Nanwan Fm

N. Dabeishan region. The type section is located nearby Nanwan Reservoir, south of Xinyang City, Henan Province. It was named by Beijing Geological College in 1961, and was published by “Regional Stratigraphical Scale of Center-South China Area” in 1974.

Schist. It is mainly composed of two-mica plagioclase schist, epidote-bearing biotite blastogranular rock, biotite blastogranular rock and sericite quartz schist, belonging to chlorite schist facies in degree of metamorphism; and its protolith is inferred to be composed of silt, fine-grained sand and claystone.

In the Liulin-Silidian section of Xinyang from north to south it can be divided into three lithological members:

North Member (D_n1), more than 1000 m thick, consists of variegated sandy shale intercalated with a few fine-grained sandstone and siltstone;

Middle Member (D_n2), 2000-3000 m thick, is characterized by grayish-green and grayish-brown fine-grained sandstone to clayey siltstone and displays flysch rhythms similar to those of turbidity current sedimentation; and

South member (D_n3), more than 1500 m thick, is composed of thick-bedded siltstone and sandy claystone.

The fine-grained sandstone to siltstone of the Middle member yield abundant fossil Spores: Archaeozonotriletes variabilis, Rhabdosporites langii, Cristatisporites triangularis, Apiculiretusispora granulata, Aneurosora graggsii etc.; Chitinozoans Bruchitina, Conochitina, Rhabdochitina chavani; Scolecodonts Nereidavus disjunctus, Menogenys summus, Comugenys decora, as well as acritarchs.

It is interpreted as a marine terrigenous deposit environment.