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Structural framework of the continental terraces northwest Gulf of Mexico
326
Oceanographic Abstracts
equipped with a 5 in. x 4 in. NaI (TI) crystal and 256-channel pulse-height analyser. Studies with a caesium-134 tracer helped to determine the most favourable conditions of pH, temperature and concentration of reagent. The procedure has been used aboard ship and in the laboratory since 1960 for oceanographic survey o f radioactive caesium in sea water in concentrations ranging between 0.03 and 0.4 pC/l.
MOORE, D. G., and J. R. CURRAY, 1963. Structural framework of the continental terraces northwest Gulf of Mexico. J. Geophys., Res., 68 (6): 1725-1747. Intricate detail of stratigraphy and structure, to depths o f about 5000 ft (probably Miocene), is shown in Rayflex Electro-Sonic Profiler records collected on the continental shelf and the upper continental slope of the northwest Gulf o f Mexico. The Rayflex Electro-Sonic Profiler is a continuousrecording, acoustic reflection surveying system which utilizes a high-intensity spark source, rather than chemical explosives. The recorded sections of the continental terrace o f this area show essentially horizontally stratified deposits underlying the continental shelf (probably shelf, littoral, deltaic, lagoonal, and continental facies) changing smoothly over the shelf break into seaward-dipping continental slope-deposits. The upper part of this terrace has thus formed during the late Tertiary and Quaternary by both up-building and outbuilding. This basic framework has been modified locally by folding and faulting, which are largely associated with salt or shale intrusion structures. The irregular topography of the upper continental slope, previously attributed to slumping, gravity tectonics, and turbidity current erosion, is shown to be controlled by these intrusive structures modified by varying amounts of contemporaneous deposition of sediment. No evidence of extensive slope erosion is shown by records of this survey. MORALES, E., 1962. Cefalopodos de Cataluna II. Inv. Pesq., Barcelona, 21: 97-t11. This is a second note on the study of the cephalopod fauna based on the specimens of the Laboratory (Spain) Collection. Biological, ecological and historical remarks are added. species: Opisthoteuthis agassizii Verrill, Heteroteuthis dispar (Ri.ipp.) Gray, and Rondeletiola Naef are new off the Catalonian Coast. The first is also a new record in the Mediterranean
Blanes Three
minor Sea.
Moss, A. J., 1963. The physical nature of common sandy and pebbly deposits. 1I. Amer. J. Sci., 261 (4): 297-343. Studies of the movement in flowing water of sand grains and larger particles indicate that they can be rolled or slid over surfaces of particles smaller than themselves but that saltation is the dominant mode o f progression if particles are moved over a surface of others their own size or larger. This conclusion can be combined with the results of Part I of this paper and other information to provide a qualitative explanation o f the formative processes of common sandy and pebbly deposits. Saltatory particles build Populations A and B; roUing and sliding particles halt to form Population C. Population A, which forms the bulk of most sandy and pebbly deposits, is built by a selective process that allows some landing saltatory particles to be retained on the bed but rejects the rest. Tile stability, in a position on the bed, of a particle depends largely on the extent to which its movability is affected by neighbouring particles, and the evidence suggests that this shielding is relatively greatest if a particle rests, in a favorable orientation, on others its own size. Population A therefore has a small size range but, because equant particles are relatively difficult to move by saltation, natural Population A's always grade from relatively small, equant particles to somewhat larger, inequant particles. The mainnaturalcapacityphenomenonisapparently dependent upon the relationship between Population A and the saltatory particles in the current-driven" traction carpet ' and, provided that the current is strong enough to lift the Population A particles at all, acceleration causes scour and deceleration causes deposition. Population B comprises relatively small particles that pass directly from saltation into positions deep in the interstices of Population A. Repeated erosion and redeposition of beach-face deposits causes Popt, lation B to be eliminated from them, and Population A is left to occur alone as wave-laid Type 1 sediments. Population C occurs in two ways--well dispersed and closely packed. Dispersed Population C comprises particles that have individually ceased to roll or slide because the current can no longer move them over a surface of finer Population A particles. If the corcentration of rolling and sliding particlcs exceeds a critical value, the halting of one individual can cause many to jam on the bed and a " traction clog ' deposit, containing closely packed Population C particles, forms; Populations A and B corAinue to accumulate between the Population C particles and the whole process is repetitive; thus thick traction clog deposits can form. Sandy river gravels are typical traction clog deposits. Equant and dense particles preferer tially enter Populations A and B, and heavy mineral concentrates apparently result from a ' chain reaction ' segregation that occurs as Population A is built; the properties of some natural garnet sands correspond closely with prediction. The growing surfaces o f sediments that are built of normal particles repeatedly reject particles that are very inequant or o f low specific gravity; these oft-rejected particles can later become locally concentrated through relative immovability, if they are, themselves, built into a Population A - - a s happens on shell beaches; an apparent example of this type of segregation is given. In natural environments, huge numbers of closely similar particles become concentrated because o f their relative immovability when built into Population A. The resulting masses of texturally homogeneous sand often dominate stretches of coastline or occur as extensive fossil deposits.
Oceanographic Abstracts
equipped with a 5 in. x 4 in. NaI (TI) crystal and 256-channel pulse-height analyser. Studies with a caesium-134 tracer helped to determine the most favourable conditions of pH, temperature and concentration of reagent. The procedure has been used aboard ship and in the laboratory since 1960 for oceanographic survey o f radioactive caesium in sea water in concentrations ranging between 0.03 and 0.4 pC/l.
MOORE, D. G., and J. R. CURRAY, 1963. Structural framework of the continental terraces northwest Gulf of Mexico. J. Geophys., Res., 68 (6): 1725-1747. Intricate detail of stratigraphy and structure, to depths o f about 5000 ft (probably Miocene), is shown in Rayflex Electro-Sonic Profiler records collected on the continental shelf and the upper continental slope of the northwest Gulf o f Mexico. The Rayflex Electro-Sonic Profiler is a continuousrecording, acoustic reflection surveying system which utilizes a high-intensity spark source, rather than chemical explosives. The recorded sections of the continental terrace o f this area show essentially horizontally stratified deposits underlying the continental shelf (probably shelf, littoral, deltaic, lagoonal, and continental facies) changing smoothly over the shelf break into seaward-dipping continental slope-deposits. The upper part of this terrace has thus formed during the late Tertiary and Quaternary by both up-building and outbuilding. This basic framework has been modified locally by folding and faulting, which are largely associated with salt or shale intrusion structures. The irregular topography of the upper continental slope, previously attributed to slumping, gravity tectonics, and turbidity current erosion, is shown to be controlled by these intrusive structures modified by varying amounts of contemporaneous deposition of sediment. No evidence of extensive slope erosion is shown by records of this survey. MORALES, E., 1962. Cefalopodos de Cataluna II. Inv. Pesq., Barcelona, 21: 97-t11. This is a second note on the study of the cephalopod fauna based on the specimens of the Laboratory (Spain) Collection. Biological, ecological and historical remarks are added. species: Opisthoteuthis agassizii Verrill, Heteroteuthis dispar (Ri.ipp.) Gray, and Rondeletiola Naef are new off the Catalonian Coast. The first is also a new record in the Mediterranean
Blanes Three
minor Sea.
Moss, A. J., 1963. The physical nature of common sandy and pebbly deposits. 1I. Amer. J. Sci., 261 (4): 297-343. Studies of the movement in flowing water of sand grains and larger particles indicate that they can be rolled or slid over surfaces of particles smaller than themselves but that saltation is the dominant mode o f progression if particles are moved over a surface of others their own size or larger. This conclusion can be combined with the results of Part I of this paper and other information to provide a qualitative explanation o f the formative processes of common sandy and pebbly deposits. Saltatory particles build Populations A and B; roUing and sliding particles halt to form Population C. Population A, which forms the bulk of most sandy and pebbly deposits, is built by a selective process that allows some landing saltatory particles to be retained on the bed but rejects the rest. Tile stability, in a position on the bed, of a particle depends largely on the extent to which its movability is affected by neighbouring particles, and the evidence suggests that this shielding is relatively greatest if a particle rests, in a favorable orientation, on others its own size. Population A therefore has a small size range but, because equant particles are relatively difficult to move by saltation, natural Population A's always grade from relatively small, equant particles to somewhat larger, inequant particles. The mainnaturalcapacityphenomenonisapparently dependent upon the relationship between Population A and the saltatory particles in the current-driven" traction carpet ' and, provided that the current is strong enough to lift the Population A particles at all, acceleration causes scour and deceleration causes deposition. Population B comprises relatively small particles that pass directly from saltation into positions deep in the interstices of Population A. Repeated erosion and redeposition of beach-face deposits causes Popt, lation B to be eliminated from them, and Population A is left to occur alone as wave-laid Type 1 sediments. Population C occurs in two ways--well dispersed and closely packed. Dispersed Population C comprises particles that have individually ceased to roll or slide because the current can no longer move them over a surface of finer Population A particles. If the corcentration of rolling and sliding particlcs exceeds a critical value, the halting of one individual can cause many to jam on the bed and a " traction clog ' deposit, containing closely packed Population C particles, forms; Populations A and B corAinue to accumulate between the Population C particles and the whole process is repetitive; thus thick traction clog deposits can form. Sandy river gravels are typical traction clog deposits. Equant and dense particles preferer tially enter Populations A and B, and heavy mineral concentrates apparently result from a ' chain reaction ' segregation that occurs as Population A is built; the properties of some natural garnet sands correspond closely with prediction. The growing surfaces o f sediments that are built of normal particles repeatedly reject particles that are very inequant or o f low specific gravity; these oft-rejected particles can later become locally concentrated through relative immovability, if they are, themselves, built into a Population A - - a s happens on shell beaches; an apparent example of this type of segregation is given. In natural environments, huge numbers of closely similar particles become concentrated because o f their relative immovability when built into Population A. The resulting masses of texturally homogeneous sand often dominate stretches of coastline or occur as extensive fossil deposits.