Sediments Of Gulf Research Articles

Correlation of Cenozoic Sediments of Gulf of Mexico Outer Continental Shelf: Part I: Galveston Area Offshore Texas Through Vermilion Area Offshore Louisiana: ABSTRACT

The Gulf of Mexico Outer Continental Shelf (OCS) regional office, Minerals Management Service (MMS), US Department of the Interior, will publish an atlas in early 1987 entitled Correlation of the Cenozoic Sediments of the Gulf of Mexico Outer Continental Shelf: Part I: Galveston Area Offshore Texas through Vermilion Area Offshore Louisiana. Part II, extending west-southwestward from Part I, and Part III, extending eastward from Part I, will be published at later dates. The Resource Evaluation office, MMS, is conducting detailed geological, geophysical, and paleontological investigations of the northwestern Gulf of Mexico OCS. The subsurface structure and stratigraphy of the northwestern Gulf of Mexico OCS for Galveston area through Vermilion area, from the Miocene through the Pleistocene production trends, are discussed in the report of Part I. This presentation includes the interpretation of over 12,000 mi of geophysical data, 1500 electric logs, and 1000 paleontological reports. Analysis of this data is presented on 19 cross sections. These cross sections contain information from 247 well data summaries, 175 paleontological reports, and 152 well velocity summaries. Examples of each of these will be available. The geophysical and companion electric log cross sections illustrate a detailed stratigraphic study of 26 horizons. These horizons aremore » included on a stratigraphic chart, copies of which will be available. the marine depth-related environments will be displayed and copies of that chart will also be available. This atlas can be used for evaluation of petroleum exploration and exploitation as well as scientific investigations in the northwestern Gulf of Mexico.« less

Trace metal and magnetic studies of sediments in greek estuaries and enclosed gulfs

Minicores of seabottom sediments from typical coastal and estuarine areas of Greece (the Gulf of Elefsis and the estuaries of the Acheloos and Louros rivers), influenced in a widely varying degree by anthropogenic inputs, were analysed for trace metal content and measured for a series of magnetic properties (i.e., total magnetic susceptibility, frequency dependent susceptibility, isothermal remanent magnetization and demagnetization). Apparent linkages between trace metal content (total or in chemically leached fractions) and magnetic properties were found in cores from all areas. Variations in the relative importance of the non-leachable fraction of metals in the Elefsis Gulf sediments closely parallel changes in the percentage frequency dependent susceptibility, which can be considered as indicator of soil derived material. By combining chemical and magnetic data, very useful information was obtained on: (a) the origin (industrial) of the rapidly deposited sediments in the Gulf of Elefsis; (b) the deposition rate, which was estimated as 0.5 cm per annum; (c) the range and nature of the major natural particle assemblages present in the Acheloos and Louros estuaries; (d) the distinction between the assemblages deriving from the erosion of surface soils and from unweathered parent material; (e) the identification of particles acting as major trace metal carriers (viz. anthropogenic particulates and soil-derived clays). In general the results confirm that integrated trace metal—magnetic studies can provide valuable data on the origin, transport and sedimentation mechanisms of trace metals associated in various ways with particles in coastal and estuarine systems. New perspectives are briefly discussed.

The lipid chemistry of sediments from the St Lawrence estuary. Acyclic unsaturated long chain ketones, diols and ketone alcohols

Long chain unsaturated ketones (C 37C 39) and two limited series of alkan-1,15-diols and alkan-15-one-1-ols (chain lengths of 30, 31 and 32 carbon atoms) have been isolated from extracts of sediments from the Gulf of St Lawrence and an associated continental slope sample. The detection of these compound classes in these sediments further extends the range of environments within which these compound classes occur. Differences in the absolute abundance of these lipid classes are probably due to variations in the abundances of E. huxleyi or related algae (in the case of the unsaturated ketones). These lipid components were below the limits of detection, however, in all sediments collected from a third, estuarine sampling site. This observation is one feature distinguishing the lipid distribution and thus differences in the contributing biota at the three sites. These data highlight the use of the biological marker approach for assessing the spatial distribution of a contributing organism to sediments within an open estuarine system. The absolute abundance of long chain ketones, diols and ketone alcohols decreased with depth in Gulf sediments (≈2.3 to less than 0.001 μg/g for long chain ketones).

