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A Promising Hybrid Strike-Slip Associated Structure for Hydrocarbon Accumulation: A Case Study on JZ27-6 Oil-Bearing Structure in the Bohai Sea Area, East China


It is well-accepted that the strike-slip motion of a fault could derive either transtensional structures (e.g. normal faults and pull-apart basins ) or transpressional structures (e.g. anticlines and push-ups) at its tails, bends and step-overs. Considering the self-similarity and scale of secondary structures developed on a strike-slip fault, a kind of hybrid structure with both transtensional and transpresional characteristics should exist as well. JZ27-6 Structure is an oil-rich structure located in a large releasing step-over of LZ 1 Fault and LZ 2 Fault, the branches of the Tan-Lu Fault Zone (TLFZ), and next to a small restraining bend of LZ 2 Fault in the Bohai Sea Area. It is roughly an anticline with its inner flank towards the center of the releasing step-over cut by some normal faults. We attribute the formation of this hybrid structure to the regional extension and local compression derived by the large releasing step-over and small restraining bend of LZ 1 and LZ 2 faults, respectively, due to the dextral strike slip of TLFZ. Such kind of hybrid structure has important significance for the hydrocarbon accumulation of the JZ27-6 Structure. Because the local compression not only favors the formation of the anticline next to the LZ 2 Fault, but also helps LZ 2 Fault to seal hydrocarbon. While the regional extension is favorable of the formation of the source rock and normal faults connecting both source rock and anticline traps between the releasing step-over of LZ 1 and LZ 2 faults, which makes the hydrocarbon migrate to the anticline traps readily. Actually, not limited to this kind of hybrid structure, we also identified many other kinds of hybrid oil-bearing structures with both transtensional and transpresional characteristics along TLFZ in the Bohai Sea Area. They are favorable strike-slip associated structures for hydrocarbon accumulation and should be paid more attention in the future.