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1.
John E Damuth 《Marine Geology》1975,18(2):17-45
The floor of the western equatorial Atlantic Ocean can be divided into several distinct provinces based on detailed characteristics of the bottom echos recorded with short-ping (< msec.) 3.5 and 12 kHz sound sources. Two major types of echos are recorded: (I) distinct echos; and (II) indistinct echos.Indistinct echos can be further sub-divided into (A) continuous prolonged echos; and (B) hyperbolic echos. Each class of echos contains two or more unique echo types. The regional distributions of the various echo types recorded from the continental rise, Amazon Cone, and abyssal plains reveal much information about sedimentary processes.In the western equatorial Atlantic, hyperbolic echos are recorded only from small, isolated portions of the continental rise. This contrasts with the continental rise of the western North Atlantic where previous investigators have shown that hyperbolic echos parallel bathymetric contours along the entire rise and thus reflect shaping of the rise by geostrophic contour currents (Heezen et al., 1966; Hollister, 1967). The fact that regions of hyperbolic echos show little or no relationship to bathymetric contours of the continental rise of the western equatorial Atlantic suggests that contour currents have been unimportant in shaping the rise in this region.The three most widespread echo types recorded from the continental rise, Amazon Cone, and abyssal plains reveal much information about terrigenous sediment dispersal and deposition in the western equatorial Atlantic. Comparison of the thicknesses and frequencies of coarse (silt- to gravel-size), bedded, terrigenous sediment in piston cores with the echo type recorded at each coring site shows a correlation between echo type and the relative amount of coarse, bedded sediment within the upper few meters of the sea floor. The regional distributions of these three echo types indicate that dispersal of coarse terrigenous sediment has been downslope across the continental rise and Amazon Cone to the abyssal plains via gravity-controlled sediment flows. The Amazon River is the major sediment source and most coarse sediment is deposited on the lower Amazon Cone and proximal portions of the Demerara abyssal plain. 相似文献
2.
K. Solli B. Kuvaas Y. Kristoffersen G. Leitchenkov J. Guseva V. Gandjukhin 《Marine Geophysical Researches》2007,28(1):43-57
Multichannel seismic data from the eastern parts of the Riiser-Larsen Sea have been analyzed with a sequence stratigraphic
approach. The data set covers a wide bathymetric range from the lower continental slope to the abyssal plain. Four different
sequences (termed RLS-A to RLS-D, from deepest to shallowest) are recognized within the sedimentary section. The RLS-A sequence
encompasses the inferred pre-glacial part of the deposits. Initial phases of ice sheet arrival at the eastern Riiser-Larsen
Sea margin resulted in the deposition of multiple debris flow units and/or slumps on the upper part of the continental rise
(RLS-B). The nature and distribution of these deposits indicate sediment supply from a line or a multi-point source. The subsequent
stage of downslope sediment transport activity was dominated by turbidity currents, depositing mainly as distal turbidite
sheets on the lower rise/abyssal plain (RLS-C). We attribute this to margin progradation and/or a more focussed sediment delivery
to the continental shelf edge. As the accommodation space on the lower rise/abyssal plain declined and the base level was
raised, the turbidite channels started to backstep and develop large channel–levee complexes on the upper parts of the continental
rise (RLS-D). The deposition of various drift deposits on the lower rise/abyssal plain and along the western margin of the
Gunnerus Ridge indicates that the RLS-D sequence is also associated with increased activity of contour currents. The drift
deposits overlie a distinct regional unconformity which is considered to reflect a major paleoceanographic event, probably
related to a Middle Miocene intensification of the Antarctic Circumpolar Current. 相似文献
3.
通过研究南沙群岛西南海区44个站表层碳酸盐沉积特征,综合分析了沉积物类型、碳酸盐的生物组成、矿物成分、地球化学等,根据碳酸盐沉积的岩性参数之间的关系及相应的沉积环境,应用主成分分析统计对比,提出该海区碳酸盐沉积的六个沉积相及其特征:大陆坡半深海-深海相,南部中、外大陆架浅海相,西部中、外大陆架浅海相,南部内大陆架浅海相,礁体相,礁体过渡相。 相似文献
4.
