Structural Geometric and Kinematic Characteristics of Grein Depression in the West African Rift System

doi:10.19657/j.geoscience.1000-8527.2022.085

Abstract

Abstract:

The West African rift system is made up of a series of Mesozoic-Cenozoic rift basins, and the Grein depression is located at the northern end of the system. Elucidating the structural geometry and kinematic characteristics of the depression is of great significance in understanding the evolution of the West African rift system.Based on the latest seismic data and the fine-scale interpretation of regional seismic profiles,the structural geometry and kinematic processes are revealed in the Grein depression. We also discussed the dynamic mechanism in combination with regional background analysis. The conclusions are as follows: (1)The Grein depression is a half-garden with gentle slope, which is characterized with fault in the east and over lapping in the west. There are fault terraces in the north and subsidence in the south;(2)The Cretaceous-Quaternary regional tectonic evolution includes two rifting phases, which can be divided into 5 stages from the Early Cretaceous,i.e.Early Cretaceous rifting(I), Late Cretaceous depression(II), End Cretaceous structural inversion(III), Paleogene rifting(IV) and Neogene and Quaternary depression(V); (3)In the Santonian (Late Cretaceous), the African-Arabian and Eurasian plates began to converge, which resulted in the Santonian and Maastrichtian intensive tectonic events in the African plate. The Maastrichtian tectonic event was clear in the Grein depression. During this period, the depression underwent tectonic inversion and the northwestern side was uplifted, resulting in the denudation of the Upper Cretaceous strata.

Key words: grein depression, structural geometry, kinematics, structural inversion, west African Rift system

CLC Number:

P542

PANG Sichen, LI Chuanxin, MAO Fengjun, WANG Tao, YUAN Shengqiang, HE Songgao, SHI Chenyi. Structural Geometric and Kinematic Characteristics of Grein Depression in the West African Rift System[J]. Geoscience, 2023, 37(02): 328-339.

Figures/Tables 11

Fig.1 Regional location (a) and geological map of Grein depression (b), and stratigraphic column of the eastern Niger Basin (c) [3,15]

Fig.2 Seismic profile and interpretation of A-A' in the southern Grein depression

Fig.3 Seismic profile and interpretation of B-B' in the central Grein depression

Fig.4 Seismic profile and interpretation of C-C' in the northern Grein depression

Fig.5 North-south seismic profile and interpretation of D-D' in the Grein depression

Fig.6 Current top structural maps of Lower Cretaceous (a) and Paleogene Sokor 1 Formation (b)

Table 1 Statistics of the key elements of Fault 1 and Fault 2 in the Grein depression

断裂		地层	A-A'剖面断裂			B-B'剖面断裂			C-C'剖面断裂
断裂		地层	上盘厚度 (m)	下盘厚度 (m)	断距 (m)	上盘厚度 (m)	下盘厚度 (m)	断距 (m)	上盘厚度 (m)	下盘厚度 (m)	断距 (m)
F₁	上白垩统		3450.98	缺失	缺失	3548.39	2838.71	425.81	1747.47	缺失	缺失
F₂	上白垩统		784.31	1705.88	缺失	1780.65	1354.84	缺失	缺失	缺失	缺失
F₁	下白垩统		2196.08	缺失	缺失	2374.19	2412.90	748.39	1676.77	缺失	缺失
F₂	下白垩统		1745.10	549.02	1705.88	1832.26	1535.48	309.68	缺失	缺失	缺失

Fig.7 3D models of Fault 1 and Fault 2 in the Grein depression

Fig.8 Contact relationship between Fault 1, Fault 2 and strata of seismic profile A-A'

Fig. 9 Contact relationship between the Sokor Formation and Madama Formation in seismic profilesC-C' and D-D'

Fig.10 Tectonic evolution models of seismic profile A-A' and C-C'

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