Palynology of the Freshwater East Formation (Upper Silurian, Pridoli), Pembrokeshire, South Wales, UK

Abstract

Upper Silurian (Pridoli) cryptospores and trilete spores are described from the type section of the Freshwater East Formation in Pembrokeshire, South Wales. This formation is the oldest stratigraphical division of the Lower Old Red Sandstone succession south of the Ritec Fault in the Anglo-Welsh Basin. It represents an incised valley fill sequence composed predominantly of red dryland alluvial sediments interbedded with four tidally influenced green-grey heterolithic units. The sequence is well known for the occurrence of an early land plant Cooksonia flora. The spore assemblages are dominated by cryptospores (67%), particularly laevigate monads and dyads. Trilete spores are less abundant but are diverse in composition and provide the principal means of accurately dating the sequence. Eleven cryptospore taxa and 31 trilete taxa are identified. Two new species, Cymbohilates richardsonii and Velamisporites edwardsae, are erected. The Freshwater East microflora contains a distinctive complex of Chelinospora taxa, here named the Chelinospora lavidensis assemblage. It represents a previously unrecognised assemblage within the Pridoli succession of the Anglo-Welsh Basin. An accurate age for this assemblage has been determined by correlation with the Upper Silurian succession of the Cantabrian Mountains in north-west Spain, where a continuous spore succession through the Pridoli Series has independent biostratigraphical age control from chitinozoans. The Freshwater East assemblages are correlated with the upper part of the Chelinospora hemiesferica (H) Biozone, which is dated by the chitinozoans Margachitina elegans and Pseudoclathrochitina carmenchui as early mid Pridoli in age. Rare occurrences of small spiny acritarchs, sphaeromorph acritarchs and prasinophyte phycomata in two of the Freshwater East assemblages support the sedimentological data that indicate the grey-green heterolithic beds were deposited in tidally influenced fluvial and estuarine environments.

Keywords:

• Silurian
• Pridoli
• cryptospores
• trilete spores
• acritarchs
• Cooksonia
• South Wales

Acknowledgements

The author thanks Dr Rob Hillier and Professor Brian Williams for their assistance in the field and for their advice and discussions concerning the stratigraphy and sedimentology of the Freshwater East section. Thanks also to Mary Lehane for laboratory preparation of samples. Thanks to Dick Waters for his helpful comments on the Silurian stratigraphy of the Anglo- Welsh Basin.

Disclosure statement

No potential conflict of interest was reported by the author.