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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 64 (1980)

Issue: 8. (August)

First Page: 1277

Last Page: 1278

Title: Geologic History of Deep Gulf of Mexico Basin: ABSTRACT

Author(s): Richard T. Buffler

Article Type: Meeting abstract


New multifold seismic reflection lines (approximately 15,000 nmi; 27,780 km) and ocean-bottom seismometer (OBS) refraction lines collected by The University of Texas Marine Science Institute, Galveston Geophysical Laboratory, in the deep Gulf of Mexico basin and its adjacent margins show a sedimentary section up to 10 km thick overlying an acoustic basement. The thick section is divided into two major depositional sequences separated by a prominent gulf-wide unconformity, tentatively assigned a middle Cretaceous (Cenomanian) age on the basis of seismic ties with core holes and comparison with global sea-level cycle charts.

Below the middle Cretaceous unconformity, the early geologic history of the gulf basin is complex. A rifted, block-faulted, and attenuated continental crust is inferred to underlie the deep gulf just north and west of the Campeche Scarp and eastward into the Straits of Florida area. A thick salt basin overlies this continental crust in the area north and west of the Campeche Scarp, where it forms a band of salt structure 50 to 100 km wide (Sigsbee salt dome province). Early deformation of the salt and the overlying thick Jurassic sedimentary section suggests a period of gravity sliding associated with early rapid subsidence of the basin.

Refraction data indicate that an oceanic crustal layer underlies the rest of the deep gulf basin. A Late Jurassic (post-salt) period of rapid seafloor spreading or oceanization probably provided a mechanism (thermal cooling) for the rapid Late Jurassic-Cretaceous subsidence.

A younger undeformed sequence of rocks onlaps and fills in on top of the oceanic crust, the outer basement high, and the early salt structures in the central deep gulf. This sequence represents the deeper water, offbank equivalent of the Late Jurassic-middle Cretaceous carbonate banks, shelves, and platforms that built up around the gulf basin as it subsided. The sequence thickens eastward to over 3 km beneath the Florida Scarp and Straits of Florida. Relief developed on these carbonate banks by middle Cretaceous time formed the proto-Florida and Campeche Straits. Location of the carbonate banks appears to be, at least in part, controlled by basement structure. Along the Florida and Campeche Scarps, there was a major middle Cretaceous shift from shallow- to deep-water sedimentation as the outer banks subsided.

The post-middle Cretaceous section in the deep Gulf is divided into five depositional sequences or seismic units, defined by major unconformities along the base of the northwestern Campeche Scarp and tentatively correlated with global unconformities and sea-level changes as follows: early Tertiary, middle Oligocene, late Miocene, and the Pliocene-Pleistocene boundary. The main source of sediment supply to the basin was on the west in Late Cretaceous-early Tertiary time, but shifted more to the north during the late Tertiary and culminated in deposition of the huge Pleistocene Mississippi fan.

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The Oligocene-Miocene section along the deep western gulf apparently was deposited as part of an older deep-sea fan complex with a western source. The lower part of the fan sequence (Oligocene-middle Miocene) is characterized by strong, discontinuous reflectors and is interpreted as relatively coarse-grained material deposited in a channelized midfan environment. The upper Miocene part of the fan consists of fine-grained laminites and is characterized by prograding clinoforms, deposited as lobes seaward of a midfan zone of bypass.

The overall upper Tertiary fining-upward sequence in the western gulf and the gradual cessation of turbidites from a western source probably were due to the late Tertiary development of the Mexican Ridges foldbelt. This foldbelt apparently formed, or is still forming, owing to large-scale downslope gravity sliding of a more competent Tertiary section over incompetent, possibly geopressured, shales.

The northern margin of the deep Gulf is defined by the Sigsbee Scarp, which represents the southern extent of a zone of salt deformation along the entire Texas-Louisiana slope. The western scarp bulges southward and is characterized by salt wedges thrust 10 to 15 km seaward over Pleistocene rise sediments. East of the bulge area the scarp is formed by the seawardmost series of vertical salt ridges that have uplifted and deformed Pleistocene sediments. The salt deformation along the scarp probably is continuing today as a result of both downslope gravity forces and massive sediment loading in a large Pliocene-Pleistocene depocenter farther upslope.

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Copyright 1997 American Association of Petroleum Geologists