Coeval Shallow Extension and Deep Shortening above and below a Salt Canopy: A Model for the Ultradeep Miocene of the Northern Gulf of Mexico

A physical model shows how radically different deformation affects the same area at the same time above and below a salt canopy. The juxtaposition of different deformation styles is enabled by two detachment levels. A deep, long detachment representing autochthonous salt is overlain by a short, shallow detachment representing allochthonous salt. The deep detachment is pinned updip on the onshore continental plain. In contrast, the shallow detachment is pinned at the head of the canopy hundreds of kilometers away on the continental slope. Deep-seated extension far inland was linked via the deep detachment to a wide zone of shortening on the continental slope, where halokinetically formed salt pillows were shortened below the canopy. Subcanopy shortening steepened pillow flanks and thrusted their crests. At the same time extension formed a roho system above the canopy via the shallow detachment. Supracanopy extension was much faster and continued longer than subcanopy shortening because the canopy roof was less resistent to deformation. Shortened pillows lifted and indented roho tilt blocks, which perturbed the fault pattern of roho extension.

The physical model supports the hypothesis that coastal uplift allowed a broad pillow fold belt to shorten during the mid-late Miocene in the northern Gulf of Mexico, almost as far landward as the paleoshelf break. In this hypothesis, subcanopy shortening on the former upper slope was nearly coeval with supracanopy roho extension. This Miocene upper slope is today’s ultradeep shelf.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California