was considered because the trace fossils described herein partially resemble a modern ant nest and the ichnofossil Daimoniobarax. The micromorphological analysis of the lobed and tunnel-like structures indicates modifications of the walls, such as the presence of inorganic fluidized linings, dark linings and oriented grains, supporting the hypothesis that they are chambers and shafts. The architecture and size of the reported nests suggest the possibility that social insect colonies existed during the Maastrichtian and are direct evidence of the social behavior and reproductive strategies of the Cretaceous pedofauna.

  5. Sedimentology of the upper Karoo fluvial strata in the Tuli Basin, South Africa

    Science.gov (United States)

    Bordy, Emese M.; Catuneanu, Octavian

    2001-08-01

    The sedimentary rocks of the Karoo Supergroup in the Tuli Basin (South Africa) may be grouped in four stratigraphic units: the basal, middle and upper units, and the Clarens Formation. This paper presents the findings of the sedimentological investigation of the fluvial terrigenous clastic and chemical deposits of the upper unit. Evidence provided by primary sedimentary structures, palaeontological record, borehole data, palaeo-flow measurements and stratigraphic relations resulted in the palaeo-environmental reconstruction of the upper unit. The dominant facies assemblages are represented by sandstones and finer-grained sediments, which both can be interbedded with subordinate intraformational coarser facies. The facies assemblages of the upper unit are interpreted as deposits of a low-sinuosity, ephemeral stream system with calcretes and silcretes in the dinosaur-inhabited overbank area. During the deposition of the upper unit, the climate was semi-arid with sparse precipitation resulting in high-magnitude, low-frequency devastating flash floods. The current indicators of the palaeo-drainage system suggest flow direction from northwest to southeast, in a dominantly extensional tectonic setting. Based on sedimentologic and biostratigraphic evidence, the upper unit of the Tuli Basin correlates to the Elliot Formation in the main Karoo Basin to the south.

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

    International Nuclear Information System (INIS)

    1985-01-01

    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)

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

    International Nuclear Information System (INIS)

    1985-01-01

    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) [fr

  8. Micromorphology of Paleosols of the Marília Formation and their Significance in the Paleoenvironmental Evolution of the Bauru Basin, Upper Cretaceous, Southeastern Brazil

    Directory of Open Access Journals (Sweden)

    Márcio Luiz da Silva

    Full Text Available ABSTRACT Deduction of associated paleoenvironments and paleoclimate, definition of the chronosequence of paleosols, and paleogeographic reconstruction have become possible through the application of micromorphology in paleopedology. Micromorphology has also been useful in recognition of weathering processes and definition of minerals formed in succession. In this respect, the objective of this study was to identify the development of pedogenic processes and discuss their significance in the paleoclimate evolution of the Marília Formation (Maastrichtian of Bauru Basin. Three sections of the Marília Formation (A1, A2, and A3 were described, comprising nine profiles. Micromorphologic al analysis was carried out according to the specialized literature. In the Marília Formation, the paleosols developed in sandstones have argillic (Btkm, Bt and carbonate (Bk horizons with different degrees of cementation, forming mainly calcretes. The evolution of pedogenic processes, in light of micromorphological analysis, evidenced three moments or stages for the genesis of paleosols with Bkm, Btk, and Bt horizons, respectively. In the Maastrichtian in the Bauru Basin, the paleosols with Bkm are older and more arid environments, and those with Bt were formed in wetter weather, but not enough to lead to the genesis of enaulic-related distributions, typical of current Oxisols.

  9. The Wiluna Uranium Project, Western Australia: Bringing a new project to the market

    International Nuclear Information System (INIS)

    Guthrie, V.

    2014-01-01

    The Wiluna Uranium Project is the first uranium mine in Western Australia to receive Government environmental approval since government policy was changed in 2008 to allow uranium mining in Western Australia. Located 960 km northeast of Perth in remote central Western Australia, the Wiluna Project comprises 76.5 million pounds U_3O_8 [~29,000 tU] in six shallow, calcrete-hosted carnotite uranium deposits. Mining is planned at a rate of 1.3 million tonnes annually to produce 2 million pounds U_3O_8 [~770 tU] production using an alkali leach process. The Project requires initial capital investment of AUD$315M and has an operating cost of US$29-31 per pound [~75-~80 USD/kgU]. During the four years it has taken to gain environmental approval, Toro also progressed technical studies to validate the economic and technical viability of the Project. These included the initial Preliminary Feasibility (PFS) to define the processing train; mining optimisation studies, a Resource Evaluation Pit (REP) and a commercial scale Pilot Plant to verify the mining and processing technologies; and finally, Phase 1 of the Definitive Feasibility Study (DFS) which focussed on the processing plant design. (author)

  10. Surficial uranium deposits: summary and conclusions

    International Nuclear Information System (INIS)

    Otton, J.K.

