The Study Of Cenozoic Lacustrine Carbonate Rocks And Its Sedimentary Model In The Western Qaidam Basin

Qaidam Basin is the largest inland basin in northern Qinghai-Tibet plateau, the development of Qaidam Basin is controlled by rise of the south of the Kunlun Mountains and of the Tibetan Plateau and by activity of the western Altyn strike-slip fault. The characteristic of Qaidam Basin is Cenozoic strata outcrop integrated, widely distributed and large sedimentary thickness.This paper is studyed on Cenozoic strata of west Qaidam Basin in northern Qinghai-Tibet Plateau. Choose Changweitai and Xichagou section which has better outcrop, successive sedimentation and high-precision chronostratigraphy control to collect lacustrine carbonate rocks samples, observe sedimentary characteristics of the wild and identify thin-section, analysis depositional sequence and sedimentary facies of lacustrine carbonate rocks, finally present lacustrine carbonate rocks depositional model of Cenozoic formation of west Qaidam Basin.By lithofacies characteristics and sedimentary structures of the wild, obtain that there are fluvial facies, lacustrine and fan delta facies. Lots of roundstone, pebbled sandstone, fine sandstone, mudstone are deposit in fluvial facies and fan delta facies which are converge at the lower part of Xiaganchaigou Formation and the upper part of Shangyoushashan Formation-Shizigou Formation. lacustrine facies is distribute from the mid-upper Xiaganchaigou Formation to the lower Shangyoushashan Formation.Based on field observation and thin-section identification, several types of lacustrine carbonate rocks are identified as follows: oosparite, calcarenite, algal clast limestones, bioclastic limestones, algal stromatolitic limestones.According to lacustrine carbonate rocks lithofacies sequence of Cenozoic strata of west Qaidam Basin, depositional environment of lacustrine carbonate rocks are analysed. Oosparite depositional environment is littoral-shallow lake riffle, underlying gravel, pebbly coarse sandstone and packsand are deposit at littoral-shallow lake sandy dam, upper packsand and mudstone are mud flat; Depositional environment of calcarenite is littoral-shallow lake mud flat, gray dark coarse sandstone, gray red sandstone, yellow gray calcareous sandstone are littoral-shallow lake sandy dam; Depositional environment of algal clast limestones and algal stromatolitic limestones are similar, both are littoral-shallow lake algal flats, underlying sandstone and are deposit at littoral-shallow lake sandy dam, upper packsand and mudstone are mud flat depositions; Depositional environment of bioclastic limestones are littoral-shallow lake shell bank and covered by mud flat mudstone and pelitic siltstone.Through the above study, and learn from predecessors of modern and ancient lacustrine depositional model of carbonate rocks, lacustrine carbonate rocks sedimentary model of the Cenozoic in western Qaidam Basin is proposed.