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1.
Bengal Submarine Fan, with or without its eastern lobe, the Nicobar Fan, is the largest submarine fan known. Most of its sediment has been supplied by the Ganges and Brahmaputra Rivers, probably since the Early Eocene. The “Swatch-of-No-Ground” submarine canyon connects to only one active fan valley system at a time, without apprent bifurcation over its 2500-km length. The upper fan is comprised of a complex of huge channel-levee wedges of abandoned and buried older systems. A reduction of channel size and morphology occurs at the top of the middle, fan, where meandering and sheet flow become more important. 相似文献
2.
Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern
of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In
contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition
on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest
of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in
the locus of deposition.
Margin setting represents fan and/or source area 相似文献
3.
Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition. 相似文献
4.
The Bengal Fan is the largest submarine fan in the world, with a length of about 3000 km, a width of about 1000 km and a maximum thickness of 16.5 km. It has been formed as a direct result of the India–Asia collision and uplift of the Himalayas and the Tibetan Plateau. It is currently supplied mainly by the confluent Ganges and Brahmaputra Rivers, with smaller contributions of sediment from several other large rivers in Bangladesh and India.The sedimentary section of the fan is subdivided by seismic stratigraphy by two unconformities which have been tentatively dated as upper Miocene and lower Eocene by long correlations from DSDP Leg 22 and ODP Legs 116 and 121. The upper Miocene unconformity is the time of onset of the diffuse plate edge or intraplate deformation in the southern or lower fan. The lower Eocene unconformity, a hiatus which increases in duration down the fan, is postulated to be the time of first deposition of the fan, starting at the base of the Bangladesh slope shortly after the initial India–Asia collision.The Quaternary of the upper fan comprises a section of enormous channel-levee complexes which were built on top of the preexisting fan surface during lowered sea level by very large turbidity currents. The Quaternary section of the upper fan can be subdivided by seismic stratigraphy into four subfans, which show lateral shifting as a function of the location of the submarine canyon supplying the turbidity currents and sediments. There was probably more than one active canyon at times during the Quaternary, but each one had only one active fan valley system and subfan at any given time. The fan currently has one submarine canyon source and one active fan valley system which extends the length of the active subfan. Since the Holocene rise in sea level, however, the head of the submarine canyon lies in a mid-shelf location, and the supply of sediment to the canyon and fan valley is greatly reduced from the huge supply which had existed during Pleistocene lowered sea level. Holocene turbidity currents are small and infrequent, and the active channel is partially filled in about the middle of the fan by deposition from these small turbidity currents.Channel migration within the fan valley system occurs by avulsion only in the upper fan and in the upper middle fan in the area of highest rates of deposition. Abandoned fan valleys are filled rapidly in the upper fan, but many open abandoned fan valleys are found on the lower fan. A sequence of time of activity of the important open channels is proposed, culminating with formation of the one currently active channel at about 12,000 years BP. 相似文献
5.
Paul Weimer 《Geo-Marine Letters》1989,9(4):185-272
The Mississippi Fan is a large, mud-dominated submarine fan over 4 km thick, deposited in the deep Gulf of Mexico during the
late Pliocene and Pleistocene. Analysis of 19,000 km of multifold seismic data defined 17 seismic sequences, each characterized
by channel, levee, and associated overbank deposits, as well as mass transport deposits. At the base of nine sequences are
a series of seismic facies consisting of mounded, hummocky, chaotic, and subparallel reflections, which constitute 10–20%
of the sediments in each the sequences. These facies are externally mounded and occur in two general regions of the fan: (1)
in the upper and middle fan they are elongate in shape and mimic the channel's distribution; (2) in the middle fan to lower
fan they are characterized by a fan-shaped distribution, increasing in width downfan. These facies are interpreted to have
formed as disorganized slides, debris flows, and turbidites (informally called “mass transport complexes”).
Overlying this basal interval, characteristic of all sequences, are well-developed channel-levee systems that constitute 80–90%
of the fan's sediments. Channels consist of high amplitude, subparallel reflections, whereas the flanking levee sediments
appear as subparallel reflections that have high amplitudes at the base changing upward to low amplitude. The vertical change
in amplitude may reflect a decrease in grain size and bed thicknesses. Overbank sediments are characterized by interbedded
subparallel to hummocky and mounded reflections, suggesting both turbidites from the channel, as well as slides and debris
flows derived both locally and from the slope updip. 相似文献
6.
