Cyclic Sequences and Depositional Systems in the Upper Cretaceous-Eogene of Southwest Tarim Basin
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摘要: 塔里木盆地西南缘K2-E海相含碳酸盐岩地层中可识别出七种类型的高频旋回层序，主要有潮下缓坡型、台地型、台地边缘型碳酸盐旋回层序及以碎屑岩为主的潮间－潮上型旋回层序。平面上，不同类型高频旋回层序成为特定古地理背景下台地碳酸盐沉积体系、滨岸沉积体系和冲积沉积体系沉积层序的代表。纵向上，各类高频旋回层序的有序叠加，其类型的变化反映了沉积环境、沉积相的演变过程。研究结果表明，研究区各类高频旋回层序下部单元至上部单元微相的转变是受高频率海平面变化的影响，低频率海平面升降控制了高频旋回层序的叠加形式，造成沉积环境由下至上滨岸→碳酸盐台地→滨岸→河流的变化。正是由于不同周期海平面变化旋回的叠加形成了塔里木盆地西南缘K2-E的复合海平面变化旋回层序。Abstract: Seven types high frequency cyclic sequences which have been distinguished in the Upper Cretaceous-Eogene marine carbonate of the southwest Tarim Basin are mainly as follows: undertidal carbonate ramp, platform, platform margin earbonate cyclic sequences and tidal flat cyclic equences which are clas-tic rock mainly. In the region, different kinds of high frequency cyclic sequences represented sedimenta-ry sequences of platform, shore bank and alluvial depositional system which deposited in specific paleo-geographic setting. In the vertical sections, high frequency cyclic sequences stacked upward, in which changing of the kinds of cyclic sequence reflects the evolution of sedimentary enviroment and facies. As a result, in the study area, high frequency sea level change affected on the sedimentary facies changes from the lower unit to the upper unit of high frequency cyclic sequence, and controlled the deposit pro-cession of cyclic sequence. The long periodic sea level changes controlled the stacking patterns of high frequency cyclic sequences, and made the sedimentary environment change from shore bank→carbonate platform→shorebank→river. In a word, stacking of different hierarchy of sea level changes resulted in cyclic sequences of composite sealevel change in the Upper Cretaceous-Eogene of the southwest border, Tarim Basin.
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