Milford Haven Waterway SSSI

Milford Haven Waterway, is a Site of Special Scientific Interest (SSSI) on Milford Haven Waterway in Pembrokeshire, South Wales, designated since 2002. The site is protected for a wide range of reasons, including its geology, marine environment and ecosystems, and to protect a diversity of flora and fauna.

Geology

Milford Haven Waterway is an exceptional example of a ria (a system of valleys drowned by post-glacial rise in sea level) that consists of a number of estuaries, embayments and inlets. Cliffs in the southern regions are mostly developed in rocks of the Old Red Sandstone, whereas the geology of the upper reaches is relatively complex. In the outer part of Milford Haven vertical cliffs are common but elsewhere the cliff profile is often composed of a slope with a vertical rock face below it, the slope being a remnant from an earlier landform - a river valley - that has not yet been eroded by the sea. In many locations stony clays mantle the middle section of the cliff profile and are exposed above the rock faces.

The cliffs and foreshore at Little Castle Head provide exposures of two air-fall tuff horizons within the Sandy Haven Formation of the Lower Old Red Sandstone, Milford Haven Group. The two tuff units, the Pickard Bay Tuff Bed and the Townsend Tuff Bed, are useful stratigraphical marker horizons, particularly the latter, which can be traced across the whole of the Old Red Sandstone outcrop in South Wales. At Little Castle Head the tuffs are exposed in an area of tight folding, and comparison of logged sections across the limbs of the folds shows lateral variations in the thickness of the tuff beds and the intervening sandstone units. Faecal pellets have been preserved as unusual trace fossils at the base of, and within, the tuffs.