Abstract: Nonmarine Sequence Stratigraphy - Impact on Source, Reservoir, and Seal Distribution in a Rift Setting: Cretaceous Songliao Basin, China

SCHWANS, P., K.M. BOHACS, V.K HOHENSEE, F.C. LIN, R.Q GAO, and J.Y. QIU, S.H SUN, and F.J LI

A nonmarine sequence-stratigraphic framework was constructed for the Songliao basin, using cores, well logs, and seismic. Synrift deposits are confined to narrow grabens and comprise thick successions of locally derived alluvial fan and fan-delta clastics interbedded with floodbasin fines, volcanics, and volcaniclastics. Increased regional subsidence during the rift-to-sag transition resulted in integration of the various subbasins. Lowstand transgressive systems tracts of nonmarine sequences feature stacks of amalgamated channels in the basin and alluvial fans or fan deltas along border faults. The reservoir-prone, lowstand-transgressive coarse-clastics are sharply overlain by fine-clastic, seal- and source-prone, floodplain fines with intercalated thin lacustrine deposits of the nonmarine highstand systems tract. Isolated channel forms of single- to multi-channel, meandering streams occur within the overbank successions. Floodplain fines feature Type III organic matter with an average TOC ~1.5%; higher TOC values occur locally in the lacustrine beds. Onset of widespread subsidence during the sag phase connected the rift to the marine, resulting in formation of an expansive brackish-water lake system; associated stacking patterns are of combined eustatic and tectonic forcing. Lacustrine fines feature Type I-II organic matter with average TOC ~4%. Source quality is best at the top of retrogradational sequence sets, while reservoir distribution is most favorable in highstand and lowstand sequence sets.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria