Bypassing sediment gravity flows play an important role in turbidite systems because they produce sole structures unconnected with the depositional processes of the casting bed. However, their role in facilitating seafloor colonization is underappreciated. The Aberystwyth Grits–Borth Mudstone turbidite system (Silurian, Welsh Basin) contains a famous ichnoassemblage with common graphoglyptids. This is interpreted to record colonization following erosion of surficial fluidal muds by flows that exposed firmer substrates. The burrows are developed at this level and formed beneath a thin, post-depositional mud blanket. They frequently cross-cut fluted surfaces indicating that basal turbidite bedding surfaces can record at least two, or more, bypassing flow events. Thus, even on a basin floor with thick mudstone deposition, the number of flow events will be under-represented. This Silurian turbidite system also illustrates that substrate conditions, not oxygenation, controlled trace fossil occurrence. Other than the burrows on turbidite soles, the remainder of the succession consists of thinly bedded and laminated strata typical of anoxic deposition but diverse geochemical proxies (e.g. iron speciation, trace metals) indicate full seabed oxygenation. The absence of macrofaunal bioturbation is attributed to a soft fluidal substrate in which only small-scale (meiofaunal) bioturbation is seen.

Flow-induced interfacial deformation structures (FIDS) are both diverse and common in turbidite successions where they form in soft, cohesive substrates beneath sediment gravity flows, but their significance has only recently been recognized. Their range of forms encompasses most of the morphological types attributed to microbially induced sedimentary structures (MISS) and the two have probably been widely conflated. Variants of FIDS include longitudinal ridges and furrows, polygonal networks and mamillated forms that are identical to structures assigned to MISS. A distinctive MISS form with flat-topped ridges and furrows called ‘Kinneyia’ is also found within the FIDS spectrum. Some FIDS may have also been assigned to Ediacaran taxa, notably the controversial Arumberia . Distinguishing FIDS from MISS in hand specimen is difficult, but their environmental context is important. Intertidal MISS occurrences are unlikely to be FIDS because the sediment gravity flows that produce deformation of the substrate are unlikely in such settings. However, MISS (mis)reported from turbidite settings are likely to be FIDS. One of the few distinctions between MISS and FIDS occurs when textured surfaces are developed on the upper surfaces of sandstone beds and they are overlain by fine-grained sediments; in this case a microbial origin is likely.

Abstract Striated grooves in tool marks are common at the base of sandstones, especially in deep‐marine successions, but their use in physical‐process and environmental reconstruction is underdeveloped. To fill this gap in knowledge, striations in the central groove of chevron marks and in chevron‐less groove marks were formed in the laboratory by dragging tools armoured with silt, sand or gravel across muddy substrates. These experiments simulated the formation of striated grooves by armoured mud clasts carried at the base of quasi‐laminar and fully laminar debris flows, aiming to: (1) delineate the bed shear strengths for the formation of striated grooves at different armour sediment sizes; (2) examine how the preservation potential of striated grooves depends on clay bed rheology and size of armour sediment and (3) discuss how the pre‐lithification clay bed consolidation state and size of armour sediment can be reconstructed from striated grooves in the geological record. The experimental results revealed that tools with small‐diameter silt and sand armours dragged along soft beds lack striations or, at best, leave poorly defined striations, whereas firm beds and gravel armours exhibit well‐defined striations. The spacing of striations formed by gravel clasts corresponds well with the clast diameter, implying that striation spacing is a good proxy for the diameter of armoured gravel under natural conditions. In contrast, the spacing of striae formed by sand armours is greater than the grain diameter, suggesting that the spacing of fine striations can only be used to predict a maximum armour sand size. A comparison of different processes of formation of armoured mud clasts demonstrated that the armouring of mud clasts most probably happens after incorporation of the clasts by erosion into the head of the debris flow and subsequent movement across a loose sandy or gravelly bed surface.

