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Turbidity currents are sediment-laden gravity currents that transfer sediments to deep sea and lake floors through erosion and deposition. These deposits form subaqueous fans in deep marine environments and can reduce reservoir storage capacity, complicating management. Deep sea deposits often contain hydrocarbons like oil and gas. Field measurements of turbidity currents are challenging due to the risk of damage to measuring instruments, and laboratory experiments do not accurately simulate these currents. Thus, numerical modeling is crucial for understanding their formation and properties, and for locating oil and gas fields within deep sea turbidites.A 3D two-phase numerical model (water and solids) is used to simulate underflow turbidity currents. This model solves the Reynolds-Averaged Navier-Stokes equations and uses the Eulerian approach, with turbulence closure achieved by the RNG k-ε model. It simulates both continuous unconfined currents and surge-like confined currents. Calibration and validation against experimental data show the model accurately replicates key features of turbidity currents.Model results indicate that fine particles remain suspended longer, providing additional density that drives the current further with increasing downstream velocity. Vertical concentration profile shows two distinct layers: a denser, faster-moving bottom layer parallel to the bed, and a slower, more diluted upper layer affected by entrainment and mixing with ambient fluid. Turbidity currents are supercritical on sloped channels and subcritical on mild sloped unconfined seafloors or reservoir bottoms. In following article, hypothetical simulations using this model will further explore various characteristics and deposits of turbidity currents on a field scale.

This study is based on the detailed sedimentological analysis of eleven sections and one well through the late Eocene–Oligocene flysch formation of the Internal Ionian Zone (IIZ) in Western Greece. The sections are spread from the northern parts of Epirus to the north and Aitolokarnania to the south. Sedimentological data combined with biostratigraphic analyses resulted in a five-stage evolutionary model for the basin. Unit I corresponds to the lower part of the examined sections, indicating the onset of clastic sedimentation. Regarding depositional environments, it is regarded as a basin plain where lobe distal fringe accumulations occur. Unit II consists almost exclusively of heterolithic facies, marking the advance of a lobe complex system. Massive sandstone facies dominate unit III and can be considered a more proximal submarine fan system. Unit IV reflects a calm period of the basin, where mud-dominated heterolithics and hemipelagic mudstones were deposited. Hemipelagic mudstone facies with intervals of heterolithics, conglomerates, and deformed and massive sandstone facies characterize unit V. The architecture resembles a slope system incised by canyons and channels. The sand-rich intervals in Units III and V could act as the most favorable reservoir levels. In contrast, the sand-rich intervals in Unit II are considered less promising due to their higher heterogeneity.

The fossil record of deep-marine environments is notoriously poor in comparison with that of their shallow-marine counterparts. Notably, deep-marine deposits are typically host to diverse and abundant trace-fossil assemblages, providing evidence of the ancient deep-sea benthos. To analyze the early colonization of the deep sea, we constructed a global dataset of trace-fossil occurrences from a survey of EdiacaranâDevonian stratigraphic units. This analysis highlights the importance of the Ordovician radiation as a pivotal time in the colonization of the deep sea. Ediacaran deep-marine trace fossils consist of very simple trails and burrows. Global and alpha ichnodiversity, as well as ichnodisparity, were extremely low. Nonspecialized grazing trails reveal the exploitation of microbial mats. These strategies persisted in the Cambrian, although with an increase in ichnodiversity (both global and alpha) and ichnodisparity. An increase in the complexity of morphologic patterns, as illustrated by the undermat mining ichnogenus Oldhamia, is apparent during the Cambrian. The face of the deep sea started to change during the end of the Cambrian and beginning of the Ordovician with the protracted expansion of farming and trapping strategies. The main architectural designs of deep-marine trace fossils (e.g. regular networks, delicate spiral burrows, guided meandering graphoglyptids) were established in the deep sea by the Early Ordovician, recording the first appearance of the Nereites Ichnofacies. Lower to Middle Ordovician deep-marine ichnofaunas are moderately diverse, and fodinichnia commonly dominates rather than graphoglyptids. A significant ichnodiversity and ichnodisparity increase occurred in the Late Ordovicianâearly Silurian, with ichnofaunas recording higher proportions of graphoglyptids and evidencing the establishment of a deep-marine ecosystem of modern aspect. The distinction between the Nereites and Paleodictyon ichnosubfacies, with the former characterized by the dominance of feeding traces in muddy turbidites and the later by the dominance of graphoglyptids in sandy turbidites, can also be tracked back to the Ordovician radiation. This trend of increased colonization of the deep sea continued through all the Silurian and the Devonian. However, colonization of carbonate turbidites may have lagged behind that of siliciclastic turbidites. The progressive increase in abundance and diversity of graphoglyptids resulted in an increased role of gallery biodiffusers. This faunal turnover in the deep sea was coincident with an increase in oxygenation in slope and base-of-slope settings, which is thought to have been a driver of Ordovician biodiversifications. The formation of permanent open burrows in the deep sea may have increased bioirrigation in the uppermost zone of the deep-sea sediment, therefore increasing ventilation and potentially generating a feedback loop between bioturbation and oxygenation, with the endobenthos engineering its environment.

Unconventional oil and gas resource development and exploration is the one of the most prospective concept in petroleum geology. High carbon Khadum facies are investigated as unconventional resources in the Precaucas basin and contain gas, gas condensate and oil accumulations. Oligocene and Lower Miocene structure, prospectivity and fields distribution are the one of the most relevant subjects nowadays. This study is focused on the main stages Late Eocene and Early Oligocene deposits formation and the paleogeography of the Khadum formation in the Precaucas oil and gas basin. The new prospective zones are developed in Khadum formation based on the complex analysis of seismic, paleogeography and lithofacies analysis.

The Forties Sandstone Member is an important deep-water reservoir in the Central North Sea. The role of depositional characteristics, grain-coating clays, and diagenesis in controlling the reservoir quality of the sandstones is poorly understood. The main aim of the study is to understand the role of depositional characteristics, grain-coating and pore-filling clays, and diagenesis in controlling the reservoir quality evolution of turbidite-channel sandstones. The study employed a multi-disciplinary technique involving thin section petrography and scanning electron microscopy (SEM) to investigate the impact of grain size, clay matrix content, mode of occurrence of grain-coating chlorite and illite, and their impact in arresting quartz cementation and overall reservoir quality in the sandstones. Results of our study reveal that porosity evolution in the sandstones has been influenced by both primary depositional characteristics and diagenesis. Sandstones with coarser grain size and lower pore-filling clay content have the best reservoir porosity (up to 28%) compared to those with finer grain size and higher pore-filling clay content. Quartz cement volume decreases with increasing clay-coating coverage. Clay coating coverage of >40% is effective in arresting quartz cementation. Total clay volume of as low as 10% could have a deleterious impact on reservoir quality. The Forties Sandstone Member could potentially be a suitable candidate for physical and mineralogical storage of CO2. However, because of its high proportion (>20%) of chemically unstable minerals (feldspar, carbonates, and clays), their dissolution due to CO2 injection and storage could potentially increase reservoir permeability by an order of magnitude, thereby affecting the geomechanical and tensile strength of the sandstones. Therefore, an experimental study investigating the amount of CO2 to be injected (and at what pressure) is required to maintain and preserve borehole integrity. The findings of our study can be applied in other reservoirs with similar depositional environments to improve their reservoir quality prediction.

Abstract Sedimentologic, oceanographic, and hydraulic engineering publications on hyperpycnal flows claim that (1) river flows transform into turbidity currents at plunge points near the shoreline, (2) hyperpycnal flows have the power to erode the seafloor and cause submarine canyons, and, (3) hyperpycnal flows are efficient in transporting sand across the shelf and can deliver sediments into the deep sea for developing submarine fans. Importantly, these claims do have economic implications for the petroleum industry for predicting sandy reservoirs in deep-water petroleum exploration. However, these claims are based strictly on experimental or theoretical basis, without the supporting empirical data from modern depositional systems. Therefore, the primary purpose of this article is to rigorously evaluate the merits of these claims. A global evaluation of density plumes, based on 26 case studies (e.g., Yellow River, Yangtze River, Copper River, Hugli River (Ganges), Guadalquivir River, Río de la Plata Estuary, Zambezi River, among others), suggests a complex variability in nature. Real-world examples show that density plumes (1) occur in six different environments (i.e., marine, lacustrine, estuarine, lagoon, bay, and reef); (2) are composed of six different compositional materials (e.g., siliciclastic, calciclastic, planktonic, etc.); (3) derive material from 11 different sources (e.g., river flood, tidal estuary, subglacial, etc.); (4) are subjected to 15 different external controls (e.g., tidal shear fronts, ocean currents, cyclones, tsunamis, etc.); and, (5) exhibit 24 configurations (e.g., lobate, coalescing, linear, swirly, U-Turn, anastomosing, etc.). Major problem areas are: (1) There are at least 16 types of hyperpycnal flows (e.g., density flow, underflow, high-density hyperpycnal plume, high-turbid mass flow, tide-modulated hyperpycnal flow, cyclone-induced hyperpycnal turbidity current, multi-layer hyperpycnal flows, etc.), without an underpinning principle of fluid dynamics. (2) The basic tenet that river currents transform into turbidity currents at plunge points near the shoreline is based on an experiment that used fresh tap water as a standing body. In attempting to understand all density plumes, such an experimental result is inapplicable to marine waters (sea or ocean) with a higher density due to salt content. (3) Published velocity measurements from the Yellow River mouth, a classic area, are of tidal currents, not of hyperpycnal flows. Importantly, the presence of tidal shear front at the Yellow River mouth limits seaward transport of sediments. (4) Despite its popularity, the hyperpycnite facies model has not been validated by laboratory experiments or by real-world empirical field data from modern settings. (5) The presence of an erosional surface within a single hyperpycnite depositional unit is antithetical to the basic principles of stratigraphy. (6) The hypothetical model of “extrabasinal turbidites”, deposited by river-flood triggered hyperpycnal flows, is untenable. This is because high-density turbidity currents, which serve as the conceptual basis for the model, have never been documented in the world’s oceans. (7) Although plant remains are considered a criterion for recognizing hyperpycnites, the “Type 1” shelf-incising canyons having heads with connection to a major river or estuarine system could serve as a conduit for transporting plant remains by other processes, such as tidal currents. (8) Genuine hyperpycnal flows are feeble and muddy by nature, and they are confined to the inner shelf in modern settings. (9) Distinguishing criteria of ancient hyperpycnites from turbidites or contourites are muddled. (10) After 65 years of research since Bates (AAPG Bulletin 37: 2119–2162, 1953), our understanding of hyperpycnal flows and their deposits is still incomplete and without clarity.

