Usk Inlier

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The Usk Inlier is a domed outcrop of rock strata of Silurian age in Monmouthshire in south-eastern Wales. It is located in the countryside between the towns of Caerleon and Pontypool and the village of Raglan. The longer axis of the dome or 'pericline', often referred to as the Usk Anticline, is aligned north-south. The inlier is largely surrounded by a sequence of Old Red Sandstone rocks of Devonian age, though both these and the Silurian rocks are largely obscured by superficial deposits. [1] [2]

Dome (geology) Deformational feature in structural geology of symmetrical anticlines that intersect each other at their respective apices.

A dome is a feature in structural geology consisting of symmetrical anticlines that intersect each other at their respective apices. Intact, domes are distinct, rounded, spherical-to-ellipsoidal-shaped protrusions on the Earth's surface. However, a transect parallel to Earth's surface of a dome features concentric rings of strata. Consequently, if the top of a dome has been eroded flat, the resulting structure in plan view appears as a bullseye, with the youngest rock layers at the outside, and each ring growing progressively older moving inwards. These strata would have been horizontal at the time of deposition, then later deformed by the uplift associated with dome formation.

The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.

Monmouthshire County

Monmouthshire is a county in south-east Wales. The name derives from the historic county of Monmouthshire of which it covers the eastern 60%. The largest town is Abergavenny. Other towns and large villages are Caldicot, Chepstow, Monmouth, Magor and Usk. It borders Torfaen and Newport to the west; Herefordshire and Gloucestershire to the east; and Powys to the north.

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Old Red Sandstone assemblage of rocks in the North Atlantic region

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The Geological Conservation Review (GCR) is produced by the UK's Joint Nature Conservation Committee and is designed to identify those sites of national and international importance needed to show all the key scientific elements of the geological and geomorphological features of Britain. These sites display sediments, rocks, minerals, fossils, and features of the landscape that make a special contribution to an understanding and appreciation of Earth science and the geological history of Britain, which stretches back more than three billion years. The intention of the project, which was devised in 1974 by George Black and William Wimbledon working for the Governmental advisory agency, the Nature Conservancy Council (NCC), was activated in 1977. It aimed to provide the scientific rationale and information base for the conservation of geological SSSIs (Sites of Special Scientific Interest, protected under British law. The NCC and country conservation agencies were established in 1990 when JNCC became established and took over responsibility for managing the GCR site assessment process, and publishing accounts of accepted sites.

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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. 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.

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Pauline is a fossil genus of ostracods from the Silurian. Genus contains two species: Pauline avibella found in 425-million-year-old rocks in the Herefordshire Lagerstätte in England near the Welsh Border and Pauline nivisis, known from the Lower Silurian Pentamerus Bjerge Formation of north Greenland.

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References

  1. Aldridge, R.J., Siveter, David J., Siveter, Derek J., Lane, P.D., Palmer, D. & Woodcock, N.H. Geological Conservation Review Series vol 19, British Silurian Stratigraphy. Joint Nature Conservation Committee, Peterborough
  2. British Geological Survey 1:50,000 scale geological map sheets 232, 233, 249 & 250 (England & Wales series)

Coordinates: 51°41′N2°55′W / 51.69°N 2.92°W / 51.69; -2.92

Geographic coordinate system Coordinate system

A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector. A common choice of coordinates is latitude, longitude and elevation. To specify a location on a plane requires a map projection.