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

Sarah M Newport,Kevin G Taylor,Rhodri M Jerrett,Richard H Worden,Edward Hough

doi:10.1144/jgs2017-036

Sarah M Newport, Kevin G Taylor + Show 3 more

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https://doi.org/10.1144/jgs2017-036

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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.

Highlights

A paucity of studies on mud-rich basin slope successions has resulted in a significant gap in our sedimentological understanding in these settings
By focusing on the sedimentology and the resulting mudstone textures and variability, this paper aims to address the knowledge gap of processes acting on mud-dominated slope successions
(3) Is there a discernible relationship between the type and content of the organic matter of facies and facies associations within a slope succession?. These detailed sedimentological observations have been made on a continuous core (Marl Hill: MHD11; British Geological Survey reference number SD64NE/20), that preserves the transition from carbonate-dominated to clastic-dominated mudstone deposition, within a marginal to basinal mudstone succession, from an active exploration play, the Bowland Shale Formation (Carboniferous, UK)

Summary

Introduction

A paucity of studies on mud-rich basin slope successions has resulted in a significant gap in our sedimentological understanding in these settings. 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. 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. By focusing on the sedimentology and the resulting mudstone textures and variability, this paper aims to address the knowledge gap of processes acting on mud-dominated slope successions. These detailed sedimentological observations have been made on a continuous core (Marl Hill: MHD11; British Geological Survey reference number SD64NE/20), that preserves the transition from carbonate-dominated to clastic-dominated mudstone deposition, within a marginal to basinal mudstone succession, from an active exploration play, the Bowland Shale Formation (Carboniferous, UK). During the Viséan and Namurian stages of the Carboniferous (347 – 318 Ma; Figs 1 and 2), a series of interconnected half-graben basins within the Pennine Province (northern England, UK) formed part of a shallow epicontinental seaway that stretched across the Laurussian continent, with long-lived palaeogeographical barriers to the north (Southern Uplands High) and to the south (Wales– London–Brabant High; Woodcock & Strachan 2002; Davies 2008; Waters et al 2009)

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