Browsing by Author "Casey, Richard E."
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Item A study in the hydrodynamics of sediment transport(1983) Singer, Jill Karen; Anderson, John B.; Casey, Richard E.; Dunbar, Robert B.Antarctica is a unique environment where sediments are influenced by the interaction of glaciers and marine currents. This results in little or no sorting of the sediment prior to its introduction into the marine environment. The existing data relating current velocity to grain size were not designed to apply to assess the ability of marine currents to winnow and sort texturally homogeneous glacial and glacial marine sediments. However, estimates from flume studies suggest currents with velocities greater than 4 cm/sec are required to erode consolidated sediments. A puzzling observation made in studying modern Antarctic sediments has been the degree to which compacted and cohesive glacial and glacial marine sediments are being reworked and re-sedimented by bottom currents which move at velocities less than 15 cm/sec. This study has focused on the role of biological mixing in the initiation of sediment erosion and entrainment at low current velocities. This more adequately reflects the conditions which occur today on high latitude seafloors. It was found that with simulated bioturbation of the bed material, particles in the silt and clay-size range were transported at current velocities less than 3 cm/sec, with sand-sized material removed from the bed by 15 cm/sec. Without simulated bioturbation, currents up to 2 cm/sec had a negligable effect on the bed. Important applications of the results from this study include understanding sediment dynamics. It does not appear likely that erosion and sorting of overcompacted and cohesive glacial and glacial marine sediments is possible without the action of bioturbation. The results from this flume study are useful in the indirect determination of the long term normalized current velocity using surface samples and physical oceanographic information. Results can also be applied in the estimation of paleocurrent velocity from downcore variations of textural data.Item Cenozoic cornutellid biostratigraphy and paleoceanography from Deep Sea Drilling Project core 77B of Leg 9 (eastern equatorial Pacific)(1978) Reynolds, Richard Alan; Casey, Richard E.Samples from Deep Sea Drilling Project core 77B of Leg 9 taken in the eastern equatorial Pacific were used to develop a biostratigraphic zonation based on the ranges of cornutellid morphotypes and to observe any paleoceanographic and geologic changes in the study region. Before the biostratigraphic zonation could be developed, definition of cornutellid morphotypes was required due to the poor state of the taxonomy of such forms. Two separate sets of cornutellid morphotypes were defined in the study: one set based on a subjective classification method (yielded 11 morphotypes), and one set based on an objective classification method (yielded 17 morphotypes). Using the ranges of the morphotypes defined by the classification methods two zonations were developed. The morphotypes defined by the objective classification method yielded four zones, and five zones were developed using the morphotypes defined by the other classification method. Casey (1971) has shown that recent cornutellids have a cosmopolitan oceanographic extent. If the ones used in this study had a similar distribution, then the zonations developed in this study might be cosmopolitan zonations. Paleoceanographic and geologic events were recognized by examining changes in the following parameters: (1) paleo-productivity, (2) relative radiolarian diversity and abundance, (3) relative cornutellid morphotype "diversity" and abundance, (4) nannophytoplankton abundance (from Hays et al, 1972), and (5) vertical thermal gradient (from Savin et al, 1975). All of the parameters are positively correlated except for the nannophytoplankton abundance. The paleoceanographic and geologic events recognized using these parameters are as follows: (1) separation of Australia from Antarctica (approximately 35 million years ago) and the associated changes in the circulation patterns in the Southern hemisphere, (2) initiation of Antarctic Miocene glaciation and the formation of the first Neogene water masses (about 2-22 million years ago), (3) intense glacial surge on the Antarctic continent in the late Miocene (approximately 5-6 million years ago), and (4) drop in intensity of Antarctic glaciation (about 3-4 million years ago).Item Distribution and ecology of recent benthonic foraminifera of the Dumont D'Urville Sea, Antarctica(1981) Milam, Robert Wilson; Anderson, John B.; Casey, Richard E.; Schwarzer, Rudy R.Six distinct benthonic foraminiferal assemblages are