陆相伸展性盆地二级层序的厘定

Determination of second-order stratigraphic sequences in continental extensional basins

对二级层序的界面、内部沉积演化及其与构造活动、盆地沉降史的耦合关系进行了分析,系统阐述了厘定陆相伸展性盆地二级层序的依据。我国东部新生代盆地古近系可划分为4～5个二级层序,层序界面普遍为一个区域性角度不整合面,界面上、下古生物组合及沉积特征存在明显变化;层序内部表现为一个大尺度的水进—水退的充填序列,层序底部发育大型低位扇体。二级层序对应于盆地的幕式构造演化阶段,其底界面的形成与构造反转、断块掀斜旋转、岩浆侵入和火山喷发、构造应立场转变等构造事件密切相关。因此,陆相伸展性盆地二级层序受控于区域性构造活动,与构造活动的耦合关系也是厘定该级别层序的关键所在。

Based on the boundaries and interior depositional evolutions of second order sequences in the continental extensional basins and their coupling relations with the tectonic actions and subsidence histories, the Paleogene strata in the Cenozoic basins of the eastern China can be divided into 4 or 5 second-order sequences. The boundaries of those second-order sequences generally belong to the regional angular unconformities. The fossil assemblages and sedimentary characteristics of a single second-order sequence in upper interface are much different from the underlying ones. Some large-scale low-stand fans are usually developed at the bottom of sequence, and a large-scale transgress-regressive succession is presented in the second-order sequences. The second-order sequences are corresponding to the episodic stages of tectonic evolution, and their boundaries are resulted from the tectonic affairs such as reverse of tectonic, tilting and rotating of fault block, intruding of magma, breaking forth of volcanic and change of tectonic stress field. The second-order sequences in the continental extensional basins are controlled by the regional tectonic actions. So, the genetic relationship of sequences with tectonic actions can be used to determine the second-order sequences.