A Special Sedimentary Type: Flood-overlake and Incised Valley Filling Deposition in Faulted Lake Depression—An Example from Huimin Depression, Bohai Bay Basin, Eastern China
Zhang, Chunming; Jiang, Zaixing; Wang, Junhui
Flood-overlake and incised valley filling deposition, a special sedimentary type was found in the lower part of the third member of Paleogene Shahejie Formation in Huimin depression which is a faulted lake depression in Bohai Bay basin, eastern China. The characteristics of sequence stratigraphy and sedimentary facies are studied based on the analysis of cores, well logs, seismic, paleontologic data and thin sections.
The stratum of the studied interval can be divided into two sequences. Sequence one can be further divided into three systems tracts: the lowstand systems tracts, the transgressive systems tracts and the highstand systems tracts. Sequence two only has the lowstand systems tracts.
In the depositional period of sequence one, the Huimin depression was in the initial stage of lake downfaulting and the water body was unstable. The climate was arid-subarid and the temperature and humidity were constantly high indicated by the paleontologic study. Sedimentation was significantly controlled by inflow of ephemeral flood. The main lithologic characteristic is that the rock types are dominated by light-colored rocks reflecting the oxidation environment with a low maturity. The grain size distribution and sedimentary structure show that the rocks have the sedimentary characters of both gravity currents and tractional currents. Plant fragments are lacking and bioturbation structures are abundant and cyclic. The sedimentary microfacies can be divided into flood channel, mud flat, sand flat and mixing flat. The microfacies of mud flat, sand flat and mixing flat displayed good continuous distribution. The flood channel had a banding distribution and was gradually disappeared in the transgressive systems tracts.
In the depositional period of sequence two, the lake basin and the water body became more stable, the sedimentary environment became normal lake gradually. The characteristics of the flood-overlake disappeared and the main subfacies were incised valley and delta front. With the lake level drops, the earlier disappeared flood channel reactivated as an incised valley and it was filled with coarse clastic such as conglomeratic sandstone. The sedimentary structures were dominated by cross bedding and parallel bedding. The incised valley filling deposits had a banding distribution.
It is pointed out that the flood channel, flood-overlake sand flat and the incised valley deposits were the favorable reservoir for petroleum exploration and exploitation.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013