Hardpan Calcrete Research Articles

Comparison of stable isotope values of Quaternary calcretes from Adana and Mersin provinces: implications on controlling factors

Calcretes are widespread in Adana and Mersin provinces and form under different morphologies. Most calcrete profiles comprise a hard laminated crust/hardpan at the top, gradually intergrading into the nodular and/or tubular/columnar horizon with depth. This study compares the δ18O and δ13C values of calcretes from both provinces and discusses the controlling factors and environmental conditions. The δ18O and δ13C values are characteristic for the pedogenic calcretes. The Adana calcrete mean δ18O values of the hardpan, nodules and tubes, and fractures-infills are 0.69‰, 0.77‰, and 1.04‰ PDB heavier than those of the Mersin calcretes,respectively. The overall difference between the two groups is 0.78‰ PDB. The differences are related to the high evaporation rate in Adana province in respect to Mersin province under similar climatic conditions, except for the evaporation rate. The high evaporation rate in Adana province is due to higher ventilation. The δ13C values of both provinces are almost the same, reflecting calcrete formation in soil with abundant C3 vegetation similar to contemporary vegetation. In addition, the mean δ18O and δ13C values of the hardpan calcretes slightly differ from those of the columnar horizon, showing a depletion in heavy isotopes. The depletion in the mean δ18O values of hard laminated crust in respect to the columnar horizon is 0.09‰ PDB for Adana calcretes and 0.12‰ PDB for Mersin calcretes. This is related to the relatively thick water film from which the calcretes formed by precipitation and displacive replacement processes. The difference in the mean δ13C values is 0.32‰ PDB for the Adana calcretes and 0.11‰ PDB for the Mersin calcretes, and the depletion in δ13C values of the hard laminated crust reflects proximity of the bioactive horizon in the soil.

Morphology and Field Association of Calcretes from Quaternary Sediments of Purna Alluvial Basin, Maharashtra

The Quaternary deposits of Purna alluvial basin are mainly represented by areno-argillaceous sediments with good development of calcretes in both lateral and vertical profiles. Calcretes from thirteen river cut sections, lying along the main channel of Purna River, have been studied for their morphological characteristics. Total six morphotypes, i.e., nodular calcrete, laminar calcrete, hardpan calcrete, root calcrete, rhizolith balls and vein calcrete, have been identified, of which the first was dominant. The lithological association of various calcretes reveals their development mostly in fine- to medium-grained sediments, whereas root calcretes and rhizolith balls are mostly restricted to clayey–silty units. The predominance of calcretes in entire basin indicates the presence of the pedogenic activities under arid to semiarid climatic conditions during the deposition of sediments.

Geochemistry of calcretes (calcic palaeosols and hardpan), Coimbatore, Southern India: Formation and Paleoenvironment

There is no major chemical variation in the late Quaternary calcic nodules formed within vertisols in the foot-hill regions, and hardpan calcretes (greater than 200 ka) formed over the Precambrian substrate that occur as duricrust horizons in the plains around Coimbatore region, Tamil Nadu, India. The bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in CaO, SiO2, Al2O3 and Fe2O3 content. The trend of trace metal content in calcic nodules and in the hardpan calcrete is Mn > Zn > Ni > Cr > Pb > Co > Cu and Zn > Mn > Ni > Co > Pb > Cu > Cr respectively. PAAS-normalised REE data of the calcretes (calcic nodules and the hardpan) demonstrate a positive Euanomaly. This could be attributed to feldspar, apatite mineral alteration and soil digenetic processes, differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in Eu. The stable isotope values of the calcic nodules do not exhibit a wide range (δ18O −3.39 to −5.84‰ and δ13C −3.01 to −6.64‰), compared to the hardpan calcretes (δ18O −2.91 to −12.98‰) and δ13C (−0.05 to −7.4‰). The palaeoenvironment during the formation of the calcretes nodules was dominated by the C4 plants with sparse vegetation cover and that the parent material/bedrock supported a thin veneer of soil column with sparse vegetation cover 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 along geological period. During the late MIS3 to the LGM period the south west monsoon was weak with mean annual rainfall (MAR) between 300 and 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.

Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U–Th series and REEs

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 mm inland. Pedogenic carbonates occur in the MAR range of 500–1200 mm. In the semi-arid zone (MAR: 500–900 mm), carbonates occur (i) as thick hardpan calcretes on pediment slopes and (ii) as nodular horizons in polygenic black soils (i.e. vertisols). In the sub-humid zone (MAR: 900–1500 mm), pedogenic carbonates are disseminated in the black soil matrices either as loose, irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size. They also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate-cemented lumps of centimetric to decimetric size. Chemical and isotopic ( 87Sr/ 86Sr) compositions of the carbonate fraction were determined after leaching with 0.25 N HCl. The corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed. The trend defined by the 87Sr/ 86Sr signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition. Considering the residual fraction of each sample as the most likely lithogenic source of Ca in carbonates, it is estimated that from 24% to 82% (55% on average) of Ca is derived from local bedrock weathering, leading to a consumption of an equivalent proportion of atmospheric CO 2. These values indicate that climatic conditions were humid enough to allow silicate weathering: MAR at the time of carbonate formation likely ranged from 400 to 700 mm, which is 2- to 3-fold less than the current MAR at these locations. The Sr, U and Mg contents and the ( 234U/ 238U) activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation. The relatively high concentrations of Sr, U and Mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite, possibly due to a better confinement of the pore waters which is supported by their high ( 234U/ 238U) signatures, and/or to higher content of dissolved carbonates in the pore waters. The occurrence of Ce, Mn and Fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation. The carbonate ages determined by the U–Th method range from 1.33 ± 0.84 kyr to 7.5 ± 2.7 kyr and to a cluster of five ages around 20 kyr, i.e. the Last Glacial Maximum period. The young occurrences are only located in the black soils, which therefore constitute sensitive environments for trapping and retaining atmospheric CO 2 even on short time scales. The maximum age of carbonates depends on their location in the climatic gradient: from about 20 kyr for centimetric nodules at Mule Hole (MAR = 1100 mm/yr) to 200 kyr for the calcrete at Gundlupet (MAR = 700 mm/yr, Durand et al., 2007). The intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils.

Genesis of tepees in the quaternary hardpan calcretes, Mersin, S Turkey

In the Mersin area, the calcretes are widespread and occur in a variety of forms. The upper surface of the hard laminated crust (hardpan calcrete) represents a distinctive surface morphology of dome-like or slightly elongated dome-like and rarely ridge-like morphologies. These antiformal surface morphologies are interpreted as calcrete-tepee structures. Their cross-sections appear as an upward buckled crust or surface undulation. Troughs are present between the dome-like morphologies, and rarely associated with vertical and subvertical fractures. Petrographic and stable isotope data suggest formation in a vadose zone under subaerial conditions. Semi-arid climatic conditions of Mediterranean type are favourable for calcrete development and furthermore for tepee formation in hardpan calcretes. Thermal and moisture related expansion and contraction seem to be the most likely mechanisms in formation of the calcrete tepees.

Petrologic analysis and geochemistry of the Late Neogene-Early Quaternary hardpan calcretes of Western Rajasthan, India

Calcretes formed over bedrock such as Precambrian hornblende-chlorite schist, rhyolite and carbonaceous phyllites in Western Rajasthan, India, were studied for their mineralogical composition and geochemistry. They form a distinct element of the Quaternary landscape of Western Rajasthan, India. The study area is located within the Nagaur–Churu–Jaipur tract of Western Rajasthan. The purpose of this study was to determine the processes governing the development of hardpan calcretes, and to evaluate the local and regional controls on their formation. Micromorphology included pedogenetic and groundwater features within the hardpan calcretes. Thickening of calcite laminae downward and tapering at the sideward edges around the unweathered minerals of quartz and feldspars indicated cumulative and compound pedogenesis, which probably occurred locally, and downward movement of carbonate solution and pore water. Carbonate solutions were probably derived from the upper horizons or surfaces bringing about the process of dissolution and recementation of individual laminae. Occurrence of fibrous palygorskite as coatings around the detrital grains and siderite (oolitic and pisolitic in shape) points to a subalkaline–subacidic process of pedogenesis in a semi-arid to arid climate. Stable δ 13C and δ 18O isotope data of the hardpan calcrete laminae vary between 0.3‰ to 1.5‰ and −5.9‰ and −1.5‰, respectively indicating their formation at or near surface (capillary fringe), probably supporting a thin column of soil. The source of most of the calcite is groundwater; however, calcite nodule formation was largely dependent on pedogenic processes associated with evaporation, evapotranspiration and /or microenvironmental changes in pH and CO 2 partial pressure. Dust is also a major source for carbonate precipitation. Although it is commonly assumed that the powdery calcretes are younger in age compared to the more complex forms, the occurrence of Middle Palaeolithic tools below the hardpan calcrete at Roopangarh and Dayalpura, and above the hardpan calcretes at Mitri, Genana and Rol, indicates that the morphology of calcretes is not a reliable indicator of age.

Dolines of the Pleistocene dune calcarenite terrain of western Eyre Peninsula, South Australia: a reflection of underprinting?

