Ashgill greywackes in the Southern Uplands of Scotland: an extension of the Ordovician succession in the Northern Belt

Abstract

ABSTRACTIn the Southern Uplands of Scotland, the youngest greywackes along the SE margin of the Northern Belt are shown to be of Ashgill age. Mudstones interbedded with the dominantly quartzose greywackes of the Shinnel Formation have yielded Dicellograptus anceps, indicating the anceps Biozone. In addition, the newly-defined mafic-rich Glenlee Formation, lying to the SE of the Shinnel Formation in the New Galloway-Moniaive area, has yielded fossils of the pacificus Subzone, the upper subzone of the anceps Biozone. Since the oldest greywackes of the Central Belt, separated from the Northern Belt by the Orlock Bridge Fault, are now confirmed as of basal Silurian acuminatus Biozone age, the stratigraphical break across the Orlock Bridge Fault is greatly reduced, lending support to the ‘single terrane’ model for the Southern Uplands.