recognized in the Dumont D'Urville Sea of Antarctica on the basis of the common occurrence and predominance of taxons. The distribution of calcareous and arenaceous faunal facies on the continental shelf coincides remarkably with the relative distribution of reworked glacial sediments and organic-rich biogenic muds. Surface productivity, seafloor topography, and bottom current velocities are thought to control the distribution of these biogenic muds, which are restricted to shelf depressions, and the surface sediments themselves are thought to control the relative distribution of arenaceous and calcareous populations on the shelf. Depth is a subsidiary factor in controlling faunal distributions on the continental shelf. A mixed calcareous and arenaceous fauna defines the contact of the lysocline with the continental slope, below which lies the oceanic CCD at 19m and a slope arenaceous fauna. Shelf assemblages are generally of low diversity, but high diversity populations underlie upwelling nutrient-rich plumes of modified Upper Circumpolar Deep Water, which have been injected along an isopycnal between underlying dense shelf water and overlying surface water. Benthonic foraminifera are therefore useful as indicators of hydrographic conditions, and models relating the distribution of high diversity standing crops of benthonic foraminifera to such upwelling plumes are discussed.Item Distribution and ecology of the shelled micro-zooplankton on the south Texas outer continental shelf, 1976 and 1977(1979) Leavesley, Ann S.; Casey, Richard E.A series of 48 vertical plankton tows taken in January, May, and September of 1976 and 1977 in the south Texas outer continental shelf waters were used to study the distribution and ecology of shelled microzooplankton. Species composition and abundance, number of species, and total standing crops of foraminiferans, radiolarians, and pteropods were correlated with physical, chemical, and biological oceanography of the study area. Using shelled microzooplankton distributions, seasonality, nearshore and offshore waters, estuarine and river runoff, upwelling and current directions can be identified on the shelf. Seasonality in shelf waters is suggested by the presence of two distinct assemblages: a cold to temperate water assemblage in January and a temperate to warm*water assemblage in September. January samples are dominated by the planktonic foraminiferan species Globigerina falconensis, Globigerina quinqueloba, Globigerina inflata, Globorotalia menardii and Globorotalia truncatulinoides and the polycystine radiolarian species Euchitonia furcata arid Cladococcus scoparius. Species in abundance in September include the planktonic foraminiferan species Globigerlnoides ruber and Globigerina bulloides and the polycystine radiolarian species Botryosyrtis scutum, Euchitonia elegans, Pterocorys zancleus and Hymeniastrum profundum. Nearshore and offshore conditions in the study area are suggested by the densities and diversities of planktonic foraminiferans and polycystine radiolarians and the ratio of nassellarian to spumellarian radiolarians. Maximum densities and diversities are found at the outer shelf along with the highest ratios of nassellarian to spumellarian radiolarians. Nearshore waters are characterized by low densities and diversities of microzooplankton in addition to an abundance of spumellarian radiolarians. A high influx of estuarine and river runoff water onto the shelf is suggested by the abundance of the benthonic foraminiferan species Bolivina lowmani found live in plankton tows, the pteropod species Creseis acicula, and the acantharian radiolarians. High volumes of runoff water are also indicated by the low densities and diversities of planktonic foraminiferans and polycystine radiolarians. Upwelling and ponds or rings of offshore water on the shelf are suggested by the presence of species commonly found at depths greater than the shelf break associated with water masses in the Central Gulf including Globigerinoides sacculifer, Globorotalia scitula, Spongotrochus glacialis, Theoconus hertwigii, Amphirhopalum ypsilon, and challengeriids. The south Texas outer continental study provides an example of how shelled microzooplankton in particular the foraminiferans and radiolarians can be used successfully as hydrological indicators of oceanographic conditions.Item Ecology and distribution of living planktonic foraminifera of the south Texas outer continental shelf(1976) Bauer, Mary Alvina; Casey, Richard E.A seasonal study of the ecology and distribution of planktonic foraminifera was undertaken for the south Texas outer continental shelf. Twelve stations were occupied for winter, spring, and summer seasons. A total of 36 vertical plankton tows were obtained using a 76 micron mesh Nansen net. Fifteen live planktonic foraminiferal species were identified. In addition, seventeen live benthonic foraminiferal species were also encountered in the plankton tows. One benthonic species, Bolivina lowmani. was a major constituent of inner shelf samples. This species is believed to undergo a meroplanktonic stage. Total live planktonic foraminiferal densities averaged 7.2, 3.91, and 8.15 individuals/m for winter, spring, and summer, respectively. The largest standing crop occurred contemporaneously with the smallest densitiy of empty planktonic foraminiferal tests. Both densities and diversities were found to increase seaward across the shelf. The approximate ecologie niche of planktonic foraminifera was ascertained from their relationship to large, solitary, centric diatoms. Multivariate numerical techniques of R and Q mode cluster analysis were utilized to discern subtle seasonal assemblages and distributional patterns. Assemblages of planktonic foraminifera and their spatial distributions across the shelf were found to be correlabe to physical oceanography and, thus, to exhibit seasonal variations. Twelve sediment samples from the study area were also examined to compare populations of planktonic foraminifera in the water column with those preserved in the fossil record. A striking discrepancy was noted between tests of planktonic foraminifera in the plankton and those in the sen diments. Sediment forams were at least two to three times larger than individuals of the same species in the plankton. Absence of these small individuals is believed caused by rapid dissolution of the fragile tests from acidic conditions initiated by decomposition of the organism's protoplasm shortly after death (McMillen, 1976). Chi-square test and cluster analysis were also utilized in plankton to sediment comparisons. Results from these statistical methods indicated that the two populations were not the same. Thus, it can be inferred that the bottom sediment samples represent relict shelf sediments.Item Ecology and distribution of microplankton of the south Texas outer continental shelf(1977) Williams, Damon Hughes; Casey, Richard E.A seasonal study of the ecology and distribution of microplankton was undertaken for the south Texas outer continental shelf. Twelve stations were occupied for winter, spring, and summer seasons during 1975 and 1976. A total of 199 thirty liter Niskin bottle samples were analyzed; 98 collected during 1975, and 11 collected during 1976. The filtered contents of these samples were examined under a plankton scope to determine the relative abundance of microplanktonic groups, density of shelled microplankton, and. density of general microplanktonic organisms. The average density of microplanktonic organisms in 1/2 photic zone samples for all stations during winter was 2.9 X lQ-5/m3 for 1375 data and 2.2 X 15/m3 for 1976 data; 5.4 X 15/m3 for 1975 data and 4.7 X 1^/m3 for 1976 data during spring; and 4.5 X 13/m3 for 1975 data and 1.5 X l<3?/m3 for 1976 data during summer. Probably a more realistic average for summer 1976 densities is 2.4 X lOfym3 (obtained by excluding one extremely dense sample, 8.7 X 1/m3, from consideration). Microplankton densities exhibited a seaward decrease with the exception of samples taken along one transect. Densities for radiolarian, forarainiferan, ostracod, and pteropod microplankton groups were calculated and were generally similar for the two years with the exception of summer seasonal data during 1976. A sharp increase in nassellarian and spume!larian radiolarians, as well as planktonic foraminiferans, and the presence of species endemic to certain water masses suggested that an anticyclonic ring containing components of Subtropical Underwater was present on the south Texas continental shelf during late spring and summer of 1976. Physical and chemical oceanographic data collected concurrently with the Niskin samples also suggest this possibility. Relative abundances of 35 microplankton groups in 1975 data and 34 microplankton groups in 1976 data were analyzed using multivariate cluster analysis techniques to determine what parameters affected the biological composition of microplankton assemblages. R-mode analyses of the two yearly data sets showed no striking differences in the composition of microplankton assemblages for 1975 and 1976. Q-mode analyses for 1975 and 1976 indicated that location of the shelf and .season of collection were important determinants on' microplankton comnunity structure. Statistical summaries of the clusters defined by these analyses Indicated that nearshore microplankton populations can be characterized by abundant numbers of diatoms and dinoflagellates, shallow offshore waters by abundant planktonic