Sea Valleys Research Articles

Giant sediment wave fields adjacent to debris-flow filled deep sea valleys: New evidence of cohesive flows transforming into dilute turbidity currents

Sediment waves are subaqueous sedimentary figures belonging to the supercritical flow domain and are of growing interest to the scientific community and industry. They are ubiquitously observed on the seafloor of world's oceans, as well as in the stratigraphic record imaged by marine seismic datasets. In this study we focus on the Cenozoic strata offshore Ivory Coast, where giant sediment waves developed at the base of slope range in height and wavelength: 10–100 m and 1–6 km, respectively. Sediment waves fields in this study developed simultaneously and adjacent to wide, rectilinear valleys, filled by mass-transport deposits. Thus, sediment waves serve as a rare example of large-scale deep-water cyclic steps formed through phase transformation (water entrainment and dilution) of laminar debris flows.The lithological nature of sediment waves can be estimated through the observation of polygonal faulting affecting the sediment waves fields, which suggest a dominant abundance of fine-grained material (clay and silt-prone). This study also shows that wide submarine valleys flanked by sediment waves do not necessarily correspond to sand-prone depositional systems, and that their potential to hold reservoir units for hydrocarbon exploration or CO2 storage should be evaluated with caution when in lower resolution datasets are used.

An Evaluation on the Sources of Türk History of the Medieval East Black Sea

Tarihi kaynaklar ışığında Doğu Karadeniz’deki Türk varlığının tarihi temellerini çok derinlere götürmek mümkündür. Orta Çağ’da ise Doğu Karadeniz’deki Türk varlığı hakkındaki bilgiler Selçukluların Anadolu’ya temasıyla önem kazanmaktadır. Selçukluların Kafkaslara ve Doğu Anadolu’ya gelmesiyle birlikte bölgedeki Gürcü ve Ermeni kaynakları Selçuklulardan bahsetmeye başlamaktadır. Aynı şekilde Anadolu’yu yöneten Bizanslılar ile bölgeyle yakından ilgilenen Araplar ve Süryanilerde bölgede gerçekleşen Türk faaliyetleri hakkında mühim kayıtlar tutmuşlardır. Orta Çağ tarihi kaynakları incelendiğinde, Selçukluların Doğu Karadeniz’in Çoruh boylarında ve Kelkit havalisinde faaliyetleri hakkında önemli kayıtlar bulunmaktadır. Ancak Doğu Karadeniz kıyılarına ulaşan Türkler hakkında bilgiler başlangıçta karanlıkta kalmaktadır. İlerleyen dönemde ise Doğu Karadeniz vadi ve sahillerindeki Türkler hakkında tarihi kaynakların yardımıyla önemli bilgiler edinilebilmektedir. Kaynaklardaki kayıtlar çoğunlukla Kelkit Havzası’ndaki Türk siyasi teşekkülleri ve Doğu Karadeniz dağlarının kuzeyini kendilerine yurt edinen Türk beylerinin, Trabzon Rum Devleti ile olan mücadelelerini konu almaktadır.

Assessment of resource selection models to predict occurrence of five juvenile flatfish species (Pleuronectidae) over the continental shelf in the western Gulf of Alaska

According to the nursery size hypothesis, flatfish recruitment is constrained by nursery area. Thus, if resource selection models can be shown to accurately predict the location and geographic extent of flatfish nursery areas, they will become important tools in the management and study of flatfish population dynamics. We demonstrate that some resource selection models derived previously to predict the presence and absence of juvenile flatfishes near shore were applicable to the broader continental shelf. For other age-species groups, derivation of new models for the continental shelf was necessary. Our study was conducted in the western Gulf of Alaska (GoA) during October 2011 on four groups of age-0 juvenile flatfishes: Pacific halibut (Hippoglossus stenolepis), arrowtooth flounder (Atheresthes stomias), northern rock sole (Lepidopsetta polyxystra), and flathead sole (Hippoglossoides elassodon); and three groups of age-1 juvenile flatfishes: northern rock sole, flathead sole, and yellowfin sole (Limanda aspera). Sampling occurred at 33 sites across the continental shelf. Fish were collected using a 3-m beam trawl, and a midwater trawl. Environmental data were collected on sediment composition and water temperature and depth. Many of the age-species groups co-occurred in the Shumagin and Barnabus sea valleys; however, age-0 arrowtooth flounder occurred at more locations than other juveniles, perhaps due to a relatively broad tolerance of environmental conditions and to the utilization of midwater habitat. Thus, the large nursery area of arrowtooth flounder may be one reason why they are currently the most abundant GoA flatfish. In fact, among all species, mean recruitment at age 3 increased with the percent occurrence of age-0 juveniles at the 33 sites, a proxy for relative nursery area, in accordance with the nursery size hypothesis, suggesting that mean recruitment among GoA flatfishes is structured by nursery size.

Gulf of Alaska continental slope morphology: Evidence for recent trough mouth fan formation

AbstractGlaciated continental shelves are host to numerous morphologic features that help understand past glacier dynamics. Southeastern Alaska is home to the St. Elias mountains, an active orogen that also hosts temperate marine glaciers. During glacial periods ice streams advance across the continental shelf, carving shelf‐crossing troughs that reach the shelf edge. We use high‐resolution multibeam data to develop the relationship between the Yakutat and Alsek Sea Valleys and the resulting continental slope morphology. The shelf and slope geomorphology can be divided into statistical groupings that relate to the relative balance of erosion and deposition. Our analysis indicates that only the Yakutat system has been able to build an incipient trough‐mouth fan. The extreme sediment supply from this region was able to overwhelm the steep initial topography of the transform margin while further to the east sediment slope‐bypass dominates. This analysis provides an extreme end member to existing studies of temperate glaciation along continental margins. The unique interplay between rapid uplift due to ongoing collision and the massive erosion caused by temperate glaciers provides for sedimentary flux far above most other systems.

Seismic stratigraphic evidence for glacial expanse during glacial maxima in the Yakutat Bay Region, Gulf of Alaska

[1] Modern shelf bathymetry bordering the Gulf of Alaska exhibits shelf-crossing sea valleys that suggest focused pathways for ice flow during glacial conditions. Using an integrated seismic data set between the present Yakutat and Alsek Sea Valleys, we investigate the glacial stratigraphic record in order to improve our understanding of the regional glacial system during maximum glacial conditions. Our investigations reveal four glacial unconformities, of which, the latter two are overlain by sediment packages hundreds of meters thick. We suggest that these unconformities are indicative of ice advance phases during the Little Ice Age (LIA), the Last Glacial Maxima (LGM), and two pre-LGM advances with glacial retreat sequences preserved from the youngest two. The advances were dominated by ice expanse from the Malaspina Glacial system and Alsek River districts rather than the Hubbard Glacial system and only show distinctive morainal bank development near the shelf edge and near the mouth of, or within, modern bays, fjords, or river valleys. This observation strongly supports rapid and continuous retreat from glacial maxima conditions during climatic warming. All, except the inferred LIA sequence, transgress the shelf and exhibit concentrated erosion in overdeepened troughs, analogous to cross-shelf troughs similar to those observed on other high-latitude glaciated shelves. The two Alaskan troughs discussed here may be end-member examples of high-sediment flux systems due to the temperate glacial setting combined with an actively exhuming orogen.

Seabed geomorphic features in a glaciated shelf of the Baltic Sea

Due to a continuous increase in human activities occurring throughout marine and coastal areas worldwide (e.g., marine traffic and construction), the lack of in-depth information on vast marine areas is problematic. However, the spatial informatics field has enabled the development of new applications based on pre-existing spatial data. This paper discusses the physical structure and complexity of the continental shelf seafloor, using geospatial modelling and GIS analysis to gain insight into the physical environment of the Baltic Sea seafloor as a basis for ecosystem management. We demonstrate the mapping of coherent features over a broad region and identify geomorphic features of the seabed by analysing and modelling bathymetric, seabed substrate, and photic depth datasets. The analysis was performed at the kilometre scale using a grid size of 200 m.In total, 18 unique seabed geomorphic features were identified from the entire Baltic Sea (including the Skagerrak). The features are similar to geomorphic seafloor structures typically occurring on glaciated continental shelves. The Baltic Sea is primarily characterized by various plains and basins, and on average, one-third of the seafloor can be regarded as a sediment accumulation area. Other seabed geomorphic features are mainly present in certain local sub regions. The archipelagos as well as the coastal areas of southern Sweden and the Bothnian Bay have a heterogeneous seafloor environment. These areas are characterized by sea valleys and holes, sea troughs, and bedrock elevations, partly due to a crystalline basement and glacial erosion. In addition, the shallow coastal areas suffer from intense wave exposure and have erosional features that differ from those in open sea areas.Effective transnational marine spatial planning requires extensive knowledge of the environmental characteristics of the region in question. Background data for marine spatial planning can be obtained through an analysis of seabed geomorphic features, which provides consistent information on the physical marine environment over a broad area.

Measuring currents in submarine canyons: Technological and scientific progress in the past 30 years

The development and application of acoustic and optical technologies and of accurate positioning systems in the past 30 years have opened new frontiers in the submarine canyon research communities. This paper reviews several key advancements in both technology and science in the field of currents in submarine canyons since the1979 publication of Currents in Submarine Canyons and Other Sea Valleys by Francis Shepard and colleagues. Precise placements of high-resolution, high-frequency instruments have not only allowed researchers to collect new data that are essential for advancing and generalizing theories governing the canyon currents, but have also revealed new natural phenomena that challenge the understandings of the theorists and experimenters in their predictions of submarine canyon flow fields. Baroclinic motions at tidal frequencies, found to be intensified both up canyon and toward the canyon floor, dominate the flow field and control the sediment transport processes in submarine canyons. Turbidity currents are found to frequently occur in active submarine canyons such as Monterey Canyon. These turbidity currents have maximum speeds of nearly 200 cm/s, much smaller than the speeds of turbidity currents in geological time, but still very destructive. In addition to traditional Eulerian measurements, Lagrangian flow data are essential in quantifying water and sediment transport in submarine canyons. A concerted experiment with multiple monitoring stations along the canyon axis and on nearby shelves is required to characterize the storm-trigger mechanism for turbidity currents.

Tectonic and climatic influence on the evolution of the Surveyor Fan and Channel system, Gulf of Alaska

Present-day seafloor morphology and sediment distribution in the deep-water Surveyor Fan, Gulf of Alaska, is dominated by the >700-km-long Surveyor Channel, an anomaly in a system with no major fluvial input or shelf canyons. The sediment supply instead has been provided by glacial erosion in the still-active Chugach–St. Elias orogen, and glacial transport across the shelf. Glaciation has periodically increased in the St. Elias Range since the Miocene, but began dominating erosion and spurred enhanced exhumation since the mid-Pleistocene transition, at ∼1 Ma. Ice associated with this glacial intensification carved cross-shelf sea valleys that connect the St. Elias Range to the Surveyor Fan. The direct deposition of newly increased terrigenous sediment flux into the fan triggered the formation of the Surveyor Channel and its growth across the Surveyor Fan. Through the formation of the Surveyor Channel, climate events created three major differentiable sequences across the Surveyor Fan that we mapped using seismic-reflection profiles. The change in morphology observed throughout the sequences allows us to characterize the influence that a glaciated orogen can have in shaping margin processes and the sediment pathway from source to sink. We show that the large variation in sediment flux between glacial-interglacial cycles together with sea valley formation leads to a glacial shelf transport process not typical of a fluvial system. This glacial shelf transport along with the channel terminus in the Aleutian Trench makes the Surveyor Fan and Channel morphologically one of the most unique systems in the world.

