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

LOWRIE, ALLEN, Consultant, Picayune, MS, and ZHIHUAI YU and IAN LERCHE, University of South Carolina, Columbia, SC

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.

Movement of salt appears to result from the continuing pressure of sediment deposition. Deposition is controlled by sea level 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 slat motion apparently may range from as high as 17 cm/yr (salt wedge migrating during Plio-Pleistocene only during lowstands) to as low as centimeters/1000 yr (salt pillows under the inner shelf, coastal plain, and interi r 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 to 100 m/m.y. up to 10 to 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 the salt bodies. The results of modeling show that (1) the higher the rate of salt motion, the larger the range of fracturing, and (2) the domain of fracturing increases with larger size and with faster migration. For large, high-speed salt features, fracturing domain apparently extends as far as 2-4 km in the vertical and 3-5 km in the lateral directions.

 

AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)