Area: 29.5 hectares, 72.9 acres.
Part of site formerly known as Sandsfoot Castle Cove and the Nothe SSSI. Site amended by extension and deletion. Adjacent to Chesil and the Fleet SSSI.
Description and Reasons for Notification:
The cliffs along the north-western shore of Portland Harbour are of outstanding geological importance. The site also includes maritime grassland and the intertidal shore itself.
There are outstanding sections in the Corallian (Oxfordian) rocks. The site includes the type localities for several formations including the Nothe Clay, and Nothe Grit, Bencliff Grit and the Sandsfoot Clay, and Grit: several of which are more thickly developed here than in the standard section a few miles to the east at Osmington. The section here covers much of the Oxfordian time interval from the Nothe Grit to the Passage Beds at the very top of the stage, and exposure of the Sandsfoot Clay – Ringstead Coral Bed interval surpasses even that of the type section. A key site in Jurassic stratigraphic studies.
The site contains the thickest baylei – cymodoce Zone Kimmeridge Clay in Dorset. Above a clear junction with the Corallian Beds, an eleven metre section is visible up to the Black Head Siltstone. Historically, Waagen defined the boundary between the Corallian and the Kimmeridge Beds in this section, and the site is important as the source of Rasenia, and in the subdivision of the cymodoce Zone on the basis of its faunal assemblages. An historic locality in studies of Kimmeridgian strata.
The Lower Kimmeridge Clay (baylei, cymodoce, mutabilis Zones) of Smallmouth Sands has yielded one of the most varied Kimmeridgian reptile faunas. It is the best site for forms such as the turtles (4 species) and the pterosaurs (3 species). The specimens collected include type specimens of one turtle, two pterosaurs, one sauropod, one ichthyosaur, and possibly a plesiosaur. A key site with a fauna complementing the Kimmeridge Clay vertebrate fauna of the type section in the Isle of Purbeck.
The causeway along the south western shore of the Harbour supports extensive, rich maritime grassland, similar to that in the adjacent Chesil and the Fleet SSSI. Characteristic species include sea couch Elytriga atherica, thrift Armeria maritima, sand sedge Carex arenariaand the local Portland spurge Euphorbia portlandica. There are also patches of saltmarsh vegetation with the uncommon shrubby seablite Suaeda vera.
Site Notified to Secretary of State on 10 July 1987