摘要
四川盆地二叠系在整个华南地区发育最为完整,是研究二叠系地质事件的良好素材。为厘清栖霞组地层划分以及海平面变化复杂多样的问题,本次研究基于四川盆地2口井的岩屑资料开展了岩性及碳同位素地层对比工作,揭示栖霞组主要以泥晶灰岩、含生屑泥晶灰岩、含云质灰岩与白云岩为主,在MX150井与LT1井中,碳同位素分别介于-1.72‰~4.75‰与2.75‰~4.91‰之间,碳同位素整体呈升高趋势,下部较为离散,上部的升高段具体表现出两段正偏-负偏-正偏-负偏的变化趋势。这些证据表明栖霞组可对应于空谷阶至罗德阶下部,时限约为283~270 Ma。栖霞组的碳同位素正偏-负偏旋回与全球海平面变化和岩性旋回呈明显相关性。空谷阶下段普遍发育的碳同位素负异常可能与火山及其伴生的野火及甲烷泄露事件有关。大量CO_(2)输入背景下气候变暖,冰川大量融化,海平面升高,因此栖霞组下部以泥质灰岩沉积为主。其上碳同位素整体的升高趋势反映了初级生产力升高和有机碳大量埋藏,最终降低了大气CO_(2)浓度,全球海平面下降,同时栖霞组中下部生屑颗粒灰岩出现标志着沉积水深变浅。中上部的两个碳同位素正偏-负偏次级旋回中,正偏大致对应低海平面时期,碳同位素负偏大致对应高海平面时期,反映了冰川型海平面变化与碳循环波动的相关性。最大正偏点附近总体上白云岩更为发育,可能反映了海平面低位时期,有利于同生-准同生期白云石化发生。
The Permian system in the Sichuan Basin is the most extensively developed stratum in South China.This paper utilizes data from two drilling wells in the Sichuan Basin to conduct a correlation study of Permian lithostratigraphy and carbon isotope stratigraphy.The objective is to clarify the stratigraphic division of the Middle Permian Qixia Formation and to understand the complex and diverse changes in sea level during its deposition.The results indicate that the Qixia Formation in the Sichuan Basin is primarily composed of micrite,bioclastic micrite,dolomitic limestone,and dolomite.In well MX150 and well LT1,the carbon isotope values of the rocks range from-1.72‰ to 4.75‰ and 2.75‰ to 4.91‰,respectively,showing an overall increasing trend.However,the isotopic values in the lower part of the Qixia Formation are relatively scattered.The upper part of the Qixia For-mation exhibits sections with increasing isotope values,displaying alternating trends of positive bias-negative bias-positive bias-negative bias.These data suggest that the Qixia Formation corresponds to the lower part of the Gonggu stage through the Luodian stage,spanning approximately from 283 to 270 Ma.The observed positive and negative carbon isotope cycles in the Qixia Formation are closely related to global sea level changes and lithology cycles.The negative carbon isotope anomalies commonly found in the lower part of the Gonggu stage may be linked to volcanic activity-associated wildfires and methane leakage events.These events likely led to a substantial input of CO_(2),causing climate warming,glacier melting,and sea level rise,which resulted in the deposition of muddy limestone in the lower part of the Qixia Formation.The overall increasing trend of carbon isotope values in the upper part of the Qixia Formation reflects an increase in primary productivity and significant organic carbon burial,which ultimately reduced atmospheric CO_(2) concentrations and global sea levels.The presence of bioclastic granular limestone in the middle and lower parts of the Qixia Formation suggests a decrease in sedimentary water depth.The positive isotope biases correspond approximately to low sea level periods,while the negative biases cor-respond to high sea level periods,reflecting the correlation between glacial-type sea level changes and carbon cycle fluctuations.The development of dolomites near the points of maximum positive skewness may indicate low sea level periods,which are conducive to contemporaneous and quasi-contemporaneous dolomitization.
作者
张高源
汪华
丁一
陈骁
叶玥豪
彭思桥
陈延贵
金鑫
宋金民
李智武
ZHANG Gaoyuan;WANG Hua;DING Yi;CHEN Xiao;YE Yuehao;PENG Siqiao;CHEN Yangui;JIN Xin;SONG Jinmin;LI Zhiwu(State Key Laboratory of Oil and Gas Reservoir Geology and Erploitation,Chengdu University of Technology,Chengdu,Sichuan610059,China;Research Institute of Eaploration and Development,PetroChina Southvest Oil&Gas Field Company,Chengdu,Sichuan 610041,China)
出处
《矿物岩石》
CAS
CSCD
北大核心
2024年第2期137-150,共14页
Mineralogy and Petrology
基金
国家自然科学基金企业创新发展联合基金(项目批准号:U19B6003)
国家自然科学基金面上项目(批准号:41872150)。
关键词
四川盆地
二叠系
栖霞组
碳同位素对比
海平面变化
Sichuan Basin
Permian System
Qixia Formation
carbon isotope correlation
sea-level variation
