Late Cretaceous changes in oceanic currents and sediment sources in the eastern Tethys: insights from Nd isotopes and clay mineralogy

Type Article
Date 2021-03
Language English
Author(s) Chenot Elise1, 2, Pucéat Emmanuelle2, Freslon Nicolas2, Deconinck Jean-François2, Razmjooei Mohammad Javad3, 4, Thibault Nicolas4
Affiliation(s) 1 : Institut Polytechnique Lasalle Beauvais, 19 Rue Pierre Waguet, BP 30313, F-60026 Beauvais, France
2 : Biogéosciences, UMR 6282, 6 boulevard Gabriel, Université Bourgogne Franche-Comté, F-21000 Dijon, France
3 : Department of Geology, Faculty of Earth Science, Shahid Beheshti University, Tehran, Iran
4 : IGN, Univ. of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark
Source Global and Planetary Change (09218181) (Elsevier BV), 2021-03 , Vol. 198 , P. 103353 (18p.)
DOI 10.1016/j.gloplacha.2020.103353
Keyword(s) Ocean circulation, Late Cretaceous, Continental weathering, Climate, Shahneshin section, Iran
Abstract

The Late Cretaceous is marked by geodynamical changes including Africa-Eurasia convergence that resulted in the narrowing of the Tethys Ocean and in ophiolite obduction along the southern margin of the various continental blocks in eastern Tethys. Geochemical and mineralogical analyses were performed on the Shahneshin section (Zagros Basin - eastern Tethys), to explore the consequences of this evolution on oceanic circulation, and to estimate the role of ophiolite weathering that can impact climate through atmospheric CO2 drawdown. [Ni] and [Cr] sharply increase in the uppermost Campanian – Maastrichtian interval and are not coeval with an increase in the Nd isotope composition (ɛNd) of the detrital fraction of the sediments. This is interpreted as reflecting weathering of the mantellic, ultramafic part of the ophiolite sequence at that time, implying that ophiolites were exposed on the continents as soon as the Coniacian in the vicinity of the Zagros Basin. Hence their weathering could have contributed to the Late Cretaceous climatic cooling. Clay mineralogy reveals an alternation of kaolinite-rich humid periods (Coniacian/Santonian and late early Campanian to latest Campanian) and kaolinite-depleted arid periods (early Campanian and the latest Campanian to late Maastrichtian). The ɛNd(t) of bathyal waters (carbonate leached fraction) appears quite radiogenic, in the range of -3.4 to -5.2 ɛ-units, about 2 to 4 ɛ-units higher than the detrital fraction. Changes in the ɛNd(t) of detrital material delivered to the Zagros Basin appear to control the ɛNd(t) of the local bottom waters from the Coniacian to the middle Campanian. By contrast, decoupling of detrital ɛNd(t) from that of the local bottom waters from the middle Campanian to the Maastrichtian points to increasing fluxes of westward flowing Pacific radiogenic water masses into the eastern Tethys at that time. These results support an intensification of the Tethyan Circumglobal Current, likely related to the narrowing of the Tethyan seaway.

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Chenot Elise, Pucéat Emmanuelle, Freslon Nicolas, Deconinck Jean-François, Razmjooei Mohammad Javad, Thibault Nicolas (2021). Late Cretaceous changes in oceanic currents and sediment sources in the eastern Tethys: insights from Nd isotopes and clay mineralogy. Global and Planetary Change, 198, 103353 (18p.). Publisher's official version : https://doi.org/10.1016/j.gloplacha.2020.103353 , Open Access version : https://archimer.ifremer.fr/doc/00656/76785/