The Milford Haven Group is a late

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

to early

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

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 group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

(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 ...

) in west

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

. The name is derived from the estuary and town of

Milford Haven Milford Haven ( ) is a town and community (Wales), community in Pembrokeshire, Wales. It is on the north side of the Milford Haven Waterway, an estuary forming a natural harbour that has been used as a port since the Middle Ages. The town was ...

in south

Pembrokeshire Pembrokeshire ( ; ) is a Principal areas of Wales, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and otherwise by the sea. Haverfordwest is the largest town and ...

. The Group comprises calcareous marls with occasional sandstones along with conglomerates and breccias. The Group unconformably overlies rocks of the Gray Sandstone Group and comprises two different successions either side of the east–west aligned Ritec Fault To the north are (in ascending order) the Red Cliff, Albion Sands/Lindsway Bay, Sandy Haven and Gelliswick Bay formations. To the south are the Freshwater East, Moor Cliffs and Freshwater West formations. The Chapel Point

Calcrete Caliche () is a soil accumulation of soluble calcium carbonate at depth, where it precipitates and binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or s ...

Member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

is recognised at the top of the Moor Cliffs Formation whilst the succeeding Freshwater West Formation is divided into a lower Conigar Pit Sandstone Member and an upper Rat Island

Mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

Member. The earlier of these formations are assigned to the Pridoli series of the Silurian. The top of the Silurian section is (according to some schemes) marked by the Townsend Tuff Member, above which lies the

Lochkovian The Lochkovian is one of three faunal stages in the Early Devonian Epoch. It lasted from 419.2 ± 3.2 million years ago to 410.8 ± 2.8 million years ago. It marked the beginning of the Devonian Period, and was followed by the Pragian Stage. It is ...

age strata. The Gelliswick Bay and Freshwater West formations are assigned to the local Dittonian series and straddle the internationally recognised Lochkovian and Pragian series. This suite of rocks is in turn conformably overlain by rocks of the Cosheston Group.Barclay, W.J. et al. 2005 ''The Old Red Sandstone of Great Britain'', Geological Conservation Review series, no 31 JNCC Peterborough. p212

References

{{Reflist Devonian System of Europe Silurian System of Europe Geology of Wales Geological groups of the United Kingdom Marl groups Sandstone groups Conglomerate groups