Calcium carbonate suspended in Arabian Gulf and Red Sea waters; biogenic and detrital, not "chemogenic"

The warm saline waters of the Arabian Gulf and Red Sea are supersaturated with respect to aragonite and magnesian calcite. Despite the local dominance of these phases in the Arabian Gulf sediment and their general abundance in southern Red Sea sediments, little or no evidence of chemogenic carbonate is found in the overlying waters; suspended carbonate grains are either biogenic or detrital. Precipitation of calcium carbonate appears limited to bottom or interstitial waters.

Biogenic hydrocarbon gases and sulfate reduction in the Orca Basin brine

The composition of light hydrocarbon gases in the Orca Basin, an anoxic, hypersaline intraslope depression on the continental slope of the northern Gulf of Mexico, indicates that both methane and ethane are biogenic in nature with a C 1 (C 2 + C 3) ratio of 730 and a δ 13 C of methane of −73%. relative to the PDB standard. The concentrations of methane (750 mM) and ethane (1300 mM) in the Orca Basin brine are higher than any other marine anoxic basin. These high levels result not from high rates of productivity, but from the long residence time of the brine in the basin, due to its high stability toward mixing with overlying seawater ( Δσ 1 ΔZ = 3.2 m ). Both methane and ethane show well mixed distributions in the brine. These distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments. Methane and ethane maxima above the pycnocline at the brine/seawater interface reflect in situ production and/or consumption in the aerobic water column. Concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter. Reduced rates of anaerobic decomposition (including sulfate reduction) in the brine sediments are inferred from preserved Sargassum fronds in the sediments, vertical sulfate profiles in most cores, and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal Gulf sediments nearby.

Sedimentary and Geochemical Systems in Transitional Marine Sediments in Northern Gulf of Mexico: ABSTRACT

The coastal zone of the northern Gulf of Mexico is marked by a series of bays and estuaries that serve as the principal depositional basins for rivers draining an area of greater than 160,000 km2. These rivers annually contribute a sediment load to the basins in excess of 12 million tons. Because each river drains a watershed of different lithologic character and each river is further characterized by a different flow regime and hydraulic properties, the sediments deposited in the marginal basins have unique characteristics. Extensive municipal and industrial dumping of effluent over the years has also acted to imprint geochemical differences on each of the depositional basins. Depending on the degree of industrialization within the watershed, the bays and estuaries may be described as heavily impacted (Mobile Bay), moderately impacted (Apalachicola Bay, Mississippi Sound), or slightly impacted (Pensacola Bay). A strong correlation was observed between the degree of heavy metal contamination and the textural and organic content of the sediments. Analyses further indicated that most metals were partitioned in the bottom sediments in forms that would permit their subsequent release back into the water column or would allow transference of the metal to fauna by ingestion. End_of_Article - Last_Page 1424------------

The stratigraphy of coastal carbonate banks and Holocene sea levels of northern Spencer Gulf, South Australia

Stratigraphic and chronologic studies of the coastal sediments of northern Spencer Gulf in the vicinity of Redcliff are described. Two Pleistocene marine units are recognised beneath an extensive Holocene peritidal sequence. The Holocene sequence is dominated by sediments of the Posidonia australis seagrass facies which form a distinctive carbonate bank fringing the coastline. Peritidal sedimentation commenced prior to 6600 radiocarbon yrs B.P. and a + 2.5 m higher relative sea level existed from about 6000 until around 1700 yrs B.P. The subsequent relative fall to present level probably resulted from local tectonic uplift. After the regression, mangrove and samphire colonization, and beach ridge progradation, occurred over the former seagrass bank.

Palaeosol development in Quaternary marine sediments and palaeoclimatic interpretations, Spencer Gulf, Australia

A series of palaeosols developed in the Quaternary marine sediments of northern Spencer Gulf when exposed during successive glacio-eustatic low sea levels over the last ca. 220,000 yrs. The palaeosols show different degrees of pedogenic development from which palaeoclimatic inferences are made. Those formed prior to the 125,000 yrs B.P. marine transgression are the most strongly developed and leached, exhibiting strong, well-structured, clay-rich B horizons, a feature not seen in later palaeosols. The younger palaeosols, formed after the late Pleistocene high sea-level phase, are not as strongly developed. Their most prominent features are carbonate accumulation horizons, even though they were, in places, exposed for as long as the pre-120,000 yrs B.P. palaeosols. Palaeoclimates inferred from the palaeosols suggest more humid conditions existed prior to ca. 125,000 yrs B.P. than have occurred since. Aeolian reworking of later palaeosols suggests arid phases occurred after ca. 125,000 yrs B.P.

