LINKED FAULT FAMILIES IN BASIN FORMATION

Recent models of faulting tectonics in basins and passive margins have emphasized the linked nature of faults in a way that is analogous to that developed for thrust regimes. A linked fault system requires three components; ramps, flats and sidewalls or transfers. Basins that are the result of other processes are not considered in this contribution, and the examples used are drawn from the Midland Valley and Northumberland basins of the U.K. where existing mapping by the British Geological Survey as well as field work undertaken by the author indicate that such models are appropriate. This paper summarizes the geometric features and constraints of such models and emphasizes the role of each of the three critical components of a linked system. For large deformations that result in the formation of major extensional and strike-slip basins, the principal geometries can be understood by reference to regionally and locally balanced fault models that involve detachment, ramp and sidewall or transfer elements. Tip strains, and both lateral and vertical accommodation zones are included in the general model but these probably account for less than 10% of the total upper crustal strain. The basic analysis of a linked basin system requires the transfer of displacement on and between the fault and shear zone components. The geometry of the stratigraphic units is used to deduce the active linkage on the fault system. In oblique-slip systems and where the dominant extensional ramp is connected to oblique transfer and detachment systems, lateral and sidewall sub-basins and intra-basin uplifts occur as part of continuing slip on the fault system. These control facies distribution and depocentre evolution. The existence of a basin-forming linked system frequently controls later deformation of basins and margins, and an appreciation of basin growth faults and stratigraphic geometry is essential in the interpretation of inverted basins and orogenic belts involving supracrustal formations. © 1990.