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Journal articles on the topic 'Calcrete geochemistry'

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Author: Grafiati

Published: 10 December 2022

Last updated: 29 January 2023

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1

Kadİr, S., M. Eren, T. Külah, N. Önalgİl, M. Cesur, and A. Gürel. "Genesis of Late Miocene-Pliocene lacustrine palygorskite and calcretes from Kırşehir, central Anatolia, Turkey." Clay Minerals 49, no. 3 (June 2014): 473–94. http://dx.doi.org/10.1180/claymin.2014.049.3.09.

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AbstractThis paper addresses the mineralogy, geochemistry, and genesis of palygorskite and associated calcretes in the Kırşehir region. In this area, the Quaternary calcretes are present within and/or on lacustrine mudstones of the Kızılırmak Formation (Late Miocene-Pliocene). The calcretes occur in the form of nodules, tubes, fracture-infills, and hard laminated crusts (hardpans). Calcrete samples are predominantly composed of calcite associated with smectite, quartz, feldspar, and minor palygorskite. The lacustrine mudstone samples consist mainly of smectite and palygorskite with minor calcite, quartz, feldspar, illite, kaolinite and amorphous material. Petrographic studies revealed that the calcrete samples are predominantly micrites that were partially converted to microsparites by recrystallization. Scanning and transmission electron microscopy images indicate that palygorskite fibres formed authigenically on and between calcite rhombs in the calcrete samples and at the edges of smectite flakes of host rocks adjacent to the calcretes. The oxygen and hydrogen stable isotope values of the calcite suggest that it precipitated from meteoric water under arid or seasonally arid climatic conditions. Calcite precipitation occurred in the vadose zone, as evidenced by desiccation cracks and vadose pisolites. The enrichment of Rb+Ba±Sr and Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE)with a distinct negative Eu anomaly are responses to the fractionation of volcanogenic feldspar and hornblende under the influence of meteoric water. The palygorskite associated with calcretes was precipitated from alkaline water rich in Si, Al and Fe and low in Mg. The palygorskite precipitation occurred at increased temperatures, characterising the advanced stage of calcrete formation which lowers the Ca content in the soil water. The required chemical elements for palygorskite and calcite were most likely derived from the dissolution of smectitic clays, ignimbrites and carbonate minerals.

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2

Larrey, Marine, Frédéric Mouthereau, Emmanuel Masini, Damien Huyghe, Eric C. Gaucher, Aurélien Virgone, and Véronique Miegebielle. "Quaternary tectonic and climate changes at the origin of travertine and calcrete in the eastern Betics (Almería region, SE Spain)." Journal of the Geological Society 177, no. 5 (June 2, 2020): 939–54. http://dx.doi.org/10.1144/jgs2020-025.

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Continental carbonate bodies are widespread in the Tabernas basin, eastern Betic Cordillera. Their relationships with the topographic evolution, climate changes and extensional regional tectonic processes recognized in the region are, however, still unclear. Travertine deposits exhibit facies of cascade and pool environments often reported as related to water–air surface processes. Calcretes show a large panel of facies, indicating control by groundwater and pedogenic processes. New U/Th dates on both travertine and calcrete reveal that they precipitated from 354 ka ± 76 to 8 ka ± 0.2. The U/Th dates obtained on calcretes are in good agreement with global climate changes and support that precipitation of recent CaCO3 is episodic and occurs mainly during warm and wet conditions. C and O stable isotope geochemistry reveals travertines are thermogenic and characterized by hydrothermal fluids enriched in CO2 that interacted with aquifers. This thermogenic origin suggests a deep source of CO2 (higher positive δ13C values) likely triggered by the presence of an anomalously hot mantle that reflects thinning of the regional lithosphere and volcanism. Further analyses of the distribution of calcrete show they are carbonate-rich fluvial terraces, whose formation is controlled by the response of the river network to regional uplift and climate.Supplementary Materials: reproducibility for δ13C and δ18O of the NSB-18 internal standard available in Supplementary Table 1 (SP1) and reproducibility for U and Th of the HU-1 standard available in Supplementary Table 2 (SP2) at https://doi.org/10.6084/m9.figshare.c.4996514

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3

Rodrigues, Ana Luísa, Maria Isabel Dias, Maria Isabel Prudêncio, Fernando Rocha, Francisco Ruiz Muñoz, Rosa Marques, María Luz González-Regalado, Dulce Russo, and Guilherme Cardoso. "Paleoenvironmental considerations based on geochemistry and mineralogy of a Miocene lacustrine calcrete, southern Portugal." E3S Web of Conferences 98 (2019): 06012. http://dx.doi.org/10.1051/e3sconf/20199806012.

