The Paleogene Foraminiferal Biostratigraphy Of The Keliyang Section In The Western Tarim Basin And Tethys Regression

Tarim basin is located in the northwest China,among the south Tianshan mountain,west Kunlun and Altun mountains.There are Tethys marine sediments since Cretaceous in the western basin,so the development and evolution of the Cenozoic paleogeographic environment in the basin are closely related with the development,evolution,and decline of the Tethys sea.The studied section,Keliyang section,which is located in eastward of the turning point of the west Kunlun mountains,is one of the sections in the study area having relatively continuous,intact Paleogene strata.It is of very important research value and great significance to the regional stratigraphic classification and correlation,the ancient ecological environment and regressive analysis.In this paper,the research methods of foraminifera biostratum are carried out in the Keliiyang section.There are 6 species of plankton foraminifera fossils,Globorotaloides quadrocameratus,Parasubbotina pseudowilsoni,Pseudohastigerina micra,Pseudohastigerina wilcoxensis,Pseudohastigerina sharkriverensis,Truncorotaloides libyaensis,which indicates the time of regressive in the Keliyang section is not later than 43 Ma.Then,there are also 27 genus and more than 40 species of benthic foraminifera.The major 11 species are Cibicides,Cancris,Baggina,Eponides,Pararotalia,Nonion,Anomalinoides,Cibicidoides,Melonis,Gavelinella,Quinqueloculina,and the quantity of Neoeponides,Nonionellina,Asterigerinata,Heterolepa,Discorbis,Gyroidinoides,Spiroloculina,Lenticulin,Fursenkoina,Reussella,Pyrulina,Guttulina,Bolivina,Pleurostomella,Rotalia,Anomalina are little.Three principal component factors were obtained by means of Q-factor analysis,they are Cibicides assembly(principle factor1),Anomalinoides assembly(principle factor2),Pararotalia assembly(principle factor3).The palaeoenvironment of Wulagen Formation is divided into five stages:1)the shallow lagoon or littoral swamp environment,2)the deep subtidal zone,3)foraminiferal biological blank stage,4)from subtidal zone gradually into upper subtidal zone,5)relative turbulent water sedimentary environment,and the sea gradually began to withdraw.In the end,Because the research results of the stratigraphic age in this paper is earlier than the previous studies of 40 Ma and 41 Ma,under the influence of global sea level change,there is still impact by the tectonic movement diachronism may exist south-westward retreat of Tethys sea at the same time,and more accurate results need further in-depth and comprehensive study.