GCR block - Precambrian of England & Wales (PRE-EG-WL)

Precambrian of England & Wales

Block Description

UK map showing distribution of GCR sites of GCR block PRE-EG-WL
Distribution of GCR sites of GCR block Precambrian of England & Wales

The GCR sites selected for this GCR Block represent the English and Welsh geological record of Earth history up to the beginning of the Palaeozoic Era, which began about 543 million years ago (Ma). ‘Precambrian’ is a broadly used term for rocks that pre-date the Cambrian Period, i.e. were formed before the Phanerozoic Eon. It encompasses such a vast span of time, extending back to at least 4000 Ma, and has been subdivided into two Eons, the Archaean and the younger Proterozoic Eon. The Precambrian rocks selected for this block belong to the latter, specifically to its youngest part, which has been given the chronological term ‘Neoproterozoic’.

In British rocks, the beginning of Cambrian time is commonly marked by a widespread unconformity, and also marked by what is often considered to be the onset of the appearance of small shelly fossils, which here therefore marks the end of the ‘Neoproterozoic’.

Scottish Precambrian rocks, which had a very different geological history have their own GCR Blocks: Lewisian, Torridonian, Moine and Dalradian. See LEW, MOINE, TOR, DAL.

Outcrop pattern

The Precambrian basement of England and Wales is exposed within a number of inliers, which are regarded as ‘windows’ through the cover strata. The rocks that are revealed are of considerable geological diversity. The Precambrian outcrops are sparsely distributed and generally occupy relatively small areas of southern Britain.

Palaeoenvironment and palaeogeography

The Precambrian basement of southern Britain is most conveniently grouped into a number of large crustal entities, called ‘terranes’. Each terrane represents a microcosm of geological evolution and its rock assemblages may have arisen from a diversity of geological processes, commonly involving episodes of volcanism, igneous intrusion, sedimentation and deformation, all of which can be framed in the context of plate tectonic interactions. Each terrane represents views Precambrian rocks not as a single basement entity, but rather as belonging to a number of crustal fragments that together formed a late Precambrian microcontinent known as ‘Avalonia’. Many of these fragments initially evolved independently of each other and were subsequently joined together, forming a ‘collage’ of terranes. This terrane amalgamation took place along major tectonic boundaries that are now seen as wide shear zones or fault complexes. Although the terrane boundaries mostly date back to late Precambrian time, others possibly formed during younger orogenic events. Many terrane boundaries were also re-activated in the relatively recent geological past. the principal terranes are:

• The Charnwood Terrane

• The Wrekin Terrane

• The Cymru Terrane

• Monian Composite Terrane

This series of 3 terranes, amalgamated into the network of GCR sites represents by far the largest exposure of Precambrian rock in southern Britain.

• Monian Supergroup (‘Terrane 1’).

• Coedana Terrane in central Anglesey (‘Terrane 2’)

• Aethwy Terrane exposed within a narrow linear belt in south-east Anglesey (‘Terrane 3’)

GCR site selection

For the purposes of site evaluation and selection, the featured GCR sites are intended to show the broad spectrum of lithologies and geological processes representative of each terrane. Consequently, there are several themes or ‘networks’:

• Volcanic sequences formed in a variety of tectonic settings

• Plutonic igneous complexes

• Sedimentary and volcaniclastic strata ranging from deep-water marine to terrestrial environments

• Low- to high-pressure metamorphic rocks

• Intricate deformational structures

Palaeontology, fauna and flora

See PRE-PAL.


Volume Introduction

Precambrian of England & Wales


Site List

Your selection found 30 GCR sites. Sites are sorted alphabetically by country, local authority and then by site name -
CodeNameCountryLocal AuthorityGrid RefGCR Site Account
744The MalvernsEnglandHerefordshire, County ofSO760372Not available
1404Bardon HillEnglandLeicestershire CC and RutlandSK455133Not available
2817Beacon HillEnglandLeicestershire CC and RutlandSK510148Not available
2897Blackbrook ReservoirEnglandLeicestershire CC and RutlandSK465172Not available
1061Bradgate ParkEnglandLeicestershire CC and RutlandSK535110Not available
1403Charnwood LodgeEnglandLeicestershire CC and RutlandSK464157Not available
2819Charnwood Lodge & Warren HillsEnglandLeicestershire CC and RutlandSK459155Not available
2815Cliffe Hill QuarryEnglandLeicestershire CC and RutlandSK475106Not available
1062Outwoods - Hangingstone HillsEnglandLeicestershire CC and RutlandSK520157Not available
2818The BrandEnglandLeicestershire CC and RutlandSK537121Not available
745Thornton & Twistleton GlensEnglandNorth Yorkshire CCSD696739Not available
2190Ashes Hollow - Devil`s MouthEnglandShropshire CCSO435930Not available
2193Hawkham HollowEnglandShropshire CCSO432975Not available
2188Jonathan`s Hollow - Long BatchEnglandShropshire CCSO445961Not available
2204Lightspout HollowEnglandShropshire CCSO435952Not available
738Lyd HoleEnglandShropshire CCSJ414055Not available
2186The PikeEnglandShropshire CCSO442950Not available
736The Wrekin rangeEnglandShropshire CCSJ617074Not available
759Braich y Pwll to ParwydWalesGWYNEDDSH135258Not available
758Mountain Cottage QuarryWalesGWYNEDDSH230347Not available
757Penrhyn Nefyn foreshore sectionWalesGWYNEDDSH290408Not available
756Cae`r SaisWalesISLE OF ANGLESEYSH268772Not available
755Carmel HeadWalesISLE OF ANGLESEYSH293928Not available
752Llanbadrig AreaWalesISLE OF ANGLESEYSH375947Not available
754Llanddwyn IslandWalesISLE OF ANGLESEYSH390630Not available
750Marquis of Anglesey`s ColumnWalesISLE OF ANGLESEYSH535715Not available
753RhoscolynWalesISLE OF ANGLESEYSH260763Not available
751South StackWalesISLE OF ANGLESEYSH203823Not available
746Dolyhir and Strinds QuarriesWalesPOWYSSO243580Not available
747St David's CoastWalesSOUTH WEST WALESSM723245Not available
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access. Search Again