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A lacustrine carbonate facies has been investigated in Middle Miocene successions of the western side of the Moura-Marmelar basin, Southern Portugal in order to evaluate paleoenvironments in which carbonates formed, by using geochemistry and mineralogy. The studied formation corresponds to a recent unearthed section of a calcrete with an homogeneous carbonate facies comprising fine, whitish, and powdery material, and the only detected difference is a slightly hardness decrease towards the top, as well as an increase of weathered rock fragments (schist). The calcrete is calcium rich, even some magnesium enrichment was observed at the middle level, which is differentiated by a general depletion of all chemical elements, particularly REE, in both the bulk and clay-size fraction. Regarding the mineralogy, calcite prevails, and dolomite is only present in the middle level of the calcrete, together with a smectite enrichment, suggesting changes to more alkaline and low drainage, lacustrine and arid to semi-arid conditions.

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4

Wang, Yifeng, Daniel Nahon, and Enrique Merino. "Geochemistry and dynamics of calcrete genesis in semi-arid regions." Chemical Geology 107, no. 3-4 (July 1993): 349–51. http://dx.doi.org/10.1016/0009-2541(93)90207-y.

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5

Lintern, M. J. "The association of gold with calcrete." Ore Geology Reviews 66 (April 2015): 132–99. http://dx.doi.org/10.1016/j.oregeorev.2014.10.029.

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6

Phani, P. Ramesh Chandra, and M. Srinivas. "Calcrete Geochemistry in identifying Kimberlite Lamproite Exploration Targets -A case study from Nalgonda district, Telangana, southern India." International Journal of Trend in Scientific Research and Development Volume-2, Issue-2 (February 28, 2018): 964–73. http://dx.doi.org/10.31142/ijtsrd9575.

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7

Reith, Frank, Steven A. Wakelin, Adrienne L. Gregg, and Andreas Schmidt Mumm. "A microbial pathway for the formation of gold-anomalous calcrete." Chemical Geology 258, no. 3-4 (January 2009): 315–26. http://dx.doi.org/10.1016/j.chemgeo.2008.10.023.

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8

Hall, S. M., B. S. Van Gosen, J. B. Paces, R. A. Zielinski, and G. N. Breit. "Calcrete uranium deposits in the Southern High Plains, USA." Ore Geology Reviews 109 (June 2019): 50–78. http://dx.doi.org/10.1016/j.oregeorev.2019.03.036.

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9

Simpson, C. J., J. R. Wilford, L. F. Macias, and R. J. Korsch. "SATELLITE DETECTION OF NATURAL HYDROCARBON SEEPAGE: PALM VALLEY GAS FIELD, AMADEUS BASIN, CENTRAL AUSTRALIA." APPEA Journal 29, no. 1 (1989): 196. http://dx.doi.org/10.1071/aj88019.

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Digital image processing of advanced aircraft and Landsat Thematic Mapper (TM) satellite remotely sensed data over sandstones of the Palm Valley Gas Field, central Australia, showed a distinct colour anomaly about 6 km long by 1.5 km wide which is not obvious in visible wavelength imagery. Field inspection showed that the colour anomaly was characterised by different rock- weathering colour, a geobotanical anomaly, calcium carbonate precipitation within rock fractures, and different soil pH. Inorganic rock geochemistry indicates significant chemical differences in some major elements. A limited number of soil gas samples were analysed and within the remotely sensed colour anomaly some had above- threshold concentrations of methane, ethane, propane and butane. Preliminary processing of airborne magnetic and gamma spectrometric data over the anticline did not indicate any significant values that suggested abnormal development of magnetite or clay minerals within the colour anomaly. Carbon and oxygen isotope analyses on calcrete from within the colour anomaly suggest, somewhat inconclusively, that hydrocarbons have not contributed significantly to the formation of the calcium carbonate component of the calcrete. Consideration of all available information suggests that the colour anomaly detectable by aircraft and Landsat TM satellite remote sensing corresponds to a zone of surface alteration resulting from long- term seepage of hydrocarbon gases. This colour anomaly, the first of its type reported from Australia, was detected because of spectral reflectance differences resulting from a combination of increased soil carbonate and different geobotanical characteristics from those of the surrounding terrain.

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10

Neymark, L. A. "Potential effects of alpha-recoil on uranium-series dating of calcrete." Chemical Geology 282, no. 3-4 (March 23, 2011): 98–112. http://dx.doi.org/10.1016/j.chemgeo.2011.01.013.

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11

Chiquet, Arnaud, Fabrice Colin, Bruno Hamelin, Annie Michard, and Daniel Nahon. "Chemical mass balance of calcrete genesis on the Toledo granite (Spain)." Chemical Geology 170, no. 1-4 (October 2000): 19–35. http://dx.doi.org/10.1016/s0009-2541(99)00240-5.

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12

Lintern, Melvyn J., Robert M. Hough, Chris G. Ryan, John Watling, and Michael Verrall. "Ionic gold in calcrete revealed by LA-ICP-MS, SXRF and XANES." Geochimica et Cosmochimica Acta 73, no. 6 (March 2009): 1666–83. http://dx.doi.org/10.1016/j.gca.2008.12.019.