A field of Middle and Late Pleistocene coastal foredunes occupies much of western Eyre Peninsula, South Australia. The rolling surface reflects the morphology of the stacks of calcarenite dunes that underlie the area. Hardpan calcrete is well developed in relation to the present, as well as to earlier dune surfaces. The region is a typical karst in that surface drainage is lacking. There are a few shallow and short caves but solution pipes and dolines are abundantly developed. Some dolines, including several of the larger forms occur high in the local topography and are also aligned in groups. They are attributed to underprinting, to the diversion of groundwaters into fractures in the pre-Pleistocene basement and the concentration of solution in the limestone above such zones. Low permeability calcrete horizons within the dune sequence have probably disturbed groundwater circulation and also form a stable framework preventing major collapse, and preserving both dolines and caves.

Calcrete morphology and karst development in the Upper Old Red Sandstone at Milton Ness, Scotland

Abstract The Upper Old Red Sandstone at Milton Ness, Scotland, is notable for its excellent preservation of calcrete textures, which are comparable with some of the best Quaternary examples. It is also significant for the implications that can be drawn from the association between karst and calcrete, with this example interpreted to have formed entirely within a semi-arid environment. Karst cavities were developed in a mature hardpan calcrete, generated in sandy fluvial sediments with associated aeolian deposits. Subsequent to karst cavity generation, clasts derived from the subaerially exposed hardpan were locally transported and deposited as a laterally traceable bed connecting the tops of all the cavities. Both this bed and the karst infills were subsequently recalcretized in the final phase of the profile’s evolution. Although calcrete-karst associations often are interpreted as the alternation between semi-arid and humid climates, respectively, this example is interpreted to be a result of water accumulating on the nearly impervious hardpan surface under fairly constant semiarid conditions, evidenced by the recalcretization of both the karst infill and the calcrete-derived breccia (‘boulder calcrete’). Additional substrate modification also has taken place by plant roots; the remarkable development of rhizoliths in these Old Red Sandstone sediments should emphasize the need to consider plant influence on other non-marine rocks of post-Silurian age.

Geomorphic evolution of Talchappar salt lake, Churu District, Rajasthan

Talchappar salt lake (4-5 km in length and 3 km in breadth) is near Devani, Churu District, Rajasthan. This saline lake is bounded on its south south-west direction by obstructed stabilized sand sheets and dunes against the Gopalpura quartzitic monadknocks. Well sections dug out in this saline lake revealed the lithological sequence of fluvio-aeolian and lacustral organic rich clays overlying the chlorite hornblende gneisses and the hardpan calcretes. The deposit at depth of 1·7m in the organic rich clays has been dated by 14 C method to 6620 ± 170 B.P. (PRL 915). The fluvio-aeolian sediments and the clastic lacustral organic-rich clays could have been deposited since the Late Middle Pleistocene period when the climate fluctuated between semi-arid to sub-humid conditions. Geomorphological, structural, sedimentological and micromorphological studies of the different lithological units of this salt lake reveal that the evolution of the lake is an early Quaternary phenomenon. Palaeoclimate and neotectonic activity in the catchment area of the basin has played a vital role in the initial phase of lake basin development.

The sedimentary facies of a late Bathonian regressive episode: the Kilmaluag and Skudiburgh Formations of the Great Estuarine Group, Inner Hebrides, Scotland

The Kilmaluag and Skudiburgh Formations of the Bathonian, Great Estuarine Group, represent a unique palaeoenvironment within the British Jurassic. The Kilmaluag Formation is divided into two distinctive facies. The ‘clastic facies’ of N Skye comprises calcareous mudstones and shales, with subordinate sandstones and argillaceous limestones. The depositional setting was one of shallow, ephemeral lagoons, closed from the sea. Sublittoral lagoon, mudflat and channel environments are identified, and fossil faunas indicate low salinity. The ‘argillaceous limestone facies’ of southern Skye, Eigg and Muck, formed in a similar depositional setting, although sandstones are not present. Alternations of carbonate rocks (some dolomitic) and calcareous shales probably reflect palaeoclimatic fluctuations between humid and arid periods. The overlying Skudiburgh Formation is interpreted as being alluvial. Floodplain, channel and overbank deposits are identified by the presence of mottled mudstones, sands and lensoidal silts. Syndepositional carbonate nodules are interpreted as calcrete, which occasionally coalesced to form extensive hardpan calcrete horizons. The vertical facies sequence reflects a late Bathonian regression. The coastal plain, terrestrial environments of the Skudiburgh Formation were transgressed during the Callovian Stage, an event which ended paralic deposition in the Hebridean Jurassic.

