Geology Reports⌕ Search

Geology topics

Research about Gulf of Mexico

Source-linked reports with geographic coverage including Gulf of Mexico.

194 records · Page 11Linked to original sources
USGS1989

Inner shelf deposits of the Louisiana-Mississippi-Alabama region, Gulf of Mexico

The late Quaternary morphology, shallow stratigraphy and sediment distribution of the Louisiana-Mississippi-Alabama inner shelf region are the product of transgressive and regressive sedimentary processes. Shelf sedimentary facies were deposited by deltaic progradation, followed by shoreface erosion and submergence. This information is based on interpretations and synthesis of more than 4,160 mi (6,700 km) of high resolution seismic profiles, 75 grab samples, and 77 vibracores. The shelf can be divided into two main depositional regions. The southwestern region, east and south of the Mississippi River plain, was formed by early Holocene delta complexes, overlying a late Wisconsinan delta. Deposits of the late Wisconsinan delta consist of well-defined coarsening-upward sequences and represent deltaic progradation during low sea level stands. The relatively recent Mississippi delta complexes have deposits which consist of fine-grained sands, silt and clay. With the late Holocene rise in sea level, asymmetrical sand ridges (16 ft, or 5 m, relief) have formed due to marine reworking of shoreline features. The northeastern region, offshore of the Mississippi-Alabama barrier islands, was formed by Pleistocene fluvial systems and Recent shoreface erosion and ravinement. Underlying the relatively thin Holocene sediment cover are relict fluvial sands which were deposited during the late Wisconsinan lowstand. Subsequent sea level rise allowed marine processes to rework and redistribute sediments forming the nearshore fine-grained facies and shelf sands sheet.

Gulf of Mexico↗
USGS1987

Maps showing distribution of the Middle Cretaceous unconformity in the eastern Gulf of Mexico

Several theories on the origin of the Gulf of Mexico basin have been introduced by various researchers (Beloussov, 1970; Freeland and Dietz, 1971; Malfait and Dinkelman, 1972; Wood and Walper, 1974; Pilger, 1978; Buffler and others, 1980; Dickinson and Coney, 1980; Gose and others, 1980; Schmidt-Effing, 1980; Walper, 1980; Schlager and others, 1984). Although no final agreement has been reached, one prominent geologic feature is generally recognized. The early evolution of the basin ended with a major middle Cretaceous event resulting in a Gulf-wide unconformity referred to as the middle Cretaceous unconformity (MCU). This event represents a major shift from Early Cretaceous shallow-water bank sedimentation to Late Cretaceous deeper water carbonates (Worzel and others, 1973; Mitchum, 1978). Seismic data collected by the U.S. Geological Survey and the University of Texas Marine Science Institute, Galveston Geophysics Laboratory (UTMSI-GGL) were used to map the MCU and its relationship to the deep stratigraphy and structure of the eastern Gulf basin east of long 90° W. In addition, data from the Deep Sea Drilling Project (DSDP) in the southeastern Gulf and along the Campeche Escarpment and dredge samples collected by Schlager and others (1984) from the Florida Escarpment provide an age for the MCU (Cenomanian, 97 m. y. ) and a detailed lithological record. This report emphasizes the salt diapirs, pillows, and ridges in the northeastern Gulf of Mexico because of the profound effect these geologic structures have on the MCU. Salt locations are shown on the isopach of post-MCU sediments (fig. 1). A second map shows pre-middle Cretaceous outcrops terminated by the MCU along the Florida Escarpment, the southeastern Gulf, and the Campeche Escarpment (fig. 2).

Miscellaneous Field Studies Map↗
USGS1981

234U and 238U concentration in brine from geopressured aquifers of the northern Gulf of Mexico basin

The 234 U and 238 U concentration in brine from six Gulf Coast geopressured aquifers has been determined. The results reveal very low uranium concentrations (from 0.003 to 0.03 μg/l) and uranium activity ratios slightly greater than unity (from 1.06 to 1.62). Reducing conditions within the aquifers are responsible for the low uranium concentrations. The uranium activity ratios observed are well below those calculated using theoretical considerations of alpha-particle recoil effects. This can be explained by interference with alpha-recoil nuclides entering the liquid phase as a result of quartz overgrowths on sand grains and high-temperature re-equilibration that tends to minimize the effects of the alpha-recoil process. The fact that the uranium activity ratios of the brines are slightly greater than unity instead of the equilibrium value of 1.000 indicates that either the alpha particle recoil blocking and re-equlibration effects are not complete or that another process is operative that enriches the fluid in excess 234 U by selectively removing uranium from radiation induced damage sites in the mineral (sand grain) matrix.

