Sequence Stratigraphy in Bohal Rift Basin Lacustrine Environments
Lijun Mi, Cao Wenxian, and Percy Chen
Sequence stratigraphic studies of the Bohai rift basin have established seven (7) unconformity-bounded seismic sequences in Paleogene Iacustrine sediments. Studies of microfossils, sedimentary facies, and shoreline onlaps show these sequences can be further divided into twelve-eighteen transgression/regression events. Two of these events, marked by high contents of salinity and rises of lake level, can be correlated to the global eustatic rises at 48-44 and 35-30 MY. Others seem to be of mainly tectonic and paleoclimatic controlled and are time-diachronous with the global sea-level variation.
Distinct shelf breaks have not been observed on seismic, and the basin
margins appear to have evolved from steep to gentle ramp geometry. Rapid lateral
facies changes have been attributed to multi-delta inputs around basin. Systems
tracts
identified on seismic include fan deltas, deep lacustrine fans, and
incised valleys in lowstands and regressive deltas in highstands. Contrary to
open marine environments, the highstand
systems
tracts
are represented by thick
mudstone sections as a result of constantly ample supply of sediments.
Drilling results have demonstrated that reservoir rock facies are mainly in
highstand and highstand systems
tracts
, and source rock facies are largely in
transgressive
systems
tracts
.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California