foraminifera, spumellarians, and relatively high numbers of copepods and naupliar larvae, and deeper offshore waters by an abundance of nassellarians, copepods, and naupliar larvae, while spumellarians and planktonic foraminifera are still common. Finally, a combination of Niskin discrete samples and Nansen tow channel samples was found to be very effective in detecting localized physical oceanographic phenomena and resultant changes in microplankton populations. The overall results of this study correlated well with other plankton studies in the area, and they Indicate that trends in microplankton distribution and relative abundance, particularly certain radiolarian and foraminiferan groups, may be very good environmental indicators of major and minor oceanographic phenomena.Item Glacial marine geology of the George V-Adelie continental shelf, East Antarctica(1980) Domack, Eugene Walter; Anderson, John B.; Casey, Richard E.; Leeman, William P.Minéralogie and textural data examined in this study suggest that glacial ice derived from the present day Cook Ice Shelf extended to the edge of the d'Urville Sea continental shelf. Based upon diatom floras and sedimentary relationships, this event took place within the last 18 years. As part of this glacial maximum, basal tills and glacial marine sediments were deposited over an irregular subglacial surface. Extensive redeposition of eroded material took place in the middle and outer portions of the continental shelf. Retreat of glacial ice was relatively rapid and was associated with widespread deposition of a thin residual glacial marine unit and turbidity current deposits in the far western and eastern parts of the region. Today, sedimentation on the continental shelf of the d'Urville Sea is controlled by biogenic and physical oceanographic processes. Deposition of ice-rafted detritus from icebergs undoubtably occurs but is relatively insignificant. Relict glacial and glacial marine deposits are being reworked on the outer and eastern portions of the shelf. This reworking is associated with an impinging Circumpolar Deep Water Mass and a westerly flowing geostrophic current. Deeper, inner portions of the continental shelf are not exposed to these currents and relatively rapid deposition of siliceous muds is occuring in these areas. Depostion of such laminated muds may be seasonal and is most likely related to the production of Saline Shelf Water.Item Glacial marine sedimentation in the Weddell Sector of the East Antarctic Rise(1981) Harlan, Janis G.; Anderson, John B.; Casey, Richard E.; Clark, Howard C.Seventeen cores were taken by John Anderson and Dennis Kurtz along two shelf-to-rise transects in the northeastern Weddell Sea during January-February 1978 as part of Islas Orcadas cruise 1578. These cores were examined by Wright (198) for mass flow characteristics and by Harlan for paleooceanography. The initial study showed that both shelf cores were comprised of basal till, twelve out of the fifteen slope-to-rise cores were mass flow deposits, and only three represented normal hemipelagic sedimentation. In this study, the three deepest rise cores were extensively analyzed to obtain sediment types and foraminifera for paleooceanography. All three cores were found to be composed predominantly of silt and sandy silt. Sediment types in the eastern Weddell Sea were analyzed as to size frequency distribution. These types were utilized to determine textural variation in each core. Each sediment type was further examined to determine paleocurrent velocities in this area. Bottom water activity was found to be persistently low in the eastern Weddell Sea. Morphological glauconite occurs throughout the cores and indicates slow sedimentation. Only two foraminlferal assemblages were found in these cores, a Uviqerina assemblage, believed to represent somewhat warmer water than present, and a Globocassidulina assemblage. Both faunas are restricted to Brunhes deposits. The overall depositional environment in this area appears to be characterized by low current activity and normal continental rise sedimentation, as evidenced by fine-grained, fairly sorted material Interspersed with Infrequent sediment slumping from the upper slope and intermittent ice-rafting of sediment. This contrasts sharply with the paleocirculation record of the western Weddell Sea, which is indicative of periodic bottom water activity.Item K♯°/AR♯° age dating on glauconites and paleontologic interpretation near the Cretaceous-Tertiary transition in Texas.