Abstract
AbstractHybrid event beds comprising clay‐poor and clay‐rich sandstone are abundant in Maastrichtian‐aged sandstones of the Springar Formation in the north‐west 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.
Highlights
Citing this paper Please note that where the full-text provided on Manchester Research Explorer is the Author Accepted Manuscript or Proof version this may differ from the final Published version
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
The range in depositional character of hybrid event beds is inferred to reflect the complexity of flow transformation in sedimentary systems that are controlled by a complex interplay of allogenic and autogenic controls
Summary
Citation for published version (APA): Kane, I., Southern, S. Interpretation: When compared with the LS penetrated in wells 2 to 5, Well 1 may represent the off-axis or distal setting of a separate, yet more proximal to source, splay off of the main fairway (i.e. coarser grain sizes, relatively low sand to mud ratio and amalgamation ratio, occurrence upstream of the Gjallar Ridge) This is difficult to constrain considering the limited context and core recovery and, subsequently, Well 1 does not form a significant part of the analysis . It is thought that the local rapid deceleration of clay-rich flow promoted increased sediment concentration and reduced fluid turbulence (cf Lowe, 1975; Vrolijk & Southard, 1997), with a subsequent reduction in the flow Reynolds number and onset of more cohesive flow behaviour (Talling et al, 2007; Barker et al, 2008) Such changes may have only occurred in the depositional boundary layer due to settling of sediment into a dense near-bed flow layer. Given the paucity of outcrops where models for flow evolution can be reliably tested it is hoped that the observations here, along with detailed coring studies of the modern sea floor (e.g. Stevenson et al, 2013; Talling et al, 2015), will provide a framework for future physical and numerical modelling studies
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