    1984-01-01

    Uranium occurs in a variety of surficial environments in calcretes, gypcretes, silcretes, dolocretes and in organic sediments. Groundwater moving on low gradients generates these formations and, under favourable circumstances, uranium deposits. A variety of geomorphic settings can be involved. Most surficial deposits are formed in desert, temperate wetland, tropical, or transitional environments. The largest deposits known are in sedimentary environments in arid lands. The deposits form largely by the interaction of ground or surface waters on the geomorphic surface in favourable geologic terrains and climates. The deposits are commonly in the condition of being formed or reconstituted, or being destroyed. Carnotite is common in desert deposits while in wetland deposits no uranium minerals may be seen. Radioactive disequilibrium is common, particularly in wetland deposits. Granites and related rocks are major source rocks and most large deposits are in regions with enriched uranium contents, i.e. significantly greater than 5 ppm uranium. Uranium dissolution and transport is usually under oxidizing conditions. Transport in desert conditions is usually as a bicarbonate. A variety of fixation mechanisms operate to extract the uranium and form the deposits. Physical barriers to groundwater flow may initiate ore deposition. Mining costs are likely to be low because of the near surface occurrence, but there may be processing difficulties as clay may be present and the saline or carbonate content may be high. (author)

  11. The preservation of the Agoudal impact crater, Morocco, under a landslide: Indication of a genetic link between shatter cones and meteorite fragments

    Science.gov (United States)

    Nachit, Hassane; Abia, El Hassan; Bonadiman, Costanza; Di Martino, Mario; Vaccaro, Carmela

    2017-10-01

    Geological studies and tomographic profiles of a locality nearby the Agoudal village (Morocco) showed the presence of a single impact crater, 500-600 m diameter, largely hidden by a limestone block, 220 m long and 40 m deep. The site was interpreted as a landslide that followed the fall of a cosmic body. The Agoudal impact crater was not affected by intense erosion. The lack of an evident impact structure, as well as the sporadic distribution of impactites and their limited occurrence, can be explained by a complex geological framework and by recent tectonics. The latter is the result of the sliding of limestone block, which hides almost two-thirds of the crater's depression, and the oblique fall of the meteoroid on sloping ground. In addition, some impact breccia dikes sharply cut the host rock in the Agoudal impact structure. They do not show any genetic relationship with tectonics or hydrothermal activity, nor are they related to any karst or calcrete formations. Altogether, the overlapping of the meteorite strewn field (11 km long and 3 km wide) with the area of occurrence of shatter cones and impact breccias, together with the presence of meteorite fragments (shrapnel) ejected from the crater, the presence of shatter cones contaminated by products of iron meteorites and the presence of impact breccias that contain meteorite fragments of the same chemical composition of the Agoudal meteorite indicate that the fall of this meteorite can be responsible for the formation of the impact structure.

  12. The eolic fluvial succession and paleoclimatic evolution of Rio Conlara, San Luis, Argentina

    International Nuclear Information System (INIS)

    Chiesa, J.

    2004-01-01

    The outcroping deposits in the ravines of the Conlara River are dominated by silt with subordinated and variable percentages of sand and clays. In the section that is described, at the south of the town of Santa Rosa del Conlara, these materials have been deposited responding generally climatic changing conditions. The base of the profile, assigned to the late Pleistocene, contains extint fauna of the Lujanense and a datation of 8950 B.P., and it is represented by fluvial sandy gravels. The overlaying succession, assigned to the Holocene, shows an intercalation of horizons generated by eolic-loessic deposits and deposits with development of pedogenetic processes. The whole succession shows characteristic of corresponding to a vegetated plain, next to the river flood plain. The discriminated horizons are the result of a detailed sampling and the representation of range parameters of the same ones, in function of the depth, this last one oscillates between 6 and 8 meters. The quaternary deposits of the region, support indistinctly as on the crystalline basement of San Luis range, as on the calcretes assigned to the Neogene [es

