Rhone Deep-Sea Fan: A review

The Rhone Fan is a large Plio-Pleistocene turbidite deposit in the western Mediterranean Sea. The fan is fed from the broad Rhone River delta, but only one canyon, the Petit-Rhone, has fed most of the major turbidite depositional sequences that have been mapped. Slumping of sediment from intercanyon areas on the delta slope also has provided much sediment for the fan. The lack of Recent turbidite deposition on the fan suggests that turbidite sedimentation dominates during glacial low stands of sea level, building major leveed valley sequences, while surficial slumping of the valley levee deposits and pelagic sedimentation seem to mark high stands of sea level during interglacial periods. Margin setting represents fan and/or source area     

Holocene sedimentation history of the major fan valleys of Monterey fan

There are three major fan valleys on upper Monterey fan. Deep-tow geophysical profiles and 40 sediment cores provide the basis for evaluation of the sedimentation histories of these valleys. Monterey fan valley leads from Monterey canyon to a major suprafan and is bounded by levees that crest more than 400 m above the valley floor. The valley passes through a large z-bend or meander. Monterey East fan valley joins Monterey fan valley at the meander at about 150 m above the valley floor, and marks an earlier position of the lower Monterey fan valley. Ascension valley, a hanging contributary to the Monterey fan valley, appears to have once been the shoreward head of the lower part of the present Monterey fan valley. The relief of Monterey fan valley appears from deep-tow profiles to be erosional. The valley is floored with sand. Holocene turbidity currents do not overtop the levees 400 m above the valley floor, but do at times overflow and transport sand into Monterey East valley, producing a sandy floor. An 1100 m by 300 m dune field was observed on side scan sonar in Monterey East valley.Ascension fan valley was floored with sand during glacial intervals of lowered sea level, then was cut off from its sand source as sea level rose. A narrow (500 m), erosional, meandering channel was incised into the flat valley floor; the relief features otherwise appear depositional, with a hummocky topography perhaps produced in the manner of a braided riverbed. The sand is mantled by about 6 m of probable Holocene mud. Hummocky relief on the back side of the northwestern levees of both Ascension and Monterey valleys is characteristic of many turbidite valleys in the northeast Pacific. The hummocky topography is produced by dune-like features that migrate toward levee crests during growth.     

Controls on the development of valleys,canyons, and unconfined channel–levee complexes on the Pleistocene Slope of East Kalimantan,Indonesia

Shallow 3D seismic data show contrasting depositional patterns in Pleistocene deepwater slopes of offshore East Kalimantan, Indonesia. The northern East Kalimantan slope is dominated by valleys and canyons, while the central slope is dominated by unconfined channel–levee complexes. The Mahakam delta is immediately landward of the central slope and provided large amounts of sediments to the central slope during Pleistocene lowstands of sea level. In the central area, the upper slope contains relatively straight and deep channels. Sinuous channel–levee complexes occur on the middle and lower slope, where channels migrated laterally, then aggraded and avulsed. Younger channel–levee complexes avoided bathymetric highs created by previous channel–levee complexes. Levees decrease in thickness down slope. Relief between channels and levees also decreases down slope.North of the Mahakam delta, siliciclastic sediment supply was limited during the Pleistocene, and the slope is dominated by valleys and canyons. Late Pleistocene rivers and deltas were generally not present on the northern outer shelf. Only one lowstand delta was present on the northern shelf margin during the upper Pleistocene, and sediments from that lowstand delta filled a pre-existing slope valley complex and formed a basin-floor fan. Except for that basin-floor fan, the northern basin floor shows no evidence of sand-rich channels or fans, but contains broad areas with chaotic reflectors interpreted as mass transport complexes. This suggests that slope valleys and canyons formed by slope failures, not by erosion associated with turbidite sands from rivers or deltas. In summary, amount of sediment coming onto the slope determines slope morphology. Large, relatively steady input of sediment from the Pleistocene paleo-Mahakam delta apparently prevented large valleys and canyons from developing on the central slope. In contrast, deep valleys and canyons developed on the northern slope that was relatively “starved” for siliciclastic sediment.     