Alongside turbidites and debrites, hybrid event beds are now recognized as a common occurrence in deep-marine environments. Yet, many variations in the standard H1–H5 facies model of Haughton et al. (2009, Marine and Petroleum Geology, v. 26, p. 1900–1918) have been described since its introduction, with the role of transient-turbulent flows, i.e., flows that are transitional between fully turbulent turbidity currents and fully laminar debris flows, being particularly enigmatic. Based on a comprehensive dataset collected from the lobe fringe and distal fringe of a submarine fan (Silurian Aberystwyth Grits Group and Borth Mudstone Formation, West Wales, United Kingdom), transitional-flow signatures were integrated into the standard hybrid-event-bed model. These signatures include muddy sandstones and sandy mudstones with large ripples (formed by turbulence-enhanced transitional flows), low-amplitude bed waves and heterolithic lamination (formed by turbulence-attenuated transitional flows), and banding (formed by turbulence-enhanced to turbulence-attenuated transitional flows). The field data reveal that: (a) H1 divisions are generated by turbulent flows that form not only massive, structureless facies but also plane-parallel-laminated and ripple-cross-laminated facies; (b) H2 divisions are formed by transitional flows that form banded facies, but also facies with large ripples and low-amplitude bed waves, as well as heterolithic facies; (c) H3 divisions are formed by laminar debris flows of varied rheology; (d) H4 divisions can form from both tractional turbulent and transitional flows; and (e) H5 divisions can be hemipelagic, deposited from the dilute tail of the flow or originate from cohesive freezing of a late-stage muddy debris flow. Based on embedded Markov-chain analysis, the vertical stacking of facies in the five principal hybrid-event-bed divisions suggests a transformation from turbidity current via transitional flow to debris flow (H1 to H3), followed by a repetition of this transformation in the H4 and H5 divisions, but in overall finer-grained sediment. In addition to this complete extended facies model for hybrid event beds, three incomplete bed types could be defined: turbulent-flow-prone, transitional-flow-prone with an H3 division, and transitional-flow-prone without an H3 division. The sedimentary successions in the study area reveal a basinward change from predominantly turbidites and turbulent-flow-prone hybrid event beds via a mixture of turbulent-flow and transitional-flow signatures in hybrid events beds to H3 missing hybrid event beds with transitional-flow and muddy-debrite signatures. Hence, sediment gravity flows became increasingly muddy and cohesive from lobe fringe to lobe distal fringe.

The geometrical characteristics of subaqueous dunes may exert a strong control on hydraulic roughness. Conventionally, the prediction of dune existence and geometry relies on phase diagrams and empirical equations tailored for uniform, cohesionless sediments. However, in deltas, estuaries, and lowland rivers, mixtures of sand, silt, and clay are prevalent, which hamper dune prediction. We study the impact of fine sand-silt mixtures on the geometry of dunes. We built a sediment recirculation facility in the Water and Sediment Laboratory at Wageningen University, capable of recirculating mixtures of sediment. The system is composed of a 15-m long tilting flume and a low reservoir where sediment is kept in suspension using a caterpillar system, from where sediment is pumped back into the flume. We systematically varied the sand and silt content for different flow rates. We measured flow velocities profiles with an acoustic Doppler velocimeter (UB-Lab 2C by Ubertone), and captured the bed geometry using a line laser scanner. The mobility of the bed is clearly influenced by the bimodal characteristics and the level of cohesion. When non-cohesive fine sand or coarse silt were introduced to medium-sand base material, we infer that the hiding-exposure effect amplified the mobility of the coarser material. This resulted in increased dune lengths, affecting dune steepness. Conversely, the addition of weakly cohesive fine silt reduced sediment mobility and suppressed dune length. As a consequence, sediment composition has an indirect influence on hydraulic roughness, which was significantly related to leeside angle. During the high flow rates, our results suggest flickering between alternative stable river bed states.

