Lithostratigraphy of the Ordovician rocks in the Southern Uplands: Crawford Group, Moffat Shale Group, Leadhills Supergroup

Abstract

AbstractA formal lithostratigraphy is erected for all the Ordovician rocks in the Southern Uplands of Scotland. At the base of the succession, the Crawford Group (Arenig–Llanvirn) encompasses the chert and lava sequences usually associated with the tract-bounding faults, and includes the only proven Arenig rocks in the Southern Uplands. The overlying Moffat Shale Group (Caradoc–Llandovery) is now restricted to the black and grey graptolitic shales which succeed the grey and red chert successions. The Leadhills Supergroup (Caradoc–Ashgill) forms the overwhelming bulk of the sedimentary succession and includes the thick Ordovician turbidite successions of the Northern Belt. Existing stratigraphical terminology is reviewed, revised or extended as appropriate to maintain maximum continuity with current usage. Type sections for each unit are either proposed, where newly defined or revised, or cited in the case of existing definitions.