A Geotechnical classification of calcretes and other pedocretes

Summary Authigenic calcareous accumulations within regoliths can be simply classified for geotechnical purposes as calcareous soils, calcified soils, powder calcretes, nodular calcretes, honeycomb calcretes, hardpan calcretes, and calcrete boulders and cobbles. Each of these categories represents a particular stage in the growth or weathering of a calcrete horizon and possesses a significantly different range of geotechnical properties. A similar classification can be applied to other pedocretes.

Pleistocene Shoreline Deposition and Sea-level History at Swartklip, South Africa

ABSTRACT A 50-m-thick succession of poorly cemented sandstone is exposed along the northern shore of False Bay, South Africa, This Late Pleistocene succession is attributed to shorezone-estuarine deposition in the last interglacial and dune activity during the highstand and early in the succeeding sea level withdrawal. Facies analyses allow us to establish that the last interglacial sea level high (120± ka) locally reached an elevation between the upper and lower boundaries of a washover sequence that is 5.1 to 8.0 m above present mean sea level. Four depositional facies are recognized on the basis of distinct lithologies and assemblages of sedimentary structures. Beachrock is present intermittently in the present intertidal zone as a seaward-dipping unit of flatbedded sandstone capped by calcrete. We interpret this facies as a beach foreshore wedge which originated in warmer climates of the 135± ka sea level high, and which developed its calcrete crust in the lowstand which immediately followed. Subsequent sea level rise at 120± ka and shoreline progradation is reflected in a two meter-thick estuarine fill containing Tomichia ventricosta. A third facies comprises landward-dipping sheetsands which overlie the estuarine fill. On the basis of facies relationships and primary sedimentary structures, this unit is attributed to washover fan deposition. The last and dominant facies comprises calcite-cemented sandstone arranged in sets of very large-scale crossbeds. Pulmonate gastropods occur throughout. Poorly developed calcretes interrupt the succession. Deposition of this facies is believed to have occurred as parabolic dunes in a coastal foredune complex near the start of the Wurm (Wisconsinan) glacial climate when atmospheric circulation was more intense. Modern pedotubule and hardpan calcretes cap the succession.

Pseudo‐anticlines and other structures in some calcretes of Botswana and South Africa

AbstractDeformation structures, within some Quaternary calcretes of Botswana and South Africa, have been classified into five types. Type 1 folds are small‐scale (< 2 m wavelength) anticlines in shale or sheet calcrete, separated by wedges of calcrete, polygonal in plan. The anticlines have resulted from horizontal expansion and buckling caused by the disruptive growth of the calcrete wedges. Type 2(a) folds are medium‐scale, strongly convoluted features in sheet calcrete and bedrock and are attributed to the introduction of calcrete along major vertical joint planes. Type 2(b) folds are large wavelength (> 20 m), but low amplitude (< 1 m), anticlines in hardpan calcrete; structural evidence suggests dominantly horizontal compression within the hardpan due either to an overall increase in volume of the calcrete, or to the disruptive formation of calcrete in joints in the synclinal areas. The mineralogy of the calcretes is dominated by low‐Mg calcite which may have inverted from a high‐Mg form; the deformation in type 1 and 2 folds was probably caused by the disruptive and displacive growth of calcite during calcretization. Type 3 folds are saucer‐shaped depressions in hardpan calcrete and may be due to the removal of soluble salts below the folded layer during or after calcretization. Finally, type 4 folds are small, diapiric anticlines resulting from the upward injection of swelling clays into calcrete or calcretized shale.

Vertical Variation in Strength and Porosity of Calcrete (Nari) on Chalk, Shefela, Israel and Interpretation of its Origin

ABSTRACT Observations and measurements on hardpan calcrete (nari) from chalk indicate that three distinct horizons can be distinguished in the nari profile, (a) a very hard thin laminar crust (500-800 kg/cm2), capping (b) a thick strongly indurated upper nari (100-500 kg/cm2) and (c) a thick soft moderately indurated lower nari (20-120 kg/cm2). Moisture content affects greatly the hardness value. If dry, the underlying chalk is harder than the lower nari. The Schmidt Test Hammer Type N was used for non-destructive measurements of relative hardness (strength) in the field. Calibration against unconfined compression strength on rock cubes in laboratory tests produced a highly significant relationship. Porosity has been shown to be the major controlling factor in determining hardness, while CaCO3 content and its microtexture are contributing factors. This indicates that induration of the nari is due to infilling of CaCO3, partial recrystallization in fissures and cracks, and some displacement of non-carbonate material. It is suggested that the process of infilling and crystal growth of carbonate in the host sediment, with some domains of recrystallization, is characteristic of calcrete formation in consolidated, but porous sediments. In unconsolidated sediments the deposition of carbonates can be accompanied by volume expansion and an increased separation of the non-carbonate grains.