Hybrid event beds dominated by transitional‐flow facies: character, distribution and significance in the Maastrichtian Springar Formation, north‐west Vøring Basin, Norwegian Sea

Abstract

Hybrid event beds comprising clay-poor and clay-rich sandstone are abundant in Maastrichtian-aged sandstones of the Springar Formation in the northwest Vøring Basin, Norwegian Sea. This study focuses on an interval, informally referred to as the Lower Sandstone, which has been penetrated in five wells that are distributed along a 140 km downstream transect. Systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings, although individual beds were not correlated. The Lower Sandstone shows an overall reduction in total thickness, bed amalgamation, sand to mud ratio and grain size in distal wells. Turbidites dominated by clay-poor sandstone are at their most common in relatively proximal wells, whereas hybrid event beds are at their most common in distal wells. Hybrid event beds typically comprise a basal clay-poor sandstone (non-stratified or stratified) overlain by banded sandstone, with clay-rich non-stratified sandstone at the bed top. The dominant type of clay-poor sandstone at the base of these beds varies spatially; non-stratified sandstone is thickest and most common proximally, whereas stratified sandstone becomes dominant in distal wells. Stratified and banded sandstone record progressive deposition of the hybrid event bed. Thus, the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer; this layer changed from non-cohesive at the front, through a region of transitional behaviour (fluctuating non-cohesive and cohesive flow), to cohesive behaviour at the rear. Spatial variation in the dominant type of clay-poor sandstone at the bed base suggests that the front of the flow remained non-cohesive, and evolved from high-concentration and turbulence-suppressed to increasingly turbulent flow; this is thought to occur in response to deposition and declining sediment fallout. This research may be applicable to other hybrid event bed prone systems, and emphasizes the dynamic nature of hybrid flows.

Dispersion, Accumulation, and the Ultimate Fate of Microplastics in Deep-Marine Environments: A Review and Future Directions

“…Sedimentary facies broadly evolve from thick high density turbidites at the lobe axis, to thin low density turbidites at the lateral and distal fringes (e.g., Johnson et al, 2001;Hodgson et al, 2006). Transformation of turbidity currents into dense cohesive flows is common in these settings, as the fine cohesive material left on the seafloor is picked up and incorporated into incoming turbidity currents (Haughton et al, 2003;Hodgson, 2009;Talling et al, 2013;Kane et al, 2017;Southern et al, 2017;Spychala et al, 2017;Fildani et al, 2018). The deposits of these flows (hybrid beds) typically have an ungraded muddy-sand division which is rich in organic material; microplastics may be incorporated into these internal divisions and, being in a distal locality are less likely to be eroded by subsequent flows.…”

Transport and deposition of mud in deep‐water environments: Processes and stratigraphic implications

“…The focus, however, has mainly been on sandstones, whereas mudstone packages are usually described as background sedimentation, deposited by pelagic or hemipelagic vertical suspension fallout in low‐energy environments with occasional turbidity currents (e.g. Scholle, ; Wynn et al ., ; Southern et al ., ; Pierce et al ., ). This interpretation is mainly due to the generally poor exposure of mudstones at outcrop that usually precludes observation and interpretation of primary sedimentary structures and bed contacts at macroscopic scale.…”

The stratigraphic record and processes of turbidity current transformation across deep‐marine lobes

“…Martinsen et al ., ; Sullivan et al ., ). In these fine‐grained systems, complicated facies and facies distributions, which diverge significantly from classical turbidite models, are reported from medial and distal lobe settings (Haughton et al ., , ; Sylvester & Lowe, ; Talling et al ., , ; Amy & Talling, ; Ito, ; Barker et al ., ; Davis et al ., ; Hodgson, ; Kane & Pontén, ; Pyles & Jennette, ; Talling, ; Grundvåg et al ., ; Terlaky & Arnott, ; Fonnesu et al ., ; Southern et al ., , ; Spychala et al ., in press). Such beds have been termed ‘hybrid event beds’ by Haughton et al .…”