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

研究成果: Article

33 引用 (Scopus)

抄録

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.

元の言語English
ページ(範囲)281-293
ページ数13
ジャーナルChemical Geology
201
発行部数3-4
DOI
出版物ステータスPublished - 2003 11 28
外部発表Yes

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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

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

これを引用

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.

:: Chemical Geology, 巻 201, 番号 3-4, 28.11.2003, p. 281-293.

研究成果: Article

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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.",
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AU - Ebihara, Mitsuru

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AU - Ray, A. K.

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AB - 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.

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