Response of Cenozoic turbidite system to tectonic activity and sea-level change off the Zambezi Delta

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.     

海盆沉积“源-汇”系统分析:南海北部珠江海谷-西北次海盆第四纪深水浊积扇

运用近年来采集的高分辨率地震资料和多波束测深数据,在珠江海谷及西北次海盆深海平原区发现大规模发育的第四纪重力流沉积体系,该沉积体系沿珠江海谷以北西-南南东方向贯穿整个北部陆坡,进入西北次海盆后呈扇形展开,形成珠江海谷-西北次海盆大型深水浊积扇系统。据沉积体系空间展布特征差异,将珠江海谷划分为北、中、南三段,北段为过路侵蚀和水道下切,中段以水道充填和天然堤沉积为主,南段以水道-天然堤和朵叶体沉积共存为特征,揭示出北部陆坡珠江海谷是珠江口外陆缘物质输送海盆深海平原的主要通道;海盆区总体以朵叶体发育为特色,呈扇形展布。深水扇系统可分为三期次沉积体,其区域结构记录了重力流沉积物从侵蚀、卸载到南海海盆作为限制性盆地接收陆源沉积物的全过程,为“源-渠-汇”的研究构建了一个完美的范例。本文以珠江海谷-西北次海盆第四纪深水浊积扇沉积体系为例,完整地揭示了水道-扇体的组构和特征,清晰呈现了陆坡-海盆砂体展布的规律,可为建立南海北部新近纪早期深水扇形成模式提供参考,有助于指导南海深水油气勘探工作。     

花东盆地晚中新世以来沉积演化特征

利用近年来在台湾东部海域采集的多道地震和多波速测深资料,对该海域花东海盆区晚中新世以来的沉积充填演化特征进行描述和分析。通过对花东海盆区域地形特征描述、层序地层格架的建立和地震剖面的解译,在本区晚中新世以来的沉积充填中刻画出6种典型地震相类型,并分析其对应的沉积相类型,包括浊积扇、浊积水道充填、块体流、沉积物波、海底峡谷-伴生沉积物滑塌变形-充填、深水扇沉积。结合地震相平面分布及垂向沉积相叠置关系,将晚中新世-第四纪沉积充填演化划分为3个阶段:晚中新世晚期开始受到块体流冲蚀阶段,到海底峡谷冲刷-沉积物失稳-峡谷充填-再侵蚀阶段,到峡谷输送的大量沉积物在上新世以来主要堆积发育了沉积物波、浊积扇、深水扇等沉积体系阶段。     

Transport processes deduced from geochemistry and the void ratio of surface core samples, deep sea Sagami Bay, central Japan

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.     

The Bengal Fan: morphology, geometry, stratigraphy, history and processes

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.     

The source and origin of the 1929 grand banks turbidity current inferred from sediment budgets

Side-scan data from the epicentral area of the 1929 Grand Banks earthquake and cores from the resulting turbidite are used to determine a sediment budget for the event. The 1929 turbidite has a volume of about 185 cubic km, which is mostly sand. Features indicating failure on the continental slope are observed only in muddy sediment. A major source of sand in the heads of the fan valleys of the Laurentian Fan is postulated to balance the sediment budget. This sand accumulated proglacially during the Wisconsinan glaciation and probably failed through liquefaction in the 1929 earthquake.     

