Salt glacier and composite sediment-salt glacier models for the emplacement and early burial of allochthonous salt sheets
- Exxon Production Research Company, Houston, TX (United States)
Allochthonous salt sheets in the northern Gulf of Mexico were emplaced as extrusive {open_quotes}salt glaciers{close_quotes} at the sediment-water interface. Massive dissolution was suppressed by a thin carapace of pelagic sediments. During emplacement, several hundred meters of bathymetric relief restricted rapid sedimentation to outside the glacial margins. The glaciers acted as sediment dams, influencing the transport and deposition of sediment from an upslope source. Because of contemporaneous sedimentation, the base of the glaciers climbed upward in all directions away from their feeder stocks, and successive sedimentary horizons were truncated against it. The local slope at the base of the sheets is equal to the local rate of sedimentation divided by the local rate of salt advance. Alternating episodes of slow and rapid sedimentation gave rise to a basal salt surface of alternating flats and ramps, which are preserved. Many salt sheets have nearly circular map patterns but are strongly asymmetric. Feeder stocks occur near upslope edges, and base-of-salt slopes are greater updip of the feeder. The asymmetry is due to more rapid sedimentation at the upslope edge and to slower advance induced by the smaller hydraulic head between the salt fountain and the upslope edge compared to the downslope edge. Rapid emplacement of the Mickey salt sheet (Mitchell dome) from a preexisting salt stock took {approximately}4 m.y, as {approximately}1 km of sediment was deposited. A three-dimensional geomechanical model for the rapid salt emplacement yields the following relationship for the diapir`s downdip radius versus time: R(t) {approx} Mt{sup q} {approx} B[({rho} - {rho}{sub w})gK{sup 3} / {eta}]{sup 1/8}t{sup q}, where M, q, b, and K are constants related to salt supply into the sheet, {rho} and {rho}{sub w} are the densities of salt water, g is the acceleration of gravity, {eta} is salt viscosity, and t is a model time extrapolated back to zero sheet volume at t = 0.
- OSTI ID:
- 585163
- Journal Information:
- AAPG Memoir, Journal Issue: 65; Other Information: PBD: 1996
- Country of Publication:
- United States
- Language:
- English
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