‘Block and basin’ style rift basins: sedimentological insights from the Mississippian Fell Sandstone Formation

The block and basin tectono-stratigraphic framework for the northern Pennine (rift) Basin, within which buoyant granite intrusions core intra-basin fault-bound blocks, has long held traction. However, many of the elements of this framework are rooted in primitive tectonic models and, perhaps unsurprisingly, corresponding depositional models often reflect this. Using sedimentological and sedimentary provenance approaches, the syn-rift (Mississippian) fluvio-deltaic Fell Sandstone Formation and age-equivalent strata within the northern Pennine Basin are examined. Highlighted divergences from classically depicted models relate to occurrences of pre-Carboniferous basement domes or monoclines, which are unbound by major vertically displacing (>100 m) fault systems. Such structures in the northern Pennine Basin are all granite-cored and their origins are associated with their buoyancy and flexural isostatic processes. One such basement dome, the Cheviot Block, confined and deflected the Fell Sandstone fluvio-deltaic system from the west, causing locally elevated net sand content and variations in dominant palaeodrainage direction. Central parts of the Alston Block, which forms a regional monocline along an E-W axis, were comparatively uplifted because of flexural isostatic responses to granite intrusions. The findings presented are not just at variance with classically depicted depositional models for the region, but also with more general depictions of dominantly normal fault-driven rift basin systems.Supplementary material: [table of data locations with derivation, trace element data, and major element (oxide) data] is available at https://doi.org/10.6084/m9.figshare.c.5733257