  13. Effect of pH change on the primary uran-mica mineralization

    Energy Technology Data Exchange (ETDEWEB)

    Shmariovich, E M; Zhil' tsova, I G; Pakul' nis, G V; Shugina, G A [Ministerstvo Geologii SSR, Moscow

    1982-01-01

    Conditions of the formation of ore bodies of hexavalent uranium minerals represented by uranyl vanadates and phosphates which are primary and sedimented from low temperature solutions (carnotite deposits in calcretes and carnotite - autunite deposits in black shale formations) are considered. Thermodynamic curves of the solubility dependence of various uranyl minerals on pH medium in the absence of SO/sub 4//sup 2 -/ and CO/sub 3//sup 2 -/ ions and for sulphate-carbonate solutions have been calculated using dissociation constants of corresponding acids and ..delta..G/sup 0/f(298.15) values. It has been ascertained that uranyl mineral compounds according to the dependence of their solubility on ph medium form a distinct series from molybdates through arsenates, phosphates, vanadates and silicates to minerals of uranophane and kasolite group. It is shown that during the formation of infiltration deposits with uranyl mineralization a decisive role is played by the contrast change of pH value of medium caused by the presence of acid geochemical barrier (uranyl molybdates, arsenates, phosphates and vanadates are precipitating) or neutralizing alkaline barriers (uran-mica and uranyl silicates are precipitating) on the path of movement of oxygen metal-bearing solutions.

  14. Inverted stream channels in the Western Desert of Egypt: Synergistic remote, field observations and laboratory analysis on Earth with applications to Mars

    Science.gov (United States)

    Zaki, Abdallah S.; Pain, Colin F.; Edgett, Kenneth S.; Giegengack, Robert

    2018-07-01

    Inverted relief landforms occur in numerous regions on Mars, ranging in age from Noachian to more recent Amazonian periods (channel features on Earth form, and the geologic records they preserve in arid settings, can yield insights into the development of inverted landforms on Mars. Inverted channel landforms in the Western Desert of Egypt are well represented across an area of ∼27,000 km2. We investigated inverted channel features at seven sites using remotely-sensed data, field observations, and lab analysis. Inverted channel features in the Western Desert record fluvial environments of differing scales and ages. They developed mainly via inversion of cemented valley floor sediment, but there is a possibility that inverted fluvial landforms in the Dakhla Depression might have been buried, lithified, and exhumed. A few examples, in the southeastern part of the Western Desert, record, instead, a resistance to erosion caused by surface armouring of uncemented valley floor sediment. We show that the grain-size distribution for investigated and reviewed inverted channels is highly variable, with boulders that are commonly 0.35 - 1 m in size; large particles provide high porosity that influences the cementation mechanism. The studied inverted channel sediments are mainly cemented with ferricrete, calcrete, gypcrete, and silcrete. Inverted channels are valuable for the reconstruction of paleoclimate cycles or episodes on Earth and Mars; observations from the Western Desert, when offered as analogs, add to the growing list of Earth examples that provide suites of observables relevant to reconstruction of paleoenvironmental conditions on Mars.

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

    Science.gov (United States)

    Muhs, Daniel R.

    2013-01-01

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

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

    International Nuclear Information System (INIS)

    Bidegain, J. C.; Bartel, A. A.; Sives, F. R.; Mercader, R. C.

    2007-01-01

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

  17. 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

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

    International Nuclear Information System (INIS)

    Duverger, Agathe

    2013-01-01

    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 (K 2 (UO 2 ) 2 [VO 4 ] 2 .3H 2 O). 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

  19. 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

  20. Growth form and seasonal variation in leaf gas exchange of Colophospermum mopane savanna trees in northwest Botswana.

