Formation and evolution of strike-slip fault zones in the eastern Sichuan Basin and identification and characterization of the fault zones: A case study of the Fuling area

doi:10.13745/j.esf.sf.2022.12.58

Abstract

Abstract:

Basement strike-slip fault zones of petroliferous basins are newly recognized high-yield hydrocarbon enrichment zones with broad prospects for oil/gas exploration and development. Increasingly more attention has been paid to the identification and geometrical/kinematical characterization of basement strike-slip faults as well as the role of “reservoir/pool controls” in this type of fault systems. This paper reports the new discovery of large-scale NW and NE-trending basement strike-slip fault zones in Fuling area, eastern Sichuan Basin, and establishes the identification criteria for strike-slip faults in this area based on characteristic fault patterns. The characteristic fault patterns include vertical faults and flower-like structures on the profile; planar linear extension of fault with staggered geological boundaries; and obvious segmentation of master faults in “ribbon-like” or “dolphin-like” strike-slip fault patterns and with changing mechanical properties. A new method is proposed for determining the strike-slip directions based on seismic analysis to measure the change of vertical displacements and the difference in tectonic-activity intensities between the two sides of the fault. It is found that the NW-trending basement strike-slip fault zone generally presents left-lateral slip but with variable strike-slip deformations in different evolutionary stages. Since its formation, the NW-trending faults zone has experienced at least 5 left-lateral and 3 right-lateral slip events which can be characterized by left-lateral slip in the deep crust, right-lateral slip in the shallow crust, high activity-intensity in the north and low activity-intensity in the south, with a cumulative left-lateral strike-slip offset reaching up to 1400-3400 m. In comparison, the NE-trending basement strike-slip fault zone is characterized by right-lateral strike-slip, and the cumulative strike-slip offset is about 1930 m. It suggests that there are significant differences in the formation and evolution of the two fault zones controlled mainly by regional tectonic movements, evolution of stress field environment in different evolutionary stages as well as stress release of regional detachment layers where the NW-trending strike-slip fault zone is affected by Lower-Triassic gypsum-salt detachment layer and the NE-trending strike-slip zone is affected by Middle-Lower-Silurian shale detachment layer.

Key words: Eastern Sichuan Basin, strike-slip faults, geometric features, kinematic characteristics, formation and evolution model

CLC Number:

P542.3

ZENG Tao, FAN Rui, XIA Wenqian, ZOU Yutao, SHI Siyu. Formation and evolution of strike-slip fault zones in the eastern Sichuan Basin and identification and characterization of the fault zones: A case study of the Fuling area[J]. Earth Science Frontiers, 2023, 30(3): 366-385.

Figures/Tables 22

Fig.1 Geotectonic location (A), tectonic environment (A, after [34]) and tectonic zoning map (B, modified after [35]) of the Sichuan Basin

Fig.2 Characteristics of sedimentary strata, regional tectonic movement and environmental evolution of stress field in the Sichuan Basin. Modified from [40].

Fig.3 High-resolution coherence attribute slices through interfaces T 1q (A), TS (C) and TP2 (E) in the study area and interpretation of the corresponding coherence maps showing the distributions of the fault arrays (B, D, F)

Fig.4 Comparison of interpreted (left) and uninterpreted (right) seismic sections a-c normal to the southern segment of No.15 basement strike-slip fault zone. Symbols (☉) and ($\otimes$) respectively represent the forward and backward movement directions (relative to the reader) of the fault blocks on either sides of the strike-slip fault

Fig.5 Comparison between interpreted (bottom penal) and uninterpreted (top penal) seismic sections 1-3 respectively normal to basement strike-slip fault zones NE-F2, NE-F3 and NE-F4

Fig.6 Interpreted seismic sections showing abrupt stratum-thickness changes on either sides of the NE-trending NE-F2 (A) or the NW-trending No.15 (B) basement strike-slip fault zones in the study area

Fig.7 Photos showing important structural features on the Erya outcrop profiles for the identification of basement strike-slip faults in the Huaying Mountain area

Fig.8 Zonal plane distribution (A) and fault offset on horizontal time slice (B) of No.15 fault zone in Fuling area

Fig.9 Grid comparison of interpreted seismic sections of mater-fault segments (A-D) of No.15 fault zone with “ribbon-like” strike-slip fault patterns

Fig.10 Sectional views of interfaces TS, TP1 and TP2 of master faults in No.15 fault zone with “ribbon-like” fault pattern

Fig.11 Grid comparison of seismic interpretation sections of “dolphin effect” of master fault in No.15 basement strike-slip fault zone in Fuling area

Fig.12 Sectional views of interfaces TS, TP1 and TP2 of master faults in No.15 fault zone with “dolphin-like” fault pattern

Fig.13 Characteristics of vertical displacements and their variation patterns used in the new method to determine strike-slip directions

Fig.14 Variation of vertical displacement of seismic-reflection profiles 1-22 along the strike of the southern segment of No.15 fault zone at interfaces TS, TP1, TP2

Fig.15 Variation of vertical displacement of seismic-reflection profiles 1-28 along the strike of the northern segment of No.15 fault zone at interfaces TS, TP1, TP2

Fig.16 Balanced geological profile of NW-SE seismic sections on either sides of No.15 fault zone in different deformation stages for calculating strike-slip directions in each stage

Fig.17 Comparisons of tectonic-activity intensity parameters between the two sides of No.15 fault zone in different geological periods for calculating strike-slip offset in each period

Fig.18 Comparison of stratum-thickness peak positions between surfaces TP1 and TP1m on either sides of No.15 fault zone for calculating strike-slip offset

Fig.19 Fault development stages revealed on seismic sections of No.15 (A) and NE-F2 (B) basement strike-slip fault zones in Fuling area

Fig.20 Relationship between formation/evolution of strike-slip fault zones and regional tectonic activity in Fuling area, eastern Sichuan Basin

Fig.21 Model for the formation and multi-stage tectonic evolution of No.15 basement strike-slip fault zone in Fuling area, eastern Sichuan Basin

Fig.22 Model for the formation and multi-stage tectonic evolution of NE-F2 basement strike-slip fault zone in Fuling area, eastern Sichuan Basin

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