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13

Durand, N., B. Hamelin, P. Deschamps, Y. Gunnell, and P. Curmi. "Systematics of U–Th disequilibrium in calcrete profiles: Lessons from southwest India." Chemical Geology 446 (December 2016): 54–69. http://dx.doi.org/10.1016/j.chemgeo.2016.06.026.

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14

Drummond, Justin B. R., T. Kurt Kyser, Robert R. Bowell, Noel P. James, and Daniel Layton-Matthews. "Diagenesis of paleodrainages in Lake Way and Lake Maitland, Western Australia, and the role of authigenic Mg-clays and dolomite in the genesis of channel and playa uranium deposits." Canadian Mineralogist 59, no. 5 (September 1, 2021): 947–84. http://dx.doi.org/10.3749/canmin.2000053.

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ABSTRACT This study integrates mineralogical and hydrogeochemical analysis of channel and playa uranium deposits to characterize aquifer evolution and the physico-chemical mechanisms that result in the accumulation of uranium into potentially economic deposits. This subset of surficial U deposits occur in Tertiary to Recent calcrete and dolomitic, clay-rich fluvial paleochannel and palustrine sediments, wherein uranium is largely bound in the potassium-uranyl-vanadate mineral carnotite [K2(UO2)2(VO4)2·3H2O]. Scanning electron microanalysis indicates that the carnotite mineralization is part of a late-diagenetic mineral assemblage that critically includes Mg-clays (sepiolite and stevensite), amorphous magnesium silicate, and synsedimentary dolomite. This authigenic mineral assemblage is observed concentrated in fractures and pores in groundwater calcrete and silty salt marsh “palustrine” sediments. Drill-hole gamma ray and conductivity data from the Centipede-Millipede uranium deposit indicate that the locus of uranium mineralization occurs near the present-day water table where oxidizing fresh-to-brackish groundwater interacts with playa brine, forming a hypopycnal groundwater estuary beneath the clay pan and salt marsh. It is interpreted that effective U fixing occurs in areas where groundwater, near-saturated with respect to carnotite, is hydrologically focused upward and into the zone of evaporation. The appreciable precipitation deficit in the Northern Yilgarn is interpreted to produce an evaporation-driven positive feedback mechanism that results in the co-precipitation of Mg-clays, dolomite, and carnotite. The presence of vanadium-rich Mn-oxide phases in high-grade U ore zones indicates that Mn-redox cycling may serve an important role in increasing the local activity of V, and thus carnotite saturation. Mineralogical comparison of other channel and playa uranium deposits throughout Western Australia and Namibia have identified a similar mineral association and paragenetic trend, suggesting that contemporaneous evaporative precipitation of Mg-clays and dolomite are integral in achieving carnotite saturation and precipitation.

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15

Chudasama, Bijal, Alok Porwal, Ignacio González-Álvarez, Sanchari Thakur, Andy Wilde, and Oliver P. Kreuzer. "Calcrete-hosted surficial uranium systems in Western Australia: Prospectivity modeling and quantitative estimates of resources. Part 1 – Origin of calcrete uranium deposits in surficial environments: A review." Ore Geology Reviews 102 (November 2018): 906–36. http://dx.doi.org/10.1016/j.oregeorev.2018.04.024.

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16

Bajnóczi, Bernadett, Zoltán Horváth, Attila Demény, and Andrea Mindszenty. "Stable isotope geochemistry of calcrete nodules and septarian concretions in a Quaternary ‘red clay’ paleovertisol from Hungary." Isotopes in Environmental and Health Studies 42, no. 4 (December 2006): 335–50. http://dx.doi.org/10.1080/10256010600991045.

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17

Bratkova, S., D. Nikolova, Y. Evstatieva, I. Dimitrov, and K. Nikolova. "Analysis of rhizospheric bacterial community in soils affected by the formation of calcrete." Journal of Geochemical Exploration 119-120 (August 2012): 44–50. http://dx.doi.org/10.1016/j.gexplo.2012.06.007.

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18

Chudasama, Bijal, Alok Porwal, Andy Wilde, Ignacio González-Álvarez, Malcolm Aranha, Umamahesh Akarapu, Martin Hirsch, and Eduard Becker. "Bedrock topography modeling and calcrete-uranium prospectivity analysis of Central Erongo Region, Namibia." Ore Geology Reviews 114 (November 2019): 103109. http://dx.doi.org/10.1016/j.oregeorev.2019.103109.

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19

ROBINSON, STUART A., JULIAN E. ANDREWS, STEPHEN P. HESSELBO, JONATHAN D. RADLEY, PAUL F. DENNIS, IAN C. HARDING, and PERCE ALLEN. "Atmospheric pCO2 and depositional environment from stable-isotope geochemistry of calcrete nodules (Barremian, Lower Cretaceous, Wealden Beds, England)." Journal of the Geological Society 159, no. 2 (March 2002): 215–24. http://dx.doi.org/10.1144/0016-764901-015.

