Applied Sequence Stratigraphy to a Lacustrine Rift Basin--The Paleogene of the Nanpu Depression, Bohai Basin, China

Yong Mo and Fuping Zhu

The Nanpu Depression is a sub-basin of the Bohai Basin, the second largest oil province of China. Regional seismic stratigraphic correlations and sedimentologic analyses were conducted with sequence stratigraphic concepts and methods. There are totally five fundamental unconformities, which separate the Paleogene strata into four depositional sequences. Some of them were identified for the first time. Lowstand, transgressive and highstand systems tracts (LST, TST and HST) are all observed, based on different log patterns and stratal onlap, downlap, and erosional truncations in seismic profiles. Two major condensed sections are recognized within the lower two sequences, which separate the TSTs and the HSTs. Six depositional systems are identified using the data from cores, cuttings, well logs and seismic lines. These are footwall fans (including footwall talus and fan-delta), hangingwall fans (including hangingwall fan-delta, proximal turbidite), distal turbidite, pelagic (and hemi-pelagic) sha e (including mudstone and organic shale), deltas and fluvial-deltaic plains. The pelagic shale exists in every systems tract. Hangingwall fans and footwall fans are well developed in TSTs and HSTs. The upper parts of HSTs in the upper three sequences are dominated by deltas. The LSTs are dominated by deltas and fluvial-deltaic plains. However, LSTs are not widely developed in the Nanpu Depression. This is interpreted as a contribution of the high rate of rift subsidence.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California