中国东部晚更新世以来的海水进退 总被引：19，自引：4，他引：19
我国东部滨海平原及其以东的浅海陆架,是第四纪冰川时期海岸线往复迁移的地带.要掌握海水的进退边界及反复过程,必须在沉积层序学和年代学的广泛研究基础上,依据古滨线沉积和残留地貌标志,与世界典型地区的海面变化模式进行对比,才能获得冰川性海面变化及构造型海面变化在我国东部海面升降及海水进退过程中互相影响、相互消长的时空表现. 相似文献
5.
Ho Il Yoon Kyu-Cheul Yoo Young-Suk Bak Yong Il Lee Jae Il Lee 《Geo-Marine Letters》2009,29(5):309-320
A deep-sea sediment core (GC98-06) from the southernmost Drake Passage, West Antarctica, shows late Quaternary depositional
environments distinctly different from sedimentary drifts commonly found along the southwestern Pacific margin of the Drake
Passage. The chronology of the core has been inferred using geochemical tracers of paleoproductivity and diatom biostratigraphy,
and represents the paleoceanographic conditions in a continental rise setting during the last 150,000 years. Three dominant
sediment types associated with distinct sedimentary processes have been identified using textural/compositional analyses:
(1) hemipelagic mud (interglacial sediments) deposited from pelagic settling of bioclasts, meltwater plumes, and ice-rafted
detritus; (2) terrigenous mud (glacial sediments) delivered by turbid meltwater plumes; and (3) massive muds marking the boundaries
from interglacial to glacial periods. The succession of the sedimentary facies in core GC98-06 is interpreted to reflect temporal
changes in environmental conditions prevailing on the continental rise of the southern Drake Passage in the course of successive
climatic stages over the last 150 ka: from the bottom upward, these are glacial, interglacial, glaciation, glacial, and interglacial
episodes. Variability in sediment flux and diatom abundance seem to have been related to changes in glacial advance, sea-ice
extent, and specific sedimentary environments, collectively influenced by mid- to late Quaternary climatic changes. 相似文献
6.
Michels Klaus H. Rogenhagen Johannes Kuhn Gerhard 《Marine Geophysical Researches》2001,22(5-6):465-485
Sedimentary processes and structures across the continental rise in the western Weddell Sea have been investigated using sediment acoustic and multichannel seismic data, integrated with multibeam depth sounding and core investigations. The results show that a network of channels with associated along-channel ridges covers the upper continental slope. The seismic profiles reveal that the channels initially developed as erosive turbidite channels with associated levees on their northern side due to Coriolis force. Later they were partly or fully infilled, probably as a result of decreasing turbidite activity. Now the larger ones exist as erosive turbidite channels of reduced size, whereas the smaller ones are non-erosive channels, their shape being maintained by contour current activity. Drift bodies only developed where slumps caused a distinctive break in slope inclination on the upper continental rise, which served to initiate the growth of a drift body fed by contour currents or by the combined action of turbidites and contourites. The history of sedimentation can be reconstructed tentatively by correlation of seismo-stratigraphic units with the stages of evolution of the drifts on the western side of the Antarctic Peninsula. Three stages can be distinguished in the western Weddell Sea after a pre-drift stage, which is delimited by an erosional unconformity at the top: (1) a growth stage, dominated by turbidites, with occasional occurrence of slumps during its initial phase; (2) during a maintenance stage turbiditiy-current intensity (and presumably sedimentation rate also) decreased, probably as a result of the ice masses retreating from the shelf edge, and sedimentation became increasingly dominated by contour current activity; and (3) a phase of sheeted-sequence formation. A southward decrease in sediment thickness shows that the Larsen Ice Shelf plays an important role in sediment delivery to the western Weddell Sea. This study shows that the western Weddell Sea has some characteristics in common with the southern as well as the northwestern Weddell Sea: contour currents off the Larsen Ice Shelf have been present for a long time, probably since the late Miocene, but during times of high sediment input from the shelves as a result of advancing ice masses a channel-levee system developed and dominated over the contour-current transport of sediment. At times of relatively low sediment input the contour-current transport dominated, leading to the formation of drift deposits on the upper continental rise. Seaward of areas without shelf ice masses the continental rise mainly shows a rough topography with small channels and underdeveloped levees. The results demonstrate that sediment supply is an important, maybe the controlling factor of drift development on the Antarctic continental rise. 相似文献
7.
