Isostacy again: Explanation of salt movements
The notion of isostacy is applicable to explain vertically-rising salt movements in those situations with large lateral extrusion of salt tongues. A salt tongue may be regarded as occurring at that depth within the earth above which the average density, regardless of lithology, is equal to that of salt, i.e., the salt tongue balances the material above it. The supra-salt tongue section can be salt diapirs or sedimentary sequences. Accumulating sediments compact and increase in their density with depth until equaling the density of the plastic balancing salt tongue. Under the heading of isostacy, with the balancing horizon being the salt tongue, the salt tongue is at the depth range where salt becomes buoyant relative to the overlying sediments. The isostatic depth/buoyancy level could then direct the advancing position depth of the salt tongue in the basin. Computer modeling of excess pressure under moving salt tongues indicates pressure build-ups of some 170 atm. The excess pressure may build up geologically instantaneously as the laterally migrating salt over-rides another column of sediment. Presumably the excess pressure evaporates as a discrete salt tongue leaves a supporting underlying sediment column. A puzzling question concerns how noses of salt tongues approach and even intersect the seafloor. Determining geologic reasons for positioning of salt tongues within terrigenous sediment complexes along passive margins is important due to major changes that salt insertion causes: impermeable barrier to rising hydrocarbons, stress fractures around advancing salt noses, possible regional faulting due to stress couple developed between dynamic salt tongue and stationary basement. Predicting potential stresses and deformation above, in front of, and below, a salt tongue is essential to successful wildcat drilling.
- OSTI ID:
- 413543
- Report Number(s):
- CONF-960525-; TRN: IM9702%%318
- Resource Relation:
- Conference: 28. offshore technology conference, Houston, TX (United States), 6-9 May 1996; Other Information: PBD: 1996; Related Information: Is Part Of 28. annual offshore technology conference: Proceedings. Volume 1: Geology, earth sciences and environmental factors; PB: 689 p.
- Country of Publication:
- United States
- Language:
- English
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Thermal and density stratification in a seafloor brine pool, northern Gulf of Mexico
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