High-density Turbidity Currents Research Articles

Ichnological and Sedimentological Characteristics of Submarine Fan-Delta Deposits in a Half-Graben, Lower Cretaceous Palnatokes Bjerg Formation, NE Greenland

ABSTRACTFault-scarp related fan deltas developed in tilted half grabens in NE Greenland during late Jurassic—early Cretaceous rifting. This study documents ichnological and sedimentological characteristics of the Lower Cretaceous interval of a submarine fan-delta succession (Palnatokes Bjerg Formation, Wollaston Forland), which represents a time of waning rift activity and transgression. For this purpose, two variably exposed ca. 150 m-thick sections were studied ∼10 km from the coeval fault scarp, near the axis of the most proximal fault block. Moreover, an additional ∼20 m thick coeval succession was studied in the next fault block ∼20 km from the coastline defining fault. The results indicate deposition on the basin floor, in the distal fan and in a mid-fan channel-overbank/splay complex of a subaqueous fan delta. The deposits are characterized mainly by various facies of high and low density turbidity currents, hybrid event beds, and transitional flow facies that grade upward into sediment starved basinal mudstones. The ichnological pattern recorded in these strata is strongly mixed, frequently containing elements of the impoverished Skolithos, Cruziana, Zoophycos ichnofacies, and more rarely of the Nereites ichnofacies. Characteristic features also include suites dominated by infaunal locomotion and feeding trails (including the “Curvolithus suite”) and the common occurrence of crustacean burrows. The results are indicative of a depositional system resembling a fjord-side delta that differs sedimentologically and ichnologically from many other gravity-flow systems of similar grain-size caliber. The ichnological pattern recorded in these strata is potentially a characteristic feature of the subaqueous fan-deltas in comparable settings, reflecting the distinct basin physiography with an abrupt change in bathymetry, a narrow basin geometry, and environmental stress resulting from unstable physical conditions. The counter slope of the rotated fault block may explain the common signs of flow concentration and abrupt fan termination.

Supercritical flows and their control on the architecture and facies of small-radius sand-rich fan lobes

New insights into flow characteristics of supercritical, high-density turbidity currents initiated renewed interest in a sand-rich lobe complex near the hamlet of Mizala in the Sorbas Basin (Tortonian, SE Spain). The field study was done using drone-made images taken along bed strike in combination with physical tracing of bounding surfaces and section logging. The studied lobe systems show a consistent built-up of lobe elements of 1.5–2.0m thick, which form the building ‘blocks’ of the lobe system. The stacking of lobe elements shows lateral shift and compensational relief infill. The new model outlined in this paper highlights three stages of fan lobe development: I. an early aggradational stage with lobe elements characterized by antidune and traction-carpet bedforms and burrowed mud intervals (here called ‘distal fan’ deposits); II. a progradational stage, where the distal fan deposits are truncated by lobe elements of amalgamated sandy to gravelly units characterized by cyclic step bedform facies (designated as ‘supra fan’ deposits). The supra fan is much more channelized and scoured and of higher flow energy than the distal-fan. Aggradation of the supra-fan is terminated by a ‘pappy’ pebbly sandstone and by substrate liquefaction, ‘pappy’ referring to a typical, porridge-like texture indicating rapid deposition under conditions of little-to-no shear. The facies-bounded termination of the supra-fan is here related to its maximum elevation, causing the lobe-feeding supercritical flow to choke and to expand upwards by a strong hydraulic jump at the channel outlet; III. a backfilling stage, characterized by backfilling of the remaining relief with progressively thinning and fining of turbidite beds and eventually with mud. The three-stage development for fan-lobe building is deducted from reoccurring architectural and facies characteristics in three successive fan-lobes. The validity of using experimental, supercritical-flow fan studies for understanding the intrinsic mechanisms in sand-rich-fan lobe development is discussed.

Autogenic influence on the morphology of submarine fans: an approach from 3D physical modelling of turbidity currents

ABSTRACT: Autogenic controls have significant influence on deep-water fans and depositional lobes morphology. In this work, we aim to investigate autogenic controls on the topography and geometry of deep-water fans. The influence of the sediment concentration of turbidity currents on deep-water fans morphology was also investigated. From the repeatability of 3D physical modeling of turbidity currents, two series of ten experiments were made, one of high-density turbidity currents (HDTC) and another of low-density turbidity currents (LDTC). All other input parameters (discharge, sediment volumetric concentration and grain size median) were kept constant. Each deposit was analyzed from qualitative and quantitative approaches and statistical analysis. In each experimental series, the variability of the morphological parameters (length, width, L/W ratio, centroid, area, topography) of the simulated deep-water fans was observed. Depositional evolution of the HDTC fans was more complex, showing four evolutionary steps and characterized by the self-channelizing of the turbidity current, while LDTC fans neither present self-channelizing, nor evolutionary steps. High disparities on the geometrical parameters of the fans, as characterized by the elevated relative standard deviation, suggest that autogenic controls induced a stochastic morphological behaviour on the simulated fans of the two experimental series.

Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

Submarine canyons have been the subject of intense studies in recent years because of their academic significance to studies of climate signals, eustasy and tectonic movement of the neighbouring area and their economic significance for hydrocarbon exploration in deep-water areas. The Central Canyon in the Qiongdongnan Basin runs parallel to the continental slope, and has a length, width and depth of 520 km, 2–15 km and 270–800 m. Using seismic and well log data, we analyses the sedimentary differences and controlling factors of the sediments in the different segments of the Central Canyon. The sediments within the Central Canyon can be subdivided into five phases of the secondary canyon filling. The most typical features of each phase of the secondary canyon are high- and low-density turbidity currents developed in the phase 1–2 of the secondary canyon, the muddy debris flows, turbidity currents and mass transport deposits in the phase 3, the high-density turbidity currents in the phase 4, the hemi-pelagic mudstone and mass transport deposits in the phase 5. There are four depositional models corresponding to the head area, upstream segment, middle reaches and downstream segment of the Central Canyon were established. It is characterized by muddy matrix-supported conglomerates and thickly massive sandstones with the feature of upward fining and thinning deposited in the head area, the thickly high net to gross sandstone infilled in the upstream segment, the thinly interbedded sandstones and mudstones and muddy mass transport deposits developed in the middle reaches, and the extensive hemi-pelagic mudstone infilled in the downstream segment. The transformation of the debris flows into turbidity currents and high-density turbidity currents into low-density turbidity in the head and upstream segment, supersaturated filling in the upstream segment, extensive development of mass transport deposits in the middle reaches, under-compensation filling and widely development of canyon wall collapse in the downstream segment are the main reasons contributing to the sedimentary differences between different segments of the Central Canyon.

ANATOMY OF CARBONATE BRECCIAS, TURBIDITE FACIES AND DEPOSITIONAL SYSTEMS OF GERCUS FORMATION IN DOKAN AREA, NORTHERN IRAQ

Four facies associations are classified based on facies types, sedimentary structures and facies successions, these are; distal slope apron siliciclasticcalciturbidites (siliciclastic/ carbonate dominated), proximal marine siliciclasticcalciturbidites (carbonate/ siliciclastic dominated), distal basinal fan siliciclastic turbidites (siliciclastic dominated) and proximal basinal fan siliciclasticcalciturbidites (carbonate/ siliciclastic dominated). The most important characteristic representative facies types are; ball and pillows dolomite (reported here for the first time), thick fissile shale, slump/ slide limestone, slump/ slide sandstone, channeled sandstone, ball and pillow sandstone, slump sandstone, convolute sandstone, crossbedded sandstone, sigmoidal channeled sandstone, disturbed sandstones, red argillaceous mudstone, gray massive claystone, flute scoured sandstone with slump carbonate breccias types. The carbonate breccias are the most important characteristic facies types observed in the formation and reported here for the first time and it is strong indication for marine environment. Examinations and anatomy of facies types and associations suggest developed marine environment, effected mainly by gravity flows and turbidity currents, forming sequences of submarine fans including high density turbidity currents in deeper margins.

Annot Sandstone in the Peïra Cava basin: An example of an asymmetric facies distribution in a confined turbidite system (SE France)

High-resolution physical stratigraphy and detailed facies analysis have been carried out in the foredeep turbidites of Annot Sandstone in the Peïra Cava basin (French Maritime Alps) in order to characterize the relationship between facies and basin morphology. Detailed correlation patterns are evidence of a distinction between a southern bypass-dominated region, coincident with a channel-lobe transition and a north-eastern depositional zone, represented by sheet-like basin plain. These depositional elements are characterized by three main groups of beds related to the downcurrent evolution of bipartite flows. These facies groups are: 1) pebbly coarse-grained massive sandstones with rip-up mudstone clasts and impact mudstone breccias (Type I and II beds) deposited by basal dense flows, 2) coarse-grained massive sandstone overlain by tractive structures (Type III and IV beds) indicating the bypass of overlying turbulent flows and 3) massive medium-grained and fine-grained laminated sandstones related to the deposition of high and low density turbidity currents (Type V and VI beds). Ponding and reflection processes, affecting the upper turbulent flows, can characterize all type beds, but especially the beds of the third group. As described in other confined basins of the northern Apennines (Italy), the lateral and vertical distribution of these type of beds, together with other important sedimentary characteristics, - such as the sandstone/mudstone ratio, bed thicknesses, amalgamation surfaces and paleocurrents - reveal that the deposition of the Annot Sandstone in the Peïra Cava basin was controlled by an asymmetric basin with a steep western margin. This margin favored, on the one hand, basal dense flow decelerations and impacts, as well as bypass and deflection of the upper turbulent flows towards the north east.

VÝVOJ LEDOVCOVÝCH SEDIMENTŮ NA KONTAKTU S ŽULOVSKÝM MASIVEM VE ŠTACHLOVICÍCH U VIDNAVY

The Žulová Upland is composed of granitoids of the Žulová batholith with relicts of Pleistocene (Elsterian) continental glaciation sediments. The investigated outcrop represents development of glacigenic sediments on rugged topography of the Žulová Upland. Investigated locality is situated on a hill located on the northern margin of the Žulová Upland. It is located near Štachlovice, local part of the Vidnava town. The exposed part of the hilltop reveals a preglacial basement covered by glacigenic sediments. The facies analysis and gravel petrology analysis of clasts with fraction 16–64 mm in b-axis were undertaken on the walls of the outcrop. The Georadar (GPR, Ground penetrating radar) was used to investigate the sedimentary landform and its relation to the basement. The granitoid basement is in places formed by elevations covered by glacigenic sediments. The height of elevation reaches 350 cmin outcrop, or ca ~400 cm according to the GPR survey. The glacitectonite, formed on the gentle side of elevation, is composed of angular blocks of granitoids of the Žulová batholith, diamicton, sand, gravel and deformed glacifluvial sand. The glacitectonite was deposited during the advancement of the continental glacier. The original subglacial cavity is enclosed by a steep side of the elevation. This cavity is filled by foreset body composed of stratified sand and gravel and nonstratified gravelly sand, gravel and diamicton. The cavity was filled by high-density turbidity currents and debris flow in subaqueous-subaerial environment. The infill of the cavity reaches ~400 cm in thickness according to the GPR survey. The cavity was filled during deglaciation in subglacial environment. The glacitectonite underlies the diamicton (supraglacial till) that was deposited as a debris flow during the retreat of the continental glacier. Unsorted gravel overlaps with erosional base the infill of the cavity, this gravel has a huge extent according to the GPR survey. This sediment represents the environment of terminoglacial stream. Gravel material of all types of glacigenic sediments is mainly composed of rocks from the Rychleby Mts. (amphibolites, Gierałtow orthogneiss, other diverse gneisses, quartzites, mica schist),quartz, and Nordic and Polish rocks. Subglacial sediments contain clasts of amphibolites (~40 %), on the other hand supraglacial and terminoglacial sediments are more polymict. Dominant subrounded shape (~60–70 %) of clasts and composition of this material indicates its origin in preglacial fluvial sediments. These fluvial sediments were deposited by river flowing from the Rychleby Mts. towards their northern foreland. The locality represents preglacial elevation of bedrock, which was glacitectonically deformed during the glaciation. Lots of different types of sediments (sub-, supra-, and terminoglacial) were deposited around the elevation during deglaciation period. The elevation was completely buried by these sediments. Deposition of these sediments was related with morphology of the elevation of bedrock. Formation of these sediments took place in environment analogous to environment of part bedrock/part till drumlin (Stokes et al. 2011).

Inside pyroclastic density currents – uncovering the enigmatic flow structure and transport behaviour in large-scale experiments

Pyroclastic density currents (PDCs) are the most lethal threat from volcanoes. While there are two main types of PDCs (fully turbulent, fully dilute pyroclastic surges and more concentrated pyroclastic flows encompassing non-turbulent to turbulent transport) pyroclastic flows, which are the subject of the present study, are far more complex than dilute pyroclastic surges and remain the least understood type despite their far greater hazard, greater runout length and ability to transport vast quantities of material across the Earth's surface.Here we present large-scale experiments of natural volcanic material and gas in order to provide the missing quantitative view of the internal structure and gas–particle transport mechanisms in pyroclastic flows. We show that the outer flow structure with head, body and wake regions broadly resembles current PDC analogues of dilute gravity currents. However, the internal structure, in which lower levels consist of a concentrated granular fluid and upper levels are more dilute, contrasts significantly with the internal structure of fully dilute gravity currents. This bipartite vertical structure shows strong analogy to current conceptual models of high-density turbidity currents, which are responsible for the distribution of coarse sediment in marine basins and of great interest to the hydrocarbon industry.The lower concentrated and non-turbulent levels of the PDC (granular–fluid basal flow) act as a fast-flowing carrier for the more dilute and turbulent upper levels of the current (ash-cloud surge). Strong kinematic coupling between these flow parts reduces viscous dissipation and entrainment of ambient air into the lower part of the ash-cloud surge. This leads to a state of forced super-criticality whereby fast and destructive PDCs can endure even at large distances from volcanoes. Importantly, the basal flow/ash-cloud surge coupling yields a characteristically smooth rheological boundary across the non-turbulent/turbulent interface, as well as vertical velocity and density profiles in the ash-cloud surge, which strongly differ from current theoretical predictions. Observed generation of successive pulses of high dynamic pressure within the upper dilute levels of the PDC may be important to understand the destructive potential of PDCs.The experiments further show that a wide range in the degree of coupling between particle and gas phases is critical to the vertical and longitudinal segregation of the currents into reaches that have starkly contrasting sediment transport capacities. In particular, the formation of mesoscale turbulence clusters under strong particle–gas feedback controls vertical stratification inside the turbulent upper levels of the current (ash-cloud surge) and triggers significant transfers of mass and momentum from the ash-cloud surge onto the granular–fluid basal flow.These results open up new pathways to advance current computational PDC hazard models and to describe and interpret PDCs as well as other types of high-density gravity currents transported across the surfaces of Earth and other planets and across marine basins.

A Sedimentological Process-Based Approach To Depositional Reservoir Quality of Deep-Marine Sandstones: An Example From the Springar Formation, Northwestern Vøring Basin, Norwegian Sea

Reservoir properties of deep-marine sandstones deposited by various sediment-gravity-flow types in the northwestern Voring Basin (Norwegian Sea) are characterized using detailed sedimentological and petrographic analyses. The sandstones are quartz arenites and subarkoses, having similar mineralogical compositions, a low degree of diagenetic modification, and low to moderate volumes of quartz cement (up to 6%). However, significant textural variability is observed for the various sandstone types, which were subdivided based upon their interpreted processes of deposition. In the studied wells there is a predominance of turbidites deposited by high-density turbidity currents (HDTs) and a range of hybrid event beds (HEBs). HDTs are coarser grained and contain less detrital clay than the various HEBs. In addition, the dominant grain size of HEBs decreases down the depositional profile whilst the content of detrital clay increases. Porosities of the various bed types span the same interval, but overall the HDTs and proximal HEBs have a higher proportion of samples with porosities higher than 20%, compared to distal HEBs. Permeabilities, in contrast, are significantly different, with the HDTs having permeabilities approximately two orders of magnitude higher than clay-rich HEBs. A comparison of the observed variability in composition and textural parameters with porosity and permeability indicates that sedimentological flow processes control the depositional reservoir quality of deep-marine sandstones; understanding these processes therefore enhances our ability to predict distribution of reservoir quality in deep-marine systems.

Submarine fans: A critical retrospective (1950–2015)

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.

Hydraulic evolution of high-density turbidity currents from the Brushy Canyon Formation, Eddy County, New Mexico inferred by comparison to settling and sorting experiments