(1984) Gammill, Laura M.; Adams, John A. S.; Casey, Richard E.; Clark, Howard C.Several exposures of the Cretaceous-Tertiary contact in Texas were searched for material suitable for radiometric age dating. Glauconites from Littig Pit, Travis County, Texas were sufficient in quality and quantity. K4/Ar4 dating on glauconites from Littig Pit indicates that 4 to 6 Ma of lowermost Tertiary section are missing. At least one nannofossil zone and at least two foraminiferal zones missing from the lowermost Tertiary limit the unconformity to 2.5 to 5 Ma. The concordant radiometric and paleontologic dates refute the view of Odin that all low potassium glauconites are suspect. The uppermost Cretaceous represents an undetermined amount of time. It is possible that the Midway Group was deposited rapidly during the last major Paleocene transgression of Vail et al (1977). The data supports the conclusion of Berggren and Aubert (1975) that the Midway fauna are correlatable worldwide. The iridium layer of Alvarez et al (1982) is missing at the Littig Pit, confirming missing section and illustrating how this iridium layer may be used as a worldwide time marker.Item Living benthonic foraminifera of the south Texas shelf: temporal variations and associated ecologic and paleoecologic implications(1979) Hueni, Camille D.; Casey, Richard E.Seasonal and monthly samples for living benthonlc foraminiferan analysis were taken from the south Texas outer continental shelf. The study area was bounded on the north by the entrance to Matagorda Bay, and on the south by the U.S.-Mexico border, and extended seaward from the 1.3 mile Texas state limit to and past the shelf break. One hundred and eleven species were counted and noted to the lowest taxonomic level. Conclusions derived from observations of this data includet Overall density and diversity were higher in the coarser sediments than in the modern homogenous mud sector. Bank stations, located to the north of the sample area, contained high densityhigh diversity populations characterized by shared dominance of all species. Hospital Rock and Southern Bank contained average densities lower than those of the northern banks, but slightly higher than densities of surrounding areas. The south Texas continental shelf can be subdivided into three faunal depth breaks. The inner shelf (to 5 m) is characterized by high density, moderate diversity, species dominance, and "eutrophic” conditions defined by a Brlzallna lowmani-Ammonia beccarli-Bullmlnella elegantisslma dominant assemblage. The mid-shelf (5-8 m) is defined by moderate density, maximum diversity, an area of dominance transition, and "mesotrophic" conditions. Low density, low diversity, and no species dominance is characteristic of the outer shelf (8-18 m). "Oligotrophic” conditions of the outer shelf are associate with Florilus grateloupi, Nonionella.basiloba, Fursenkoina pontoni, Virgullnella pertusa. and Buliminella cf. B. bassendorfensis. Greatest effects of seasonality occur in the inner and midshelf regions. High denstiy of the inner and mid-shelf in the north in Winter, 1976, switched to the south in Spring. In Summer/Fall, this density high migrated back to the north via a mid-shelf route and re-established itself. In the Winter, 1976, inner shelf forms were found out to the shelf edge. Outer shelf forms were brought in to the mid-shelf region in Spring. Distribution of assemblages were related to oceanographic parameters of the bottom and surface movement and related primary productivity in Spring, 1976 by the extent of the mixed seasonal layer in Winter and effect of an anticyclonic gyre the previous Summer/Fall; and by "open estuarine upwelling" in Spring, 1976. Brlzalina lowmanl was used to delineate eutrophic conditions at the sediment-water interface and in the water column. It is defined as an opportunist in the sense that it takes advantage of eutrophic conditions at the substrate interface in the Spring and Winter, 1976 as a primary consumer or detritlvore, but develops in a meroplanktonic form to take advantage of eutrqphism in the water column as a primary producer, or primary consumer, when bottom conditions were generally oligotrphic in the Summer/Fall. Analysis of gravity cores from the south Texas shelf area illustrated paleotemperature fluctuations for Fleistocene-Holocene sediments.Item Radiolaria in the Holocene sediment of the Gulf of Mexico and the basins off southern California: assemblage changes with water depth and eutrophism(1982) Wigley, Cynthia R.; Casey, Richard E.; Anderson, John B.; Clark, Howard C.Radiolarian assemblages in Holocene sediments from the Gulf of Mexico and Caribbean and the southern California borderland reflect overlying oceanographic conditions, such as general productivity, upwelling, and preservational parameters. A reconnaissance investigation of the lateral variations in the radiolarian assemblage with increasing water depth indicates that the changes are not consistent enough in either region for the establishment of a definite depth