Louisiana, Texas↗
USGS1980

Distribution of salt structures in the Gulf of Mexico map and descriptive text

Slender diapiric stocks, broad massifs, anticlinal masses, low-relief swells, and pillowy lobes of Middle to Upper Jurassic salt (Viniegra, 1971; Kirkland and Gerhard, 1971; Imlay, 1980) dominate the structural fabric of large parts of the continental margins and deep basin of the Gulf of Mexico (sht. 1, A). These structures, known collectively as "salt domes," are almost exclusively features of the terrigenous elastic margins of the northern and southwestern Gulf and the central Sigsbee Plain (sht. 2, A). Some salt structures may be present in the East Mexico Slope province of the western gulf, but they are difficult to distinguish from diapiric and nondiapiric shale anticlines, which are the dominant structures on this margin. Except for some piercement domes and nonpiercement uplifts in the northern Florida shelf region and in the eastern Golfo de Campeche, salt structures are not known in the extensive carbonate platform provinces off western Florida and the Yucatan Peninsula. The accompanying compilation from seismic-reflection data documents the distribution of Gulf of Mexico salt features and helps to define boundaries of structural provinces formed mainly, or in part, by tectonic movement of salt.

Miscellaneous Field Studies Map↗
USGS1979

Outer Continental Shelf oil and gas information program; Gulf of Mexico index (January 1977 - June 1979)

The Outer Continental Shelf Lands Act of 1953, as amended in 1978 (43 U.S.C. 1331 et seq.), grants to the Secretary of the Interior the authority to issue leases for minerals on the U.S. Outer Continental Shelf (OCS). It provides the authority and guidelines which the Secretary utilizes fo7 expeditious exploration and development of the OCS while ensuring timely access to information by affected states and local governments in order that appropriate planning will anticipate and ameliorate impacts from such OCS activities.

Alabama, Florida, Louisiana, Mississippi, Texas↗
USGS1978

Statistical analysis of re-bid federal offshore Gulf of Mexico oil and gas leases

Through 1977, there were 178 cases where exactly the same Federal offshore oil and gas bonus bid lease was offered and received bids in 2 sales. (In addition, there were 131 cases where there was an overlap of acreage between a lease offered and receiving bids in 2 sales.) Table 1 summarizes these exact re-bid leases which are in 2 categories: (1) Leases re-bid after rejection of any and all bids received as a result of a prior offering, and (2) Leases re-bid after prior offering, issue, and relinquishment of a lease. We will call the former category rejected re-bid leases, the latter relinquished re-bid leases. Table 1 shows there were 120 of the former and 58 of the latter. The purpose of this study was simply development and analysis of the statistics of re-bid leases. The reasons why the data behave as they do are subjective and unavoidably involve nontechnical value judgments. Therefore, we do not speculate on the reasons in this report. The data source for this study was the LPR-5/-10 data base maintained by the General Services Administration, Fort Worth, Texas.