The early Silurian Llandovery–Wenlock boundary interval is marked by significant marine perturbations and biotic turnover, culminating in the Ireviken Extinction Event and the Early Sheinwoodian Carbon Isotope Excursion. Here, we apply multiple independent redox proxies to the early Wenlock Buttington section, which was deposited in a mid-shelf location in the Welsh Basin, UK. To account for the regional geochemical variability in marine sediments due to factors such as sediment provenance, we first define oxic baseline values for the Welsh Basin, utilizing deeper water, well-oxygenated intervals of late Llandovery age. Our approach documents unstable, oscillating redox conditions on the mid-shelf at Buttington. We suggest that these dynamic redox fluctuations are likely to relate to changes in the position of the chemocline or a migrating oxygen minimum zone. Benthic biota, such as trilobites, brachiopods, bivalves and gastropods, appear to have been relatively unaffected by fluctuating oxic-ferruginous conditions, but were more severely impacted by the development of euxinia, highlighting the inhibiting role of toxic sulfides. By contrast, the redox perturbations appear to have placed extreme stress on graptolites, causing many extinction losses regardless of the specific development of euxinia. Supplementary material: The geochemical data for the Buttington section is available at https://doi.org/10.6084/m9.figshare.c.7165009 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system

ABSTRACT Sole structures on the base of turbidites, and other bed types, are typically classified into scour marks and tool marks, such as flutes, grooves, skim marks and prod marks. Yet, there are a range of other common sole marks that are unrelated to scouring or tools, and whose origin is poorly understood. Prominent among these sole structures are longitudinal ridges and furrows, and ‘dinosaur leather’ structures associated with mud ripples. Herein, these features are described and it is argued that they are the product of deformation of the substrate during a sediment gravity flow event. In these flow‐induced interfacial deformation structures (FIDS), a soft cohesive substrate undergoes deformation in response to a buoyant force induced by the denser basal component of an overriding flow, and the flow interacts with this buoyant deformation through shear to remould the substrate. Variations in the relative strength of these buoyant and shear‐induced forces explain the wide range of FIDS that can form. This FIDS model reinterprets the formation of longitudinal ridges and furrows, which have previously been classified as scour marks, and explains their distinctive spatial patterns. Furthermore, the new model builds on the seminal work of Dżułyński and colleagues in the 1960s and 1970s, who identified that these structures contain key palaeocurrent information, and it is argued that such information is largely under‐utilized. Importantly, alongside their utility as palaeocurrent indicators, FIDS provide insights into the rheology of the substrate at the time of their formation, and thus the nature of basal flow conditions in the formative flows.

AbstractCoral reefs are hard calcified structures, mainly found in warm tropical water. These ecosystems serve important roles as, for example, a source of food, shelter and nursery for different organisms, and in coastal protection. Reef‐building organisms have evolved to inhabit a narrow ecological niche and thus are particularly susceptible to rapid changes in their environment, for example, under predicted climate‐change scenarios. Anthropogenic climate change is widely accepted as the leading cause of rising ocean temperatures, sea water acidity and sedimentation rate, which all affect a coral's productivity, health and, to some extent, skeletal strength. High‐energy weather events, such as storms and hurricanes, can erode reefs, thereby increasing the amount of suspended sediment and consequently the turbidity of the water. The removal of suspended sediment from the reef is vital for the health of reef producers, and a natural process that removes suspended sediment from reefs are sediment gravity flows. A key factor that controls the ability of sediment gravity flows to transport sediment is cohesion, as cohesion determines the run‐out distance of a flow through changes in its rheological properties. This study examines the cohesive nature of sediment gravity flows laden with fine‐grained CaCO3. These gravity flows laden with mud‐grade calcite are compared with flows carrying non‐cohesive, silt‐sized, silica flour, weakly cohesive kaolinite clay and strongly cohesive bentonite clay, by means of laboratory experiments. The results of these experiments show that the mud‐grade calcite flows behave more akin to the silica‐flour flows by reaching maximum mobility at considerably higher volumetric suspended sediment concentrations (47% for silica flour and 53% for CaCO3) than the kaolinite and bentonite flows (22% for kaolinite and 16% for bentonite). Fine CaCO3 gravity flows can therefore be regarded as physically non‐cohesive, and their high mobility may constitute an effective mechanism for removing suspended sediment from coral reefs, especially at locations where a slope gradient is present, such as at the reef front and forereef. However, biological cohesion, caused by ‘sticky’ extracellular polymer substances produced by micro‐organisms, can render mud‐grade calcite cohesive and sediment gravity flows less mobile. The present study should therefore be seen as a first step towards a more comprehensive analysis of the efficiency of removal of suspended sediment from coral reefs.

