Depositional setting of the Lower Old Red Sandstone at Pantymaes Quarry, central South Wales: new perspectives on the significance and occurrence of ‘Senni Beds’ facies
Geraint Owen, Duncan Hawley, 2000. "Depositional setting of the Lower Old Red Sandstone at Pantymaes Quarry, central South Wales: new perspectives on the significance and occurrence of ‘Senni Beds’ facies", New Perspectives on the Old Red Sandstone, P. F. Friend, B. P. J. Williams
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The 200 m long face of Pantymaes Quarry, central South Wales, exposes part of the upper (Dittonian) Red Marl Group (Lower Old Red Sandstone). A lower Sandstone Facies Association (up to 15m thick) comprises interbedded grey–green micaceous sandstones, pebbly intraformational conglomerates, and grey siltstones. Major bounding surfaces define stacked channel complexes, representing the deposits of braided river systems. An erosively overlying Mudstone Facies Association (up to 15 m thick) comprises tabular-bedded, bioturbated and calcretized red siltstones and fine sandstones representing overbank deposits, possibly from a meandering system. The change in fluvial style is interpreted as a local response to pulses of oblique-slip movement on nearby fault systems. The period of fault activity resulted in the braided Sandstone Facies Association, the Mudstone Facies Association recording a gradual return to a meandering system. Individual pulses of activity produced the stacked channels within the Sandstone Facies Association. The Sandstone Facies Association is similar in character to the overlying Senni Beds, suggesting that ‘Senni Beds’ may describe a recurring, possibly tectonically controlled, braided channel facies in the Lower Old Red Sandstone.
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New Perspectives on the Old Red Sandstone
From the 1960s onwards, the Old Red Sandstone of both borders of the Atlantic Ocean has acted as a test-bed for the development of new ideas on the interpretation of fluvial, lacustrine and aeolian sedimentary rocks, and the investigation of tectonically-active basins. Much of the earlier reconnaissance work is now being reviewed in the light of further detailed field study, along with new developments in the understanding of the biostratigraphy, palaeobiology, geochronology, pedogenesis and tectonics.
Three general papers review recent work on the stratigraphical and chronological analysis of the Late Silurian, Devonian and Early Carboniferous strata, and summarize present understanding of the tectonics of the basins. These are then followed by twenty-seven contributions covering new work in Eastern USA, Canada, Ireland, Britain, Norway, Greenland and Spitsbergen.