The Mississippi Fan is a Quarternary accumulation composed of more than seven elongated fan lobes. Isopach and structure maps
show frequent shifting of these lobes. The Mississippi Canyon, formed by retrogressive slumping, connects to the youngest
fan lobe. The upper fan-lobe is characterized by a large, incised, partially infilled, leveed channel. The middle fan-lobe
is aggradational, convex in cross section, with a channel-levee complex on its apex. The lower fan-lobe contains a recently
active small channel and several abandoned ones. Depositional patterns can be explained by several processes: “fluvial,” debris
flows, and turbidity currents.
Margin setting represents fan and/or source area 相似文献
7.
Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland.
The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present
onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions
into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual
turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene
depositional processes.
Margin setting represents fan and/or source area 相似文献
8.
C. Hans Nelson 《Geo-Marine Letters》1984,3(2-4):65-70
The Astoria Fan, a modern system, is located on a subducting oceanic crust and fills a north-south-trending trench along the
Oregon continental margin. Well-developed channels cross the entire fan length; they display classic inner-fan leveed profiles
but evolve into distributaries in the midfan area where the gradient decreases sharply. During periods of low sea level, inner-
and middle-fan channels funnel sand to distal depositional sites in the outer-fan area where the sand/shale ratios are highest.
This pattern of sand displacement and efficiency of transport appears to be characteristic of elongate fans fed by a major
river and submarine canyon.
Margin setting represents fan and/or source area 相似文献
9.
The Delgada Fan, an irregularly shaped turbidite deposit extending more than 350 km offshore from northern California, consists
of two large leveed-valley units each fed by a separate complex of coalescing submarine canyons and slope gullies. Although
the leveed-valley units head within 25 km of each other, both appear to have developed independently during fan growth. The
larger southern leveed-valley system has not developed middle-fan distributary channels and appears to illustrate a period
of progressive valley abandonment. Although the lower-fan area is underlain by sandy sediments, little sand has been recovered
in piston cores from the leveed-valley unit.
Margin setting represents fan and/or source area 相似文献
10.
The upper Indus Fan is characterized by an average 1∶500 gradient, chanels with 100 m high levees, several continuous subbottom
reflectors on 3.5-kHz records, and generally fine-grained sediments. Multichannel seismics show the levee complexes typified
by overlapping wedge-shaped reflection sets and channel axis by high-amplitude discontinuous reflections. The middle fan has
1∶500–1∶1000 gradients and channels with ≈20 m high levees. The lower fan has gradients less than 1∶1000, channels with 8–20
m high levees, few or no subbottom reflectors on 3.5-kHz records, and high sand content. Besides the dominant unchannelized
turbidity currents, channelized and overbank flows also played a significant role in the sedimentation of the lower fan.
Margin setting represents fan and/or source area 相似文献
11.
C. Hans Nelson 《Geo-Marine Letters》1983,3(2-4):65-70
The Astoria Fan, a modern system, is located on a subducting oceanic crust and fills a north-south-trending trench along the Oregon continental margin. Well-developed channels cross the entire fan length; they display classic inner-fan leveed profiles but evolve into distributaries in the midfan area where the gradient decreases sharply. During periods of low sea level, inner- and middle-fan channels funnel sand to distal depositional sites in the outer-fan area where the sand/shale ratios are highest. This pattern of sand displacement and efficiency of transport appears to be characteristic of elongate fans fed by a major river and submarine canyon. 相似文献
12.
Wonn Soh 《Progress in Oceanography》2003,57(1):109-124
Sagami Bay is a deep-water foreland basin with an average sedimentary rate of approximately 0.1 g/cm2/year. It is an appropriate area to study for better understanding of sedimentary processes in a setting with a high sedimentation rate. Seven multiple core samples, 30-50 cm thick, were obtained from Sagami Bay. Four of the core samples were taken from the Tokyo submarine fan system (Tokyo canyon floor, Tokyo fan valley and its levee, the distal fan margin). Two samples were obtained from the Sakawa fan delta and the adjacent topographic high. The remaining one was from an escarpment of the Sagami submarine fault. Variations in chemical composition can be recognized at every coring site. They show two different sediment sources: the sediments of the Tokyo submarine fan system and those from Sakawa fan delta. Further, there are differences in chemical composition between canyon floor and levees even within the Tokyo submarine fan system. The results suggest that the sedimentary process is strongly controlled not by vertical particle settling but by a hyperpycnal flow process. The proxies obtained from the core samples do not reflect conditions in the water column immediately overlying the sea floor. Rather, they are controlled by conditions on the adjacent continental shelf or/and shallow basins, which are the areas of primary accumulation. 相似文献
13.
