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1.
An examination of split core photographs from the north-central Pacific reveals the presence of three different burrow morphologies. Simple burrows occur throughout the region. Halo burrows are present in water deeper than 4,000 m (3,000 m along the equator) and removed from continental areas. Imbricate burrows are uncommon and have an irregular distribution. Organisms responsible for the burrows are interpreted as surface to near-surface feeders which do not penetrate deeply into the sediments. Thus, the zone of sediment mixing caused by burrowing ranges from 10 to 30 cm and averages 20 cm. 相似文献
2.
The textural, mineralogical, compositional and paleontological characteristics of an iron-cemented allochthonous sediment
slab recovered from a zone of slumping between water depths of 2,100 and 2,350 m on the lower continental slope off Cape Hatteras
are summarized. Results support interpretation of the sediment slab as the oxidized equivalent of pyrite-cemented Pleistocene
to Recent sediment, an uncommon form of lithification in deep sea sediments. We propose that exposure of such slumped sediment
slabs to seawater has produced an alteration sequence from pyrite-cement to iron oxide-cement. These observations extend the
range of pyrite-cemented sediment initially reported from water depths between 4,770 and 4,950 m on the lower continental
rise off Cape Hatteras. 相似文献
3.
《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(10):2289-2307
In the sedimentary column, a combined quantification of burrows and macrobenthic community provides evidence of bioturbation features in the submarine canyon of Cap-Ferret between 2000 and 3000 m depth. An image-processing technique allows accurate quantification of burrow volumes with depth in the sedimentary column. The major bioturbation mode seems to be different in the channel compared to the interfluve. Macrobenthic activity is more inclined to mix the sediment in the channel in response to increased organic matter supplies. Sediment mixing leads to burrow destruction in the upper mixed layer of sediment in the canyon. Burrows are better preserved on the interfluve where mixing is slower. Under the mixed zone, the volume of recorded burrows is higher when sedimentation rate increases, as in the upper canyon. In this transition layer, the burrow volume is estimated to be between 3 and 64% of the total sediment volume depending on the sediment depth. The fill-down of numerous burrows with surface sediment by bioregeneration suggests that anaerobic degradation of fresh organic matter is dominant in this canyon. In the sedimentary column, the negative relationship between carbonate content and macrobenthic abundance confirms that carbonate dissolution is largely influenced by bioturbation. 相似文献
4.
Functional group analysis was used to determine the major bioturbators in the Dry Tortugas, Florida Keys. The surface community
is dominated by surface deposit feeding polychaetes and burrowing bivalves capable of mixing the top 0–4 cm of the sediment
on time scales of days to weeks. Bioturbation by the Notomastus sp. and Callianassa sp. deep community effectively removes primary sedimentary structures. Their fossilized burrow structures may be geologically
important in this system. Surface microtopography is controlled by stabilizing and destabilizing forces that determine the
potential for surface resuspension and sediment transport in the Dry Tortugas. 相似文献
5.
Sedimentological studies were undertaken in the Dry Tortugas to examine environmental influences on the formation of sedimentary
fabric. 234Th, 210Pb, grain size, porosity, and fabric analyses reveal the presence of a soft, fine-grained, well mixed surface layer underlain
by compact, shelly, intensely bioturbated carbonate muds. Vertical zonation of biogenic structures indicates that deep bioturbation
is advective and results in transport of fine material to the seabed surface. The impact of physical oceanographic processes
appears to be restricted to the surface layer; however, potential for preservation of this layer in the sediment record is
low due to intense mixing in deeper sediments. Thus, preserved sediments retain an incomplete record of the dominant benthic
processes at the study area. 相似文献
6.
Gerhardt F. Riedel James G. Sanders Richard W. Osman 《Estuarine, Coastal and Shelf Science》1987,25(6)
From the distribution of dissolved and solid arsenic species in a contaminated estuarine sediment and measured rates of flux of the various arsenic species we propose an empirical model for the cycling of arsenic between sediments and water column. The chemical form of arsenic in the sediment was largely determined by the redox state of the sediment. Arsenite was the dominant dissolved and solid species in the deeper reduced sediment, and arsenate was dominant in the oxidized surface layer. Arsenite in the interstitial water diffused toward the surface layer, where it was mostly oxidized to arsenate prior to leaving the sediments. Some arsenate adsorbed to the surface sediments and produced a surface layer enriched in arsenic. Small concentrations of methyl and dimethyl arsenic were produced in the sediments, and these also diffused into the overlying water.Nereis succinea, a burrowing polychaete, affected distribution and flux of arsenic from the sediments by its production of irrigated burrows. These burrows increased both the effective surface area of the sediment and the diffusion of arsenic by a factor of five. When the relative effects of the activities of Nereis succinea and physical resuspension are compared, results indicate that although physical resuspension can produce large pulses of materials from contaminated sediments, continuous biological activity is likely to be more important in the mobilization of contaminants from sediments in many estuarine environments. 相似文献
7.