北黄海盆地东部坳陷东南部层序地层特征及沉积体系

以层序地层学为理论指导,通过对地震、钻井、测井及古生物等资料的研究,建立了北黄海盆地东部坳陷东南部的层序格架。研究区的中生界可分为1个一级层序、2个二级层序、5个三级层序,在此层序格架内进行了沉积相划分及沉积体系研究,厘定了扇三角洲、辫状河三角洲、浊积扇和湖泊沉积等4种沉积体系。断陷早期,JSQ1的西部与东部分别发育了中型的扇三角洲与辫状河三角洲沉积体系;断陷中期,西部的扇三角洲沉积体系逐步扩展并在其前端多发育小型浊积扇,东部的辫状河三角洲沉积体系亦持续扩张且在JSQ4沉积期规模达到最大;断陷晚期,KSQ1内仅发育盆缘的小型扇体和滨浅湖相沉积,东部、南部隆起区未接受沉积或沉积较薄并剥蚀殆尽。沉积体系的平面展布和纵向演化受古构造与古地貌的控制。     

Delgada Fan: Preliminary interpretation of channel development

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     

Fan delta development and processes offshore a seasonal river in a seismically active region, NW Gulf of Corinth

High-resolution geophysical surveys (seismic, side-scan sonar) offshore of the Eratini River, a seasonally flowing river in the NW Gulf of Corinth, Greece, revealed a small fan delta with a variety of bottom features (blocky deposits, chutes and sediment instabilities). Considering the relatively small size of this river, however, these features could not be explained as being produced solely by river flow processes. Based on morphological features, the fan delta can be subdivided into a high- and a low-energy area. Sedimentation processes in the fan delta are associated with flood-derived sediment input, hyperpycnal flows which erode the fan surface, mud settling from suspension plumes, shelf sedimentation and sediment failures. The observed blocky deposits are considered to be the result of earthquake-induced mass flows in 1965 and 1995, whereas the chutes would be produced both by erosive mass flows and by hyperpycnal currents. The bulk block sediment volume has probably resulted from the 1965 earthquake. The 1965 evacuation zone and the related chutes were buried by the prograding fan delta. The main causative factor triggering the observed sediment instabilities is considered to be liquefaction, which is caused by (1) frequent earthquake-induced cyclic loading and (2) low sediment shear strengths created by rapid deposition during floods, in both cases associated with high pore-water pressures.     

Physiography and deposition on a distal deep-sea system: The Valencia Fan (Northwestern Mediterranean)

The Valencia Fan developed as the distal fill of a deep-sea valley, detached from the continental slope and the main sedimentary source. A survey of side-scan sonar, Sea Beam and reflection seismics shows that the sediment is largely fed through the Valencia Valley. The upper fan comprises large channels with low-relief levees, and the middle fan has sinuous distributary channels. Depositional bedforms predominate on the valley floor and levees, and erosional bedforms are common in the valley walls. A change to slope on the fan apex and the presence of volcanoes on the upper fan are the main factors influencing fan-growth pattern.     

Growth of a post-Little Ice Age submarine fan, Glacier Bay, Alaska

A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed in the early 1900s at the head of Queen Inlet. The Late Holocene Queen fan is comparable to large Pleistocene fans that formed in the Gulf of Alaska and differs from trough-mouth fans formed by cooler climate glacier systems. Received: 7 January 1999 / Revision received: 3 June 1999     

Study on the Cretaceous turbidite and reservoir features in the Qingshankou Formation in northern Songliao Basin,NE China

