This study documents the character and occurrence of hybrid event beds deposited across a range of deep-water sub-environments in the Cretaceous-Palaeocene Gottero system, north-west Italy. Detailed fieldwork (>5200 m of sedimentary logs) has shown that hybrid event beds are most abundant in the distal confined basin plain domain (>31% of total thickness). In more proximal sectors, HEBs occur within outer-fan and mid-fan lobes (up to 15% of total thickness), whereas they are not observed in the inner-fan channelised area. Six hybrid event bed types (HEB-1 to HEB-6) were differentiated mainly on basis of the texture of their muddier and chaotic central division (H3). The confined basin plain sector is dominated by thick (max 9.57 m; average 2.15 m) and tabular hybrid event beds (HEB-1 to HEB-4). Their H3 division can include very large substrate slabs, evidence of extensive auto-injection and clast break-up, and abundant mudstone clasts set in a sandy matrix (dispersed clay ca 20%). These beds are thought to have been generated by highly This article is protected by copyright. All rights reserved.energetic flows capable of delaminating the sea-floor locally, and carrying large rip-up clasts for relatively short distances before arresting. The unconfined lobes of the mid-fan sector are dominated by thinner (average 0.38 m) hybrid event beds . Their H3 divisions are characterised by floating mudstone clasts and clay-enriched matrices (dispersed clay >25%) with hydraulically-fractionated components (mica, organic matter and clay flocs). These hybrid event beds are thought to have been deposited by less energetic flows that underwent early turbulence damping following incorporation of mud at proximal locations and by segregation during transport. Although there is a tendency to look to external factors to account for hybrid event bed development, systems like the Gottero imply that intrabasinal factors can also be important; specifically the type of substrate available (muddy or sandy) and where and how erosion is achieved across the system producing specific hybrid event bed expressions and facies tracts. (A) INTRODUCTIONBed character and bed stack architecture are two key elements controlling the heterogeneity of deep-water turbidite systems. The former represents the depositional record of sediment gravity flows at a given location with the vertical sequence of grain-size, textures and sedimentary structures recording flow evolution in time and space (Bouma, 1962; Lowe, 1982; Mutti, 1992; Kneller, 1995; Kneller & McCaffrey, 2003). The latter is set by the longer term response of the system to variations in flow volume and concentration over many events modulated by the inherited seafloor topography (Prélat et al., 2010; Brunt et al., 2013b; Marini et al., 2015a). Both define the character and distribution of sedimentary sub-environments in deep-water systems.A wide range of sediment gravity flow deposits have been recognised in turbidite systems; they include the well-known Bouma-type graded sandstones an...

10The outer parts of deep-water fans, and the basin plains into which they pass, are often described as 11 areas where erosion is negligible and turbidite systems have net aggradation. Nevertheless 12 sedimentological and stratigraphic analysis of outer fan lobe and confined basin plain deposits in 13Cretaceous-Paleocene Gottero Sandstone (NW of Italy) has revealed extensive but cryptic bedding-14 parallel substrate-delamination features at the base of many sheet-like event beds. These comprise well layered substrate (e.g. muddy outer fans or confined or ponded basins with thick mudstone 25 caps). Delamination is therefore suggested as an alternative mechanism leading to the formation of 26 hybrid event beds following local substrate entrainment on the basin floor as opposed to on more 27 remote slopes and at channel-lobe transition zones. 28

7Sea-floor topography can constrict, deflect, or reflect turbidity currents resulting in a range of 8 distinctive deposits. Where flows rebound off slopes and a suspension cloud collects in an enclosed 9 basin, ponded or contained turbidites are deposited. Ponded turbidites have been widely recognized 10 in slope mini-basins and on small, structurally confined basin floors in strike-slip and foreland-basin 11 settings. They can have a variable internal structure the significance of which remains poorly 12 understood in terms of flow behavior. New experiments demonstrate that the ponding process can 13 comprise up to four phases: 1) cloud establishment, 2) inflation, 3) steady-state maintenance, and 4) 14 collapse. The experiments explored the behavior of sustained turbidity currents draining into small 15 basins and show that the ponded suspensions that form are characterized by an important internal 16 interface; this divides a lower outbound-moving layer from an upper return layer. The basal layer 17 evolves to constant concentration and grain size, whereas the upper layer is graded (concentration 18 and grain size decrease upward). During the cloud inflation stage, the concentration and velocity 19 profiles of the ponded suspension evolve, and this phase can dominate the resulting deposit. 20Outbound internal waves can travel along the interface between the outbound and return layers and 21 impinge against the confining slope, and their amplitude is highest when the density contrast 22 between layers is greatest, e.g., when the input flows are thin and dense. The experiments show 23 that flow reversals can arise in several ways (initial rebound, episodic collapse of the wedge of fluid 24 above the counter slope, "grounding" of the internal velocity interface) and that despite steady 25 2 input, velocities decay and the deposit grades upwards. Internal waves emanate from the input 26 point, i.e., do not form as reflections off the counter slope. The internal grain-size interface within 27

Hybrid event beds are now recognized as an important component of many deep-sea fan and sheet systems. They are interpreted to record the passage of rheologically complex sediment gravity currents (hybrid flows) that comprise turbulent, transitional, and/or laminar zones. Hitherto, the development of hybrid flow character has mainly been recognized in system fringes and attributed to distal and lateral flow transformations and/or declining turbulence energy expressed over lateral scales of several kilometers or more. However, new field data show that deposition from hybrid flows can occur relatively proximally, where flows meet confining topography. Turbidity currents primed to transform to hybrid flows by up-dip erosion and incorporation of clay may be forced to do so by rapid, slope-induced decelerations within 1 km of the slope. Local flow transformation and deposition of hybrid event-beds offer an alternative explanation for unusual facies developed at the foot of flow-confining seafloor slopes.

Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep sea. Fast-moving, large-volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localized, but important, deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in the design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardizing data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation.