The Solva Group is a

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

group (a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

) in west

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. The name is derived from Solva on the west coast of Pembrokeshire where the

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

are well exposed in coastal cliffs. This rock succession was formerly known as the ''Solva Series'' and ascribed to the British regional stratigraphic unit ‘’St David’s Epoch’’, though these terms are now obsolete.

Outcrops

These rocks are exposed, along the north coast of St Brides Bay south of

St Davids St Davids or St David's ( cy, Tyddewi, , "David's house”) is a city and a community (named St Davids and the Cathedral Close) with a cathedral in Pembrokeshire, Wales, lying on the River Alun. It is the resting place of Saint David, W ...

and in particular at Caer Bwdy Bay just southeast of the city where they are seen to overlie the Caerbwdy Sandstone Formation. They are exposed again in the sides of the ria at Solva and occur more widely inland of the village though exposures are less frequent. There are less extensive outcrops further west at St Justinian and on Ramsey Island. To the east they occur again north of Newgale and at Tancredston and to the west of Wolf's Castle.

Lithology and stratigraphy

The Group comprises around five hundred metres thickness of occasionally pebbly, green and purple

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s together with mudstones and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

Trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

and

acritarch Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity refl ...

fossils are present.

Trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s suggest that the sediments were laid down in shallow marine conditions though the thick middle sequence is characterized by

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites w ...

s and is much less

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

iferous.

References

{{Reflist Cambrian System of Europe Geology of Wales Geological groups of the United Kingdom Geologic formations of the United Kingdom