The graptolite biostratigraphy of a Llandovery outlier near Llanystumdwy, Gwynedd, North Wales

Abstract

SummaryLlandovery strata at Llanystumdwy are described. Ninety graptolite species have been identified enabling the establishment of the following zones: acinaces, cyphus, triangulatus, magnus, leptotheca, convolutus, ?sedgwickii, turriculatus and crispus. The name Llanystumdwy Mudstone Formation is proposed for previously undescribed mudstones cropping out on the River Dwyfor at Llanystumdwy and includes all strata referable to the acinaces to turriculatus zones. Comparison is made between Llanystumdwy and other areas, notably Northern England and Southern Scotland