International workshop on the Toarcian Anoxic Event-IWTOAE , 2017-10-04

Title : ( Radiolarian content, fossil traces and REE reveal general bottom anoxia in the Kermanshah Radiolarite basin (West Iran) during the Pliensbacian-early Toarcian )

Authors: Asad Abdi , Mohamad Hosein Mahmudy Gharaie ,

Citation: BibTeX | EndNote

Abstract

The Pliensbachian–Aalenian succession in Kermanshah radiolarite basin (Kermanshah, Zagros orogenic system, West Iran) allows recognizing the imprint of the Pliensbacian–early Toarcian long-term warming and long-term middle Toarcian–Aalenian cooling trends on thecirculation pattern controlling nutrient supply and radiolarian productivity. Low radiolarian productivity within Pliensbachianp.p.–lower Toarcian sponge spicule-radiolarian limestones (J.2 member)was related to weak thermohaline circulation andweak upwelling currents;by contrast,middle Toarcian–Aalenian ribbon cherts(J.3 member) reflect high radiolarian productivity due to strong upwelling currents(Abdi et al., 2016).Microfacies and trace fossil analyses of the Pliensbachian p.p.–lowerToarcianpelagic limestonesof J.2indicate the general conditions of weak thermohaline circulation, stratified waters and bottom dysoxia/anoxia were interrupted by short pulses of highradiolarianproductivity and bottomoxygenation, probablylinkedtovolcaniceruptions and turbulenceeventsgeneratedbyinternalwaves(Abdi et al., 2016).Preliminary geochemical trace element and REE analyseshave been performedhere topotentially confirm thereturn to anoxic conditions after these short pulses of bottom oxygenation. J.2 encompasses an 18 m-thick limestone succession includingdiscrete intercalations of pyroclastic beds (vitric tuffs) and internal wave deposits (Abdi et al., 2014). The dominant faciesindicating general dysoxic/anoxic bottom waters are grey sponge-spicule mudstones to wackestones with <2 % radiolarian fossils and absent or very scarce bioturbation (mainly Chondritesfilled byfine-grained framboidal pyrites). Discretebeds of radiolarian-richpyroclasticdeposits and bioturbatedlimestones located on top of interval wave depositsrecorded short pulses of highradiolarianproductivity and bottomoxygenation. These limestone have Thalassinoidestracesfilledwith fine-graineddarkGreen, gray and darkradiolarianmuddyinternalsedimentthat are cross-cutbyChondriteswithdark radiolarian filling sediment andframboidalpyriteswithintheradiolarianskeletons(Fig. 1). Therefore,thecross-cuttingrelationship and nature of internalfillingsediment of traces reflectthechangefromtheshort pulses of bottomoxigenationto general dysoxic/anoxicconditions. Trace element and REE analyses of3 samples (siliceous-radiolarian filling sediment andpyroclastic deposits) indicate Ce negative values and low Th/U ratio (Fig. 2),which confirmanoxic conditions(e.g. Kakuwa and Matsumoto, 2006).

Keywords

, Radiolarian content, Trace fossil, bottom anoxia, Kermanshah Radiolarite, West Iran, Pliensbacian, Toarcian
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@inproceedings{paperid:1066241,
author = {Abdi, Asad and Mahmudy Gharaie, Mohamad Hosein},
title = {Radiolarian content, fossil traces and REE reveal general bottom anoxia in the Kermanshah Radiolarite basin (West Iran) during the Pliensbacian-early Toarcian},
booktitle = {International workshop on the Toarcian Anoxic Event-IWTOAE},
year = {2017},
location = {Jaen},
keywords = {Radiolarian content; Trace fossil; bottom anoxia; Kermanshah Radiolarite; West Iran; Pliensbacian; Toarcian},
}

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%0 Conference Proceedings
%T Radiolarian content, fossil traces and REE reveal general bottom anoxia in the Kermanshah Radiolarite basin (West Iran) during the Pliensbacian-early Toarcian
%A Abdi, Asad
%A Mahmudy Gharaie, Mohamad Hosein
%J International workshop on the Toarcian Anoxic Event-IWTOAE
%D 2017

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