Carbon and oxygen isotopic variations in stromatolitic dolomites of Palaeoproterozoic Vempalle Formation, Cuddapah Basin, India

Chakrabarti, Gopal; Shome, Debasish; Kumar, Subhasish; Armstrong‐Altrin, John S.; Sial, Alcídes N.

doi:10.1007/s13146-011-0054-5

Cited by 14 publications

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References 49 publications

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“…). On the other hand,Chakrabarti et al (2011Chakrabarti et al ( , 2014, using isotopic ( 13 C and  18 O) and elemental (Mg, Ca, Fe, Mn, Sr and SO 4 -2 ) data, concluded that VF dolomite is primary in nature and precipitated either from 18 O depleted marine water or from a geochemically distinct mixed fluid source. Based on collective geochemical signatures,  13 C and  18 O isotopic values, flat REE patterns along with Ce, Eu and Gd anomalies, and chondritic to superchondritic Y/Ho ratios, have recently…”

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A Palaeoproterozoic dolomite (Vempalle Formation, Cuddapah Basin, India) showing Phanerozoic-type dolomitisation

Banerjee

Słowakiewicz

Majumder

et al. 2019

Precambrian Research

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The Palaeoproterozoic Vempalle Formation of the Cuddapah Basin, India, significantly adds to our understanding of the evolution of Precambrian marine carbonate systems and the redox state of the Earth's early oceans. A faciesmicrofacies-diagenetic-geochemical examination of samples from a 900-m long exposure in a freshly-cut canal section shows that 10 to 15 % of precursor limestone is still preserved in the Vempalle Formation in the form of remnant patches of calcimicrite and ooids with calcite spar cement. The ooids, preserving primary radial and concentric fabrics and radial fractures, are considered to have been originally precipitated as calcite, which may have been low-Mg. In places the preserved calcite spar, that is partially replaced by fabric-destructive dolomite, shows Type I calcite twin lamellae. Petrographic observations demonstrate that Vempalle Formation dolomite formed through very early precipitation, which in stromatolites preserved microbial filaments, as well as through fabric-destructive dolomitization during shallow to moderate burial. Vempalle Formation dolomite is characterized by micritic dolomite crystals which suggest rapid early dolomitization of lime mud and micritic calcite from a supersaturated Mg-Ca-rich solution, probably near-surface or during shallow burial. Depletion of Na and Sr contents of Vempalle Formation dolomite along with negative 18O values indicate dolomite recrystallisation during burial and further replacement. Dolomite 13C values of-0.5 to 2 ‰ are likely inherited original marine values. Geochemical proxies (trace elements and rare earths) imply that Cuddapah Basin seawater and dolomitizing fluids were anoxic and ferruginous but not euxinic. Geochemical analyses also indicate that the burial diagenetic fluids evolved from Eu-enriched seawater that probably resulted from continental rifting around 1.9-2.0 Ga. This probable ocean chemistry is in contrast with the anoxic, ferruginous and extremely high Mg/Ca "dolomite oceans" that prevailed during Proterozoic time. The Vempalle dolomite shows more similarities with dolomitised Phanerozoic platform carbonates than typical Precambrian dolomite with its well-preserved textures and burial dolospar cements.

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confidence: 99%