The influence of layering and pre-existing joints on the development of internal structure in normal fault zones: the Lodève basin, France

Abstract

Abstract This paper examines the role of mechanical stratigraphy on the evolution of normal fault geometry and fault zone internal structure, using a well-exposed normal fault system from the Permian Lodève Basin, southern France. Faults formed early during the syn-deformation tilting history of the basin tend to have steeper segments in the competent sandstone layers due to refraction, assisted by pre-existing early bedding-perpendicular joints, where displacement remained on the order of bed thickness. Faults which continued to slip during tilting have a more complex structure of splays due both to the space incompatability problem of slip at fault bends of this irregular geometry, and because tilting favours the generation of new splays at a different angle to the earlier faults experiencing rotation. Continued deformation between faults and their splays often causes both distributed deformation in between the two, and reconnection of splays to the main fault forming isolated lenses. Thus, fault zone complexity increases greatly as slip exceeds competent bed thickness, owing both to the presence of the mechanical layering, and the fact that this layering is being tilted.