There are many large-scale Cenozoic sedimentary basins with plentiful river deltas, deep-water fans and carbonate platforms in the southern South China Sea. The Crocker Fan was deposited as a typical submarine fan during the late Eocene–early Miocene, and stretches extensively across the entire Sarawak–Sabah of the northern Borneo area. However, systematic analyses are still lacking regarding its sediment composition and potential source suppliers. No consensus has been reached yet on the provenance evolution and sedimentary infilling processes, which seriously impeded the oil-and-gas exploration undertakings. By combining with sedimentary-facies identification, heavy mineral assemblages, elemental geochemistry and detrital zircon U-Pb dating, this paper aims to generalize an integrated analysis on the potential provenance terranes and restore source-to-sink pathways of the Crocker Fan. In general, the Crocker Fan was initially formed over the Cretaceous–lower/middle Eocene Rajang Group by an angular Rajang unconformity. The continual southward subduction of the proto-South China Sea resulted in magmatic activities and subsequent regional deformation and thrusting along the Lupar Line in the northern Borneo. The lowermost Crocker sequence is featured by a thick conglomerate layer sourced from in-situ or adjacent paleo-uplifts. From the late Eocene to the early Miocene, the Crocker Fan was constantly delivered with voluminous detritus from the Malay Peninsula of the western Sundaland. The Zengmu Basin was widely deposited with delta plain and neritic facies sediments, while the Brunei-Sabah Basin, to the farther east, was ubiquitously characterized by turbiditic sequences. The Crocker Fan successions are overall thick layers of modest-grained sandstones, which formed high-quality reservoirs in the southern South China Sea region. 相似文献
14.
The Bounty Channel and Fan system provides the basis for a model for deep-sea channel and fan development in a rifted continental margin setting. The sedimentary system results from an interplay between tectonics (fan location; sediment source), turbidity currents (sediment supply), geostrophic currents (sediment reworking and distribution) and climate (sea level, and hence sediment supply and type). Today, sediment is shed from the collisional Southern Alps, part of the Pacific/Indo-Australian plate margin, and passes east across the adjacent shelf and into the Otago Fan complex at the head of the Bounty Trough. Paths of sediment supply, and locations of sediment deposition, are controlled by the bathymetry of the Bounty Trough, with axial slopes as high as 37 m/km (2°) towards the trough head, diminishing to around 3.5 m/km (0.2°) along the trough axis. The Bounty Fan is located 800 km further east, where the Bounty Channel debouches onto abyssal oceanic crust at the mouth of the Bounty Trough. The Bounty Fan comprises a basement controlled fan-channel complex with high leveed banks exhibiting fields of mud waves, and a northward-elongated middle fan. Channel-axis gradients diminish from 6 m/km (0.35°) or more on the upper fan to less than 1 m/km (<0.06°) on the lower fan. Parts of the left bank levee and almost the entire middle fan are being eroded and re-entrained within a Deep Western Boundary Current (DWBC), which passes along the eastern New Zealand margin at depths below 2000 m. The DWBC is the prime source of deep, cold water flow into the Pacific Ocean, with a volume of ca. 20 Sv and velocities up to 4 cm/s or greater. The mouth of the Bounty Channel, at a depth of 4950 m at the south end of the middle fan, acts as a point source for an abyssal sediment drift entrained northward under the DWBC at depths below 4300 m. The Bounty Fan probably originated in the early to middle Neogene, but has mostly been built during the last 3 Myr (Plio-Pleistocene), predominantly as climate-controlled sedimentary couplets of terrigenous, micaceous mud (acoustically reflective; glacial) and biopelagic ooze (acoustically transparent; interglacial), deposited under the pervasive influence of the DWBC. 相似文献
15.
