A reappraisal of the conditions of deposition of the Maentwrog Beds (Upper Cambrian) at Porth Ceiriad, North Wales

Summary The marine Maentwrog Beds comprise a repetition of sand and mud facies and follow a non-sequence. A shallow water depositional environment is inferred from the nature of the basal unit (with stromatolites and intraformational conglomerate), and hummocky cross-stratification and mud-draped erosion surfaces. The bulk of the formation was deposited between fair weather and storm wave base, the sand facies representing storm depositional events.