Gulf of Mexico↗
USGS1974

Tectonic evolution of the southern Gulf of Mexico

A detailed magnetic survey in the southern Gulf of Mexico shows subdued irregular magnetic anomalies that are similar in wave length to those attributed to sea-floor spreading on present-day oceanic rises. The small amplitude of these anomalies, about 75γ, would be compatible with an oceanic basalt source at a depth of 10 km, and previous seismic refraction studies in this area have shown that layer 2 of the oceanic crust (presumed to be basalt) does indeed lie at approximately that depth. Palynomorphs in Deep Sea Drilling Project samples of cap-rock material from the Sigsbee Knolls have shown the associated salt to be Jurassic. A crustal model, based on seismic refraction evidence and on new gravity data, suggests that, whereas the salt-dome belt of the southern gulf is underlain by a thick layer with a density of 2.2 g per cm 3 (presumed to be halite rock), adjacent deeper areas of the basin seem to lack this low density layer. In northeastern Mexico, Triassic red beds fill grabens that are correlative with the Newark Group of the Atlantic Coast and suggest that the Gulf of Mexico originated at the time of the initial rifting of the North Atlantic. When the gulf was about half-opened during the Jurassic, oceanic circulation was restricted; and thick deep-basin evaporite deposits, analogous to those found in the Mediterranean Sea by the Deep Sea Drilling Project, were laid down. Further opening established normal salinity and led to the development of salt-free areas of oceanic crust that separated the Sigsbee Escarpment (together with adjacent ridges of offshore Mexico) from the Sigsbee Knolls and salt domes of Cuba. The subsequent structural evolution of the Gulf of Mexico basin is believed to have been mainly a result of interaction between it and tectonic plates of the Pacific area. After opening of the gulf, subduction began along the Cuban arc, where Atlantic rifting had created a nearly uninterrupted tract of oceanic crust extending from the Pacific between Yucatán and Colombia. Then, folding and gravity sliding associated with Laramide deformation on the west side of the gulf led to salt anticlines that underlie the ridges offshore from Mexico. Except for continued diapirism and subsidence associated with sediment loading, present tectonic activity is confined to the southwestern corner of the gulf, where volcanism and intermediate-focus earthquakes are a distant manifestation of subduction along the Middle America Trench on the Pacific side of Mexico.

Gulf of Mexico↗
USGS1973

Bidding and production relationships for federal OCS leases: Statistical studies of wildcat leases, Gulf of Mexico, 1962, and prior sales

The relationships between bids received on wildcat leases issued on federal OCS lands in the Gulf of Mexico from 1954 through 1962 and subsequent drilling on, production from, and relinquishment of these leases were studied. The results provided quantitative answers to questions regarding bidding as prescribed by current laws and regulations. Perhaps the most notable result is the finding that, while leases receiving the most and highest bids tend, on the average, to produce more revenue, such leases tend to produce less revenue per dollar of bonus spent on the lease.

Gulf of Mexico↗
USGS1972

Crust and mantle of the Gulf of Mexico

A SEEMING paradox has puzzled investigators of the crustal structure of the Gulf of Mexico since Ewing et al. 1 calculated that a unit area of the rather thick crust in the gulf contains less mass than does a combination of the crust and enough of the upper mantle to make a comparable thickness in the Atlantic Ocean. They also noted that the free-air gravity of the gulf is essentially normal and fails by a large factor to be low enough to reflect the mass difference that they calculated. We propose a solution to this problem.

Gulf of Mexico↗
USGS1972

Distribution of selected elements in surficial marine sediments of the northern Gulf of Mexico continental shelf and slope

Analyses for barium, beryllium, boron, calcium, cobalt, chromium, copper, iron, lanthanum, magnesium, manganese, molybdenum, niobium, nickel, lead, scandium, tin, strontium, titanium, vanadium, yttrium, zinc, and zirconium were performed on 1,304 sediment samples from the continental shelf and slope of the northern Gulf of Mexico. Approximately 40 percent of the samples were collected in two relatively small regions, one seaward of Galveston, Texas, between long. 94° and 95° W. and the other around the Dry Tortugas on the south Florida shelf. The is remaining samples represent a broad reconnaissance survey extending from the Rio Grande to the Florida Keys.

Open-File Report↗
USGS1969

Geochemistry of pore waters from Shell Oil Company drill holes on the continental slope of the northern Gulf of Mexico

Pore waters were analyzed from 6 holes drilled from M.V. “Eureka” as a part of the Shell Oil Co. deeper offshore study. The holes were drilled in water depths of 600–3,000 ft. (approximately 180–550 m) and penetrated up to 1,000 ft. (300 m) of Pliocene-Recent clayey sediments. Salt and anhydrite caprock was encountered in one diapiric structure on the continental slope. Samples from holes drilled near diapiric structures showed systematic increases of pore-water salinity with depth, suggestive of salt diffusion from underlying salt plugs. Anomalous concentrations of K and Br indicate that at least one plug contains late-stage evaporite minerals. Salinities approaching halite saturation were observed. Samples from holes away from diapiric structures showed little change in pore-water chemistry, except for loss of SO 4 and other variations attributable to early-stage diagenetic reactions with enclosing sediments. Thus, increased salt concentrations in even shallow sediments from this part of the Gulf appear to provide an indicator of salt masses at depth.

Chemical Geology↗