A petrographic reconnaissance survey of 23 Pleistocene deep-sea sand layers from the Hatteras Abyssal Plain and adjacent deep-sea environments was undertaken in an attempt to delineate the provenance of the Hatteras Abyssal Plain sands. Data from 18 widely spaced piston cores reveal that subarkosic sands on the Hatteras Abyssal Plain derive from widely separated, characteristically different source areas. When the diverse character of the Hatteras Abyssal Plain sands is compared to that of the Hatteras Fan and adjacent continental margin, differences in composition suggest a portion of the coarse fraction derives north of Cape Hatteras via Wilmington Canyon System or the Sohm Abyssal Plain. The presence of certain diagnostic grain assemblages (schistose metaquartz, schistose, basic, and meta-volcanic rock fragments), not found in adjacent continental margin sands, indicates the glaciated areas that feed the Hudson Canyon/Fan and Sohm Abyssal Plain are a principal source. The data substantiate that premise of previous studies, that channelization and overflow of turbidity currents through the Sohm Abyssal Gap has played a major role in sedimentation on the Hatteras Abyssal Plain.Aside from the obvious Pleistocene contributions from the adjacent Hatteras Fan, which fed southerly flowing littoral drift material into the deep ocean, a more southerly continental shelf source is also indicated. The occurrence of certain carbonate grain types (ooids and peloid-algal biomicrites) is generally restricted to the continental shelf south of Hatteras Canyon system. The presence of these diagnostic grain types on the Abyssal Plain suggests a two-step process involving northerly transport via the Gulf Stream into canyon tributaries offshore Cape Hatteras during lower sea levels and eventual redistribution by density currents into the deep ocean. This process appears to have been responsible for the emplacement of carbonate-rich sands on the Hatteras Abyssal Plain. 相似文献
8.
P. Dewangan T. RamprasadM.V. Ramana A. MazumdarM. Desa F.K. Badesab 《Marine and Petroleum Geology》2010
Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, Krishna–Godavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor. 相似文献
9.
10.
The pore water concentrations of dissolved silica in sediment cores from the continental slope offshore from Cape Hatteras, North Carolina, varied from 150 to almost 700 μ,M with depth in the top 40 cm of sediment. Sediment cores from 630 to 2010 m depth had very similar profiles of dissolved silica in their pore waters, even though these cores came from regions greatly different in slope, topography, sedimentation rate, and abundance of benthic macrofauna. Cores from 474 to 525 m were more variable, both with respect to pore water dissolved silica profiles, and with respect to sediment texture. Experiments indicate that both the rate of dissolution of silica and the saturation concentration decrease as sediment depth below the sediment-seawater interface increases. These data are consistent with depletion of a reactive silica phase in surface sediment, which may be radiolarian tests, or the alteration of biogenic silica to a less reactive form over time. Experimental results suggest that the pore water dissolved silica concentration in sediments below the top few centimeters may be higher than the sediments could now achieve. The flux of dissolved silica out of these sediments is estimated to be 15 μmoles cm−2 yr−1. 相似文献
11.
Neal E. Blair Gayle R. Plaia Susan E. Boehme David J. DeMaster Lisa A. Levin 《Deep Sea Research Part II: Topical Studies in Oceanography》1994,41(4-6)
The sources and fates of metabolizable organic carbon were examined at three sites on the North Carolina slope positioned offshore of Cape Fear, Cape Lookout and Cape Hatteras. The13C/12C compositions (δ13C) of the solid phase organic matter, and the dissolved inorganic carbon (ΣCO2) produced during its oxidation, suggested that the labile fraction was predominantly marine in origin. The ΣCO2 concentration gradient across the sediment-water interface, and by inference the ΣCO2 flux and production rate, increased northward from Cape Fear to Cape Hatteras. Methane distributions and ΣCO2 δ13C values suggest that the rate of anaerobic diagenesis increased northward as well. The differences in sedimentary biogeochemistry are most likely driven by an along-slope gradient of reactive organic carbon flux to the seabed. This trend in reactive organic carbon flux correlates well with macrofaunal densities previously observed at the three sites. Proximity to the shelf and the transport of particulate material by surface boundary currents may control the deposition of metabolizable material on the Carolina slope.Evidence for methanogenesis was found only on the Cape Hatteras slope. The methane, which was produced at a depth of approximately 1 m in the seabed, was consumed nearly quantitatively in the biologically mixed layer as it diffused upward. Irrigation of the sediments by infauna may have provided the necessary oxidant for the consumption of the methane. 相似文献
12.
