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 stratigraphical nomenclature in the areas surrounding the Mid North Sea High and onshore, and sparse biostratigraphical data have hindered systematic regional understanding of the timing and controls on stacked source and reservoir-rock intervals. Over 125 well re-interpretations, 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 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 stratigraphical framework.

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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 for the first time and, in so doing, names the Spireslack Sandstone, a distinctive erosively based, sandstone-dominated unit in the Upper Limestone Formation. The Spireslack Sandstone comprises 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 role. The lower channel set appears confined to erosional palaeovalleys of limited lateral extent and significant relief. The upper channel set is much more laterally extensive and displays 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 glacioeustatic scale commonly attributed to Carboniferous fluvio-deltaic cycles. 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 stratigraphical traps.