Ecology of small neritic fishes in the western Gulf of Alaska. I. Geographic distribution in relation to prey density and the physical environment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 392:223-237 (2009) - DOI: https://doi.org/10.3354/meps08160 Ecology of small neritic fishes in the western Gulf of Alaska. I. Geographic distribution in relation to prey density and the physical environment Matthew T. Wilson* Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, Washington 98115, USA *Email: matt.wilson@noaa.gov ABSTRACT: Physical heterogeneity affects the geographic structure of coastal ocean ecosystems by influencing the spatial distribution of zooplankton and their nektonic predators. This was examined in the western Gulf of Alaska (GOA) during late summer (2000, 2001, and 2003) when seasonal increases in the Alaska Coastal Current flow and additions of Age-0 fishes to the nektonic community of small neritic fishes coincided with declining zooplankton abundance. The 48-site sampling grid was divided into 5 meso-scale areas based on physical condition (temperature, salinity, net current velocity). Larval crabs and fishes, and krill were the only zooplankton taxa for which the population density consistently differed by area regardless of diel period (day, night) or year. Larval crabs and fishes concentrated near shore in warm, low-salinity water. Krill concentrated in high-flow areas, which, over the shelf, were associated with sea valleys. Dominant fishes were walleye pollock Theragra chalcogramma, capelin Mallotus villosus, and eulachon Thaleichthys pacificus. Few fish occurred beyond the shelf in the cold, swift-flowing Alaskan Stream boundary current. Over the shelf, Age-1+ walleye pollock and eulachon aggregated with krill in high-flow areas. Smaller fishes (Age-0 walleye pollock and capelin) were more variably distributed, and were not well associated with taxon-specific zooplankton densities. Thus, relatively high flow in proximity to sea valleys was associated with concentrations of krill and fishes that presumably were able to efficiently forage on krill in high-flow areas. The year-to-year consistency in patterns is a noteworthy indication that geographic structure in the coastal GOA ecosystem may resist climate forcing. KEY WORDS: Walleye pollock · Capelin · Eulachon · Zooplankton · Population density · Body size Full text in pdf format PreviousNextCite this article as: Wilson MT (2009) Ecology of small neritic fishes in the western Gulf of Alaska. I. Geographic distribution in relation to prey density and the physical environment. Mar Ecol Prog Ser 392:223-237. https://doi.org/10.3354/meps08160Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 392. Online publication date: October 19, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Sea Valleys and Related Depositional Systems in the Gulf of Lion and Ebro Continental Margins (1)

Four main types of sea valleys, submarine canyons, gullies, channels of turbidite systems, and a mid-ocean channel, have been characterized in the Ebro and the Gulf of Lion distal margins in the Catalan Sea, together with three main types of depositional bodies, Pyrenean Canyon deep-sedimentary body (PCDSB), apron deposits, and channel-levee complexes related to the development of these sea valleys. Erosion and deposition, mainly during the Quaternary, have formed the majority of these sea valleys, although some structurally controlled sea valleys also exist. As an example, a Messinian entrenchment has been confirmed in the Petit Rhone Canyon. The evolution of the drainage patterns is established from the detailed analysis of the sedimentary structure. This analysis revea s the presence of buried sedimentary bodies and older drainage systems differing from those observed in the bathymetric charts. Specific factors determine the evolutionary differences between both margins, including the absence or presence of underlying evaporitic Messinian layers and the regional geodynamic evolution during and after the Alpine orogeny. We propose a dual evolutionary model from the end of the Miocene to the Quaternary.

Development of slope valleys in the glacimarine environment of a complex subduction zone, Northern Gulf of Alaska

Abstract Morphological, seismic-reflection, and sedimentological evidence indicates that glacial ice tongues cut large sea valleys into the Gulf of Alaska continental shelf during the Pleistocene. During the Holocene, glacially-derived sediments from the Copper River and other meltwater streams have been prograding seaward across the shelf, covering the glacial and glacimarine upper Yakataga diamicts that blanketed the shelf and accumulated on the upper slope seaward of the sea valleys during the Pleistocene. GLORIA imagery near Middleton Island provides a new perspective on the glacimarine depositional environment on the continental slope in a collision zone between the Pacific and North American plates. Southwest of Middleton Island, along the subduction margin, sinuous valleys funnel sediment around shelf-edge-parallel, subduction-created, anticlinal ridges that have deflected and locally trapped glacimarine sediment. The slope south and southeast of Middleton Island where oblique convergence occurs, is incised by dendritic, erosional gulley systems, contains no compressional ridges, and thus, the apparently active sediment pathways to the trench are unrestricted. However, below the sea valley mouths, apparently both glacial and glacimarine sediments blanket the upper slope, covering any dendritic gulley systems that may have formed during or since the Pleistocene low stands of sea level.

GLORIA Imagery Links Sedimentation in Aleutian Trench to Yakutat Margin via Surveyor Channel: ABSTRACT

GLORIA side-scan sonar imagery shows that the continental slope developing along the active margin of the Gulf of Alaska is devoid of large submarine canyons, in spite of the presence of large glacially formed sea valleys that cross the continental shelf. In the western and northern Gulf, discontinuous, actively growing deformation structures disrupt or divert the downslope transport of sediment into the Aleutian Trench. To the east of Middleton Island, the slope is intensively gullied and incised only by relatively small canyons. At the base of the gullied slope between Pamplona Spur and Alsek Valley, numerous small slope gullies coalesce into three turbidity current channels that merge to form the Surveyor deep-sea channel. About 350 km from the margin, the channel crosses the structural barrier formed by the Kodiak-Bowie Seamount chain and heads south for another 150 km where it bends northerly, perhaps influenced by the oceanic basement relief of the Patton Seamounts. The channel, now up to 5 km wide and deeply entrenched to 450 m, continues northerly for 200 km where it intercepts the Aleutian Trench, some 700 km from the Yakutat margin. South of Surveyor Channel, GLORIA imagery revealed evidence of another older channel. The older channelmore » meanders through a gap in the seamount chain and eventually bends northwesterly. This now inactive, largely buried channel may have carried turbidity currents to the Aleutian Trench concurrent with the active Surveyor Channel.« less

Seismic reflection characteristics of glacial and glacimarine sediment in the Gulf of Alaska and adjacent fjords

Glaciation together with tectonism have been dominant factors affecting sedimentation in the Gulf of Alaska area from at least the late Miocene throughout the Quaternary. The effects of tectonism are apparent in high mountains that border the gulf, raised terraces of Middleton Island and the eastern gulf coastal zone, and numerous active faults and related earthquakes. Glacial evidence includes magnificent glaciers and their onshore deposits, spectacular fjords, large sea valleys incised in the continental shelf, submarine morainal ridges at mouths of bays and sea valleys, and thick glacimarine sedimentary sequences (diamicts) that are exposed onshore and at the sea floor along the outer shelf. Seismic-reflection profiling and sampling of the uppermost marine sedimentary sequences in the Gulf of Alaska and adjacent fjords and bays have allowed identification of three discrete glacially related stratigraphic units. These units were delineated on the basis of seismic signature, geometry, physiographic location, stratigraphic position, and sedimentologic characteristics. The oldest unit, a Quaternary diamict, is portrayed on seismic profiles by irregular, discontinuous reflections. This unit probably includes till, outwash and glacimarine sediment. A geographically restricted unit, one incorporating Holocene end moraines at bay mouths and associated with some sea valleys, consists of jumbled masses of discontinuous reflections and very irregular surface morphology. The youngest unit, a blanket of Holocene sand to clayey silt prograding as a sediment wedge across the shelf, contains nearly horizontal, parallel reflections except where disrupted by mass movement. Although seismic-reflection data alone cannot provide definitive proof of the presence of glacial sediment, when combined with sea-floor sampling, seismic profiling is a powerful tool for determining the continuity of marine sedimentary units and relationships to past and modern glaciers.

Glacially Influenced Submarine-channel Sedimentation in the Yakataga Formation, Middleton Island, Alaska

ABSTRACT The Yakataga Formation (Miocene to Recent) is a 5-km sequence of marine and glaciomarine sediments underlying a large area of the Gulf of Alaska continental shelf. The upper, early Pleistocene part of the formation, some 1.25 km thick, is exposed on Middleton Island. A 200-m-thick sequence of channelized sand and gravel lithofacies at the base of the exposed succession outcrops on extensive wave-cut platforms. These facies fill channels up to 500 m wide and 70 m deep and are associated with lenticular units of diamict. Eight major facies types are identified within the channel infills: chaotic gravel/diamict, massive gravels and sands, inversely and normally graded gravels and sands, and massive diamict. Channelized gravel and sand facies were deposited by different types of sediment-gravity flows, including debris flows, turbidity currents, and density-modified grain flows; lenticular diamict units probably formed by the passive infilling of abandoned channels by marine muds and ice-rafted debris. The facies described in this paper infill a broad submarine-channel complex, cutting the Alaskan continental shelf edge and upper slope. The complex was fed by glacial meltstreams draining a grounded or partially floating ice sheet extending out onto the continental shelf. This paper provides the first detailed descriptions of extensive outcrops of glacially influenced submarine-channel-fill facies and provides important data as to the infills of large sea valleys and submarine canyons in both glacially influenced and nonglacial settings elsewhere.

Submarine valleys in the northeastern Gulf of Alaska: Characteristics and probable origin

The continental shelf of the northeastern Gulf of Alaska Between Prince William Sound and Cross Sound is cut by at least eight major valleys. From west to east, these are Hinchinbrook Seavalley, Egg Island Trough, Kayak Trough, Bering Trough, Pamplona Troughs, Yakutat Valley, Alsek Valley and Yakobi Valley. Evidence common to most of these troughs or valleys indicating that the present morphology is due to glacial processes includes: (1) a pre-Holocene subbottom erosional surface incised into the underlying lithified strata of the shelf; (2) U-shaped cross sections, both at the sea floor and at the pre-Holocene erosional surface; (3) concave longitudinal sections, commonly shoaling at the seaward end; (4) till-like sediments collected from the walls or outer shelf adjacent to the troughs; and (5) seismic stratigraphy that can be correlated with bottom samples indicative of glacially derived strata. Depressions with tens of meters of relief are present on the pre-Holocene subbottom erosional surface beneath most of these valleys. These depressions have been partially filled by a seaward-thinning wedge of Holocene glacial flour (clayey silt) that is filling the valleys and blanketing the inner shelf at rates as high as 15 mm/yr (based on 210Pb measurements). Although glaciation played a dominant role in the modern morphology of these sea valleys, structural features, including structurally controlled topographic highs on the shelf (e.g. Tarr Bank, Kayak Island, Pamplona Spur and Fairweather Ground) influenced the flow directions of the glacial lobes.

Book Review

Book review in This Article: Currents in Submarine Canyons and Other Sea Valleys, by F. P. Shepard, N. F. Marshall, P. A. McLaughlin and G. G. Sullivan. Deltaic Sand Bodies, by J. M. Coleman and D. B. Prior. A.A.P.G. Continuing Education Course Note Diagenesis in Sediments and Sedimentary Rocks, ed. by G.Larsen and G.V. Chilingar. NOAA Atlas 3. The Central North Atlantic Ocean Basin and Continental Margins, by P. A. Rona Continental Red Beds, by P. Turner. Sedimentation in Oblique‐Slip Mobile Zones, ed. P. F. Ballance and H. G. Reading. Concepts and Models of Dolomitization, ed. by D. H. Zenger, J. B. Dunham and R. L. Ethington.

