Portishead Pier to Black Nore

Also within

Bristol CountySomerset County King Charles Way - Old Passage, Aust to Wain's Hill, Clevedon National Trail

Condition (Natural England)

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Geology & landscape

Geological Period: Carboniferous, Devonian · Rock Type: Carboniferous Limestone, Limestone, Sandstone, Shale

Landscape processes: Coastal, Fluvial

Description

Area, 71.8 ha. 177.4 ac. Description 1. Portishead Pier Section This section of alluvial sandstones is the best exposure of Upper Carboniferous rocks in the Avonmouth Coalfield. It represents a southwards extension of the Forest of Dean Coalfield, which together formed a peninsula projecting southwards from St George’s Land during most of the Westphalian. Only at the very end of the Westphalian did it become an area of deposition. This section is thus of great interest for helping understand the palaeogeography of the time. 2. Portishead Point Cliff and foreshore exposures here provide important exposures of geological structures formed during the Variscan mountain building episode orogeny in the Carboniferous Period of geological history. The rocks here consist of layers of limestone and shale, contorted by well developed fold structures and cut by a number of dislocation faults. The quality of the exposures enables the structures to be studied in considerable detail. This is a rare opportunity in this district and provides valuable information about the complex geological structure of the region. This is also the best locality for detailed examination of the geological structures developed at the eastern end of the visible Variscan orogenic belt in Britain, since east of Bristol the Variscan belt is masked by younger rocks. 3. Portishead This site shows important exposures of the Devonian sequence south of the Bristol Channel, in an area which is intermediate between the mainly continental sequence of South Wales and the continuous, largely marine sequence of North Devon. The Lower Old Red Sandstone is here represented by the Black Nore Sandstone. It consists of complex fluvial sandstones equivalent to the Brownstones to the north. The Upper Old Red Sandstone contains a wide variety of lithologies, including the Woodhill Bay Fish Bed. Facies in both Old Red Sandstone divisions and the transition to the Lower Carboniferous are not known in detail. The section is important for showing the southward thickening of the Old Red Sandstone and this area in comparison with outcrops in South Wales and for showing whether or not the boundary between the Upper Old Red Sandstone and Carboniferous Limestone in the Bristol Channel area is diachronous. This section also contains fossil interest. Fossils are very rare in the Upper Old Red Sandstone south of the Bristol Channel, so the Woodhill Bay Fish Bed which occurs here, is important because it yields several species of fossil fishes which help to ‘date’ these beds. Holoptychius scales are the most abundant fossils, but teeth scales of other species are also relatively common. Notably amongst the collection from this bed are plates of arthrodires, including Groenlandaspis sp. This is the only English record of this genus which is known worldwide from Upper Devonian rocks in Greenland, Ireland, Australia and Antarctica.