    Science.gov (United States)

    Veenendaal, Elmar M; Mantlana, Khanyisa B; Pammenter, Norman W; Weber, Piet; Huntsman-Mapila, Phillipa; Lloyd, Jon

    2008-03-01

    We investigated differences in physiological and morphological traits between the tall and short forms of mopane (Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard) trees growing near Maun, Botswana on a Kalahari sandveld overlying an impermeable calcrete duricrust. We sought to determine if differences between the two physiognomic types are attributable to the way they exploit available soil water. The tall form, which was located on deeper soil than the short form (5.5 versus 1.6 m), had a lower leaf:fine root biomass ratio (1:20 versus 1:6), but a similar leaf area index (0.9-1.0). Leaf nitrogen concentrations varied between 18 and 27 mg g(-1) and were about 20% higher in the tall form than in the short form. Maximum net assimilation rates (A sat) occurred during the rainy seasons (March-April 2000 and January-February 2001) and were similar in the tall and short forms (15-22 micromol m(-2) s(-1)) before declining to less than 10 micromol m(-2) s(-1) at the end of the rainy season in late April. As the dry season progressed, A sat, soil water content, predawn leaf water potential (Psi pd) and leaf nitrogen concentration declined rapidly. Before leaf abscission, Psi pd was more negative in the short form (-3.4 MPa) than in the tall form (-2.7 MPa) despite the greater availability of soil water beneath the short form trees. This difference appeared attributable to differences in root depth and density between the physiognomic types. Stomatal regulation of water use and carbon assimilation differed between years, with the tall form having a consistently more conservative water-use strategy as the dry season progressed than the short form.

  1. Major uranium provinces: Yilgarn block and Gascoyne Province, Western Australia

    International Nuclear Information System (INIS)

    Butt, C.R.M.

    1988-01-01

    The Archaean Yilgarn Block and the adjacent Proterozoic Gascoyne Province, Western Australia, form the basement and source rocks for numerous occurrences of surficial uranium mineralization, the largest being the Yeelirrie deposit (35 million tonnes at 0.15% U 3 O 8 ). The mineralization, almost exclusively in the form of carnotite, has been deposited in the regolith and appears to be less than 1 Ma old, with some deposits still forming. The nature and distribution of the mineralization are controlled by basement and surface geology, geomorphology, hydrology and climate, being restricted to deeply weathered, semi-arid terrain with granitoid source rocks. A few small occurrences in the Gascoyne Province may be pedogenic in origin but the majority, in the north of Yilgarn Block, occur in unrejuvenated palaeodrainage channels now choked by colluvial, alluvial and chemical sediments. These sediments, which are aquifers for the present, predominantly sub-surface, drainage, can exceed 10-15 m. Uranium released from the weathering granitoids has been transported in groundwaters in uranyl carbonate complexes and precipitated as carnotite where, (i) concentrations of uranium and potassium have been elevated by evaporation and, (ii) dissolved vanadium has been oxidized to the 5-valent state. Precipitation is in calcretes and associated sediments in the drainage axes, in 'chemical deltas' where the drainages enter playas and in the playas themselves. This style of mineralization was first recognized in 1969-1970 as the result of investigations into the source of radiometric anomalies delineated by airborne surveys. The majority of discoveries have similarly been by radiometric surveys but hydrogeochemical surveys have promise and may become important in future search for blind mineralization and/or young deposits not in radioactive equilibrium. (author). 61 refs, 6 figs

  2. Paleoweathering features in the Sergi Formation (Jurassic-Cretaceous), northeastern Brazil, and implications for hydrocarbon exploration

    Science.gov (United States)

    Pierini, Cristina; Mizusaki, Ana M.; Pimentel, Nuno; Faccini, Ubiratan F.; Scherer, Claiton M. S.

