Glan Pibwr Stream Section

Site of Special Scientific Interest · 51.8377, -4.2994

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Also within

Dyfed County

Habitats

Fast flowing river and stream

Geology & landscape

Geological Period: Ordovician · Rock Type: Mudstone

Description

Description An historic Arenig faunal locality; the type locality for the 'Ogygia marginata Beds' with their abundant trilobite faunas. These mudstone outcrops have recently been designated as the type locality for the Pibwr Member of the new Carmarthen Formation. The rich asaphid, raphiophorid and trinucleid trilobite faunas of the site occur together with species of Phyllograptus, a rare Welsh occurrence. A key Lower Ordovician faunal and stratigraphic locality. In layman's terms, the interest of this site may be expressed more simply, and such a statement is provided below. This should not be taken as definitive and further information as to details of the interest can be obtained from the Nature Conservancy Council. Glan Pibwr is of particular importance as it is regarded as the 'type locality' for part of the Lower Ordovician sequence of South Wales. The strata exposed in this stream section were laid down as a blanket of mud on a sea floor which existed in this area during Lower Ordovician times some 500 million years ago. Over the years, the section has yielded a great diversity of fossil animals, the most notable of which are the trilobites. Remains of these sea-dwelling arthropods, a group of animals which is now extinct, are well-preserved in the mudstones at Glan Pibwr and the section has yielded a number of species which are only rarely found elsewhere in Britain.

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