In this Glossary, selected terms and concepts associated with submarine fans are defined.

When we look back the contributions on submarine fans during the past 65 years (1950–2015), the empirical data on 21 modern submarine fans and 10 ancient deep-water systems, published by the results of the First COMFAN (Committee on FANs) Meeting (Bouma et al., 1985a), have remained the single most significant compilation of data on submarine fans. The 1970s were the “heyday” of submarine fan models. In the 21st century, the general focus has shifted from submarine fans to submarine mass movements, internal waves and tides, and contourites. The purpose of this review is to illustrate the complexity of issues surrounding the origin and classification of submarine fans. The principal elements of submarine fans, composed of canyons, channels, and lobes, are discussed using nine modern case studies from the Mediterranean Sea, the Equatorial Atlantic, the Gulf of Mexico, the North Pacific, the NE Indian Ocean (Bay of Bengal), and the East Sea (Korea). The Annot Sandstone (Eocene–Oligocene), exposed at Peira-Cava area, SE France, which served as the type locality for the “Bouma Sequence”, was reexamined. The field details are documented in questioning the validity of the model, which was the basis for the turbidite-fan link. The 29 fan-related models that are of conceptual significance, developed during the period 1970–2015, are discussed using modern and ancient systems. They are: (1) the classic submarine fan model with attached lobes, (2) the detached-lobe model, (3) the channel-levee complex without lobes, (4) the delta-fed ramp model, (5) the gully-lobe model, (6) the suprafan lobe model, (7) the depositional lobe model, (8) the fan lobe model, (9) the ponded lobe model, (10) the nine models based on grain size and sediment source, (11) the four fan models based on tectonic settings, (12) the Jackfork debrite model, (13) the basin-floor fan model, (14) supercritical and subcritical fans, and (15) the three types of fan reservoirs. Each model is unique, and the long-standing belief that submarine fans are composed of turbidites, in particular, of gravelly and sandy high-density turbidites, is a myth. This is because there are no empirical data to validate the existence of gravelly and sandy high-density turbidity currents in the modern marine environments. Also, there are no experimental documentation of true turbidity currents that can transport gravels and coarse sands in turbulent suspension. Mass-transport processes, which include slides, slumps, and debris flows (but not turbidity currenrs), are the most viable mechanisms for transporting gravels and sands into the deep sea. The prevailing notion that submarine fans develop during periods of sea-level lowstands is also a myth. The geologic reality is that frequent short-term events that last for only a few minutes to several hours or days (e.g., earthquakes, meteorite impacts, tsunamis, tropical cyclones, etc.) are more important in controlling deposition of deep-water sands than sporadic long-term events that last for thousands to millions of years (e.g., lowstand systems tract). Submarine fans are still in a stage of muddled turbidite paradigm because the concept of high-density turbidity currents is incommensurable.

Veacute;rard et al. (2015, Journal of Palaeogeography, 4(1): 64-84) claim that their global geodynamic model allows one to reconstruct the surface features of topography on land and in adjacent oceans (i.e., paleobathymetry) anywhere on the globe and at any geological time during the past 600 million years (Ma). Such a grand model requires a rigorous scrutiny. The purpose of this discussion is to illustrate that the model suffers from (1) the selective omission of real-world datasets that do not fit the model, (2) the inclusion of datasets without revealing their original sources or without citing relevant peer-reviewed publications, (3) the emphasis on ‘unpublished’ internal company datasets that disallow open access to the international scientific community, and (4) the use of poorly understood concepts without providing the basic conceptual clarity. These deficiencies undermine the credibility of the heuristic model.

The depositional environment of the Teikangas formation in southwestern Finland has been studied. The formation is an isolated, ice marginal accumulation of coarse-grained sediments north of the Hämeenkangas ridge, related to the Weichselian ice sheet. The results indicate that the Teikangas feature represents subaqueous ice-contact fan built by the onlapping of several smaller fans that have prograded from different directions. The fan system was developed during the final retreat of the Weichselian ice-sheet (the Näsijärvi-Jyväskylä Lobe), at its terminus in the Baltic Yoldia Sea.