    2010-03-01

    Paleoweathering in the Sergi Formation has been classified and analyzed to ascertain its origin and relationship with stratigraphic evolution. The Sergi Formation belongs to the pre-rift sequence of the Recôncavo Basin (northeastern Brazil) and comprises a complex association of eolian and fluvial sandstones and lacustrine mudstones. This formation can be subdivided into three depositional sequences bounded by regional unconformities. Four paleoweathering types, each one related to a distinct origin, have been described in the Sergi Formation: (1) textural mottling, which is distinguished by alternating rock colors as a result of the iron oxide mobilization within mineral phases that evolved under alternating oxidation (yellowish, brownish and reddish shades) and reduction (grayish or greenish hues) conditions; (2) non-textural mottling, which displays a discoloration pattern that is independent of the original rock texture; (3) carbonate concentrations, usually related to carbonate nodule formation, which display a massive internal structure that reveals their origin through continuous growth or crystallization; and (4) banded carbonates (silicified), associated with the beginning of regular surface formation due to the chemical precipitation of carbonates within lacustrine environments. Both mottling color motifs and carbonate accumulation usually represent groundwater oscillation rather than pedogenesis. Only carbonate intraclasts and banded carbonate (silicified) have their origin ascribed to pedogenesis sensu stricto, although the carbonate intraclasts do not represent soil deposits in situ, but calcretes eroded from areas close to channels, and the banded carbonates (silicified) have strong diagenetic modifications. Therefore, it is reasonable to assume that fluvial and meteoric water have controlled paleoweathering evolution as well as deposition, yet both aspects are ruled by the same mechanisms (relief, sedimentation rate and, above all, climate).

  3. Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago

    Science.gov (United States)

    Meco, J.; Muhs, D.R.; Fontugne, M.; Ramos, A.J.; Lomoschitz, A.; Patterson, D.

    2011-01-01

    The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate-region locust (cf. Dociostaurus maroccanusThunberg 1815). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420ka), MIS 5.5 (ca. 125ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full-glacial arid-cold climate (calcareous dunes), early interglacial arid-sub-humid climate (African dust inputs and locust plagues), peak interglacial warm-humid climate (marine deposits with Senegalese fauna), transitional arid-temperate climate (pedogenic calcretes), and again full-glacial arid-cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro-African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts. ??? Locust plagues, Canary Islands, Late Pliocene, Pleistocene, Holocene, palaeoclimatology. ?? 2010 The Authors, Lethaia ?? 2010 The Lethaia Foundation.

  4. What do we really know about early diagenesis of non-marine carbonates?

    Science.gov (United States)

    De Boever, Eva; Brasier, Alexander T.; Foubert, Anneleen; Kele, Sándor

    2017-11-01

    Non-marine carbonate rocks including cave, spring, stream, calcrete and lacustrine-palustrine sediments, are susceptible to early diagenetic processes. These can profoundly alter the carbonate fabric and affect paleoclimatic proxies. This review integrates recent insights into diagenesis of non-marine carbonates and in particular the variety of early diagenetic processes, and presents a conceptual framework to address them. With ability to study at smaller and smaller scales, down to nanometers, one can now observe diagenesis taking place the moment initial precipitates have formed, and continuing thereafter. Diagenesis may affect whole rocks, but it typically starts in nano- and micro-environments. The potential for diagenetic alteration depends on the reactivity of the initial precipitate, commonly being metastable phases like vaterite, Ca-oxalates, hydrous Mg-carbonates and aragonite with regard to the ambient fluid. Furthermore, organic compounds commonly play a crucial role in hosting these early transformations. Processes like neomorphism (inversion and recrystallization), cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex, primary microtextures. If early diagenetic modifications are completed in a short time span compared to the (annual to millennial) time scale of interest, then recorded paleoenvironmental signals and trends could still acceptably reflect original, depositional conditions. However, even compact, non-marine carbonate deposits may behave locally and temporarily as open systems to crystal-fluid exchange and overprinting of one or more geochemical proxies is not unexpected. Looking to the future, relatively few studies have examined the behaviour of promising geochemical records, such as clumped isotope thermometry and (non-conventional) stable isotopes, in well-constrained diagenetic settings. Ongoing and future in-vitro and in-situ experimental approaches will

  5. Uranium resources potential for Asia and the Pacific

    International Nuclear Information System (INIS)

    Tauchid, M.

