ABSTRACT: Influence of Active Subsalt Normal Faults on the Growth and Location of Suprasalt Structures
GE, HONGXING* and BRUNO C. VENDEVILLE
The location and deformation style of suprasalt structures induced by active subsalt normal faulting vary greatly: in some areas, diapirs appear to have formed independently of the location of underlying faults, whereas elsewhere, diapirs formed systematically near the faults, or the sediment overburden was forced-folded above the subsalt fault. We used dynamically scaled physical experiments and analytical models to (1) investigate the influence of subsalt faulting onto the formation of suprasalt structures and (2) evaluate how changing selected parameters (e.g., salt thickness, strain rate, or syntectonic sedimentation) affects this influence.
Both physical experiments and analytical models predict that initially thick salt or slow subsalt faulting favors decoupling of the overburden from the subsalt basement. Instead of transmitting stress and strains upward, salt flows laterally from the footwall to the hangingwall. Thus, the salt layer thins above the footwall and thickens above the hangingwall. Once the source layer above the footwall has been thinned or depleted, salt can no longer flow fast enough to entirely accommodate subsalt faulting. Hence the fault propagates upward as a broad forced fold whose upper hinge is affected by crestal normal faults that accommodate subsequent extension. Experimental and analytical results indicate that initially thick salt, slow or moderately fast subsalt faulting, and slow or absent syntectonic sedimentation promote decoupled deformation. Conversely, initially thin salt, very rapid subsalt faulting, rapid syntectonic sedimentation, or all three promote coupled deformation and formation of diapirs or overburden faulting above or near the subsalt fault.
AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana