Palynology of Yanchang Formation of Middle and Late Triassic in Eastern Gansu Province and Its Paleoclimatic Significance

Xifeng (西峰) oilfield was recently found in the southwest of the Ordos basin. The oil source rocks are the Chang 7 Section of Yanchang (延长) Formation. In order to study the paleoclimate that controlled the formation of source rocks， a systemically palynological research on related beds in Yanchang Formation has been carried out. The core samples were analyzed with classical palynological techniques and the organic-walled sporomorphs from these samples were observed， identified and photographed under a light microscopy and a fluorescence microscopy. Abundant sporopollen were found in drilling cores from Chang 8 and Chang 7 sections， and two assemblages were distinguished: the Aratisporites- Punctatisporites assemblage and the Asseretospora-Walchiites assemblage. Their characteristics are similar to those of the assemblage of Tongchuan (铜川) Formation and the assemblage of Yanchang Formation in southeast Ordos basin， respectively. Their geological times are Ladinian of late Middle Triassic and Carnian of early La...