    1988-01-01

    Only four countries in Asia, India, Japan, the Republic of Korea and Turkey, reported having uranium resources in response to a Nuclear Energy Agency of the OECD/International Atomic Energy Agency questionnaire circulated before preparation of the report on Uranium: Resources, Production and Demand (the 'Red Book'). The reasonably assured resources (RAR) of these countries, which are recoverable at costs of up to US $130/kg U, amount to 67,690 t U or 3% of the total for the World Outside the Centrally Planned Economies Area (WOCA). It is believed that the largest uranium resources in Asia are in China; however, no official published figures are available to substantiate this fact. Within the framework of the International Uranium Resources Evaluation Project (IUREP) it was estimated that the speculative resources (SR) for Asia and the Far East outside the Centrally Planned Economies Area (CPEA) are of the order of 300,000 t U. This is 4.7% of the total for WOCA. With the exception of Proterozoic unconformity related deposits, all types of uranium deposits and occurrences are known to exist in Asia. Most deposits are of the vein and sandstone hosted types. Several published reports indicate that deposits in China are mainly of the volcanic type and those associated with granitic intrusion. For undiscovered deposits, probably India and China have the best possibility of finding deposits of the Precambrian quartz-pebble conglomerate and Proterozoic unconformity related types. In South-East Asia the deposits most likely to be found are those associated with Mesozoic granites and those in the intramontane basin sediments adjacent to these intrusions. The less known acid volcanic type is also a possibility. Only in China, India and Pakistan does there appear to be the possibility of finding calcrete type deposits. Uranium can still be recovered as a by-product of the phosphate rocks, monazite placer deposits and carbonatite known in many parts of Asia. (author). 21 refs

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

    Science.gov (United States)

    Williams, Martin

    2014-05-01

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

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

    International Nuclear Information System (INIS)

    Kneupper, G.; Scivetti, N.

    1981-01-01

    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

  8. Moving to world's best uranium address

    International Nuclear Information System (INIS)

    Noakes, Frank

    2006-01-01

    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 CO 2 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

  9. The III working days of the Cenozoic

    International Nuclear Information System (INIS)

    2012-06-01

    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

  10. Origin of the late quaternary dune fields of northeastern Colorado

    Science.gov (United States)

    Muhs, D.R.; Stafford, T.W.; Cowherd, S.D.; Mahan, S.A.; Kihl, R.; Maat, P.B.; Bush, C.A.; Nehring, J.

    1996-01-01

    Stabilized eolian deposits, mostly parabolic dunes and sand sheets, cover much of the landscape of northeastern Colorado and adjacent parts of southwestern Nebraska in four geographically distinct dune fields. Stratigraphic and soil-geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka, possibly between 11 ka and 4 ka, and within the past 1.5 ka. Thus, eolian sand deposition took place under both glacial and interglacial climatic conditions. In the youngest episodes of eolian sand movement, Holocene parabolic dunes partially buried Pleistocene sand sheet deposits. Late Holocene sands in the Fort Morgan and Wray dune fields, to the south of the South Platte River, have trace element ratios that are indistinguishable from modern South Platte River sands, but different from Ogallala Formation bedrock, which has previously been cited as the main source of dune sand on the Great Plains. Sands in the Greeley dune field, to the north of the South Platte River, have trace element concentrations that indicate a probable Laramie Formation source. Measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields, in good agreement with resultant drift directions calculated for nearby weather stations. Thus, paleowinds were probably not significantly different from present-day winds, and are consistent with a South Platte River source for the Fort Morgan and Wray dune fields, and a Laramie Formation source for the Greeley dune field. Sand accumulated downwind of the South Platte River to form the Fort Morgan dune field. In addition, sand was also transported farther downwind over the upland formed by the calcrete caprock of the Ogallala Formation, and deposited in die lee of the upland on the southeast side. Because of high wind energy, the upland itself served as a zone of sand transport, but little or no sand accumulation took place on this surface. These

  11. The role of major forest fires on rock physical decay in a Mediterranean environment

    Science.gov (United States)

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

    2017-04-01

    Massive destruction of carbonate rocks occurred on the slopes of Mt. Carmel (Israel), during a 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 extent of the physical disruption depends on rock composition: 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. Scorched and blackened faces under the upper layer of spalls provide 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. These flakes seem to play an important role in reforming the soil after the fire, especially by increasing the coarse particles percentage. These, in spite of the absence of vegetation cover, improve soil infiltration and percolation rates and cause long-term changes to the hydrological regime. It is difficult to estimate the frequency of high-intensity fires in the Carmel region over the past 2-3 million years, as well as the extension and density of the vegetation. It is even harder to assess the frequency of fires (and the destruction) of a single rock outcrop. Our findings show that rock outcrop may lose even 20 cm of its thickness in a single fire. This

  12. 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

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

    Directory of Open Access Journals (Sweden)

    Dahlkamp F. J.

