Hydrocarbon Trap Types and Deformation Styles Modeled Using Quantified Rates of Salt Movement, Louisiana Margin

Abstract

ABSTRACT Definitions are proposed for the various salt features along the Louisiana continental margin. The nine general features include salt wedges, salt tongues, pillows, diapirs, wings, canopies, sheets, sills, and dikes. The definitions are derived from the interpreted salt geometry and contain an implied genesis. These definitions are here proposed with the hope of promoting a dialogue to result in a suite of accepted definitions. Movement of salt appears to result from the confining pressure of sediment deposition. Deposition is controlled by sealevel oscillations, subsidence, and source. Salt movements include lateral flow, buoyancy, and isostacy. Lateral flow may occur under the Louisiana shelf-break, terminating basinward at the present Sigsbee Escarpment; isostacy may occur under the upper- middle slope and outer shelf. Buoyancy appears to be dominant under the middle and inner shelf, coastal plain, and South Louisiana and Northern Louisiana-Arkansas interior basins. Calculated rates of salt motion apparently may range from as high as 17cm/yr (salt wedge migrating during Plio-Pleistocene only during lowstands) to as low as cms/1000 yrs (salt pillows under the inner shelf, coastal plain, and interior basins). Given these calculations, it has been possible to prepare computer-derived plots of fracturing models around the various salt features. Salt movements from 10-100 m/m y up to 10-200 km/m y have been modeled, using Mohr's criterion for failure, in order to examine the domains of primary and secondary fracturing around salt bodies. The results of modeling show that (1) the higher the rate of salt motion, the larger the range of fracturing; (2) the domain of fracturing increases with larger size and with faster migration. For large, high speed salt features, the fracturing domain apparently extends as far as 2-4 km in the vertical and 3-5 km in the lateral directions.