Palynofacies in a Late Silurian regressive sequence in the Welsh Borderland and Wales

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Abstract
The Upper Whitcliffe and lower part of the Downton Castle Sandstone Formations (Ludlow and Pridoli Series) have been sampled from sequences distributed over an area roughly 4800 square km in west-central England and Wales. Ludfordian age rocks have been interpreted as the deposits of shelf and basin environments, and those of the lower Downton Group as near-shore to beach. Sections sampled from the ‘shelf’ area are in the Ludlow type area, and in the Usk, May Hill and Woolhope inliers. ‘Basin’ sediments were sampled at Knighton, the Long Mountain, Capel Horeb and Kington. The samples were analysed for their palynological content, and all the organic-walled microfossils were studied together with the fragmentary remains of larger plants and animals. Using a series of ratios between different groups of microfossils, it is apparent that there are consistent changes through time in both the palynomorph assemblages and in the structured and unstructured organic material. Dominance of some microplanktic groups/taxa is used to define a new microphytoplanktic phase concept and to compare the sequence of palynoevents. Depositional environments inferred from palynofacies interpretation of the Ludlow type area are closely comparable with those proposed previously from sedimentological data. Palynofacies sequences differ for the shelf and basin areas but show similar trends. We have also recognized a dramatic shift in palynofacies at a level within the Downton Castle Sandstone Formation and its correlatives in both shelf and basin areas; this change is tentatively interpreted as a ‘storm’ event.