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20

Nash, David J., Sue J. Mclaren, and John A. Webb. "Petrology, geochemistry and environmental significance of silcrete-calcrete intergrade duricrusts at Kang Pan and Tswaane, central Kalahari, Botswana." Earth Surface Processes and Landforms 29, no. 12 (2004): 1559–86. http://dx.doi.org/10.1002/esp.1138.

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21

Lintern, Mel, Malcolm Sheard, and Nicky Buller. "The gold-in-calcrete anomaly at the ET gold prospect, Gawler Craton, South Australia." Applied Geochemistry 26, no. 12 (December 2011): 2027–43. http://dx.doi.org/10.1016/j.apgeochem.2011.06.032.

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22

Schmidt Mumm, Andreas, and Frank Reith. "Biomediation of calcrete at the gold anomaly of the Barns prospect, Gawler Craton, South Australia." Journal of Geochemical Exploration 92, no. 1 (January 2007): 13–33. http://dx.doi.org/10.1016/j.gexplo.2006.06.003.

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23

Pentecost, Allan, and Heather Viles. "A Review and Reassessment of Travertine Classification." Géographie physique et Quaternaire 48, no. 3 (November 23, 2007): 305–14. http://dx.doi.org/10.7202/033011ar.

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ABSTRACTThis paper provides a review of the classification of travertines with emphasis on their morphology. Three criteria are used to describe them: geochemistry, microfabric and morphology. Geochemically, travertines may be divided into two groups, the meteogene travertines, where the carrier carbon dioxide originates in the soil and epigean atmosphere, and the thermal (thermogene) travertines where the carbon dioxide comes from thermally generated sources. Many travertine fabrics are influenced by bacteria and plants. These include 'stromatolitic' forms, many oncoids, shrubs, tufts, mats and moss travertines. Morphologically, travertines are conveniently divided into autochthonous (spring mounds and ridges, cascades, barrages, fluvial and lacustrine crusts, paludal deposits and cemented rudites) and the allochthonous or clastic travertines (valley-fills, back-barrage deposits, alluvial cones). Travertine deposits often include a wide range of fabrics and morphologies in one system. They are influenced locally by discharge, slope, vegetation, climate and human activity. Intergradations occur, both within travertine types but also with other freshwater deposits, e.g. calcrete and lake chalk. The influence of travertine deposition on the local hydrology and geomorphology is also discussed. The review emphasises the significance of scale and hydrology and aims to provide a unified scheme of travertine classification.

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24

Khoury, H. N., E. M. salameh, and I. D. Clark. "Mineralogy and origin of surficial uranium deposits hosted in travertine and calcrete from central Jordan." Applied Geochemistry 43 (April 2014): 49–65. http://dx.doi.org/10.1016/j.apgeochem.2014.02.005.

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25

Lintern, M. J., M. J. Sheard, and A. R. Chivas. "The source of pedogenic carbonate associated with gold-calcrete anomalies in the western Gawler Craton, South Australia." Chemical Geology 235, no. 3-4 (December 2006): 299–324. http://dx.doi.org/10.1016/j.chemgeo.2006.08.001.

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26

Lintern, M. J. "Exploration for gold using calcrete – lessons from the Yilgarn Craton, Western Australia." Geochemistry: Exploration, Environment, Analysis 1, no. 3 (August 2001): 237–52. http://dx.doi.org/10.1144/geochem.1.3.237.

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27

Reith, Frank, Barbara Etschmann, Robert C. Dart, Dale L. Brewe, Stefan Vogt, Andreas Schmidt Mumm, and Joël Brugger. "Distribution and speciation of gold in biogenic and abiogenic calcium carbonates – Implications for the formation of gold anomalous calcrete." Geochimica et Cosmochimica Acta 75, no. 7 (April 2011): 1942–56. http://dx.doi.org/10.1016/j.gca.2011.01.014.

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28

Josh, Matthew, Melvyn J. Lintern, Anton W. Kepic, and Mike Verrall. "Impact of grain-coating iron minerals on dielectric response of quartz sand and implications for ground-penetrating radar." GEOPHYSICS 76, no. 5 (September 2011): J27—J34. http://dx.doi.org/10.1190/geo2010-0321.1.

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An unexpected result of ground-penetrating radar (GPR) surveys in the Great Victoria Desert (South Australia) was the lack of returning signal in what appeared to be a favorable environment for GPR, with dry silica sand and calcrete aggregates in the near surface. We found that the dielectric response of the dry sand samples had much higher dielectric losses than comparable sands from Western Australia and that the dielectric losses are controlled by the presence of iron oxide minerals, although iron concentrations themselves are only around 0.4%. The samples contained over 90% quartz, with subsidiary amounts of carbonates, kaolin, and smectite occurring with the iron oxide minerals as a coating on the quartz grains. An acid washing procedure removed the reducible iron oxide minerals from the clay coating but left the clays substantially unaltered. Subsequent dielectric and magnetic analysis of the samples indicates that the iron oxide minerals removed during the washing process are responsible for the reduction of GPR penetration at 250 MHz from approximately 10 m to only 1 m.

