The Paleogene multi-phase tectono-sedimentary evolution of the syn-rift stage in the Nanpu Sag, Bohai Bay Basin, East China

Siding Jin,Haiyang Cao,Shanbin Chen,Hua Wang

doi:10.1177/0144598718772318

Siding Jin, Haiyang Cao + Show 2 more

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https://doi.org/10.1177/0144598718772318

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Abstract

The Bohai Bay Basin is the second largest oil-producing basin in China located on the east Asian margin. The Bohai Bay Basin contains numerous depressions, sub-basins, and sags. One of these, the Nanpu Sag, has played a particularly important role in oil and gas exploration in recent years. Four depositional systems are recognized in the Nanpu Sag, fan-delta, braided-river delta, turbidite deposits, and lacustrine systems. In the Paleogene, the Nanpu Sag underwent complex and multi-phased rifting evolution. Two evolutionary phases have been identified: the syn-rift phase and the post-rift phase, the syn-rift stage can be further sub-divided into four episodes. This study reveals the considerable faulting activity and associated strong subsidence that occurred during the deposition of the Dongying Formation in the fourth episode of the syn-rift stage. The depositional systems and the tectonic activity during the fourth episode in the Nanpu Sag have very different characteristics compared to those of other depressions or sub-basins in the Bohai Bay Basin. Boundary fault activity was extremely intense during the deposition of the Dongying Formation, especially the east to west trending faults, including the Xinanzhuang Fault and the Gaoliu Fault. Moreover, the migration of subsidence centers from the Shahejie Formation to the Dongying Formation is a result of the strong down-warping that occurred during the fourth episode of the syn-rift stage. In the Nanpu Sag, the Dongying Formation is of great significance to hydrocarbon exploration, which is affected by both the intensity of fault activity and magnitude of basement subsidence.

Highlights

Tectono-sedimentary analysis is a critical component of basin analysis, contributing to our understanding of the relationship between the tectonic regime and sedimentary infill in continental rift basins (Deng et al, 2008; Hou et al, 2012; Strecker et al, 1999)
With a close relation to the tectonic activities including fault activity and basement subsidence, numerous investigation focused on the sedimentary infill and spatial distribution that are controlled by dynamic tectonic and sedimentation in the Paleogene of the Nanpu Sag, Bohai Bay Basin (Dong et al, 2014; Chen et al, 2016; Cong and Zhou 1998; Zhang et al, 2009)
This observation indicates that intense subsidence occurred in the Nanpu Sag during the deposition of the Dongying Formation (Chen et al, 2012), which is not seen in the other sub-basins or depressions in the Bohai Bay Basin

Summary

Introduction

Tectono-sedimentary analysis is a critical component of basin analysis, contributing to our understanding of the relationship between the tectonic regime and sedimentary infill in continental rift basins (Deng et al, 2008; Hou et al, 2012; Strecker et al, 1999). The Nanpu Sag underwent both a syn-rift and a post-rift subsidence stage like the other sub-basins/depressions in the Bohai Bay Basin, and it is filled with formations deposited in continental environments including alluvial, fluvial, and lacustrine (Kang et al, 2016; Zhang et al, 2016). The Es2 member consists of red mudstones in the Shichang sub-sag and gray siltstones and finegrained sandstones in the Beipu anticlinal structure zone, representing alluvial fan depositional systems; (3) Episode III: Weakened rifting episode during Es1, the master fault of the Gaoliu Fault, becomes active and divides the Nanpu Sag into two separate sedimentation regions. Using the isochronous sequence stratigraphic framework, the subsidence history of the Paleogene in the Nanpu Sag has been simulated quantitatively and dynamically based on erosion recovery basin modeling (Figures 11 to 13)

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