Foraminifera Biostratigraphy Of The Qimugen Formation In Kuzigongsu Section,Western Tarim Basin And Its Response To PETM Events

The PETM event is a rapid global warming event caused by massive methane injection into the atmosphere around the Paleocene and Eocene lines?56Ma?,which caused mass extinction,replacement and climate system mutation,and is one of the most important climate events in the Cenozoic era.In China,due to the limited distribution of Marine strata,the PETM event was reported only in the carbonate strata in south Tibet.But more recently,our team has found that PETM events have also been recorded in marine clastic formations in the western Tarim basin.Tarim basin of western Tianshan,and Kunlun mountains area have developed the late cretaceous to the marine strata in Paleogene,including paleogene Qimugen formation not only corresponds to one of the biggest since the late cretaceous transgressive events,also recorded the PETM event,the PETM event and related stratigraphy and ancient environment research is of great significance.The Kuzigongsu section is located in Tianshan area,the Qimugen formation is well developed,and there are abundant foraminifera fossils.In this study,foraminifera fossils and carbon and oxygen isotopes of the Qimugen formation in the Kuzigongsu profile were mainly studied to explore the age and PETM event of the Qimugen formation in the western Tarim basin.Through the analysis of foraminifera fossils of Qimugen formation in the Kuzigongsu section,it is preliminarily identified that there are 7 species of planktonic foraminifera in 4 genera and 11 species of benthic foraminifera in 6 genera.According to the distribution age of planktonic foraminifera fossils in the strata,it is inferred that the Qimugen formation spans the four fossil zones of P4,P5,E1 and E2,namely the late Paleocene and early Eocene.Benthic foraminifera are also mostly molecules above and below the Paleocene-Eocene line.The above foraminiferal fossil evidence indicates that the Paleocene-Eocene line lies in the middle of the Qimugen formation.The carbon isotope test results of the Qimugen formation showed that delta¹³C_PDB showed a significant negative deviation in the dark mudstone in the middle of the Qimugen formation,from-0.30‰in the lower gray-green mudstone to-3.82‰in the dark mudstone,and then recovered to 0.50‰.The most direct evidence of PETM events is the large scale negative deviation of carbon isotopes in a short period of time.Based on the previous evidence of planktonic foraminifera and the large-scale negative deviation of carbon isotopes,PETM event is believed to have occurred in the dark mudstone layer in the middle of the Qimugen formation in the Kuzigongsu profile in this study.The carbon isotopes corresponding to the PETM event layer in the middle of the Qimugen formation in the Kuzigongsu profile can be compared not only with the adjacent profile,but also with those in the Tethys region and other parts of the world,with a complete record of negative carbon isotopes.Paleoecological analysis of foraminifera suggests that the PETM event in the study area may also have coincided with a rise in sea level and the extinction of foraminifera.After the PETM event?after sample M63?,most benthic foraminifera species were extinct,and only a few species remained.