湘西北杨家坪寒武纪层序地层

湘西北杨家坪地区在寒武纪时位于扬子地台边缘，主要发育一套碳酸盐岩沉积，其沉积环境经历了从滞流盆地、台前斜坡至台地，且盐度不断增高的过程。根据露头层序地层学原理与方法，首次将该区寒武系划分为４个Ⅰ型层序，各层序的低水位体系域发育较全，且均可在扬子地区进行追踪对比，并阐述了各层序的对应层位、组成和其形成的沉积动力学机制以及海平面变化对沉积过程、生物迁移和环境的控制作用。认为研究区寒武纪存在４个海平面变化旋回，第一个旋回发生于梅树村期至沧浪铺期初期；第二旋回为沧浪铺期早期至龙王庙期中期；第三旋回为龙王庙期晚期至徐庄期早期；第四旋回为徐庄期中期至寒武纪末期，并识别出３个平衡型碳酸盐沉积体系。含油性分析表明，层序Ⅰ的海进体系域、高水位体系域和层序２的低水位体系域为有利的生油层段；层序２、层序３和层序４的海进体系域及高水位体系域为有利的储集层段。

Cambrian Sequence stratigraphy in the Yangjiaping District of Northwestern Hunan

The Yangjiaping district of northwestern Hunan belonged to the southeastern margin of the Yangtze Platform during the Cambrian.The Cambrian rocks in the study area are well developed and is mainly composed of carbonte rocks.The sedimentary environment experienced a process from stagnant basin,platform frontal slope to platform during the Cambrian Period and a process of gradully rising of salinity.The Cambrian System in the Yangjiaping district are divided into four I type sequences by using the principle and method of outcrop sequence stratigraphy,and the lowerstand system tracts of each sequence are devloped well and can be correlated with various sedimentary units in the Yangtze Platform. The horizon,composition and dynamic mechanism of each sequence and control of the sea level changes on the sedimentary process,the immigration of organisms and the environment are elucidated in this paper.It is believed that there are four sea level change cycles during the Cambrian Preriod in the study area:the first one occurred from the Meishucun Age to the beginning of the Tsanglangpu Age;the second from early Tsanglangpu Age to middle Lungwangmiao Age;the third from late Lungwangmiao Age to early Hsuchuang Age;and the fourth from middle Hsuchuang Age to the end of the Cambrian.Three keep up type carbonate systems are recognized.The analysis of oil bearing sequence show that the transgressive system tract and the highstand system tract of Sequence 1 and the lowerstand system tract of the Sequence 2 are good oil generative beds,while the transgressive system tracts and the highstand system tracts of the Sequences 2,3 and 4 are good reservoirs.