The nature and regional distributions of various types of bottom echoes recorded on 3.5-kHz echograms from the East Brazilian continental margin (8–30°S) provide valuable information about sedimentary processes which have been active on a regional scale. The ten types of echoes observed fall into two major classes: distinct and indistinct. Indistinct echoes have two sub-classes; prolonged and hyperbolic. A qualitative correlation is observed between three types of distinct and indistinct-prolonged echoes and the relative abundance of coarse, bedded sediment (silt, sand, gravel) in piston cores. Regions returning distinct echoes with continuous parallel sub-bottoms contain little or no coarse sediment; regions returning indistinct very prolonged echoes with no sub-bottoms contain very high concentrations of coarse sediment; and regions returning indistinct semiprolonged echoes with intermittent sub-bottoms contain moderate or intermediate amounts of coarse sediment. Thus the regional distributions of these three echo types reflect the dispersal of coarse terrigenous sediment throughout the region. High concentrations of coarse sediment are restricted to relatively small areas which are generally proximal to large deep-sea channels, whereas very low concentrations occur in distal regions such as the lowermost continental rise and adjacent abyssal plain. Moderate concentrations of coarse sediment occur throughout most of the continental rise. Five of the six types of hyperbolic echoes observed are reflected from erosional/depositional bed forms. Although some of these bed forms (especially on the upper continental rise) have probably been produced by gravity-controlled mass flows (turbidity currents, slumps, etc.) the fact that the most extensive and widespread regions of hyperbolic echoes occur in distal regions beneath the present axis of flow of the Antarctic Bottom Water suggests that most of these bed forms are the result of sediment reworking by the contour-following bottom currents of this water mass. 相似文献
8.
B. Kuvaas Y. Kristoffersen J. Guseva G. Leitchenkov V. Gandjukhin G. Kudryavtsev 《Marine Geophysical Researches》2004,25(3-4):247-263
Multichannel seismic reflection data from the Cosmonaut Sea margin of East Antarctica have been interpreted in terms of depositional
processes in the continental slope and rise area. A major sediment lens is present below the upper continental rise along
the entire Cosmonaut Sea margin. The lens probably consists of sediments supplied from the shelf and slope, being constantly
reworked by westward flowing bottom currents, which redeposited the sediments into a large scale drift deposit prior to the
main glaciogenic input along the margin. High-relief semicircular or elongated depositional structures are also found on the
upper continental rise stratigraphically above the regional sediment lens, and were deposited by the combined influence of
downslope and alongslope sediment transport. On the lower continental rise, large-scale sediment bodies extend perpendicular
to the continental margin and were deposited as a result of downslope turbidity transport and westward flowing bottom currents
after initiation of glacigenic input to the slope and rise. We compare the seismostratigraphic signatures along the continental
margin segments of the adjacent Riiser Larsen Sea, the Weddell Sea and the Prydz Bay/Cooperation Sea, focussing on indications
that may be interpreted as a preglacial-glaciomarine transition in the depositional environment. We suggest that earliest
glaciogenic input to the continental slope and rise occurred in the Prydz Bay and possibly in the Weddell Sea. At a later
stage, an intensification of the oceanic circulation pattern occurred, resulting in the deposition of the regional plastered
drift deposit along the Cosmonaut Sea margin, as well as the initiation of large drift deposits in the Cooperation Sea. At
an even later stage, possibly in the middle Miocene, glacial advances across the continental shelf were initiated along the
Cosmonaut Sea and the Riiser Larsen Sea continental margins. 相似文献
9.
10.
