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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 47 (1997), Pages 169-176

Influence of Active Subsalt Normal Faults on the Growth and Location of Suprasalt Structures

Hongxing Ge (1), Bruno C. Vendeville (2)

ABSTRACT

The location and deformation style of salt and overburden structures that form during subsalt normal faulting vary greatly between and within salt provinces. In some areas, diapirs and overburden faults appear to have formed independently of the location of the underlying basement faults. Elsewhere, diapirs and faults formed systematically above or near the subsalt faults, or the overburden was force-folded above the subsalt fault into a monocline whose shape reflects the offset along the underlying basement blocks. We used dynamically scaled physical experiments and conceptual models to (1) understand how much subsalt faulting controls the formation and localization of structures in the salt and overburden, and (2) evaluate how this control is affected by changing selected parameters, such as salt thickness, strain rate, or sedimentation rate.

Both experimental and conceptual models predict that initially thick salt or slow subsalt faulting favors decoupling of the overburden from the subsalt basement. Instead of transmitting stresses and strains upward from basement, through salt, and into the overburden, the salt layer diffuses localized basement slip by laterally flowing from the footwall to the hangingwall. Thus, the salt layer thins above the basement 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, along which further extension is accommodated. Experimental and conceptual models 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.


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