EARLY AND MIDDLE TRIASSIC BASIN-SLOPE ENVIRONMENTS IN THE HEZUO REGION,GANSU

The Hezuo region, Gansu studied in this paper may be ascribed stratigraphically to the Middle Qinling subprovince, including the southern (Zhayougou), and northern (Xiaohegou) zones. In this paper, the sedimentary characteristics of the two zones are discussed in detail. Five physical features have been distinguished at some length: turbidity current deposits, terrigenous clastic deposits and non-gravity flow normal deep-sea deposits in the southern zone, and turbidity current deposits, carbonate debris flow deposits and non-gravity flow carbonate deposits in the northern zone. The chemical and physical features of the nodules from the Early Triassic turbidites suggest that they are formed in deep water in the southern zone. Two trace fossil assemblages are also established. They are Loenzinia-Glockeria and Paleodictyon-Planolities which have the same ecologic features as those in slope environments. This paper deals in particular with the Early Triassic calcareous nannofossils and subdivision of the deep marine environments in the southern zone.
It is concluded from the above-mentioned organic or inorganic characteristics that the evolution of the study area from basin to slope during the Early to Middle Triassic represents the historical development of the northern slope of the ancient Qinling sea.