Abstract: Cenozoic Tectono-Stratigraphic Sequences of the Shelf Rift Basin, East China Sea

John M. Armentrout, Mark Prebish, Alan C. Cunningham, Ronald J. Echols, Philip Braithwaite, J. Frederick Sarg, John W. Norris, Dieter K. Letsch, Byron B. Bracken, Chris N. Denison

The Tertiary section of the Jiaojiang, Qiantang, and Fushi depressions of the East China Sea Basin consists of at least eight rift-related depositional sequences identified seismically by regional onlap and truncation surfaces. Delineation of these sequences is based on interpretation of multifold seismic reflection profile data calibrated with several wells, including the Wenzhou 6-1-1 well.

Upper Cretaceous(?) to Eocene synrift graben-restricted strata consist of two tectonically enhanced unconformity bounded sequences as evidenced by large angular discontinuities between each sequence. Discontinuous inclined-reflection seismic facies adjacent to the hanging wall correlate with nonmarine conglomeratic sandstone and are interpreted as possible alluvial fan facies. High-amplitude parallel reflections within the graben axes correlate with coaly siltstone strata and are interpreted as coastal plain and possibly lacustrine facies with source rock potential. Clinoform seismic facies prograding from the northwest footwall correlate with nonmarine to marginal marine conglomerate, sandstone, and siltstone, and are interpreted as possible delta or fan-delta facies with reservoir p tential.

Six postrift thermal-sag sequences drape the graben bounding highs, and are of Eocene age based on biostratigraphy from the Wenzhou well. All six of these sequences are characterized by

parallel and relatively continuous seismic reflections and locally developed clinoform packages. These facies correlate with shallow marine sandstone and siltstone, suggesting deposition in normal marine shelf environments. Third-order depositional cycles are identified from log-motif and biofacies analysis within these thermal-sag postrift strata.

Integration of seismically defined sequences, seismic facies analysis, and well data, including rock type, biostratigraphy, and geochemistry, clearly define potential hydrocarbon source rock and reservoir facies. These data, combined with thermal maturation modeling, aid prediction of hydrocarbon potential in undrilled areas of the East China Sea Shelf Basin.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994