Trace metal composition of and accumulation rates of sediments in the Upper Gulf of Thailand

Sediment cores and grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs. Accumulation rates of sediments in the Upper Gulf measured using the 210Pb method, appear to vary from ca. 4 to 11 mm yr −1. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately transported to the Lower Gulf. Metal concentrations in Upper Gulf sediments appear to be dominantly controlled by natural inputs.

Thermogenic Gas Hydrates in the Gulf of Mexico

Thermogenic gas hydrates were recovered from the upper few meters of bottom sediments in the northwestern Gulf of Mexico. The hydrates were associated with oil-stained cores at a water depth of 530 meters. The hydrates apparently occur sporadically in seismic "wipeout" zones of sediments in a region of the Gulf continental slope at least several hundred square kilometers in area.

General bathymetry of the Gulf of Carpentaria and the Quaternary physiography of Lake Carpentaria

A generalized bathymetric map of the Gulf of Carpentaria has been prepared from Royal Australian Navy sounding data. The results confirm earlier work of Nix and Kalma and indicate that a closed basin Lake Carpentaria (below −53 m present water depth) could have existed during Quaternary low sea-level stands. An evaluation of previous and present work, shallow seismic records of the Canadian Superior Mining Co. (Australia), and oil company fathometer profiles indicate the preservation of lake sediments at −65 m and −53 m water depth, preserved shoreline feature at −19 m, −29 m and −65 m, as well as extensive underlying erosion and incision. These findings are consistent with erosion and incision of gulf sediments during sea-level lowering, aeolian infilling and “dune” formation on the present Arafura sill during the dry phase of Maximum glaciation and subsequent Lake Carpentaria formation and lacustrine sediment deposition most probably during the sea-level rise phase. Lake Carpentaria clearly dominates the physiography and climatology of this land bridge during Quaternary time.

Facies Analysis and Petroleum Potential of Smackover Formation, Western and Northern Areas, East Texas Basin: ABSTRACT

The Smackover Formation (Upper Jurassic) in northeast Texas is a transgressive-regressive carbonate sequence which has been extensively dolomitized. The extent of dolomitization is directly related to the presence of the overlying Buckner anhydrite which has provided the magnesium-rich brines necessary for dolomitization. The Smackover Formation is subdivided informally into a lower and upper member based on distinctive lithologic characteristics. The lower member, which rests conformably on the fluvial-deltaic sandstones of the Upper Jurassic Norphlet Formation, contains a laminated, organic carbonate mudstone facies that grades into an overlying locally fossiliferous, pelletalmicritic facies. The vertical sequence of facies indicates a transgression of the sea. They are interpreted to represent an inter-tidal mudflat to shallow-marine, low-energy platform or protected lagoonal environment. The upper member of the Smackover Formation consists mainly of broken skeletal debris and pelletal allochems in a micritic matrix. The sediments are better winnowed and better sorted upward in the sequence. Interbe ded with and overlying the skeletal-pelletal facies is a clean well-sorted dolomitized oolitic-grainstone facies. This uppermost informal member marks the beginning of a progradational sequence which lasts throughout the remainder of Smackover deposition and continues through deposition of the evaporites and red beds of the overlying Buckner Formation. Deposition of the Smackover Formation most closely resembles Holocene carbonate sedimentation in the southern Persian Gulf. Both areas are represented by a similar carbonate ramp depositional framework together with closely approximated salinity and climatic conditions. Most of the Smackover production in northeast Texas occurs along the Mexia-Talco fault zone in the deeper gentle salt-related anticlines and salt-graben systems. Reservoir rocks are primarily leached and dolomitized oolitic grainstones and dolomite. Laminated organic carbonate mudstones which characterize the lower, transgressive phase of the Smackover Formation provide an excellent source rock for petroleum. Exploration targets for the Smackover Formation are the areas where dolomitized oolitic and skeletal grainstones occur on top of structurally high areas such as over salt ridges or swells in the deeper portions of the basin. Along with this are those areas along the updip limit of the Smackover Formation in which the upper member has been leached and dolomitized and occurs in a stratigraphically favorable position. End_of_Article - Last_Page 478------------

Distribution of heavy metals in sediments of the Patraikos gulf (Greece)

Distribution of heavy metals in sediments of the Patraikos gulf (Greece)

Biogenic and abiogenic components of laminated hemipelagic sediments in the central Gulf of California