Debris flow deposits of large aerial extent have been detected on the lower continental rise off northwest Africa using GLORIA long-range dual sidescan sonar. A preliminary interpretation of the sonographs with high-resolution (3.5 kHz) seismic profiles and gravity cores illustrates the potential for spatial mapping of these deposits. The transport directions indicated on the sonographs show that these sediments, emplaced by mass transport, are the downslope continuation of the Saharan Sediment Slide. The distance from an observed “toe” of a debris flow lobe to the most southerly slide scar is of the order of 1,000 km. 相似文献
11.
Debris flow deposits of large aerial extent have been detected on the lower continental rise off northwest Africa using GLORIA
long-range dual sidescan sonar.
A preliminary interpretation of the sonographs with high-resolution (3.5 kHz) seismic profiles and gravity cores illustrates
the potential for spatial mapping of these deposits. The transport directions indicated on the sonographs show that these
sediments, emplaced by mass transport, are the downslope continuation of the Saharan Sediment Slide. The distance from an
observed “toe” of a debris flow lobe to the most southerly slide scar is of the order of 1,000 km. 相似文献
12.
台西南盆地地质构造特征及油气远景 总被引：7，自引：3，他引：7
杜德莉 《海洋地质与第四纪地质》1991,11(3):21-33
本文从盆地的基本地质特征入手,分析了台西南盆地的地层、沉积、构造特征及油气条件,在进行盆地的定性分析的基础上,对盆地内的次级构造单元进行了类比,对盆地的含油气远景进行了评价,提出了该盆地的油气勘探方向。 相似文献
13.
The relationship between acoustic backscatter, sediment characteristics and benthic habitat is examined using high-resolution sidescan sonar data collected at the Loch Linnhe artificial reef site on the west coast of Scotland. The site is typical for the continental shelf of NW Europe, with a mix of seabed environments from muddy to coarse, stony substrata on a 10–100 m length scale. A sidescan sonar mosaic was produced and classified according to derived backscatter parameters (mean, median and standard deviation of the backscatter values) using an unsupervised classification procedure. The accuracy of the final classified map was assessed by comparison with a ground-truthing survey in which the biological habitat was derived from underwater video footage. The sidescan correctly predicted seabed surface characteristics of observed biological habitat with 78% accuracy. A second, and more challenging test of the acoustic data to correctly predict biological habitat was made by comparing it with data from 21 grab sampling stations. These stations were divided into three groups using multivariate statistical techniques based on their backscatter properties. Benthic assemblage structure was found to be significantly distinct between the high and low, and the medium and low backscatter stations. There was a low to moderate but significant correlation between the multivariate patterns of acoustic backscatter, benthic assemblage structure, and particle size distribution. The work shows that even in areas with subtle and gradational changes in substratum, the sidescan was able to predict biological community with an acceptable accuracy. 相似文献
14.
Stratigraphic framework of sediment-starved sand ridges on a mixed siliciclastic/carbonate inner shelf; west-central Florida 总被引：1，自引：0，他引：1
J. H. Edwards S. E. Harrison S. D. Locker A. C. Hine D. C. Twichell 《Marine Geology》2003,200(1-4):195-217
Seismic reflection profiles and vibracores have revealed that an inner shelf, sand-ridge field has developed over the past few thousand years situated on an elevated, broad bedrock terrace. This terrace extends seaward of a major headland associated with the modern barrier-island coastline of west-central Florida. The overall geologic setting is a low-energy, sediment-starved, mixed siliciclastic/carbonate inner continental shelf supporting a thin sedimentary veneer. This veneer is arranged in a series of subparallel, shore-oblique, and to a minor extent, shore-parallel sand ridges. Seven major facies are present beneath the ridges, including a basal Neogene limestone gravel facies and a blue-green clay facies indicative of dominantly authigenic sedimentation. A major sequence boundary separates these older units from Holocene age, organic-rich mud facies (marsh), which grades upward into a muddy sand facies (lagoon or shallow open shelf/seagrass meadows). Cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies (ravinement or sudden termination of seagrass meadows). The shelly sand facies grades upward to a mixed siliciclastic/carbonate facies, which forms the sand ridges themselves. This mixed siliciclastic/carbonate facies differs from the sediment on the beach and shoreface, suggesting insignificant sediment exchange between the offshore ridges and the modern coastline. Additionally, the lack of early Holocene, pre-ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively. Radiocarbon dating has indicated that these sand ridges can form relatively quickly (1.3 ka) on relatively low-energy inner shelves once open-marine conditions are available, and that frequent, high-energy, storm-dominated conditions are not necessarily required. We suggest that the two inner shelf depositional models presented (open-shelf vs. migrating barrier-island) may have co-existed spatially and/or temporally to explain the distribution of facies and vertical facies contacts. 相似文献
15.
