燕山地区冀北坳陷中元古界杨庄组沉积特征与层序地层

燕山地区冀北坳陷中元古界蓟县系杨庄组主要为一套碳酸盐岩沉积.通过对该地区野外仔细观察、测量,结合室内薄片资料和地球化学分析,认为该区杨庄组沉积相为碳酸盐岩台地相,可进一步划分碳酸盐岩潮坪亚相以及潮上带、潮间带2种微相.在此基础上,结合层序界面特征,对杨庄组层序进行了探讨,由于研究区在杨庄期处于浅水陆表海沉积环境,层序界面主要以浅水环境的沉积物及沉积构造作为识别标志.沉积体系域以海侵体系域和高位体系域为主,普遍缺少低位体系域或陆棚边缘体系域,同时,也不具备形成凝缩层的环境,以最大海泛面沉积物与深海中的凝缩层相对应,最终划分出1个二级层序和3个三级层序.系统地阐述了每个层序的岩石、构造及体系域等特征.

Sedimentary Characteristics and Sequence Stratigraphy of the Mesoproterozoic Yangzhuang Formation,in Jibei Depression of Yanshan Region

MesoproterozoicYangzhuang Formations in Jibei Depression of Yanshan region are mainly a carbonates sedimentary system.Through the cautious observation,measuring,data of indor-slice and the geochemistry analyzation,the author holds that the sedimentary facies of Yangzhuang Formation was carbonate platform facies.It can be furtherly devided into tidal-flat subfacies and 2 micro-phases consists of supratidal,intertidal micro-facies.On the basis of sedimentary facies,combined with sequence characteristics of the interface,the Yangzhuang Formation sequence was studied.Yangzhuang deposition in this area belongs to a shallow continental sea sedimentary environment.Sequence boundaries were mainly indicated by sediments and sedimentary structures of the shallow water environment.Thus the depositional systems tracts belong mainly to transgressive systems tract and highstand systems tract,commonly with the lack of lowstand systems tract or shelf marginal sysrems tract.It does not have the environment for the formation of condense section either,which makes the maximum flooding surface and deep-sea condense section correspondingly.Finally one second-order sequence and three third-order sequences were recognized in Yangzhuang Formation.Rock,structure and characteristics of systems tract of each sequence were described systematically.