James A. Blake Robert J. Diaz 《Deep Sea Research Part II: Topical Studies in Oceanography》1994,41(4-6)
The studies reported in this special issue ofDeep-Sea Research are largely derived from data collected as part of programs supported by the U.S. Department of the Interior, Minerals Management Service (MMS) in response to concerns about the effect of oil and gas exploration on the largely unknown continental slope environment. Results of the MMS U.S. South Atlantic continental slope and rise program conducted off the Carolinas from Cape Hatteras to off Charleston in depths ranging from 600–3500 m identified the importance of the slope off Cape Hatteras in cycling of materials from the shelf to the deep sea. Other more detailed investigations followed which filled numerous gaps in our knowledge of the role played by such special regions of the continental slope in the global cycling of carbon and other materials. 相似文献
13.
The coupling between biogenic reworking activity and reactive organic matter patterns within deposits is poorly understood and often ignored. In this study, we examined how common experimental treatments of sediment affect the burrowing behavior of the polychaete Nephtys incisa and how these effects may interact with reactive organic matter distributions to alter diagenetic transport – reaction balances. Sediment and animals were recovered from a subtidal site in central Long Island Sound, USA. The upper 15 cm of the sediment was sectioned into sub-intervals, and each interval separately sieved and homogenized. Three initial distributions of sediment and organic substrate reactivity were setup in a series of microcosms: (1) a reconstituted natural pattern with surface-derived sediment overlying sediment obtained from progressively deeper material to a depth of 15 cm (Natural); (2) a 15 cm thick sediment layer composed only of surface-derived sediment (Rich); and (3) a 15 cm thick layer composed of uniformally mixed sediment from the original 15 cm sediment profile (Averaged). The two last treatments are comparable to that used in microcosms in many previous studies of bioturbation and interspecific functional interaction experiments. Sediment grain size distributions were 97.5% silt-clay and showed no depth dependent patterns. Sediment porosity gradients were slightly altered by the treatments. Nepthys were reintroduced and aquariums were X-rayed regularly over 5 months to visualize and quantify spatial and temporal dynamics of burrows. The burrowing behaviour of adult populations having similar total biovolume, biomass, abundance, and individual sizes differed substantially as a function of treatment. Burrows in sediment with natural property gradients were much shallower and less dense than those in microcosms with altered gradients. The burrow volume/biovolume ratio was also lower in the substrate with natural organic reactivity gradients. Variation in food resources or in sediment mechanical properties associated with treatments, the latter in part coupled to remineralization processes such as exopolymer production, may explain the burrowing responses. In addition to demonstrating how species may respond to physical sedimentation events (substrate homogenization) and patterns of reactive organic matter redistribution, these experiments suggest that infaunal species interactions in microcosms, including the absolute and relative fluxes of remineralized solutes, may be subject to artifacts depending on exactly how sediments are introduced experimentally. Nonlocal transport and cylinder microenvironment transport – reaction models readily demonstrate how the multiple interactions between burrowing patterns and remineralization rate distributions can alter relative flux balances, decomposition pathways, and time to steady state. 相似文献
14.
G. Randy Cutter Jr Robert J. Diaz John Lee 《Deep Sea Research Part II: Topical Studies in Oceanography》1994,41(4-6)
The recent benthic meiofaunal foraminiferal assemblage from the continental slope (590-2 003 m) off Cape Hatteras, North Carolina exhibits high species richness and evenness, moderate diversity values, and lacks numerically dominant species. The preserved planktic assemblage has relatively low species richness, high evenness, low diversity, and a few numerically dominant species. Approximately 9% of the benthic species are those that typically live within continental shelf depth ranges. The benthic assemblage abundances and diversities do not follow depth patterns or geophysical characteristics. No biogeographic boundary can be described within the study area for meiofaunal foraminifera. Oxygen limitation does not appear to be a factor affecting the benthos of the North Carolina continental slope based upon the community structure of the benthic foraminifera, if total assemblage is assumed to reflect the recently living community. The high carbonate content of sediments in the area may be explained by foraminiferal tests. Within the study area, the foraminiferal assemblages are uniform, and probably reflect relative consistency of primary environmental variables as well as dynamic downslope transport and high influx of material from the water column in the vicinity where the Gulf Stream and the Western Boundary Undercurrent cross. 相似文献
15.
