Carbonate geochemistry across the Eocene/Oligocene boundary of Kutch, western India: Implications to oceanic O2-poor condition and foraminiferal extinction

A. Sarkar, S. Sarangi, Mitsuru Ebihara, S. K. Bhattacharya, A. K. Ray

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Major, trace, and rare-earth element (REE) analyses of larger benthic foraminifera-bearing carbonates have been carried out across the Eocene/Oligocene boundary (EOB) of Kutch, western India. REEs of these carbonates display LREE-depleted-HREE-enriched patterns with low average Lan/Lun, and Lan/Ybn ratio (<1; 0.1-0.6), ∑REE values (average 10.4 ppm), and high Er/Nd ratio (mol/mol; 0.12-0.28). The data along with petrographic, Sr/Ca ratio, and Mn concentration, etc. indicate a rather pristine character of these carbonates. Depth profiles of several chalcophile elements, e.g., Fe, Ni, Mo, Co, Cr, Zn, As, V, and U show enrichment near the EOB, suggesting a serious oxygen-deficient (suboxic/anoxic) condition in the overlying water column with possible subsequent modification within pore water. The enrichments are almost synchronous to ∼ 3 °C δ18O cooling of ocean water, a positive Ce/Ce* anomaly (maximum 1.1), and authigenic precipitation of glauconites and framboidal pyrites, all indicating slowly accumulating, sediment-starved, semiconfined, suboxic to anoxic depositional environment. The O2-poor condition at the EOB probably developed due to a lowering of sea level and consequent cessation of open-ocean circulation. Simultaneously, several catastrophic climatic and environmental shifts occurred across the EOB, namely, decrease in sea surface temperature (SST), a regression and consequent O2 deficiency, and reduced phytoplankton production which perturbed the existing life processes.

Original languageEnglish
Pages (from-to)281-293
Number of pages13
JournalChemical Geology
Volume201
Issue number3-4
DOIs
Publication statusPublished - 2003 Nov 28
Externally publishedYes

Fingerprint

Eocene-Oligocene boundary
Geochemistry
Carbonates
extinction
geochemistry
Rare earth elements
carbonate
rare earth element
Water
Bearings (structural)
Phytoplankton
Sea level
Sediments
benthic foraminifera
open ocean
depositional environment
anoxic conditions
Oxygen
Cooling
pyrite

Keywords

  • Carbonate
  • Eocene/Oligocene boundary
  • Extinction
  • Geochemistry
  • India

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

Cite this

Carbonate geochemistry across the Eocene/Oligocene boundary of Kutch, western India : Implications to oceanic O2-poor condition and foraminiferal extinction. / Sarkar, A.; Sarangi, S.; Ebihara, Mitsuru; Bhattacharya, S. K.; Ray, A. K.

In: Chemical Geology, Vol. 201, No. 3-4, 28.11.2003, p. 281-293.

Research output: Contribution to journalArticle

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