Understanding of the formative conditions of many sole structures is limited, with chevron marks and striated groove marks being particularly enigmatic. These sedimentary structures are examined here through laboratory modelling. An idealized tool, resembling an armoured mud clast, was dragged through substrates of kaolinite–seawater mixtures of different yield strengths while submerged in seawater. The experiments suggest that armoured mud clasts are the likely tools producing fine striae in striated grooves and, given the common occurrence of striated groove marks in outcrops, that these clasts are more prevalent in deep‐marine settings than previously thought. Chevron marks were observed to form over a narrow range of substrate yield stresses, likely explaining their relative rarity. Furthermore, their form is shown to be a function of substrate rheology, with chevron angle relative to the movement direction of the tool being less in weaker substrates. Moreover, the size of cut chevron marks, characterized by a narrow central cut, bears no relationship to the size of the incising tool, but rather reflects a substrate with a low yield stress that is sufficiently mobile to close behind the tool. In contrast, interrupted chevron marks, characterized by a distinct central groove, reflect greater substrate strength. Striated grooves without chevrons formed at the highest yield stresses simulated in the experiments. The relationship between tool mark type and yield stress, in combination with changes in chevron angle, enables these sole structures to be utilized as indicators of palaeosubstrate rheology. The conditions required to preserve such features include a prolonged period of bed consolidation, flow bypass and lack of bioturbation. Given changes in seafloor communities and bioturbation over time and their impact on substrate rheology, particularly during the early Palaeozoic, the present work supports the idea that the frequency of these sole structures likely changed over geological time.

Wave–current ripples that develop on seabeds of mixed non-cohesive sand and cohesive clay are commonplace in coastal and estuarine environments. While laboratory research on ripples forming in these types of mixed-bed environments is relatively limited, it has identified deep cleaning, the removal of clay below the ripple troughs, as an important factor controlling ripple development. New large-scale flume experiments seek to address this sparsity in data by considering two wave–current conditions with initial clay content, C0, ranging from 0 % to 18.3 %. The experiments record ripple development and pre- and post-experiment bed clay contents to quantify clay winnowing. The present experiments are combined with previous wave-only, wave–current, and current-only experiments to produce a consistent picture of larger and smaller flatter ripples over a range of wave–current conditions and C0. Specifically, the results reveal a sudden decrease in the ripple steepness for C0 > 10.6 %, likely associated with a decrease in hydraulic conductivity of 3 orders of magnitude. Accompanying the sudden change in steepness is a gradual linear decrease in wavelength with C0 for C0 > 7.4 %. Ultimately, for the highest values of C0, the bed remains flat, but clay winnowing still takes place, albeit at a rate 2 orders of magnitude lower than for rippled beds. For a given flow, the initiation time, when ripples first appear on a flat bed, increases with increasing C0. This, together with the fact that the bed remains flat for the highest values of C0, demonstrates that the threshold of motion increases with C0. The inferred threshold enhancement, and the occurrence of large and small ripples, is used to construct a new three-dimensional phase diagram of bed characteristics involving the wave and current Shields parameters and C0, which has important implications for morphodynamic modelling.

