Topic
Welsh Basin
About: Welsh Basin is a research topic. Over the lifetime, 172 publications have been published within this topic receiving 3949 citations.
Papers published on a yearly basis
Papers
TL;DR: In this article, it was shown that many of the major strike faults in the British and Irish Caledonides were active as sinistral strike-slip zones in the end-Silurian to pre-mid-Devonian period.
Abstract: Evidence is presented that many of the major strike faults in the British and Irish Caledonides were active as sinistral strike-slip zones in the end-Silurian to pre-mid-Devonian period. Some, such as the Highland Boundary Fault, moved in this way at an earlier stage in the Ordovician. These data allow the Caledonian rocks lying between the Laurentian miogeocline (whose basement is represented by the Lewisian, Moine and possibly the Dalradian) and the Gondwanaland miogeocline (Midland Platform and Welsh Basin) to be re-analysed as a group of disorganized terranes which originated to the southwest in North America and southwest Europe/Africa prior to the Silurian. The Highland Border Terrane and Northern Belt Terrane are interpreted as duplicated pieces of a mid-Ordovician sequence which was a back are to northwest subduction. The Midland Valley Terrane is interpreted as a slice of Laurentian foreland onto which ophiolites were obducted in the lower Ordovician but which became the basement of a continental margin arc to northwest subduction in the mid-Ordovician. The Cockburnland Terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip. The Connemara Terrane is regarded as an allochthonous piece of the Dalradian miogeocline and the South Mayo Terrane as a remnant of an early Ordovician arc and fore arc which in mid-Ordovician times became a back arc/marginal basin to northwest subduction. The Lake District-Wexford Terrane is part of an arc to southeast subduction under Gondwanaland whose activity climaxed in the mid-Ordovician. The Central Terrane is interpreted as a Silurian overstep assemblage which blankets the junction between Laurentian- and Gondwanaland-derived oceanic terranes, and therefore Iapetus is regarded as an Ordovician ocean which closed prior to the Silurian. The model suggests that at the end of the Silurian, a clockwise-rotating Gondwanaland, having carried Laurentia into collision with Baltica, broke free and created a major sinistral strike-slip zone which disrupted the Ordovician palaeogeography in the British Isles/North American sector of Iapetus.
195 citations
TL;DR: The greywacke beds were deposited from turbidity currents in a region within the mud belt as mentioned in this paper, which came from an area lying to the south-west and south-southwest, its configuration varying with time.
Abstract: The greywacke beds were deposited from turbidity currents in a region within the mud belt. These currents came from an area lying to the south-west and south-south-west, its configuration varying with time. Variation in type of deposit is correlated with distance from land, and evidence of successive rejuvenations of the source area is presented. Sedimentary injection dykes occurring in the south are held to prove that some currents were set in motion by earthquakes, but slumping from the edge of the sedimentary terrace caused by loading, together with the action of storms (in the south), probably also assisted in the transfer of material to deeper water.
195 citations
TL;DR: In this paper, the authors reviewed the evidence for the timing of collision between the microcontinent of Eastern Avalonia (southern Britain and adjacent areas) and the Laurentian continent.
Abstract: The evidence is reviewed for the timing of collision between the microcontinent of Eastern Avalonia (southern Britain and adjacent areas) and the Laurentian continent. Recent palaeomagnetic results placing Eastern Avalonia in a high (50°) southern latitude in mid Ordovician time are now consistent with faunal evidence for the first time. The resulting apparent polar wander path is evaluated and suggests that Eastern Avalonia detached itself from a southern peri-Gondwanan latitude in the early Ordovician, moved northwards, and approached Laurentia by the late Ordovician. Its western corner probably impinged on Laurentia in the early Silurian and it docked against the Laurentian margin during Silurian and early Devonian time with a component of anticlockwise rotation.This kinematic history is supported by a compilation of sediment dispersal patterns on Eastern Avalonia. A low-volume Ordovician and earliest Silurian supply from within the microcontinent was overwhelmed in late Llandovery time by a large volume of southwest-derived turbidites, probably from the uplifting impact zone to the west. This source was later augmented by a high-volume clastic supply to the north margin of the microcontinent. Eastward migration of this source through Wenlock and Ludlow time reflects the progressive anticlockwise docking of Eastern Avalonia against the Laurentian margin. The earliest sign of a large-volume supply from Baltica is in the late Wenlock, arguing against any earlier hard collision.
