依-伊断裂带成堑阶段的沉积环境变化和生物演变

EVOLUTION IN THE YILAN-YITONG FAULTED ZONE DURING THE GRABEN-FORMING STAGES

摘要:

依(兰)-伊(通)断裂带和密(山)-抚(顺)断裂带(又称敦-密断裂带)斜穿辽吉黑三省(图1),穿过了中朝淮地台和吉黑地槽系,被认为是郯庐断裂北延部分的两个分支。前者长约1000km,后者长近800km,在两个断裂带内发育了一系列含煤、含油盆地。这些盆地多为断陷盆地,具有地堑或反地堑性质,很多都是半地堑,它们的成堑活动主要发生在第三纪,其构造发展过程与断裂带内的沉积环境变化、生物演变有密切关系。本文讨论范围除依-伊断裂带外,包括了密抚断裂带南段的抚顺盆地。

Abstract:

The Yilan-Yitong faulted zone crosses obliquely the northeastern part of China. The Tertiary period was the graben-forming stage. With increasingly intense faulting, the graben followed the evolving style of sedimentation from the early graben-forming stage when the graben started to sink to the main subsidence stage and later graben-forming stage when the graben was levelled up. There were also regular variations in sedimentary environments within the graben. During the early graben-forming stage, volcanic eruption or river environments predominated, followed by river, swamp and lake environments. Four types are suggested for the sedimenttary evironments within the faulted zone. They are:(1)the swamp-lake-type exhibiting a continuous change from rivers through swamps to lakes during the early and middle graben-forming stages;(2)the swamp-type with a longer period of swamp development in the course of graben development;(3)the lake-type with a longer period of lake development, and;(4)the flood plain-type dominated by fluvial flood-plain environments. These environmental changes have an important effect on the biological evolution within the faulted zone. Geomorphically, the faulted zone displays a linear valley within which the climates might be relatively warm and humid than those on both sides, thus resulting in the differences in vegetation types in the faulted zone and on both sides. The faunal fossils were recognized mostly in the southern part of the faulted zone. The insects were many and diverse during the swamp development stage, whereas during the lake development stage, multiplied the fresh-water lacustrine biotas consisting of fresh-water fishes, molluscs, ostracods, insects and plants.