Uriconian
Encyclopedia
The Uriconian rocks of Shropshire (Wrekin Terrane) are thought to be potentially related to the Longmyndian Supergroup
of the Stretton Hills, Shropshire, United Kingdom. Current geological profiling of the terranes suggests that the Uriconian rocks are of Precambrian
age. The Uriconian Rocks outcrop to the southeast of the Long Mynd
area of the Welsh Borderlands and beyond the Church Stretton Fault which trends northeast-southwest across the area. The Stretton Hills are composed primarily of arenaceous beds subscribed to the Longmyndian Supergroup
. The Longmyndian are a c.6 km thick group of volcaniclastic and bentonitic sediment
horizons. The Uriconian have long thought to be older than the Longmyndian and generally outcrop to the southeast of the latter within northeast-southwest trending lineaments suggesting basement influence for the regional structure.
The Uriconian rocks outcrop in areas from Wellington, Shropshire
to Primrose Hill on the southwest side of The Wrekin
,east of Caer Caradoc and in the Craven Arms Inlier. Primarily the strata exist as fault-bounded slices within splays of, and to the southeast of, the main Church Stretton
fault system.
The Uriconian rocks comprise both intermediate to acidic and basic volcanic suites that reflect largely intraplate origins for the complex although some subduction
signatures have been identified. Further work has led to suggest that the locality of this kind of volcanism is related to marginal basin volcanicity (behind the main arc) influenced by trans-tension brought about by oblique subduction
.
, the Uriconian the tectonic events can be classed as pre-Atdabanian. Zircon dating
has given similar ages of 566.6+/-2.9Ma from the Longmyndian and 566+/-2Ma for the Uriconian Volcanics.
This leads to suggest that the area was affected by (Uriconian)volcanism
and associated events between 570-550Ma including the intrusion of the Ercall Granophyre. This potentially created a thermal extension of the area allowing sedimentation to occur within the basin.
Longmyndian Supergroup
The Longmyndian Supergroup is a c.6000m thick sequence of rocks that outcrop between the Pontesford-Linley Fault System and the Church Stretton Fault System in the Welsh Borderland. The supergroup consists of two major geological groups, the Stretton Group and the overlying Wentnor Group. The rocks...
of the Stretton Hills, Shropshire, United Kingdom. Current geological profiling of the terranes suggests that the Uriconian rocks are of Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
age. The Uriconian Rocks outcrop to the southeast of the Long Mynd
Long Mynd
The Long Mynd in Shropshire, England, is a part of the Shropshire Hills Area of Outstanding Natural Beauty. It is south of the county town Shrewsbury, and has an area of over 22 square kilometres , most of which takes the form of a heathland plateau. Most of the land on the Long Mynd is owned by...
area of the Welsh Borderlands and beyond the Church Stretton Fault which trends northeast-southwest across the area. The Stretton Hills are composed primarily of arenaceous beds subscribed to the Longmyndian Supergroup
Longmyndian Supergroup
The Longmyndian Supergroup is a c.6000m thick sequence of rocks that outcrop between the Pontesford-Linley Fault System and the Church Stretton Fault System in the Welsh Borderland. The supergroup consists of two major geological groups, the Stretton Group and the overlying Wentnor Group. The rocks...
. The Longmyndian are a c.6 km thick group of volcaniclastic and bentonitic sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
horizons. The Uriconian have long thought to be older than the Longmyndian and generally outcrop to the southeast of the latter within northeast-southwest trending lineaments suggesting basement influence for the regional structure.
The Uriconian rocks outcrop in areas from Wellington, Shropshire
Shropshire
Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...
to Primrose Hill on the southwest side of The Wrekin
The Wrekin
The Wrekin is a hill in east Shropshire, England. It is located some west of Telford, on the border between the unitary authorities of Shropshire and Telford and Wrekin. Rising to a height of above the Shropshire Plain, it is a prominent and well-known landmark, marking the entrance to Shropshire...
,east of Caer Caradoc and in the Craven Arms Inlier. Primarily the strata exist as fault-bounded slices within splays of, and to the southeast of, the main Church Stretton
Church Stretton
Church Stretton is a small town and civil parish in Shropshire, England. The population of the town was recorded as 2,789 in 2001, whilst the population of the wider parish was recorded as 4,186...
fault system.
The Uriconian rocks comprise both intermediate to acidic and basic volcanic suites that reflect largely intraplate origins for the complex although some subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
signatures have been identified. Further work has led to suggest that the locality of this kind of volcanism is related to marginal basin volcanicity (behind the main arc) influenced by trans-tension brought about by oblique subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
.
Geological Relationships
There is much uncertainty about the exact age of the Uriconian rocks primarily due to the complex structure of the folded and faulted rocks. All contacts are discordant, hence no direct relationships with the Longmyndian can de deduced, and a relative age has not been established.Other Notes
Given the steep dip of the Uriconian rocks relative to the shallow inclination of the CambrianCambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
, the Uriconian the tectonic events can be classed as pre-Atdabanian. Zircon dating
Uranium-lead dating
Uranium-lead is one of the oldest and most refined of the radiometric dating schemes, with a routine age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1-1 percent range...
has given similar ages of 566.6+/-2.9Ma from the Longmyndian and 566+/-2Ma for the Uriconian Volcanics.
This leads to suggest that the area was affected by (Uriconian)volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
and associated events between 570-550Ma including the intrusion of the Ercall Granophyre. This potentially created a thermal extension of the area allowing sedimentation to occur within the basin.