Xiehao Fm

The type section is at Qiqiaogou in Xiehao, Wuwei, Gansu. The Xiehao Fm is derived from the Xiehao Shale Fm proposed by Mu Enzhi and Zhang Youkui in 1964. In 1982, Lai Caigen renamed the Xiehao Shale Fm the Xiehao Fm. In 1974, Gansu Party of Regional Geological Survey found a sequence yielding Dalmanitina at Shichengzi in Gulang, which was named the Shichengzi Fm by Qu Xinguo(1976, 1984). Wang Jianzhong (1978, unpublished) followed Qu's suggestion, and named the strata underlying the Shichengzi Fm as the Hongtuwan Fm. Considering the similar lithology of Shichengzi Fm and Hongtuwan Fm to that of the Xiehao Fm, the present book includes the Hongtuwan Fm and Shichengzi Fm in the Xiehao Fm, and suggests an Ashgill age for it.

Synonym: (斜壕组）

The formation is dominated by black shale and gray fine-grained sandstone. In the type area, the Xiehao Fm recorded an incomplete thickness of 135 m.

The lower part yields graptolites of Climacograptus ensiformis assemblage, Climacograptus papilio assemblage and Paraorthograptus pacificus assemblage, in ascending order, and the top yields trilobite Dalmanitina, indicating a horizon roughly equivalent to P. linearis zone to D. bohemicus zone. The Xiehao Shale Fm had previously been correlated with the Pleurograptus linearis zone in Britain based on the graptolites of Climacograptus papilio assemblage found in this formation. Zhao Fengyou (1978) established three graptolite zones, i.e. Climacograptus ensiformis zone, C. papilio zone and Paraorthograptus angustus zone, in ascending order, and correlated them with the Dicellograptus szechuanensis zone to Diplograptus bohemicus zone in South China.