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Chakrabarti G.,Education Directorate | Shome D.,Jadavpur University | Kumar S.,Jadavpur University | Armstrong-Altrin J.S.,National Autonomous University of Mexico | Sial A.N.,Federal University of Pernambuco
Carbonates and Evaporites

The marine stromatolitic dolomites of Palaeoproterozoic Vempalle Formation, of Cuddapah Basin, South India show significantly depleted δ 18O (-8.19 to -18.25%) and δ13C (-0.03 to -5.74) values and are consistent with the global Proterozoic data. A comparison of the stable isotope values from major localities of Proterozoic Basins of India has also been attempted in this study. Significantly depleted18O values of Vempalle carbonate samples could not be considered to be postdepositional modifications as there exists an inverse correlation relationship between C and O isotopic values. The Vempalle stromatolitic dolomite is likely to be precipitated in equilibrium with marine waters significantly depleted in oxygen isotopes (-10 to -15% SMOW) with respect to modern sea water. The negative δ13C values of the Vempalle carbonates are likely to be interpreted at the backdrop of global ''icehouse'' as there is an indication of dropstone-like features in the lower part of the Vempalle Formation just 2 km, southwest of the study area. © Springer-Verlag 2011. Source

Chakrabarti G.,Education Directorate | Shome D.,Jadavpur University | Kumar S.,Jadavpur University | Armstrong-altrin J.S.,National Autonomous University of Mexico | Sial A.N.,Federal University of Pernambuco
Carpathian Journal of Earth and Environmental Sciences

A shallowing-upward succession of intertidal to subtidal stromatolitic dolomites of the upper Palaeoproterozoic (Orosirian) Vempalle Formation of Cuddapah basin, Peninsular India, is preserved in the Bramhanapalle area (14°25 ́15″ N, 78°12 ́19″ E), near Pulivendla, south India. The δ13Ccarb and δ18OV-PDB values of some selected stromatolitic dolomite samples from this succession vary from +1.25 to -5.74 per mil and from -5.42 to -18.25, respectively. These values are consistent with the global data during the upper Palaeoproterozoic time. A positive to negative δ13C shift in the studied stratigraphic section is indicating (i) a gradual decrease in the biomass productivity during the deposition of Vempalle sediments (ii) the decline of stromatolite type carbonate rocks due to the volcanic activity during the deposition of the Vempalle sediments (iii) an advent of " snowball earth " - like condition in the Indian Peninsular region at the onset of Vempalle sedimentation. Source

Chakrabarti G.,Education Directorate | Shome D.,Jadavpur University | Kumar S.,Jadavpur University | Stephens G.M.,University of Tennessee at Knoxville | Kah L.C.,University of Tennessee at Knoxville
Journal of Asian Earth Sciences

Sedimentological investigation of the late Paleoproterozoic (Orosirian) Vempalle Formation of the Cuddapah Basin, Dharwar craton, India, reveals three facies association that range from supratidal to deep subtidal. Sedimentary rocks of this succession are dominated by heterolithic carbonate mudstone, intraformational carbonate conglomerate, and a variety of columnar, domal, and stratiform microbialite facies. Deposition occurred in an extensional regime during development of a low-gradient ramp, where the distribution of microbialite facies is distinctly depth-partitioned. A gradual increase in synoptic relief of columnar stromatolites through the section, and the upward transition from stratiform to columnar microbialites, record a prolonged marine transgression with little or no influx of terrigenous detritus. Siliciclastic influx along the northeastern side of the shelf reflects the redistribution of topographic highs concomitant with large scale volcanic activity. Redistribution of topographic highs eventually led to progradation of peritidal facies and shutting down of the carbonate factory. Earthquake-induced ground shaking and voluminous volcanism experienced by this platform point to the reactivation of a deep-seated mantle-plume that resulted in thermal doming of the Dharwar crust prior to the onset of Cuddapah deposition. Isotopic and elemental chemistry of a selection of Vempalle Formation carbonate rocks record elevated Mn2+ and Fe2+ concentrations and depleted carbon isotope values in inner ramp lagoonal facies, relative to more open marine stromatolitic facies. Patterns of isotopic and elemental variation suggest the presence of geochemically distinct water masses-either within the water column or within substrate pore fluids-that resulted from a combination of globally low marine oxygenation and restricted oceanographic circulation in inner ramp environments. These data suggest that, even in the aftermath of Early Paleoproterozoic oxygenation, that ocean chemistry was heterogeneous and strongly affected by local basin conditions. © 2014 Elsevier Ltd. Source

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