Letteratura scientifica selezionata sul tema "Sub-Marine canyon"

ABSTRACT Submarine slopes prograde via accretion of sediment to clinoform foresets and degrade in response to channel or canyon incision or to mass-wasting processes. The timescales over which progradation and degradation occur, and the large-scale stratigraphic record of these processes, remain unclear due to poor age constraints in subsurface-based studies and areally limited exposures of exhumed systems. We here integrate 3D seismic reflection and borehole data to study the geometry and origin of ancient slope canyons developed in late Mesozoic strata of the Måløy Slope, offshore Norway. Slope degradation and canyon incision commenced during the late Kimmeridgian, coincident with the latter stages of rifting. Later periods of canyon formation occurred during the Aptian to Albian and the Albian to Cenomanian, during early post-rift subsidence. The canyons are straight, up to 700 m deep, and 10 km wide on the upper slope and die out downdip onto the lower slope. The canyons trend broadly perpendicular to and crosscut most of the rift-related normal faults, although syn-filling fault growth locally helped to preserve thicker canyon-fill successions. The headwalls of the oldest (late Kimmeridgian) canyons are located at a fault-controlled shelf edge, where younger canyons overstep this fault, which was inactive when they formed, extending across the paleo-shelf. Downslope, Aptian to Albian canyons either erode into the older, late Kimmeridgian to Barremian canyon fills, forming a complicated set of unconformities, or in the case of the Albian to Cenomanian canyons, die out into correlative conformities. Boreholes indicate that the canyon bases are defined by sharp, erosional surfaces, across which we observe an abrupt upward shift from shallow- to deep-marine facies (i.e., late Kimmeridgian canyons), or deep marine to deep marine facies (Aptian to Albian and Albian to Cenomanian canyons). Missing biostratigraphic zones indicate the canyons record relatively protracted periods (c. 2–17 Myr) of structurally enhanced slope degradation and sediment bypass, separated by > 10 Myr periods of deposition and slope accretion. The trigger for slope degradation is unclear, but it likely reflects basinward tilting of this tectonically active margin, enhanced by incision of the slope by erosive sediment gravity flows. The results of our study have implications for the timescales over which large-scale slope progradation and degradation may occur on other tectonically active slopes, and the complex geophysical and geological record of these processes. We also show that canyon formation can cause large volumes of margin-derived sediment to bypass proximal sub-basins within rifted terranes, an important process not currently captured by marine rift-basin tectono-stratigraphic models.

The Gambier Sub-basin lies on the southern Australian passive continental margin that formed during continental breakup and seafloor spreading between the Australian and Antarctic plates. In addition to the numerous modern submarine canyons reported on the southern Australian margin, three palaeo-canyon systems have been identified within the Gambier Limestone of the South Australian Gambier Sub-basin. Favourable environmental conditions during the Oligocene and Early Miocene led to deposition of the Gambier Limestone, a widespread, prograding extra-tropical carbonate platform. A world-wide glacio-eustatic sea level fall in the Early Oligocene exposed the shelf in the Gambier Subbasin, causing widespread erosion and minor fluvial incision on the shelf and subsequent formation of nick points at the shelf edge. During the following marine transgression later in the Oligocene, the shelf was inundated and the nick points provided conduits for erosive turbidity currents to enlarge the canyons to the spectacular dimensions observed on seismic data. No less than 20 successive canyon cut and fill events ranging from Late Oligocene to Middle Miocene have been observed and mapped on seismic data across the shelf in the Gambier Sub-basin. The thick, dominantly fine-grained carbonate sheet logically represents a potential regional seal to underlying clastic reservoirs. However, the possibility exists for carbonate reservoir sands to be present within the palaeo-canyons, sealed by surrounding fine-grained carbonates. Although no hydrocarbons have yet been identified in the carbonates of the Gambier Sub-basin, the canyons provide an analogue useful for establishing the scale, internal architecture and geometry of canyon fill systems.

AbstractThis paper presents a revised sequence stratigraphy for the lower, middle and upper Badenian depositional systems of the Austrian Vienna Basin based on the integration of 3D seismic surveys and well data. The study area in the central and northern part of the Austrian Vienna Basin is covered with 3D seismic data. According to a new sequence stratigraphic framework established in the southern part of the Vienna Basin, the Badenian is subdivided into three 3rd order depositional sequences. For each sequence, paleogeographic maps are created, representing coeval depositional systems within a chronostrati-graphic interval. Lower Badenian sediments of the 1st sequence (Ba1) represent fillings of the pre-Badenian sub-basins with a major change of sediment transport direction. The early stage of the 1st sequence is dominated by subaerial braided river deposits which use two pronounced canyon systems (Mistelbach Canyon and Reinthal Canyon) on the northwestern margin of the Vienna Basin as a bypass zone towards the marine depositional system of the North Alpine-Carpathian Foredeep. The late stage of the 1st sequence reflects the change from subaerial to marine depositional environments with main sediment influx from the west, creating two major eastwards prograding delta systems (Zistersdorf Delta and Mühlberg Delta). Depositional systems of the middle Badenian 2nd sequence (Ba2) reflect the interplay between ongoing extensional fault tectonics and major sea-level changes. Lower Badenian paleo-highs in the northern part are drowned during the 3rd sequence (Ba3), thus the Mühlberg Delta and the Zistersdorf Delta merge into one delta system. During the Ba3 the drowning of the Spannberg Ridge initiates a clockwise rotation of the Zistersdorf Delta. Thus, the former Zistersdorf Delta transforms into the Matzen Delta covering the Spannberg Ridge. Together with the Mühlberg Delta, they represent the last full marine depositional system of the eastward prograding paleo-Danube Delta in the Austrian Vienna Basin.

We processed the raw multi-beam bathymetry data acquired in the central and northeastern part of the South China Sea by eliminating noise and abnormal water depth values caused by environmental factors, and a high resolution bathymetric map with a 20-m grid interval was constructed. Various scales of seafloor geomorphological features were identified from the data, including an image of Shenhu canyon, which is located in the northern continental margin of the South China Sea; submarine reticular dunes in the north of the Dongsha atoll; submarine parallel dunes in the northeast of the Dongsha atoll; and several seamounts in the southwest sub-basin and in the east sub-basin. In the processing step, various anomalies in the multi-beam bathymetry data were corrected. The optimal swath filtering and surface filtering methods were chosen for different scales of seafloor topography in order to restore the true geomorphological features. For the large-scale features with abrupt elevation changes, such as seamounts (heights of ~111–778 m) and submarine canyons (incision height of ~90–230 m), we applied swath filtering to remove noise from the full water depth range of the data, and then surface filtering to remove small noises in the local areas. For the reticular dunes and parallel dunes (heights of ~2–32 m), we applied only surface filtering to refine the data. Based on the geometries of the geomorphological features with different scales, the marine hydrodynamic conditions, and the regional structure in the local areas, we propose that the Shenhu submarine canyon was formed by turbidity current erosion during the Sag subsidence and the sediment collapse. The submarine reticular dunes in the north of the Dongsha atoll were built by the multi-direction dominant currents caused by the previously recognised internal solitary waves around the Dongsha atoll. The submarine parallel dunes in the northeast of the Dongsha atoll were built by the repeated washing of sediments with the influence of the tidal currents and internal solitary waves. The conical, linear and irregular seamounts identified from the bathymetry data were formed during the spreading of the southwest sub-basin and the east sub-basin. The identified seamounts in the multi-beam bathymetry data are correlated to deep magmatic activities, the Zhongnan transform fault and the NE-trending faults.

This study focuses on the inversion of sub-bottom profile (SBP) data in the northern South China Sea using an empirical relationship derived from sediment acoustic data. The sub-bottom profile is primarily utilized for various marine applications, such as geological mapping and resource exploration. In this research, we present a study conducted in the northern slope canyon of the South China Sea. Firstly, we obtained the seabed reflection coefficient from sub-bottom profiles obtained by the autonomous underwater vehicle (AUV) detection system. Secondly, we utilized the acoustic empirical relationship in the northern South China Sea to establish relationship equations between the seabed reflection coefficient and the porosity, density, and average particle size of the sediment at a main frequency of 4 kHz (the AUV shallow profile main frequency). Then, using these equations, we were able to invert the physical parameters such as porosity, density, and average particle size of the seabed surface sediments. Finally, the inverted results are compared and analyzed by using the sediment samples test data. The overall deviation rate of the inverted physical parameters is within the range of ±10% when compared. The inverted results closely match the measured values, accurately reflecting the dynamic changes in the physical properties of seabed surface sediments. Notably, the average grain size is a direct indicator of the sediment particles size with smaller particles found in deeper water. The variation characteristics of sediment physical parameters align well with the variation of sediment types in the canyon, which is consistent with changes in the water depth, topography, and hydrodynamic conditions of the area. This further demonstrates the reliability of the inversion results.

