Gravity Flow Events Research Articles

Reconstruction of the 1908 Messina gravity flow (central Mediterranean Sea) from geophysical and sedimentological data

Earthquakes, tsunamis and gravity flows are common processes offshore Eastern Sicily and pose a significant hazard to coastal communities and infrastructure. The 1908 Messina earthquake and tsunami resulted in >60,000 casualties. It caused a large turbidity current, which broke the Malta-Zante telegraph cable. Yet, this gravity flow remains poorly characterised in terms of its route and flow behaviour. A comprehensive analysis of multibeam echosounder data, sub-bottom profiles, and sediment cores has been carried out to improve our understanding about gravity flow activity within conduit systems of the western Ionian Basin to reconstruct the characteristics of the 1908 sediment flow (e.g., erosion, velocity, source region). Three main canyon-channel systems can be distinguished within the study area. The easternmost system (C3) appears to be the most active in terms of sediment transport. There are numerous erosional and depositional bedforms, including large-scale scours (>100 m-long), turbidite sediment waves and channel wall collapses that are not overprinted by younger events. The other two canyon-channel systems (C1, C2) do not show many bedforms indicative of repeated and recent gravity flow activity. Indeed, the transport of the majority of sediment discharged into the western system (C1) is limited to <25 km downslope from the continental slope, while the central system (C2) facilitates sediment deposition from gravity flows. C3 is, thus, suggested to have been the main passageway of the 1908 sediment flow. It also leads directly to two of three cable break locations. The most likely source areas for the gravity flow are north-eastern Sicily and southern Calabria. Bedforms indicate a flow thickness of >170 m along the upper channel portion of C3 and > 140 m along its lower portion close to the cable breaks. An average flow velocity of 5.6 to 6.3 ms−1 is reconstructed, given the timing of the breaks and length of the canyon-channel system. The flow may have locally decelerated and accelerated while bypassing morphologic highs and knickpoints. These new findings significantly improve our understanding of the 1908 gravity flow (e.g., passageways, depositional/erosional behaviour, thickness, velocity) and provide important insights into gravity flow events in general, especially those with a large run-out. This knowledge is needed to assess potential hazards associated with these events.

Sedimentological analysis and bed thickness statistics from a Carboniferous deep-water channel-levee complex: Myall Trough, SE Australia

This investigation presents an outcrop-based integrated study of internal division analysis and statistical treatment of turbidite bed thickness applied to a Carboniferous deep-water channel-levee complex in the Myall Trough, southeast Australia. Turbidite beds of the studied succession are characterized by a range of sedimentary structures grouped into two main associations, a thick-bedded and a thin-bedded one, that reflect channel-fill and overbank/levee deposits, respectively. Three vertically stacked channel-levee cycles have been identified. Results of statistical analysis of bed thickness, grain-size and internal division patterns applied on the studied channel-levee succession, indicate that turbidite bed thickness data seem to be well characterized by a bimodal lognormal distribution, which is possibly reflecting the difference between deposition from lower-density flows (in a levee/overbank setting) and very high-density flows (in a channel fill setting). Power law and exponential distributions were observed to hold only for the thick-bedded parts of the succession and cannot characterize the whole bed thickness range of the studied sediments. The succession also exhibits non-random clustering of bed thickness and grain-size measurements. The studied sediments are also characterized by the presence of statistically detected fining-upward sandstone packets. A novel quantitative approach (change-point analysis) is proposed for the detection of those packets. Markov permutation statistics also revealed the existence of order in the alternation of internal divisions in the succession expressed by an optimal internal division cycle reflecting two main types of gravity flow events deposited within both thick-bedded conglomeratic and thin-bedded sandstone associations. The analytical methods presented in this study can be used as additional tools for quantitative analysis and recognition of depositional environments in hydrocarbon-bearing research of ancient deep-water channel-levee settings.

A sedimentological model of organic-matter preservation and phosphogenesis in the Miocene Monterey Formation at Haskells Beach, Goleta (central California)

At Haskells Beach, west of Santa Barbara (CA, U.S.A.), the upper part of the Miocene Monterey Formation is predominantly composed of organic-rich mudstone, which is interstratified with phosphatic laminae and lenses. Minor lithologies consist of dolomite, volcanic ash, porcelanite, chert and condensed phosphate. These sediments date from the end of the Serravallian and almost the entire Tortonian (11.05–7.85Ma) based on calcareous nannofossils and the δ13Corg record, which correlates well with the global record. Sediments have total organic-carbon values between 2.75 and 9.15wt.% (average value=6.48 wt.%; n=61). Rock-Eval analyses show the dominance of type-II kerogen. The sediment accumulation rate varied between 5.9 and 84.7m/Ma. Correspondingly, organic-carbon accumulation rates range between 0.08 and 1.43 g/cm2/ky (average value=0.48 g/cm2/ky). Total phosphorus contents in the organic-rich mudstone vary between 0.001 and 3.48 wt.% and Corg/Porg ratios show high values of up to 4727 (average value=2232), whereas Corg/Ptotal values are low (up to 185; average value=52). This indicates that early diagenetic organic-matter degradation was a source of phosphate in phosphogenesis. In addition, other sources of phosphate were necessary in order to explain the abundance of phosphate relative to organic matter such as the transfer of dissolved inorganic phosphate into the sediments. Slumps, angular unconformities, erosive surfaces, reworked clasts and nodules, and condensed phosphatic layers suggest that hydrodynamic conditions were important and likely variable, leading to frequent erosion and sediment reworking. Under these circumstances, organic-matter was predominantly delivered during gravity-flow events, which were followed by longer periods of low sediment accumulation and phosphogenesis of the uppermost sediment layer. Associated pore occlusion by phosphate minerals may have considerably enhanced the preservation of organic-matter. During the early Late Miocene, a progressive change is observed from the mixed accumulation of organic, phosphate, biosilica and carbonate sediments, to the predominant accumulation of biosilica-rich sediments. This change is related to more intense upwelling, a shift of the upwelling center to the Californian coastline, and a leveling out of basin topography leading to a more even spread of biosilica.

Status and Trends in Research on Deep‐Water Gravity Flow Deposits

AbstractDeep‐water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study, significant achievements have been made in terms of classification schemes, genetic mechanisms, and depositional models of deep‐water gravity flows. The research history of deep‐water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep‐water gravity flow theory; improvement and perfection of deep‐water gravity flow theory; and comprehensive development of deep‐water gravity flow theory. Currently, three primary classification schemes based on the sediment support mechanism, the rheology and transportation process, and the integration of sediment support mechanisms, rheology, sedimentary characteristics, and flow state are commonly used. Different types of deep‐water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows, sandy debris flows, and surge‐like turbidity currents. Resuspension of deposits by storms leads to quasi‐steady hyperpycnal turbidity currents (hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows, sandy debris flows, and hyperpycnal flows. Deep‐water fans, which are commonly controlled by debris flows and hyperpycnal flows, are triggered by sustainable sediment supply; in contrast, deep‐water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep‐water fine‐grained sedimentary deposits are derived primarily from fine‐grained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes, transformation between different types of gravity flow deposit, and monitoring and reproduction of the sedimentary processes of deep‐water gravity flows as well as a source‐to‐sink approach to document the evolution and deposition of deep‐water gravity flows are the most important research aspects for future studies of deep‐water gravity flows study in the future.

