Xiaoxiyu Fm

It was named originally by the Hunan Team for Regional Geological Survey at Xiaoxi, Ruitapu, Sangzhi County, Hunan Province in 1966. Zhao Ruxuan et al. (1978) renamed it Xiaoxiyu Fm and considered it belongs to the age of Givetian of Middle Devonian. Wang Genxian et al. (1985, 1988) revised the formation and assigned it to the deposits of Wenlock. Wang et al. (2010) revised the formation according to the microfossils (including phytodebris microfossils) from the Xiaoxi Fm in the Zhangjiajie-Sangzhi area, northwestern Hunan Province. The original Xiaoxi Fm is subdivided into two parts: the upper part being the Xiaoxi Fm (sensu stricto), and the lower part being the Huixingshao Fm. However, the name Xiaoxi Fm is occupied by the terrestrial-volcanic rock unit of Early Cretaceous by Fujian Team for Regional Geological Survey in 1977. Consequently, we considered the name Xiaoxiyu Formation by Zhao Ruxuan et al. (1978) is valid. The revised Xiaoxiyu Fm is consistent with the concept of Xiaoxi Fm as Wang et al. (2010) proposed.

Synonym: (小溪峪组); Xiaoxi Fm

It is dominated by yellowish green thin-bedded muddy siltstone and silty mudstone, intercalated with grey green medium-thick bedded fine grain sandstone or medium- to thin-bedded quartz sandstone. It is 136.4 m thick in the named section.

It yields abundant stout tubular trace fossils and microfossils, including phytodebris microfossils, and chitinozoan Eisenackitina venusta Tsegelnjuk, E. rimosa Umnova, E . cf. cyrtopleura (Tsegelnjuk, 1982), Lambdachitina crassispina ( Eisenack, 1964), etc.