Paper No. 31-10
Presentation Time: 11:15 AM
INDEX OF SYNGENETIC PYRITE - A NEW PROXY FOR ESTIMATE REDOX CONDITIONS OF DEPOSITIONAL SYSTEMS
PISARZOWSKA, Agnieszka, Institute of Geological Sciences - Research Centre in Krakow, Polish Academy of Sciences, Senacka 1, Krakow, 31-002, Poland, BERNER, Zsolt, Institute for Mineralogy & Geochemistry, Karlsruhe Institute of Technology, Adenauerring 20b, Geb. 50.40, Karlsruhe, 76131, Germany and RACKI, Grzegorz, Faculty of Earth Sciences, University of Silesia, Będzińska 60, Sosnowiec, 41-200, Poland
Sediments deposited under euxinic conditions contain a relative high portion of syngenetic pyrite which is forming in the water column, but also diagenetic pyrite, because the formation of pyrite proceeds also within the sediment, until the pools of reactive iron or organic carbon are exhausted. Based on compositional differences between pyrite formed within the sediment and in seawater column, we propose the use of the proportion between oxyanionic trace elements comparatively abundant in seawater (like As, Mo, Se, Sb) and common transition metals (Co, Ni, Cu, Zn) to evaluate the relative amount of syngenetic pyrite within a sample (Pisarzowska et al. 2014). The proposed by us a new proxy parameter, index of syngenetic pyrite (ISPY), should have low values for oxic–dysoxic environments and should be close to 1 for euxinic environments with a high portion of syngenetic pyrite. Relative high values are expected also for anoxic conditions with pyrite formed at the water-sediment interface.
We tested the ISPY in the Lower Frasnian pyrite-ammonoid level in the Holy Cross Mountains, Poland (Pisarzowska et al. 2014) and the Toarcian Posidonia Shale, Germany (Berner et al. 2013). The ISYP values suggest dysoxic environment interrupted by short- or long-lived episodes of more restricted bottom water conditions during the deposition of the pyrite-ammonoid level. While, the Lower Toarcian Posidonia Shale depositional system evolved from dysoxic towards euxinic bottom waters. The distribution of the ISYP along the studied sections is in concert with conclusions inferred from paleoecologic data and other geochemical parameters but it is more sensitive for short-term variation in geochemical systems.
Acknowledgments
AP acknowledges financial support from the Polish National Science Centre grant UMO-2011/03/B/ST10/04602.
Reference
Berner et al. (2013) Sedimentology 60, 548–573. Pisarzowska et al. (2014) Sedimentary Geology 308, 18–31.
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