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29

Guedria, A., J. Trichet, and E. Wilhelm. "Behaviour of lead and zinc in calcrete-bearing soils around Bou Grine, Tunisia — its application to geochemical exploration." Journal of Geochemical Exploration 32, no. 1-3 (April 1989): 117–32. http://dx.doi.org/10.1016/0375-6742(89)90051-4.

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30

Gürel, Ali. "Geology, mineralogy, and geochemistry of late Miocene paleosol and calcrete in the western part of the Central Anatolian Volcanic Province (CAVP), Turkey." Geoderma 302 (September 2017): 22–38. http://dx.doi.org/10.1016/j.geoderma.2017.04.016.

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31

Ghavami-Riabi, R., H. F. J. Theart, and C. De Jager. "Detection of concealed Cu–Zn massive sulfide mineralization below eolian sand and a calcrete cover in the eastern part of the Namaqua Metamorphic Province, South Africa." Journal of Geochemical Exploration 97, no. 2-3 (May 2008): 83–101. http://dx.doi.org/10.1016/j.gexplo.2007.11.003.

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32

Bull, William B., and Philip A. Pearthree. "Frequency and size of quaternary surface ruptures of the pitaycachi fault, northeastern Sonora, Mexico." Bulletin of the Seismological Society of America 78, no. 2 (April 1, 1988): 956–78. http://dx.doi.org/10.1785/bssa0780020956.

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Abstract Movements along the Pitaycachi fault since the Miocene juxtaposed different alluvial units and created 2- to 45-m-high fault scarps downslope from a pedimented mountain front prior to 1887. In 1887, a major earthquake formed a 75-km-long, 12- to 4-m-high scarp along the trace of prehistoric surface ruptures. Diverse evidence from many study sites indicates that about 200,000 yr elapsed between the prior (youngest Pleistocene) event and the 1887 surface rupture. Cumulative displacements of Pliocene(?) to mid-Pleistocene alluvial fans and stream terraces decrease with decreasing age. The trace of the prior rupture was largely buried by sheets of late Pleistocene and Holocene piedmont alluvium. Late Pleistocene soils are offset about the same amount as the height of the 1887 scarp. Valleys that are as much as 40 m deep and 0.5 to 0.9 km wide have been eroded since the prior event; they contain multiple late Pleistocene and Holocene stream terraces that were not faulted until 1887. Pre-1887 alluvial fault scarps were degraded to 2° to 9° slopes before the 1887 event, even in resistant materials such as clay-rich soil horizons with unweathered rhyolite cobbles and calcrete. Scarp height-maximum slope regressions and diffusion-equation analyses for reconstructed pre-1887 scarp profiles indicate that the prior event occurred more than 100,000 yr ago. Acceleration of scarp degradation rates during the Holocene, and/or relatively resistant materials exposed in the scarps, would increase the age estimates to 200,000 yr or more. Very long recurrence intervals are the characteristic style of movement on the Pitaycachi fault. At one site, six ages of diverse valley fills were inset into pedimented granodiorite upslope from the fault between the prior and 1887 events. Only 3 m of relief remained before the 1887 rupture increased the scarp height from 3 to 6 m. Some hillslopes have triangular talus facets of carbonatecemented colluvium that resulted from infrequent fault movements and intervening periods of erosion. Smooth hillsides of resistant volcanic rocks between the facets show that virtually all of the prior surface-rupture event scarps had been removed by prolonged slope degradation.

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33

Menezes, Maurícius Nascimento, Patrick Führ Dal' Bó, Jon J. Smith, Amanda Goulart Rodrigues, and Álvaro Rodríguez-Berriguete. "Maastrichtian atmospheric pCO2 and climatic reconstruction from carbonate paleosols of the Marília Formation (southeastern Brazil)." Journal of Sedimentary Research 92, no. 9 (September 7, 2022): 775–96. http://dx.doi.org/10.2110/jsr.2021.060.

