Paper Number: 1269
New ammonoid aragonite 87Sr/86Sr records of Mesozoic environmental change
Zakharov, Y.D.1, Dril, S.I.2, Tanabe, K. 3, Shigeta, Y.4 Baraboshkin, E.Y.5 and Michailova, I.A.5
1Far Eastern Geological Institute, Russian Academy of Sciences (Far Eastern Branch), Stoletiya Prospect 159, Vladivostok, 690022, Russia. E-mail: yurizakh@mail.ru
2Institute of Geochemistry of Russian Academy of Sciences (Siberian Branch), Favorsky Street 1a, Irkutsk, 664033, Russia,
3The University Museum and the Department of Earth and Planetary Science. The University of Tokyo, Tokyo, 113-003, Japan.
4National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan.
5Moscow State University, Leninskiye Gory MGU 1, Moscow, 11991, Russia
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Much of data on Phanerozoic Sr-isotope stratigraphy has been derived from whole-rock samples and calcitic fossils. We focus in this paper on some Mesozoic Sr-isotope oscillations, based on data on the following aragonite-preserved ammonoid shells: (1) Hedenstroemia hedenstroemi from the lowest Olenekian of the Buur River basin, Arctic Siberia (87Sr/86Sr=0.708043); (2) Boreomeekoceras keyserlingi from the uppermost Olenekian of the Olenek River basin, Arctic Siberia (87Sr/86Sr=0.709041), showing very close Sr-isotope composition with the living Nautilus pompilius from Philippines (0.709148) (10); (3) Arctohungarites sp. from the Anisian of Taimir, Arctic Siberia (87Sr/86Sr=0.707744); (4) Harpoceras falcifer and Hildaites serpentinum from the lower Toacian of western Switzerland (87Sr/86Sr=0.707300-0.707382); (5) Procerites funatus from the lower upper Callovian of the Ulyanovsk area (87Sr/86Sr=0.707429); (6) Deshaesites volgensis – sp. 45/96 and 50/96 from the lower Aptian of the Ulyanovsk area (87Sr/86Sr=0.707333-0.707382); (7) Douvilleiceras sp., Eotetragonites umbilicostatus and Cleoniceras besairei from the lower Albian of Madagascar (87Sr/86Sr=0.707241-0.707276) (8) Pseudoschloenbachia umbulazi from the upper Santonian of British Columbia (87Sr/86Sr=0.707281); (9) Submortoniceras from the lower Campanian of California (87Sr/86Sr=0.707198) (Fig. 1).
Following partly Jones and Jenkins [1], we presume that there is the close correspondence in time between episodes of increased hydrothermal activity at ocean ridges, significantly controlled by negative seawater Sr-isotope excursions, and sea level rises, usually resulted in the OAEs activity and climatic warming. The surprising event, exceedingly large swing in 87Sr/86Sr ratio between the Capitanian minimum and the latest Olenekian maximum, seems to be a result of strongest plate tectonic activity at the end of Palaeozoic time and some contrast conditions of the Early Triassic.
Figure 1. The seaway 87Sr/86Sr curve [2], corrected and confirmed in outline by data on Sr-isotope composition of Mesozoic ammonoid and living Nautilus aragonite. 1-10 – cephalopods (this study); a and b – Data from Cochran et al. [3, 4]
References
[1] Jones and Jenkyns (2001) Amer J Sci 301: 112-149
[2] McArthur et al. (2012) The Geol Time Scale DOI: 10.1016/B978-0-444-59425-9.00007.X
[3] Cochran et al. (2003) Palaepgeogr Palaeoclimatol Palaeoecol 191: 45-64
[4] Cochran et al. (2015) Swiss J Palaeontol 134: 153-165