A record of Late Ordovician to Silurian oceanographic events on the margin of Baltica based on new carbon isotope data, elemental geochemistry, and biostratigraphy from two boreholes in central Poland
Abstract New stable isotope data from organic carbon (δ13Corg) and inorganic elemental geochemistry data have been generated from Upper Ordovician to Silurian strata in two boreholes in the Lublin Basin of Poland: Grabowiec-6 and Zwierzyniec-1. They have been integrated here with biostratigraphical data from graptolites, acritarchs, and chitinozoans. Faunal assemblages from Grabowiec-6 indicate that it spans from the Katian (clingani graptolite Biozone) to the Gorstian (scanicus graptolite Biozone); δ13Corg values from this section record the Sheinwoodian Ireviken Excursion, the Homerian Mulde Excursion, and a minor positive shift associated with the lower Ludfordian leintwardinensis Biozone. The second section, Zwierzyniec-1, spans the Sandbian through Gorstian (nilssoni Biozone); δ13Corg values record the Hirnantian carbon isotope excursion (HICE) and the Ireviken Excursion as well. Elemental geochemistry data is used to recognize subtle changes in provenance and lithology. Significant increases in the abundance of V and Mo are recognized in strata deposited above the Ireviken Excursion. The enrichment of these redox sensitive elements suggests that persistent regional anoxia and euxinia may be associated with the aftermath of these oceanographic disturbances. Some of these same trace elements, along with Fe2O3, and Pb are also abundant in strata coeval with, or just below the Ireviken and HICE excursions. This may have a causal link with malformed palynomorphs observed at these intervals by some workers, which are thought to reflect toxic levels of dissolved heavy metals in the world's oceans.