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Abstract Paleosols are the product of ancient physical, chemical, and biological processes on the Earth's surface and, as such, may record information that can be used to reconstruct the paleoatmospheric and paleoenvironmental conditions under which they formed. In Brazilian continental sedimentary successions, few studies using ancient soils have focused on the relationship between paleopedogenesis and paleoclimate. The Marilia Formation is a 160-m-thick section of the Bauru Basin in which ∼ 66% of the deposits show some evidence of pedogenic modification as paleosols. In this paper, paleosol profiles in the Marilia Formation containing thick calcrete intervals are described and attributed to three pedotypes: Avencas, Monte Alto, and Garça. Macro and microscopic pedogenic features of each pedotype are described in detail. Moreover, the analysis of clay mineralogy, whole-rock geochemistry, and stable-isotope composition are used to define pedogenic processes, paleoclimate proxies, and atmospheric pCO2 estimates. The Avencas pedotype is composed of six polygenetic profiles with different phases of carbonate precipitation, clay illuviation, and biogenic actions. The Monte Alto pedotype is moderately developed and composed of calcic horizons formed mainly by rhizoliths, with higher degrees of calcification and oxidation compared to Avencas profiles. The Garça pedotype is well developed with five polygenetic profiles presenting high carbonate content and low accumulation of clay minerals (CIA-K) and leaching. Estimates of paleoprecipitation and paleotemperature from the studied paleosols using climofunctions of molar ratio of base to alumina, depth of carbonate accumulation, salinization, oxygen composition, and paleosol weathering index proxy (PWI) show values ranging from 242 to 718 mm/yr and 11° to 14°, respectively. Climofunction values suggest a paleoclimate of semiarid to subhumid during deposition of the Marília Formation. The climate data also suggests that during the Maastrichtian, the Bauru Basin was geographically within the Southern Hot Arid Belt zone, though showing strong influence of the lower latitudinal Equatorial Humid belt. Furthermore, atmospheric pCO2 values calculated from pedogenic carbonates may correlate with a cooling interval during the latest Maastrichtian (68.5–66.25 My).

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34

Okujeni, C. D., P. Ackon, W. Baugaard, and N. Langa. "Controls of element dispersion in aeolian sand and calcrete-dominated regolith associated with gold mineralization in the Kraaipan greenstone belt, South Africa." Geochemistry: Exploration, Environment, Analysis 5, no. 3 (July 19, 2005): 223–31. http://dx.doi.org/10.1144/1467-7873/05-076.

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35

Salomon, G. W., T. New, R. A. Muir, B. Whitehead, S. Scheiber-Enslin, J. Smit, V. Stevens, et al. "Geomorphological and geophysical analyses of the Hebron Fault, SW Namibia: implications for stable continental region seismic hazard." Geophysical Journal International 229, no. 1 (November 22, 2021): 235–54. http://dx.doi.org/10.1093/gji/ggab466.

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SUMMARY This study explores the geomorphological expression and geological context of a normal fault scarp in a stable continental region (SCR) which we interpret as having failed in large (Mw >7) earthquakes. Records of such large normal faulting events in an SCR (or even in more rapidly deforming regions) are extremely rare, and so understanding this feature is of international interest. The scarp is exceptionally well-preserved due to the extensive calcrete/silcrete cementation. In areas where this cementation is reduced or absent the scarp is more diffuse, as expected for a feature formed by one or more paleoearthquakes. The exceptional preservation aids comparison with data sets based on scarps which have formed more recently. Our analysis is based on a high-resolution digital elevation model of the Hebron Fault scarp in southern Namibia using pan-sharpened Worldview-3 satellite stereophotos (0.31 m resolution). We make scarp height measurements at 160 locations providing improved estimates of the average displacement (5.9 m), maximum displacement (10.1 m), and the minimum fault length (45 km). No consistent evidence of lateral displacements in water courses or alluvial fan margins were found implying predominantly normal displacement. A newly described section in the northwest has en-echelon scarps consistent with a component of strike-slip motion that may be explained by its difference in strike from the central section. Most channels crossing the fault show a single knick-point. The displacement varies smoothly as it crosses a number of different generations of alluvial fan surfaces. No evidence of a multiscarp or a composite scarp were observed. We have therefore found no evidence for a mutiple-event origin for the scarp, although, this lack of evidence does not conclusively demonstrate a single-event origin. Published regressions, based on the limited data available for SCRs, suggest that the mean expected average displacement ($\bar{D}_{\rm av}$) for a faults of this length is 1.2–3.1 m implying that the scarp is likely to have formed in 2–5 events with an expected Mw = ∼7.1 though displacements in individual events may exceed these average values. Comparison with the regional geology and aeromagnetic data sets suggests that the fault reactivates a Mesoproterozoic ductile structure, the Nam Shear Zone, and that the location, orientation and segmentation of the scarp is controlled by the alignment of pre-existing structurally weak zones with the present-day stress regime. The fault has undergone repeated brittle reactivation, accumulating ∼110 m of vertical offset since the deposition of the Ediacaran-to-Cambrian Nama Group. This is less than expected from global compilations of total displacement and fault length data, suggesting that the fault rapidly attained its current length by recruiting an existing weak zone and is expected to accumulate displacement at a relatively constant length in the future.

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36

Colson, J., I. Cojan, and M. Thiry. "A hydrogeological model for palygorskite formation in the Danian continental facies of the Provence Basin (France)." Clay Minerals 33, no. 2 (June 1998): 333–47. http://dx.doi.org/10.1180/000985598545516.

