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Book Chapter


January 01, 2000


Deposition of the Silurian (Wenlock) siliciclastic Gray Sandstone Group of south-west Pembrokeshire took place within littoral environments close to the palaeogeographical shelf-margin of the Welsh Basin. Sedimentation described a northerly, basinward progradation across an earlier Late Ordovician? to Aeronian rift basin. Changes in relative sea level (rs1) had profound effects on depositional environments, and five depositional sequences are recognized. During highstands of rs1, the area was influenced by wave-dominated, shallow-marine conditions. During lowstands of rs1, shelf incision and sediment bypass occurred. Associated valley fills vary in nature from high-sinuosity estuarine channels, tidal flats and tidally-influenced, high-sinuosity fluvial channels. The last of these predominate within the youngest sequence, with abundant subaerial emergence indicators heralding the onset of true continental deposition, and the conformable transition into the overlying Old Red Sandstone Red Cliff Formation within the Marloes Peninsula. A renewal of tectonic activity ensued within the Lower Old Red Sandstone, with pebbly low-sinuosity alluvium of the Albion Sands Formation, and fanglomerates of the Lindsway Bay Formation reflecting reactivation of earlier rift-margin faults, probably within a transtensional tectonic regime.

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Geological Society, London, Special Publications

New Perspectives on the Old Red Sandstone

Geological Society of London
ISBN electronic:
Publication date:
January 01, 2000




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