河南省寒武系研究进展

RECENT ADVANCES IN THE STUDY OF THE CAMBRIAN IN HENAN PROVINCE

河南省寒武系分布广泛,层序齐全,具有不同类型的沉积和古生物群。根据大地构造单元、沉积特征、古生物群面貌,地层发育及出露情况,可将地层区系划分为华北区及秦岭区,进而又可进一步划出分区及小区。

Henan province is situated somewhat to the east of the centre of China, spanning geologically the southern margin of the North China platform and the eastern sector of the Qinling fold system. Based on the tectonic position, sedimentary type and faunal type, the Cambrian in Henan province may be divided into the North China and Qinling Stratigraphical Regions. In the North China Stratigraphic Region, the Cambrian may be divided into three series and eight formations. According to recent study, the Lower Cambrian Xinji Formation is subdivided into four lithological members. The present boundary between the Cambrian and Precambrian is located at the base of Member One of the Xinji Formation, i. e. the base of the Parak-orilithes-Anabarella drepanoida-Auricalatespira assemblage. This boundary is probably equivalent to the base of the Canglangpu Stage. The Cambrian trilobite sequence of the North China Region is shown in Table 2. The Cambrian strata of the Qinling Region are chiefly exposed in the Xichuan area. The Cambrian in the northern Xichuan area, the subdivision and trilobite sequence of which are shown in Table 2, is similar to that in the Yangtze Gorges area, Hubei. In this region, the Early Cambrian deposits mainly consist of thin-bedded siliceous rocks and thin-bedded limestone intercalated with shale and dolomite; the Middle and Upper Cambrian deposits consist of dolomite. Cambrian deposits in the southern Xichuan area are quite different from those in the northern Xichuan area in lithology and faunas. In the southern Xichuan area, the Cambrian sequence is subdivided into three groups: the Lower Cambrian Zushimiao Group, the Middle Cambrian Hujiazhuang Group and the Upper Cambrian Xujiazhuang Group. The Zushimiao Group is composed of siliceous and carbonaceous slate and clayrock. The Hujiazhuang Group is composed of dolomite and thin-bedded limestone intercalated with shale, contaisting of Pagetia, Goniaynostus nothorsti (Brogger), Prohedinia attenuata Lermontova, Hypaynostus guadratus Lu etc. The Xujiazhuang Group consists of limestone and dolomite, yielding trilobites: 'Chuangiella' and Eokaolishania; conodonts: Prooneotodus rotundatus (Druce et Jones), Prodistacodus palmeri (Muller) etc. Based on study of the stratigraphy and paleontology, the Cambrian biogeography, lithofacies and paleogeography, tectonic framework are also discussed in this paper.