Shimentan Fm

Depressions north of Taiwan. The naming section is located in Shimentan No. 1 well of the Oujiang depression in the East China Sea shelf basin, named by the Shanghai Marine Geological Party, former Ministry of Geology and Mineral Resources in 1987.

Lying between the Lingfeng Fm and pre-Tertiary granodiorite and andesite, this formation takes the strata in the 2571–3306 m interval of well Shimentan No. 1 as the stratotype section. Its lower part is a red bed and the upper part is dark-colored sandy mudstone. Seismically its upper boundary is the T₅⁰ wave and the lower boundary is the T₆⁰ wave. The apparent thickness is 414 m. The formation is divided into two members: Lower member, a red bed, at 3041–3306 m depth, with an apparent thickness of 265 m, dominated by brownish red, brownish purple and dark brown mudstone with gray and grayish white sandstone; Upper member, sandy mudstone, at 2571–3041 m depth, with an apparent thickness of 149 m, consisting dominantly of light gray feldspar lithic sandstone and feldspathic quartz sandstone with grayish black mudstone and sandy mudstone.

Fossils contained in the formation are scarce and only sporopollen, dinoflagellates and foraminifera are found. Sporopollen in the upper member is characterized by the presence of the Lingfengpollis and Cassuarinaepollenites in addition to Ulmipollenites, Parcisporites and Aquilapollenites and sporopollen in the lower member is represented by the Triporate type pollen-Lygodiumsporites-Ulmipollenites assemblage. Dinoflagellates are dominated by chorate cysts, mainly including Areoligera volata, Senegalinium microgranulatum and Denea cf. californica. For foraminifera, Subbotina triloculinoides appears at 2984 m of Shimentan No. 1 well and Globorotalia (T.) pseudobulloides, Eoglobigerina eobulloides simplicissima and Globorotalia (A.) praecursoria appears at 2902–2749 m depth of Mingyuefeng No. 1 well, belonging to zones P1–P2 of the international foraminifera zones. The age is Early Paleocene.

The “red bed” of the lower member of the Shimentan Formation consists of continental fluvial-flood plain deposits, while the dark-colored mudstone of the upper member, littoral-deltaic deposits of transitional facies.