Structural Analysis and Fractures Kinematics Using Seismic 2D and Geological Maps

Abstract

ABSTRACT: A comparative approach is applied in the north part of the Hoggar shield to highlight the subsurface architecture and determine the kinematics, the dip, and the geometry of the major fault sets that affect the Ahnet and the Mouydir basins by using a combination of seismic 2D profiles and the surface geological maps. The analysis of geological maps shows that a dense fracture network affects the Paleozoic series. The N-S fault network constitutes large and long fracture corridors that design the edges of the two basins. These faults are strike-slip faults trending dextral and sinistral. The NNE-SSW and NW-SE are also strike-slip faults trending sinistral. They are also strike-slip faults trending dextral and sinistral. On the other hand, the structural analysis of 2D seismic profiles reveals that the deep strike-slip faults that affect the Ahnet and Mouydir basin are not only pure strike-slip trending sinistral and dextral, but they have also vertical components trending as normal and reverse faults. The outcomes suggest that the Hercynian orogeny could be considered as a continuous deformation instead of separate tectonic events. 1. INTRODUCTION The Paleozoic analog overlays in the north part of the Hoggar shield and in the southern edges of Ahnet, Mouydir, and Illizi basins. It is mainly composed of the Cambro-Ordovician, Silurian, and Devonian formations. The Cambro-Ordovician formations are characterized by brittle tectonic style, linked with the major basement fractures inherited from the Pan-African orogeny (Arab et al, 2011 and Djezzar et al, 2020a). The latter were reactivated during the Hercynian orogeny, creating the actual basins’ architecture in horst and graben in a major part of the Saharan platform. The Mouydir basin is designed as horst and graben where two main horsts constitute the edges of the basin and are clearly visible through the 2D seismic data. In addition, other horsts in the center of the basin are highlighted and constitute positive structures where several wells were drilled. The structural analysis revealed that the Saharan platform has been marked by several tectonic phases where the Hercynian orogeny that occurred at the end of the Carboniferous is the most important event that structured the Saharan platform (Boualam et al. 2019). A comparative approach is used to highlight the subsurface architecture of the Mouydir basin and determine the kinematics, the dip, and the geometry of the major fault sets that affect the Ahnet and the Mouydir basins by using a combination of seismic 2D profiles and the surface geological maps. The analysis of surface geological maps shows that a dense fracture network affects the Paleozoic series. The fracture network is composed of 3 main fracture sets oriented N-S, NNE-SSW, and NW-SE, respectively. The N-S fault network constitutes large and long fracture corridors that structured the edges of the two basins namely Idjerane and Amguid spurs. These faults are strike-slip faults trending dextral and sinistral. The NNE-SSW and NW-SE are also strike-slip faults trending dextral and sinistral. On the other hand, the structural analysis of 2D seismic profiles reveals that the deep strike-slip faults that affect the Ahnet and Mouydir basins are not pure strike-slip trending sinistral and dextral, but they have also vertical components trending as normal and reverse faults (Djezzar et al, 2020b). They are mainly generated through transpressional and transtensional strain regimes that affected the area of study during the Hercynian orogeny. The 2D seismic profiles show clearly that the area of study was affected at least by two tectonic events oriented N040 and N120, expressed by compressive and distensive structures generating anticlines/reverse faults and synclines/normal faults. The results suggest that the Hercynian orogeny could be considered as a continuous deformation instead of separate tectonic events.