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

宾夕法尼亚冰期的海平面变化导致了世界范围内陆表海循环沉积物的沉积。研究了美国和俄罗斯旋回层中牙形石磷灰石的氧同位素，以限制这些海平面变化的幅度。美国中大陆旋回层牙形石的氧同位素比值表明，冰川-海平面变化可能大于120米。这一估计无法证实的牙形石的氧同位素分析，从俄罗斯旋回层（莫斯科盆地和乌拉尔前渊）。这种差异可以解释为地表水盐度的变化，在间冰期期间，河流流量增加的结果，一个因素，以前没有考虑在我们的解释。该项目的重点是美国-大陆中部海表层沃茨的潜在盐度变化。我们打算研究牙形刺的氧同位素从间冰期黑色页岩沿着从远端（得克萨斯州）到近端部分（俄亥俄州）的美国中部大陆盆地，以记录在盆地的盐度梯度。如果阿巴拉契亚和沃希托造山带的流量在间冰期期间增加，预计会出现盐度梯度。新的数据预计将有助于更好地了解宾夕法尼亚冰川海平面变化的幅度。

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.