川西南二叠纪火山岩喷发古地理环境及演化

Paleogeographic Environment and Evolution of Permian Volcanic Eruption in Southwest Sichuan

通过川西南二叠纪火山岩喷发古地理环境及演化分析,旨在明确火山喷发时古陆位置及分布,从而圈定有利储层分布.利用火山岩中代表喷发古地理环境的系列标志,结合室内地球化学、测井资料及火山喷发前岩溶古地貌等分析,认为该地区火山岩喷发古地理环境存在海相和陆相两类.火山喷发时古地理环境受控于康滇古陆的形成与演化,火山喷发早期,东吴运动第二幕发生强烈构造运动导致康滇古陆形成,海水由石棉-天全一带向南北退去,仅在研究区南部的石棉-汉源-峨边-珙泉一线以南地区和北部的宝兴北部一带保留海相沉积环境;中-晚期,宝兴及以北地区继承了早期碳酸盐台地沉积环境,甘洛-马边-盐津一带由缓坡沉积环境演变为滨岸沉积环境.二叠纪火山喷发时,川西南地区为古陆,成都-简阳一带发育的熔结凝灰岩和熔结角砾岩,溶蚀孔洞发育,储集性最好,是目前四川盆地二叠纪火山岩勘探的重要目的层;周公山-宜宾一带发育的自碎角砾岩,由于处于溢流相上部亚相,火山喷发间歇期的风化淋滤作用产生溶蚀孔洞,储层较好,周公山地区获得油气突破,证实了其油气勘探潜力.

Through the analysis of the paleogeographic environment and evolution of Permian volcanic eruptions in Southwest Sichuan,the paleogeographic location and distribution of paleolands during volcanic eruptions were analyzed,so as to delineate the distribution of favorable reservoirs.Based on a series of markers representing the eruption paleogeographic environment in volcanic rocks,combined with the analysis of indoor geochemistry,well logging data and karst paleogeomorphology before volcanic eruption,it is considered that there are two types of paleogeographic environment of volcanic eruption in this area:marine and continental.In the early stage of volcanic eruption,strong tectonic movement occurred in the second episode of the Soochow movement,which led to the formation of the Kangdian ancient land.The sea water retreated from Shimian-Tianquan area to the north and south.The marine sedimentary environment was only retained in the south of Shimian-Hanyuan-Ebian-Gongquan line in the south of the study area and the north of Baoxing in the north.In the middle-late period,Baoxing and its north inherited the early carbonate platform sedimentary environment,and the Ganluo-Mabian-Yanjin area evolved from gentle slope sedimentary environment to shore sedimentary environment.During the Permian volcanic eruption,Southwest Sichuan was an ancient land.The fused tuff and fused breccia developed in Chengdu-Jianyang area,with developed dissolution holes and the best reservoir,is an important target layer for Permian volcanic exploration in Sichuan Basin.Self broken breccia developed in Zhougongshan-Yibin area is the better reservoir because the weathering and leaching during the intermittent period of volcanic eruption produced dissolution holes since it is located in the upper subfacies of overflow facies.The oil and gas breakthrough in Zhougongshan area confirms its oil and gas exploration potential.