Inversion tectonics in S.W. Dyfed

Powell, C. M.

doi:10.1016/s0016-7878(87)80037-8

Cited by 26 publications

(17 citation statements)

References 8 publications

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“…The inliers are exposed within the cores of anticlines related to the inversion of long-lived extension faults during the Variscan Orogeny (Dunne 1983;Powell 1987Powell , 1989.…”

Section: Geological Contextmentioning

confidence: 99%

Process regime change on a Silurian siliciclastic shelf: controlling influences on deposition of the Gray Sandstone Formation, Pembrokeshire, UK

Hillier

Morrissey

2009

Geological Journal

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Shallow marine deposits comprising the Silurian Gray Sandstone Formation (GSF) exhibit pronounced process regime changes through time. The formation was deposited on the southern shelf of the Lower Palaeozoic Welsh Basin (UK), and conformably overlies the Coralliferous Formation. The basal Lithofacies Assemblage A (of Sheinwoodian age) is dominated by a storm-dominated process regime, comprising shoreface and offshore shelf facies associations. The overlying Lithofacies Assemblage B records a mixed process regime, with units being deposited under both storm-and tide-influenced conditions. Tidal-influence prevailed during deposition of the overlying Lithofacies Assemblage C, with proximal to distal facies variations across a significant tide-influenced river delta being observed. A return to stormdominated shoreface conditions is seen in the succeeding Lithofacies Assemblage D. Lithofacies Assemblage E (Homerian age) records the return of a tide-influenced river delta to the area, prior to the conformable transition into the overlying Old Red Sandstone (ORS) Red Cliff Formation (of Ludlow age). Northward thickening of the formation across southern Pembrokeshire into the Musselwick Fault indicates a tectonic control on sedimentation, the formation infilling accommodation space developed in an intra-shelf half-graben. Recurring changes in process regime from storm-to tide-influenced sedimentation may be related to the onset and subsequent cessation of tidal resonance in subbasins across the shelf area which itself was probably controlled by episodic tectonism. It is proposed that the Coralliferous and Gray Sandstone formations comprise the newly erected Marloes Group.

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“…The inliers are exposed within the cores of anticlines related to the inversion of long-lived extension faults during the Variscan Orogeny (Dunne 1983;Powell 1987Powell , 1989.…”

Section: Geological Contextmentioning

confidence: 99%

Process regime change on a Silurian siliciclastic shelf: controlling influences on deposition of the Gray Sandstone Formation, Pembrokeshire, UK

Hillier

Morrissey

2009

Geological Journal

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“…Internally, these blocks exhibit structural homogeneity, more specifically fold geometries and cleavage development, as recognized by Hancock et al (1981Hancock et al ( , 1982Hancock et al ( , 1983. The major WNW-ESE-trending faults were shown by Powell (1987Powell ( , 1989, and subsequently by Hayward and Graham (1989), to be intrinsically related to the inversion of preexisting extension faults. Two types of fault were recognized (Figures 3 and 4), namely those still demonstrating an extensional throw subsequent to inversion (the Benton, Wenall and Ritec Faults), and their corresponding footwall shortcuts (the Johnston and Musselwick Thrusts).…”

Section: R D Hilliermentioning

confidence: 97%

Depositional environment and sequence architecture of the Silurian Coralliferous Group, Southern Pembrokeshire, UK

Hillier¹

2002

Geological Journal

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The Lower Silurian siliciclastic Coralliferous Group is shown to have been deposited in an intra-shelf position 10-15 km south of the palaeogeographic shelf-break of the Welsh Basin. After a phase of thermal subsidence related to the development of the predominantly Llandovery Skomer Volcanic Group, the shelf basin was transgressed. This transgression was punctuated by an episode of tectonic uplift in southern Pembrokeshire, resulting in subaerial exposure of the shelf and a significant basinward shift in sedimentary environments. Erosion and sediment bypass ensued, with coarse-grained low-sinuosity fluvial channels transporting sediment to the northerly Welsh Basin, where significant submarine fans developed. During the early Telychian, renewed transgression took place, with lowstand gravels being ravined and reworked into parasequences of the transgressive systems tract. These thin, coarse-grained parasequences record deposition within high-energy wave-dominated shoreface/inner shelf environments. Further coastal onlap resulted in the closing down of significant coarse-grained sediment supply, with the remaining Coralliferous Group being dominated by wave-influenced silts, mud-shales and thin sandstones comprising the highstand systems tract.

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“…The greater thickness of strata in the Cosheston Group is not surprising since it is interpreted as accumulating in an area of complex relief with syn-depositional faulting (e.g. Allen & Williams, 1978Allen, 1985;Powell, 1987). The Senni Beds accumulated in part of the basin where there was presumably less subsidence and hiatuses are possibly of greater significance.…”

Section: Geological Significance 4a Stratigraphical Correlationmentioning

confidence: 99%

“…The environment of deposition is interpreted as an extensive alluvial plain traversed by streams and rivers flowing out of the Caledonian uplands to the north and draining into the Rheic Ocean to the south (Allen, 1979(Allen, , 1985Bluck, Cope & Scrutton, 1992). The 'Lower Old Red Sandstone' deposits in southwest Wales are separated from the main outcrop by the Benton Fault, and are divided into two zones of contrasting sequence by the Ritec Fault (see Powell, 1987, and references therein). These deposits are considered to have accumulated in an area of complex relief with syn-depositional faulting (Allen & Williams, 1978;Allen, 1985;Powell, 1987).…”

Section: Geological Settingmentioning

confidence: 99%

“…The 'Lower Old Red Sandstone' deposits in southwest Wales are separated from the main outcrop by the Benton Fault, and are divided into two zones of contrasting sequence by the Ritec Fault (see Powell, 1987, and references therein). These deposits are considered to have accumulated in an area of complex relief with syn-depositional faulting (Allen & Williams, 1978;Allen, 1985;Powell, 1987). An outcrop map and stratigraphical successions of the 'Lower Old Red Sandstone' in the Anglo-Welsh Basin are illustrated in Figures 1 and 2 respectively.…”

Section: Geological Settingmentioning

confidence: 99%

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The Cosheston Group (Lower Old Red Sandstone) in southwest Wales: age, correlation and palaeobotanical significance

Wellman

Thomas²,

Edwards

et al. 1998

Geol. Mag.

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Upper Silurian–Lower Devonian ‘Lower Old Red Sandstone’ facies deposits cropping out in southwest Wales are poorly age-constrained and difficult to correlate. Spore assemblages have been recovered from sequences of these deposits belonging to the lower part of the Cosheston Group. The spore assemblages are equated with the breconensis–zavallatus and polygonalis–emsiensis Spore Assemblage Biozones and indicate an early Devonian age (late Gedinnian (late Lochkovian)–Siegenian (Pragian)). The new biostratigraphical data enable correlation of the lower part of the Cosheston Group with the Senni Beds from the main outcrop of the Lower Devonian in South Wales and the Welsh Borderland. In addition, the new age data and stratigraphical correlation place important plant megafossil assemblages from the Cosheston Group and Senni Beds in a more secure stratigraphical framework, thus facilitating comparisons with other Lower Devonian plant megafossil assemblages and enhancing palaeobotanical understanding. Evidence from palynofacies analysis supports sedimentological interpretations which suggest that the ‘Lower Old Red Sandstone’ facies deposits belonging to the Cosheston Group accumulated in a continental fluviatile environment.

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Inversion tectonics in S.W. Dyfed

Cited by 26 publications

References 8 publications

Process regime change on a Silurian siliciclastic shelf: controlling influences on deposition of the Gray Sandstone Formation, Pembrokeshire, UK

Process regime change on a Silurian siliciclastic shelf: controlling influences on deposition of the Gray Sandstone Formation, Pembrokeshire, UK

Depositional environment and sequence architecture of the Silurian Coralliferous Group, Southern Pembrokeshire, UK

The Cosheston Group (Lower Old Red Sandstone) in southwest Wales: age, correlation and palaeobotanical significance

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