Böhm, Florian

Eisenhauer, Anton

Farkaš, J.

Krabbenhöft, André

Liebetrau, Volker

Tomašových, A.

Vollstaedt, Hauke

Véizer, J.

English

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Geophysical Research AbstractsVol. 13, EGU2011-7257, 2011EGU General Assembly 2011© Author(s) 2011The Paleozoic δ88/86Sr record of marine carbonates – Implications toocean carbonate chemistry and mass extinction eventsHauke Vollstaedt (1), Anton Eisenhauer (1), André Krabbenhöft (1), Volker Liebetrau (1), Florian Böhm (1), JurajFarkas (2), Adam Tomasovych (3), and Ján Veizer (4)(1) Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR), Wischhofstr. 1-3, D-24148 Kiel, Germany (correspondence:hvollstaedt@ifm-geomar.de), (2) Czech Geological Survey, Geologicka 6, 152 00 Praha 5, Czech Republic, (3) University ofChicago, Dept of the Geophysical Sciences, 5734 S. Ellis Avenue, Chicago, Illinois 60637 USA, (4) Carleton University andOttawa-Carleton Geoscience Centre, Ottawa, ON, Canada K1S 5B6Within the Phanerozoic Eon stratigraphic boundaries are often associated with the extinction of marine organ-isms. However, the reasons for these events are still discussed. Strontium (Sr) is one of the most important di-valent cations in calcium carbonate minerals and an important carrier of proxy information. In terms of the Sroutput flux of the ocean, isotopically light carbonates represent the major Sr sink. Therefore, the geochemistryand stable Sr isotope composition is strongly coupled to the marine carbonate system. Consequently, variationsin [Sr] and δ88/86Sr becoming a suitable tool to investigate in the global carbonate budget in earth’s historyincluding the biotic turnover of calcifying organisms at stratigraphic boundaries which are expected to havea large influence on Sr geochemistry and isotope composition of seawater. We extended the conventional ra-diogenic Sr isotope system (87Sr/86Sr) by a simultaneous measurement of radiogenic and stable Sr isotopes(δ88/86Sr = ((88Sr/86Srsample)/(88Sr/86SrNBS987)−1)∗1000). With that we are able to add new constraintsto Strontium Isotope Stratigraphy (SIS) and the ocean chemistry of the past. By taking Sr isotope fractionationinto account we add an additional dimension to the radiogenic Sr isotope system. This allows us to gain quan-titative information about the Sr output of the ocean. Applying a 87Sr/84Sr-double spike (DS), we measuredpaired δ88/86Sr-87Sr/86Sr ratios of 100 modern and Paleozoic marine brachiopod samples which were screenedfor diagenetic alteration prior to the measurement [1]. Data reduction and DS denormalization follows an itera-tive routine [2]. External reproducibility of δ88/86Sr based on an international coral carbonate standard (JCp-1)is 0.026h (2SD, n=26). We found that modern brachiopods have similar values independent of habitat location,species and water temperature with a mean of 0.18h ± 0.02h (2SD, n=13). This provides further support thatbrachiopods provide a reliable carbonate recording phase for δ88/86Srseawater. In Paleozoic Eon we observe vari-ations in δ88/86Srseawater in the range of 0.25 – 0.45h . On longterm timescales ( 100 Ma) these variationsin δ88/86Srseawater follow the general distribution of “calcite seas” and “aragonite seas” [3], implying a controlmechanism by Mg/Caseawater ratios and further global spreading rates. On shorter timescales (residence timeof Sr in the ocean of 5 Ma) we observe a positive correlation of δ88/86Srseawater and the number of marinegenera [4] during mass extinction events in late Ordovician and mid-Devonian. This indicates the strong influenceof marine calcifiers on the Sr budget of the ocean and gives us the opportunity of tracing back major extinctionevents in the Phanerozoic with sudden drops in the δ88/86Srseawater record. Furthermore, with changes in marinePhanerozoic [Sr] [5] and 87Sr/86Sr we are able to correlate these changes in Sr out- or influxes of the ocean.Ultimately, the combined measurement of radiogenic and stable Sr isotopes enhances our understanding of oceanchemistry of the past and increases the precision of SIS with the addition of a second Sr isotope reference curve.[1] Veizer et al. (1999), Chem Geol. 161, 59-88; [2] Krabbenhöft et al. (2009), J. of Analytical Atomic Spectr., 24,1267-1271; [3] Stanley and Hardie (1998), P3, 144, 3-19; [4] Sepkoski (1997), J. of Paleontology 71, 533-539; [5]Steuber and Veizer (2002), Geology, 30, 1123-1126

The Paleozoic δ88/86Sr record of marine carbonates – Implications to ocean carbonate chemistry and mass extinction events

The Paleozoic δ88/86Sr record of marine carbonates – Implications to ocean carbonate chemistry and mass extinction events

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