Xu, Qiang1, Ye Jiang1
(1) Peking University & CNOOC Research Center, Beijing, China
ABSTRACT: Study on a Modified-Density Flow, Shedding Flow and Their Significance in the Oil and Gas Exploration in the Yinggehai Basin, South China Sea
hrough the detailed sedimentology study, the sediments of characteristic modified-density and shedding flow were discovered in basin centered diapir and transitional zones. Formed in the background of the lower plate of the No.1 faults, bathyal environment, the rock of modified-density and shedding flow is mainly sandwiched with a suite of turbidity on the bottom and turbidity or slump deformation depositing on the top.
With grain-supported structure and irregular undulating surface, the sediments of modified-density flow are gray, pebble-granule gravel. The grain size varies from 0.3-0.5 to 0.7-0.8 cm, and they have the typical graded beds of fining-upward and coursing-upward rhythmites varying from 6 to 10 cm in thickness. It is suggested that the bottom of the Yinggehai basin has ever been a slope of 9 degrees dip angle that formed slope wedge and slope foot apron sediments.
The sediments of shedding flow are almost terrigenous clastics, with middle to fine grain size and yellow-gray color. They are shallow sediments formed in the sea level oscillation (on high frequency and high amplitude), and sprayed unrealistically to the nearby deep basin following the sea water. The lenticular and band laminations are common and characteristic. There are few other structures, especially in the inner of the lenticular sands. The bottoms of those sandy muddy ribbons and sand lenses don't have any erosion surfaces contrasting to the internal-wave tide sediments.
It seems that these kinds of sediments are formed in the suited formations of the transitional zone from basin-centered diapir zones to basin slope. Developed in deep sea and bathyal environment, within good souce-reservoir-caprock assemblage, these thick sandstones turn to be the exploration object of subtile trap in the Yinggehai basin in the future.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.