Assessment of relative slope stability of Kodiak shelf, Alaska, using high‐resolution acoustic profiling data

Abstract The use of marine high‐resolution geophysical profiling data, seafloor soil samples, and accepted land‐based methods of analysis have provided a means of assessing the regional geotechnical conditions and relative slope stability of the portion of the Gulf of Alaska Continental Margin known as the Kodiak Shelf. Eight distinct types of soils were recognized in the study; the seafloor distribution of these indicates a complex geotechnical setting. Each soil unit was interpreted as having a distinct suite of geotechnical properties and potential foundation engineering problems. Seven categories of relative slope stability were defined and mapped. These categories range from “highest stability”; to “lowest stability,”; and are based on the degree of slope of the seafloor, type of soil underlying the slope, and evidence of mass movement. The results of the analysis indicate that the highest potential for soil failure exists on (1) the slopes forming boundaries between the submarine banks and the broad sea valleys, and (2) the upper portion of the continental slope, where evidence of past slope failure is common. Also of concern are gently sloping areas near the edges of submarine banks where evidence of possible tension cracks and slow downhill creep was found.

Morphology and sedimentary processes in and around Tortugas and Agassiz Sea Valleys, southern Straits of Florida

Continuous seismic reflection profiling and new bathymetry data in the southern Straits of Florida over an area dominated by the Tortugas and Agassiz Valley systems have allowed a more detailed analysis of the morphology and sedimentary processes active in this region. Four dives in the submersible DSV “Alvin” supplement the seismic and bathymetric data. The continental slope in the study area can be divided into two physiographic provinces: (I) an irregular topography controlled by the Florida Escarpment west of Tortugas Valley; and (II) the remainder of the continental slope which contains the majority of features under investigation. Seismic data indicate that the valleys are being filled shoreward of 290 fathoms (530 m) by a wedge of prograding sediments derived from the Florida shelf. The morphology of the two valley systems reflects probable differences of origin. Tortugas Valley appears to have originated coincident with the eastern terminus of the Florida Escarpment and province-I-type topography. The Agassiz valleys may have an origin associated with jointing patterns observed by divers aboard DSV “Alvin”. Current meter readings and bottom photographs from “Alvin” indicate that currents are relatively sluggish and not very effective in the transport of sediment within the valleys. An area of undulations west of Pourtales Terrace was investigated and concluded to be erosional in origin. Slumping appears to have played a large part in shaping many features in the study area. The bottom morphology and sediment distribution on the continental slope and in the axis of the Straits of Florida suggest that bottom currents are active in shaping the entire area.

Submarine Canyons and Other Sea Valleys. Francis P. Shepard , Robert F. Dill

Previous articleNext article No AccessReviewsSubmarine Canyons and Other Sea Valleys. Francis P. Shepard , Robert F. Dill Robert L. MillerRobert L. Miller Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 77, Number 6Nov., 1969 Article DOIhttps://doi.org/10.1086/627484 Views: 4Total views on this site Copyright 1969 The University of ChicagoPDF download Crossref reports no articles citing this article.

Interaction of Rivers and Oceans--Pleistocene Petroleum Potential

The common association of a river (with or without a delta), submarine canyon, and abyssal fan implies a genetic relation. The formation of these features must be considered as one dynamic system and not as independent events. A river entering the ocean may deposit most of its load near its mouth. Factors such as fluctuating discharge and saltwater encroachment, resuspension of material by current action, and other processes may cause much of this material to be conveyed to the deeper parts of the ocean basins. These sediments, commonly transported through submarine canyons or sea valleys, ultimately will be deposited on the abyssal plains, either in the form of a submarine cone or redistributed by deep currents to form a continental rise. The Los Angeles basin and some fields in the Gulf Coast contain prolific petroleum reserves in deep-water turbidites. The accumulations are in reservoirs of different Cenozoic ages. Oil and gas fields have been discovered in sediments of Pleistocene age; however, the known accumulations are only modest. As exploration moves seaward, greater volumes of late Cenozoic sedimentary strata and petroleum accumulations can be anticipated. During the Pleistocene, the regimens of rivers were altered significantly. For long periods of time, lowered sea level, increased river gradients, and voluminous glacial meltwater in flood-swollen rivers prevented the formation of large deltas. The net result was transportation of great sediment volumes across the continental shelf and slope with attendant canyon cutting and the deposition of the material at the base of the slope as submarine fans. The associated reservoir rocks of these fans may contain petroleum reserves as great as those of their shoreline equivalents, the deltas.