--> ABSTRACT: Sedimentation within a Pull-Apart Basin, Stratigraphic Details from Yacheng Field, South China Sea, by M. A. Cucci, S. P. Ross, S. J. May, P. R. Thompson, W. H. Abbott, T. P. Bulling, and S. W. Prior; #91021 (2010)

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Sedimentation within a Pull-Apart Basin, Stratigraphic Details from Yacheng Field, South China Sea

CUCCI, MAURICE A., STEVEN P. ROSS, S. JUDSON MAY, PETER R. THOMPSON, WILLIAM H. ABBOTT, THOMAS P. BULLING, and SCOTT W. PRIOR

A synrift (pull-apart) section typically comprises a vertical succession of non-marine sediments at its base to marine sediments at its top. However, at Yacheng Gas Field a variation in this vertical succession is observed in late synrift to early post-rift time: fluvial valleys incise shelfal synrift strata. initial synrift deposits comprise Early Oligocene non-marine, ramp-like, alluvial units. These depositional systems emanated from northwesterly axial and northeasterly lateral drainages. As the region underwent a gradual 20 Ma long subsidence-generated transgression, syn rift deposition changed from fluvial processes to estuarine processes. Provenance continued to supply coarse grained clastics to the area. By the Late Oligocene, clastic sediment supply was shifted to other areas giving way to carbonate deposition on submerged highs. In late synrift to early post-rift time (Early Miocene), the area was subjected to uplift and rotation of synrift strata. A prolonged lowstand occurred, eroding rotated strata on structural highs, and creating a prominent regional unconformity. Within structurally low areas, erosion incised synrift strata creating several valley systems more than 1 km wide and 100 m deep. These incised valleys appear to exploit previous axial and lateral drainage systems. Core and biostratigraphic analyses show that valley fill comprises fluvial to shallow marine sandstone units overlain by neritic to bathyal muds representing another transgression-highstand sequence. Later post-rift (Middle Miocene) deposition was comprised of hemipelagic sediments. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.