HIGH-RESOLUTION PAIRED ORGANIC AND CARBONATE CARBON ISOTOPE CHEMOSTRATIGRAPHY OF THE IREVIKEN EXCURSION (SILURIAN) FROM THE ALTAJME CORE, GOTLAND, SWEDEN

The Silurian Period (443-416 Ma) was defined by extensive changes to the biogeochemistry of the Earth and marked by a series of extinction events and global carbon cycle perturbations. The Ireviken Event (Llandovery-Wenlock boundary, ~430 Ma) was one of these Silurian biogeochemical events and is marked by the Ireviken positive carbon isotope excursion. This global carbon cycle perturbation produced a positive carbon isotope excursion in both the organic and carbonate carbon records and this study is the first high-resolution investigation of the paired carbon isotope record through this interval.

Upon examining the synchronicity between the organic and carbonate carbon records from this study, the data demonstrate a +2‰ increase in ∆¹³C, the difference between carbonate and organic carbon values, as well as a slight variation in the timing of the onset of events in each isotopic record. If taken as a proxy for atmospheric pCO₂ concentrations, the data suggest an increase in CO₂, and thus global temperatures. However, this is in opposition to previously published data using the oxygen isotope temperature proxy, which shows a roughly 4 degree Celsius cooling during this interval. If the oxygen isotope temperature proxy is considered to be valid, an alternative explanation for the ∆¹³C record is required. One possibility is that changes to the fractionation coefficient of marine phytoplankton, ε_p, driven by changes in global nutrient availability, could produce the changes seen in the δ¹³C_org record, even in the presence of global cooling.