摘要
四川盆地寒武系岩盐分布广泛,面积约20万km2,主要分布于川东南、滇东北、渝东北、黔西北和鄂西北等地。含盐层位主要为中下寒武统(寒武系第二统与第三统)。不同地区的含盐层位不同,根据含盐盆地的分布与含盐系地层,将四川盆地大致划分为两个膏盐聚集区(次盐盆地):(1)川东南次盐盆地;(2)渝东北次盐盆地。川东南次盐盆地含盐层位为下寒武统清虚洞组(寒武系第二统第四阶中上部);渝东北次盐盆地含盐层位为中寒武统覃家庙组(寒武系第三统)。前人对四川盆地在岩相古地理与找钾水化学等方面进行了较多研究,但缺少寒武系钻孔样品的碳酸盐岩碳氧同位素分析其含盐盆地的演化研究。所以本文首次选取四川盆地寒武系3个具有代表性的钻孔岩屑样品(丁山1井、临7井与建深1井),对碳酸盐岩碳氧同位素组成进行对比分析,认为四川盆地寒武系碳酸盐岩δ13 C负漂移多与海退及生物灭绝事件有关,δ13 C的正漂移则多受海侵事件影响。四川盆地寒武纪海进、海退交替较为频繁,有利于组成良好的生储盖组合而形成油气藏。四川盆地下寒武统龙王庙阶(第四阶中上部)在川东南地区环境相对封闭,蒸发作用强烈,形成以江津—泸州为沉积中心的膏盐岩沉积区。中寒武世建深1井碳酸盐岩样品的δ13 C相对临7井较高,盐度也相对较高。结合四川盆地岩相古地理研究,认为从早寒武世至中寒武世古海水的浓缩方向有由川东南次盆地向渝东北次盆地演化的趋势,该认识对该区寒武系成盐找钾提供重要的依据,对成油气条件研究也有一定的参考价值。
The Cambrian evaporite basin developed in Sichuan Basin covers an area of 200000 km2 ; the salt- bearing areas are mainly distributed in the central part of the evaporite basin, e.g. southeastern Sichuan, northwestern Guizhou, northeastern Chongqing, and northwestern Hubei （Jiannan）. The main salt-bearing strata in this area are the Lower Cambrian and Middle Cambrian （second and third series）, which are different in various areas. According to the characteristics of salvbearing strata and its spatial distribution, the evaporite basin is broadly divided into two gypsum-halite accumulation areas （subbasins） ： the southeastern Sichuan subbasin and northeastern Chongqing subbasiru The main sal^bearing horizon in southeastern Sichuan is mainly the Lower Cambrian Qingxudong Formation （mid-upper part of the fourth stage of the Cambrian） ; the salt-bearing horizon in northeastern Chongqing is mainly the Middle Cambrian Qinjiamiao Formation （third series）. Previously, many studies on lithofacies paleogeography and potash finding hydrochemistry had been done, but lack of the study on carbon and oxygen isotope analyzes for drilling samples of Cambrian carbonate in studying the evolution of salt basin. The present study chooses Cambrian carbonate samples from the three representative drillings （Dingshan No1 well, Lin No7 well and Jianshen Nol well） to analyze the carbon and oxygen isotope composition. We hold the opinion that the ~13C negative drift is related with marine regression and biological extinction events and 813 C positive drift is mainly effected by marine transgressive events. The frequently alternation of transgression and regression in Cambrian is good for the formation of source-reservoir- caprock system in Sichuan Basin, and the formation of ancient reservoirs. Southeastern Sichuan subbasin is a closed and strongly evaporation environment in Longwanniao formation（the middle and upper part of the fourth stage）, forming the depocentres of gypsum-halite accumulation areas in Jiangji-Luzhou area. The 8la C value and salinity of Jianshen 1 well is higher than that of Lin 7 well. Combing with Sichuan Basin lithofacies paleogeography research, we consider that from early to mid-Cambrian the seawater was more and more highly concentrated from southeastern Sichuan subbasin to northeastern Chongqing subbasin, which is significant for potash finding and the study on hydrocarbon forming conditions in Sichuan BasirL
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2016年第5期202-220,共19页
Earth Science Frontiers
基金
国家自然科学基金青年项目(41403019)
中国地质调查局项目(1212010011810
12120113078500)
关键词
四川盆地
寒武系
碳氧同位素
含盐盆地
盆地演化
Sichuan Basin
Cambrian
carbon and oxygen isotope
salt-bearing basin
sedimentary evolution
