吉林大阳岔上寒武统凤山组—下奥陶统冶里组层序地层和化学地层研究

Study on Sequence stratigraphy and Chemostratigraphy of the Upper Cambrian Fengshan Formation Lower Ordovician Yehli Formation at Dayangcha (Jilin)

根据岩相序列、沉积、成岩作用特征，将吉林省大阳岔地区晚寒武世凤山期至早奥陶世冶里期层序地层分为６个三级层序，代表了６个三级海侵—海退旋回；与之相应，该时期碳酸盐岩δ１３Ｃ值变化曲线出现５个低谷，其中凤山期至冶里早期泥晶灰岩δ１３Ｃ值出现４次幅度较大的上升、下降飘移，而冶里中、晚期泥晶灰岩的δ１３Ｃ值是在负值范围内波动。δ１３Ｃ值低谷与层序界面和海退事件基本拟合。牙形类Ｃ．ｉｎｔｅｒｍｅｄｉｕｓ带下部海绿石质凝缩段是寒武纪末—奥陶纪初期最大海泛事件沉积，也是寒武纪与奥陶纪之交等时性的年代地层对比标志。

Based on the characteristics of the lithofacies,sedimentation and diagenesis,the outcrop sequence stratigraphy of the Upper Cambrian Fengshan Formation to the Lower Ordovician Yehli Formation at Dayangcha,Jilin, is divided into six third order sequences:two in the Fengshan Formation and four in the Yehli Formation,representing six third order transgression regression cycles.Coincidently,there occur five low value wave troughs and three high value wave crests on the carbonate δ 13 C profile.From the Fengshanian to the early Yehlian,the δ 13 C values display four markedly rising and dropping cycles;the δ 13 C low value wave troughs separately occur at the transitions betwen the top of the Procono dontus muellier Zone and the bottom of the Cambrooistodus Zone,the top of the C.proaus Zone and the bottom of the C.intermedius Zone, and the top of the C.lindstromi Zone and the bottom of the C.angulatus Zone.During the middle and late Yehli Stage,the δ 13 C values fluctuate within the low value wave trough.The third order transgression regression cycles of some sequences are well fit in with the carbon isotope curves.The δ 13 C low value wave troughs are coincident with the sequence boundary surfaces and with the regression events.The glauconitic condensed section in the lower part of C.intermedius Zone represents the deposits of the maximum marine flooding event during the Late Cambrian Early Ordovician,which may be taken as an isochronous marker for the stratigraphical correlation.