Oil & Gas Geology ›› 2023, Vol. 44 ›› Issue (3): 720-734.doi: 10.11743/ogg20230315

• Petroleum Geology • Previous Articles     Next Articles

Zonation and dynamic genetic mechanism of the Indosinian thrust nappe system in Bohai Sea

Dingyou LYU(), Haifeng YANG, Haibo YU, Pengbo LIU, Hui DENG, Shen ZHANG   

  1. Tianjing Branch,CNOOC,Tianjin 300452,China
  • Received:2023-01-22 Revised:2023-04-06 Online:2023-06-01 Published:2023-06-05

Abstract:

The Indosinian orogeny is a key period shaping the intracontinental deformation pattern in eastern China. Current understanding of the Indosinian tectonism period is mainly based on the study of the orogenic belt around the North China Craton and the continental area of the Bohai Bay Basin. However, little research attention has been paid to the Mesozoic tectonic evolution in the Bohai Sea. Based on the latest three-dimensional seismic reflection data, we present a detailed structural analysis of the Indosinian deformation in the Bohai Sea and propose that the Indosinian thrust nappe system can be divided into the three thrust zones as follows. The first thrust zone along Shaleitian salient, Bozhong 19-6 structural zone and the Bonan sub-salient, is a high-angle trust structure as shown by the Archaean basement thrust at high angle along reverse fault with part outcropped and subject to long-term weathering and denudation during the Indosinian period, resulting in the absence of the Paleozoic. The high-angle thrust faults turned into strike-slip faults as shown by the present-day Bohai Bay section along the Zhangjiakou-Penglai fault zone. The second one, the central thrust-fold zone located in the Bozhong and Bodong sags, is mainly characterized by fault-related fold deformation in the Paleozoic strata, especially in the Bodong Sag, where typical imbricates and duplex structures can be identified. The third thrust zone, the front belt of the thrust nappe located in the Liaodong Bay Depression, is mainly characterized by extensive and gentle anticlines and synclines under the Paleozoic deformation, typical fault-propagation or fault-detaching folds, which are associated with the hidden thrust nappe faults of slope-plateau type in the basin basement during the Indosinian. We may conclude through the seismic section across the entire Bohai Sea and previous research data, that the spatial association of three thrust nappe zones is controlled by the three-step basement detachment layers during the Indosinian period. The dynamic genetic mechanism of the Indosinian thrust nappe system in the Bohai Sea may be related to the differential basement features in the North China Craton, that is, the thrusting of Luxi basement against Yanliao basement along the decollement layer during the Indosinian, leading to the overlying Paleozoic caprock characterized by fold deformation in zonation.

Key words: genetic mechanism, detachment layer, tectonic zonation, thrust nappe system, Indosinian, Bohai Sea

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