Llafar River Section (Trychiad Afon Llafar)
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Geology & landscape
Geological Period: Cambrian
Description
Description Trychiad Afon Llafar is of special scientific interest because it contains the stratotype of the Clogau Formation, and is the only locality at which the formation is represented by a full complement of trilobite biozones. The site is located 3 km east of Trawsfynydd and incorporates strata exposed for a distance of 800 m on the bed and banks of the Afon Llafar. The section in the Afon Llafar ranges from the upper part of the Gamlan Formation (Harlech Grits Group), through the Clogau Formation into the Maentwrog Formation (both in the Mawddach Group), all of middle-upper St David’s Series age. This is the type section of the Clogau Formation, the unit being important in regional stratigraphical studies because of its succession of varied faunas of trilobites and other taxa Tomagnostus fissus - Ptychagnostus punctuosus Biozones. The site is one of only two localities to have yielded Middle Cambrian fossils Lejopyge laevigata Biozone from the Maentwrog Formation, showing that the Middle- Upper Cambrian boundary is to be placed within this unit rather than below it. The succession at Afon Llafar can be correlated with those in the St David’s and Nuneaton areas, and also in Scandinavia. Remarks: The site lies within Snowdonia National Park.