晚三叠世卡尼期梅雨事件(CPE)在陆相盆地中的沉积学响应——以鄂尔多斯盆地延长组为例

Sedimentological Response of a Lacustrine Basin to the Late Triassic Carnian Pluvial Episode(CPE):Case study from the Yanchang Formation,Ordos Basin

卡尼期梅雨事件(CPE事件)是三叠纪地球上最显著的气候突变事件之一,而气候环境突变对内陆湖盆沉积物特征具有重要控制作用。以我国陆上最主要的含油气盆地——鄂尔多斯盆地三叠系延长组为例,在充分借鉴国内外有关全球古气候、事件沉积、陆相盆地烃源岩发育机理及异整合面等最新研究进展基础上,对延长组沉积与成藏问题重新思考与研究,取得了如下3点新认识:1)重新厘定了盆地上三叠统延长组卡尼期时限,明确了延长组CPE事件的沉积响应,认为卡尼阶底界大致相当于延长组长7与长8之间的地层界限,顶界相当于长4+5与长3之间的地层界限,CPE事件大致与“长7黑色页岩事件”沉积相对应;2)在卡尼期及CPE事件期间,延长组沉积期湖盆表现为“快速湖侵、震荡式缓慢湖退”特点,十分有利于优质烃源岩的发育;3)受卡尼期古气候及CPE事件影响,延长组内部发育上下两个由于气候环境突变而形成的异整合面,它们对油气分布均具有明显控制作用。该研究对于深入探讨延长组湖盆形成演化机理、沉积层序充填演化特征及指导油气勘探实践均有积极意义。

The Carnian Pluvial Episode(CPE)in the Triassic was one of the most abrupt known climatic events in the Earth’s history.It strongly influenced sediment deposition in inland lakes.The case considered here(the Yan⁃chang Formation in the Ordos Basin)is the most important terrestrial petroliferous basin in China.A comprehensive review of research progress in China and elsewhere was carried out for global paleoclimate,event sedimentation,source rock development mechanisms and xenoconformity in terrestrial basins.Rethinking and investigating some of the sedimentation and accumulation questions related to the Yanchang Formation has revealed the following three points.(1)The Yanchang Formation,which developed during the Carnian stage at the beginning of the Upper Trias⁃sic,is redefined and its sedimentary depositional response to the CPE is clarified.The upper boundary is equivalent to the stratigraphic boundary between the Chang 4+5 members and the Chang 3 member.The CPE roughly corre⁃sponds to the deposition of the so-called“Chang 7 member black shale event”.(2)During the Carnian and CPE,the Yanchang Formation sedimentary lake basin underwent rapid transgression and oscillating slow retreat,very condu⁃cive to the development of high-quality hydrocarbon source rocks.(3)Due to the paleoclimatic conditions and CPE,upper and lower xenoconformities were formed in response to the abrupt climatic and environmental changes.These both significantly influenced the distribution of oil and gas.This study is of positive significance for in-depth discus⁃sion of the formation and evolution mechanisms of the Yanchang Formation lake basin,as well as sedimentary se⁃quence filling and evolution,and as a guide for oil and gas exploration.