关键词: 断陷湖盆, 缓坡带, 湖平面变化, 层序地层学

Abstract:

Rifting activity and lake basin base subsidence would drop down the lake level. There is no real impact on water depth of deep fault-depression zone and steep gradient zone as well as types of sediments when the lake level changes, therefore,a relatively fluctuation of the lake level could mainly show in slow gentle gradient. The presentation of three vertical successions of progradation, aggradation and retrogradation would bring about difficulties for the stratigraphic correlation of small units of well sections only because of the rift lake basin commonly with characteristics of multi-clastic-source supply for the same IV to VI order sequence and various types of variation for different accommodation spaces at different sites. Coarse depositional facies are not found to be developed everywhere along the lake margin, instead this system could be only developed near the main river mouth. Coarse sediments are chiefly developed in low stand system tract under damp climate; whereas coarse sediments are easily developed in high stand phase deposition under dry climate. The axial zone where horizontally coarse depositional system is very well developed. The changes of the lake level is believed to be effected commonly by a large cycle of tectonic subsidence and a small cycle of climate change.

Key words: rift lake, gentle gradient zone: lake level change, sequence stratigraphy