Trace element variations as a proxy for reconstruction of palaeoenvironmental changes during the Late Aeronian faunal and carbon isotope perturbations: new data from the peri-Gondwanan region

Abstract

Trace element variations in the Upper Aeronian (Llandovery, Lower Silurian), deep-water, black shale succession of the Barrandian area (Perunica) were studied across an interval associated with a graptolite mass extinction and global, positive carbon isotope anomaly. The main aim of the paper is to test whether distinct changes in graptolite diversity during Late Aeronian were linked with changes in deep sea water oxygenation. Using multiple geochemical proxies we documented high-frequency changes in oxygenation of sea water from sediments of the convolutus to linnaei (guerichi) biozones. Detailed comparison of graptolite diversity with those high-frequency oxygenation changes suggests that the long-term and step-wise Late Aeronian graptolite crisis was not significantly influenced by changes in oxygen level and thus it probably resulted by another causes. The collapse of global carbon cycle during the Late Aeronian probably only temporarily increased extinction rate of the long-term graptolite crisis and considerably decreased evenness of the uppermost Aeronian graptolite communities. The Aeronian graptolite mass extinction was thus primarily driven by other biotic and/or abiotic causes