Alternating light and dark submillimeter to millimeter thick layered sediments (rhythmites) are found along the slopes of the central and southern Gulf of California where a strong oxygen minimum zone intersects the sediment—water interface. Two short intervals of distinct alternations were sampled lamina by lamina from two cores in the central Gulf. Both cores are from the slope of the Guaymas Basin, one core is from the mainland side, the other core is from the Baja side. Each lamina sample was analyzed for its opal micro-floral assemblage, textural character, trace metal and bulk chemical (Cu, Mn, Fe, Ni, Zn, Ca, K, Al, SiO 2 and C-org) content, and mineralogy. On both sides of the gulf the light laminae contain more diatom frustules (up to 90%) and less terrigenous and organic material than the dark laminae. The sediment is predominantly silt sized. The dark laminae contain more terrigenous material which is primarily clay size (< 4 μm) on the mainland side and fine silt size (4–20 μm) on the Baja side. All chemical species analyzed, except SiO 2, are always higher in the dark laminae and show a high positive correlation to organic carbon. SiO 2 is higher in the light laminae and shows a high negative correlation to organic carbon. Non-opaline material is a secondary constituent, primarily consisting of quartz, plagioclase and calcite. The <2- μm fraction is dominated by opal and quartz. Smectite, illite, and kaolinite are present in the laminae from the mainland side, but are almost absent on the Baja side. On both sides of the gulf the light laminae apparently represent sedimentation during the dry winter season of northwesterly winds, whereas the dark laminae represent the wet summer season of southeasterly winds.

Geochemistry of uranium in sediments of the Bohai Gulf, China

The following conclusions can be drawn from the work reported in this paper: (1) Sixteen samples were determined for uranium by spectrophotometric method. The uranium content in the sea floor sediments of the Bohai Gulf ranges from 1.6 to 6.3 ppm, with an average of 4.3 ppm. (2) Statistical data show close relationship between U concentration and grain size. Relatively larger amount of uranium was found accumulated in mud than in sand. The bulk of uranium is assumed to be derived from terrestrial detrital minerals. (3) A positive correlation between U and Fe is recognized. Similar relation also can be seen between U and Al. The plot of U concentration vs. Fe is linear, and can be expressed by the linear regression equation:Y=−0.37+1.35X. The plot of U against Al gives an equation ofY=−2.48+1.01X. (4) The average U/Corg. ratio for these sediments is 7×10−4, and the average ratios of U/P, U/Mn, and U/CaCO3 are 100×10−4, 50×10−4 and 2×10−4, respectively. (5) Compared with the abundances of other shelf sediments, the average concentration of U in the area under consideration is close to that of sediments on the selves of Japan and the Gulf of Mexico, and the Black Sea. Uranium concentration in the Bohai Gulf sediments is comparable to that of the continental crust, but differs from that of deep-sea clay.

Mineral assemblages and their distribution patterns in the sediments of the gulf of Bohai Sea

Mineral assemblages and their distribution patterns in the sediments of the gulf of Bohai Sea

EFFECT OF CRUDE OIL ON MICROBIAL PROCESSES IN MARINE SEDIMENTS

ABSTRACT Studies were carried out to detect and quantitate 12 microbial processes occurring in sediments in the north central Gulf of Mexico, and to determine the impact of low-level concentrations of oil on these processes. Under the simulated in situ conditions employed, photosynthesis, nitrification, dentrification, nitrogen fixation, sulfate reduction, and phosphate uptake were minimal, while sulfur oxidation and catabolic carbonaceous processes (heterotrophic activity, lipolysis, proteolysis cellulolysis, and chitinolysis) were present with varying degrees of activity. Little difference in metabolic activity was detected between oil-production platform sites and corresponding control sites, among different sediment types, or among three sampling seasons, and the presence of oil at up to 200 microliter per milliliter sediment had no significant impact on reaction rates. Pure culture studies confirmed that low-level concentrations of crude oil had essentially no effect on these processes.

Models for Formation of Organic-Rich Diatomaceous Laminae in Miocene Monterey Formation: Documentation from Analogous Recent Sediments in Gulf of California: ABSTRACT

