四川盆地东北部中—晚侏罗世沉积环境与古气候  

Sedimentary Environments and Paleoclimate of the MiddleLate Jurassic in the Northeastern Sichuan Basin

作　　者：周敏 李祥辉[1] 王旌羽 ZHOU Min;LI XiangHui;WANG JingYu(School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)

机构地区：[1]南京大学地球科学与工程学院,南京210023

出　　处：《沉积学报》2024年第3期1003-1015,共13页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41672097)。

摘　　要：【目的】侏罗纪是典型的温室气候时期,期间存在着气候长期变化和短期波动,且在陆相盆地有响应。我国同期发育多个大型陆相盆地,但各个盆地中的记录有差异,本文试图对四川盆地东北部沉积环境及古气候变化做较为细致的刻画。【方法】基于该地区中—上侏罗统陆相红层的野外详细观察,开展了显微碎屑组分统计分析,碳—氧同位素分析,二氧化碳浓度重建等研究。【结果】下部岩性以红棕色泥岩为主,向上绿灰、浅灰色长石类砂岩增多;沉积环境单元分为曲流河、湖泊和古土壤;相序上表现为中侏罗统沙溪庙组以低砂泥比的曲流河泥岩为主,常土壤化改造形成古土壤相,上侏罗统遂宁组下部湖泊泥岩和粉砂岩占优,遂宁组上部和蓬莱镇组演变为高砂泥比的曲流河,岩性变粗地层变厚;相对于川西和川中地区,川东北地区沉积环境单元和相序较为单一。依据F/Q和F/L指数,将研究区中—晚侏罗世气候变化分为半干旱—干旱两个半旋回,分别对应下沙溪庙组、上沙溪庙组+遂宁组下部、遂宁组上部+蓬莱镇组。二氧化碳浓度变化指示中侏罗世相对温凉,晚侏罗世早期转为温暖,中—晚期属于高温炎热气候,与全球同期古海洋气候格局相似。【结论】总体而言,四川盆地东北部中—晚侏罗世属于温凉—温暖的干旱—半干旱气候,与四川盆地其他地区相似,但晚侏罗世中—晚期东、西部可能存在高温炎热与半湿润间断的差异。[Objective]The Jurassic was a period of typical fluctuating greenhouse climate that resulted in the deposition of sediments in terrestrial basins.In China,a number of large terrestrial basins were formed during the Jurassic,and the discrepancies in sedimentation records have been preserved in several basins.This study focused on the MiddleUpper Jurassic terrestrial redbeds in the northeastern Sichuan Basin to determine changes in the sedimentary environment and paleoclimate.[Methods]Based on the observation of outcrops,analyses of microscopic clastic composition and C-O isotopes,and to estimate the atmospheric CO_(2) concentration in this area.[Results]Medium-to-fine clastic rocks are the predominant lithologies,and five sandstones are further classified by composition and lithological content.Three sedimentary environmental units are recognized:meandering river,lake,and paleosol,which represents a simpler system than in the western Sichuan Basin.The upwards facies sequence is pedogenic,beginning with low sand/mud ratio meandering mudrocks in the Middle Jurassic Shaximiao Formation,lacustrine mudrocks with siltstones in the lower Suining Formation of the lower Upper Jurassic,and upward-coarsening and thickening high sand/mud ratio meandering sandstones in the upper Suining and Penglaizhen Formations of the Middle-Upper Jurassic.Two and a half cycles of semi-arid and arid climate were distinguished in the MiddleUpper Jurassic sequence by F/Q and F/L indices,corresponding to the lower Shaximiao Formation,the upper Shaximiao Formation+lower Suining Formation,and the upper Suining Formation+Penglaizhen Formation,respectively.From the pCO_(2),it is postulated that the Middle Jurassic was relatively cool,becoming warmer in the early Late Jurassic and hot in the middle-to-late Late Jurassic,roughly consistent with the framework of global marine climates.[Conclusion]The climate was(semi-)arid overall in northeastern Sichuan,similar to that in other regions of the Sichuan Basin.It will be necessary to further verify that

关 键 词：沉积环境 干旱—半干旱 古气候 侏罗纪 四川盆地 

分 类 号：P512.2[天文地球—地质学]