Bruce D. Trudgill¹, Mark G. Rowan²

(1) Imperial College, London, United Kingdom
(2) Rowan Structural Consulting, Boulder, CO

ABSTRACT: Controls on the 3-D Evolution of a Complex Stepped Counter-Regional Salt System, Offshore Louisiana, USA

The West Delta/South Pass (WDSP) area contains a complex stepped counter-regional salt system that evolved from a salt tongue canopy. Interpretation of a large 3-D seismic survey, and regional 2-D seismic lines has revealed a complex interplay between the evolution of the salt system and associated fault families. The evolution of the salt system over the past 10my has been reconstructed using both 2-D and 3-D structural restorations. These sequential restorations are best viewed as interactive movies that fully illustrate the changing salt geometry during emplacement and subsequent evacuation.

Combining the restorations with isopach maps leads to a six-stage history of the interaction between salt movement and sedimentary loading. From 9.9 to 7.5 Ma, sediment loading drove deep level salt basinward leading to the growth of isolated salt tongues at the surface. Between 7.5 and 6.4 Ma continued feeding of salt into the system led to growth and amalgamation of salt tongues into a salt tongue canopy. From 6.4 to 5.0 Ma, the main Mississippi depo-centre lay across the WDSP area as the shelf margin prograded basinward from the north. The salt supply was cut off as deep feeders "welded out", starting the counter-regional evacuation of the canopy. Continued evacuation of salt into salt walls occurred between 5.0 and 2.55 Ma, as the salt tongue canopy was gradually dissected. Between 2.55 and 0.5Ma the salt walls evacuated producing "fault welds" and isolated salt domes. In the last 0.5my, the system has been gradually buried by sediment from the Mississippi delta.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado