The volcanic rocks of the area between Fishquard and Strumble Head, Pembrokeshire

Publisher Website
Google Scholar
Abstract
Summary: Volcanic rocks of Ordovician age, of widespread occurrence within North Pembrokeshire, attain their maximum development in the Pen Caer peninsula, embracing the area immediately north-west of Fishguard and culminating seawards in Strumble 1 Head. Referred to as the Fishguard Volcanic Series, these rocks are assignable to the Lower Llanvirnian. They reach a maximum thickness of some 3600 feet near Strumble Head itself, but attenuate rapidly towards the south and east so that at Lower Fishguard Harbour they are reduced to some 850 feet. A well-defined tripartite subdivision is evident over the greater part of this area ; these components in upward succession are the Lower Rhyolite Division, the Pillowlava (Spilite) Division and the Upper Rhyolite Division. Although pillow-lavas predominate within the Pillow-lava Division, this is made up of a diverse group of rocks, the detailed petrography of which reveals many unusual features. Its thickness of approximately 3000 feet in the extreme north of the Pen Caer peninsula contains the greatest local development of pillow-lavas in Wales. A discovery of particular interest is the presence of an intra-formational series intercalated within the dominant pillow-lavas. Near Goodwick the two rhyolite divisions reach a combined vertical thickness of some 2500 feet, easily the greatest thickness of Ordovician rhyolitic rocks recorded in Pembrokeshire. Breccias, agglomerates, intercalated ashes or tuffs and perlitic or nodular varieties are of common occurrence, but flinty flour-banded types predominate.

This publication has 11 references indexed in Scilit: