Abstract:

The Cretaceous-Paleogene interval in the northeastern part of the eastern Tethys witnessed a large-scale transgression event that resulted in the formation of the trumpet-shaped bay in the western Tarim Basin. The Late Cretaceous to Eocene marine deposits in the western Tarim Basin record the evolutionary history of the eastern Tethys including a series of major climatic events, but studies so far lacked a comprehensive chronostratigraphic division and correlation framework achievable through detailed lithostratigraphic, biostratigraphic and stratigraphic investigations. In this study, we improved the stratigraphic division and correlation framework using the aforementioned approaches, and we also discussed a series of major geological events. The Cretaceous to Paleogene strata in the western Tarim Basin constitute the Kezilesu Group and the Kukbai, Wuyitake, Yigeziya, Tuyiluoke, Altashi, Qimgen, Gaijitage, Kalatar, Wulagen and Bashibulake Formations. These formations are rich in foraminifera, ostracods, calcareous nannofossils, dinoflagellates, spores and pollens, bivalves, and gastropods, and contain a few ammonites, brachiopods, sea urchins, and fish teeth. The western Tarim Basin has become an important site for studying climatic events, such as the Paleocene-Eocene Thermal Maximum (PETM). Based on the comprehensive biostratigraphic and chronostratigraphic studies, the age of the Kezilesu Group is recorded as Barremian-Albian and the ages of the Kukebai, Wuyitake and Yigeziya Formations as Cenomanian-Maastrichtian. The Tuyiluoke Formation is the transitional period of the Cretaceous-Paleogene, whereas the age of the Altashi Formation is early to middle Paleocene. The age of the Qimugen Formation is late Paleocene to early Eocene, and the ages of the Gaijitage, Kalatar, and Wulagen formations are early to middle Eocene. Finally, the Bashibulake Formation is of late Eocene in age. The Late Cretaceous to Eocene strata from the western Tarim Basin were biostratigraphically and chronostratigraphically correlated with those from the surrounding Kuqa, Fergana and Tajik Basins as well as the Karakoram region. Additionally, five large transgression-regression cycles from the late Cretaceous-Paleogene were summed. A possible small marine transgression of the western Tarim Basin began in the middle and upper parts of the Kezilesu Group (late Albian to early Aptian); however, the first large transgression began in the Cenomanian Kukebai Formation. There were five large-scale transgression-regression cycles in the western Tarim Basin from the late Cretaceous to Eocene. The seawater retreated from the Kunlun Mts. subregion of the western Tarim Basin at approximately 41 Ma and retreated from the Tianshan Mts. subregion of the western Tarim Basin at approximately 34 Ma. These transgression-regression events were controlled by regional tectonic events and global sea-level changes; however, the tectonic events mainly controlled the beginning and end of the Tethys Sea in the western Tarim Basin. The major climatic and geological events in the western Tarim Basin, such as OAE2, K/Pg, PETM, as well as transgression and regression, are discussed in detail. We successfully marked the PETM events in the Qimgen Formation, providing significant scientific clues for the study of PETM events in the global nearshore area. The western Tarim Basin should be further explored stratigraphically to establish a more refined biostratigraphic and chronostratigraphic framework to strengthen our study of major climatic and geological events in future.

Key words: Tarim Basin, Cretaceous, Paleogene, marine, stratigraphy, Tethys, sea level, Paleocene-Eocene Thermal Maximum