EFFECTS OF EPISODIC DIFFERENTIAL SUBSIDENCE ON THE CHANGES OF LAKE LEVEL AND WATER DEPTH IN RIFT LAKE BASINS

Relative and absolute lake level and water depth are two essential parameters controlling lake-basin sedimentation. In a rift lake basin, the differential subsidence of basement in the gentle slope zone of the basin resulted from the episodic movement of boundary faults in the basin can lead to the discordant changes of relative and absolute lake level, water depth and other parameters, that is, the discordant changes of relative lake level, absolute lake level and water depth and those of relative lake level or water depth at different structural location of the lake basin. In the same sedimentary time unit, the water depth of a lake basin had both increasing and decreasing zones, or not only rising but also falling zones existed in relative lake level; but the absolute lake level to the same lake basin had concordant changes. Episodic diffe-rential subsidence controlled the changes of accommodating space in a basin. This kind of discordant changes were the comprehensive response of the neogenic volume of accommodating space(△V_a), the net incurrent volume of external water(△V_w)and the infilling volume of sediments(△V_s)three parameters du-ring a certain period of time. Especially when △V_a>△V_w>△V_s, the differential subsidence of basement resulted in forced regression in a lake basin and formed sequence interfaces.