Journal of Petroleum Geology, Vol.16, No.3, pp. 285-312, 1993

©Copyright 2000 Scientific Press, Ltd.

THE EFFECT OF BASEMENT FAULTING ON DIAPIRISM

H. Koyi(1), M. K. Jenyon(2) and K. Petersen(3)

(1) The Hans Ramberg Tectonic Laboratory; Institute of Geology, Uppsala University, Box 555, 751 22 Uppsala, Sweden. Present address: Applied Geodynamic Laboratory, Bureau of Economic Geology, The University of Texas at Austin, University Station, Box X, Austin, Texas 78713-7508, USA.

(2) c/o Department of Geology, Birkbeck College, University of London, Malet Street. London, WCIE 7HX

(3) Geologisk Institut, Aarhus University, DK-8000 Arhus C, Denmark. Present address: Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA.

Abstract

Experimental and natural examples illustrate the inf1uence of sub-salt horizon basement faults on diapirism. In a series of experimental models, viscous diapirs were observed to form above or close to basement faults. In all the models, basement faults initiated a half-graben, where thicker overburden units enhanced differential loading on an underlying buoyant layer. The buoyant material flowed updip to the low-pressure zones in the uplifted block, and updip along the tilted upper boundary of the hanging-wall. Basement faulting extended the overburden, and provided the space through which the buoyant layer could rise. Subsidence and faulting of overburden layers allowed diapirism along the faulted zones. In all cases, the deformation in the overburden was accommodated within a wider zone of faulting than the discrete basement fault which initiated the deformation. Differential compaction enhances differential loading and accumulation of thicker overburden on the downthrown sides of basement faults.