Oxygen isotopes of Pennsylvanian conodonts: surface water salinity in the US Midcontinent Sea

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Pennsylvanian glacio-eustatic sea-level variations resulted in the worldwide deposition of cyclic sediments in epeiric seas. Oxygen isotopes of conodont apatite from cyclothems in the USA and Russia were studied to constrain the amplitude of these sea-level changes. Oxygen isotope ratios of conodonts from the US Midcontinent cyclothems suggested that glacio-eustatic changes in sea-level were probably larger than 120 m. This estimate could not be confirmed by oxygen isotope analyses of conodonts from Russian cyclothems (Moscow basin and Ural foredeep). This discrepancy could be explained by changes in surface water salinity as consequence of enhanced river discharge during interglacial times, a factor previously not considered in our interpretation. This project focuses on potential salinity changes in surface waters of the US-Midcontinent Sea. We intend to study oxygen isotopes of conodonts from interglacial black shales along a transect from distal (Texas) to proximal parts (Ohio) of the US Midcontinent basin in order to document a salinity gradient in the basin. A salinity gradient is expected in case discharge from the Appalachian and Ouachita orogenic belts increased during the interglacial intervals. The new data are expected to contribute to a better understanding of the magnitudes of Pennsylvanian glacio-eustatic sea level changes.