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Wales |
Shell Research and Technical Services (EPT-AE), Postbus 60, 2280 AB, Rijswijk, The Netherlands j.d.marshall{at}siep.shell.com
The Upper Devonian to Lower Carboniferous Skrinkle Sandstones of the Pembroke Peninsula are predominantly continental deposits from the post-Caledonian syn-rift succession at the southern margin of the Late Palaeozoic Welsh Landmass. The Sandstones record deposition in the 30 km x 10 km Tenby-Angle fault block, the southernmost of a series of fault-bounded depositional basins in SW Dyfed. Activity on the bounding faults strongly influenced sedimentation through Lower Palaeozoic time. The Skrinkle Sandstones are conventionally assigned to a phase of relative fault inactivity, passive transgression of the area and southward drainage off the landmass. The Ritec Fault at the northern block boundary defined a temporary shoreline during final submergence. In contrast to this, it is argued that the lower half of the Skrinkle Sandstones represent a separate structural configuration, where SE-directed palaeocurrents and the high textural maturity of two superimposed basin-fill sequences indicate axial basin fill and potential closure to the south. The upper half records an influx of immature clastic deposits as fluvial sediments that disperse to the southwest, indicating relative uplift of either the Ritec or a more northerly fault. This phase records the true transgression, during which a thick barrier-lagoon coastline is preserved against the footwall ramp of the Ritec Fault.
