雪峰山西侧震旦纪—早古生代海相盆地演化与油气地质条件

摘要

对古地理格架的重新认识和台缘礁滩相的识别是油气勘探突破的关键环节之一.在前人研究的基础上,综合最新的调查研究成果,对雪峰山西侧震旦系—早古生代的重点层系开展了较大比例尺的古地理研究与编图.研究表明,中上扬子海相盆地经历了裂谷盆地(820～720Ma)、被动大陆边缘碎屑岩陆架建设与初始碳酸盐台地(720～540Ma)、被动大陆边缘统一碳酸盐台地的形成与发展(540～490Ma)、淹没台地与前陆盆地充填(490～420Ma)4个大的演化阶段.除第一阶段因热演化程度过高(R.＞3％)外,后3个阶段在雪峰山西侧地区都具有很好的油气地质条件:灯影期、清虚洞期和红花园期台边缘相带发育,陡山沱期、牛蹄塘期、五峰—龙马溪期发育区域性优质烃源岩,黔东世、武陵世和早志留世分别发育区域性厚层泥页岩、含膏岩系和沙泥岩封盖层,生储盖组合完整,油气地质条件优越.系列图件编制和重要认识的提出为深入开展雪峰山西侧地区有利勘探区块优选和评价提供了依据.%The reunderstanding of the paelogeographic framework and the discrimination of the reef and beach fades of the platform margin constitute the key links for the breakthrough of oil and gas exploration. Based on the data available and the summarization of the related data obtained in recent survey and study, the authors carried out detailed pelogeographic mapping and researches on the important marine layers from Sinian to early Paleozoic in the middle-upper Yangtze marine basin. The results show that the middle-upper Yangtze marine basin underwent four stages of evolution: the rift basin stage (820-720Ma), the early stage of passive continental margin basin (720-540Ma, clastics shelf and primary carbonate platform construction), the last stage of passive continental margin basin (540-490Ma, the formation and evolution of the united carbonate platform), and flood platform and foreland basin filling (490 -420Ma). Except for the first stage characterized by excessively high thermal evolution (R0>3％), the other three stages had favorable conditions of oil and gas potential on the west side of the Xuefeng Mountain: reef and beach facies were well-developed in Dengying, Qingxudong and Honghuayuan periods; excellent source rocks were developed in Doushantuo, Niutitang, Wufeng and Longmaxi pe- riods; excellent cap rocks comprising thick shale, gypsum-bearing series, and sandy clays were developed in Qiandong, Wuling, and early Silurian periods respectively. Therefore, paleogeographic mapping of the key marine layers and the important conclusions drawn above have provided important foundation for evaluation of favorable oil and gas exploration blocks in the west of Xuefeng Mountain.