A series of experiments in Willapa Bay, Washington, indicates the degree to which the presence of spilled oil modifies the burrowing behavior of infauna and the extent to which the animals redistribute oil into interridal sediment. Small amounts of North Slope crude oil introduced at low tide directly into burrow openings (mostly made by the crustacean Callianassa) resulted in a limited and temporary reduction in the number of burrow openings. In contrast, a layerof oil-saturated sand 1 cm thick buried about 5 cm below the sediment surface sharply reduced the number of burrow openings. After a year, the few new burrows penetrated only the margins of the experimental plot, and bioturbation below the buried oil saturated sand layer declined dramatically.The experiments suggest that small amounts of oil temporarily stranded by tides in themselves have no long-range effect on burrowing behavior. The fauna, however, are capable of introducing measurable amounts of oil into the subsurface, where it is retained long after the rest of the stranded oil has washed away. A buried layer of oil-saturated sand greatly reduces infaunal activity; the oil presents an effective barrier that can persist for years.The oil incorporated into the sediment from burrow openings showed evidence of degradation after 7 months. In contrast, the layer of buried oil remained essentially undegraded after a period of two years, even though oil in lower concentrations above the layer was degraded after a period of one year. This variation in degree of dgradation of the buried oil, as well as the heterogeneity of oil distribution wherever the oil has been incorporated from the surface, emphasises the importance of careful sampling in any attempt to locate or monitor the presence of spilled oil in the substrate. 相似文献
16.
James A. Blake Brigitte Hilbig 《Deep Sea Research Part II: Topical Studies in Oceanography》1994,41(4-6)
Unusually dense assemblages of benthic infaunal invertebrates have been discovered in continental slope sediments off Cape Hatteras, North Carolina. Densities were highest on the upper slope, ranging from 24,055 to 61,244 (X¯=46,255) individuals m−2 in nine samples taken at a 600-m site in 1984 and 1985, and from 15,522 to 89,566 (X¯=37,282) individuals m−2 in single samples at 15 stations over a wider depth range of 530 to 1535 m in 1992. A lower slope station at 2000 m sampled six times in 1984–1985 and again in 1992, had densities consistently higher than 8500 individuals m−2. Species richness and diversity are consistently lower on the Cape Hatteras slope than at other locations off North Carolina and elsewhere in the western North Atlantic. The 1992 studies indicated that the upper slope infaunal assemblages (600m) were dominated by oligochaetes, while the middle slope assemblages (800–1400 m) were dominated by the polychaeteScalibregma inflatum. This latter depth range could be defined into two assemblages based upon suites of less abundant species. At depths of 1500–2000 m, a lower slope assemblage dominated by various deposit feeding polychaetes and oligochaetes was found. Results from the 1984–1985 studies suggest seasonal or year-to-year patterns in the dominance ofS. inflatum andCossura longocirrata. Unusually high sedimentation rates and organic carbon flux have been recorded from the slope off Cape Hatteras and may account for the high infaunal productivity in the area. Most of the dominant infaunal organisms are species more typical of shallow, coastal habitats rather than deep-sea species that dominate other areas of the U.S. Atlantic continental slope. Parallel investigations regarding the nature of organic matter in the Cape Hatteras sediments have revealed a mixture of both marine and terrestrially derived carbon, only a small percentage of which is composed of the smaller molecular weight polyunsaturated fatty acids more typical of continental slope sediments. It is likely that the high percentage of refractory organic matter would favor the survival of preadapted shelf species over those from adjacent slope environments. 相似文献
17.
The velocities of near-bottom currents were measured at six locations on a 180-km transect of the Gulf Stream adjacent to Cape Hatteras. The average velocities indicate a southwesterly flow - the Western Boundary Undercurrent. Maximum recorded velocities at each of the six locations ranged from 15 to 47 cm/sec. Depth distributions of suspended particulate matter over the transect indicated that near-bottom nepheloid layers were present and that relatively large amounts of suspended matter were being carried to the southwest. Bottom photographs taken over the same transect, however, showed no evidence that the sediment surface was being affected by the active bottom currents. These results indicate that swift bottom currents do not always leave a record of their work on deep ocean sediment. 相似文献
18.
