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Title: Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico

Abstract

Salt structures in a 4000-km{sup 2} region of the continental slope, the northeast Green Canyon area, include stocks, massifs, remnant structures, and an allochthonous sheet. Salt-withdrawal basins include typical semicircular basins and an extensive linear trough that is largely salt-free. Counterregional growth faults truncate the landward margin of salt sheets that extend 30-50 km to the Sigsbee Escarpment. The withdrawal basins, stocks, and massifs occur within a large graben between an east-northeast-trending landward zone of shelf-margin growth faults and a parallel trend of counterregional growth faults located 48-64 km basinward. The graben formed by extension and subsidence as burial of the updip portion of a thick salt sheet produced massifs and stocks by downbuilding. Differential loading segmented the updip margin of the salt sheet into stocks and massifs separated by salt-withdrawal basins. Initially, low-relief structures evolved by trap-door growth as half-graben basins buried the salt sheet. Remnant-salt structures and a turtle-structure anticline overlay a salt-weld disconformity in sediments formerly separated by a salt sheet. Age of sediments below the weld is inferred to be be late Miocene to early Pliocene (4.6-5.3 Ma); age of sediments above the weld is late Pliocene (2.8-3.5 Ma). The missing interval of time (1-2.5 Ma)more » is the duration between emplacement of the salt sheet and burial of the sheet. Sheet extrusion began in the late Miocene to early Pliocene, and sheet burial began in the late Pliocene in the area of the submarine trough to early Pleistocene in the area of the massifs.« less

Authors:
 [1]
  1. (Univ. of Texas, Austin (United States))
Publication Date:
OSTI Identifier:
7262422
Report Number(s):
CONF-910403--
Journal ID: ISSN 0149-1423; CODEN: AABUD
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States); Journal Volume: 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CONTINENTAL SLOPE; SALT DEPOSITS; GULF OF MEXICO; TECTONICS; GEOLOGIC FAULTS; GEOLOGIC HISTORY; GROUND UPLIFT; STRATA MOVEMENT; TERTIARY PERIOD; ATLANTIC OCEAN; CARIBBEAN SEA; CENOZOIC ERA; CONTINENTAL MARGIN; GEOLOGIC AGES; GEOLOGIC DEPOSITS; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; SEAS; SURFACE WATERS 580000* -- Geosciences

Citation Formats

Seni, S.J.. Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico. United States: N. p., 1991. Web.
Seni, S.J.. Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico. United States.
Seni, S.J.. 1991. "Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico". United States. doi:.
@article{osti_7262422,
title = {Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico},
author = {Seni, S.J.},
abstractNote = {Salt structures in a 4000-km{sup 2} region of the continental slope, the northeast Green Canyon area, include stocks, massifs, remnant structures, and an allochthonous sheet. Salt-withdrawal basins include typical semicircular basins and an extensive linear trough that is largely salt-free. Counterregional growth faults truncate the landward margin of salt sheets that extend 30-50 km to the Sigsbee Escarpment. The withdrawal basins, stocks, and massifs occur within a large graben between an east-northeast-trending landward zone of shelf-margin growth faults and a parallel trend of counterregional growth faults located 48-64 km basinward. The graben formed by extension and subsidence as burial of the updip portion of a thick salt sheet produced massifs and stocks by downbuilding. Differential loading segmented the updip margin of the salt sheet into stocks and massifs separated by salt-withdrawal basins. Initially, low-relief structures evolved by trap-door growth as half-graben basins buried the salt sheet. Remnant-salt structures and a turtle-structure anticline overlay a salt-weld disconformity in sediments formerly separated by a salt sheet. Age of sediments below the weld is inferred to be be late Miocene to early Pliocene (4.6-5.3 Ma); age of sediments above the weld is late Pliocene (2.8-3.5 Ma). The missing interval of time (1-2.5 Ma) is the duration between emplacement of the salt sheet and burial of the sheet. Sheet extrusion began in the late Miocene to early Pliocene, and sheet burial began in the late Pliocene in the area of the submarine trough to early Pleistocene in the area of the massifs.},
doi = {},
journal = {AAPG Bulletin (American Association of Petroleum Geologists); (United States)},
number = ,
volume = 75:3,
place = {United States},
year = 1991,
month = 3
}

