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Bryneglwys Fault is a geological fault in Wales.
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Bryneglwys Fault is a geological fault in Wales.
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An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations.
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Faults may also displace slowly, by aseismic creep.
The geology of Wales is complex and varied; its study has been of considerable historical significance in the development of geology as a science. All geological periods from the Cryogenian to the Jurassic are represented at outcrop, whilst younger sedimentary rocks occur beneath the seas immediately off the Welsh coast. The effects of two mountain-building episodes have left their mark in the faulting and folding of much of the Palaeozoic rock sequence. Superficial deposits and landforms created during the present Quaternary period by water and ice are also plentiful and contribute to a remarkably diverse landscape of mountains, hills and coastal plains.
See also Line (geometry)
An inlier is an area of older rocks surrounded by younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited exposure of the older underlying rocks. Faulting or folding may also contribute to the observed outcrop pattern. A classic example from Great Britain is that of the inlier of folded Ordovician and Silurian rocks at Horton in Ribblesdale in North Yorkshire which are surrounded by the younger flat-lying Carboniferous Limestone. The location has long been visited by geology students and experts. Another example from South Wales is the Usk Inlier in Monmouthshire where Silurian age rocks are upfolded amidst Old Red Sandstone rocks of Devonian age.
In geology, a disturbance is a linear zone of disturbed rock strata stretching for many miles across country which comprises a combination of folding and faulting. The British Geological Survey record a number of such features in South Wales including the Neath Disturbance, Pontyclerc Disturbance, Carreg Cennen Disturbance and the Cribarth Disturbance, the latter sometimes also known as the Tawe Valley or Swansea Valley Disturbance. The southwestward continuation of the Carreg Cennen Disturbance is known as the Llandyfaelog Disturbance.
The Aber Dinlle Fault is a SW-NE trending fault in North Wales. It forms part of the Menai Strait Fault System, with the Berw and Dinorwic Faults. It lies close to the epicentre of the 1984 Llŷn Peninsula earthquake, although it is not thought to have been responsible for that event. The fault was active during deposition of Ordovician rocks in the Welsh Basin. It was reactivated as a normal fault in the Carboniferous with a downthrow to the northwest and again reactivated as a reverse fault during Late Carboniferous inversion associated with the Variscan Orogeny.
The 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 2,500 metres (8,200 ft) of Lias Group. Onshore it is responsible for the lineament which runs through Bala and south of Cadair Idris to the coast at Tywyn. At its northeastern end it links to the similarly orientated Llanelidan Fault.
The Benton Fault is a geological fault in southern Pembrokeshire in Wales that was active as a normal fault during the deposition of the Old Red Sandstone during the Devonian period, forming a thick half graben. During the Carboniferous, the Benton Fault was strongly inverted as part of the Variscan Orogeny.
The Berw Fault is a SW-NE trending fault in North Wales. It forms part of the Menai Strait Fault System, with the Dinorwic Fault and the Aber Dinlle Fault. It has a long history of movement with early ductile fabrics preserved from a sinistral strike-slip sense shear zone active at the end of the Precambrian and into the early Cambrian. Any Caledonian deformation is unclear but the fault zone was reactivated in the Carboniferous as a NW-throwing normal fault with seismic reflection data showing the formation of a half-graben in its hanging wall. There are no indications of inversion during the Variscan Orogeny, but the fault was reactivated in a normal sense during the Permian and Triassic and again during the Cenozoic with a sinistral strike-slip sense.
The Bristol Channel Fault Zone or Central Bristol Channel Fault Zone is a major south-dipping geological fault, or zone of faulting, running approximately west–east in the Bristol Channel between England and Wales. It makes landfall just south of Weston-super-Mare and the Mendip Hills. It forms a divide between the late Palaeozoic age South Wales basin to the north and the Culm Basin to the south. It marks a major change in the pre-Variscan geology of the United Kingdom, juxtaposing very different sequences of Devonian and Lower Carboniferous rocks. During the Variscan, the fault may have acted as either a strike-slip fault or a thrust fault or indeed both; its nature remains uncertain. During the Triassic to Jurassic, the fault zone was active as an extensional fault, controlling the development of the Bristol Channel Basin.
The Bronnant Fault is a geological fault affecting the lower Palaeozoic rocks of the counties of Ceredigion and Pembrokeshire in West Wales. The feature is mapped over part of its length as the Bronnant Fault Zone and is closely associated with the Glandyfi Lineament, a similarly aligned zone of faulting and folding. The rocks of the Aberystwyth Grits Group dating from the Llandovery epoch of the Silurian period thicken markedly to the west of the fault suggesting it was active at the time of their deposition. North of Lledrod its alignment is affected by cross-cutting east–west faults, including the Ystwyth Fault Zone. Its alignment is sub-parallel to the coast of Cardigan Bay thus curving from a north–south alignment in the north through a northeast–southwest alignment until it merges with broadly east–west aligned faults in northeast Pembrokeshire.
The Carmel Head Thrust is a geological fault on Carmel Head in north Anglesey, Wales, where rocks of the Precambrian Mona Complex are thrust over Lower Paleozoic sedimentary rocks.
The Ceibwr Bay Fault is a WSW-ENE trending fault zone that cuts Ordovician rocks of the Ashgill Nantmel Mudstones Formation and the Caradoc Dinas Island Formation. The fault is exposed on the south side of Cardigan Bay in Wales and forms part of the Fishguard-Cardigan Fault Zone. It extends from the coast at Ceibwr Bay at its western end to the coast at Aberporth at its eastern end. The fault zone is thought to have been active as a normal fault throughout the deposition of the Ordovician sequence.
The Claerwen Fault is a major SW-NE trending fault in central Wales. It was active as a normal fault during deposition of Late Ordovician to mid-Silurian sedimentary rocks, downthrowing to the northwest. The estimated throw on the fault increases from about 100 m at a shallow level to about 1000 m at depth. There is no discernible change in the grade of metamorphism associated with the Caledonian Orogeny across the fault, suggesting that it was not reactivated later.
The Cwm Llwyd Fault is a fault in the west of the Black Mountain of South Wales. It runs north, parallel to the A4069 road, for over 4 km from near Brynaman to meet the Carreg Cennen Disturbance near Brest Cwm Llwyd. It moved as a sinistral strike-slip fault during the Variscan Orogeny. Together with the Llwyn Celyn Fault it formed a left-stepping offset that created a pull apart structure, which preserved the Cwm Llwyd Outlier of Namurian rocks.
The Cwm Pennant Fault is a SSW-NNE trending normal fault system in North Wales. It forms part of the structures that bound the Snowdon graben. The main faults of the Cwm Pennant fault system throw down to the east.