Architectural analysis of a Triassic fluvial system: The Sherwood Sandstone of the East Midlands Shelf, UK

Abstract

The Sherwood Sandstone Group of the northeast UK (East Midlands Shelf) has hitherto never been studied in detail to ascertain it's palaeoenvironment of deposition, largely because it is poorly exposed. As such, this paper aims to provide the first modern sedimentological interpretation of the Sherwood Sandstone in the east of England based on a field outcrop at the disused quarry at Styrrup. This is in stark contrast to the western parts of England where the Sherwood Sandstone is well exposed and offshore in the North Sea Basin where it is represented by a substantial library of core material where it is also relatively well understood.The outcrop at Styrrup Quarry allows contrasts to be made with the style and expression of the Sherwood Sandstone between eastern and western England. Specifically, this highlights differences around the variation in fluvial discharge (between lowstand and highstand) and the absence of aeolian facies types. It is interpreted that these differences relate to discharge variations between ephemeral and perennial systems with a perennial model proposed for Styrrup Quarry. This model draws upon inferences of additional water input from more local areas, likely topographic uplands of the London-Brabant and Pennine Highs which supplement the primary source of the Variscan Mountains in France with additional water and sediment.

Sedimentary flow heterogeneities in the Triassic U.K. Sherwood Sandstone Group: Insights for hydrocarbon exploration

“…The assemblage of lithofacies present in the succession of the Sherwood Sandstone Group demonstrates accumulation under the influence of an arid to semiarid climatic regime, which characterized the Permian and Triassic basins in England and South West Scotland (Figure ) during the Early and Middle Triassic times (Brookfield, , ; Meadows, ; Schmid, Worden, & Fisher, ). Indeed, the absence of fossils, palaeosols, and root traces (rhizocretions) in the fluvial deposits of the Sherwood Sandstone Group of Induan and Olenekian ages in the Carlisle, Vale of Eden, and eastern Irish Sea Basin supports the inference of arid climate conditions (Brookfield, , ; Holliday et al, ; N. S. Jones & Ambrose, ; Wakefield et al, ). Additionally, red beds of fluvial and aeolian affinity have widely been interpreted as indication of aridity in the Triassic deposits of NW Europe (Bourquin, Rigollet, & Bourges, ; Mader, ; Olivarius et al, ; Preto et al, ; Simms & Ruffell, ; Tucker & Benton, ).…”

“…Although detailed mineralogical and isotopic analyses are not available in the eastern England Shelf, palaeocurrent evidence from fluvial strata indicates a northward transport, parallel to the axis of this shelf‐edge basin as for the other Triassic basins (Figure a, b; Edwards, ; Gaunt, ; Gaunt et al, ; Powell et al, ; Smith & Francis, ). Additionally, a northward decrease in both mean grain size and maximum clast size (Allen et al, ; Smith & Francis, ; Wakefield et al, ) in the eastern England Shelf confirms a southern sediment source, which is likely represented by one or a combination of the Armorican or the London Brabant massifs (Figure ). Indeed, quartzitic breccias with clasts of similar size occur both in the southern part of the eastern England Shelf and in the Worcester, Needwood, and Staffordshire basins, where isotopic and mineralogical analyses have confirmed the Armorican Massif as the principal source (Campbell‐Smith, ; Edwards, ; Fitch et al, ; Manger et al, ; Tyrrell et al, ; Warrington et al, ).…”

“…The majority of the accumulated deposits of the “Sherwood Sandstone” have long been ascribed to a mixed aeolian and fluvial origin (Figure , Bachmann et al, ; Holliday et al, ; Mountney & Thompson, ; Newell, , ; Thompson, , ). Such fluvial deposits have been related to braided fluvial systems in the Triassic realm of Great Britain, due to the dominance of accreting barform deposits, characterized by a low spread of foreset cross‐dip azimuths, and the bifurcation of flow around midchannel longitudinal bars (Brookfield, ; Medici, Boulesteix, Mountney, West, & Odling, ; Steel & Thompson, ; Wakefield et al, ).…”

“…Palaeocurrent data (Figure a) from fluvial facies are chiefly derived from cross‐stratification of sand‐prone channel fills (Edwards, ; Gaunt, ; Gaunt, Fletcher, & Wood, ; N. S. Jones & Ambrose, ; Medici et al, ; Powell, Cooper, & Benfield, ; Smith, ; Smith & Francis, ; Steel & Thompson, ; Wakefield et al, ). Palaeocurrents from fluvial channel lithofacies indicate a northward palaeoflow from the southern Wessex Basin via a series of linked basins to the eastern Irish Sea, Vale of Eden, and Carlisle basins in northern regions (Brookfield, ; N. S. Jones & Ambrose, ; McKie & Williams, ; Newell, , ; Smith, ).…”

“…(a) Fluvial and aeolian palaeocurrents (data sources are discussed in the text). (b) Triassic basins in Great Britain (from Wakefield, Hough, & Peatfield, ): Worcester (WKB), Staffordshire (SB), Needwood (NB), eastern England Shelf (EES), Cheshire (CB), Eastern Irish Sea (EISB), Vale of Eden (VEB), and Carlisle (CAB) basins [Colour figure can be viewed at wileyonlinelibrary.com]…”