Hydraulic transformations in turbidity currents are commonly driven by or reflected in changes in suspended sediment concentrations, but changes preceding transformations can be difficult to diagnose because they do not produce qualitative changes in resultant deposits. This study integrates particle settling experiments and in situ detection of hydraulically contrasting particles in turbidites in order to infer changes in suspended sediment concentration during deposition of massive (Bouma Ta) sandstone divisions. Because grains of contrasting density are differentially sorted during hindered settling from dense suspensions, relative grading patterns can be used to estimate suspended sediment concentrations and interpret hydraulic evolution of the depositing turbidity currents.Differential settling of dense particles (aluminum ballotini) through suspensions of hydraulically coarser light particles (silica ballotini) with volumetric concentration, Cv, were studied in a thin vessel by using particle-image-velocimetry. At high Cv, aluminum particles were less retarded than co-sedimenting silica particles, and effectively settled as hydraulically coarser grains. This was because particles were entrained into clusters dominated by the settling behavior of the silica particles. Terminal settling velocities of both particles converged at Cv≥25%, and particle sorting was diminished.The results of settling experiments were applied to understand settling of analogous feldspar and zircon grains in natural turbidity flows. Distributions of light and heavy mineral grains in massive sandstones, Bouma Ta divisions, of turbidites from the Middle Permian Brushy Canyon Formation were observed in situ by X-ray fluorescence microscopy (μXRF). Hydraulic sorting of these grains resulted in characteristic patterns of zirconium abundance that decreased from base to top within Ta divisions. These profiles resulted from upward fining of zircon grains with respect to co-occurring feldspar grains. Although calculated settling velocity distributions for zircon grains in structureless sandstones were slower than those for feldspar grains at infinite dilution, calculated settling velocity distributions for zircon and feldspar grains in overlying black siltstone layers were identical. This evidence suggests that these sandstone divisions were deposited from hyperconcentrated suspensions where particle segregation was diminished and hydraulically fine grains were entrained with hydraulically coarse particles. Hydraulic fining of zircon grains during deposition implies that the suspended sediment concentration at the bases of turbidity currents increased even as the overall current evolved toward lower density as reflected by cessation of Ta deposition and by hydraulic equivalence of zircon and feldspar grains in overlying low-density turbiditic siltstones. This evolution likely resulted from volumetric collapse of the turbidity currents.

Outcrop characterization of a submarine channel-lobe complex: The Lower Mount Messenger Formation, Taranaki Basin, New Zealand

The Upper Miocene Lower Mount Messenger Formation (LMMF) exposed in cliffs along the west coast of the North Island, New Zealand, includes 650 m of thick-bedded, fine-to very fine-grained sandstone, interbedded sandstone and mudstone, mudstone, and mass transport deposits. Deposition was from low- and high-density turbidity currents and small to very large, intraformational slumps, slides, and debris flows. The LMMF comprises five major facies associations (FA) representing the principal depositional settings within which the sediments accumulated: (FA1) distal to medial frontal lobes and lobe complexes, (FA2) more proximal frontal lobes and crevasse and/or overbank splays; (FA3) submarine channels; (FA4) levees; and (FA5) mass transport deposits (MTDs). The lower, northern part of the LMMF is dominated by FA1 and FA2 deposited as part of a large, amalgamated frontal lobe system. This section is overlain and, near the top, interbedded with FA3 levee deposits. The top of the LMMF includes a channel complex that interfingers with the levees and related lateral splay deposits. The submarine channel belt was nearly 3 km wide and delivered the sediments to the lobe complex more than 15 km downslope.The channels are filled largely with the deposits of low-density turbidity currents characterized by plane lamination and climbing-ripple cross-lamination. In contrast, lobes contain thick-bedded massive and cross-stratified sandstones deposited by high-density flows. This contrast of apparently higher energy, high-density turbidite divisions in the lobes and lower energy, low-density deposits in the upslope channel fill is thought to reflect diachronous deposition of these otherwise contiguous parts of the deposystem. When sand deposition was occurring on the lobe complex, large, high-density flows moved through and largely bypassed or actively eroded the upslope channels. As flow volumes and strength declined, deposition on the lobe complex waned and sand deposition from low-density currents occurred within the channels, with little sediment other than mud reaching the lobe complex.The overall northward paleoflow direction in the outcrop window is parallel to the inferred eastern paleoslope. The abundance of massive turbidites in the most downslope deposits and evidence for correlative deposits with south- and southwest-directed paleocurrents a short distance to the north suggest that the basin may have been ponded.

Compositional differences between Besko and Otryt sandstones of the Krosno Beds (Oligocene) in Eastern part of the Silesian Tectonic Unit [abstract

The aim of this research was to quantitatively and qualitatively analyse under microscope sandstones representing two lithofacies called Otryt and Besko (or Lesko) facies of the Krosno Formation (Oligocene), Silesian Tectonic Unit in the E part of the Polish Outer Carpathians. Four samples were taken into consideration — two from each lithofacies. Special attention was paid to structural and textural characteristics and mineral composition that reflects mainly provenance. The results have been compared and analysed between and within facies, in terms of source and transport of the material, mineralogical and textural maturity and sedimentary processes that affect the deposition. Ślączka & Unrug (1972) and Shideler at al. (1976) concluded that mineralogical variations exhibited by sandstones in Krosno Formation were attributed to both regional (provenance) and local (sorting) effects. The samples have been taken from the northern (Otryt) and southern (Besko) limbs of the Otryt Syncline. They represent different sources of the material - Silesian Ridge in NW in case of Besko facies and Maramures Massif in the the SE in case of Otryt facies (Wendorff 1981). The result of the analysis confirm statement about two different sources. Transport and deposition mechanism results in considerable difference in grain size and its distribution. Besko facies sandstones display classic Bouma sequence at structures (T b - c ) indicative of deposition from normally diluted, waning turbidity currents, with incremental deposition layer-by-layer (Talling 2012) and this results in very fine grained sandstones and in better sorting. Deposits of that lithofacies appear much relatively uniform and well organized (Wendorff 1987). By contrast, sedimentary features of the Otryt facies suggest deposition from rapidly decelerating high density turbidity currents — “sandy debris flows” (Talling 2012), conditions and mechanisms of transportation and deposition must have been very variable (Wendorff 1987). These sandstones are medium grained, but the bottom sample is characterized by coarse tail caused by rapid deposition. The detrital material of the top sample was deposited also of high density turbidity current, however slightly less dense than that of the bottom sample. The diversity of mineral composition between Besko and Otryt lithofacies is very clear. There are probably three reasons for that — completely different source rocks, initially different maturity of the detritus involved in density flows and the depositional processes within the basin . Besko (Leslo) lithofacies is dominated by nonundulatory quartz. Other components are rather minor. The only difference between carbonate components is in the proportion of detrital calcite/limestone (or dolomite) to carbonate cement, which may have resulted from diagenetic processes. Carbonate cements are very rich in both samples. In Otryt facies mineral composition is more differentiated. Quartz predominates, but not as distinctly as in Besko facies. The most abundant and the coarsest are polycrystalline grains. Nonundulatory quartz is similarly abundant. Altered K-feldspars and metamorphic rock fragments are important however they occur less frequently. The bottom and top samples differ in quantity of coarse to very coarse metamorphic rock fragments and polycrystalline quartz — the bottom sample is richer in such grains. This is the result of grain-size sorting — coarser grains have been deposited first and this sorting process affects the mineral composition of the top-of-bed sample in which the coarse tail is absent and the proportion of metamorphic grains is less pronounced. There is very little cement in both samples. Next to high mineralogical maturity, Besko facies sandstones show also high textural and mineralogical maturity (presence of well-rounded grains and high quartz content). On the other hand, Otryt facies sandstones are immature both texturally and mineralogically, which results from both source area composition and rapid deposition. According to provenance diagrams (Dickinson 1983), source of the Besko facies is recycled orogen, but close to craton interior field. Whereas source of the Otryt facies should be recycled orogen too. Despite the fact that all samples are the same age and occur in one formation, they are totally different. In summary, differences in mineral composition and textural features, observed under the microscope, between the analysed samples of the Besko/Lesko and Otryt lithofacies turbidite sandstones reveal different mineral composition of the source areas and are comparable to the macroscopically observed sedimentary features. The latter indicate pronounced differences in the transportation and deposition mechanisms – from normally diluted turbidity currents to rapidly decelerating high sandy debris flows.

Reservoir geology of the Paleocene Forties Sandstone Member in the Fram discovery, UK Central North Sea

AbstractThe Fram discovery, located in the UK Central North Sea, comprises the Paleocene-aged Forties Sandstone Member with an oil rim and primary gas-cap trapped within a four-way dip closure around a pierced salt diapir. The Forties Sandstone Member reservoir at Fram is characterized by very-fine- to fine-grained sandstones interbedded with shales with post-depositional small-scale slumping and sand injection, interpreted to be the product of high-density turbidity currents and debris flows. Deposition was in an overall distal and marginal, basin-floor lobe environment. The Forties reservoir interval is considered to comprise a series of offset-stacked, turbidite lobes characterized by a systematic variation from axial amalgamated sandstone facies to more distal, marginal and thinner-bedded heterolithic sandstone facies, producing an overall sheet-like reservoir architecture. The Forties reservoir at Fram is thinner and poorer when compared with more proximal parts of the Forties submarine fan system, and reservoir quality is strongly controlled by sedimentary facies. The architecture of the reservoir is expected to result in poorer vertical, but greater lateral, stratigraphic continuity when compared with more channelized Forties reservoirs such as the Nelson and Forties fields further to the north. A key step in understanding and characterizing the Fram reservoir was the appraisal drilling in 2009, which included coring, comprehensive wireline logging, formation pressure data acquisition and a drill stem production test. This paper provides an overview of the Fram reservoir geology and demonstrates how integration of data acquired in the 2009 29/3c-8,8z appraisal wells with 3D seismic datasets, existing E&A wells and analogues has helped to improve reservoir characterization and identify the major subsurface uncertainties needing to be addressed during the field-development planning.