Based on analysis of well and drilling data, cores, sediment grains and 3D seismic data, four types of turbidites–slope fan, channelized, laminated and sublacustrine fan turbidite–are identified in Members 1 and 2 of the Qingshankou Formation in northern Songliao Basin. The slope fan turbidite is located in Members 1 and 2 of the Qingshankou Formation. It is dominated by silt and fine sand and is distributed in an SN-trending ribbon zone along the slope break at delta front in the western part of the basin. The channelized turbidite is located at the bottom of Member 1 of the Qingshankou Formation. It is dominated by silt and fine sand and is distributed in an SN-trending strip-shaped zone along the Qijia-Gulong sag, with funnel-shaped sublacustrine fans at the end. The laminated turbidite body is located in Member 2 of the Qingshankou Formation. It is dominated by siltstone and argillaceous siltstone and is distributed continuously in a tongue-shaped zone along the northern delta front towards the lacustrine region, with belt-like distributaries at the central part and sublacustrine fans at the end. Low-permeability and low-yield lithologic reservoirs are formed near the delta front within the slope fan turbidite and channelized turbidite. There are “sweet spots” in local regions, where reservoir reform techniques are required to attain high industrial yields. Laminated turbidite and sublacustrine fans can form unconventional and continuous reservoirs that generally have no natural productivity; industrial production is impossible until horizontal drilling and multistage volume fracturing are employed. Therefore, the research results are important to the exploration of unconventional oil and gas reservoirs in northern Songliao Basin.     

Current titles in marine geology

The asymmetrical Astoria Fan (110 × 180 km) developed off the Columbia River and Astoria submarine canyon during the Pleistocene. Morphology, stratigraphy, and lithology have been outlined for a Pleistocene turbidite, and a Holocene hemipelagic sedimentary regime to generate geologically significant criteria for comparison with ancient equivalent deposits. Both gray silty clay of the Late Pleistocene and olive-gray clay of the Early Holocene are interrupted by turbidites. The few deeply incised fan valleys of the more steeply sloping upper fan contain thick, muddy and very poorly sorted sand and gravel beds that usually have poorly developed internal sedimentary structures. The numerous shallower fan valleys and distributaries of the flatter middle and lower fan contain thick, clean, and moderately sorted medium to fine sands that are vertically graded in texture, composition and well-developed internal sedimentary structures. Tuffaceous turbidites (containing Mazama ash, 6600 B.P.) can be traced as thick deposits (ca. 30–40 cm) throughout the Astoria Channel system and as thin correlative interbeds (ca. 1–2 cm) in interchannel areas. Similarly, sand/shale ratios are high throughout the fan valleys and the middle and lower fan areas of distributaries, but are low in the upper-fan interchannel areas.These depositional trends indicate that high-density turbidity currents carry coarse traction loads that remain confined in upper but not lower fan valleys. Fine debris selectively sorts out from channelized flows into overbank suspension flows that spread over the fan and deposit clayey silt. A high content of mica, plant fragments, and glass shards (if present) characterizes deposits of the overbank flows, a major process in the building of upper fan levees and interchannel areas.In the Late Pleistocene, turbidity currents funneled most coarse-grained debris through upper channels to depositional sites in middle and lower fan distributaries that periodically shifted, anastomosed and braided to spread sand layers throughout the area. At this time, depositional rates were many times greater (>50 cm/1000 years) than in the Holocene (8 cm/1000 years).During the Holocene rise of sea level, the shoreline shifted, the Columbia River sediment was trapped, and turbidity-current activity slackened from one major event per 6 years in the Late Pleistocene, to one per 1000 years in the Early Holocene, to none since the Mt. Mazama eruption (ca. 6600 B.P.). Turbidites became muddier and deposited as thick beds within main channels, in part explaining Holocene deposition rates three times greater there (25 cm/1000 years) than in interchannel regions. Turbid-layer debris, funneled through channel systems and trapped from flows off the continental terrace, also contributed to rapid sedimentation in valleys; however, less than 2% of the suspended sediment load of the Columbia River has been trapped in fan valleys during the Holocene.By the Late Holocene, continuous particle-by-particle deposition of hemipelagic clay with a biogenous coarse fraction was the predominant process on the fan. These hemipelagites contain progressively more clay size and less terrigenous debris offshore, and are finer grained, richer in planktonic tests and dominated by radiolarians compared to the foraminiferal-rich Pleistocene clays. The hemipelagic sedimentation of interglacial times, however, is insignificant compared to turbidite deposition of glacial times.     