131 citations
TL;DR: The lower Palaeozoic Welsh Basin was founded on immature continental crust and volcanic activity was largely influenced by NE-SW-trending faults which defined the NW and SE margins of the basin this paper, with the locus of arc volcanism sited further N, in the Lake District-Leinster Zone of the Caledonides.
Abstract: Summary The Lower Palaeozoic Welsh Basin was founded on immature continental crust. During late Precambrian-early Cambrian times, volcanism and sedimentation were influenced by NE-SW-trending faults which defined the NW and SE margins of the basin. During the Cambrian, marine sediments infilled a graben and at the end of the Tremadoc widespread tectonism was associated with an island-arc volcanic episode. In the Ordovician this subduction-related activity was succeeded by mainly tholeiitic volcanism related to back-arc extension, with the locus of arc volcanism sited further N, in the Lake District—Leinster Zone of the Caledonides. In Wales, the Ordovician volcanic activity shifted in time and space. In S Wales volcanism persisted from the middle Arenig through the Llanvirn. In N Wales the volcanism can be broadly divided into dominantly pre-Caradoc activity in southern Snowdonia and an intra-Caradoc episode in central and northern Snowdonia. In eastern Wales, including the Welsh Borderland, and in Llŷn, both episodes are represented. In all areas faults greatly influenced both volcanism and sedimentation. Intrusive activity was dominated by high-level emplacement of sills. Granite (s.l.) stocks are restricted to central and northern Snowdonia and Llŷn and many were coeval with extrusive volcanism. Volcanism in the basin was essentially bimodal with voluminous eruptions of tholeiitic basalts with ocean-floor affinities, and of rhyolites. Minor volumes of andesite to rhyodacite resulted from low-pressure fractional crystallization of the tholeiitic basalts. Available evidence suggests that the rhyolites resulted mainly from crustal fusion, although in some instances evolution by crystal fractionation from intermediate magma has been proposed. Calc-alkaline assemblages are petrographically distinct, of minor occurence and, contrary to previous conclusions, are relatively insignificant in the characterization of the tectonic environment of the basin. Throughout the basin, volcanism was generally succeeded by deposition of black muds and then turbidite-dominated sequences.
131 citations
TL;DR: In the Karadere-Zirze area, east of Safranbolu (Pontides, northern Turkey) as mentioned in this paper, lower Palaeozoic lower palaeoencoderic rocks have been found to range from Early Ordovician to Silurian.
Abstract: Lower Palaeozoic rocks in the Karadere-Zirze area, east of Safranbolu (Pontides, northern Turkey), range from Early Ordovician to Silurian. Overlying the probably Tremadoc Bakacak Formation are Aydos Formation quartzites, followed conformably by the Karadere Formation, dated as Early Arenig to Early Llanvirn by means of graptolites which are assigned to seventeen genera and include three new forms: Eoglyptograptus bouceki, Prolasiograptus haplus praecursor and Undulograptus ? mui. Late Arenig trilobites from the Karadere Formation include Bergamia, Cyclopyge, Dionidella ? , Leioshumardia and Seleneceme. In the Limestone Member of the overlying Ketencikdere Formation, uncommon trilobites suggest only a mid- to late Ordovician age, but con-odonts with Colour Alteration Index 5–6 indicate the Amorphognathus tvaerensis Biozone (early Caradoc). Macrofossils are rare in the Siltstone Member, but conodonts from the middle of the unit suggest the highest subzone of the A. tvaerensis Biozone; the youngest visible strata are, on acritarch evidence, at least as high as Caradoc, but the Ashgill is not confirmed and the contact with overlying Silurian rocks is unexposed. The Findikli Formation comprises: a Lower Member, black argillites with Llandovery graptolites and acritarchs; and an Upper Member, grey shales with late Wenlock graptolites, overlain unconformably by Devonian rocks. The succession differs significantly from contemporaneous deposits in southern Turkey and its affinities lie with western Europe, including the Welsh Basin.
111 citations
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| Year | Papers |
|---|---|
| 2021 | 2 |
| 2020 | 2 |
| 2019 | 2 |
| 2017 | 2 |
| 2016 | 3 |
| 2015 | 2 |