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1.
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
2.
Jude A. Castelino Christian Reichert Wilfried Jokat 《Marine Geophysical Researches》2017,38(3):209-226
Submarine fans and turbidite systems are important and sensitive features located offshore from river deltas that archive tectonic events, regional climate, sea level variations and erosional process. Very little is known about the sedimentary structure of the 1800 km long and 400 km wide Mozambique Fan, which is fed by the Zambezi and spreads out into the Mozambique Channel. New multichannel seismic profiles in the Mozambique Basin reveal multiple feeder systems of the upper fan that have been active concurrently or consecutively since Late Cretaceous. We identify two buried, ancient turbidite systems off Mozambique in addition to the previously known Zambezi-Channel system and another hypothesized active system. The oldest part of the upper fan, located north of the present-day mouth of the Zambezi, was active from Late Cretaceous to Eocene times. Regional uplift caused an increased sediment flux that continued until Eocene times, allowing the fan to migrate southwards under the influence of bottom currents. Following the mid-Oligocene marine regression, the Beira High Channel-levee complex fed the Mozambique Fan from the southwest until Miocene times, reworking sediments from the shelf and continental slope into the distal abyssal fan. Since the Miocene, sediments have bypassed the shelf and upper fan region through the Zambezi Valley system directly into the Zambezi Channel. The morphology of the turbidite system off Mozambique is strongly linked to onshore tectonic events and the variations in sea level and sediment flux. 相似文献
3.
A large submarine slide on the southern flank of the Bear Island Trough Mouth Fan, southwestern Barents Sea continental slope, has a run-out distance of about 400 km, a total volume of about 1100 km3, and is younger than 330 ka. Three seismic units, comprising mainly hemipelagic sediments has partly filled the slide scar. An increased sedimentation rate on the Bear Island Trough Mouth Fan from Late Pliocene time, probably in combination with abundant earthquakes, is the most likely cause of the slide. Based on these and previous studies, we suggest that large-scale slides were important sediment transport processes during Plio-Pleistocene. 相似文献
4.
Escanaba Trough, the median valley of Gorda Ridge, is partly filled with terrigenous sediment which was eroded mostly from rocks in the Klamath and Columbia River drainage basins and transported across the sea floor to the trough by turbidity currents. Basal or lower cores contain sand derived from the south-central metamorphic belt of the Klamath Mountains, whereas the upper cores have sand derived from the Columbia River drainage basin. Columbia River sediment reached Escanaba Trough either after a barrier at Blanco Valley had been destroyed by tectonic movement or after a gradient, sufficient to maintain turbidity current momentum, had developed between the Astoria Fan apex and the trough. Sediment in Escanaba Trough is young and most probably was deposited when sea level was lower than at present, perhaps during the Wisconsin Glacial Age. 相似文献
5.
Near-seabed (<50 m) sediments were studied throughout the Irish sector of the Rockall Trough (ca. 123,000 km2) based on a combined analysis of shallow seismic (3.5 kHz) and multibeam swath data acquired by the Irish National Seabed Survey and reprocessed here at higher resolution. The detailed identification of seven acoustic facies served to classify the Rockall Trough into six main sedimentary provinces, incorporating the well-known Feni Drift, Donegal-Barra Fan and Rockall Bank mass flow. In the northern part of the study area, extensive mass transport deposits from both flanks of the trough are the dominant depositional features. Debris flow deposits formed by ice streaming of the British-Irish ice sheet characterise most of the Donegal-Barra Fan, whereas turbidite deposition occurs towards the toe of the fan. On the western margin of the trough, the post-glacial Rockall Bank mass flow deposit displays a rough topography with no acoustic penetration. Several failure scarps are visible on the flank of the bank where the mass flow originated, and pass downslope into large sediment lobes and smaller debris flow deposits. Smaller-scale mass transport deposits were also discovered close to some canyons indenting the eastern slope. High seismic penetration characterises the Feni contourite drift deposit, and precise mapping of its geographical extent shows that it is considerably wider than previously reported. The sediment waves that drape this drift are interpreted as predominantly relict features, and their varied geometry suggests a complex oceanographic regime. In the deeper part of the trough, the data reveal novel evidence of the widespread occurrence (about 12,000 km2) of distinct seismic and backscatter signatures indicating the possible presence of fluid escape structures within fine-grained sediments of mixed contouritic, hemipelagic and turbiditic origin. Sediment overloading and increased pore pressure resulting from extensive mass wasting to the north of the area is a likely cause of dewatering-rooted fluid migration towards the seabed, but further investigations are required to confirm the nature and origin of such fluids in the Rockall Trough. 相似文献
6.
Deep currents such as the Pacific Deep Western Boundary Current (DWBC) are strengthened periodically in Milankovitch cycles. We studied periodic fluctuations in seismic reflection pattern and reflection amplitude in order to detect cycles in the sedimentary layers of Bounty Trough and bounty fan, east of New Zealand. There, the occurrence of the obliquity frequency is caused only by the DWBC. Therefore, it provides direct evidence for the spatial extent of the DWBC. We can confirm the extent of the DWBC west of the outer sill, previously only inferred via erosional features at the outer sill. Further, our data allow an estimation of the extent of the DWBC into the Bounty Trough, limiting the DWBC presence to east of 178.15°E. Using the presented method a larger dataset will allow a chronological and areal mapping of sedimentation processes and hence provide information on glacial/interglacial cycles. 相似文献
7.
A Deep-sea Channel in the Northwestern Mediterranean Sea: Morphology and seismic structure of the Valencia Channel and its surroundings 总被引：2，自引：0，他引：2
Belen Alonso Miquel Canals Alberto Palanques Jean-Pierre Rehault 《Marine Geophysical Researches》1995,17(5):469-484
The 400 km long Valencia Channel occupies the axis of the Valencia Trough in the Northwestern Mediterranean. Four different types of seismic reflection profiles were used to analyze the morphology and structure of the Valencia Channel with regard to the role played by both margins, Balearic and Iberian, of the Valencia Trough. From a detailed morphoseismic analysis of the Valencia Channel, its upper, middle, and lower courses can be characterized as follows: (1) in the upper course, tributaries are short and only slightly incised, with recent mass-transport deposits occurring on the adjacent continental slopes; (2) in the middle course, the channel deepens, and tributary valleys merge into it; and (3) the lower course begins after a sudden change in the direction of the channel, has a meandering path, is flanked by levees, and is fed by some valleys.During the Pliocene and Quaternary, at least four erosional and filling phases are observed in seismic profiles of the lower course of the Valencia Channel. The varying intensity of mass-transport processes and associated retrogressive slumping, which are related with fluctuations in sediment supply and relative sea-level changes, have played a major role in the formation, maintenance and deepening of the Valencia Channel. In addition to these sedimentary processes, a basement tectonic control and some morphostructural features affect the direction of the Valencia Channel locally. 相似文献
8.
Jan Sverre Laberg Martyn S. Stoker K.I. Torbjrn Dahlgren Henk de Haas Haflidi Haflidason Berit O. Hjelstuen Tove Nielsen Pat M. Shannon Tore O. Vorren Tjeerd C.E. van Weering Silvia Ceramicola 《Marine and Petroleum Geology》2005,22(9-10):1069
Based on studies of sediment accumulations deposited from-and erode by-alongslope flowing ocean currents on the European continental margin from Porcupine (Ireland) to Lofoten (Norway), the evolution of the Cenozoic paleocirculation was reconstructed as part of the STRATAGEM project. There is evidence of ocean current-controlled erosion and deposition in the Rockall Trough, in the Faeroe-Shetland Channel and on the Vøring Plateau since the late Eocene, although the circulation pattern remains ambiguous. The late Palaeogene flow in the Rockall Trough was almost probably driven by southerly-derived Tethyan Outflow Water. The extent and strength of any northerly-derived flow is uncertain. From the early Neogene (early-mid-Miocene), there was a massive regional expansion of contourite drift development both in the North Atlantic and in the Norwegian-Greenland Sea. This was most probably related to the development of the Faroe Conduit, the opening of the Fram Strait and the general subsidence of the Greenland-Scotland Ridge. These may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the Arctic and Atlantic Oceans. An early late Neogene (late early Pliocene) regional erosional event has been ascribed to a vigorous pulse of bottom-current activity, most probably the result of a global reorganisation of ocean currents associated with the closure of the Central American Seaway. During the late Neogene, contourites and sediment drifts developed in deep-water basins, between units of glacigenic sediments as well as infill of several paleo-slide scars. These sediments were derived from areas of bottom-current erosion as well as from the development of Plio-Pleistocene prograding sediment wedges, incorporating the extensive sediment supply derived from shelf-wide ice sheets. Presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of Atlantic water. Depocentres of sediments derived from the winnowing are located (locally) in lower slope embayments and in slide scars. 相似文献
9.
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.
Margin setting represents fan and/or source area 相似文献
10.
Edward L. King Hans Petter Sejrup Haflidi Haflidason Anders Elverhi Inge Aarseth 《Marine Geology》1996,130(3-4):293-315
Approximately 1000 km of high resolution sleeve-gun array transects on the North Sea Fan, located at the mouth of the Norwegian Channel, reveal three dominant styles of sedimentation within a thick (> 900 m) Quaternary sediment wedge comprising numerous sequences. These are interpreted as: terrigenous hemipelagic sedimentation, large scale translational slides, and aprons of glaciogenic debris flow deposits contributing to considerable fan construction. Four large, buried translational slides involved sediment volumes upwards of 3000 km3 each and preceded the similarly dimensioned “first” Storegga Slide on the NE fan flank. Several thick (> 100 m) terrigenous hemipelagic deposits apparently represent long-lived (150–200 kyr) periods of sedimentation whose distribution indicates fan input via the Norwegian Channel. The upper sequences are each made upper sequences are each made up of one or several thick (> 100 m) aprons comprising stacked lensoid and/or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness. They characterize debris flows attributed to periodic input from several phases of a Norwegian Channel ice stream reaching the shelf edge. Subsidence in the outer Norwegian Channel allowed preservation of several glaciation cycles represented by sheet erosion-bounded tills and progradational units. Much of the shelf/slope transition has been preserved, allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the Norwegian Channel. Debris flows, which signal the initial shelf-edge glaciation, are not recognized from the initial glaciation in the Channel (> 1.1 Myr) but are associated with a Middle Pleistocene and all following glacial erosion surfaces (GES) in the outer Norwegian Channel. This was followed by six further sequences, probably totalling over 13,000 km3 of sediment. At least four of these were shelf-edge ice-maximum events the last of which was Late Weichselian age (14C AMS). Considering earlier glaciation-related hemipelagic sedimentation, material since removed by the large slides, and extensive unmapped areas, total Quaternary fan sedimentation was in the vicinity of 20,000 km3. 相似文献
11.
闽江河口沉积结构与沉积作用 总被引：9，自引：0，他引：9
结合已有的闽江河口航道整治研究成果，在该河口采集了130多个表层沉积物样品。根据对沉积结构、河口沙坝类型和水动力条件的分析，探讨了闽江河口沉积物的分布规律和沉积作用机制。研究结果表明，1）闽江河口可划分为砂质、混合和泥质3个沉积区，它们分别代表三角洲前缘、前缘斜坡和前三角洲沉积环境；2）闽江河口各汊道径、潮流强度对比不同，河口沉积过程有显著差异。径流在川石水道的发育中居主导作用，潮流是塑造梅花水道的主要因素；3）河口沙坝类型受制于输出水流的扩散形式，闽江河口有多种类型的河口沙坝，川石水道的河口沙坝为水下突堤型，乌猪水道北侧发育了水下突堤型沙坝，熨斗水道为拦门沙型河口沙坝，梅花水道则是潮流脊型的河口沙坝。 相似文献
12.