《Marine and Petroleum Geology》2003,20(6-8):823-849
Quantifying the characteristics of the turbidity currents that are responsible for the erosion, lateral migration and filling of submarine channels maybe useful for predicting the distribution of lithofacies in channel fill and levee reservoirs. This paper uses data from a well-studied submarine channel in Amazon Fan in an attempt to reconstruct the velocity, thickness, concentration, duration, recurrence rates and vertical structure of turbidity currents in this long sinuous channel. Estimates of flow conditions are derived from the morphology of the channels and the characteristics of the deposits within them. In particular, the availability of information on the sediment distribution with respect to the channel topography at the time of deposition allows for insights into the vertical structure of the flow, a key property that has been so far poorly understood. Integration of flow constraints from well and seismic data or from detailed analysis of outcrop with numerical flow models is a critical step toward a complete understanding of the flow and associated deposits. Turbidity currents in sinuous submarine channels, exemplified by Amazon Channel, are found to last for tens of hours and occur on a regular, quasi-annual basis. Model results suggest that these flows had, on average, velocities ranging from 2 to 4 m/s in the canyon/upper fan which decreased to 0.5–1 m/s in the lower fan, travelling in excess of 800 km. The model turbidity currents were subcritical over most of the channel length, indicating a low degree of water entrainment and low rate of deceleration down the channel. The formation of such long, sinuous channels is intrinsically associated with frequent, long-duration, subcritical turbidity currents carrying a silt-dominated sediment load. 相似文献
16.
A. S. Subrahmanyam K. S. R. Murthy S. Lakshminarayana M. M. Malleswara Rao K. Venkateswarlu T. C. S. Rao 《Geo-Marine Letters》1997,17(3):202-206
Magnetic data over the eastern continental margin of India and adjacent Bengal fan demarcate two major lineaments. A high
amplitude N–S-trending lineation of the Cauvery offshore Basin corresponds to the offshore fragment of the 80°E lineament
recorded onland. A N–S lineation of very high amplitude anomaly off Chilka lake considered as the possible northward extension
of the 85°E ridge delineated, hitherto in Bengal Fan. A subdued magnetic anomaly zone is demarcated seaward of the continent–ocean
boundary (COB) in the Bengal Fan. Over the northern Bengal Fan this zone is delineated east of 85°E lineation. This quiet
zone might have evolved during the Early Cretaceous period of normal magnetic polarity between M0 and 34 (120–84 Ma) anomalies.
Received: 6 April 1995 / Revision received: 3 September 1996 相似文献
17.
The Magdalena Fan can be divided into: upper fan—1:60–1:110 gradients, channels with well-developed levees, generally several
subbottom reflectors on 3.5-kHz records, and fine-grained sediments; middle fan—1:110–1:200 gradients, channels with very
subdued levees, several to few subbottom reflectors on 3.5-kHz records, and chaotic and discontinuous reflections on multichannel
seismic (MCS) records; lower fan—<1:250 gradients, small channels and relatively smooth seafloor, generally coarsegrained
sediments, few or no subbottom reflectors on 3.5-kHz records, and flat continuous reflections on MCS records. In addition
to the turbidity currents, slumping along the continental slope and elsewhere also influenced sedimentation in the fan.
Margin setting represents fan and/or source area 相似文献
18.
Using bathymetry and reflection seismic profiles this study reveals the nature of the modern ponded Fangliao Fan within a framework of sediment infilling of an intra-slope basin on a tectonically active margin off southwestern Taiwan. The Fangliao Fan begins at the mouth of Fangliao Canyon at a water depth of 900 m and terminates down-slope at the escarpment of a linear ridge north of the Kaoping Slope Valley at a water depth of about 1,100 m, sediment gravity flows being prevented from farther down-slope transport due to ponding against this bathymetric high. The fan appears as a distinct basinward-opening triangular depocenter confined by ridges on both sides and the NW–SE trending ridge aligned normal to the elongation of the fan. These topographic ridges were formed by mud-diapiric intrusions. The external form of the ponded Fangliao Fan is characterized by a fan-valley fill pattern that has a concave cross-sectional morphology, in contrast to typical mounded fans deposited on slope-basin plains having a smooth topography. Sediment episodically funneled through the Fangliao Canyon from upslope areas and derived from the flanks of the mud-diapiric ridges are mainly transported by mass movement before being re-dispersed by unconfined channels to infill the intra-slope basin, thereby building up channelized fan complexes with poorly developed levees. The sediment flows from the mouth of Fangliao Canyon flow down-slope along the west flank of the Fangliao Ridge. In the process, a feeder channel has been eroded into the seafloor along which sediment is transported to the distal parts of the fan. Sediment west of the feeder channel is mainly redistributed by mass movement and/or fan channels to fill up the irregular topographic low in the slope. Due to a very low sediment supply, Fangliao Fan represents a starved ponded slope fan. As such it provides insights into the processes by which ponded fans develop and can therefore serve as an analog for similar fans developed on topographically complex slopes elsewhere. The morpho-structural features of the Fangliao Fan resulted from the interplay between sediment supply, uplift of the mud-diapiric ridge, mass movements, and alternating incision and deposition. 相似文献
19.
