--> Abstract: Thermohaline Convection Around Salt Sheets, by J. A. Nunn, A. Sarkar, and J. S. Hanor; #90937 (1998).

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Abstract: Thermohaline Convection Around Salt Sheets

NUNN, JEFFREY A., Louisiana State University; ALOK SARKAR, Louisiana State University; and JEFFREY S. HANOR, Louisiana State University

Our previous results demonstrate that dissolution of allochthonous salt sheets is a viable mechanism for inducing kilometer-scale vertical migration of pore fluids. Recently, we have worked on thermohaline convection at the leading edges of two allochthonous salt sheets that are amalgamating into a salt canopy. As the edges of salt sheets dissolve, inversion of pore fluid density creates downwelling solute plumes. For an isolated salt sheet, the underlying less saline pore water displaced by the downwelling brine moves laterally away from the leading edge of the salt sheet. As two or more salt bodies amalgamate into a salt canopy, the displaced pore water cannot move laterally indefinitely. As displaced pore fluids converge, they are forced upward. Thus, an upwelling of less saline pore water from deep sediments occurs in the gap inbetween the two salt sheets. For permeabilities and spatial scales appropriate for the offshore Gulf of Mexico, Darcy velocities for upwelling pore fluid are ~ 2 mm/yr which is similar in magnitude to estimates of compaction-driven flow. Thus, we have identified a potential new mechanism for transporting pore fluids from sediments far below an allochthonous salt sheet upwards into sediments deposited on top of the salt sheets. Thermohaline convection is likely to be a more significant process for complex, deforming salt geometries because of a larger surface area for salt dissolution and the dynamic feedback between salt deformation and salt dissolution. Thermohaline convection also may be an effective mechanism for focusing and trapping fluids underneath a convex downward remnant salt structure as differential loading divides a salt sheet into stocks and massifs.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah