Turbidite Deposits Research Articles

Transformation of Mackinawite to Interlayered Greigite-Pyrrhotite and Pyrite in the Gaoping Submarine Canyon Sediments off Southwestern Taiwan

Iron monosulfides and neoformed pyrite below the sulfate‒methane transition zone (SMTZ) of rapidly accumulating turbiditic sediments from the Gaoping submarine canyon off southwestern Taiwan were examined by SEM-EDS-EBSD, HRTEM, and HAADF STEM to investigate their microstructural characteristics and processes of formation and transformation. Within a few meters below the SMTZ, mackinawite (Mkw) is largely replaced by interlayered greigite-pyrrhotite (Grg-Po) with {111}Grg//{001}Po and Grg//Po, followed by pyrite neoformation in clusters of disseminated matrix grains consisting of coalescing pyrite microcrystals, arrays of polycrystalline interlayer pyrite grains between the cleavage planes of layer silicates, with each grain’s core having inclusions of interlayered Grg-Po locally containing relict Mkw, and amassed pyrite microcrystals on the surface of porous interlayered Grg-Po micronodules. In the deeper sediments, neoformed pyrite is absent and Mkw is largely preserved, with partial replacement by interlayered Grg-Po having an overall topotactic relationship of ⟨110⟩Grg//⟨110 ⟩Po//⟨100⟩Mkw and {111}Grg//(001)Po//~{011}Mkw and a sharp reaction front without transitional profiles. The mineral grain boundaries and structural discontinuities with Mkw resulting from extensive interlayering between Grg {111} cubic close-packed segments and Po {001} hexagonal close-packed layers could serve as conduits for fluid flow and mass transport to drive the replacement reaction. The conversion of Mkw to metastable interlayered Grg-Po is inferred to occur through interface-coupled dissolution‒reprecipitation processes associated with partial oxidation while the partial replacement of interlayered Grg-Po ± minor relict Mkw by pyrite microcrystals with irregular grain boundaries and orientations probably occurred via a dissolution‒precipitation mechanism. Mkw could be initially formed by sulfate reduction driven by anaerobic oxidation of methane in reactive iron-rich sediments in paleo-SMTZs and subsequently transformed into interlayered Grg-Po followed by pyrite neoformation in the sulfidization front below the SMTZ or recent SMTZs in the Gaoping submarine canyon sediments.

Late Miocene Uplift and Exhumation of the Lesser Himalaya Recorded by Clumped Isotope Compositions of Detrital Carbonate

AbstractThe Himalaya orogen evolved since the Eocene as the Tethyan‐, Greater‐, Lesser‐ and Sub‐Himalaya thrust sheets were uplifted and exhumed in sequence. Reconstructing the provenance of sediment in Himalayan River systems can inform on stages in the tectonic history of the orogen. Here, we analyze the oxygen, carbon and “clumped” isotope compositions of carbonate minerals from Himalayan bedrock, Ganga River sediments and Bengal Fan turbidite deposits. We demonstrate that river sediments consist of a mixture of Himalayan‐derived and authigenic calcite precipitated in the river system. The relative abundance and clumped isotope apparent temperatures of detrital calcite in turbidite deposits decreased between the Late Miocene and Pliocene, while chemical weathering intensity did not increase during this interval. Considered together, these results reflect the establishment of the Lesser Himalaya as an important carbonate sediment source for Himalayan rivers, driven by the uplift and exhumation of this thrust sheet.

Reservoir connectivity in deep-water turbidite deposits over geological and production time scales: an integrated study of the Shwe field, Bay of Bengal

Reservoir connectivity in deep-water turbidite deposits over geological and production time scales: an integrated study of the Shwe field, Bay of Bengal

Deciphering Permian wetland deposits of the Parnaíba Basin through an integrated study of lithofacies and palynofacies in Western Gondwana

During the Permian, the northwestern portion of the supercontinent Gondwana experienced significant climate changes, among which the increasing aridity in the Parnaíba Basin, located between Brazil's northern and northeastern regions. The marine influence associated with the Panthalassa Ocean, evident in the Silurian and Devonian deposits, was progressively attenuated in the late Carboniferous, culminating in extensive continental deposits during the Permian and the Early Triassic in this region. In this paper, we present the first palynofacies analysis of the Permian Pedra de Fogo Formation, conducted concurrently with the description and association of sedimentary facies from outcrops located in the state of Maranhão, southwest of the Parnaíba Basin. A total of 15 m of sedimentary succession was described, and 28 samples were selected for palynofacies analysis. As a result, we identified six sedimentary facies, which were grouped into two distinct facies associations: Fa1 – Central Lake and Fa2 – Playa Lake. The palynofacies analysis considered the sedimentary organic matter, classifying it into amorphous organic matter, phytoclasts (subdivided into eight subgroups), and palynomorphs (with six subgroups). Integrating the results enabled an understanding of the depositional context, which is closely related to water dynamics and climate seasonality. The shallow lake system interpreted during the wet phases recorded interruptions in the normal sedimentation of the central lake due to turbidite deposits associated with ephemeral rivers. Conversely, during dry phases, salt precipitation occurred with subsequent substitution and aerial exposure of the surface when the water balance was negative. Eodiagenetic events were inferred and are considered throughout the article. The alternation of the hydrological regime allowed the deposition in proximal, transitional, and distal environments, creating a distinctive mosaic of wetland landscapes. The data presented indicate humid conditions within a context of increasing aridity in the studied location, particularly in the upper part of the Pedra de Fogo Formation.

Using pollen in turbidites for vegetation reconstructions

ABSTRACTTurbidites, deposited by sub‐aqueous gravity flows, are common in sedimentary archives worldwide and present a unique challenge and opportunity when reconstructing past vegetation through pollen analysis. When sampling pollen from a sediment core for palaeovegetation records, it is common practice to target background sediments (i.e. pelagic sediment) and avoid sampling turbidites, as they are presumed to portray a misleading picture of past vegetation. This assumption stems from our limited understanding of pollen abundance and distribution through turbidites, meaning that palynologists overlook deposits that could potentially be used to reconstruct past vegetation and climate. We present pollen assemblage and sedimentological data from four recent (<150 years) deep marine turbidite deposits from the Hikurangi Subduction Margin, Aotearoa‐New Zealand, with the aim of understanding the abundance and distribution of pollen in fine‐grained turbidites. We find that pollen is diluted in the bases of turbidites, but despite this dilution, the proportions of different pollen taxa remain consistent through each turbidite. These results confirm that pollen can be sampled from turbidites for palaeovegetation reconstructions and that sampling the fine‐grained upper parts of turbidites will provide the best pollen recovery.

Post-glacial stratigraphy and late Holocene record of great Cascadia earthquakes in Ozette Lake, Washington, USA

Ozette Lake is an ~100-m-deep coastal lake located along the outer coast of the Olympic Peninsula (Washington, USA); it is situated above the locked portion of the northern Cascadia megathrust but also relatively isolated from active crustal faults and intraslab earthquakes. Here we present a suite of geophysical and geological evidence for earthquake-triggered mass transport deposits (MTDs) and related turbidite deposition in Ozette Lake since ca. 14 ka. Comprehensive high-resolution bathymetry data, seismic reflection profiles, and sediment cores are used to characterize the post-glacial stratigraphic framework and examine paleoseismic evidence in the lacustrine sediments. Stacked sequences of MTDs along the steep eastern flanks of the lake appear to grade basin-ward from thick, chaotic, blocky masses to thin, parallel-bedded turbidite beds. The discrete turbidite event layers are separated by fine-grained (silt and clay) lake sedimentation. The event layers are observed throughout the lake, but the physical characteristics of the deposits vary considerably depending on proximity to primary depocenters, steep slopes, and subaqueous deltas. A total of 30–34 event deposits are observed in the post-glacial record. Radiometric dating was used to reconstruct a detailed sedimentation history over the last ~5.5 k.y., develop an age model, and estimate the recurrence (365–405 yr) for the most recent 12 event layers. Based on sedimentological characteristics, temporal overlap with other regional paleoseismic chronologies, and recurrence estimates, at least 10 of the dated event layers appear to be sourced from slope failures triggered by intense shaking during megathrust ruptures; the recurrence interval for these 10 events is 440–560 yr. Thus, Ozette Lake contains one of the longest and most robust geological records of repeated shaking along the northern Cascadia subduction zone.

Sources and composition of organic matter as a tool for understanding the complex variation in paleoenvironments and the connectivity of an epicontinental basin: The Miocene in the northern Pannonian Basin

Epicontinental basins are extremely prone to major paleogeographic changes, and this will directly affect any organic matter (OM) preserved in the depositional record. In this study the Middle–Late Miocene successions in the northern Pannonian Basin System were investigated via sedimentological, petrographic, and geochemical analyses of cores from the Danube Basin to reveal the interplay of factors driving the character of the OM. In the late Middle Miocene (~12.3 Ma), the Central Paratethys Sea maintained normal marine salinity, with dysoxic bottom waters in a distal basin floor environment rich in aquatic OM. The last rifting phase followed during the Late Miocene and led to formation of the deep Lake Pannon. Like seawater, the brackish lake water still also contained sulfate. These open lacustrine deposits (~11.6–10.0 Ma) reveal OM sourced from submerged/floating macrophytes and algae, and humid conditions are indicated by the preponderance of deciduous trees and shrubs on shores. The study identifies hybrid event beds (HEBs) on Lake Pannon's floor (~10.0–9.3 Ma), with currents redepositing mud and OM, resulting in similarities between the Middle Miocene and Late Miocene successions. Turbidite deposition (~9.3–9.0 Ma) from the paleo-Danube induced a shift in OM, replacing algae with terrestrial input. Complete isolation from the main water masses of Lake Pannon (~9.0–8.9 Ma) altered its sources of OM, transitioning from algae to macrophytes, and caused a drop in salinity, likely associated with a humidity peak. The subsequent deltaic dominance (~8.9–8.6 Ma) features well-developed topset lakes, swamps, and floodplain forests, reflecting warm temperate to subtropical climates. The Middle–Upper Miocene deposits studied here are source rocks with fair to very good richness and poor to fair generative potential, and contain kerogen types III and IV, while type II is rare. The rapid paleoenvironmental changes observed over the order of ~100 kyr caused the complete switching of OM type and delivery, giving an indication of the complexity of epicontinental basins.

The Manhattan Schist, New York City: Proposed Sedimentary Protolith, Age, Boundaries, and Metamorphic History

There are some persistent basic questions pertaining to the bedrock schist of New York City (NYC). How many mappable schist formations are exposed in NYC, and what was the sedimentary protolith of the Manhattan schists? Our proposed answers are based in part on a blending of published paleontological and radiometric dating results that constrain the timing of Taconic subduction and the best choice of a pelitic protolith for the schists of NYC. We have chemically analyzed some samples of schist and shales at key locations to evaluate the plausibility of our proposals. The compelling published evidence indicates that the Taconic Orogeny began about 475 Ma, when peri-Laurentian plates began the process of east-dipping subduction under the Moretown Terrane, resulting in a magmatic flareup of the Shelburne Falls arc that carried the Moretown Terrane west across NYC. East-dipping subduction accounts for early Ordovician metamorphism until an oceanic slab break-off event at about 466 Ma. Our review of the biostratigraphic data indicates a continuation of subduction and the deposition of pelitic sediments until about 455 Ma, during the transition to deep-water turbiditic sediment deposition. This disqualifies all post-455 Ma turbidites as viable protoliths for the NYC Manhattan schists but does include the Late Cambrian to lowermost Late Ordovician pelites of the Jutland Sequence that are exposed directly west of NYC in New Jersey. Our new chemical analyses of Jutland sediments and each of the three named schists from the NYC plot as a single geochemical population. We, therefore, propose that the schists of NYC could collectively be referred to as the Manhattan schist of the Late Cambrian to lower Late Ordovician.

Carbonate‐rich megabeds within a Triassic siliciclastic deep‐water system, West Qinling orogenic belt, Central China: Character, processes and implications

AbstractDeep‐water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep‐water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep‐marine systems. Less documented are carbonate‐rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep‐water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate‐rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow‐water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast‐supported conglomeratic division (Division I), an intermediate matrix‐supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep‐water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally‐supplied carbonate‐rich megaflows that eroded and incorporated the substrate during transport.

Effect of Hydrate Saturation on Permeability Anisotropy for Hydrate-Bearing Turbidite Sediments Based on Pore-Scale Seepage Simulation

The permeability of natural gas hydrate (NGH) turbidite reservoirs typically exhibits significant anisotropy, with anisotropy being a crucial basis for evaluating reservoir production. The presence of hydrates, as a crucial constituent of the solid framework, not only impacts the overall permeability but also influences the permeability anisotropy. To investigate the saturation sensitivity of permeability anisotropy, a series of simulations are performed by integrating particle flow and computational fluid dynamics methods to construct the homogeneous and layered numerical samples and compute the evolution of permeability anisotropy. It is shown that the permeability is isotropic for homogeneous sediments and the isotropy remains unchanged regardless of variations in hydrate saturation. The permeability of layered sediments, in contrast, exhibits significant anisotropy due to the presence of dominant channels within the coarse layer. For uniformly distributed hydrates, the more effective blockage in coarse layers results in a reduction in anisotropy. While for preferentially distributed hydrates, the excess blocking of coarse layers makes the dominant channels transfer to the fine layers, the further blocking causes a U-shaped anisotropy–saturation curve characterized by a decrease–increase transformation. During the reservoir production process, the preponderance channels blocked by hydrates will be cleared and the horizontal permeability will significantly increase. As a result, the production efficiency of horizontal wells may exceed expectations. The findings offer a parameter support for production estimation and environmental assessment.

Testing turbidite conceptual models with the Kaikōura Earthquake co-seismic event bed, Aotearoa New Zealand

ABSTRACT The 2016 Mw7.8 Kaikōura Earthquake in Aotearoa New Zealand provides an opportunity to test widely applied turbidite sedimentation models because it triggered a co-seismic turbidity current. The resultant Kaikōura event bed (KEB), interpreted as a turbidite, is sampled for ∼ 1300-km down-flow along the depositional system. Sediment core lithologies, computed tomography (CT), and particle-size data are used to test event-bed thickness, silt content, facies distribution, and stacking patterns against the foundations of the turbidite conceptual model of Bouma (1962). KEB thickness is variable to ∼ 100 km down-flow distance and attains a maximum thickness at ∼ 700 km down-flow distance before thinning distally, similar to the predicted bell-shaped proximal to distal trend. Silt content is high throughout the KEB from canyon to fan. The KEB is dominated by laminated Td facies and Te facies that evolve down-system from laminated, then graded, to homogeneous muds. CT and granulometry data are key to differentiating subtle density and textural variations in fine-grained deposits and reveal that KEB Td and Te facies in the KEB that are often not preserved or readily observed in older deposits. The KEB highlights a fine-grained sedimentary system that contrasts with more widely studied sandy turbidite basins. In particular, the KEB example reveals that Td and Te facies are ubiquitous in this fine-grained, silt-rich system. A varied conceptual model developed from the KEB may be applicable to many modern deep-sea turbidite systems and crucial for understanding present-day particulate transport to the deep sea and interpreting evidence from the stratigraphic record.

Detrital Tourmalines in the Cretaceous–Eocene Julian and Brkini Flysch Basins (SE Alps, Italy and Slovenia)

In the SE Alps, two Cretaceous–Eocene flysch basins, Julian and Brkini, filled with turbidite sediments, are present. This study novelly reports heavy mineral assemblage counts and detrital tourmaline characterization for 11 samples. It is possible to define three different groups, characterized by the presence of (1) a clinopyroxene–epidote–low-ZTR (zircon+tourmaline+rutile; 5%) sample association, (2) a high-ZTR (>48%)–garnet–apatite association and (3) a low-ZTR (<40%)–Cr-spinel–garnet association. Detrital tourmalines from both the Julian and Brkini flysch basins are rather similar in composition, associated with metapelites and metapsammites coexisting or not coexisting with an Al-saturating phase, ferric-iron-rich quartz–tourmaline rocks and calc–silicate rocks; however, their number is drastically different. In fact, even if the percentage of heavy minerals is very low and similar in both basins (0.17–1.34% in weight), in the Julian basin, the number of tourmaline crystals is much lower than that in Brkini (1–14 vs. 30–100), suggesting an important change in the provenance area. Interestingly, the presence of a high amount of tourmaline derived from ferric-iron-rich quartz–tourmaline rocks and calc–silicate rocks makes these two basins different from all the Cretaceous flysch basins of Bosnia and the Northern Dinaric zone, where these supplies are missing or very limited.

A Study on the Heterogeneity and Anisotropy of the Porous Grout Body Created in the Stabilization of a Methane Hydrate Reservoir through Grouting

To solve the sand problem during the depressurization of methane hydrate (MH), we proposed a method to build a porous grout body with sufficient permeability and strength around the wellbore through inhibitor pre-injection and grouting, and verified its effectiveness and potential in our previous research using artificial cores created with silica sand and alternative hydrates such as TBAB- hydrate and iso-butane hydrate. However, all of the artificial cores mentioned above were created with high homogeneity, injected, cured, and had their physical properties measured in the vertical direction, which differs from real reservoir conditions. To investigate the effects of grouting in a more realistic fluid flow, we conducted further experiments using horizontal 1D cores, 1D cubic models, and a 2D cross-sectional model mimicking the near wellbore. These experiments revealed that (1) the generated gas somewhat suppressed the effects of grouting as in the case of previous experiments, and (2) grouted reservoirs would be heterogenous and anisotropic due to the fluid densities and the distribution of grout particles and turbidite sediments, but sufficient permeability and satisfactory strength could still be attained. The above series of experiments demonstrated that our method has the potential to effectively produce actual MH, preventing sand problems even in heterogeneous and anisotropic grouted reservoirs.

Exploration potential of Papua New Guinea – latest multiclient 3D provides new insight into the underexplored Papuan Basin over the Papuan and Eastern Plateaus

The Gulf of Papua, part of the regional Papuan Basin, is characterised by extensional to passive margin tectonics from the Triassic to Late Oligocene and collisional tectonics from the Late Oligocene until the present day. The basin has experienced rapid clastic deposition in the late Neogene which covers an underlying extensive Miocene carbonate shelf with local bioherms and associated carbonate facies. Underlying the carbonates, an array of deformed and complex rift basins are present, with potential petroleum plays in undifferentiated Mesozoic sediments which onlap basement highs. The Miocene carbonates are the primary exploration targets, along with Pliocene clastic turbidite sediments in the Fly River Delta, Western Gulf of Papua. It is postulated that these were charged by Mesozoic marine–deltaic/terrestrial source rocks that were deposited during the opening of the Coral Sea. The offshore Papuan Basin is underexplored and the Gulf of Papua play types seen in the onshore Aure Fold Belt and offshore Fly River Platform could potentially extend offshore into the Coral Sea area. New broadband Pre‐Stack Depth Migration seismic data covering a part of the Eastern and Papuan Plateaus reveals new insights into the structural development of the region, rift basin geometries, configuration, and association of rift clastics and post-rift carbonates. Internal carbonate features can be observed on the new seismic data set, and new plays in the yet undifferentiated rift sediments of Mesozoic age are proposed in this study.

Pockmarks Offshore Big Sur, California Provide Evidence for Recurrent, Regional, and Unconfined Sediment Gravity Flows

AbstractRecent surface ship multibeam surveys of the Sur Pockmark Field, offshore Central California, reveal >5,000 pockmarks in an area that is slated to host a wind farm, between 500‐ and 1,500‐m water depth. Extensive fieldwork was conducted to characterize the seafloor environment and its recent geologic history, including visual observations with remotely operated vehicles, sediment core sampling, and high‐resolution, near‐bottom Chirp and multibeam surveys collected with autonomous underwater vehicles to capture the morphology and stratigraphy of the pockmarks. No evidence of high methane concentrations in sediments, chemosynthetic biological communities, or methane‐derived diagenetic byproducts was found. Chirp data and sediment cores showed alternating layers of slowly accumulating hemipelagic drapes interrupted by more reflective turbidite horizons that extend throughout the pockmark field and beyond. Chirp data showed multiple episodes of lateral migration over time in some of the pockmarks in association with erosion and infilling events. Laterally continuous turbidite horizons that overlay erosional surfaces indicated that pockmark migration occurred synchronously in multiple pockmarks separated by tens of kilometers. These shifts are presumed to be the result of asymmetrical erosion of the pockmark flanks caused by passing sediment gravity flows. While some pockmarks occur in chains, most are not clustered or randomly spaced but are regularly dispersed within the pockmark field. We hypothesize that intermittent, unconfined sediment gravity flows occurring over at least the last 280,000 years are the source of the regionally continuous turbidite deposits and the mechanism that maintained the regularly dispersed pockmarks.

Mixed siliciclastic-carbonate-tuffaceous sedimentation in a rift lacustrine basin: A case study of the Lower Cretaceous Jiufotang Formation in the Luxi sag, Songliao basin

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins.

Sedimentological characterization of earthquake-generated turbidites in fault-proximal glacial lakes: a case study from Jenny Lake, Teton range, Wyoming

Lakes in seismically active regions preserve valuable sedimentary archives of paleoseismic activity within their catchment and beyond. A series of glacially-excavated lakes positioned directly along the surface trace of the Teton normal fault at the base of the Teton Range, WY, are ideally situated to record past fault activity since their formation approximately 15,000 years ago. Here, we focus on the sediment fill contained in Jenny Lake (5 km2; approximately 73 m max depth) located at the bottom of Cascade Canyon, in the central Tetons, where postglacial slip rates are greatest. Past earthquakes that generated slope failures in and around Jenny Lake are expressed stratigraphically as coseismic turbidite deposits. These deposits were previously identified and dated in sub-bottom profiles and in sediment cores taken from multiple locations around the basin. In this study, we focus on the six thickest turbidites (ranging from 6 to 34 cm thick) present in multiple cores recovered from the central depositional basin and analyze them at sub-centimeter resolution for changes in physical, biological, and geochemical parameters, including sediment density, magnetic susceptibility, grain size distributions, organic content, and elemental composition. Results reveal each deposit contains a well-defined, three-component sedimentary sequence composed of a relatively homogenous and thick basal sandy unit with a sharp bottom contact, a similarly thick silt-rich middle unit, and a thin top unit of very fine-grained sediments. The characteristics of these components and their similarity between individual deposits suggest consistent sediment sources and transport pathways during successive earthquake events. Based on our analyses and the unique local geomorphic setting, we create a mechanistic model of coseismic turbidite formation in Jenny Lake, which may provide an improved framework for identifying, characterizing, and correlating earthquake-generated disturbance deposits in other Teton lakes and lakes in similar tectonic-geomorphological settings, for example, in the Basin and Range Province, USA or beyond.

The impacts of profile concavity on turbidite deposits: Insights from the submarine canyons on global continental margins

Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons.

Geomorphologic and infilling characteristics of the shelf-incising submarine canyon in the eastern Makran accretionary prism, offshore Pakistan

Seven shelf-incising submarine canyon systems are developed in the Makran accretionary prism, offshore Pakistan. This paper uses multibeam bathymetric data and multichannel seismic profiles to study the geomorphologic and infilling characteristics of E Canyon in the east of accretionary prism. The E Canyon extends nearly north–south from the upper slope to lower slope, the bottom of the canyon is located in 1000 to 3000 m water depth, the main axis extends about 55 km, and the width varies from 5 to 9 km. The E Canyon shows U-shaped concave features in the northern cross-section view and V-shaped concave features in the southern cross-section view. Two continuous erosion pools are developed at the fifth and third ridges of the southern segment, respectively. The steepest sidewall (with slopes of 25.75° and 40.47°) of E Canyon was found near the third ridge. The filling sequence of coarse channel lags, slump debris flows, stacked channel sands and mass transported deposits and turbidite deposits from bottom to top is developed in the northern segment of the canyon. Strong erosion is developed in the southern part of the canyon and there is no sedimentation inside. On the abyssal plain, the continuation of the E Canyon is clearly erosive. Our preliminary analysis shows that the factors controlling the evolution of E Canyon may include sediment gravity flow, tectonic activity, sea-level change, climate and onshore rivers activity. The correlation between evolution of E Canyon and gas hydrates was explored, and it is believed that the erosion of E Canyon plays a destructive role in hydrate accumulation. At the same time, the destruction of hydrate-bearing layer induces the escape and leakage of hydrocarbon-bearing fluid, leading to the development of pockmark on the sidewalls of E Canyon. And the evolution model of gas hydrate accumulation in the development area of E Canyon was established.

Sensitivity Testing of Marine Turbidite Age Estimates along the Cascadia Subduction Zone

ABSTRACT Marine turbidite studies infer that 19–20 ∼Mw 9 earthquakes ruptured the full Cascadia subduction zone (CSZ) in the past 10 kyr, a hypothesis that relies on concurrent turbidite deposition generated from seismogenic strong ground motion along the ∼1100 km margin. Correlation of marine turbidite deposits is based on petrophysical characteristics and radiocarbon geochronology, the latter of which relies on a series of age corrections and calibrations for marine radiocarbon age and sedimentological parameters. In this work, I isolate several key variables in turbidite age assessment and systematically test how previous assumptions and new calibration curves affect estimated ages, and thus whether geochronologic analyses independently support coeval turbidite deposition. For radiocarbon age calibration, I test the impact of (1) updating global marine reservoir age corrections; (2) updating local marine reservoir age estimates; and (3) selectively applied marine reservoir age excursions. From the calibrated radiocarbon ages, I calculate turbidite age and uncertainty using a Monte Carlo approach with a broad range of sedimentation rates and substratal erosion. By simply updating the global marine radiocarbon calibration, individual radiocarbon ages differ from published estimates by several hundred years. Updates to the local reservoir age corrections are minimal because existing data remain limited yet have potential for great impact on turbidite ages. Of the sedimentological parameters tested, sedimentation rate has the largest impact on estimated turbidite age, with individual ages changing up to 500 yr from published estimates. For radiocarbon samples of turbidites previously inferred to correlate, the individual ages typically show increased scatter and overall uncertainty, even for models that only update the global marine reservoir calibration. These results highlight the major age uncertainty associated with current coseismic turbidite age analyses in Cascadia and how independent constraints on local reservoir corrections and sedimentation rate are critical for accurate turbidite age estimates in the Pacific Northwest.