| Site of Special Scientific Interest | |
 | |
  Location within Devon | |
| Location | Devon Cornwall |
|---|---|
| Coordinates | 50°20′46″N4°07′19″W / 50.3461°N 4.12208°W /50.3461; -4.12208 |
| Interest | Geological |
| Area | 44.3 hectares (0.443 km2; 0.171 sq mi) |
| Notification | 1997 (1997) |
| Natural England website | |
Plymouth Sound, Shores and Cliffs is aSite of Special Scientific Interest (SSSI) around thePlymouth Sound, a large area of water where theRiver Plym andTamar meet. It stretches across the two ceremonial counties ofDevon andCornwall and the unitary authority area ofPlymouth. It contains fossils of plants and sea creatures and its cliffs show a timeline of the Middle to EarlyDevonian period hundreds of millions of years ago
Lower to early MiddleDevonian units of rock are visible from sections through the coastal cliffs andintertidal zones, which were laid down 417–354 million years ago.[1] There are fossil remains ofcorals,brachiopods,bryozoa,gastropods, rareorthoconicnautiloids,ostracods,trilobites,phacopids),crinoids,ostracoderm andacanthodian fish.[2]
Jennycliff Bay has steeply inclined folds, which flexure into open recumbent folds — some withchevron form. The folds have developedcleavage in theslate and in thesiltstones andsandstones, although it is more widely spaced throughout the silt and sandstones. To the south, the cleavage dips at moderate low angles and thestrata, which become overturned in places, dip steeply. The original direction of the strata can be established using the graded and cross-bedding of sedimentary structures. It demonstrates that the section is situated on the overturned, steep or northern limb of the DartmouthAntiform, which can be traced fromNewquay toDartmouth.[2] This is evidence a period of tectonic plate collision between 330 and 300 million years ago, which exerted pressure on the rock.[1] Folds of three generations with cleavages are visible through the section in Bovisand Bay. Generally, the first generation folds have gently southern dipping limbs which are overturned or steep. The cleavage consistently dips about 40 degrees south. This indicates that this section has the Dartmouth Antiform passing through it.[2] The far south consists of red and green slates with sandstones that were deposited in rivers and lakes.[1]
On the western flank (Cornwall), there are harder rocks such as StaddonGrit, which form a headland from Staddon Point. There are also deposits of sandstones in the shape of marine sand bars. Along most of the coast dramatic faults and folds in the rocks can be seen and, in some places, a chevron pattern is visible.[1]