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AbstractThe Danian of the Provence basin (SE France) is characterized by a strong subatmospheric alteration processes throughout the basin. A wide range of facies, depositional and weathering, were recognized in an interval of 5 Myr and include floodplain fine-grained alluvium, palustrine limestones, playa dolostones, mottled palaeosols, vadose and phreatic calcretes, and phreatic dolocretes. Palygorskite was invariably found in laminar, massive and honeycomb vadose calcretes and phreatic dolocretes, as well as in playa dolostones, and only exceptionally in floodplain siltstones, nodular calcretes and palustrine limestones. Regardless of the facies, palygorskite is associated with smectites. An authigenic origin, based on the morphology of the fibres and the vertical distribution of clay minerals, is proposed for palygorskites in all of the facies. The simultaneous occurrence of palygorskite in these environments is interpreted as a sign of a stable seasonal semi-arid climate and low detrital input during a period of low lake level (-0.5 Myr). The occurrence of authigenic palygorskite in siltstones around the lake was attributed to the rising of the water table, retention of the already saturated water in the pore spaces of the sediment, and its subsequent evaporation in a confined environment. A hydrogeological model is proposed for the distribution of palygorskite. The elongated shape of the Provence basin enhanced the influence of lateral inflow of freshwater during the low lake period which explains the distribution of palygorskite in different environments of the Provence basin as well as spatial distribution of phreatic calcretes and dolocretes. During the high lake level, palygorskite formed in the few remaining ephemeral ponds and on the floodplain along the lake margin.

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37

Achyuthan, Hema, Navin Shankar, Martina Braida, and Syed Masood Ahmad. "Geochemistry of calcretes (calcic palaeosols and hardpan), Coimbatore, Southern India: Formation and Paleoenvironment." Quaternary International 265 (June 2012): 155–69. http://dx.doi.org/10.1016/j.quaint.2012.01.037.

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38

Alonso-Zarza, A. M., and C. Arenas. "Cenozoic calcretes from the Teruel Graben, Spain: microstructure, stable isotope geochemistry and environmental significance." Sedimentary Geology 167, no. 1-2 (May 2004): 91–108. http://dx.doi.org/10.1016/j.sedgeo.2004.02.001.

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Achyuthan, Hema. "Petrologic analysis and geochemistry of the Late Neogene-Early Quaternary hardpan calcretes of Western Rajasthan, India." Quaternary International 106-107 (January 2003): 3–10. http://dx.doi.org/10.1016/s1040-6182(02)00158-1.

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40

Lauriol, Bernard, and Ian Clark. "Fissure calcretes in the arctic: a paleohydrologic indicator." Applied Geochemistry 14, no. 6 (August 1999): 775–85. http://dx.doi.org/10.1016/s0883-2927(98)00090-0.

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41

Chiquet, A. "Calcium Atmospheric Transport Recorded in the Moroccan Calcretes: Sr Isotope Evidence." Mineralogical Magazine 62A, no. 1 (1998): 325–26. http://dx.doi.org/10.1180/minmag.1998.62a.1.171.

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42

Mirnov, R. V., and T. V. Alekseeva. "Paleosols in the Kashira deposits in the south of the East European Craton (Republic of Bashkortostan): characteristics, paleoecological and stratigraphic signiﬁcance." LITHOSPHERE (Russia) 22, no. 5 (November 4, 2022): 694–704. http://dx.doi.org/10.24930/1681-9004-2022-22-5-694-704.

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Research subject. Paleosols discovered in the Kashira sequence of the Pennsylvanian in the southeastern part of the East European platform. Aim. To study the structure and composition of the paleosols.Materials and methods. Core material from wells was studied by X-ray analysis, scanning electron microscopy and a detailed description of the core and thin sections.Results. Four types of paleosols were identiﬁed, three of which are developed on a dolomite substrate. The dolomites are characterized by the following features: microcrystalline structure with a crystal size of 5–10 microns; predominantly euhedral form of crystals, high intercrystalline porosity (up to 38%), inclusions of in situ halite, gypsum and anhydrite, ubiquitous ﬁlaments of sepiolite. In paleosols based on a limestone substrate, beta-calcretes with Microcodium were found. The study of fossil roots (rhizoliths) revealed the correlation between their types and substrate composition. Thus, petriﬁed rhizoliths and root casts ﬁlled with sedimentary rock and developed clay cutans were found on a dolomite substrate, while calcite tubules around root channels were developed on a limestone substrate. The latter show the presence of abundant Microcodium formations.Conclusions. The revealed morphological and compositional features of the paleosols under study, such as the presence of in situ halite and sulfates (anhydrite and gypsum), sepiolite, and beta calcretes, point to the semiarid climate during the Kashira age on the area under study.

