Arnold H. Bouma

Deep-sea dune-like features

Abstract Three different types of dune-like features in depths between 2,500 and 4,000 m were observed on what is supposed to be the outer Magdalena Fan, Colombian Basin. Each feature has its own characteristic height and length pattern as well as its location with regard to the local slope of the sea bottom. They have in common, however, that internal reflectors all dip in a westerly direction. Reflectivity changes on 3.5-kHz records may indicate the presence of textural variations. Since the area is generally considered to be void of any continuous, deep currents, it is suggested that these large bodies are fan lobes emplaced by high-viscosity turbidity currents or debris flows. Temporal, locally induced currents, moving at least partly in easterly direction, may have caused a winnowing effect resulting in textural variations.

Peira-Cava Turbidite System, France

The Upper Eocene turbidites in the eastern French Maritime Alps can be thought of as consisting mainly of lateral migratory channel fills and overbank deposits in a middle and lower submarine fan setting. This interpretation is primarily based on:1) the lenticular shapes of shale pebble nests and their lateral continuation as scattered pebbles along internal amalgamated contacts in the sandstone beds that are inferred to be lag deposits 2) some large foreset bedding with preserved upper foreset and bottomset contacts overlain by finer material 3) contacts tangential to the overall bedding within the sandstones, and 4) the variation in paleocurrent directions from sole markings on successive layers.

Suspended matter in the Caribbean Sea: A gravimetric analysis

Abstract Total suspended matter in the water column of the Caribbean was determined quantitatively by means of filtration through 0.45 μ membrane filters. Results show that prior values obtained by centrifuging methods are too low, and that the existence of a nepheloid layer cannot be gravimetrically demonstrated in the Caribbean.

Comparison of Geological and Engineering Parameters of Marine Sediments

Abstract : Various tests are conducted on sediment cores taken from the Gulf of Mexico in order to determine possible correlations between fast survey techniques and time-consuming laboratory tests.

Depositional Processes and Reservoir Characteristics of Siltstones, Mudstones and Shales

Siltstones, mudstones and shales have been studied mainly with regard to general transportdeposition processes and clay mineralogy. A small group of investigators, with differing backgrounds, have worked on these fine-grained deposits. Recent studies on deepwater deposits from cores and outcrops indicate that the presence of finer-grained deposits greatly affect the fluid flow properties of deepwater reservoirs. Characteristics and rock properties of these deposits, which resulted from a variety of depositional processes, are just beginning to be understood.

Framework of Mississippi Fan, Gulf of Mexico: ABSTRACT

The Mississippi fan is a broad, arcuate Pleistocene accumulation of displaced shallow-water sediments. The fan consists of elongate fan lobes that shift position at the onset of each active sedimentation event, probably related to the lowering of sea level and the outbuilding of the shelf. Isopach and structure maps, based on eight acoustical reflectors of regional extent, demonstrate this shifting as well as changes in the location of the source area, and a progradation basinward. The youngest fan lobe is a suitable model for the underlying ones. It can be divided into four major morphologic units: (1) canyon--the Mississippi canyon resulted from retrogressive slumping during the late Wisconsin and was nearly filled thereafter; (2) upper fan lobe--a large, nearly filled erosional channel with low levees and a recent active central channel; (3) middle fan lobe--convex upward in cross section with a sinuous 3-km (2-mi) wide migratory and aggradational channel on its apex; (4) lower fan lobe--the central channel becomes smaller, less sinuous, shifts position periodically (as indicated by the indistinct abandoned channels), bifurcates, and terminates. Fan lobes are primarily channel-levee-overbank complexes, erosional in the upper fan and aggradational basinward. The channel is an active conduit; deposition in the channel took place during and after an active transport period. Accumulation rates on the middle and lower fan are high, ranging from 6 to 12 m/1,000 yr (20 to 40 ft/1,000 yr). A major portion of the sand is transported to the lower fan area. End_of_Article - Last_Page 464------------

Offshore Geologic Hazards: A Short Course Presented at Rice University, May 2-3, 1981 for the Offshore Technology Conference

Practically all parts of the United States continental shelves and some segments of the adjacent upper continental slopes are presently subject, or will be in the near future, to exploration and development. The same is true for many continental margins all over the world. Unless the potential influence of hazards is taken into account in the design, installation, and operation of any offshore structure, such structures can pose a threat that could result in pollution, damage, or loss of lives and equipment. This publication, written to accompany an AAPG Short Course, provides some kind of summary of current [at the time of writing] knowledge. Higher categories of geologic hazards as well as individual potentially hazardous geologic phenomena are described and discussed.

Bottom Characteristics of Northern Gulf of Mexico Continental Shelf: ABSTRACT

Photographs of the Gulf of Mexico continental shelf floor between Panama City, Florida, and Galveston, Texas, were examined for evidence of sediment texture, structure, and biologic activity. Sediment size is distinctively coarser in areas of reef growth near the continental slope. Bioturbation was recognized by the presence of burrows, mounds, furrows, tracks, and excrements. Water turbidity of varying degrees at times obscured the real water-sediment interface. Current direction and inferred velocity were indicated by compass and sediment cloud. A program of extensive photography, complemented by shallow cores, grab samples, and box samples, is needed to understand fully the different physiographic provinces of the Gulf of Mexico and their local variations. End_of_Article - Last_Page 1899------------

High-Resolution, Subbottom Profiles and Sediment Characteristics of Mississippi Delta: ABSTRACT

High-resolution subbottom profiling and sediment coring within a 100-sq mi area off South Pass of the Mississippi delta have resulted in: (1) a detailed bathymetric chart of the area; (2) a three-dimensional structural chart of the sediments to a subbottom depth of 100 m; and (3) characterizing the surface sediments in terms of lithology, shear strength, water content, bulk density, and compressibility. The bathymetric chart was constructed on a 1/2 mi grid supplemented by surveys of the area of other agencies. One of the more interesting features of the area was the delineation of a series of gullies. These features are compared with those contoured by F. P. Shepard in 1940. The seismic data revealed that the subbottom structure of the delta front and of the area seaward is characterized by numerous slump features. The sediment in the area is classified as a high water content, low shear strength, underconsolidated, rather homogeneous silty clay. End_of_Article - Last_Page 1903------------