Summer (1968) Field meeting in Pembrokeshire, South Wales

Owen, T.R.; Bloxam, T. W.; Jones, D. G.; Walmsley, V. G.; Williams, Brian P.

doi:10.1016/s0016-7878(71)80029-9

Cited by 12 publications

(2 citation statements)

References 27 publications

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“…A continuous succession approximately 4 km thick is recognizable in the northern zone; it has in the past been subdivided into the Red Marls below and the Cosheston Group above, and correlated purely lithologically (Strahan, Cantrill, Dixon, Thomas and Jones 1914;Cantrill, Dixon, Thomas and Jones 1916). In contrast, the locally much thinner development south of the Ritec Fault, probably with a depositional break (Allen 1965) beneath the southerly-derived Ridgeway Conglemerate (Owen, Bloxam, Jones, Walmsley and Williams 197 1;Williams 1971), was extensively subdivided and partiy dated by vertebrates and spores (Dixon 1921(Dixon , 1933a(Dixon , 1933bKing 1934;White 1938White , 1946White , 1950Richardson and Lister 1969).…”

Section: Introductionmentioning

confidence: 99%

The sequence of the earlier lower old red sandstone (siluro‐devonian), north of milford haven, southwest dyfed (wales)

Allen

Williams²

1978

Geological Journal

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The Red Marls are renamed the Milford Haven Group (thickness approximately 2 · 4 km) and divided between the Red Cliff, Albion Sands, Lindsway Bay, Sandy Haven and Gelliswick Bay Formations, in ascending order. The lowest three, totalling approximately 230 m in thickness, are largely restricted to the Marloes area, where they succeed the marine Silurian rocks sharply and with a distinct facies change, indicative of a possibly substantial stratigraphical break. Northwards the Red Cliff and Albion Sands Formations are overlapped, the Lindsway Bay Formation in the Winsle area resting disconformably on marine Silurian rocks older than the youngest of the marine Silurian beds exposed at Marloes. The Sandy Haven and Gelliswick Bay Formations are more widely distributed and closely resemble the Red Marls of the Pembroke Peninsula and the main outcrop north of the Benton Fault. They are Gedinnian in age on the basis of ostracoderms, but the Gelliswick Bay Formation may range into the Siegenian. The thick Cosheston Group, which grades up from the Gelliswick Bay formation, probably represents the remainder of the Siegenian and may possibly be partly Emsian in age. The character of the Milford Haven Group lends no credence to the idea that allochthonous blocks are assembled in southwest Dyfed as the result of Variscan movements.

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Section: Introductionmentioning

confidence: 99%

The sequence of the earlier lower old red sandstone (siluro‐devonian), north of milford haven, southwest dyfed (wales)

Allen

Williams²

1978

Geological Journal

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“…Previous accounts of these volcanic rocks have been included in papers by Reed (1895), Part (1922), Thomas & Cox (1924), Cox (1915Cox ( , 1930, Cox et al (1930a, b), Pringle (1930), Evans (1945), Thomas & Thomas (1956), Bloxam (1971) and Owen et al (1971). This paper is concerned with the volcanic rocks which crop out within the northern part of Pembrokeshire (now SW Dyfed).…”

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confidence: 99%

Early Ordovician volcanism in Dyfed, SW Wales

Bevins

Roach

1979

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A review of early Ordovician volcanism in SW Dyfed, Wales is presented in the light of recent work. There were a number of major and minor volcanic episodes within the area during Arenig and Llanvirn times. For the most part, submarine volcanism occurred within a restricted basin, in which black muds were deposited and to which coarse terrigenous material had very limited access. Basic and intermediate magmas were generally erupted as flows. Acidic magmas were also erupted quietly, to produce thick, frequently autobrecciated flows and domes. Volcaniclastic rocks resulted by deposition from sediment gravity flows originating on unstable flanks of lava domes. Evidence for occasional episodes of explosive activity is provided by sediment gravity flows carrying a high proportion of pyroclastic debris. Subaerial or shallow water conditions are suggested only for the oldest volcanic rocks on Ramsey Island. Numerous basic and less frequent intermediate and acid high-level intrusive sheets have a close temporal, spatial and genetic relationship with the volcanic rocks.

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The Ridgeway Conglomerate Formation of SW Wales, and its implications. The end of the Lower Old Red Sandstone?

Hillier

Williams

2007

Geological Journal

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The Devonian Old Red Sandstone Ridgeway Conglomerate Formation crops out in Pembrokeshire, SW Wales. It was deposited as part of a dryland alluvial fan, axial fluvial valley deposystem. It conformably overlies the mid Lochkovian Freshwater West Formation and probably predates deposition of the Lower Cosheston Group Mill Bay Formation indicating an Early Devonian (latest Lochkovian to earliest Pragian) age, rather than a Middle Devonian age as suggested by previous workers. It therefore represents the youngest preserved formation of the Milford Haven Group south of the Ritec Fault. The Formation thickens drastically into the Ritec Fault, indicating its control on sedimentation. The half-graben topography initiated deposition of a hangingwall alluvial fan that was sourced from a southerly Lower Palaeozoic/Precambrian provenance within the present-day Bristol Channel. The Formation is heterolithic in nature, with deposits on the fan reflecting a mixture of processes. Conglomerates were deposited primarily by laterally extensive sheetfloods, and as bars in low-relief, laterally accreted channels. Sandstones were also predominantly deposited by sheetfloods. Gritty mudrocks in comparison demonstrate deposition by cohesive debris flows.The fan prograded northward and interfingered with a low-gradient, high-sinuosity fluvial channel system dominated by inclined and non-inclined heterolithic stratification. Thinly laminated mudstone and sandstone interbeds were deposited in ephemeral fan-toe and axial valley lakes that may have developed during sub-humid climatic episodes. The lacustrine heterolithic association has associated matgrounds and possible 'algal roll-up' structures. Calcretized peetee structures and root traces comprise a lake margin calcrete association.Fan gravels prograded into the axial fluvial valley during periods of increased sediment flux that may represent semi-arid conditions and/or episodes of tectonic activity. Calcretes of varying development were established in both the fan and axial valley zones. Calcretes with lower stages of development are more proximal to the Ritec Fault reflecting decreased soil residence times and high deposition rates within the axial valley. More strongly developed soil profiles on the fan may indicate sequence boundaries associated with low sediment flux, or increased soil residence time due to active fan-channel migration (the pedofacies concept). Groundwater calcretes have sharp-based and layer-bound calcrete profiles. Gully-bed cements are locally developed within the fan gravels.

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Summer (1968) Field meeting in Pembrokeshire, South Wales

Cited by 12 publications

References 27 publications

The sequence of the earlier lower old red sandstone (siluro‐devonian), north of milford haven, southwest dyfed (wales)

The sequence of the earlier lower old red sandstone (siluro‐devonian), north of milford haven, southwest dyfed (wales)

Early Ordovician volcanism in Dyfed, SW Wales

The Ridgeway Conglomerate Formation of SW Wales, and its implications. The end of the Lower Old Red Sandstone?

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