zonation; however a number of radiolarian species and higher taxa show some general trends with depth. Symbiotic taxa, and spumellaria in general, are more abundant in the thanatocoenosis of the Gulf region than off California and are indicative of oligotrophic conditions. Low oxygen content and high dissolved silica concentration in the bottom water of the Gulf of Mexico's Orca Basin lead to good preservation in this locality. Diversity, up to the family level, is greater in the California assemblages due to a mixing of radiolarian faunas and better preservation. There are more deep-water radiolarian taxa present at shallower depths, and all depths, in the California assemblages as compared to those of the Gulf due to more dynamic upwelling conditions which enhance these species both in the biocoenosis and thanatocoenosis.Item Radiolarian densities, diversities, and taxonomic composition in recent sediment and plankton of the southern California continental borderland: relationship to water circulation and depositional environments(1985) Cleveland, Michael N.; Casey, Richard E.; Anderson, John B.; Clark, Howard C.The California Current, the eastern limb of the North Pacific gyre, exhibits the following characteristics‘common to eastern boundary currents: wide, shallow, slow, diffuse boundaries, common upwelling, great seasonal variation, invasions of water masses from outside the system, and cold, low salinity waters. Studies on plankton tows and Holocene sediments have correlated components of the siliceous microplankton (radiolarians and some diatoms) with a number of those characteristics such as: the main directions of movement of the invading waters, the provenance of these waters, the presence and degree of upwelling, seasonality and its impact on the underlying sediments. Certain types of radiolarians have been found to be potentially useful in determining fossil anoxic and oxic conditions as well as paleodepth. This study involved analysis of box core sediment and plankton tow samples from the southern California continental borderland for radiolarian density, diversity, taxonomic makeup, and other features which were related to oceanographic and environmental conditions. Depositional environments were defined for the sediment samples and radiolarian indicators useful for paleoenvironmental interpretation were defined. A number of borderland environments were identified and the anoxic nearshore basin was found to have the best preservational qualities for radiolarians and thus the most representative radiolarian biocoenosis.Item Radiolarian responses to the 1957-1958 and 1964 El Ninos and 1963 anti-El Nino and a search for similar events in the fossil record(1985) Weinheimer, Amy; Casey, Richard E.; Anderson, John B.; Dunbar, Robert B.Radiolarian distributions and physical oceanographic data from the southern California borderlands indicate the following: Strong anti-El Nino periods can be characterized by 1) average radiolarian standing crop, 2) high percentage of transition-central radiolarian fauna, and 3) low percentage and number of warm water radiolarian fauna. This distribution pattern is attributed to strong wind-driven upwelling and reduced northward transport by the California Countercurrent during anti-El Nino periods. Strong El Nino periods were typically 1) high in radiolarian standing crop, 2) low percentage and high number of cold water fauna, and 3) high percentage and number of warm water fauna. This distribution is attributed to reduced wind-driven upwelling, enhanced northward countercurrent transport, and geostrophic doming of the cold water masses in the shear zone between the California Current and California Countercurrent. Preliminary work on a varved sample from the Monterey Formation, Lompoc, California indicates that variations of radiolarian populations appear to represent changes in oceanic circulation similar to those recorded in the Santa Barbara Basin varved sediments.Item Radiolarian responses to the 1982-83 California El Nino and their implications(1985) Carson, Thomas; Casey, Richard E.; Clark, Howard C.; Dunbar, Robert B.Radiolarian responses to the 1982-83 California El Nino event were unusually high standing crops of both warm and cold water radiolarians, high diversity, and the appearance of distinctly central gyre and eastern tropical Pacific faunas. These and other observations suggest that anomalously strong transport from the west and south occurred through at least November 1953 and that the California Current had shifted eastward over the Southern California Eorderland. A generic group of radiolarians, the spongasterids, was used effectively in monitoring these water mass influences. Radiolarian distributions in 3.