Dol-cyn-Afon

Site of Special Scientific Interest · 52.8415, -3.7926

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Also within

Gwynedd County Eryri / Snowdonia National Park

Habitats

Fast flowing river and stream

Geology & landscape

Geological Period: Cambrian, Ordovician

Description

Description Dôl-cyn-afon is of special scientific interest because it contains the basal stratotype of the Dôl- cyn-afon Formation and thereby contributes to the recognition and correlation of the Cambrian- Ordovician boundary in Wales and elsewhere. The site is located approximately 10 km south-east of Trawsfynydd and incorporates sedimentary rock outcrops exposed along the bed and banks of a small tributary stream that enters the upper reach of the Afon Mawddach. The sequence exposed here contains the transition from the Dolgellau Formation (Merioneth Series, Upper Cambrian) to the Dôl-cyn-afon Formation (Tremadoc Series, Lower Ordovician), this being the type section for the Dôl-cyn-afon Formation. A low Tremadoc zonal fossil assemblage (Dictyonema and trilobites) is present in this formation. The uppermost Upper Cambrian Acerocare Zone is represented in the Dolgellau Formation, yielding a diagnostic suite of fossils and showing affinities with faunas in Scandinavia, South America and the former U.S.S.R. This is the only area in Britain known to contain the Acerocare Zone and to fully demonstrate the Cambro-Ordovician transition, and therefore this section forms an important complement to the nearby Bryn-llin-fawr SSSI. Remarks Dôl-cyn-afon has been selected as a result of the former Nature Conservancy Council’s Geological Conservation Review, a national survey and evaluation of sites of geological and geomorphological interest. The site is described in the GCR volume entitled British Cambrian to Ordovician Stratigraphy (Rushton et al., 1999). The site lies within Snowdonia National Park.

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea