VENDEVILLE, BRUNO C., M. P. A. JACKSON, and H. GE, Univ. of Texas at Austin, Bureau of Economic Geology, Austin, TX

ABSTRACT: Detached Salt Tectonics during Basement-Involved Extension

Seismic interpreters commonly attribute parallel or aligned diapirs and faults in pre- or syn-rift salt basins to the presence of small underlying basement faults. Yet scaled experiments and analytical models suggest that under typically low geological extension rates, a salt layer 500 m or more in thickness decouples its brittle overburden from an extending basement. Rock salt has a low viscosity and cannot transmit large differential stresses necessary for basement faults to propagate upward as faults or abrupt forced folds into the brittle overburden. Salt isolates localized deformation in the basement by flowing away from rising basement blocks toward sinking basement blocks. Basement extension is not transmitted to the overburden vertically but horizontally by widening the salt b sin. Faults and fault-induced diapirs in the overburden form perpendicular to the direction of regional extension but their location, spacing, throw, and orientation are virtually independent of all but the largest basement faults. Faults in the overburden and diapiric walls initiated by such faults are typically localized by the following overburden structures: lateral change' in stratigraphy or thickness, preexisting faults, and faults that propagate laterally into the salt basin. Experiments and analytical models show thatbasement faults can propagate upward through the salt into the overburden only if salt viscosity is very high, regional extension is rapid, or the salt layer is thin or depleted.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.