The South China Sea (SCS) shows favorable conditions for gas hydrate accumulation and exploration prospects. Bottom simulating reflectors (BSRs) are widely distributed in the SCS. Using seismic and sequence stratigraphy, the spatial distribution of BSRs has been determined in three sequences deposited since the Late Miocene. The features of gas hydrate accumulations in northern SCS were systematically analyzed by an integrated analysis of gas source conditions, migration pathways, heat flow values, occurrence characteristics, and depositional conditions (including depositional facies, rates of deposition, sand content, and lithological features) as well as some depositional bodies (structural slopes, slump blocks, and sediment waves). This research shows that particular geological controls are important for the presence of BSRs in the SCS, not so much the basic thermodynamic controls such as temperature, pressure and a gas source. Based on this, a typical depositional accumulation model has been established. This model summarizes the distribution of each depositional system in the continental shelf, continental slope, and continental rise, and also shows the typical elements of gas hydrate accumulations. BSRs appear to commonly occur more in slope-break zones, deep-water gravity flows, and contourites. The gas hydrate-bearing sediments in the Shenhu drilling area mostly contain silt or clay, with a silt content of about 70%. In the continental shelf, BSRs are laterally continuous, and the key to gas hydrate formation and accumulation lies in gas transportation and migration conditions. In the continental slope, a majority of the BSRs are associated with zones of steep and rough relief with long-term alternation of uplift and subsidence. Rapid sediment unloading can provide a favorable sedimentary reservoir for gas hydrates. In the continental rise, BSRs occur in the sediments of submarine fans, turbidity currents. 相似文献
16.
Kathryn M. Scanlon 《Geo-Marine Letters》1984,4(1):1-4
The first continuous overview of a large segment of the continental slope and rise off the northeastern United States has been obtained using the GLORIA II long-range sidescan-sonar system. Extensive dissection by canyon and gully systems and evidence of possible large-scale sediment sliding are seen on the slope. The style and degree of incision, as well as the numbers and locations of canyons, have been found to differ significantly from previously published maps. It is suggested that the slope is a significant source of the sediment that has been deposited on the rise, and that some abrupt changes in the courses of canyons may be the result of local structural control. 相似文献
17.
《Marine Geology》2007,236(1-2):1-13
The direct record of Late Miocene–Early Pliocene Antarctic Peninsula Ice Sheet expansions from a previously published seismostratigraphic study of the outer shelf at Ocean Drilling Program Site 1097 is compared to the glacial history we deduced from published proxy evidence within coeval sections on the adjacent continental rise. The proxies are sedimentary structures (laminated vs. massive/bioturbated facies) and clay minerals (predominantly smectite and chlorite contents) from Ocean Drilling Program Site 1095 located on the distal part of a large drift. The comparison shows that more sedimentary cycles are evident on the continental rise for three of the four diatom biozones we considered. This indicates that the continental-rise sedimentology may indeed be related to local or regional paleoenvironmental variability, including Antarctic Peninsula Ice Sheet grounding events on the adjacent outer continental shelf. If correct, this would be a promising result because unlike the outer continental shelf sequences drilled thus far, the continental rise record is relatively continuous and can be dated using paleomagnetic and biostratigraphic data. However, our study also shows that no objective criteria provide direct linkages between the glacial history we deduced from the two continental rise proxies and that previously derived from the continental-shelf seismic stratigraphy. Furthermore, the two sedimentologic proxies on the continental rise do not always provide a consistent picture of glacial history when compared against each other. 相似文献
18.
