LITHOSTRATIGRAPHY OF THE ORDOVICIAN ROCKS IN THE SOUTHERN UPLANDS - CRAWFORD GROUP, MOFFAT SHALE GROUP, LEADHILLS SUPERGROUP

A formal lithostratigraphy is erected for all the Ordovician rocks in the Southern Uplands of Scotland. At the base of the succession, the C rawford Group (Arenig-Llanvirn) encompasses the chert and lava sequenc es usually associated with the tract-bounding faults, and includes the only proven Arenig rocks in the Southern Uplands. The overlying Moffa t Shale Group (Caradoc-Llandovery) is now restricted to the black and grey graptolitic shales which succeed the grey and red chert successio ns. The Leadhills Supergroup (Caradoc-Ashgill) forms the overwhelming bulk of the sedimentary succession and includes the thick Ordovician t urbidite successions of the Northern Belt. Existing stratigraphical te rminology 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.