Middle And Late Eocene Foraminifera Response To The Tethys Regressive Event In The Wuqia Area,Western Tarim Basin

The Tarim Basin is located in the northwest of China,in the western part of the basin where the Tianshan Mountains and the West Kunlun Mountains intersected.There are well preserved stratigraphic records of the Tethyan transgressions since the Cretaceous,and the paleo-environmental changes in the Cenozoic were also largely influenced by the Tethyan evolution.The Ulukqati section in Wuqia area studied in this paper is located in the connection of Tianshan Mountains and Pamir Plateau,and the Paleogene strata are developed completely and continuously,which is of great significance to the study of the Tethys regression event in the southwest of Tarim.Four genera and five species of planktonic foraminifera were found after the study of the foraminifera biostratigraphy in Urukqati section,Parasubbotina eoclava,Parasubbotina pseudowilsoni,Globorotaloides quadrocameratus,Subbotina yeguaensis,Acarinina bullbrooki.According to the comprehensive study of the age delay,the age of the retreat of the sea was no later than 43 Ma.Thirteen genera and 32 species of benthic foraminifera were identified,Discorbis-Cibicides,NonionAnomalinoides-Cibicides,Melonis-Spiroplectammina.Combined with the two sedimentary facies,four subfacies and five microfacies,the overall sedimentary environment of the middle and late Eocene strata in Urukqati section is analyzed comprehensively: The Wulagen Formation basically transformed from intertidal zone to subtidal zone,and then rapidly transformed into supratidal and lagoonal salt marsh in the later stage,and gradually transformed to subtidal zone after entering Bashibulake Formation.Finally,since the stratigraphic age of this paper is earlier than the previous studies of 40 Ma and 41 Ma,it is believed that the Tethys regressive event in the southwest of Tarim was affected by tectonic factors to a certain extent,not only caused by the global sea level change.