How and Where Is the Sigsbee Escarpment Advancing?

Martin P. Jackson¹, Michael R. Hudec¹, and Teunis Heyn^2
1Bureau of Economic Geology, University of Texas at Austin, Austin, TX
²BP America, Houston, TX

Because of its vast size and unrivaled coverage by reflection seismic data, the Sigsbee Escarpment in the northern Gulf of Mexico is the type example for the leading edge of an advancing salt canopy. However, no systematic study has ever been published of the structural styles along the escarpment. We surveyed the 750 km-length of the Sigsbee Escarpment using ~1300 seismic profiles, mostly from 3D seismic datasets. We infer that ~40% of the Sigsbee Escarpment is static over escarpment distances as long as 130 km. These static lobes of the salt canopy are not advancing but are commonly inflating, overlain by draped but continuous roof strata. In contrast, the other ~60% of the Sigsbee Escarpment is actively advancing. Advance by salt extrusion may have dominated in the past, but <1% of the advancing scarp length now exposes salt. In contrast, more than 99% of the active salt front is buried. It advances by thrusting, most commonly as a thrust rooted into the tip of the salt sheet. The salt sheet and its protective roof advance together, minimizing salt dissolution. Additionally, imbricate thrust wedges sole into either the salt tip or the salt floor. These accretionary wedges comprise thrust slices of thin, weak strata. They form rapidly during surges of canopy advance. Stacked imbricate wedges record cycles of shortening then burial then detachment climb during renewed shortening. Salt-roof thrusts are rare and form where the sedimentary roof advances faster than the underlying salt.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas