Neath Disturbance
Encyclopedia
The Neath Disturbance is a geological structure which stretches across south Wales
from Swansea Bay
northeastwards as far as Hereford
in western England
. It comprises a series of both faults and associated folds
which were active during the mountain-building period known as the Variscan orogeny
. This line of weakness probably featured in the earlier Caledonian Orogeny
and perhaps reflects a more ancient line of weakness in the basement
rocks.
The Disturbance gives rise to a lineament
crossing the region, that is to say that it is responsible for a number of significant landscape features along its 100km length. Prominent amongst these is the Vale of Neath, a deep valley incised by a glacier during the ice ages along this line of weakness in the Earth's crust and now occupied by the River Neath
between Pontneddfechan and Swansea Bay
. The hill of Moel Penderyn
also lies on the Disturbance a little further east. A part of the Vale of Grwyne
north of The Sugarloaf and the northeast-southwest aligned section of the Monnow valley on the English/Welsh border are also excavated along this line of weakness.
The Neath Disturbance is possibly the southernmost geological feature within Britain which can be described as following the Caledonoid trend. The phrase describes a suite of major geological structures
associated with the closure of the former Iapetus Ocean
in the middle Palaeozoic era and giving rise to the Caledonian orogeny or mountain-building period. The Cribarth
or Swansea Valley
Disturbance and the Carreg Cennen Disturbance
are similar features found a little further north in south Wales. The Bala Fault
, Menai Strait Fault, Southern Uplands Fault
, Highland Boundary Fault
and Great Glen Fault
are other major Caledonoid
structures of Britain.
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
from Swansea Bay
Swansea Bay
Swansea Bay is a bay on the Bristol Channel on the South Wales coast. Places on the bay include Mumbles, Swansea and Port Talbot. The River Neath, River Tawe, River Afan and Blackpill stream flow into the bay....
northeastwards as far as Hereford
Hereford
Hereford is a cathedral city, civil parish and county town of Herefordshire, England. It lies on the River Wye, approximately east of the border with Wales, southwest of Worcester, and northwest of Gloucester...
in western England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. It comprises a series of both faults and associated folds
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
which were active during the mountain-building period known as the Variscan orogeny
Variscan orogeny
The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...
. This line of weakness probably featured in the earlier Caledonian Orogeny
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
and perhaps reflects a more ancient line of weakness in the basement
Basement Rock
Basement or Basement Rock music was a sub-genre coined in 2006 in an article by music magazine TGR. This was first in relation to the existence of underground record label Criminal Records but more for the independent bands they represent. The roots of the sub-genre are noted to be as far back as...
rocks.
The Disturbance gives rise to a lineament
Lineament
See also Line A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will comprise a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these...
crossing the region, that is to say that it is responsible for a number of significant landscape features along its 100km length. Prominent amongst these is the Vale of Neath, a deep valley incised by a glacier during the ice ages along this line of weakness in the Earth's crust and now occupied by the River Neath
River Neath
River Neath is a river in south Wales running south west from its source in the Brecon Beacons National Park to its mouth at Baglan Bay below Briton Ferry on the east side of Swansea Bay.Several minor rivers rise on the southern slopes of Fforest Fawr...
between Pontneddfechan and Swansea Bay
Swansea Bay
Swansea Bay is a bay on the Bristol Channel on the South Wales coast. Places on the bay include Mumbles, Swansea and Port Talbot. The River Neath, River Tawe, River Afan and Blackpill stream flow into the bay....
. The hill of Moel Penderyn
Moel Penderyn
Moel Penderyn is a hill on the edge of Penderyn village, in the Brecon Beacons National Park in the county borough of Rhondda Cynon Taff, south Wales. It also appeared on older maps as 'Y Foel Penderyn'. Its summit at 371m is marked by a trig point...
also lies on the Disturbance a little further east. A part of the Vale of Grwyne
Grwyne Fawr
The Grwyne Fawr is a river in the Brecon Beacons National Park in south Wales. A section of it forms the administrative border between Powys and Monmouthshire and also of the historic counties of Brecon and Monmouth. The river and its major tributary the Grwyne Fechan flow into the River Usk at...
north of The Sugarloaf and the northeast-southwest aligned section of the Monnow valley on the English/Welsh border are also excavated along this line of weakness.
The Neath Disturbance is possibly the southernmost geological feature within Britain which can be described as following the Caledonoid trend. The phrase describes a suite of major geological structures
Geological structure of Great Britain
The geological structure of Great Britain is complex, resulting as it does from a long and varied geological history spanning more than two billion years...
associated with the closure of the former Iapetus Ocean
Iapetus Ocean
The Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
in the middle Palaeozoic era and giving rise to the Caledonian orogeny or mountain-building period. The Cribarth
Cribarth Disturbance
The Cribarth Disturbance is a geological structure forming a lineament which stretches across south Wales from Swansea up the Swansea Valley then northeastwards to Brecon and beyond. It comprises both a series of faults and associated folds which were active during the mountain-building period...
or Swansea Valley
Swansea Valley
The Swansea Valley , one of the South Wales Valleys is the name often given to the valley of the River Tawe area in South Wales, UK. It reaches southwest and south from the Brecon Beacons National Park down to the city of Swansea. Today, administration of the area is divided between the City and...
Disturbance and the Carreg Cennen Disturbance
Carreg Cennen Disturbance
The Carreg Cennen Disturbance is a zone of geological faults and folds in south and mid Wales which forms a part of both the Church Stretton Fault Zone and the Welsh Borderlands Fault System...
are similar features found a little further north in south Wales. The Bala Fault
Bala Fault
Bala Fault is a SW-NE trending geological fault in Wales that extends offshore into Cardigan Bay. In the offshore area it is a major normal fault and forms the bounding structure to the Cardigan Bay Basin, with a fill including about 2500 m of Lias Group. At its northeastern end it links to the...
, Menai Strait Fault, Southern Uplands Fault
Southern Uplands Fault
The Southern Uplands Fault is a fault in Scotland that runs from Girvan to Dunbar on the East coast. It marks the southern boundary of the Scottish Midland Valley....
, Highland Boundary Fault
Highland Boundary Fault
The Highland Boundary Fault is a geological fault that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east...
and Great Glen Fault
Great Glen Fault
The Great Glen Fault is a long strike-slip fault that runs through its namesake the Great Glen in Scotland. However, the fault is actually much longer and over 400 million years old.-Location:...
are other major Caledonoid
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
structures of Britain.