Active tectonic morphology and submarine deformation of the northern Gulf of Eilat/Aqaba from analyses of multibeam data 总被引：1，自引：0，他引：1
Gideon Tibor Tina M. Niemi Zvi Ben-Avraham Abdallah Al-Zoubi Ronnie A. Sade John K. Hall Gal Hartman Emad Akawi Abdelrahmem Abueladas Rami Al-Ruzouq 《Geo-Marine Letters》2010,30(6):561-573
A high-resolution marine geophysical study was conducted during October-November 2006 in the northern Gulf of Aqaba/Eilat,
providing the first multibeam imaging of the seafloor across the entire gulf head spanning both Israeli and Jordanian territorial
waters. Analyses of the seafloor morphology show that the gulf head can be subdivided into the Eilat and Aqaba subbasins separated
by the north-south-trending Ayla high. The Aqaba submarine basin appears starved of sediment supply, apparently causing erosion
and a landward retreat of the shelf edge. Along the eastern border of this subbasin, the shelf is largely absent and its margin
is influenced by the Aqaba Fault zone that forms a steep slope partially covered by sedimentary fan deltas from the adjacent
ephemeral drainages. The Eilat subbasin, west of the Ayla high, receives a large amount of sediment derived from the extensive
drainage basins of the Arava Valley (Wadi ’Arabah) and Yutim River to the north–northeast. These sediments and those entering
from canyons on the south-western border of this subbasin are transported to the deep basin by turbidity currents and gravity
slides, forming the Arava submarine fan. Large detached blocks and collapsed walls of submarine canyons and the western gulf
margin indicate that mass wasting may be triggered by seismic activity. Seafloor lineaments defined by slope gradient analyses
suggest that the Eilat Canyon and the boundaries of the Ayla high align along north- to northwest-striking fault systems—the
Evrona Fault zone to the west and the Ayla Fault zone to the east. The shelf–slope break that lies along the 100 m isobath
in the Eilat subbasin, and shallower (70–80 m isobaths) in the Aqaba subbasin, is offset by approx. 150 m along the eastern
edge of the Ayla high. This offset might be the result of horizontal and vertical movements along what we call the Ayla Fault
on the east side of the structure. Remnants of two marine terraces at 100 m and approx. 150 m water depths line the southwest
margin of the gulf. These terraces are truncated by faulting along their northern end. Fossil coral reefs, which have a similar
morphological appearance to the present-day, basin margin reefs, crop out along these deeper submarine terraces and along
the shelf–slope break. One fossil reef is exposed on the shelf across the Ayla high at about 60–63 m water depth but is either
covered or eroded in the adjacent subbasins. The offshore extension of the Evrona Fault offsets a fossil reef along the shelf
and extends south of the canyon to linear fractures on the deep basin floor. 相似文献
20.
C. Hans Nelson Andres Maldonado Francis Coumes Henri Got Andre Manaco 《Geo-Marine Letters》1984,3(2-4):125-131
The Ebro Fan System consists of en echelon channel-levee complexes, 50×20 km in area and 200-m thick. A few strong reflectors
in a generally transparent seismic facies identify the sand-rich channel floors and levee crests. Numerous continuous acoustic
reflectors characterize overbank turbidites and hemipelagites that blanket abandoned channel-levee complexes. The interlobe
areas between channel complexes fill with homogeneous mud and sand from mass flow and overbank deposition; these exhibit a
transparent seismic character. The steep continental rise and sediment “drainage” of Valencia Trough at the end of the channel-levee
complexes prevent the development of distributary channels and midfan lobe deposits.
Margin setting represents fan and/or source area 相似文献