--> ABSTRACT: Sequence Patterns and Episodic Tectonic Evolution of Various Types Structural Slope-Break and Their Petroleum Geological Significance in Paleogene Qikou Sag, Bohaiwan Basin, East China, by Chen, Si; Wang, Hua; Huang, Chuanyan; Xiang, Xuemei; Ren, Peigang ; #90142 (2012)

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Sequence Patterns and Episodic Tectonic Evolution of Various Types Structural Slope-Break and Their Petroleum Geological Significance in Paleogene Qikou Sag, Bohaiwan Basin, East China

Chen, Si *1; Wang, Hua 1; Huang, Chuanyan 1; Xiang, Xuemei 2; Ren, Peigang 3
(1) Faculty of Earth Resources, China University of Geosciences, Wuhan, China.
(2) China Petrochemical Nanjing Petroleum and Geophysical Institute, Nanjing, China.
(3) Department of Geology & Logging, Jiangsu Petroleum Exploration Bureau, Yangzhou, China.

The sequence stratigraphic pattern is closely related to the basin configuration, sedimentary filling, and depositional system, which is common controlled by regional tectonic evolution, climate cycle, sea level change, and provenance system. It is of marked significance to study the coordinating, restrictive, coupled interrelationship and response of synchronous changes among them.

Huanghua Depression is one of the most typical reformed depressions in Bohaiwan Basin in East China, whose tectonic feature presents superposition in space and order feature in time. Qikou sag locates at the middle part of Huanghua depression and has developed since Tertiary, whose rifting episode can be divided into three rifting stages. According to the research approach of ‘point-line-plain’, three types of structural slope-break were distinguished in Qikou Sag, which are the fault controlled steep slope, flexure slope-break and multistage fault terrace. The sequence patterns evolve in vertical time series in the same structural slope-break unit and are diverse in various type structural slope-break units in transverse space.

From rifting stage1 to stage3, the thickness centers had migrated from near fault to sag centers gradually, as the slope-break point had migrated from lake to the bank, which indicate the reducing of controlling of boundary faults. In the early period, the sequence thickness is obviously thick because of the intense fault activity, and the fault throw is evident. In the later period, as the reducing of synsedimentary fault controlling and enhance of the depression, the thickness of the sag seems to become homogeneous at last. The total subsidence rate and tectonic subsidence rate has reduced form stage1 to stage3, when the tectonic subsidence rate reduced more quickly. The faults controlling action was the dominant mechanism during stage1, as the depression was the dominant mechanism during stage3, which was a process from intense differential fault rifting to integral subsidence in Paleogene.

In one hand, the distinct episodic evolution of Qikou Sag deeply influences the development and evolution of sediment filling. In the other hand, the sediment filling characters responses to the evolution of basin, which represents the general control of episodic rift. The combination of particular tectonic units, geomorphic units and sequence patterns, and their effective allocation with qualitative source rocks, provide conditions for hydrocarbon accumulation.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California