Interpreting complex fluvial channel and barform architecture: Carboniferous Central Pennine Province, northern England.

The Bashkirian Lower Brimham Grit of North Yorkshire, England, is a fluvio-deltaic sandstone succession that crops out as a series of tors and pinnacles, the three-dimensional arrangement of which allows high-resolution architectural analysis of genetically related lithofacies assemblages. Detailed lithofacies, architectural and palaeocurrent data have been collated from 34 locations comprising 88 individual outcrops spread over ~280 km2. The field-derived dataset comprises 34 location catalogue tables, 34 annotated outcrop images (showing graphic logs, architectural panels and related data), 16 annotated lithofacies descriptions and examples, 34 metrics plots that provide details of 427 individual sub-facies sets/cosets, and graphic logs encompassing facies successions that collectively describe 304 m of exposed outcrop. Metrics relating to sets/cosets include characterisation of 1,558 individual set components, 1,444 foreset palaeocurrent readings and 698 bounding surface palaeocurrent readings for a range of lithofacies types. Collectively, these data are used in facies and architectural-element analysis to describe, interpret and reconstruct the morphology, sedimentology and environment of deposition of the palaeo-river system represented by the preserved succession, including estimations of individual dune and cumulative dune/bar heights, and related channel depths. Detailed analysis has enabled three-dimensional geometrical relationships to be established for a suite of architectural elements so as to develop a comprehensive depositional model. Fluvial channel-fill elements bounded by erosional surfaces are characterised internally by a hierarchy of sets and cosets with varying compositions, textures and structures. Simple, cross-bedded sets represent in-channel migration of isolated mesoforms (dunes); cumulative cosets of both trough and planar-tabular cross-bedded facies represent both downstream-accreting and lateral-accreting macroforms (bars) characterised by highly variable, yet predictable, patterns of palaeocurrent indicators. Relationships between sandstone-dominated strata bounded by third-order and fifth-order surfaces, which represent in-channel bar deposits and incised channel bases, respectively, chronicle the origin of the preserved succession in response to autocyclic barform development and abandonment. Major episodes of fluvial incision were likely influenced by episodic tectonic subsidence and differential tilting associated with slip on the nearby North Craven Fault system. Overall, the succession represents the preserved product of an upper-delta plain that was traversed by a migratory fluvial braid-belt system comprising a poorly-confined network of transient fluvial channels developed between major sandy barforms that evolved via a combination of mainly downstream-accretion and subordinate lateral-accretion. This study demonstrates how detailed field-based research methods have been used to collate a sedimentological dataset at a level of detail that has rarely attempted previously. Results indicate that the Lower Brimham Grit was dominated by facies associations relating to downstream-accretion within an broad upper-delta plain succession consisting of an active multi-channel braided fluvial system dominated by medium- large-scale bed- and barforms which migrated within large channels, many >6.0 m deep. These novel results have advanced the state of the science more generally by showing how small-scale facies observations can be used to determine the geometry and make-up larger-scale architectural elements, which themselves represent various sub-environments within a major sedimentary system.