川西北部地区寒武系—奥陶系的地层格架新认识及地质意义  

New understanding and geological significance of Cambrian-Ordovician stratigraphic framework in northwestern Sichuan Basin

作　　者：张亚[1] 李勇[1] 陈骁[1] 李成龙[1] 龙虹宇 刘冉[1] 钱红杉 侯乾 黄茂轩 王启宇 陈曦[1] 向柱 ZHANG Ya;LI Yong;CHEN Xiao;LI Chenglong;LONG Hongyu;LIU Ran;QIAN Hongshan;HOU Qian;HUANG Maoxuan;WANG Qiyu;CHEN Xi;XIANG Zhu(Exploration and Development Research Institute,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610041,China;Chengdu Geological Survey Center(Southwest Geological Science and Technology Innovation Center),China Geological Survey,Chengdu,Sichuan 611230,China;Key Laboratory of Sedimentary Basin and Oil and Gas Resources,Ministry of Natural Resources,Chengdu,Sichuan 611230,China)

机构地区：[1]中国石油西南油气田公司勘探开发研究院 [2]中国地质调查局成都地质调查中心(西南地质科技创新中心) [3]自然资源部沉积盆地与油气资源重点实验室

出　　处：《天然气勘探与开发》2023年第3期14-24,共11页Natural Gas Exploration and Development

基　　金：中国地质调查局地质调查项目“四川盆地及周缘页岩气调查评价”(编号:DD20221661)。

摘　　要：为查明川西北部地区是否发育完整的寒武系—奥陶系的地层格架,以赋予该地区地震资料新提出的德阳—绵阳拗陷地质意义以及支撑厘清该地区构造—沉积演化过程,从而更加精准服务于油气的风险勘探部署工作。利用野外剖面精测以及锆石U-Pb同位素定年分析等手段对川西北部地区多个寒武系—奥陶系剖面的岩石类型、沉积序列以及年代归属等进行了研究。研究结果表明:①川西北部地区原定义的“筇竹寺组”顶部最大沉积年龄峰值约为505 Ma,磨刀垭组最大沉积年龄约为479 Ma;前者限定了筇竹寺组顶部的沉积时限晚于芙蓉世,后者限定了其沉积时限晚于中奥陶世。综合表明研究区可能发育连续的寒武系—奥陶系,并非缺失中上寒武统—中下奥陶统。②川西北地区寒武纪—奥陶纪时期发育潮坪→浅水陆棚→滨岸→三角洲→碳酸盐岩台地沉积环境,经历了细粒碎屑岩→粗碎屑岩→碳酸盐岩的沉积充填过程。③沉积环境可能受到加里东期的郁南、都匀、广西等多幕次构造运动的影响。④研究结果不仅为前人新提出的该地区发育寒武纪—奥陶纪局部拗陷提供地质证据,而且为四川盆地西北缘构造—沉积格局的进一步厘定奠定了基础。Identifying whether a complete Cambrian–Ordovician stratigraphic framework has developed in the northwestern Sichuan Basin is necessary to provide geological significance for the Deyang-Mianyang depression newly derived from the seismic data and determine the tectonic-sedimentary evolution process in this area,which are conducive to the accurate exploration for oil and gas.In this study,the rock types,sedimentary sequences,and ages of several Cambrian-Ordovician sections in the area were investigated by using the precise measurement of field sections and U-Pb isotope dating of zircon.The results show that,in the northwestern Sichuan Basin,the maximum sedimentation age of the top of the previously defined“Qiongzhusi Formation”is approximately 505 Ma,indi-cating that the sedimentation of the top occurred later than the Furongian Stage;and the maximum sedimentation age of the Modaoya Formation is approximately 479 Ma,indicating that the sedimentation occurred later than the Middle Ordovician.It is thus inferred that in the study area,there may develop a set of continuous Cambrian-Ordovician strata rather than the strata lack of the Middle-Up-per Cambrian to Middle-Lower Ordovician.In the Cambrian-Ordovician period,a series of sedimentary environments were developed,including tidal flat,shallow water shelf,shoreland,delta,and carbonate platform,successively,and a sedimentary filling process in-volving fine-grained clastic rocks,coarse clastic rocks,and carbonate rocks was experienced.The sedimentary environments might have been influenced by multi-episode tectonic movements,such as the Yunan,Duyun,and Guangxi,in the Caledonian stage.This study provides geological evidences for the new proposition that the Cambrian-Ordovician depression is developed locally in the area,and lays a foundation for further delineating the tectonic-sedimentary pattern in the northwestern Sichuan Basin.

关 键 词：碎屑锆石U-Pb同位素定年 地层格架 构造—沉积格局 寒武系—奥陶系 川西北部 

分 类 号：P618.13[天文地球—矿床学]