Robert P. Griffiths Bruce A. Caldwell William A. Broich Richard Y. Morita 《Estuarine, Coastal and Shelf Science》1982,15(2):183-198
Subarctic marine sediments were exposed to fresh and ‘weathered’ crude oil from Cook Inlet, Alaska. The crude oil was thoroughly mixed with the sediment at various concentrations and some of the oil-sediment mixtures were placed on top of unamended sediments. Both sediments with added oil and those overlain by oiled sediments were investigated. These sediments were placed either in trays or aquaria. The trays were incubated in situ near the site from which the sediments were originally collected. The aquaria were maintained at simulated in situ conditions by maintaining a continuous flow of fresh seawater through them. The sediments were exposed to crude oil for periods up to 1.5 years. Sediments exposed to 50‰ fresh crude oil showed significant decreases in nitrogen fixation and denitrification rates and redox potentials. Also observed were increases in CO2 production rates and methane concentrations. These same changes were observed in sediments exposed to 1‰. When ‘weathered’ crude oil was added to the sediments, the same changes were observed except there was no reduction in nitrogen fixation activity. In most cases, the observed effects were less marked when the sediments were amended with ‘weathered’ crude oil than with the same concentration of fresh crude oil. Untreated sediments that were overlain with treated sediments showed the same changes as those sediments that were thoroughly mixed with crude oil. The presence of fresh crude oil at 50‰ essentially eliminated burrowing activity of the benthic infauna. Under these conditions, there was an accumulation of detritus particles on the oiled sediments that was not present in the untreated controls. 相似文献
19.
Laurie Biscara Thierry MulderPhilippe Martinez François BaudinHenri Etcheber Jean-Marie JouanneauThierry Garlan 《Marine and Petroleum Geology》2011,28(5):1061-1072
In order to define the nature and distribution of the organic matter (OM) preserved in the modern Ogooué deep sea turbidite system (Gabon), bulk geochemical techniques (Rock-Eval pyrolysis, elemental and isotopic analyses) and palynofacies were applied to three piston cores collected in the Cape Lopez Canyon and lobe and on the continental slope, north of the canyon.The hemipelagic sedimentation in the study area is characterized by high accumulations of well-preserved OM (∼2-3 wt. TOC %). Bulk geochemical and palynofacies analysis indicate both a marine and terrestrial origin of the OM. Contribution of the marine source is higher on the slope than in the canyon and lobe.OM accumulation in turbidites is strongly controlled by the combined influence of the Cape Lopez Canyon and littoral drift. In the canyon and lobe, turbidites show generally low TOC content (0.5 wt. %) and OM is oxidized. The origin of the OM is interpreted as both marine and terrestrial, with a higher contribution of continental source versus marine source. The low TOC contents are due to the large siliciclastic fraction transported by the littoral drift and diverted in the Cape Lopez Canyon during high energy processes (e.g. storms) which tend to dilute the OM in the turbidites. Transport by long-shore currents and/or turbiditic flows leads to oxidation of the OM.On the continental slope located north of the Cape Lopez Canyon, large amounts of OM are deposited in turbidites (up to 14 wt. %). The OM is predominantly derived from terrestrial land plants and has not been subjected to intense oxidation. These deposits are characterized by high hydrocarbon potential (up to 27 kg HC/t rock), indicating a good potential as gas-prone source rock. Because Cape Lopez Canyon captures a significant part of the sediment transported by the littoral drift, the siliciclastic sedimentary flux is reduced north of the canyon; OM is thus concentrated in the turbidites. Variation in TOC content within turbidite laminae can be explained by the burst and sweep deposition process affecting the boundary layer of the turbulent flow.This study confirms that gravity flows play a preponderant role in the accumulation and preservation of OM in deep water and that deep sea turbidite systems could be regarded as an environment where organic sedimentation occurs. 相似文献
20.
The vertical distribution of 30 species of benthic infauna from continental slope (583–3000 m) sediments off Cape Lookout, North Carolina was closely correlated with feeding types. Carnivores, omnivores, filter feeders, and surface deposit feeders were mostly concentrated in the upper 0–2 cm of the cores. The depth distribution of subsurface deposit feeders was more variable, even among related taxa. 相似文献