AbstractsEarth & Environmental Science

Geochemical proxy records identifying climatic and environmental changes across the Permian-Triassic boundary of key sections in NW Iran

by Martin Amandus Schobben

Institution: Freie Universität Berlin
Department: FB Geowissenschaften
Degree: PhD
Year: 2015
Record ID: 1100172
Full text PDF: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000098713


This thesis presents quantitative evidence for climatic and environmental changes, which characterize the transition from the Palaeozoic into the Mesozoic. The study concentrates on better resolving the causes and causal relationships, which are responsible for the end-Permian mass extinction, the largest mass extinction of the Phanerozoic. This is achieved by investigating the geochemical signatures locked in the sedimentary rocks and their fossil content of sections in northwestern Iran. The geochemistry of sedimentary rocks as well as fossil organisms and their shells is known to archive information about the physical and chemical parameters of the ambient environment in which the studied minerals were precipitated. Excursions in geochemical records visualized by isotopic analysis of conodont apatite, carbonate-associated sulphate and bulk-sedimentary rock, straddling the Permian-Triassic interval, are indicative of profound climatic and environmental changes. The oxygen isotope record from conodonts strongly supports an abrupt warming event paralleling the end-Permian mass extinction. This climate change is associated with synergistic effects acting on global warming and corroborates with a scenario of a more active hydrological cycle and subsequent increase of weathering fluxes from the continent, possibly documented as a contemporaneous lithological change in the studied sections to more clay-rich deposits. Simultaneous sulphur and oxygen isotope fluctuations measured in sulphate, which is structurally substituted in carbonate, provides an insight into the sulphur biogeochemical cycle within the extinction interval. A change towards increased organic matter production and consequential remineralization by sulphate-reducing bacteria is a scenario that can explain the patterns observed in the isotope proxies from sulphate associated with carbonate. This is likely linked to eutrophication of marine shelf settings by large fluxes of terrestrial material entering the ocean, a potential effect of climatic warming. These observations underline the interactions between Earth surface processes and imply proximal causes, such as thermal stress and widespread marine anoxia as well as euxinia, as drivers behind the mass extinction. The findings presented in this study cannot unequivocally be assigned to an ultimate cause for the environmental and biotic catastrophe in the latest Permian. However, large-scale volcanism related to time-equivalent emplacement of Siberian trap basalts is a likely culprit that could have initiated this CO2 induced climate catastrophe. A volcanic injection of isotopically depleted carbon into the ocean/atmosphere could explain the long-term negative carbon isotope excursion of the studied marine bulk-carbonate rock. This carbon isotope pattern is similar to that observed at other localities worldwide. Die vorliegende Arbeit befasst sich mit paläoklimatischen und paläoökologischen Veränderungen am Paläozoikum–Mesozoikum-Übergang. Die Studie konzentriert sich auf Ursachen und…