峡东地区奥陶系庙坡组地球化学异常与海平面变化研究

STUDY ON GEOCHEMICAL ANOMALIES AND SEA-LEVEL CHANGES OF ORDOVICIAN MIAOPO FM. IN THE EAST OF YANGTZE RIVER GORGES

通过对峡东地区陈家河剖面奥陶系庙坡组笔石动物群及稀土元素地球化学、有机碳同位素异常和Ce异常的研究 ,讨论了庙坡组沉积时期的海平面变化及相应的层序地层的划分 ,整个庙坡组可以划分为一个三级层序 ,其海侵域相当于H .teretiusculus带的沉积 ,当海平面达到最大海泛面附近时的凝缩沉积及其后的高位域则与N .gracilis带的沉积相当。并认为这一时期笔石的生态差异主要受温度的控制而非地理阻隔的影响。

Based on the study of graptolites fauna, REE distribution patterns, Ce anomalies (δCe ) and stable carbon isotopes (δ 13C) in the Ordovician Miaopo Formation, sea level changes and the corresponding sequence stratigraphy classification are discussed in this paper. The Miaopo Formation, as a whole, is considered to be a third ordered sequence: the H. teretiusculus Zone is equivalent to the transgression systems tract (TST); the N.gracilis Zone is corresponding to the condensed deposits (CS) when the sea level rose to the maximum flooding surface (mfs) and the highstand systems tract (HST) at the top of the Miaopo Formation. And it is also considered that the ecological variation of graptolites is controlled mainly by surface water temperature rather than geographical barrier.