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

Research output: Contribution to journalArticle

  • Amlan Banerjee
  • Mirosław Słowakiewicz
  • Tuasha Majumder
  • Sayani Khan
  • Sarbani Patranabis-Deb
  • Maurice E. Tucker
  • Dilip Saha
Original languageEnglish
Pages (from-to)9-26
Number of pages18
JournalPrecambrian Research
Volume328
Early online date5 Apr 2019
DOIs
DateSubmitted - 13 Dec 2018
DateAccepted/In press - 4 Apr 2019
DateE-pub ahead of print - 5 Apr 2019
DatePublished (current) - 15 Jul 2019

Abstract

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 facies-microfacies-diagenetic-geochemical examination of samples from a ∼1000-m long exposure in a freshly-cut canal section shows that 10–15% 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 δ 18 O values indicate dolomite recrystallisation during burial and further replacement. Dolomite δ 13 C 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.

    Research areas

  • Dolomitization, Fluid chemistry, Proterozoic carbonate rocks, Redox

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    Rights statement: This is the accepted author manuscript (AAM). The final published version (version of record) is available online via Elsevier at https://doi.org/10.1016/j.precamres.2019.04.013 . Please refer to any applicable terms of use of the publisher.

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    Embargo ends: 5/04/20

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    Licence: CC BY-NC-ND

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