Modern Analogs for the Importance of Seaward Migration of the Equilibrium Point and Bayline and Production of Subareal Accommodation Space and Widespread Fluvial Reservoirs and Stratigraphic Traps: Late Highstand Systems Tracts on the Broad Continental Margin of the East China Sea
Louis R. Bartek and Robert Wellner
Geopulse seismic reflection (2,825 km) data collected during a survey of the East China Sea (ECS) in September of 1993 have been used to reconstruct the shallow stratigraphic architecture of the ECS continental margin. This area is characterized by a broad continental shelf and has extremely high sediment supply relative to other margins. On the inner to middle portions of the ECS margin we indentified extensive areas outside of several incised valleys that contain channelized seismic facies that are interpreted as fluvial sequences deposited as sea level fell prior to the last low-stands. These deposits lie above highstand silts and clays and beneath a transgressive surface, above which sediments appear to have been extensively reworked. Historical records suggest that t e tremendous sediment load of the Yellow River caused the river to avulse over an area of hundreds of kilometers during the Holocene and deposition of thick sheet of fluvial sands in "interfluvial" areas. We suggest that as sea level fell in this area, the equilibrium point and bayline synchronously migrated seaward, and subareal accommodation was created during the latter stages of highstands, in a manner similar to that proposed in published models. The high sediment supply of the area and increasing subareal accommodation space provided an opportunity for deposition of the laterally extensive fluvial facies we observe on the seismic data. The upper portions of these "interfluvial" fluvial deposits were reworked during the ensuing transgression and downlapped upon by muddy highstand de osits, but the lower fluvial sheet-sand facies are preserved in place. This situation creates a laterally extensive, braided fluvial sand type reservoir with a potential for a stratigraphic seal that is within close proximity to hydrocarbon source rocks. Thus, the Pleistocene stratigraphy of the ECS shelf may serve as an analog for extensive fluvial sequences in the foreland basins of Cretaceous Western Interior Sea Way and the Carboniferous sequences of the eastern US and it may provide valuable insight into how to best explore and produce from such systems.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California