Middle Paleocene-early Eocene inter-regional correlations and palaeoclimatic changes in eastern Tethys Sea: Calcareous nannofossil evidence for Paleocene-Eocene Thermal Maximum (PETM) and sea-level change from the western Tarim Basin, NW China

Calcareous nannofossil assemblages from the interval covering the middle Paleocene to early Eocene (P/E), studied in sediments from two sections located in the western Tarim Basin (Kuzigongsu and Bashibulake), indicate that the record of the PETM (Paleocene-Eocene Thermal Maximum) is inscribed in a transgressionregression cycle. A large sea transgression occurred concomitant to the Qimugen Formation, according to earlier studies. Here we present detailed evidence of richness and abundance of calcareous nannofossils to study the PETM and sea-level change in the western Tarim Basin. The gradually increasing sea level from the base of the Qimugen Formation is dated to the nannofossil zones NP7 to 9a (Thanetian), in which the first occurrences of H. riedelii and of D. multiradiatus have been recorded. The highstand of the sea level cycle coincides with increasing Discoaster spp. amounts near the Paleocene/Eocene boundary (NP9a-10), which is dated by the occurrence of RD assemblages (namely, Rhomboaster spp. and Discoaster araneus group). Evidence of regression, observed in the top of Qimugen Formation (NP10-11) corresponds to low abundance and diversity of nannofossils, and is characterized by a rapid increase of Micrantholithus spp. in the assemblage. Inter-regional correlations between the two sections show that in the Tianshan Mountain area the highest relative sea level occurred near the middle part of NP9a.