海进体系域碳氧同位素地球化学响应——以黔西南地区三叠系为例  

Response of Carbon and Oxygen Isotopic Geochemistry to Transgressive Systems Tract:An Example From Triassic Stratigraphy in Southwestern Guizhou Province

作　　者：李荣西[1] 魏家庸[1] 肖家飞[2] 王兴理[2] Lehrmann D J 

机构地区：[1]长安大学地球科学与国土资源学院,陕西西安710054 [2]中国科学院地球化学研究所,贵州贵阳550002 [3]威斯康星大学奥什科什分校地质系

出　　处：《地球科学与环境学报》2007年第1期1-5,21,共6页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(40173005)

摘　　要：层序地层研究表明,位于扬子地块西南缘的黔西南地区在中三叠世末期(相当于Ladinian-Carnian期)出现了一次与全球同步的大规模海侵,形成了一个向上变深的碳酸盐岩台地淹没沉积层序。垄头组顶部和竹竿坡组分别是海进体系域(TST)的下、上部分。碳、氧同位素研究表明,垄头组顶部自下而上δ(18O)持续增大,而δ(13C)先逐渐增大,后在顶部界面附近快速下降,反映了垄头组顶部在暴露环境下氧化作用的结果。竹竿坡组δ(13C)自下而上逐渐增大,δ(18O)总体呈现逐渐减小趋势,反映了海平面变化特征。研究认为,海进体系域的δ(13C)和δ(18O)演化不但反映了海平面和沉积环境变化,同时对密集段(CS)、层序界面和古暴露面等也有很好的识别作用,在层序地层研究中具有重要的意义。There was a large regression of sea-level in the Later Middle Triassic in Yangtze Block （the famous Ladinia large regression in China）. But a large transgression of sea-level took place synchronously with the global sea-level changes in the southwest corner of Yangtze Block at the southwest region of Guizhou Province during the same period. The Yangtze carbonate platform was drawn and a transgressive sequence was formed during that time. The transgressive systems tract （TST） comprised the top section of Longtou Formation and Zhuganpo Formation. Studies to the variations of δ（^13 C） and δ（^18 O） of the TST show that the δ（^18 O） of Longtou Formation increased upward while the δ（^13 C）increased in lower part but decreased abruptly at the top, which reflects the diagenetic alteration to the top of Longtou Formation due to exposure under continental weathering environment. The δ（^13 C） increasing significantly while the δ（^18 O） decreasing gradually upward within Zhuganpo Formation indicates a major sea-level rise. The δ（^13 C） and δ（^18 O） values of TST reflect sea level fluctuation and paleoenvironment changes. The condensed section （CS） and the strata boundary can be reflected with carbon and oxygen isotopic composition.

关 键 词：碳同位素 氧同位素 层序地层 三叠系 黔西南 

分 类 号：P588.2[天文地球—岩石学]