Depositional modeling of the Monterey Formation has traditionally focused on basin scale models. Analysis of homogeneous and laminated, organic- and diatom-rich sediments from the central Gulf of California permits modeling of small-scale depositional environments that may be useful in mapping within the Monterey Formation. Sedimentologic, micropaleontologic, and geochemical characteristics of recent Gulf of California sediments permit definition of three depositional environments. (1) Thick (~ 1 cm) lamination of the silled anoxic San Pedro Martir Basin. The laminae are indistinct in color and contain a uniformly mixed opal phytoplankton population of both oceanic and upwelling floras. Only the darker laminae contain the silt- and clay-sized material washed into the area during the rainy season. (2) Thin (~ 1 mm) lamination of slope sediments where the oxygen minimum zone impinges the sea floor (~ 400 to 1,300 m water depth) on both the Baja and mainland sides of the Guaymas Basin Slope. Laminae are generally distinct in color and consist of alternating oceanic and upwelling opal phytoplankton assemblages. Dark laminae contain clay- and silt-sized terrigenous material. Dark laminae on the Baja side also contain an upwelling microfloral assemblage. Dark laminae on the mainland side contain an oceanic microfloral assemblage. (3) Homogeneous sediments overlie laminated sediments off Santa Rosalia. The homogeneous sediments are characterized by uniformly distributed microfloral and macrofloral elements and terrigeneous material due to bioturbation by a mollusk infauna. The differences between the various laminated and the nonlaminated (= homogeneous-bioturbated) facies are due to differing levels of primary productivity in surface waters which in turn controls oxygen consumption. Oxygenated bottom water underlies low primary productivity areas while anoxic bottom water underlies high primary productivity areas. End_of_Article - Last_Page 891------------

Trace metal contamination of shallow marine sediments near a lead smelter, Spencer Gulf, South Australia

The surface (&lt; 10 cm) marine sediments of Spencer Gulf, a hypersaline seagrassed embayment, near Port Pirie, South Australia; were examined for concentrations of Ca, Cd, Cu, Mg. Mn, Ni, Pb, Zn, total organic carbon, clay, silt, sand. shell, and 'undissolved fraction' (resistant plant debris). Elevated concentrations of Pb, Cu. Zn, Mn and Cd were found in sediments adjacent to the liquid effluent discharge from a lead smelter. Outside the immediate discharge area the concentrations of Cu and Mn rapidly approached background levels where their concentrations were correlated to those of non- contaminant sediment parameters. The highest concentrations of Cd were found further from the source of effluent than those of the other four contaminant metals (Cu, Mn, Pb: Zn), and decreased to undetectable levels at the furthest sites. Pb and Zn also occurred at background concentrations at sites away from the effluent discharge. but no correlations were found between these two metals and other sediment parameters. At sites away from the immediate discharge area no interaction was detected between contaminant metals, sediment parameters, and presence or type of seagrass meadow.

Regional Stratigraphy of Upper Jurassic Smackover Carbonate Rocks of Southwest Alabama: ABSTRACT

ABSTRACT Upper Jurassic Smackover deposition in southwest Alabama was primarily controlled by the Mississippi interior salt basin and the Manila and Conecuh embayments and closely approximated carbonate sedimentation in the present-day Persian Gulf. These depositional sites are characterized by distinctive lithofacies and fossil assemblages. Early salt movement produced local variations in carbonate sediment distribution and pre-Jurassic paleo-highs, such as the Wiggins uplift and Conecuh arch, also modified carbonate sedimentation. Throughout much of southwest Alabama, the Smackover Formation consists of a lower predominately mudstone lithofacies which overlies the Norphlet sandstone and an upper lithofacies sequence dominated by grain-supported textures which is overlain by the Buckner anhydrite. Where present, the lower Smackover lithofacies include laminated mudstone and on occasion peloidal wackestone, peloidal-oncolitic packstone, or dolomite are present. The upper lithofacies sequence consists of oolitic and/or oncolitic grainstone, peloidal and/or oncolitic wackestone to packestone, and occasionally dolomite or mudstone. Petroleum traps in southwest Alabama are principally combination traps involving favorable stratigraphy and salt anticlines, faulted salt anticlines, or extensional faults associated with salt movement. Reservoir rocks include grainstones; leached and dolomitized wackestones, packstones, and grainstones; and dolomite. Porosity is facies-selective and is developed chiefly in lithofacies of the upper Smackover. Porosity includes primary interparticulate, secondary grain moldic, intercrystalline dolomite, vuggy, and fracture. The algal mudstones that characterize the lower Smackover and are interbedded with upper Smackover lithologies throughout most of southwest Alabama make excellent petroleum source rocks. The flanks of the Wiggins-Conecuh ridge and updip Smackover grainstones associated with salt structures are excellent areas for petroleum exploration in southwest Alabama. The key to successful prospecting is the delineation of traps associated with salt movement and recognition of either high to moderate energy lithofacies that have had their primary interparticulate porosity preserved or of lithofacies that have been dolomitized and/or leached with the development of intercrystalline dolomite and/or secondary grain moldic porosity.