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

宾夕法尼亚冰川-上升海平面变化导致了世界范围内表海旋回沉积物的沉积。研究了美国和俄罗斯环礁牙形石磷灰石的氧同位素，以限制这些海平面变化的幅度。美国中大陆旋回牙形刺的氧同位素比值表明，海平面的冰川-上升变化可能大于120 m。这一估计不能通过对俄罗斯环礁（莫斯科盆地和乌拉尔前深）牙形刺的氧同位素分析来证实。这种差异可以用间冰期河流流量增加导致的地表水盐度变化来解释，这是我们之前的解释中没有考虑到的一个因素。该项目侧重于美国中大陆海地表水潜在的盐度变化。我们打算研究沿美国中大陆盆地远端（德克萨斯州）到近端（俄亥俄州）样带的间冰期黑色页岩牙形刺的氧同位素，以记录盆地的盐度梯度。如果阿巴拉契亚造山带和瓦希托造山带的流量在间冰期增加，预计会出现盐度梯度。预计新的数据将有助于更好地了解宾夕法尼亚冰川-海平面上升变化的幅度。

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.