PAIRED ORGANIC AND CARBONATE CARBON ISOTOPE CHEMOSTRATIGRAPHY OF THE MULDE EXCURSION FROM THE ALTAJME CORE, GOTLAND, SWEDEN

The Mulde Event is an extinction event that occurred during the Wenlock Epoch of the Silurian Period. It is also coincident with a perturbation in the global carbon cycle known as the Mulde positive carbon isotope excursion, which is recorded in the rock record by a two-peaked positive isotope excursion. Previous low-resolution studies have indicated that the onset and end of the Mulde Excursion are not precisely synchronous between carbonate and organic carbon. The purpose of this study is to evaluate the synchronicity between carbonate and organic carbon records of the Mulde Excursion at extremely high resolution.

To test this synchronicity, a core (Altajme) was drilled from the Swedish island of Gotland that contains more than 180 meters of Homerian strata. Over 300 samples were taken for organic carbon isotope analysis for this project and compared with greater than 500 carbonate carbon samples from the same core. This provided the ability to demonstrate small scale variations in the onset and end of the Mulde positive carbon isotope excursion at the highest resolution ever produced for this interval. What was demonstrated is that there is indeed a small offset in the onset of the excursion in the carbonate versus organic carbon isotope records, indicating they are not precisely synchronous. The ∆13C record also demonstrates a series of transitions during the first peak of the Mulde Excursion. In order to determine if these are global signals, additional data at similar resolution from other sections will be required.