    2006-11-01

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

  14. 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

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

    International Nuclear Information System (INIS)

    Bianchi, R.E.

    2009-01-01

    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)

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

    International Nuclear Information System (INIS)

    Hetland, Donald L.; Michie, Uisdean McL.

    1981-01-01

    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

  17. 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

  18. Past and present vegetation ecology of Laetoli, Tanzania.

    Science.gov (United States)

    Andrews, Peter; Bamford, Marion

    2008-01-01

    -Croton-Lepidotrichilia; and, finally, recent ash falls have produced immature alkaline soils with calcrete formation and short grass vegetation. All of these vegetation associations have been modified by human disturbance to greater or lesser degrees, and we have attempted to allow for this both by basing the associations on the least modified areas and by predicting how the associations, or parts of associations, have been altered by human action. Past land forms at Laetoli have been based on the geology and geomorphology of the area. Past vegetation patterns were estimated by superimposing present distributions of plant associations on equivalent landforms in the past, assuming similar climate to the present. This indicates the overall pattern of vegetation at Laetoli to have been a mosaic of low and tall deciduous woodlands and with riverine woodland and forest associations along water courses. Low woodlands would have been dominated by Acacia species, and tall woodlands by Combretum-Albizia species, with increasing increments of montane species, such as Croton species, to the east of the area. Riverine woodlands would have been dominated by Acacia-Euclea species, with wetter associations (downriver or linked with spring activity) supporting gallery forest with Ficus, Celtis, and Croton species. These are all species associations common in the area today, and with landforms little changed in the past, and assuming similar climate, there is every reason to predict that they would have been present in the past. Moreover, Pliocene environments lack the human disturbance that has destroyed much of the present day vegetation. Presence of woodlands is supported by fossil wood attributed to several of the tree species present in the area today and by similarities in the mammalian community structure between past and present. Having established the pattern for Pliocene vegetation based on climatic variables existing today, we then predict the effects of past variations in climate.

  19. Estimation of groundwater recharge via deuterium labelling in the semi-arid Cuvelai-Etosha Basin, Namibia.

    Science.gov (United States)

    Beyer, Matthias; Gaj, Marcel; Hamutoko, Josefina Tulimeveva; Koeniger, Paul; Wanke, Heike; Himmelsbach, Thomas

    2015-01-01

    The stable water isotope deuterium ((2)H) was applied as an artificial tracer ((2)H2O) in order to estimate groundwater recharge through the unsaturated zone and describe soil water movement in a semi-arid region of northern central Namibia. A particular focus of this study was to assess the spatiotemporal persistence of the tracer when applied in the field on a small scale under extreme climatic conditions and to propose a method to obtain estimates of recharge in data-scarce regions. At two natural sites that differ in vegetation cover, soil and geology, 500 ml of a 70% (2)H2O solution was irrigated onto water saturated plots. The displacement of the (2)H peak was analyzed 1 and 10 days after an artificial rain event of 20 mm as well as after the rainy season. Results show that it is possible to apply the peak displacement method for the estimation of groundwater recharge rates in semi-arid environments via deuterium labelling. Potential recharge for the rainy season 2013/2014 was calculated as 45 mm a(-1) at 5.6 m depth and 40 mm a(-1) at 0.9 m depth at the two studied sites, respectively. Under saturated conditions, the artificial rain events moved 2.1 and 0.5 m downwards, respectively. The tracer at the deep sand site (site 1) was found after the rainy season at 5.6 m depth, corresponding to a displacement of 3.2 m. This equals in an average travel velocity of 2.8 cm d(-1) during the rainy season at the first site. At the second location, the tracer peak was discovered at 0.9 m depth; displacement was found to be only 0.4 m equalling an average movement of 0.2 cm d(-1) through the unsaturated zone due to an underlying calcrete formation. Tracer recovery after one rainy season was found to be as low as 3.6% at site 1 and 1.9% at site 2. With an in situ measuring technique, a three-dimensional distribution of (2)H after the rainy season could be measured and visualized. This study comprises the first application of the peak displacement method using a

  20. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-07-01

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

  2. 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

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

    Science.gov (United States)

    Quantin, Paul

    2010-05-01

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

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

    Directory of Open Access Journals (Sweden)

    Michele Louise Francis

    2012-03-01

    Full Text Available

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