Deep Water Gulf of Mexico Sub-Salt Structural Framework

Abstract

Abstract Structural styles in the deep-water Gulf of Mexico are largely a function of the distribution of salt, its interaction with sedimentary depo-centers, the specific Gulf of Mexico linked system involved, and position in that linked system. Nearly basin wide coverage of high quality 3D seismic data coupled with existing regional 2D data has allowed interpretation of sub-salt structural features and assembly into a broad regional framework. We identify and characterize the following provinces and subsalt structural elements. 1) A deep salt basin and frontal salt napppe; 2) Perdido fold belt and Alaminos Canyon gravity minima; 3) Eocene and Miocene regional welds; 4) an " egg crate?? province of isolated primary depo-centers separated by older salt and younger mini-basins; 5) an area of amalgamated salt and linked primary depo-centers; 6) Mississippi Canyon/Atwater, and Spirit fold belts; 7) Sigsbee salt lobe and allochthonous carapace basins; and 8) " ramps?? between weld and canopy levels. Introduction There is natural spatial organization of thin skinned structural provinces in the deep-water Gulf of Mexico. Each province contains characteristic structural elements and structural styles, resulting from a particular history of deformation, governed by the interaction of mechanically weak salt with younger and stronger classic and carbonate rocks. Boundaries between provinces are real but gradational, and although the provinces are unique they are not independent from one another. Quite the opposite, these structural provinces are genetically and geometrically linked to one another by regional salt tectonics. Salt tectonics in the Gulf of Mexico has occurred in gravitationally driven linked systems with up-dip extension balanced by down-dip shortening in one form or another. The post salt structural framework is best described in the context of large scale salt structural elements, their spatial relationships and the tectonic links between them. This paper borrows concepts liberally from previous regional compilations (McBride, 1998; Diegel, et al., 1995; Peel, et al. 1995) that have become widely accepted and deeply ingrained among workers in the Gulf of Mexico. The additions herein largely result form the more recent availability of regionally extensive high quality 3D seismic data and its interpretation. The present day distal limit of the deep Louann salt is the most distinct and fundamental of province boundaries. It is the outboard limit of detached deformation below the Sigsbee canopy and forms the distal edge for Gulf of Mexico linked systems below allochthonous salt. Not surprisingly it has localized compressional structures ranging from salt cored folds to extruded salt bodies. Up-dip from the distal limit of deep salt, linked structural processes have lead to a regional framework of provinces and structural elements that we identify, characterize and describe below. Deep Salt Basin and Frontal Salt Nappe Chief among structural elements are the deep Louann salt, its primary container, which we call the deep salt basin, and the outboard limit of the Louann salt which defines the limit of detached deformation. For our purposes we will ignore the fundamentals of pre-salt basin genesis and salt deposition. Instead we define the deep salt basin by the present day distribution of Louann salt that is both above older sub-salt rocks and below younger rocks. This definition excludes allochthonous salt in canopies but does not necessarily restrict the deep salt basin to the area of original salt deposition.