Sr isotope of fossil foraminiferal assemblages in the Nihewan Group

摘要

Debate on depositional environment about foraminifera-rich strata in many Cenozoic continental basins in East China has existed for a long time. Research results achieved in recent years show that it is difficult to distinguish foraminiferal assemblages in modern salty lakes from those in weakly marine environments such as supratidal zone and lagoon. However, shell geochemistry may be an outlet for this problem because of great difference in chemical and isotopic compositions between lake water and sea water. So fossils of Nonion shansiensis (Evolutononion shangiensis N. Wang), which is a sole foraminiferal species preserved in upper part of bed 27 and bed 28 in Xiaodukou section in the Nihewan Basin, were selected for Sr isotopic measurements. Thesequence is larger than 12m in length and was sampled consecutively. Because of requirement of analytical amount, the samples (25 cm X 25 cm X 20 cm) containing 300 foraminifera fossils per kilogram were chosen in this work (fig. 1).