Early history of the southern margin of the Tywi anticline in the Carmarthen area, South Wales

Summary The area SW of Carmarthen exposes Precambrian, Cambrian, and Ordovician rocks, unconformably overlain by Old Red Sandstone. Frequent depositional breaks and derived fragments of igneous and metamorphic rocks suggest a nearby land area. Periodic movement along the Llandyfaelog disturbance may have controlled sedimentation locally. Complex Caledonian structures in the area involve Lower Old Red Sandstone and may be due to the presence of basement at shallow depth.