Wave ripples can provide valuable information on their formative hydrodynamic conditions in past subaqueous environments by inverting dimension predictors. However, these inversions do not usually take the mixed non-cohesive/cohesive nature of sediment beds into account. Recent experiments involving sand–kaolinite mixtures have demonstrated that wave-ripple dimensions and the threshold of motion are affected by bed clay content. Here, a clean-sand method to determine wave climate from orbital ripple wavelength has been adapted to include the effect of clay and a consistent shear-stress threshold parameterisation. From present-day examples with known wave conditions, the results show that the largest clay effect occurs for coarse sand with median grain diameters over 0.45 mm. For a 7.4% volumetric clay concentration, the range of possible water-surface wavelengths and water depths can be reduced significantly, by factors of three and four compared to clean sand, indicating that neglecting clay when present will underestimate the wave climate.

Cohesive sediment particles are ubiquitous in environmental flows. The cohesive properties of clay promote the formation of clay flocs and gels and relatively small suspended clay concentrations can enhance or suppress turbulence in a flow. Furthermore, flows are naturally non‐uniform, varying in space and time, yet the dynamics of non‐uniform open‐channel clay suspension flows is poorly understood. For the first time, the adaptation time and length scales of non‐uniform clay suspension flows were quantified using novel experiments with spatially varying but temporally uniform flow. Different levels of turbulence enhancement and attenuation were identified as the flow decelerates or accelerates. Results highlight that decelerating clay suspension flows crucially have a longer adaptation time than accelerating clay suspension flows. This is explained by the longer timescale required for the formation of bonds between cohesive particles in turbulence attenuated flows after deceleration than the rapid breakdown of bonds in turbulent flows after acceleration of clay suspension flows. This hysteresis is more pronounced for higher concentration decelerating flows that pass through a larger variety of clay flow types of turbulence enhancement and attenuation. These different adaptation time scales and associated clay flow type transitions are likely to affect clay flow dynamics in a variety of fluvial and submarine settings.

ABSTRACT Sediment gravity flows exhibit a large range of flow behaviours, making their flow dynamics hard to predict and the resulting deposits a challenge to interpret. Cohesive sediment gravity flows containing clay are particularly complex, as their behaviour is controlled by the balance of turbulent and cohesive forces. A first set of laboratory lock‐exchange experiments investigated the effect of adding 25% very fine sand by volume to high‐density cohesive sediment gravity flows with strongly suppressed turbulence. This caused these mixed clay–sand flows to become more cohesive, have shorter runout distances, and have lower head velocities than the original pure‐clay flows, despite the increase in density difference and the non‐cohesive properties of the sand. Yield stress measurements confirmed that adding the non‐cohesive very fine sand increases the cohesive strength of dense clay suspensions. This higher cohesive strength outcompetes the enhanced density difference and reduces the flow mobility. A second set of experiments across a larger range of clay concentrations showed that, for low‐density cohesive sediment gravity flows dominated by turbulent mixing, the addition of 25% very fine sand increased the head velocities because of the enhanced density difference and weak cohesive forces. Thus, the addition of very fine sand may increase or decrease the mobility of cohesive sediment gravity flows, depending on the initial type of flow and the balance between turbulent and cohesive forces. In the natural environment, this study proposes that very fine sand can only increase the cohesive strength and reduce the flow mobility of cohesive sediment gravity flows that have a sufficiently strong matrix strength to fully support the sand particles. The contribution of very fine sand to the cohesive strength of high‐density cohesive sediment gravity flows may have important implications for flow transformation on submarine fans, especially in distal regions where transient–turbulent, cohesive flows are particularly common.

Sediments composed of mixed cohesive clay and non-cohesive sand are widespread in a range of aquatic environments. The dynamics of ripples in mixed sand–clay substrates have been studied under pure current and pure wave conditions. However, the effect of cohesive clay on ripple development under combined currents and waves has not been examined, even though combined flows are common in estuaries, particularly during storms. Based on a series of large flume experiments, we identified robust inverse relationships between initial bed clay content, C0, and wave–current ripple growth rates. The experimental results also revealed two distinct types of equilibrium combined–flow ripples on mixed sand–clay beds: (a) large asymmetrical ripples with dimensions and plan geometries comparable to clean-sand counterparts for C0 ≤ 10.6%; and (b) small, flat ripples for C0 > 11%. The increase in bed cohesion contributed to this discontinuity, expressed most clearly in a sharp reduction in equilibrium ripple height, and thus a significant reduction in bed roughness, which implies that the performance of existing ripple predictors can be improved by the incorporation of this physical cohesive effect. For C0 ≤ 10.6%, strong clay winnowing efficiency under combined flows resulted in the formation of equilibrium clean-sand ripples and clay loss at depths far below the ripple base. In natural environments, this ‘deep cleaning’ of bed clay may cause a concurrent sudden release of a large amount of pollutants during storms, leading to a sudden reduction in post-storm resistance to erosion of mixed sand–clay substrates.

Mixtures of cohesive clay and noncohesive sand are widespread in many aquatic environments. Ripple dynamics in sand-clay mixtures have been studied under current-alone and wave-alone conditions but not combined wave-current conditions, despite their prevalence in estuaries and the coastal zone. The present flume experiments examine the effect of initial clay content, C 0, on ripples by considering a single wave-current condition and, for the first time, quantify how changing clay content of substrate impacts ripple dimensions during development. The results show inverse relationships between C 0 and ripple growth rates and clay winnowing transport rates out of the bed, which reduce as the ripples develop toward equilibrium. For C 0 ≤ 10.6%, higher winnowing rates lead to clay loss, and thus the presence of clean sand, far below the base of equilibrium ripples. This hitherto unquantified "deep-cleaning" of clay does not occur for C 0 > 10.6%, where clay-loss rates are much lower. The clay-loss behavior is associated with two distinct types of equilibrium combined flow ripples: (a) Large asymmetric ripples with dimensions and plan geometries comparable to their clean-sand counterparts for C 0 ≤ 10.6% and (b) small, flat ripples for C 0 > 10.6%. The 10.6% threshold, which may be specific to the experimental conditions, corresponds to a more general 8% threshold found beneath the ripple base, suggesting that clay content here must be <8% for clean-sand-like ripples to develop in sand-clay beds. This ripple-type discontinuity comprises a threefold reduction in ripple height, with notable implications for bed roughness.

Lock-exchange experiments were carried out to investigate the effect of biologically cohesive extracellular polymeric substances (EPS) on the mobility of sediment gravity flows laden with physically cohesive clay, non-cohesive coarse silt and non-cohesive fine sand. The results reveal significant differences in the head velocity, run-out distance and deposit shape of these flows related to differences in physical cohesion, particle size, and EPS content. These differences are captured in a three-way coupling model of turbulent forces, cohesive forces, and particle settling velocity. In general, biological cohesion reduces flow mobility, demonstrated most clearly by a progressive decrease in the run-out distance of the silt and clay flows, as the EPS concentration is increased. This reduction in flow mobility is caused by the dominance of cohesive forces over turbulent forces, which comprise turbulence attenuation and the bulk settling of a biologically cohesive gel in which EPS form a pervasive network of bonds between the sediment particles. However, sand-laden gravity flows were found to behave in a markedly different way, in that the head velocity and run-out distance first increase and then decrease, as the EPS concentration is increased. The increase in sand flow mobility is inferred to be caused by a reduction in the settling velocity of the sand particles, as the EPS cause an increase in flow viscosity at EPS concentrations that are sufficiently low to maintain turbulent flow. Once the EPS concentration is high enough for turbulence attenuation, the sand flows start to agree with the silt and clay flows in establishing a negative correlation between flow mobility and EPS concentration caused by gelling. The experimental data also uncovered that deposits formed by EPS-rich, turbulence-attenuated flows are shorter and thicker and have more abrupt terminations than deposits formed by EPS-free or EPS-poor turbulent flows. The larger thickness of these deposits is partly caused by the ability of EPS to retain water and form matrix-supported textures. Earlier work has shown that EPS is common in many sedimentary environments, including those where sediment transport takes place regularly by particulate density currents. Combined with the increasing rate at which man-made structures, such as pylons and communication cables, appear in these environments, we argue that there is a need to incorporate the results of this study in applied models that aim to mitigate damage to such structures by sediment gravity flows.