Interaction of Gravity Flows With a Rugged Mid-Ocean-Ridge Seafloor: An Outcrop Example from Macquarie Island

Rugged bathymetry along slow-spreading mid-ocean ridges has the potential to impinge a strong control on gravity flows derived from oceanic fault scarps. Sedimentary lithofacies from the Macquarie Island ophiolite supports this hypothesis by displaying systematic variations that correspond with volcanic substrate differences and proximity to rift-related faults. Pillow-basalt terranes are associated with tightly confined bedrock corridors that funnel gravity flows into one direction. Vertical lithofacies variations formed from high-density to low-density turbidity currents record successive fill stages of the corridor axis. During initial stages tight confinement in the axis suppressed flow dilution and fluid turbulence. With continued corridor-axis filling, more dilute gravity flows predominated and formed lateral gradations from axial coarse-grained turbidites into thinly interbedded overbank lithofacies along corridor margins. These gravity-flow lithofacies converge into very thin muddy condensed intervals along inter-corridor highs where significant bottom-current reworking occurred. Conversely, partly confined tabular-basalt-floored basins promoted lateral expansion and dilution of gravity flows throughout the duration of basin filling. Variable paleocurrent-indicator directions record multiple reflections of single gravity-flow events off basin-bounding fault barriers. Coarsening-upward trends in these partly confined basins from thinly interbedded pelagic chert and ripple-bedded sandstones up into stacked turbidites preserves the ponding of sediment-starved submarine fans. In general, these ponded basins preserve the fine-grained distal ends of a gravity-flow continuum from coarse-grained fault-proximal en masse failures and cohesionless debris flows into medial high-density turbidity flows and distal dilute turbidity flows.

Origins of large crescent-shaped bedforms within the axial channel of Monterey Canyon, offshore California

Crescent-shaped bedforms with wavelengths from 20 to 80 m, amplitudes to 2.5 m, and concave down-canyon crests occur in the axial channel of Monterey Canyon (offshore California, USA) in water depths from 11 to more than 350 m. The existence of these features may be an important new clue as to how sediment moves through submarine canyons. Three complementary studies were initiated in 2007 to understand the origin and evolution of these bedforms. (1) Vibracoring. Three transects of closely spaced remotely operated vehicle–collected vibracores were obtained across these bedforms. The seafloor underneath these features is composed of gravity-flow deposits. (2) Acoustic array. Three boulder-sized concrete monuments containing acoustic beacons were buried just below the surface of the canyon floor in ∼290 m water depth and their locations were redetermined on 17 subsequent occasions. Although the beacons became more deeply buried >0.6 m below the seafloor, they still could be tracked acoustically. Over a 26-month period the position of 1 or more of the beacons moved down-canyon during at least 6 discrete transport events for a total displacement of 994–1676 m. The movement and burial of the monuments suggest that the seabed was mobilized to >1 m depth during gravity-flow events. (3) Autonomous underwater vehicle (AUV) repeat mapping. AUV-acquired high-resolution multibeam mapping, and CHIRP (compressed high-intensity radar pulse) subbottom profiling surveys of the seafloor in the active channel were repeated four times in the first half of 2007. In addition, the movement of large instrument frames deployed in 2001–2003 within the axis of Monterey Canyon in the area now known to be associated with the crescent-shaped bedforms is documented. The fate of the frames has helped elucidate the frequency, transport potential, and processes occurring within the axis of Monterey Canyon associated with these bedforms. The crescent-shaped bedforms appear to be produced during brief gravity-flow events that occur multiple times each year, commonly coincident with times of large significant wave heights. Whether the bedforms are generated by erosion associated with cyclic steps in turbidity flows or internal deformation associated with slumping during gravity-flow events remains unclear.

Palaeoenvironments and weathering regime of the Neoproterozoic Squantum ‘Tillite’, Boston Basin: no evidence of a snowball Earth

The snowball Earth hypothesis describes episodes of Neoproterozoic global glaciations, when ice sheets reached sea-level, the ocean froze to great depth and biota were decimated, accompanied by a complete shutdown of the hydrological cycle. Recent studies of sedimentary successions and Earth systems modelling, however, have brought the hypothesis under considerable debate. The Squantum ‘Tillite’ (Boston Basin, USA), is one of the best constrained snowball Earth successions with respect to age and palaeogeography, and it is suitable to test the hypothesis for the Gaskiers glaciation. The approach used here was to assess the palaeoenvironmental conditions at the type locality of the Squantum Member through an analysis of sedimentary facies and weathering regime (chemical index of alteration). The stratigraphic succession with a total thickness of ca 330 m documents both glacial and non-glacial depositional environments with a cool-temperate glacial to temperate non-glacial climate weathering regime. The base of the succession is composed of thin diamictites and mudstones that carry evidence of sedimentation from floating glacial ice, interbedded with inner shelf sandstones and mudstones. Thicker diamictites interbedded with thin sandstones mark the onset of gravity flow activity, followed by graded sandstones documenting channellized mass gravity flow events. An upward decrease in terrigenous supply is evident, culminating in deep-water mudstones with a non-glacial chemical weathering signal. Renewed terrigenous supply and iceberg sedimentation is evident at the top of the succession, beyond which exposure is lost. The glacially influenced sedimentary facies at Squantum Head are more consistent with meltwater dominated alpine glaciation or small local ice caps. The chemical index of alteration values of 61 to 75 for the non-volcanic rocks requires significant exposure of land surfaces to allow chemical weathering. Therefore, extreme snowball Earth conditions with a complete shutdown of the hydrological cycle do not seem to apply to the Gaskiers glaciation.

High frequency of sediment gravity flow events in the Var submarine canyon (Mediterranean Sea)

This study aimed to analyze the role river floods play in triggering gravity flows and to investigate the role of submarine canyon systems as a conduit for terrigenous material to the deep sea. Two years of measurements in the Var canyon at depths ranging from 1200 m to 2350 m indicate that six floods of the Var River triggered hyperpycnal flows, an important mechanism for transporting particulate matter to the deep-sea floor. These sediment gravity flows were characterized by a sudden increase of current velocity that lasted 8 to 22 h and by downward particle fluxes that reached up to 600 g m − 2 d − 1 of particles and 3.1 g m − 2 d − 1 in terms of organic carbon. These large inputs of sediment and organic carbon may have a significant impact on deep-sea ecosystems and carbon storage in the Mediterranean Sea.

Reservoir modelling of the Hamitabat Field, Thrace Basin, Turkey: an example of a sand-rich turbidite system

Abstract The inter-montane, fault bounded Thrace Basin of northwestern Turkey is one of the largest Tertiary sedimentary basins in Turkey. Tertiary sedimentation within the basin comprises interbedded fine- to coarse-grained clastics from a variety of depositional environments, muddy carbonates with local reef developments, and tuff horizons. A thick pile of Quaternary alluvial deposits overlies this marine-dominated succession. Accommodation space, and hence sedimentation, has been influenced by the structural history of the basin, reflecting the active compressional setting adjacent to the North Anatolian Fault System. The Hamitabat Field, located towards the northern basin margin, is the largest developed gas field in the Thrace Basin. The trapping mechanism is by an anticlinal structure bounded to the north by a northwest-southeast striking reverse fault and to the south by a set of antithetic normal faults with a general east-west strike orientation. The main reservoir is the middle to upper Eocene Hamitabat Formation, comprising sandstones deposited by episodic gravity flow events in a shallow marine shelf to slope environment, with sediment sourced from fluvial/deltaic systems to the north and northeast. Correlation, based mainly on upward-fining cyclical successions, indicates lobate depositional geometries and topographic control on sediment dispersal (compensation). Progradational shallow marine sandstones, which infill earlier topography, overlie the turbidite succession. A three-dimensional geocellular reservoir model of the field, based on well and seismic data, has been constructed. The model has been subdivided on the basis of the stratigraphical correlation and populated with facies objects with dimensions based on analogue data. These facies have then been populated with petrophysical parameters. The model has been upscaled and simulated fluid flow through the modelled volume has been compared with the production history. This history matching provides an opportunity to assess and refine the model and to determine a strategy for future field development.

Caught in the act: the 20 December 2001 gravity flow event in Monterey Canyon

A sediment gravity flow descended through the axis of Monterey Canyon on 20 December 2001 at 13:35 Pacific standard time. The timing of this event is documented by a current-meter package which recorded an 11.9-dbar pressure increase in less than 10 min and was found 550 m down-canyon from its deployment site, buried completely within a >70-cm-thick gravity flow deposit. This event is believed to have started in less than 290 m of water because an instrument at this location was also lost at the same time. A 178-cm core collected after the event from the axis of the canyon at 1,297-m water depth contained fresh, greenish, chlorophyll-rich organic material at 32-cm sub-bottom depth, suggesting the event extended to this water depth. The only trigger identified for this mass movement event appears to be moderate sea and surf conditions. Thus, gravity flow events of this magnitude do not require an exceptional triggering event.

Overview of Late Quaternary stratigraphy in Saanich Inlet, British Columbia: results of Ocean Drilling Program Leg 169S

Abstract Continuous coring in Saanich Inlet (Ocean Drilling Program, ODP Leg 169S), British Columbia, Canada, yielded a detailed record of Late Quaternary climate, oceanography, marine productivity, and terrestrial vegetation. Two sites (1033 and 1034) were drilled to maximum depths of 105 and 118 m, recovering sediments ranging in age from 13,300 to less than 300 14 C yr. Earliest sediments consist of dense, largely massive, gray glaciomarine muds with dropstones and sand and silt laminae deposited during the waning stages of glaciation. Deposition of organic-rich olive gray sediments began in the fjord about 12,000 14 C yr ago, under well-oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community. At about 10,500 14 C yr, a massive, gray unit, 40–50 cm thick, was emplaced in a very short span of time. The unit is marked by a sharp lower contact, a gradational upper contact and an abundance of reworked Tertiary microfossils. It has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the Fraser Valley of mainland British Columbia. Progressively greater anoxia in bottom waters of Saanich Inlet began about 7000 14 C yr ago. This is reflected in the preservation of varved sediments consisting of diatomaceous spring–summer laminae and terrigenous winter laminae. Correlation of the sediments was based on: marked lithologic changes, the presence of massive intervals (reflecting localized sediment gravity flow events), the Mazama Ash, occasional thin gray laminae (indicative of abnormal flood events in nearby watersheds), varve counts between marker horizons, and 71 accelerator mass spectrometry (AMS) radiocarbon dates.

Abstract: Characterization and 3D Modeling of Turbidite Reservoir: A Case Study in Miocene Slope Deposits, Main Pass Area, Offshore Gulf Coast of Mexico&amp;nbsp;

ABSTRACT A case study of a detailed characterization and 3-D modeling of a turbidite reservoir has been completed. Well correlation and seismic attribute analysis revealed a clear three dimensional facies architecture of a turbidite deposit reservoir. The study shows that a turbidite lobe is developed along with multiple and relatively high density gravity flow events. Reservoir property and heterogeneity are controlled by facies architecture in a predictable pattern. The turbidite lobe has a typical mounded shape with a fairly straight feeder channel. The main body of the lobe is composed of stacked lenticular sand bodies, each representing a single gravity flow event. Reservoir sand is cleaner and thicker at the center lobe, rapidly becoming finer grained, with increasing shale interbeds, and finally pinches out towards the edge. Inside the lenticular sandbodies, thin shale patches can serve as vertical barriers to fluid flow during production. Facies distributions together with the structural pattern control the hydrocarbon resource potential and production performance in this area. They also provide important information for further exploration and development. A 3-D reservoir model is built using stochastic object based techniques. To preserve the observed facies architecture in the model, the General Marked Point Process algorithm is employed. Specific object shapes are designed in the computer program for different facies. Multiple stage facies modeling enables the preservation of different levels of reservoir heterogeneity. Major geological features are preserved in the model and can be incorporated in future flow simulations.