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  • GLORIA II long-range side-scan data provide a mosaic of the continental slope in the northern Gulf of Mexico, seaward of the Texas-Louisiana coast. A swath as wide as 30 km and a 10% overlap of the data between parallel track lines provide a continuous picture of the complex slope morphology, which is largely controlled by salt deformation. Morphologic features range from piercement structures approximately 2 km in diameter to basins as much as 30 km across. The GLORIA data delineate the East Breaks submarine slide, where surface lineations are suggestive of deformation features. High-resolution 10 kHz seismic-reflection profiles indicate thatmore » the very irregular surface on the slide has a relief of 10 m. The 3 types of intraslope basins (blocked canyon, interdomal, and collapse) described by A.H. Bouma can be identified on the GLORIA data. The walls of Gyre basin, an example of a blocked canyon, have what are interpreted to be gullies, which are commonly associated with submarine canyons. Another basin downslope has similar gully-like features on the walls, which suggest that it may have been part of the original canyon system. Although many canyon-like features direct the movement of sediment downslope, the present data show that all conduits end in closed basins. No system of basins can be shown to transport sediment across the entire slope between the Mississippi Canyon and the East Breaks slide. Small-scale slumps, which can be identified on the flanks of some of the diapiric structures, also contribute sediments to basins such as Gyre basin.« less
  • Regional multichannel seismic data are used to develop a seismic stratigraphic framework for the continental slope-upper Mississippi fan region in the northern Gulf of Mexico. In the Mississippi canyon area, upper Pliocene and Pleistocene paleontologic zones from wells provide age control for major seismic sequence boundaries. A major unconformity and high-amplitude reflector identified as the base of Pleistocene represents a break in sedimentation and probably marks onset of fan deposition. This unconformity and others within the Pleistocene define sequences showing cyclic patterns of deposition, which are related to Pleistocene sea level changes and salt mobilization. Interpretation of seismic facies andmore » their relationships to sea level changes, glaciations, and salt movement results in a model for the depositional history of the Mississippi fan from the canyon area to the deep-water part of the fan. Low-amplitude, chaotic, onlapping facies are interpreted as slump or debris-flow deposits associated with canyon cutting by retrogressive failure and initiation of large-scale mass movement due to a relative lowering of sea level. High-amplitude, parallel, continuous reflectors at sequence boundaries represent pelagic and hemipelagic sediments associated with a succeeding rise in relative sea level. In the shelf-upper slope area, isolated salt diapirs influence sedimentation on a localized scale. In the lower slope to upper fan, most Pleistocenen section is extensively disrupted by parallel sets of salt ridges that result from differential loading of fan sediments. Shifting depocenters and migratory channel systems funnel sediment through this area onto the lower fan. Salt wedges in the eastern study area appear to represent detached salt masses isolated within the Pleistocene section.« less
  • A study of more than 1200 of 72-fold, migrated, seismic reflection profiles, from the eastern part of the East Breaks flexure trend, Gulf of Mexico, indicates that, although individual seismic reflectors cannot be traced across the entire area, seismic depositional units can be recognized and correlated from basin to basin in most instances. Three tentative conclusions are evident from this study: (1) salt diapirs appear to have grown through a series of intermittent movements to form structurally separate intraslope basins; (2) sedimentation is probably channeled by differential dome growth, which creates local stratigraphic differences between basins; and (3) packages ofmore » distinctive seismic depositional units can be successfully used to map sediment cycles between separate basins. Fluctuations of Pleistocene sea level appears to be the dominate depositional control on the upper continental slope in this area. During high sea level stands, turbidity currents were confined to depressions between diapirs, whereas pelagic deposition blanketed the slope. But during low sea level stands, sediment bypassed the shelf and deposited directly onto the upper slope, which increased the sediment load and helped initiate diapirism. Repeated sea level fluctuation would then lead to the cyclic pattern of seismic depositional packages that is commonly seen on upper slope seismic records.« less
  • Updip sediment loading on the continental shelf of the northern Gulf of Mexico produces lateral movement of the Jurassic salt at its frontal edge under the continental slope. Numerous salt tongues, salt scarps, and extensive concordant and discordant salt layers result from such movement of salt. Salt scarps bulge out seaward, ahead of the depocenter. In response to lateral shifting of the depocenter, the arcuate bulge changes position while the older scarp is deactivated. New bulges form contiguously with old ones or in a new place. The Sigsbee Scarp represents a composite bulge formed when depocenters shifted during the middlemore » Miocene-Pleistocene. Several types of traps suitable for hydrocarbon accumulation form as a consequence of lateral salt movement. The genesis of the following types of traps is discussed with examples from the continental slope of the northern Gulf of Mexico: (1) stratigraphic traps associated with scarp margin basins, (2) truncation traps and other structural traps below salt tongues, (3) fault and faulted anticlinal traps near the frontal edge, and (4) thrust-faulted anticlinal traps between salt lobes.« less
  • The late Pleistocene Brazos-Trinity Fan, a structurally ponded fan completely exposed and undisturbed on the seafloor, was mapped with a combination of conventional and high-resolution seismic data. This fan occupies three salt-withdrawal mini-basins (1, 2, 4) and a graben (3), each filled with an onlapping package consisting of alternating bedded and non-bedded units evident on high-resolution data. Basins 1--3 are filled to their topographic spill points; the onlap-fill succession of each is incised by a channel system which bypassed sediment to the next basin(s) downdip. Seismic continuity generally increases distally in the system and within individual basins, believed to reflectmore » the increasing prevalence of turbidity currents over high-density sediment gravity flows.« less