Pinghu Fm

Basins offshore NE Zhejiang. The naming section is located in Pinghu No. 1 well in the Pinghu depression of the eastern Zhejiang depression in the East China Sea shelf basin, at 124º55′13"E and 29º04′08"N. Named by the Shanghai Marine Geological Party, former Ministry of Geology and Mineral Resources.

The Pinghu Formation is a sequence consisting dominantly of dark gray, lime-bearing to lime mudstone with sandstone and coals between the Oligocene Huagang Fm and Eocene Bajiaoting Fm or other strata that have not yet been encountered by drilling, the upper part of which is intercalated with thin-bedded micrite. The formation is divided into three members: Lower member, alternating beds of dark gray mudstone and light gray silty and fine sandstone, with coal beds; Middle member, dominated by dark gray lime or lime-bearing mudstone, with light gray silty and fine sandstone and bituminous coal beds; Upper member, alternating beds of dark gray mudstone and light gray silty and fine sandstone, with thin-bedded micrite, with a number of coal beds. The total thickness is 204–1550 m. According to the data from 20 exploratory wells and seismic wave groups, this formation is thicker in the eastern part of the depression but contains a smaller number of coal beds and the cumulative thickness is also small; westward the slope zone becomes thin and the number of coal beds increases and the cumulative thickness also increases, and the formation also displays a wedge shape that is thick in the west and thin in the east. In Pinghu No. 3 well and Pingxi No.1 well the upper part of this formation is eroded and the third cycle is absent.

Fossils are rich, and according to the distribution of foraminifera in 12 wells two foraminifera assemblage zones may be distinguished, i.e. the Haplophragmoides assemblage in the middle member of this formation, whose main elements are Haplophragmoides cf. carinatum and H. amakusaensis, and the Cibicidoides hilgardi-Elphidium eocenicum assemblage, whose common elements are Nonion rotulum, Nonionella hankeni sipissa, Elphidium cynicalis, Anomalina pinghuensis and Cibicides spp.; in addition, there are the planktic foraminifera Globigerina pseudovenezuelana, Dentaglobigerina galavisi, Globorotalia (T.) centralis and Subbotina angiporodes lindiensis of zones P13–P15. Ostracods are marked by the Spinileberis assemblage, Sinocypris-Candona assemblage and Chinocythere-Candoniella assemblage; Calcareous nannofossil mainly are Reticulofenestra umbilica, Zygrhablithus bijugatus, Blackites spinosus, Discoaster saipanensis, Sphenolithus primus etc. and mainly distributed in zones NP14-NP20. Dinoflagellates include Hystrichokolpoma granulatum and Impletosphaeridium insolitum etc.; the sporopollen assemblage is Alnipollenites-taxodiaceaepollenites-gothanipollis. Charophytes fossils occur in the middle and upper members of the formation, represented by the Obtusochara jianglingensis-Rhabdochara kisgyonensis assemblage and the Raskyaechara pinghuensis-Krassavinella lagenalis assemblage.

The Pinghu Formation belongs to paralic, semi-enclosed bay deposits.