冲绳海槽中段表层沉积物物质来源的定量分离:Sr-Nd同位素方法 总被引：16，自引：2，他引：16
利用1994年85－904航次获取的冲绳海槽中段表层沉积物样品，测定其硅酸盐相的^87Sr/^86Cr和^143Nd/^144Nd比值，以定量研究冲绳海槽中段表层沉积物硅酸盐物质的来源，结果表明，冲绳海槽中段陆坡区表层沉积物硅酸盐相的^87Sr/^86Sr/^143Nd/^144Nd与东海陆架沉物硅酸盐相的^87Sr/^86Sr和^143Nd/^143Nd相当，槽底和东坡沉积物硅酸盐相的^87Sr/^86Cr和^143Nd/^144Nd值介于中国大陆硅酸盐物质和海槽水山碎屑的^87Sr/^86Sr,^143Nd/^144Nd比值之间，并大致具有两端员混合特征，利用以Sr同位素为参数的二端员混合方程进行物源定量分析的结果表明，冲绳海槽中段的西坡和槽底表层沉积物硅酸盐相以陆源物质为主，最大值为91．07％，由西向东，陆源物逐渐减少，在海槽东坡含量最小，最小值为9．93％，火山源物质在东坡含量最高，量大值为64．92％，由东向西，由北向东，火山源物质逐渐减少为零。 相似文献
13.
C. Hans Nelson Andres Maldonado Francis Coumes Henri Got Andre Manaco 《Geo-Marine Letters》1983,3(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. 相似文献
14.
冲绳海槽晚更新世以来沉积速率的时空差异及其控制因素 总被引：2，自引：0，他引：2
李军 《海洋地质与第四纪地质》2007,27(4):37-43
收集和分析了冲绳海槽内不同区域的33个站位柱状样的测年资料,计算了不同时段的沉积速率。结果表明,冲绳海槽内晚更新世以来的沉积速率有较大的时空差异,在空间上,由北向南有沉积速率增加的趋势,而靠近海槽西坡的站位沉积速率要大于东坡;在时间上,晚更新世期间的沉积速率要明显大于全新世。冲绳海槽内不同区域和不同时段沉积速率的差异反映了海槽内沉积环境和物质来源的复杂性,这种差异性主要是由不同区域沉积作用和物源供应变化的结果引起,末次冰消期以来的古海洋环境的变化、黑潮的摆动等因素也起到一定的作用,而事件沉积(如火山—热液作用和浊流沉积)的影响也不容忽视。 相似文献
15.
Oceanology - In AMK-4474 marine sediment core, retrieved from the northern part of the eastern (left) levee of the Northwest Atlantic Mid-Ocean Channel, two stratigraphic units were identified. The... 相似文献
16.
The Cap Creus and Lacaze-Duthiers canyons, cut on the narrow subsiding margin off the eastern Pyrenees, play an important role in downslope sediment transport in the northwestern Mediterranean. This conclusion is based on an evaluation of the surficial sediment distribution patterns, cores, direct visual observations of the sea floor made in 24 submersible dives and tight-grid seismic survey data. Down-canyon sediment movement (mostly by slump and gravity flow mechanisms) since the end of the Pliocene has resulted in the formation of the Catalonia Fan at the base of the slope west of the Rhone Cone. 相似文献
17.
