LOWER ORDOVICIAN GRAPTOLITES FROM THE DACHENGSI FORMATION IN HANYUAN-YINGJING AREA, WESTERN SICHUAN, CHINA
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Abstract:
A graptolite fauna of the Baltogratus deflexus Biozone (Dachengsi Formation, Lower Ordovician) was obtained recently from the Well-CYD2 cores from Hanyuan-Yingjing area, western Sichuan. Five species belonging to two genera of graptolites have been identified and described in the present paper. They include Baltograptus deflexus (Elles and Wood, 1901), B. enshiensis (Ni, 1979), B. scanicus (Tjernvik, 1960), B. stratus (Chen and Xia, 1979), and Corymbograptus v-fractus minor (Li, 1979). The terminologies for the development types of the proximal end of the turbaria in the present material are after Malatz (1994, 2018). The validity of the genus Norvegiograptus Li, 2014 is discussed herein. The low diversity of the B. deflexus fauna in the Hanyuan-Yingjing area might be due to the limited specimens obtained from drilling core. The B. deflexus Biozone marks the top of the Dachengsi Formation in the studied area. It is overlain directly by the Lower Permian Liangshan Formation. This disconformity extends eastwards to the Emeishan area of SW Sichuan, indicating a regional, long-term erosion.
