Amnodd-Bwll Stream Section

Site of Special Scientific Interest · 52.9153, -3.7762

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Also within

Gwynedd County Eryri / Snowdonia National Park

Habitats

Fast flowing river and stream

Geology & landscape

Geological Period: Ordovician

Description

Description Amnodd-bwll Stream Section is of special scientific interest because it exposes a Lower to Upper Tremadoc (early Ordovician) sequence with the best-preserved fauna of the Conophrys salopiensis Biozone in Wales, and is a proposed basal stratotype for the Migneintian Stage of the Tremadoc Series. The site is located 12 km west of Bala and incorporates strata exposed for a distance of 650m along the bed and banks of a tributary of the Afon Amnodd-bwll which flows off the northern flank of Moel Llyfnant. Amnodd-bwll Stream Section provides a classic and highly fossiliferous sequence through the Nant-ddu Bellopheron Beds, Tai-hirion Asaphellus Flags and Amnodd Shumardia Shales, all of which are locally recognized members of the Dol-cyn-afon Formation. At Amnodd-bwll, this sequence, which ranges in age from Lower to Upper Tremadoc, contains the proposed boundary stratotype for the base of the Migneintian Stage of the Tremadoc Series. The exposure of the Amnodd Shales is particularly important because of the loss of good exposures at equivalent levels in the type Tremadoc sequence at Penmorfa, near Porthmadog. Amnodd-bwll Stream Section is an historic locality of great significance to studies of the Tremadoc Series in North Wales. Remarks: 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