A revision of the popular equation of Richardson and Zaki (1954a, Transactions of the Institute of Chemical Engineering, 32, 35–53) for the hindered settling of suspensions of non‐cohesive particles in fluids is proposed, based on 548 data sets from a broad range of scientific disciplines. The new hindered settling equation enables predictions of settling velocity for a wide range of particle sizes and densities, and liquid densities and viscosities, but with a focus on sediment particles in water. The analysis of the relationship between hindered settling velocity and particle size presented here shows that the hindered settling effect increases as the particle size decreases, for example, a 50% reduction in settling velocity is reached for 0.025 mm silt and 4 mm pebbles at particle concentrations of 13% and 25% respectively. Moreover, hindered settling starts to influence the settling behaviour of sediment particles at volumetric concentrations of merely a few per cent. For example, the particle settling velocity in flows that carry 5% silt is reduced by at least 22%. These observations suggest that hindered settling greatly increases the efficiency of natural flows to transport sediment particles, but also particulate carbon and pollutants, such as plastics, over large distances.

ABSTRACTDeposits of sediment gravity flows in the Aberystwyth Grits Group (Silurian, west Wales, United Kingdom) display evidence that sole marks are suitable for reconstructing depositional processes and environments in deep-marine sedimentary successions. Based on drone imagery, 3D laser scanning, high-resolution sedimentary logging, and detailed descriptions of sole marks, an outcrop 1600 m long between the villages of Aberarth and Llannon was subdivided into seven lithological units, representing: a) mudstone-poor, coarse-grained and thick-bedded submarine channel fills, dominated by the deposits of erosive high-density turbidity currents with flute marks; b) mudstone-rich levee deposits with thin-bedded, fine-grained sandstones formed by low-density turbidity currents that scoured the bed to form flute marks; c) channel–lobe transition-zone deposits, dominated by thick beds, formed by weakly erosive, coarse-grained hybrid events, with pronounced mudstone-rich or sandstone-dominated debritic divisions and groove marks below basal turbiditic divisions, and with subordinate amounts of turbidites and debris-flow deposits; d) tabular, medium- to thick-bedded turbiditic sandstones with flute marks and mixed sandstone–mudstone hybrid event beds mainly with groove marks, interpreted as submarine lobe-axis (or off-axis) deposits; and e) tabular, thin- to medium-bedded, fine-grained, mainly turbiditic sandstones mostly with flute marks, formed in a lobe-fringe environment. Both lobe environments also comprised turbidites with low-amplitude bed waves and large ripples, which are interpreted to represent transient-turbulent flows. The strong relationship between flute marks and turbidites agrees with earlier predictions that turbulent shear flows are essential for the formation of flute marks. Moreover, the observation as part of this study that debris-flow deposits are exclusively associated with groove marks signifies that clay-charged, laminar flows are carriers for tools that are in continuous contact with the bed. A new process model for hybrid event beds, informed by the dominance of tool marks, in particular grooves, below the basal sand division (H1 division of Haughton et al. 2009) and by the rapid change from turbidites in the channel to hybrid event beds in the channel–lobe transition zone, is proposed. This model incorporates profound erosion of clay in the channel by the head of a high-density turbidity current and subsequent transformation of the head into a debris flow following rapid lateral flow expansion at the mouth of the channel. This debris flow forms the groove marks below the H1 division in hybrid event beds. A temporal increase in cohesivity in the body of the hybrid event is used to explain the generation of the H1, H2, and H3 divisions (sensuHaughton et al. 2009) on top of the groove surfaces, involving a combination of longitudinal segregation of bedload and vertical segregation of suspension load. This study thus demonstrates that sole marks can be an integral part of sedimentological studies at different scales, well beyond their traditional use as indicators of paleoflow direction or orientation.