Keele Research Repository

The Anglesey Dinantian succession records the establishment and growth of a land-attached carbonate platform. Onlap of underlying basement terrain and marginal terrigenoclastic accumulations is readily demonstrated. Carbonate deposition however was repeatedly
interrupted, palaeokarstic surfaces recording the periodic lowering of sea level and the emergence of extensive areas of the limestone shelf. The sequence is constructed therefore of numerous transgressive/regressive minor cycles. These have been grouped together into five broader, lithostratigraphically based formations.
During periods of raised sea level active carbonate production was achieved in a mosaic of fades of variable but not pronounced water depth. During periods of marine regression and emergence the carbonate platform was subject to the effects of subaerial weathering. Wind-blown volcanic ash accumulated on the exposed limestone surfaces and was colonised and stabilised by vegetation. Complex pedogenic alteration effects were promoted in the underlying carbonate sediment whilst dissolution beneath such soil covers led to the distinctive huninocky topography of palaeokarstic surfaces.
The lowering of erosive base level during regressive periods also resulted in the rejuvination of siliciclastic source areas within the adjacent hinterland of older rocks. Marginal alluvial fans prograded onto the emergent shelf and rivers incised complex channel
systems. Beyond the marginal fans transportation and deposition of terrigenous sediment appears to have been largely confined to such channels.
Marine transgressions saw the drowning of the channel complexes and the shutting down of terrigenous supply, and culminated in the inundation of palaeokarstic levels and the re-establishment of carbonate facies mosaics on the shelf.