甘肃合作地区早、中三叠世盆地一斜坡沉积环境分析

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

摘要:

合作地区位于甘肃省南部,区内三叠系十分发育。殷鸿福等系统研究了区内三叠系地层,确定本区属中秦岭地层分区（图1）,并分出南、北两带。南带以扎油沟剖面为典型代表,自老至新的地层单位为下三叠统山尕岭群（T₁s）、中三叠统古浪堤组（T₂g）;北带以小河沟—土门关剖面为典型代表,自老至新划分出下三叠统隆务河群（T₁l）、中三叠统古浪堤组（T₂g）研究该区三叠纪沉积环境对了解秦岭印支期构造发展史以及区内沉积矿产的成因及分布规律有着极重要的意义。

Abstract:

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.