The Nile Cone: Submarine fan development by cyclic sedimentation

The Quaternary sections of the Nile Cone in the eastern Mediterranean are formed by regionally extensive repetitions of sediment sequences (cyclothems s.l.) showing a successive, orderly arrangement of sediment types. Detailed lithofacies analysis reveals the recurrence of three basic terms in many cores: a basal olive-gray hemipelagic mud and turbidite sequence; a middle sapropel sequence; and an upper yellowish-orange hemipelagic sequence, including calcareous ooze, and a turbiditic sequence. This cyclic sedimentation closely reflects the Quaternary dynamics. The development of the Nile submarine fan in an enclosed, silled basin has resulted in a particularly close relation between biogenic-terrigenous depositional patterns and climatic and oceanographic factors affecting the Mediterranean.     

辽河拗陷东部凹陷南部地区古近系沉积体系与储层评价

Detailed studies on a number of core sections,well logs and seismic date of the paleogene systems of the southern part of eastem sag in Liaohe Depression revealed theat six sedimentary systems,i,e.delta,lake,fan delta,braided river,delta,river and alluvial fan,were distinguished,The sedimentation in the studied area remarkably controlled reservoir and the variability of sedimentary facied caused the diversity of reservior sand bldies and the inhomogeneity of reservoir properties plane distribution;The best reservoir properties are the sand bodies of deltaic front and braided-river deltaic front;the better are the sand bodies of braided-river deltaic plain,deltaic front,braided river and meandering river;the medium reservoir properties are the sand bodies of delta plain,the fan-delta front,the alluvial-middle fan,beach-bar and turbidite fan;the wores are the sand bodies of upper fan and lower fan of alluvial fan,alluvial plain.The favorable sedimentary facies belt controlled the distribution of favorable reservoir and it was an important evidence for prediction favorable stratigraphiv reservoir.     

渤海湾盆地渤中凹陷古近系沉积体系演化及物源分析

综合运用地质、测井、地震及分析化验等资料,对渤海湾盆地渤中凹陷古近系沉积体系进行了较深入的研究,研究表明渤中凹陷古近系的沉积体系主要受构造升降和湖平面变化的控制,经历了3期裂陷和湖侵,发育5套沉积体系,其中沙河街组沉积时期为裂陷期,以扇三角洲、湖底扇沉积为主,并发育特征的滩坝及浅水台地相沉积;东营组沉积时期为湖侵期,主要发育大型湖泊三角洲沉积,并逐渐向辫状河相过渡。构造及沉积体系分析认为,沙三段沉积时期物源丰富,主要来自石臼坨凸起、渤南和庙西凸起,沙一、二段沉积时期物源有限,东三沉积期物源主要来自石臼坨和沙东南凸起,东二沉积期大面积的湖侵使得本区处于浅湖-半深湖环境,凹陷周边大量古水系将石臼坨凸起、沙垒田凸起的物源带入凹陷中沉积,使得大型三角洲叠覆体广泛发育。     

Impacts of sediment supply and local tectonics on clinoform distribution: the seismic stratigraphy of the mid Pleistocene-Holocene Indus Shelf

We present results from the first high-resolution seismic reflection survey of the inner Western Indus Shelf, and Indus Delta, Arabian Sea. The results show major regional differences in sedimentation across the shelf from east to west, as well as north to south, both since the Last Glacial Maximum (~20?ka) and over longer time scales. We identify 10 major regional reflectors, interpreted as representing sea level lowstands. Strong compressive folding is observed underlying a reflector we have called Horizon 6 in the north-western shelf, probably compression associated with the transpressional deformation of the Murray Ridge plate boundary. Downslope profiles show a series of well developed clinoforms, principally at the shelf edge, indicating significant preservation of large packages of sediment during lowstands. These clinoforms have developed close to zones of deformation, suggesting that subsidence is a factor in controlling sedimentation and consequently erosion of the Indus Shelf. These clinoforms fan out from dome features (tectonic anticlines) mostly located close to the modern shoreline.