Heol Senni Quarry
Climate exposure
This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.
Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.
Habitats
Geology & landscape
Mining / Industrial: Quarry · Geological Period: Devonian · Rock Type: Alluvium, Sandstone
Landscape processes: Coastal, Fluvial
Description
Description The site is of special geological interest on two scores: (i) Non-marine Devonian: the site has cliff exposures of the Brownstones (the upper part of the Welsh Lower Old Red Sandstone). The Brownstones here consist of pebbly, cross-bedded sands, which formed in a large braided river system. The cliffs allow reconstruction of bar morphologies and river size, and show the way channels were stacked vertically to build up the sequence. The well developed stream topography between bars and channels that is seen in the deposits here is typical of the eastern outcrops of the Brownstones, and contrasts with the deposits of the western Brownstones in south Wales. This locality is the best of the eastern Brownstone outcrops, showing a distinct form of river alluvium. (ii) Vertebrate palaeontology: the type and only locality for Althaspis senniensis. Chordates are extremely rare in the Senni Beds and are know only from two other sites. Althaspis senniensis is a typical pteraspid of the ‘Dittonian’ and is very similar to, and might even be conspecific with Althaspis leachi, a form known throughout north-west Europe at the top of the Gedinnian Stage. Another Senni Beds quarry locally yields Rhinopteraspis dunensis, which occurs in the type area of the Siegenian Stage. Taken together these two quarries show that the Gedinnian/Siegenian boundary lies somewhere within the Senni Beds between these two fossil-bearing horizons. At present, work is being concentrated on these two species, and future research potential lies in determining the stratigraphical and facies controls on their distribution in Europe. Remarks: The site lies within the Brecon Beacons National Park.
Plant communities
A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream
Potamogeton natans community
Show 20 indicator speciesSchoenoplectus 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
Show 15 indicator speciesIsolepis 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
Show 11 indicator speciesBerula 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
Show 12 indicator speciesFontinalis 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