渤海北域早白垩世地层及介形虫化石组合

THE EARLY CRETACEOUS STRATA AND OSTRACODS IN THE NORTH BOHAI GULF

石臼坨组是渤海北部地区白垩系新建的地层单位,系一套以泥岩为主的沉积,含介形虫化石7属11种(包括4个新种),文中分析了这些化石的地质、地理分布,据此指出,石臼坨组的时代应归于早白垩世,并很可能为早白垩世中期,同松辽盆地姚家组,北京地区丰台组,河北临城组的地质时代大致相当。

Lower Cretaceous volcanic rocks are well developed in the Bohai Gulf. Sediments dominanted by mudstone are found only in its northern part. This paper describes 7 genera and 11 Species of ostracods (including 4 new specieS) therein and discusses the age of the strata. The strata are named the Shijiutuo Formation by Lin Yunzhou. According to the lithologicat characters and ostracod assemlblage, the Shijiutuo Formation is subdivided into 3 members from bottom to top:Tile First Member: grey black mudstone intercalated with clastic limestone, the base of which is intercalated with thin-bedded basalt, tuffaceous sandstone and tuff. No ostracods have been found. 157m The Second Member: light grey, dark grey, dark grey, brown mudstone intercalated with calcareous dolomite in the middle and basalt in the lower part, containing the Cypridea unicostata-Ziziphocypris simakovi assemblage. Ostracoda arc: Cypridea unicostata, Ziziphocypris simakovi, Darwinula subreniformis, D. bozhongensis and Lycopterocypris sp. 95mThe Third Member. purplish red, variegated mudstone and clastic limestone with intercalations of greyish green calareous mudstone, containing the Cypridea curtorostrata-Lycopterocypris subtrapezoidea assemblage. Ostracods are Cypridea curtorostrata, Lycopterocypris debilis, L. infantilis, L. subtrapezoidea, Candona larga, Mongolianella minuta and Rhinocypris obstipa. 52mBasing on a detailed study of the strbtigraphical distribution of ostracods, the authors consider that the Shijiutuo Formation is or Early Cretaceous age and is most likely to be or middle Early Cretaceous age.