Abstract The Spireslack surface coal mine exposes a section in the Carboniferous Lawmuir Formation (Brigantian) into the Upper Limestone Formation (Arnsbergian). This paper describes the stratigraphy exposed at Spireslack and, in so doing, names for the first time the Spireslack Sandstone, a distinctive erosively based, sandstone-dominated unit in the Upper Limestone Formation. The Spireslack Sandstone consists of two fluvial sandstone channel sets and an upper, possibly fluvio-estuarine, succession. From an analysis of their internal architectural elements, the channel sets are interpreted as a low-sinuosity, sand-dominated, mixed-load fluvial system in which avulsion and variations in sediment load played a significant part. The lower channel set appears to be confined to erosional palaeovalleys of limited lateral extent and significant relief. The upper channel set is much more laterally extensive and shows evidence of a generally lower sediment load with a greater degree of lateral accretion and flooding. Consequently, the Spireslack Sandstone may represent a system responding to base level changes of higher magnitude and longer duration than the glacio-eustatic scale commonly attributed to Carboniferous fluvio-deltaic cycles. The Spireslack Sandstone may represent an important correlative marker in the Carboniferous of the Midland Valley and may provide an alternative analogue for some Carboniferous fluvial sandstone stratigraphic traps.

Abstract Spatially and temporally variable Tournaisian to Namurian Carboniferous fluvial, fluvio-deltaic, platform carbonate and shale-dominated basin sedimentary successions up to 3.5 km thick are preserved in a complex series of basins from the Outer Moray Firth (Quadrant 14) to the Silverpit Basin (Quadrant 44). Differences in stratigraphic nomenclature in the areas surrounding the Mid North Sea High and onshore, combined with sparse biostratigraphic data, have hindered the systematic regional understanding of the timing and controls on stacked source and reservoir rock intervals. Over 125 well reinterpretations, tied to seismic interpretations, provide evidence of the inception and extent of a delta system. Regional time slices highlight a long-lived laterally equivalent basinal, mud-rich succession across Quadrants 41–44. They also show that the area from the Outer Moray Firth to the Silverpit Basin was part of the same sedimentary system up to at least Namurian times. All of this is placed within a simplified stratigraphic framework. Supplementary material: Appendix A in the Supplementary Material contains the stratigraphic intervals interpreted on each well and highlights which intervals have biostratigraphic control. Supplemental Figures 1 and 2 are larger scale versions of Figures 6 – 8 . The Supplementary Material is available at https://doi.org/10.6084/m9.figshare.c.4087046