The sedimentology, architecture and depositional setting of the fluvial Spireslack 1 Sandstone of the Midland Valley, Scotland: insights from Spireslack surface coal mine.

Abstract

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.