Sedimentology and microfacies of a mud-rich slope succession: in the Carboniferous Bowland Basin, NW England (UK)

Abstract

A paucity of studies on mud-rich basin slope successions has resulted in a significant gap in our sedimentological understanding in these settings. Here, macro-and micro-scale analysis of mudstone composition, texture and organic matter was undertaken on a continuous core through a mud-dominated slope succession from the Marl Hill area in the Carboniferous Bowland Basin. Six lithofacies, all dominated by turbidites and debrites, combine into three basin slope facies associations: sediment-starved slope, slope dominated by low-density turbidites and slope dominated by debrites. Variation in slope sedimentation was a function of relative sea-level change, with the sediment-starved slope occurring during maximum flooding of the contemporaneous shelf, and the transition towards a slope dominated by turbidites and then debrites occurring during normal or forced shoreline progradation towards the shelf margin. The sediment-starved slope succession is dominated by Type II kerogen, whereas the slope dominated by low-density turbidites is dominated by Type III kerogen. This study suggests that mud-dominated lower slope settings are largely active depositional sites, with consistent evidence for sediment traction. Additionally, the composition and texture of basin slope mudstones, as well as organic content, vary predictably as a function of shelf processes linked to relative sea-level change.

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

“…Debrites and transitional flow deposits have also been recently recognized in other deep‐water mudstone successions (Konitzer et al ., ; Harazim & McIlroy, ; Newport et al ., ). Therefore, these energetic flows, usually associated with sandy deep‐water systems, may be more common in deep‐water mudstone successions than previously thought.…”

“…turbidity currents, debris flows, transitional flows and mass‐wasting processes) may be responsible for the transport and deposition of mud in deep‐water environments (e.g. Schieber, ; Loucks & Ruppel, ; Trabucho‐Alexandre et al ., ; Konitzer et al ., ; Knapp et al ., ; Ayranci et al ., 2018a; Newport et al ., ). These findings have started to challenge the traditional view that suspension fallout is the dominant depositional process in deep‐water mudstones, with major implications for the estimation of depositional rates and the correct interpretation of times of clastic starvation in deep‐water environments.…”

Can One-Run-Fixed-Arrhenius Kerogen Analysis Provide Comparable Organofacies Results to Detailed Palynological Analysis? A Case Study from a Prospective Mississippian Source Rock Reservoir (Bowland Shale, UK)

“…This paper aims to establish whether organofacies interpretations based on kerogen kinetics derived from the One-Run-Fixed-Arrhenius (ORFA) technique proposed by Waples et al (2002), Waples and Nowaczewski (2013) and Waples (2016) are directly comparable to organofacies interpretations based on palynofacies analysis (Tyson 1995). The study material is a continuous core (Marl Hill: MHD 11; British Geological Survey reference number SD64NE/20) from an active exploration play, the Bowland Shale Formation (Andrews 2013;Clarke et al 2018), which has previously undergone detailed sedimentological analysis (Newport et al 2017). Organofacies interpretations based on both ORFA and palynological analysis were used to (i) describe the dominant organofacies in the Bowland Shale and (ii) identify whether there is a discernible relationship between organofacies and depositional setting (previously described lithofacies and facies associations).…”

“…Previous studies of the MHD 11 core have established six lithofacies, comprising calcareous claystone, calcareous mudstone, argillaceous mudstone, calcareous siltstone, calcareous sandy mudstone and matrix-supported carbonate conglomerate, present in core MHD 11 (Newport et al 2017). Three facies associations were identified: a sediment-starved slope, a slope dominated by turbidites and a slope dominated by debrites.…”

“…Three facies associations were identified: a sediment-starved slope, a slope dominated by turbidites and a slope dominated by debrites. Conditions of sediment starvation on the slope occurred during flooding of the contemporaneous shelf, when shorelines and loci of active clastic and carbonate sedimentation were furthest away from the slope, while the transition toward a slope dominated by turbidites and then debrites occurred during normal or forced shoreline progradation toward the shelf margin (Newport et al 2017). The core was logged for visible textural (grain size) and compositional changes, sedimentary features and fossil content at a 10 cm resolution.…”