Louis Howell, Andrew James Mitten, Stuart Egan, Stuart M Clarke, Graham Leslie

Local low-density basement anomalies are an important part of a rift basin’s inherited structural framework that can influence basin stratigraphy. Large granitic intrusions can cause local alterations in the basement’s density and often spatially correlate with fault-bounded highs (blocks) or convex-shaped regional flexural highs due to their isostatic responses. We investigate the influence of local low-density basement anomalies on the deposition of the fluviodeltaic Fell Sandstone Formation in the northern Pennine rift basin, northern England. The integration of a variety of data sources has enabled regional correlation of the Fell Sandstone Formation with basinal, time-equivalent stratigraphy. Spatial variations in the preserved facies, palaeocurrent and sedimentological characteristics of the Fell Sandstone are documented and the most important controls upon these variations are considered. Along the eastern margin of the granite-cored, flexural Cheviot High, the Fell Sandstone fluvial system is locally confined by the High leading to preservation of ~98% well-sorted sandstone. In the Northumberland-Solway Basin, the Fell Sandstone fluvial system is less confined, leading to sediment dispersal and downstream reduction of net sand. Based on this study, proximity to the dominant clastic sediment source, regional subsidence variations and basin palaeotopography are considered important controls upon spatial variations across the Fell Sandstone Formation. Regional subsidence variations and basin palaeotopography in the northern Pennine Basin are influenced by the Cheviot High and the Maryport-Stublick-Ninety Fathom fault system, which bounds the Northumberland-Solway Basin and the Lake District and Alston Blocks. Both the Cheviot High and the Lake District and Alston Blocks are structures caused by the isostatic responses of local granite-induced low-density basement anomalies. This study shows that flexural highs can act as baffles to fluvial systems, locally confining them and leading to the deposition of high quality reservoir. Fault-bounded highs can act as barriers and their deep bordering half-graben troughs can act as confines for clastic sediment, leading to starvation further down system.