Unincised Perched Lake Versus Incised Valley During Lake Lowstand and Early Expansion Stages at the Steep Margin of Dongying Depression, Eastern China

Abstract

Two contrasting depositional styles and basin-filling processes had occurred during lake lowstand and early expansion stages at the steep margin of Dongying Depression, Eastern China: an unincised perched lake and a deep incised valley. Both are developed directly above the unconformities and their correlative conformities, interpreted as sequence boundaries, and capped by locally traceable conformities, interpreted as flooding surfaces. Wireline log, core, and 3-D seismic data are integrated to delineate their location, size, thickness, geometry, and sedimentological and stratigraphic characteristics. The perched lake is developed at the mountain front, displaying an overall oval geometry with an area of ~11 km long and 5.3 km wide. It is filled by coarse-grained fan systems at the basin margin and sublittoral-profundal lacustrine shale away from the basin margin during lake lowstand and early expansion stages. The incised valley occurs at the NE corner of the basin, oblique to the border fault. It comprises a 4.5 km long by 3 km wide main valley and two bifurcated lobes at the downslope reach of the main valley. It is gradually filled by fluvial, shoreface, deltaic systems during lake lowstand stage, and fan-lacustrine systems during lake early expansion stage. Formation of the two contrasting depositional styles can be caused by interplay of multiple allo- and auto-genic factors and processes, including tectonic uplift or tilt, rapid lake level fall, time, enhancement of river power, rejuvenation of river discharge, channel migration and wall failure. This study provides an example of contrasting depositional styles developed during lake lowstand and early expansion stages at the steep margin of a rift basin. The results can serve as an ancient counterpart for other studies in lacustrine basins.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018