-3.5 Ma circuoi-northeastern Pacific sediments indicate a warm North Facific at this time. Marked breaks in distributional trends off southern Baja California suggest an oceanic frontal zone in this area, To the south radiolarian assemblages exhibit a distinctly eastern tropical Pacific character. Spongaster pentas occurs as far north as Deep Sea Prilling Site 173. This suggests periodic breakdowns of this frontal zone (El Ninos?) may have occurred.Item Sediment gravity transport on the Weddell Sea continental margin(1980) Wright, Robyn; Anderson, John B.; Casey, Richard E.; Clark, Howard C.Understanding sediment gravity transport and continental slope processes has become increasingly important, especially with the current emphasis upon oil and gas exploration in the deep marine environment. Core x-radiography and textural and mineralogic analysis of sediment samples from Weddell Sea piston cores has enabled identification of several mechanisms of sediment mass transport which significantly influence sedimentation on the continental slope, abyssal plain, and continental shelf. End member processes such as debris flows and turbidity currents are found to occur throughout the eastern Weddell Sea, between °W and 45°W; however textural and visual evidence also substantiates the presence of sediment gravity flow processes which are transitional between end-member mechanisms. Downslope transition in sediment character between slump, debris flow, and turbidite deposits is related to a corresponding transition in the mechanics of grain support and transport. Because most material transported to the marine environment in the Weddell Sea is of poorly sorted glacial origin, analysis of the competence of the marine transport agents is augmented. Textural and mineralogic sorting within the turbidity current mechanism, for example, is found to be extremely efficient. Generation of well sorted quartz-rich sands from poorly sorted lithic source material occurs over relatively short distances, and proves to be a mechanism by which potentially large amounts of quartz sands are produced in the Weddell Sea. The intimate association of these sands with glacial sediments offers an alternative explanation for the quartzite/diamictite associations in ancient sequences which have been cited as evidence against a glacial origin for these deposits.Item Sedimentation in the north San Clemente basin, California continental borderland(1979) Pratt, David E.; Warme, John E.; Casey, Richard E.; Clark, Howard C.Three broad sedimentary environments within the north San Clemente Basin have been defined. The south slope of San Clemente Island and the northernmost part of the San Clemente Basin receive predominantly siliciclastic sediments shed from San Clemente Island. Clastic sediments deposited in San Clemente Canyon are sorted and transported by the action of tidally generated currents. Currents measured in the canyon show upcanyon and downcanyon reversals of flow nearly every 12 hours, and currents reached velocities of 18 cm/second during periods of peak flow. The currents have winnowed silt and clay from sediments at the head of the canyon, leaving a sandy lag deposit. Pine-grained sediment is transported into the basin and slowly deppsited as the currents lose velocity. Three piston cores from the northern part of the basin penetrated the Holocene-Plelstocene boundary. Slightly more than a meter of Holocene sediment was measured in each core, as determined by mlcropaleontologic methods. The central part of the north San Clemente Basin is dominated by pelagic sedimentation. Basin physiography effectively blocks transport of clastic sediments from San Clemente Island and mainland California to the area. Hemipelagic sediments and distal turbidites are transported through the Navy Fan of the south San Clemente Basin and into the southern part of the study area. The observed distal turbidites may be a result of Early Holocene sea-level regressions. Sediments within the north San Clemente Basin are in a reducing environment, as indicated by their color and the presence of authigenic sulfides. Micropaleontologic data from this study indicate that kummerform Globlgerina pachyderma tests are a result of displacement into unfavorable environments.Item Sedimentation on the Weddell Sea continental margin and Abyssal Plain, Antarctica(1983) Fisco, Mary Pamela P.; Anderson, John B.; Casey, Richard E.; Dunbar, Robert B.Abyssal sediments collected in piston cores were examined to determine sediment distribution patterns and active sedimentary processes in the Weddell Sea. Pelagic, hemipelagic, debris flow, and turbidite deposits were identified and distinguished by their individual characteristics of grain-size, sorting, texture, bedding, and sediment source. Sediment distribution patterns