Lower Old Red Sandstone fluvial dispersal systems in the British Isles

Abstract

ABSTRACTAn evolving pattern of fluvial dispersal responsible for the Lower Old Red Sandstone magnafacies has emerged from a stratigraphical and geographical consideration of palaeocurrent structures, clast lithology and fauna, sandstone composition, and sandstone detrital heavy-mineral assemblages. The evidence suggests that the Post-Ludlow (Downton) and lower Gedinnian rocks formed mainly in the joined Dingle–Shannon and Anglo–Welsh basins, fed from metamorphic complexes in NW Britain or beyond. Contemporaneous sedimentation in the Caledonian basin was restricted to its northeastern end. Later in the Gedinnian, the Dingle–Shannon and Angle–Welsh basins appear to have become separated by the uplift of a broad and extensive belt of mainly Lower Palaeozoic sedimentary and volcanic rocks; included in this belt were outcrops of Post-Ludlow strata representing the earlier stream of metamorphic detritus. Granite intrusion, which reduced the density of and consequently uplifted the crust, occurred widely in the regions dividing and bordering these basins, and may be causally connected with their separation in the Gedinnian. The Caledonian basin appears to have remained a separate feature.