Abstract. Anaerobic oxidation of methane (AOM) and sulfate reduction (SRR) were investigated in sediments of the western Black Sea, where upward methane transport is controlled by diffusion. To understand the regulation and dynamics of methane production and oxidation in the Black Sea, rates of methanogenesis, AOM, and SRR were determined using radiotracers in combination with pore water chemistry and stable isotopes. In the Danube Canyon and the Dnjepr palaeo-delta AOM did not consume methane effectively and upwards diffusing methane created an extended sulfate-methane transition zone (SMTZ) that spread over more than 2.5 m and was located in brackish and limnic sediment. Measurable AOM rates occurred mainly in the lower part of the SMTZ, sometimes even at depths where sulfate seemed to be unavailable. The inefficiency of methane oxidation appears to be linked to the paleoceanographic history of the sediment, since in all cores methane was completely oxidized at the transition from the formerly oxic brackish clays to marine anoxic sediments. The upward tailing of methane was less pronounced in a core from the deep sea in the area of the Dnjepr Canyon, the only station with a SMTZ close to the marine deposits. Sub-surface sulfate reduction rates were mostly extremely low, and in the SMTZ were even lower than AOM rates. Rates of bicarbonate-based methanogenesis were below detection limit in two of the cores, but δ13C values of methane indicate a biogenic origin. The most δ13C- depleted isotopic signal of methane was found in the SMTZ of the core from the deep sea, most likely as a result of carbon recycling between AOM and methanogenesis.

Callovian to Tithonian syn-rift sediments in the eastern Barrow Sub-basin can be subdivided into five depositional sequences, each separated by regionally correlatable unconformities. Sequence boundary development can be closely related to periods of major changes in basin configuration associated with the sequential breakup of eastern Gondwanaland. Synchronism of major faulting with sequence boundary development during the early and late Callovian, mid Kimmeridgian, and mid Tithonian times supports tectonism being a dominant control on the development of Type 1 unconformities in the eastern Barrow Sub-basin.Upper Jurassic depositional sequences in the eastern Barrow Sub-basin, whether of tectonic or eustatic origin, consist primarily of lowstand systems tracts comprised, wholly or in part, of detached basin floor fan complexes, channelised and canyon-fed fan systems, slump deposits, outer shelf to slope deposits, and deep marine claystones. Inner shelf to shoreface sediments of the transgressive and highstand systems tracts are absent due to episodic, post-depositional uplift and erosion along the Peedamullah Shelf and Flinders Fault System during the Late Jurassic. The periods of uplift and erosion provided much of the sediment redeposited in basinal areas during lowstand times.Depositional models based on regional sequence stratigraphic studies can be integrated with local seismic stratigraphy to provide a mechanism for estimating likely reservoir quality, once controls on sedimentation (namely tectonics, eustasy, and sediment supply) are understood. This is demonstrated by the recognition of at least seven sandstone facies within the Upper Jurassic sedimentary section. Each sandstone has particular characteristics which can be related to the depositional setting. Reservoir quality is best developed in dominantly medium grained, moderate to well sorted sandstones, deposited as detached, basin floor submarine fan sands or interbedded turbidites. In contrast, reservoir quality is poorly developed in the remaining sand-prone facies deposited as slope fans, slumps, or distal turbidites.

The upper part of the Krka River estuary and Prokljan Lake are a specific example of a well-stratified estuarine environment in a submerged river canyon. Here, we reconstructed the geomorphological evolution of the area and classified the data gathered in the study, integrating multibeam echosounder data, backscatter echosounder data, side-scan sonar morpho-bathymetric surveys, and acoustic sub-bottom profiling, with the addition of ground-truthing and sediment analyses. This led to the successful classification of the bottom sediments using the object-based image analysis method. Additional inputs to the multibeam echosounder data improved the segmentation of the seafloor classification, geology, and morphology of the surveyed area. This study uncovered and precisely defined distinct geomorphological features, specifically submerged tufa barriers and carbonate mounds active during the Holocene warm periods, analogous to recent tufa barriers that still exist and grow in the upstream part of the Krka River. Fine-grained sediments, classified as estuarine sediments, hold more organic carbon than coarse-grained sediments sampled on barriers. A good correlation of organic carbon with silt sediments allowed the construction of a prediction map for marine sedimentary carbon in this estuarine/lake environment using multibeam echosounder data. Our findings highlight the importance of additional inputs to multibeam echosounder data to achieve the most accurate results.

A population of northern bottlenose whales (Hyperoodon ampullatus) uses the Gully, a submarine canyon off the coast of Nova Scotia, Canada. Eleven years of photo-identification records has permitted estimation of population size using mark-recapture techniques. The population estimate was small (133 individuals, 95% CI = 111-166 from left side identifications; 127 individuals, 95% CI = 106-160 from right side identifications). The population was not closed, with the combined mortality, mark change and emigration rate estimated at 13% per year for left side identifications (95% CI = 9-17) and 14% for right side identifications (95% CI = 10-18). There was no significant increase or decrease in the population size between 1988-1999 (change in population size: left side: –0.13% per year, 95% CI = -3.4 to 3.9; right side: –0.43% per year, 95% CI = -4.5 to 3.1). The sex ratio was roughly 1:1, with equal numbers of sub-adult and mature males. Over the summer field season, individuals emigrated from, and re-immigrated into the Gully, spending an average of 20 days within the Gully before leaving (left side identifications 19 days, SE = 17; right side identifications 23 days, SE = 10). Approximately 34% of the population was present in the Gully at any time. Individuals of all age and sex classes displayed similar residency patterns although there were annual differences as individuals spent less time in the Gully in 1996 than in 1990 and 1997. Sighting rates were similar in all years with extensive fieldwork, indicating little variability in the number of whales in the Gully each summer. Accurate estimates of population size and residency patterns will be useful in determining the regulations and required coverage for a marine protected area in the Gully.

Abstract. We have determined stable carbon isotope ratios of epifaunal and shallow infaunal benthic foraminifera in the Mediterranean Sea to relate the inferred gradient of pore water δ13CDIC to varying trophic conditions. This is a prerequisite for developing this difference into a potential transfer function for organic matter flux rates. The data set is based on samples retrieved from a well-defined bathymetric range (400–1500 m water depth) of sub-basins in the western, central, and eastern Mediterranean Sea. Regional contrasts in organic matter fluxes and associated δ13CDIC of pore water are recorded by the δ13C difference (Δδ13CUmed-Epi) between the shallow infaunal Uvigerina mediterranea and epifaunal species (Planulina ariminensis, Cibicidoides pachydermus, Cibicides lobatulus). Within epifaunal taxa, the highest δ13C values are recorded for P. ariminensis, providing the best indicator for bottom water δ13CDIC. In contrast, C. pachydermus reveals minor pore water effects at the more eutrophic sites. Because of ontogenetic trends in the δ13C signal of U. mediterranea of up to 1.04 ‰, only tests larger than 600 µm were used for the development of the transfer function. The recorded differences in the δ13C values of U. mediterranea and epifaunal taxa (Δδ13CUmed-Epi) range from −0.46 to −2.13 ‰, with generally higher offsets at more eutrophic sites. The measured δ13C differences are related to site-specific differences in microhabitat, depth of the principal sedimentary redox boundary, and TOC content of the ambient sediment. The Δδ13CUmed-Epi values reveal a consistent relation to Corg fluxes estimated from satellite-derived surface water primary production in open-marine settings of the Alboran Sea, Mallorca Channel, Strait of Sicily, and southern Aegean Sea. In contrast, Δδ13CUmed-Epi values in areas affected by intense resuspension and riverine organic matter sources of the northern to central Aegean Sea and the canyon systems of the Gulf of Lion suggest higher Corg fluxes compared to the values based on recent primary production. Taking regional biases and uncertainties into account, we establish a first Δδ13CUmed-Epi-based transfer function for Corg fluxes for the Mediterranean Sea.

Les canyons sous-marins sont des corridors majeurs pour le transfert des sédiments des continents vers les bassins sous-marins profonds. Considérés comme des structures de transit scellées par des boues distales, les canyons ont peu fait l'objet de prospective en termes de géologie de réservoir. La source des sédiments, le moment des apports, les mécanismes de transport dans les canyons sous-marins diffèrent d'une marge à l'autre en fonction des contextes climatique et géodynamique, ce qui en fait un vaste champ d'étude. Ce travail présente les résultats d'une étude sismique 3D haute résolution d'un canyon du SE du delta du Niger, le canyon de Galabor. Le volume sismique étudié, calé au puits (gamma ray et calibration biostratigraphique), a été et exploré à travers (i) des coupes verticales réalisées le long et en travers des thalwegs du canyon et (ii) des cartes d'attributs sismique des horizons-clés. Après une revue bibliographique, deux articles soumis au BSGF sont présentés dans ce mémoire. Le premier article se concentre sur la géomorphologie sismique et les relations entre la déformation gravitaire (argilocinèse, failles de détachement) et la dynamique du canyon. Le confinement des écoulements turbiditiques dans des ensellements bordés par des reliefs diapiriques explique une grande partie du piégeage du sable dans le haut de pente. Les processus de chenal sont responsables du tri et de la concentration de sable dans des ceintures méandriformes qui débordent largement de l'incision initiale. Le deuxième article concerne la stratigraphie séquentielle. Deux séquences de dépôt de 100 000 ans sont identifiées, séparées par un horizon daté à 0,99 Ma. Dans chaque séquence, le sable n'est pas sourcé par une vallée incisée mais par l'érosion régressive sous-marine de deltas de bordure de plateforme. Le sable est en bypass dans le cortège de chute, dominé par des écoulements de débris boueux, et stocké dans le cortège de bas niveau. Le cortège transgressif, épais et formant une excellente couverture au-dessus du réservoir sableux, est dominé par une sédimentation fine hémipélagique et le cortège de haut niveau est absent. Des questions demeurent, comme celle du sourçage du sable et des transformations de l'écoulement entre les mécanismes gravitaires et tractifs
Submarine canyons are major corridors for transferring sediments from continents to deep submarine basins. Considered transit structures sealed by distal mud, canyons have little perspective in reservoir geology. The source of the sediments, the timing of inputs, and the transport mechanisms in submarine canyons differ from one margin to another depending on the climatic and geodynamic contexts, making it a vast field of study. This work presents the results of a high-resolution 3D seismic survey of a south-eastern submarine canyon in the Niger Delta, the Galabor Canyon. After a literature review, two articles submitted to BSGF are presented in this dissertation. The first article focuses on seismic geomorphology and the relationships between gravity deformation (shale ridges, detachment faults) and canyon dynamics. The seismic volume studied, wedged at the well (gamma ray and biostratigraphic calibration), was explored through (i) vertical sections along and across the thalwegs of the canyon and (ii) seismic attribute maps of key horizons. The confinement of turbiditic flows in intra slope basin bordered by shale ridges explains much of the trapping of sand at the upper slope. Channel processes are responsible for sorting and concentrating sand in meander belts that extend far beyond the initial incision. The second article concerns sequential stratigraphy. Two 100,000-year-old deposition sequences are identified, separated by a dated horizon of 0.99 Ma. In each sequence, the sand is not sourced by an incised valley but by the regressive submarine erosion of shelf-edge deltas. The sand is bypassed in the falling stage system tract, dominated by mass transport deposits, and preserved in the low stand system tract. The transgressive system tract, which is thick and forms an excellent seal above the sandy reservoir, is dominated by fine hemipelagic sedimentation and the high stand system tract is absent. Questions such as sediment source and flow transformations between gravity and tractive mechanisms remain unanswered

Abstract The biogeography of salps and pyrosomas has so far been treated only by the classical approach of tabulating individual distributions, combining them into a limited number of inferred areas of endemism, and comparing these with abiotic parameters such as temperature and ocean current patterns (Van Soest, 1975, 1979; Van der Spoel and Heyman, 1983). This ecological approach emphasizes salp and pyrosoma recent ecology, ignoring the historical causes underlying the distribution patterns. However, it cannot answer such questions as: why are there no Arctic salp species?; where and when did the (sub)Antarctic species arise?; why are so many tax.a restricted to the Indo-West Pacific? Such questions might perhaps be answered by inferring possible scenarios for the observed distribution patterns from the geological history of the oceans (e.g. Van Soest, 1975). However, although this approach may work well in certain land and freshwater areas and much less well in benthic marine areas, in the pelagic environment it is virtually useless since there are great uncertainties about palaeoecology and palaeocurrent patterns earlier than the Pleistocene.

ABSTRACT Exploration in the offshore Nile Delta province has revealed several hydrocarbon plays. Deep marine Turbidites is considered one of the most important plays for hydrocarbon exploration in the Nile Delta. These turbidites vary from submarine turbidite channels to submarine basin floor fans. An integrated exploration approach was applied for a selected area within West Delta Deep Marine (WDDM) Concession offshore western Nile Delta using a variety of geophysical, geological and geochemical data to assess the prospectivity of the Pre-Messinian sequences. This paper relies on the integration of several seismic data sets for a new detailed interpretation and characterization of the sub-Messinian structure and stratigraphy based on regional correlation of seismic markers and honoured the well data. The interpretation focused mainly on the Oligocene and Miocene mega-sequences. The seismic expression of stratigraphic sequences shows a variety of turbidite channel/canyon systems having examples from West Nile delta basin discoveries and failures. The approach is seismically based focusing on seismic stratigraphic analysis, combination of structure and stratigraphic traps and channels interpretation. Linking the geological and geophysical data together enabled the generation of different sets of geological models to reflect the spatial distribution of the reservoir units. The variety of tectonic styles and depositional patterns in the West Nile delta provide favourable trapping conditions for hydrocarbon generations and accumulations. The shallow oil and gas discoveries in the Pliocene sands and the high-grade oils in the Oligo-Miocene and Mesozoic reservoirs indicate the presence of multiple source rocks and an appropriate conditions for hydrocarbon accumulations in both biogenic and thermogenic petroleum systems. The presence of multi-overpressurized intervals in the Pliocene and Oligo-Miocene Nile delta stratigraphic column increase the depth oil window and the peak oil generation due to decrease of the effective stress. Fluids have the tendency to migrate from high pressure zones toward a lower pressure zones, either laterally or vertically. Also, hydrocarbons might migrate downward if there is a lower pressure in the deeper layers. Well data and the available geochemical database have been integrated with the interpreted seismic data to identify potential areas of future prospectivity in the study area.

Abstract Everyone is used to seeing graphs predicting unprecedented growth for the offshore wind industry over the next decades. Whether or not these ambitious goals are achieved remains to be seen, as it will require nothing less than an industrial revolution in offshore construction and installation. Never have such growth projections been backed by a global sense of urgency, but unfortunately, it is not just the growth challenge that has to be met and resolved. Data from insurance companies show a significant growth in financial losses in the offshore wind industry. For an expanding industry, an increase in insurance claims may be a result of the growth, however, even when normalizing the financial losses against industry CAPEX, number of turbines, or installed capacity, worrying trends are seen. For offshore wind to be a viable energy source in the future, the quality of design, installation and operation needs to improve significantly. Furthermore, the industry cannot continue to scale developments until it has overcome some serious reliability issues. In offshore wind, we have seen how an extreme focus on reducing CAPEX in projects has led to low-quality engineering and choice of sub-standard products that are not fit for long-term applications exposed to dynamic loading in marine environments. Standardization is needed, reflecting the best insight, experiences, methods, and tools. Although the challenges were never as extensive in oil and gas as in offshore wind today, the situation still resembles the quality and technology challenges faced by the offshore oil and gas industry some two decades ago. Many of the design challenges that have been overcome in oil and gas have been incorporated into codes, standards, and well-established engineering practices. Seen from a distance, the offshore wind industry experience similar trends. However, with the ongoing rapid growth, the learning and improvement processes need to be accelerated by leveraging the experiences from oil and gas. On the shoulders of a mature offshore industry and today's digital capabilities, standardization and up-scaling of offshore wind have better opportunities than oil & gas had 25 years ago. However, to leverage this opportunity a true life-of-field approach is required.