H.A. Karl W.C. Schwab A.St.C. Wright D.E. Drake J.L. Chin W.W. Danforth E. Ueber 《Ocean & Coastal Management》1994,22(3)
The oceans have been and will continue to be disposal sites for a wide variety of waste products. Often these wastes are not dumped at the designated sites or transport occurs during or after dumping, and, subsequent attempts to monitor the effects the waste products have on the environment are inadequate because the actual location of the waste is not known. Acoustic mapping of the seafloor with sidescan sonar is a very effective technique for locating and monitoring dredge-spoil material and other debris. Sidescan sonar provides an acoustic image or sonograph of the sea floor that is similar to a satellite image of the Earth's land surface. In effect sidescan sonar allows the water column to be stripped from the sea floor, thereby providing a clear, unobstructed view of the sea bed.An example of the potential of this technique is summarized herein for the Gulf of the Farallones region. More than 47 800 drums (55 gallon) and other containers of low-level radioactive waste were dumped on the continental margin offshore the San Francisco Bay between 1946 and 1970. These drums now litter a large area (1200 km2) of the sea floor within the Gulf of the Farallones National Marine Sanctuary (GFNMS). The exact location of the drums and the potential hazard the drums pose to the environment are unknown. To evaluate the risk, samples of the sediment, biota and water must be collected near and distant from the concentrations of barrels. To do this the exact location of the barrels must be known prior to sampling. The USGS, through a cooperative research agreement with GFNMS, used sidescan sonar to map two areas within the sanctuary. Total sea-floor coverage was obtained and computer-processed sonographic mosaics were constructed on board ship. Many small nongeologic targets were distributed throughout the survey areas that covered about 70 km2 on the shelf and 120 km2 on the slope. Analysis of the sidescan data suggests that the targets are 55-gallon drums. This interpretation was confirmed at one site with an underwater video and 35-mm camera system. Data were collected with both a 30-kHz and a 120-kHz sidescan system within a 15-km2 area on the shelf. We found that the barrels were more easily detected with the mid-range 30-kHz system than with the higher resolution 120-kHz system. Maps of barrel distribution derived from the sonographs are being used to design sampling schemes to evaluate the risk that the radioactivity may have on the biota and environment. 相似文献
19.
Evidence from over 200 sediment cores, numerous submersible dives, and bottom photographs prove that bioturbation and bioerosion are ongoing processes affecting northeastern U.S. continental slope and rise sedimentation. Evidence of biological activity was found in greater than 95% of the cores examined. Submersible dive observations reveal that the results of biological activity often dominate sea-floor microtopography. Bioturbation can disturb sediments several centimeters deep in a matter of seconds and is in some areas the primary sediment transport mechanism. Many cores with sandy intervals were profoundly disturbed by bioturbation. Biologically camouflaged sand-rich intervals can easily be missed by visual observation. 相似文献
20.
《Marine Geology》2005,214(4):431-449
The dependence of acoustic backscatter on sediment grain size distribution is examined using dual frequency (100 and 410 kHz) sidescan sonar and 22 sediment grab samples from the Loch Linnhe artificial reef site on the west coast of Scotland. The sidescan data were processed to remove an empirically estimated average grazing angle dependence on backscatter. The processed data were analysed by forming histograms of pixels extracted from a 20 m2 box around each ground truth site. A positive correlation (r=0.73) between mean backscatter intensity and mean grain size was obtained, i.e., the coarsest samples had the brightest backscatter. A positive correlation (r=0.59) was also found between the standard deviations of the backscatter and grain size distributions, i.e., poorly sorted sediments gave the most variable backscatter. The performance of the sidescan data was compared to results from a co-incident single-beam echo-sounder RoxAnn survey. The RoxAnn roughness index E1 compared well with the sidescan, whilst the RoxAnn hardness index E2 did not. This may be due to a physical link between the acoustic measures. The comparison showed the sidescan to have delivered a significantly higher-resolution image of the seabed for a similar amount of ship-time. Imaging of the artificial reef modules themselves was found to be frequency dependent. 相似文献