Erosional and depositional patterns in the Valencia Channel mouth: An example of a modern channel-lobe transition zone 总被引：1，自引：0，他引：1
Recent deep-towed, high resolution sidescan sonar records and seismic profiles have been collected on the lower Valencia Fan (Northwestern Mediterranean). Three morphological zones, channelled, transition and unchannelled, have been recognized in the Valencia Channel mouth. Sonographs from the transition zone show a progresive transversal gradation from depositional to erosional bedforms. This asymmetry may be due to the lateral inputs of sediment flows from the Rhone deep-sea fan and to the effect of the Coriolis force, which could have diverted the flows to the southwest. Bedforms recorded in the study area include trains of starved ripples and dunes, sand ribbons, and fields of elongated scours. Most morphological features, bedforms and seismic characteristics of the Valencia Channel mouth are typical of channel-lobe transition zones. 相似文献
18.
Recent deep-towed, high resolution sidescan sonar records and seismic profiles have been collected on the lower Valencia Fan (Northwestern Mediterranean). Three morphological zones, channelled, transition and unchannelled, have been recognized in the Valencia Channel mouth. Sonographs from the transition zone show a progresive transversal gradation from depositional to erosional bedforms. This asymmetry may be due to the lateral inputs of sediment flows from the rhone deep-sea fan and to the effect of the Coriolis force, which could have diverted the flows to the southwest. Bedforms recorded in the study area include trains of starved ripples and dunes, sand ribbons, and fields of elongated scours. Most morphological features, bedforms and seismic characteristics of the Valencia Channel mouth are typical of channel-lobe transition zones. 相似文献
19.
Based on seismic profiles, multibeam bathymetry and sediment cores, an improved understanding of the deglaciation/postglacial history of the southern part of the Norwegian Channel has been obtained. The Norwegian Channel Ice Stream started to recede from the shelf edge ca. 15.5 ka BP (14C ages are used throughout). Approximately 500–1000 years later the ice margin was located east of the deep Skagerrak trough. At that time, the Norwegian Channel off southern Norway had become a large fjord-like embayment, surrounded by the grounded ice sheet along the northern slope and possibly stagnant ice remnants at the southern flank. The Norwegian Channel off southern Norway has been the main sediment trap of the North Sea, and south of Egersund more than 200 m of sediments have been deposited since the start of the deglaciation. Five seismic units are mapped. The oldest unit E occurs in some of the deepest troughs, and was deposited immediately after the ice became buoyant. Unit D is acoustically massive and comprises mass-movement deposits in eastern Skagerrak and south of Egersund. Unit C (in the channel southwest of Lista/Egersund) is interpreted to comprise mainly bottom current deposits derived from palaeo-rivers, e.g. Elben. During deposition of unit C (ca. 14.5–13 ka BP), there was limited inflow of Atlantic water. A change in depositional environment at ca. 13 ka BP is related to an increased inflow of saline water and more open hydrographic circulation. Widely distributed, acoustically stratified clays of unit B were deposited ca. 13–10 ka BP. The Holocene Unit A shows a depositional pattern broadly similar to that of unit B. 相似文献
20.
济州岛南部海域海底声呐图像分析与声学底质分类 总被引：2，自引：2，他引：0
东海北部外陆架靠近济州岛南部海域,是黄海槽向冲绳海槽延伸的部分,属于黑潮分支黄海暖流的通道入口,分布着脊槽相间的海底底形,对其海底声呐图像的处理分析及声学底质分类的分析研究,有助于了解该通道海底底形表层纹理特征及沉积物分布规律。基于在济州岛南部海域获取的多波束声呐数据,应用图像处理技术和方法,对数据进行了处理,获得了海底声呐影像图,并对其表层纹理特征进行了描述和分析;同时,基于多波束反向散射强度数据,结合19组海底地质取样数据,建立研究区海底反向散射强度与沉积物粒度特征之间的统计关系模型,并以改进的学习向量量化神经网络方法,实现对海底粉砂质砂、黏土质砂以及砂-粉砂-黏土3种底质类型的快速自动分类识别。 相似文献