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Srivastava, Ashok K., Mangla N. Bansod, Ajab Singh, and Natwar Sharma. "Geochemistry of paleosols and calcretes from Quaternary sediments of Purna alluvial basin, central India: An emphasis on paleoclimate." Rhizosphere 11 (September 2019): 100162. http://dx.doi.org/10.1016/j.rhisph.2019.100162.

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44

Durand, N., S. M. Ahmad, B. Hamelin, Y. Gunnell, and P. Curmi. "Origin of Ca in South Indian calcretes developed on metamorphic rocks." Journal of Geochemical Exploration 88, no. 1-3 (January 2006): 275–78. http://dx.doi.org/10.1016/j.gexplo.2005.08.055.

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Eren, Muhsin. "Stable isotope geochemistry of Quaternary calcretes in the Mersin area, southern Turkey – A comparison and implications for their origin." Geochemistry 71, no. 1 (2011): 31–37. http://dx.doi.org/10.1016/j.chemer.2010.12.002.

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46

Wang, Yifeng, Daniel Nahon, and Enrique Merino. "Dynamic model of the genesis of calcretes replacing silicate rocks in semi-arid regions." Geochimica et Cosmochimica Acta 58, no. 23 (December 1994): 5131–45. http://dx.doi.org/10.1016/0016-7037(94)90299-2.

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Pracejus, Bernhard, Narasimman Sundararajan, Salah Al-Khirbash, Talal Al-Hosni, A. Ebrahimi, Shakil Al-Bulushi, Ali Al-Lazki, and Musadem Al-Maashani. "Aspects of U-Th fractionation in Tertiary limestones and calcretes of Dhofar, southern Oman." Geochemistry 78, no. 4 (December 2018): 479–89. http://dx.doi.org/10.1016/j.chemer.2018.09.003.

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48

Dash, B., K. N. Sahu, and D. R. Bowes. "Geochemistry and original nature of Precambrian khondalites in the Eastern Ghats, Orissa, India." Transactions of the Royal Society of Edinburgh: Earth Sciences 78, no. 2 (1987): 115–27. http://dx.doi.org/10.1017/s0263593300011020.

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ABSTRACTThe quartz-sillimanite-garnet rocks of the Precambrian khondalite assemblage of Orissa consist dominantly of SiO2 + Al2O3 + Fe2O3 + FeO (average c. 95%) with Fe2O3 > FeO. An average analysis (H2O and CO2 free) also shows MgO, CaO and Na2O having 1·0, 0·5 and 0·4%, respectively. Compared with average crustal abundances, enrichment is shown in SiO2, Al2O3 and Fetot and depletion shown in MgO, CaO, Na2O and P2O5 with that for CaO being more than an order of magnitude and that for Na2O being a factor of >7. On an SiO2–Al2O3–Fetot plot a clearly defined field, elongate nearly parallel to the SiO2–Al2O3 sideline, is similar to that for deeply weathered soil profiles in Brazil. This correspondence also extends to enrichment, stability or depletion, compared to crustal averages, for Ce, Co, Cu, Ga, La, Ni, Nb, Th, U, Y, Zn and Zr, but not for Ba, Cr and Rb. In addition comparison of the proportions and ratios of alkalis and alkaline earths in average khondalite and in a weathering profile over a granodiorite, considered to be typical of the weathering of continents, shows remarkable similarities.The major and trace element data are consistent with the khondalites being granulite facies—upper amphibolite facies metamorphic equivalents of a deeply weathered soil profile. Associated quartzites and calc-silicate granulites are interpreted as having been silcretes and calcretes, respectively. This interpretation implies (1) the previous existence of a large stable cratonic mass on which the soil profile formed, (2) climatic conditions suitable for the development of such a profile, (3) topography, drainage systems and groundwater movement in Precambrian times similar to those of present day peneplane regions, (4) the presence of free oxygen in the atmosphere, (5) rapid covering (e.g. by products of volcanism) to preclude mass wasting, (6) a Precambrian stratigraphy in the crystalline rocks of the Eastern Ghats region similar to that of South India, and (7) orogenesis that involved tectonic repetition of lithological units and a mechanism for taking products of surface weathering down to granulite facies P–T conditions and subsequently elevating them.

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Wang, Z. S., E. T. Rasbury, G. N. Hanson, and W. J. Meyers. "Using the U-Pb system of calcretes to date the time of sedimentation of clastic sedimentary rocks." Geochimica et Cosmochimica Acta 62, no. 16 (August 1998): 2823–35. http://dx.doi.org/10.1016/s0016-7037(98)00201-4.

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Chiquet, Arnaud, Annie Michard, Daniel Nahon, and Bruno Hamelin. "Atmospheric input vs in situ weathering in the genesis of calcretes: an Sr isotope study at Gálvez (Central Spain)." Geochimica et Cosmochimica Acta 63, no. 3-4 (February 1999): 311–23. http://dx.doi.org/10.1016/s0016-7037(98)00271-3.

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