Journal of African Earth Sciences, ( ISI ), Volume (134), No (1), Year (2017-5) , Pages (33-47)

Title : ( Benthic foraminiferal response to environmental changes across Cenomanian/Turonian boundary (OAE2) in the northeastern Tethys, Kopet-Dagh basin )

Authors: behnaz kalanat , Mohammad Vahidinia , H.Vaziri-Moghaddam , Mohamad Hosein Mahmudy Gharaie , Fujio Kumon ,

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Abstract

In order to evaluate Oceanic Anoxic Event 2 (OAE2) at the Cenomanian-Turonian boundary and its effects on benthic foraminifera, the Taherabad stratigraphic section in the east of Kopet-Dagh basin was studied for pattern of changes in benthic foraminiferal communities. Total Organic Carbon (TOC) concentration at the Taherabad section shows that black shale was not deposited in this succession but TOC increases up to 0.68 wt% in the three intervals of Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. Also, Total Nitrogen (TN) values were measured in our study succession. High TOC/TN ratios (up to 18) occur in the intervals of TOC enrichment. Foraminiferal assemblages, TOC, TOC/ TN and Detrital Index (DI, an index for detrital input) changes in the study section allowed us to divided study section into 4 intervals. Interval A and C are associated with low abundance and diversity of benthic assemblages coeval with lack of planktic foraminifera. Benthic assemblages are strongly dominated by shallow and deep infaunal agglutinated foraminifera including Lagenammina, Saccammina, Reophax and Tritaxia. The foraminiferal composition associated with higher TOC, TOC/TN and DI suggest an influx of fresh water to the basin in the warm-wet periods, which diminished hospitable conditions for planktic foraminifera and probably enhanced land-derived organic matter and/or primary productivity. The hyposaline cap led to development of salinity-stratified water and induce bottom water oxygen depletion. By contrast, the assemblages found in the interval B and D are more diverse and contain high abundance of planktic and calcareous benthic foraminifera. Common benthic taxa in these parts are praebuliminids, lenticulinids, gavelinellids and Valvulineria. These assemblages associated with lower TOC, TOC/TN and DI indicate decreased detrital input and more normal marine condition resulted in improved ventilation of sea-floor, which is favorable for planktic and benthic taxa.

Keywords

, Benthic foraminifera, Cenomanian-Turonian boundary, Kopet-Dagh basin, Oceanic anoxic event 2, Oxygen fluctuation
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@article{paperid:1063273,
author = {Kalanat, Behnaz and Vahidinia, Mohammad and H.Vaziri-Moghaddam and Mahmudy Gharaie, Mohamad Hosein and Fujio Kumon},
title = {Benthic foraminiferal response to environmental changes across Cenomanian/Turonian boundary (OAE2) in the northeastern Tethys, Kopet-Dagh basin},
journal = {Journal of African Earth Sciences},
year = {2017},
volume = {134},
number = {1},
month = {May},
issn = {1464-343X},
pages = {33--47},
numpages = {14},
keywords = {Benthic foraminifera; Cenomanian-Turonian boundary; Kopet-Dagh basin; Oceanic anoxic event 2; Oxygen fluctuation},
}

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%0 Journal Article
%T Benthic foraminiferal response to environmental changes across Cenomanian/Turonian boundary (OAE2) in the northeastern Tethys, Kopet-Dagh basin
%A Kalanat, Behnaz
%A Vahidinia, Mohammad
%A H.Vaziri-Moghaddam
%A Mahmudy Gharaie, Mohamad Hosein
%A Fujio Kumon
%J Journal of African Earth Sciences
%@ 1464-343X
%D 2017

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