A Research of the Cretaceous-Paleogene Boundary in the Pingyi Basin, Shandong Province

摘要

The Bianqiao Formation (in the Pingyi Basin, Shandong Province, China) is a typical set of continuous lacustrine carbonate deposits during the Cretaceous-Paleogene period, which is considered as an ideal stratigraphic unit for KPB research. This study is based on the borehole PYZK01, which is located at Tongjiazhuang village in Bianqiao Town of Pingyi country. According to biostratigraphy research, the Bianqiao Formtion establishes one charophyte assemblage: Porocharaanluensis-Charayuntaishanensis var. acuta-Turbocharaspecialis , and one sporopollen assemblage: Deltoidosporaadriensis-Rugubivesiculites- Schizaeoisporites . This result indicates that the stratigraphic age during 0 - 12.25 m is the Paleogene, 37.8 m - 60 m is the Late Cretaceous, and 12.25 - 37.8 m is a transition stage from the Late Cretaceous to the Paleocene. By geochemical study, it was established carbon and oxygen isotopic strata in the drill. Through the magnetostratigraphy research, we find eight positive polarity zones and seven reversed polarity zones, build the magnetic polarity sequences of the borehole, and propose a contrast scheme with the international standard magnetic polarity time column. After comprehensive discussion, it is preliminarily believed that the Cretaceous-Paleogene boundary is located at the depth of 31.98 m in PYZK01, namely, in the first section of the Bianqiao Fm.