Delta progradation mechanisms and their stratigraphic record: the Namurian (Carboniferous) Kinderscout Delta, Pennine Basin, UK

The Kinderscout Delta (Hebden Formation, Upper Carboniferous, Pennine Basin, UK) represents a well-exposed example of a river-dominated delta prograding into a relatively unconfined, deepening basin. High-resolution sedimentary logs, palaeoflow measurements, and UAV-derived virtual outcrop models were used to characterize facies, architectural elements and delta front depositional processes. This delta was fed by a major fluvial system, with distributaries 2–10 m deep, and mouth bars that prograded into water depths of at least ∼50 m. Facies and architectural element analyses indicate a continuum of processes from shallow-water, bed-friction-dominated deposition in the landward clinothems to gravity-driven sedimentation on deeper-water foresets. Mass-failure of oversteepened foresets facilitated sediment bypass, contributing sediment directly to the prodelta and, in some cases, steering distributary avulsion. This behaviour resulted in the successive formation and abandonment of mouth bars at quasi-stationary fluvial outlets. This study highlights the interaction between two endmember conceptual models of deltaic deposition: “topset-dominated” autocycles driven by distributary avulsion in shallow, low-gradient settings, and “foreset-dominated” processes driven by gravitational instability on steep foresets in deeper-water shelf environments. Our results demonstrate that delta systems can hybridize, i.e., show downslope continuity between, endmember behaviours during progradation into deepening basins, with autogenic foreset processes and delta-top avulsion operating simultaneously.