Mass Transport Deposits Research Articles

Reinterpreting glacial deposits as a MTD ponding sediment gravity flows in the upper Mojón de Hierro Formation (Tepuel–Genoa Basin, Argentina)

The Late Paleozoic Ice Age (LPIA) was the longest and most extensive glacial interval during the Phanerozoic, lasting from the Late Devonian to the late Permian (362–254 Ma). Numerous questions remain on the spatial and temporal extent of the ice centers, the timing of expansion and contraction of the ice sheets, and the distribution of ice across Gondwana through time. The Tepuel–Genoa Basin, in Patagonia (Argentina) was situated within the paleo South Polar Circle and contains a nearly continuous lower Carboniferous (Tournasian) to lower Permian (Artinskian) succession. The Mojón de Hierro Formation has been described as both non-glacial and glacial in origin, but lacks detailed sedimentological descriptions. This research investigates a ∼50 m succession with sedimentological and geochemical analysis within strata in the upper portion of the Mojón de Hierro Formation at Arroyo Garrido (Chubut Province). Five stratigraphic sections were measured and the strata were categorized into five lithofacies: 1) deformed sandstones, 2) thin-bedded diamictites, 3) graded rhythmites, 4) laminated mudstones with dispersed clasts, and 5) laminated mudstones. Deposition occurred in a slope environment from debris flows, turbidity currents, mass-movements, hemipelagic sedimentation, and ice rafting. The Chemical Index of Alteration (CIA) indicates values similar to average marine shales, which suggests that the muds were supplied from temperate terrestrial sediment sources. This indicates that icebergs from a distant source transited the basin and grounded glaciers were not present in the catchment area. Vanadium/chromium ratios (V/Cr) indicate dysoxic (restricted water circulation) values in samples between the mass-transported blocks and oxic values (well circulated water) in samples stratigraphically above the filled/leveled ponded mini basin. These oxygenation conditions suggest that the mass-transport deposit formed a topography on the sea floor, resulting in a mini basin that ponded sediments within the blocks. A local glacial source was not substantiated for the upper Mojón de Hierro Formation at Arroyo Garrido neither through the detailed facies analysis nor through geochemical proxies.

Late Devensian to Holocene environmental change, Loch Lomond, UK: A seismic sedimentary record of deglaciation, paraglacial and postglacial landscape evolution

We present an interpretation of two-dimensional sub-bottom profiling data from Loch Lomond, Scotland, UK. Sediments deposited during and following the last glacier advance have been investigated for decades around the shores of Loch Lomond. For the first time, this study presents an interpretation of the subsurface providing a window into the late Quaternary and Holocene history of Loch Lomond and its surrounding. The seismic stratigraphy records the infill of the loch during the final stages of the Loch Lomond Stadial (LLS, 12.9–11.7 ka BP), through the Holocene and into the present day. Results reveal the presence of distinct seismic facies (SF) identifying four principal seismic horizons; SF-I, SF-II, SF-III, and SF-IV. The SF-I horizon represents the glaciated surface, interpreted as subglacial till (locally forming drumlins), glacial moraines or bedrock. Ice retreat was accompanied by glaciolacustrine sedimentation in a proglacial lake setting, depositing up to 44 m of laminated sediments and ice marginal fans (SF-IIa, b). A period of landscape instability followed with extensive deposition of mass transport deposits (SF-III). These deposits, characterised by chaotic seismic facies with an erosional basal surface, are up to 43 m thick and may represent up to 50 % of the sediment fill. SF-IV comprises finely laminated sediments deposited during the Holocene and highlights slower sedimentation rates in comparison to earlier phases of sedimentation. This study reveals new insights into the deglaciation of Loch Lomond, including previously unrecognised extensive mass transport deposits buried in the subsurface, associated with a period of paraglacial adjustment.

The Maracangalha injectite complex: An overlooked hydrocarbon play in the Lower Cretaceous Recôncavo Basin, NE Brazil

The Recôncavo Basin is the third major natural gas producer in Brazil. Lower Cretaceous sandstones of the Maracangalha Formation (Caruaçu and Pitanga Members) hold the largest volumes of non-associated gas in this basin. However, these reservoirs are extremely complex due to a range of soft-sediment deformational process that modify the depositional architecture and impact on the original structure of the porous system. The cause of soft-sediment deformation is still contradictory because both mass movements and post-depositional fluidization has been proposed by previous studies. This uncertainty has drastic implications for reservoir predictability in the subsurface since mass-transport deposits and fluidization-remobilization complexes have very different architectures. To test these hypotheses, this study examines soft-sediment deformation structures (SSDS) in outcrop and core in order to interpret remobilization processes and to infer the main trigger mechanisms involved. Outcrop description was carried out in the coastal zone of the Todos os Santos Bay, NE Brazil, where the Maracangalha Formation is very well exposed. High-resolution core images from four producing fields located northward (Miranga, Jacuípe, Lamarão and Massapê) were also described. SSDS include a great variety of structures: 1) dish, 2) pillar, 3) consolidation lamination, 4) load structures, 5) tilted, convoluted, distorted and disrupted laminations, 6) flames, ball and pillow structures and pseudonodules, 7) large-scale mounded geometries, 8) penecontemporaneous faults and 9) sandstone intrusions/extrusions (dikes, sills, breccias and volcanoes). Intensely deformed sandstones are connected to sandstone intrusions that cut through finer-grained, low-permeability strata. Orientation of normal faults and sandstone intrusions suggests that they are genetically related. The Pitanga and Caruaçu Members are better described as facies, since they differ only by the degree of deformation. Pitanga facies is the product of remobilization of an undeformed (Caruaçu) facies. Unlike previous interpretations that indicated the action of slumps, we concluded that the upward movement of interstitial fluids (liquefaction and fluidization) was the main mechanism of remobilization, deformation and mixing of sediments. The overpressure of pore fluids and syn-rift faults propagation broke up seal-strata, releasing the fluids pressure and driving the upward movement of sediments. Key architectural elements of a sand complex are recognized in outcrop and core, including parent units, host-strata and sandstone intrusions. For the origin of this injectite complex we suggest a seismic trigger related to extensional tectonics of the rift system. The Maracangalha injectite complex comprises a new hydrocarbon play to be considered in further exploration and production (E&P) activities in the Recôncavo Basin.

Connecting link between a sediment source and its deep-sea sink: Ilan Shelf offshore northeastern Taiwan

The northeast Taiwan margin provides an excellent example of the route of sediment flux from a small mountainous river, the Lanyang River, to a deep-sea basin, the Southern Okinawa Trough (SOT), via a very narrow（8–14 km in width）Ilan Shelf at different time scales. Based on seismic and sub-bottom chirp profiles and onshore borehole and offshore core data, we identify three echo types on the Ilan Shelf that delineate sheets of sediment, mass movement deposits, and echoes indicative of igneous activity. By recognizing lithofacies and seismic facies changes, the Last Glacial Maximum Unconformity and maximum flooding surface are correlated in onshore cores and offshore reflection seismic profiles. With the aids of sequence stratigraphic analysis, the postglacial sedimentation rates on the Ilan Shelf are estimated to range from 0.04 to 1.53 cm/yr. Considering its sediment budget in a source-to-sink system, the Ilan Shelf can be regarded primarily as a temporary trap for fluvial sediment discharged from the Lanyang River. Overall, it has trapped at least 50% of the discharged sediment during the Holocene, and the bulk of sediment was transported, primarily via mass movement to SOT. We deduce that earthquake-induced faulting, axial incision in the channel, and retrogressive failures appear to be triggers for mass wasting, which then combined with channel transport, can play leading roles in rapid downslope transportation to the trough. This inference is indicated by high deposition rates in the western end of SOT and widely distributed mass transport deposits observed in the shallow strata of SOT. We found that the deep strata of SOT are deformed by normal faults, indicating that the sediment accommodation space is structurally controlled by the active back-arc extension. This study documents that frequent typhoons and flooding events, together with strong tidal currents, are significant agents of sediment input over the short term. In contrast, earthquakes and volcanic events occasionally affect sediment dispersal from the Ilan Shelf to SOT.

Identification and differentiation of vertical movement through morphological changes and stratigraphic imprint: Two distinct uplifting mechanisms in the upper Calabrian accretionary wedge, western Ionian Sea

AbstractThe seafloor morphology reflects both past and on‐going sedimentary, oceanographic and tectonic processes. Vertical movement is one of the drivers responsible for reshaping the seafloor through forming steep flanks that decrease slope stability, favour landslides, change current paths, form minibasins and control the sediment deposition, distribution and geometry. Here, we make use of these interactions to derive vertical movements and constrain the active tectonic processes at the western termination of the upper Calabrian accretionary wedge from the integrated analysis of bathymetric, backscatter, surface attributes and high‐resolution reflection seismic data. Within this area, we identify two types of deformational features and mechanisms that affect the depositional, erosional and tectonic processes at different scales. These include the deviation of channels, landslide scars, mass transport deposits (MTDs), separated drifts, sediment waves, lineaments and offset seafloor structures. The first type (long‐wavelength uplift) is an uplifted 22‐km‐wide region, in which seismic onlap relationships and the dip of deep reflectors suggest long‐lasting but slow tectonic uplift affecting sedimentation, and the second type (short‐wavelength uplift) includes three narrow elongated structures and one circular dome encircling the first region of uplift. We interpret that the first type of uplift feature was caused by tectonic deformation, while the second type is interpreted as formed by the fast uplift, tilting and faulting of modern sediments caused by diapirism due to rapid sedimentation in response to the first tectonically driven uplift. The study provides insight into the complex interaction of tectonic and sedimentary processes in the upper Calabrian accretionary wedge.

Submarine-Channel Element Architecture Demonstrates Facies Heterogeneity in Both Strike and Dip Views: Miocene Modelo Formation, Lake Piru, California, USA

Submarine channels deliver vast quantities of sediment into ocean basins and the deposits left by these systems host important archives of paleoenvironmental change and are major targets for hydrocarbon production and carbon sequestration. However, similarities between channel subenvironments often make their identification difficult, particularly because some subenvironments are transitional or quite variable. While large channel complexes can often be resolved on seismic data, only outcrop data yields high-resolution detail of their internal heterogeneity. This study integrates 10 measured sections with drone-based photography to document lateral and vertical changes in depositional architecture in a well exposed outcrop of a submarine-channel element in the Miocene Modelo Formation at Lake Piru, California. The channel-element architecture is well constrained by erosional-surface mapping and lateral and vertical facies changes. The 3-dimensionality of the outcrop provides a unique example to demonstrate this heterogeneity in both strike (i.e., cross-sectional view) and dip orientations (i.e., longitudinal view). This channel element has a predictable vertical facies succession of thin sandstones and mudstones, mass transport deposits and amalgamated sandstones. The element is capped by a siliceous mudstones that provide a unique marker of hemipelagic deposition and the presence of an abandonment surface. The amalgamated sand packages are thickest in axial locations and thin over a distance of 500 m in the dip direction, but thin over 150 m in the strike direction toward two locations along the same margin. This thinning is used to constrain the dimensions and sinuosity of the channel element. We interpret a channel-element width of 550 m, a thickness of 29 m and an aspect ratio of 19:1, which is in agreement with previously published ranges of channel-element dimensions. With the documentation of lateral facies heterogeneity in orientations slightly oblique to both strike and dip, this study provides important data for understanding channelized sediment gravity flow dynamics in submarine channels and aids in evaluating reservoir-model volume and connectivity estimates.

Lithofacies and sequence stratigraphic analysis of the glaciomarine lower Wynyard Formation (Pennsylvanian–early Permian, Tasmanian Basin)

Glaciation during the Late Paleozoic Ice Age climatic interval (~370–260 Ma) was likely dynamic; consisting of numerous ice centers that grew and shrank asynchronously through time. Improvements in understanding of the spatial and temporal depositional complexity of glaciomarine sedimentary systems have shown that in order to characterize the conditions of Late Paleozoic glaciation, glaciogenic depositional systems and their stratigraphy must fundamentally be understood at the local level. To that end, this study reexamines the physical sedimentology and sequence stratigraphy of the type-section of the Permo-Carboniferous, glaciomarine Wynyard Formation (Wynyard Tillite) of the Tasmanian Basin by describing a 415 m thick interval of the formation, beginning at its basal erosional unconformity with the Proterozoic Burnie (Oonah) Formation.The glaciogenic nature of the Wynyard Formation stratigraphy is indicated by the characteristics of clasts throughout the succession (striated, faceted, angular, and variable lithologies and grain sizes). Three glacial depositional environments were interpreted: a grounding zone wedge deposited in an ice-contact setting, glacier-proximal portion of a grounding line fan and/or morainal bank, and cyclopelites deposited in a glacier-intermediate to glacier-distal setting. Mass transport and turbidite deposits are common throughout all facies associations, as is soft sediment deformation likely caused by slumping. Several boulder pavements occur throughout the succession, indicating periodic glacier grounding. Together, these facies associations indicate that this Wynyard Fm succession is composed of glaciogenic sediments that were deposited in sub-aqueous, marine, predominantly proglacial environments. The sequence stratigraphic analysis indicates that this entire succession of the Wynyard Fm was likely deposited during the single retreat phase of the “Wynyard Glacier”, with one notable readvance over the area.The interpretations made by this work enhance the understanding of glaciation of the Tasmanian Basin during the LPIA through facies analyses and a sequence stratigraphic approach, which allowed for detailed subdivision of lithologies that enabled inferences regarding the type, timing, and extent of the “Wynyard glacier”. This Wynyard Fm succession was likely deposited during a single glacier retreat with some minor readvances that may have occurred on the order of decades to years. Additionally, the glacier's grounding line was likely never more than a few kilometers upglacier (south) of this location during deposition.These findings are significant, because the massive diamictites that comprise this succession had previously been considered homogenous and therefore resisted detailed interpretations. Constraining the often-complex depositional histories of glaciogenic strata in similar fashions across the Tasmanian Basin allows us to better understand how these glaciogenic deposits fit into the global climate system of the Late Paleozoic Ice Age.

Morphology of the submerged Ferdinandea Island, the ‘Neverland’ of the Sicily Channel (central Mediterranean Sea)

ABSTRACT We present the bathy-morphological map at a scale of 1: 50,000 of the area around the submerged Ferdinandea Island, the ‘Neverland’ of the Sicily Channel (central Mediterranean Sea). We investigate an area of 100 km2, between 10 and 350 m, which is part of a triangular morphological high, 360 km2 wide, representing the SE-wards prolongation of the Adventure Bank. The study is based on the morphometric analysis based on high resolution multibeam, and sub-bottom CHIRP profiles collected in 2015. The area around the remains of Ferdinandea Island is morphologically shaped by the interplay between volcanic, tectonic, fluid seepage, and oceanographic processes. Since the study area is considered a hot spot of biodiversity affected by maritime traffic (especially in Ferdinandea Channel) and hosting communication pipelines, this map provides insights both for habitat mapping purposes and preliminary marine geohazard assessment due to the occurrence of historically active submarine volcanoes, pockmarks, and mass transport deposits.

Using shallow hydroacoustic data to image seafloor mass transport deposits on the North West Shelf of Australia: links to neotectonics

Abstract Mass transport deposits have long been known on the Exmouth Plateau, offshore NW Australia, identified in 2D and 3D industry seismic lines. The expedition SO257 in 2017 collected 30 high-resolution, shallow seismic lines along targeted transects on the northern Australian margin. Many of these imaged mass transport deposits, with the top 700–800 m of the section captured in detail not available with industry seismic data. We present nine new high-resolution seismic lines from three separate areas of the North West Shelf. Slides in the Roebuck Basin show complex anastomosing ductile extensional mechanisms, with multiple slip surfaces and no headscarps or adjacent faults. Slides on the Exmouth Plateau have fault control, with surface fault offsets of up to 300 m, indicating seismicity as a likely triggering mechanism. Slumps along the western margin of Western Australia are more limited in extent, associated with surface notches, with indications of previous activity at depth. All areas show a repeated history of mass transport deposits. The area of the active landslide province offshore of NW Australia is far larger than the individual slides recognized on the Exmouth Plateau.

Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

AbstractFlood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods.

Distinguishing different classes of mass-transport deposits in LPIA strata exposed in eastern Paraná Basin, Brazil

Ice age mass-transport deposits (MTD) occur in multiple stratigraphic intervals within the Permocarboniferous Itararé Group, in the Paraná Basin, and are exposed in several disconnected quarries and road cuts around the region of Mafra, southern Brazil. The most typical deposits are diamictites with muddy matrix, but silty-sandy diamictites and metric intercalations of deformed layers of sandstones and siltstones occur subordinately. Similar MTD facies have been described from better exposed and time equivalent successions in western Argentina. There, because of the km-scale exposures, MTDs can be mapped in their plenitude, giving better insights about their emplacement. In this paper, we describe the Brazilian MTDs and infer their modes of transport and deposition supported by comparisons with published Argentinean examples. Based on matrix constitution, presence of coherent blocks and rafts, and sedimentation phases, at least four types of MTDs can be identified: 1) Mud-rich MTD and isolated sandstone blocks; 2) Resedimented MTD represented by diamictites with folded blocks of diamictite, possibly corresponding to two phases of remobilization; 3) Sand/silt-rich MTD (evolved stage), and formed by deformed bands of sandstones and siltstones (mature stage); and 4) MTD with rafts of heteroliths and sandstone blocks. Usually MTDs rest on and scour into a fine-grained substrate such as thin-bedded turbidites and shale. The regional geological setting at Mafra points to an open embayment. The collapse of inclined depositional slopes related to high sediment supply associated with deglaciation was the major control on MTD development. However, the inferred proximity of the ice margin during slope failure was variable, suggesting MTD formation during different stages of a glacial cycle.

Sand-rich Pleistocene deep-water channels and their implications for gas hydrate accumulation: Evidence from the Qiongdongnan Basin, northern South China Sea

Deep-water turbidite channels are conduits for transporting terrigenous clastic sediments into the ocean, and channel deposits can also act as high-quality hydrocarbon reservoirs. In this study, based on high-resolution 3D seismic data and logging-while-drilling data, four Pleistocene turbidite channels are identified and characterized in the deep-water area. These deep-water channels are sinuous with V- or U-shaped on the seismic profiles, and their evolutionary history can be divided into Unit 1 (Erosion-dominated stage), Unit 2 (Erosion-Deposition stage), Unit 3 (Erosion-Deposition stage), and Unit 3 (MTDs-dominated stage). The internal fillings of these channels are almost basal lags with high-amplitude reflections at the bottom, pelagic sediments with low-amplitude reflections, and mass transport deposits with translucent/transparent seismic facies. Since sand-rich sediments dominate the deep-water channel-levee systems in Unit 3 in the study area, they could act as shallow gas reservoirs and facilitate the accumulation of gas hydrates. By analyzing the source-to-sink systems around the basin, the source of the sediments within the deep-water channels is discussed, which are mainly from the Truong Son Belt. Floods, sea level fluctuations, and earthquakes are the most likely triggering mechanisms of turbidity currents in the Qiongdongnan Basin. This study provides new insights into the Quaternary deep-water sedimentary process, gas hydrate exploration, and source-to-sink systems in the northwestern South China Sea.

On the applicability of seismic attributes in the description and interpretation of mass-transport deposits

Mass transport deposits (MTDs) have gained economic importance in the last years because of their significance as seals or stratigraphic trapping mechanisms in deep water turbidite prospects. The analysis of MTDs in 3D seismic data provides a better understanding of their characteristics when compared to outcrop or 2D seismic data, as it is possible to capture both internal and external features over large areas in 3D. Moreover, this analysis can be further improved by applying seismic attributes, which have been employed only to describe specific aspects of these deposits. In this study, we applied several seismic attributes systematically in the characterization of an MTD, located in the northern Santos Basin (offshore southeastern Brazil), aiming to identify their applicability in the description and interpretation of 33 characteristics of this kind of deposit. As a result, it was possible to identify which features of the MTD the application of seismic attributes is indispensable, helpful, or redundant.

Late Pleistocene-Holocene age and stratigraphy of the Currituck Slide Complex, U.S. mid-Atlantic continental slope: Implications for landslide triggering

Considerable effort has been made to link submarine slope failures to changes in local and global-scale environmental conditions, in order to assess landslide hazard probability. Here we provide the first radiocarbon dates of hemipelagic sediment overlying mass transport deposits and inferred failure surfaces of the Currituck Slide Complex (CSC), a prominent landslide scar on the U.S. mid-Atlantic continental slope. The dates, taken from both the upper and lower scars of the complex, constrain the age of the last major failure event to 13,835 and 16,020 years BP. Time correlation of the hemipelagic sediments across the landslide scar and proximal deposit suggests a single failure of both the upper and lower parts of this 160 km3 volume. A higher rate of sediment supply from the periglacial Appalachian Mountains and from glacial melt-water pulses, with an exposed continental shelf at that time, may have enlarged a shelf-edge delta at the site of the CSC, which may have facilitated or triggered failure. A smaller landslide at the southern edge of the complex with a less well-defined geomorphologic footprint is dated at 5500 BP and possibly represents the reshaping of the seafloor around the CSC triggered by low-frequency earthquakes on the nearby continental margin.

Formation of undulating seafloor bedforms during the Minoan eruption and their implications for eruption dynamics and slope stability at Santorini

The Minoan eruption of Santorini is one of the largest Holocene volcanic events and produced several cubic kilometers of pyroclastic flows emplaced on the submerged flanks of the volcano. Marine geophysical surveys reveal a multitude of undulating seafloor bedforms (USBs) around Santorini. While similar structures are known from other volcanoes worldwide, Santorini offers the unique opportunity to relate USB formation with volcanic processes during one of the best-studied volcanic eruptions worldwide. In this study, we combine high-resolution seismic reflection data with multibeam echosounder bathymetry to reveal the internal architecture of USBs around Santorini and to relate their morphological characteristics to formational processes. The USBs around Santorini were formed during the Minoan eruption and represent the seafloor expression of mass transport deposits. Three types of deposits differ in composition or origin. (1) Depositional USBs, which can only be found to the north of the island, where Minoan eruption ignimbrites reach their maximum thickness and the undulating topography is the result of thrusting within the deposit. (2) USBs related to slope failures of volcaniclastics from the entire Thera Pyroclastic Formation, which can be found east, south, and west of the island. (3) USBs associated with deep-seated deformation, which occurs on the southwestern flank along an area affected by rift tectonics and extends to a depth of more than 200 m below the seafloor. In cases (2) and (3), the USBs are formed upslope by block rotation and downslope by thrusting. Our study indicates that these processes may have contributed to the generation of the devastating Minoan tsunami. Since Santorini is located in one of the most tectonically active regions in the Mediterranean, capable of producing earthquakes with magnitude M7+, our study has important implications for hazard assessment. A strong earthquake located close to the island may have the potential to reactivate slope instabilities posing a previously undetected but potentially significant tsunami hazard.

Morphology, seismic stratigraphy, and tectonic control of the Yitong submarine canyons – fan apron system in the northern South China Sea

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high, YCFS receives limited supply of the shallow-water sediments.

Morphological and seismostratigraphic evidence of Quaternary mass transport deposits in the North Ionian Sea: the Taranto landslide complex (TLC)

The Taranto Landslide Complex (TLC) is a large submarine landslide area located along the continental margin of the Puglia Region, in the Gulf of Taranto (North Ionian Sea), between 200 and 800 m water depth. Based on very high-resolution multibeam data, a morphological analysis was performed by measuring different physical and spatial parameters (i.e., surface, headwall height and length, slope in the source area, and blocks in the accumulation zone). In addition, we use nine high-resolution sub-bottom CHIRP profiles to reconstruct the stratigraphic architecture. The main results show five phases of Quaternary mass transport deposits (MTDs) in the study area. The oldest to the youngest are MTD1, with a volume of about 0.032 km3 and an area of about 4 km2; MTD2, which is the largest of the identified deposits, covering an area of ∼26 km2 and having an estimated volume of ∼0.35 km3; and MTD3 and MTD4, with volumes of about 0.033 km3 and 0.035 km3 and an area of 7 km2 and 5 km2, respectively. The final submarine landslide is represented by MTD5, which has a volume of 0.02 km3. The deposits are internally characterized by chaotic acoustic facies with reflectors with moderate amplitude and laterally continuous in time, showing likely erosive characteristics defined as “bounding surfaces”. The main transport direction of the MTDs is from north/northeast to south/southwest. This represents the trend of the continental slope, but there is also slope failure evidence coming from west/northwest to east/southeast (MTD5). The correlation between topographic and seismo-stratigraphic features allows the documentation of the characteristics, distributions, sources, and the triggering mechanisms of the Late Quaternary MTDs in the area. We suggest that still the unknown trigger mechanisms could be based on the performed analysis, related to the anomalously high sedimentation rates and/or sea level fluctuation.

Exploiting image logs to reduce drilling hazards: an innovative Artificial Intelligence methodology applied in East Africa

SUMMARY Image logs are crucial for petrophysical and structural characterization of drilled formations. Logging while drilling (LWD) image logs allow near real-time characterization of formations during drilling. Interpretation time required by humans can become critical, as structural interpretation provides the most crucial information for decision-making steps with respect to drilling operations. An example of this occurred in a deepwater system of reservoirs in East Africa. During the drilling of some wells, drilling was interrupted by unexpected borehole stability issues observed in a mass transport deposit. Those problems can detrimentally affect operations by impacting the efficiency of drilling. Therefore, a procedure for the automation of LWD data analysis was developed aimed at reducing drilling risk associated with borehole stability. A workflow is proposed based on an innovative assortment of AI methodologies for automatic real-time interpretation of LWD image log, applied to density image logs. The goal is to mimic manual human dip picking, combining computer vision, numerical series analysis and machine learning. Computer vision techniques are applied to detect the main density contrasts, representing the most likely surfaces. Sharp contrasts in the image are then investigated by dynamic time warping for similarity analysis. Finally, the geological plane is defined as a regression plane passing through the most similar contrasts, and a surface confidence criterion is defined based on the homogeneity of contrast along the curve suggested by the regression. Feature identification by a geologist was used as benchmark for comparison and metrics. Accuracy is referred to the difference between apparent dip and azimuth of geological surfaces coming from human and automated workflows, following the idea that two similar geometric results would eventually lead to equally similar geological considerations, and thus to similar operational measures. In general, a prediction accuracy of 60 per cent for the tested wells is observed, considering the total set of surfaces coming from the model. Nevertheless, the results suggest a positive correlation between the apparent dip of the discontinuities and the model error and a general less confidence for the surfaces with greater dip. By isolating the subset of low dipping features generated by the model, that is up to 35°, the accuracy appears to increase up to more than 70 per cent, suggesting that correlation is more difficult for high dipping geological planes. This class of curves also shows a general lower confidence and much of this latter class of surfaces are more likely to be found in the depth interval in which borehole stability issues occurred.

Basin-wide erosion and segmentation of the Plio-Pleistocene forearc basin in central Japan revealed by tephro- and biostratigraphy

The basement of the Tokyo metropolitan area consists of the Miocene–Pleistocene forearc basin fills that are well exposed around Tokyo Bay, especially on the Miura and Boso peninsulas. The forearc basin fills on these two peninsulas are called the Miura and Kazusa groups, and they were deposited during the late Miocene–Pliocene and Pliocene–middle Pleistocene, respectively. Because many biostratigraphic datum planes, paleomagnetic reversal events, and other chronostratigraphic tools are available for these deposits, they provide the “type stratigraphy” of other equivalent sedimentary sequences on the Japanese islands and in the northwest Pacific. However, the use of such stratigraphic markers has not been fully applied to understand the architecture of a basin-wide unconformity between the Miura and Kazusa groups called the Kurotaki unconformity. For our study, we made correlations among the Pliocene vitric tephra beds based on their stratigraphic levels, lithologic characteristics, the chemical compositions of glass shards, and calcareous nannofossil biostratigraphy. As a result, we were able to correlate tephra beds Ng-Ky25 just above the C3n.3n normal subchronozone (4.7 Ma), IkT16-An157.5 and IkT19-An158.5 near the top of the Mammoth reverse polarity subchronozone (3.21 Ma), and Ahn-Onr (2.6–2.7 Ma) across Tokyo Bay on the Miura and Boso peninsulas. We were able to recognize erosional surfaces and coeval mass-transport deposits immediately below the top of the Mammoth reverse polarity subchronozone, which suggests that submarine landslide(s) may have produced the lack of stratigraphic horizons (4.5–3.2 Ma) in the Miura and eastern Boso regions. Basal pebbly sandstone beds pervasively cover the erosional surfaces, and they show lateral variations into the thick (up to 60 m) mass-transport deposits and overlying turbidite sandstones. The lateral variations in sediment thickness of the post-failure deposits suggest that the basin-wide erosion was associated with the initial growth of a basin-bounding structural high that separates two distinct sub-basins in the forearc basin, which resulted in the subsequent onlapping deposition in the earliest stage of the Kazusa forearc basin. The basin-wide erosion marks the initiation of tectonic reconfigurations that led to segmentation of the forearc basin around the Tokyo Bay region.

Sensitivity analysis of seismic attributes parametrization to reduce misinterpretations: Applications to deepwater channel complexes

Geoscientists apply algorithms such as seismic attributes to better interpret depositional systems that enhance various aspects of the seismic data. However, they are limited by the original seismic amplitude or frequency content, data quality, and algorithm parameters considered.Additionally, our capacity to interpret depositional system architecture is limited by seismic resolution, which results in potential misinterpretations associated with the correct position of stratigraphic features. Resolution also sets a minimum thickness that can be observed in seismic data. This is particularly important as mapping reservoir architecture (geobody size, shape, and stacking patterns) in the subsurface is critical for exploring and producing hydrocarbons, CO2 storage, and geothermal resource development since it can define connectivity or compartmentalization of flow zones.To address these concerns, we investigated five synthetic seismic volumes from low to high-dominant frequencies of 15 Hz, 30 Hz, 60 Hz, 90 Hz, and 180 Hz based on an architectural model of an outcropping deepwater channelized slope system in the Magallanes Basin, Chile. We analyzed 1) how seismic bandwidth affects the resolution of stacked stratigraphic features (i.e., deepwater channel elements and Mass Transport Deposits (MTDs)) and their subsequent seismic interpretation, and 2) the effect of different seismic attributes commonly employed in channel interpretation on our data to understand the “mixing” or “vertical smearing” of stratigraphic features by comparing the seismic with the true geological model 3) we explored how the attributes’ parametrization affects the imaging of differently sized features by modifying the analysis window in each case from ± 2ms to ± 50 ms. Finally, 4) we evaluated the effect of different noise levels in the sensitivity analysis. Resultsshow that the “mixing” of events occurs mainly as a result of 1) the seismic bandwidth, 2) the algorithm used for each seismic attribute calculation, 3) the attribute vertical analysis window, and 4) the signal-to-noise ratio of the data. Broadband, higher frequency data, and small analysis windows provide clearer images of the stacked channels. In contrast, low-frequency data and larger analysis windows result in more mixing or “composite” appearances, affecting interpretations and net-to-gross estimates, especially in small-size stratigraphic features such as individual channel elements and Mass Transport Deposits (MTDs). Our observations warn of potential misinterpretations in applying default attributes to actual seismic data, especially in geometrical attributes and window-dependent ones. Recognizing these misinterpretations is paramount for reconstructing deepwater architecture (this study), sedimentary and structural studies for drilling locations, reserves estimation, and overall uncertainty assessment.