Genetic Mechanism of Antiformal Negative Flower Structure in the Doseo Depression, Southern Chad Basin

doi:10.19657/j.geoscience.1000-8527.2023.007

Abstract

Abstract:

The Doseo depression in the South Chad Basin is an important petroliferous basin in the Central African Shear Zone.A new kind of flower structure composed of normal faults (termed antiformal negative flower structure), is developed on the ENE-WSW-trending strike-slip fault zone.The faults there exhibit an en echelon arrangement in plane view, and have characteristics of positive flower-like and negative flower-like structures in the seismic profile, which are shown as a flower structure of lower "synform" and upper "antiform" shape.According to the development characteristics of the faults and the regional stress evolution, combined with 2D and 3D seismic data interpretation, the Doseo depression is divided into five evolution stages by the balanced cross-section reconstruction technique.Based on the strike-slip displacement, we analyzed the genetic mechanism of the antiformal negative flower structure in the depression.We considered that it is the result of superposition of the ENE-WSW-trending basement normal fault in the middle part of the depression in the formation stage of negative flower structure in the Early Cretaceous transtension period, and the antiform formation stage in the Paleogene transpression reversal.The early transtension strength is much greater than the later transpression reversal strength, and the difference between the strike-slip displacement components of the two is 10 to 30 times.The difference in strength makes it mainly present the negative flower structural style composed of normal faults, and only the antiform style formed during the inversion period is superimposed.

Key words: Doseo depression, antiformal negative flower structure, strike slip fault, structural inversion, genetic mechanism

CLC Number:

P618

ZHOU Xiaorong, CHEN Shi, ZHANG Xinshun, DING Baotong, SONG Xingguo, PAN Chuqi, PENG Zijun. Genetic Mechanism of Antiformal Negative Flower Structure in the Doseo Depression, Southern Chad Basin[J]. Geoscience, 2023, 37(05): 1146-1154.

Figures/Tables 9

Fig.1 Structure (a) and basement burial depth (b) in the Doseo depression

Fig.2 Stratigraphic column of the Doseo depression

Fig.3 Comparison of the different flower structure types in cross-sections

Fig.4 Fault plan of the study area in the Doseo depression

Fig.5 Structural interpretation of 2D seismic profile in the Doseo depression (seeing Fig.4 for the locations of section AA’ and BB’)

Fig.6 Tectonic evolution profiles of the Doseo depression (seeing Fig.4 for the location of section AA’)

Fig.7 Evolution models for the antiformal negative flower structures in the Doseo depression

Fig.8 Fracture system diagram for the top Kedeni Formation in central low uplift zone of the Doseo depression (seeing Fig.4 for the location)

Table 1 Statistics of strike-slip displacement of the various faults in the Doseo depression

	断层	最大离距 OO’(m)	走滑断层与派生断层夹角α	走滑分量 D_i(m)
张扭断层	F01	291.42	72.00	943.05
	F02	401.31	70.50	1202.22
	F03	129.86	76.91	573.38
	F04	205.57	75.46	818.82
	F05	273.69	73.50	963.65
	F06	318.79	63.58	716.47
	F07	585.21	62.83	1281.58
压扭断层	F08	69.32	0.50	69.32
	F09	38.44	17.15	40.23
	F10	70.62	22.70	76.55
	F11	49.35	6.27	49.65
	F12	40.06	8.34	40.49

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