Soft-sediment deformation structures in seismically affected deep-sea Miocene turbidites (Cilento Basin, southern Italy)

Abstract Soft-sediment deformation structures (SSDS) are widespread in the upper part of the S. Mauro Formation (Cilento Group, Middle-Late Miocene). The succession is represented mainly by thick and very thick, massive, coarse-grained sandstones, deposited by rapid sedimentation of high-density turbidity currents. The most common SSDS are short pillars, dishes, sedimentary sills and convolutions. They occur mostly in the upper parts of sandstone beds. Vertical tubes of 4-5 cm in diameter and up to 50 cm long constitute the most striking structures. They begin in the middle part of sandstone beds, which are basically massive or contain faint dish structures. These tubes can bifurcate upwards and/ or pass into bedding-parallel veins or dikes. The vertical tubes sometimes form sand volcanoes on the then sedimentary surface. The SSDS are interpreted as the result of earthquake-triggered liquefaction and/or fluidisation of the turbidites that were affected by the seismic shocks. This implies that the deformed layers should be considered as seismites.

Syneruptive and intereruptive lithofacies in lacustrine environments: The Cretaceous Beolkeum Member, Wido Island, Korea

The Cretaceous Beolkeum Member was deposited in a lacustrine environment affected by explosive volcanism, and a number of syneruptive lithofacies are intercalated with lacustrine mudstones. The syneruptive lithofacies were formed by primary volcanic processes and resedimented depositional processes during and after eruptions and exhibit unique depositional features, which can be grouped into four syneruptive lithofacies assemblages (SLA-1–to SLA-4, from bottom to top).Primary syneruptive lithofacies are represented by welded massive lapilli tuff in SLA-1 and a normally graded lapilli tuff in SLA-2. In SLA-1, sustained pyroclastic density currents were able to displace lake water and rarely interacted with lake water, resulting in the formation of a welded texture and columnar joints. In SLA-2, unsteady pyroclastic density currents rapidly disintegrated, mixed with ambient water, and transformed into high-density turbidity currents, depositing thick normally graded lapilli tuff.Resedimented syneruptive lithofacies were primarily controlled by volcaniclastic sediment supply after eruptions. When volcaniclastic sediments were continuously supplied into the lake by debris flows, a volcaniclastic fan can be formed (SLA-1), resulting in a coarsening-upward trend and progradational geometry. In case of relatively small amounts of volcaniclastic sediment supply, turbidity currents would be a main depositional process, depositing a series of normally graded tuff on the primary syneruptive lithofacies (SLA-2), showing a fining-upward trend. In SLA-3 and SLA-4, there are only a few cm thick, normally graded tuff, reflecting minor volcaniclastic sediment supply. However, overlying normally graded sandstones in SLA-3, showing a coarsening-upward trend, and a thick normally graded sandstone in SLA-4 suggest favorable conditions for the generation of the sediment gravity flows, probably due to an increase in volcaniclastic sediment supply after eruptions.

Concentration-Dependent Flow Stratification In Experimental High-Density Turbidity Currents and Their Relevance To Turbidite Facies Models

Basal divisions of turbidite deposits often show characteristics that are interpreted as expression of high-density layers forming at the bases of turbidity currents; however, this link between deposit characteristics and the flow process occurring in these basal high-density layers is still poorly constrained. Here we present the results of a set of experiments were the flow dynamics of high-density layers within turbidity currents were studied, and linked to their depositional behavior. The experiments showed the formation of three types of flow layers depending on the initial sediment concentration and slope. As the sediment concentration increases, the layers show different rheological properties with characteristics expressions in the velocity and turbulence profiles of the flows. Internal flow instabilities, arising from the different density interfaces within the stratified flows, are shown to be increasingly suppressed as sediment concentrations step up over the different flow layers. Suppression of these internal instabilities in the basal layers is shown to have a distinct effect on variations in the aggradation rate, which at lower sediment concentrations can be directly linked to these instabilities. Suppression of these fluctuations in aggradation rate is here used to link the different type of high-density flow stratification to different turbidite facies.

Direct sediment transfer from land to deep-sea: Insights into shallow multibeam bathymetry at La Réunion Island

Abstract Submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins. This contribution offers a detailed picture of canyon heads off La Reunion Island, with high-resolution multibeam bathymetry in the water depth range of 4–220 m. The present feeding of the Cilaos turbidite system, one of the largest modern volcaniclastic systems in the world, is deduced from morphological and sedimentological interpretations of newly acquired data. The study highlights small-scale sedimentary features indicating hydrodynamic and sedimentary processes. A direct connexion between the Saint-Etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar. This direct connection, supplied by river torrential floods (cyclonic floods every two or three years), suggests the continuity of high-density fluvial flows to submarine gravity flows, forming hyperpycnal flows in the canyon. The initiation of secondary submarine gravity flows by storm waves (large austral waves and cyclonic waves) is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar. Bedforms in active canyon axis are considered as an indicator of the frequent activity of high-density turbidity currents. Moreover, a morphological record of last glacial and deglacial sea level variations is preserved, and particularly the Last Glacial Maximum sea level with the presence of small vertical cliffs, observed in this bathymetric data, which likely corresponds to a paleo-shoreline or paleo-reefs.

The Importance of Coaxial and Non-coaxial Components of Shear Strength of Sediments in Submarine Slumping and Initiation of Turbidity Currents

The conditions and the processes under which submarine slumping occurs and the agencies causing them are discussed. Special attention is given to the role of coaxial and non-coaxial components of shear strength of sediments. It is of interest to note that slumps can result in a wide variety of sedimentary structures and many of these structures are associated with liquefaction. The influence of under consolidation due to high rates of sedimentation on the strength of marine sediments is treated in this paper. The drained and un-drained failures and mechanics of slumping are analyzed by applying coaxial and non-coaxial components of shear strength of sediments. It is thought and believed that some slumps transform into high density turbidity currents, if the pore pressures induced at failure are high enough. This paper does not deal with turbidity currents. It is only limited to the extent of explaining the role of coaxial and non-coaxial components of shear strength of sediments in initiating turbidity currents.

Sedimentation and volcanism in the Panamanian Cretaceous intra-oceanic arc and fore-arc: New insights from the Azuero peninsula (SW Panama)

Abstract The Azuero Peninsula, located in SW Panama, is a region characterized by a long-lived intra-oceanic subduction zone. Volcanism began in Late Cretaceous time, as the result of subduction of the Farallon plate beneath the Caribbean plate. Usually, ancient volcanic arcs related to intra-oceanic subduction zones are not preserved, because they are in areas with difficult access or covered by modern volcanic arc material. However, on the Azuero peninsula, a complete section of the volcanic arc together with arc basement rocks provides the opportunity to study the sedimentation and volcanism in the initial stages of volcanic arc development. The lithostratigraphic unit which records fore-arc evolution is the “Río Quema” Formation (RQF), a volcanic apron composed of volcanic and volcaniclastic sedimentary rocks interbedded with hemipelagic limestones, submarine dacite lava domes, and intruded by basaltic-andesitic dikes. The “Río Quema” Formation, interpreted as a fore-arc basin infilling sequence, lies discordantly on top of arc basement rocks. The exceptionally well exposed arc basement, fore-arc basin, volcanic arc rocks and arc-related intrusive rocks provide an unusual opportunity to study the relationship between volcanism, sedimentation and magmatism during the arc development, with the objective to reconstruct its evolution. The “Río Quema” Formation can be divided into three groups: 1) proximal apron, a sequence dominated by lava flows, interbedded with breccias, mass flows and channel fill, all intruded by basaltic dikes. The rocks represent the nearest materials to the volcanic source, reflecting a coarse sediment supply. This depositional environment is similar to gravel-rich fan deltas and submarine ramps; 2) medial apron, characterized by a volcanosedimentary succession dominated by andesitic lava flows, polymictic volcanic conglomerates and crystal-rich sandstones with minor pelagic sediments and turbidites. These rocks were deposited from high-density turbidity currents and debris flows, directly derived from erupted material and gravitational collapse of an unstable volcanic edifice or volcaniclastic apron; 3) distal apron, a thick succession of sandy to muddy volcaniclastic rocks, interbedded with pelagic limestones and minor andesitic lavas, intruded by dacite domes and by basaltic to andesitic dikes. Bedforms and fossils suggest a quiet, relatively deep-water environment characterized by settling of clay and silt (claystone, siltstone) and by dilute turbidity currents of reworked volcaniclastic detritus. The timing of the initial stages of the volcanic arc has been constrained through a biostratigraphic study, using planktonic foraminifera and radiolarian species. The fossil assemblage indicates that the age of the “Río Quema” Formation ranges from Late Campanian to Maastrichtian, providing a good constraint for the development of the volcanic arc and volcaniclastic apron, during the initial stages of an intra-oceanic subduction zone.