show a large turbidite fan complex extending across the northeastern portion of the basin. Recent turbidite deposition in the Weddell Sea has occurred under polar glacial conditions. This has produced sequences distinctly different from those occurring in temperate glacial environments, as in the northern high latitudes. Polar turbidites consist of massive, thick-bedded gravels, sands, silts, and muds, which are significantly depleted in silt. Temperate turbidites are rich in silt, and typically consist of interlaminated, graded, silts and muds. Similarities exist between Weddell Basin and Bellingshausen Basin seismic data. These data suggest that turbidite deposits constitute most of the sediment fill in these basinsItem Sedimentologic and paleoceanographic implications of terrigenous deposits on the Maurice Ewing Bank, southwest Atlantic Ocean(1984) MacDonald, Scott Edward; Anderson, John B.; Casey, Richard E.; Dunbar, Robert B.The Maurice Ewing Bank (MEB) provides a unique environment in which to study deep-sea clastic sedimentation as the observed sedimentary sequences are not readily explained by traditional depositional models. Grain size distributions of sediment samples are utilized to identify styles of sediment transport and current velocities at the benthic boundary layer. These data, along with physical oceanographic information, allow for examination of the relationship between sedimentation on the bank and circumpolar currents. Causal relationships between glacial episodes, current intensification, and bottom current scour were previously postulated. Results indicate that modern sediment distribution is controlled by both bottom and surface currents, and is modified by mass-flow processes. Indirect determinations of current velocities, using a curve relating sediment transport to current velocity, suggest a uniform energy regime of 8-12 cm/sec over the bank. These moderate velocities are supported by geostrophic velocity profiles. The results of this study also demonstrate that misinterpretations regarding current velocities may result when statistical parameters, such as mean grain size and sorting, are used as indicators of fluctuations in bottom current velocities. Similar conclusions can be drawn concerning the use of bottom photographs and nephelometer profiles to infer the relative strength of bottom energy regimes. Current velocities assigned to down-core samples indicate no major fluctuations in circumpolar current intensity since PIio-Pleistocene time. Similar results were obtained from examination of Argentine Basin cores. These results refute the previously inferred causal relationship between current intensification and glacial episodes. The identification of mass-flow deposits provides an alternate explanation for the depositional and erosional history of the MEB.Item Sedimentology of the North Victoria land continental margin, Antartica(1983) Brake, Christopher F.; Anderson, John B.; Casey, Richard E.; Dunbar, Robert B.Item Studies of the recent foraminifera of the Sunda Shelf and the Java Sea(1974) Yau, Mary Wing-Chi; Casey, Richard E.Five foraminiferal assemblages based on benthonic foraminifera are established on the wide Sunda Shelf and the java Sea. The inner shelf (18-2 fm) assemblage is represented by Amphistegina radiata (Fichtel and Moll), Calcarina spengleri (Gmelin), Elphidium crispum (Linné), Operculina ammonoides (Gronovius), and Quinqueloculina seminula (Linné). The central shelf (27-3 fm) assemblage is represented by Quinqueloculine-Rotalia spp., Asterorotalia trispinosa (Thalman), and Elphidium craticulatum (Fichtel & Moll). The outer shelf (36-42 fm) is represented by BolivinaBulimina-Uvigerina spp., cancris auriculus (Fichtel & Moll), Quinqueloculina cf. akneriana d'Orbigny and Rolshausenia rolshauseni (Cushman & Bermundez). The shelf edge (97 fm) assemblage is poorly defined. The lower middle bathyal (832 fm) assemblage is represented by Bolivina-Uvigerina spp., Cassidulina subglobosa Brady and Cibicides tapoengensis LeRoy. Five zones developed by using faunal breaks of planktonic foraminifera could be correlated with the benthonic foraminiferal assemblages. The shelf is dominated by shallow-water benthonic foraminiferal species, while the planktonic foraminifera dominate the lower middle bathyal area. High species diversity are found to correlate with possible relict assemblages at a time of lower sea-level. Relict distributions of Elphidium spp. and Rotalia beccarii indicate a possible stillstand of sea-level at 37-42 fm. Core V19-135 was chosen for detailed studies of possible sea-level fluctuations. Three possible explanations are proposed based on the limited data, and the eustatic change of sea-level seems to provide the best explanation of the results.