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Sequence Stratigraphy and Structure of the Miocene Guantao and Pliocene Minghuazhen Formations, Zhao Dong Field, Bohai Bay, Eastern China

Hugo A. Castellanos1, Paul Mann2, and Alan Clare3
1 The University of Texas at Austin, Austin, TX
2 Jackson School of Geosciences, The University of Texas at Austin, Austin, TX
3 Apache Corporation, Houston, TX

The Cenozoic tectonic evolution of the southeastern Bohai basin has been documented through the interpretation of 8,000 km of offshore 2D seismic data, a 3D seismic volume, and 38 well logs that are tied to these reflection data. Three major unconformity-bound tectonosequences (pre-rift, rift, and post-rift or sag) were identified and mapped on the 15,700 km2 scale of the western Bohai basin. Thickening trends and ages indicate rifting occurred from early Eocene to late Oligocene and produced a set of NS-trending half-grabens. The widespread distribution of rifts in the Bohai basin and adjacent plains supports a regional extension possibly related to a previously proposed rollback of the Pacific plate subducted beneath the Bohai basin. Rifting ended during the late Oligocene and a regional uplift and erosional unconformity affected the basin. The Miocene to recent interval was marked by the formation of sag basins deformed by widely-spaced, NW-striking right-lateral strike-slip faults.

The Miocene-Recent sag basins of the western Bohai basin have been previously subdivided in two lithostratigraphic units (Minghuazhen and Guantao formations) using well logs and seismic data. We have further subdivided the sag tectonosequence of Zhao Dong field in westernmost Bohai Bay into at least ten regional correlatable accommodation/supply cycles. Guantao formation is made up of amalgamated fluvial channels deposited under low accommodation/supply conditions. Minghuazhen formation on the other hand is characterized by isolated channel systems encased by floodplain facies. Accommodation/supply cycles establish a high-resolution correlation framework and provide an alternative approach for correlating continental seismic units.