A review of the nature and outcrop of the ‘White Lias’ facies of the Langport Member (Penarth Group: Upper Triassic) in Britain

Swift, A.D.

doi:10.1016/s0016-7878(08)80236-2

Cited by 25 publications

(17 citation statements)

References 22 publications

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“…The topmost micritic limestone bed displays erosive-based sets of laminae defining erosive-based troughs (typically 10 cm wide and 1 cm high) that somewhat resemble the internal lamination of oscillatory ripples. Ripple structures have been reported from elsewhere in the topmost beds of the White Lias (Donovan & Kellaway, 1984;Swift, 1995). However, such bedforms could not develop in such fine-grained micritic sediment.…”

Section: Sectionmentioning

confidence: 75%

“…Previous studies of the White Lias have noted the restricted range of marine taxa and occasional presence of evaporite minerals (celestine) and postulated a variable salinity regime in a somewhat restricted marine environment (Hallam, 1981;Hallam & El-Shaaraway, 1982;Swift, 1995). The uniformly fine-grained carbonate further indicates tranquil depositional conditions, albeit occasionally interrupted by seismic events, responsible for the slump horizon, and storms.…”

Section: Environmental Change At the T-j Transitionmentioning

confidence: 94%

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Sedimentology of the Triassic-Jurassic boundary beds in Pinhay Bay (Devon, SW England)

Wignall

2001

Proceedings of the Geologists' Association

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in Pinhay Bay (SE Devon) of the White Lias (Langport Member of the Lilstock Formation) and basal Blue Lias reveal rapidly changing palaeoenvironments during the Triassic-Jurassic (T-J) boundary interval. During deposition of the topmost White Lias a soft seafloor of micritic mudstone was lithified and bored. The resultant hardground was locally eroded, probably in a shallow marine setting, to form a spectacular intraformational conglomerate that was itself lithified. Brief subaerial emergence then followed and produced a fissured and pitted top surface to the White Lias. The regression was short lived and rapid transgression at the base of the Blue Lias established organic-rich shale deposition with a small framboidal pyrite population and low Th/U ratios indicative of a stable, sulphidic lower water column (euxinic conditions). The White Lias/Blue Lias contact thus records a short duration, high amplitude relative sea-level change. This sea-level oscillation has also been postulated for other T-J boundary sections in Europe, although the failure to identify it in regional-scale sequence stratigraphic studies is probably due to its brief duration. Deposition of the basal beds of the Blue Lias was marked by a discrete phase of syn-sedimentary folding and small growth fault activity that may record a regional pulse of extensional tectonic activity.

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Section: Sectionmentioning

confidence: 75%

Section: Environmental Change At the T-j Transitionmentioning

confidence: 94%

Sedimentology of the Triassic-Jurassic boundary beds in Pinhay Bay (Devon, SW England)

Wignall

2001

Proceedings of the Geologists' Association

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“…The Westbury Formation is described as lying uncomformably on Carboniferous limestone, followed by the Cotham beds, Langport beds and the Jurassic Inferior Oolite (Moore, 1867;Richardson, 1911). The Cotham and Langport beds consist of micritic limestones, believed to have formed during a temporary regression in the late Rhaetian, before a second transgression turned the area fully marine in the Hettangian (Swift, 1995;Hallam, 1997;Hesselbo et al, 2004). Curtis measured the Rhaetian sediments to be 0.5 m thick, consisting of yellow limestone shales, sandstone beds and black clays (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

A marine vertebrate fauna from the Late Triassic of Somerset, and a review of British placodonts

Nordén

Duffin

Benton

2015

Proceedings of the Geologists' Association

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“…The upper member of the Lilstock Formation, the Langport Member, is of Rhaetian or Hettangian age depending on boundary definition. The unit consists of limestone or calcareous mudstone and was deposited in a fully marine environment (Richardson 1911;Hallam 1960a;Swift 1995). The junction with the underlying Cotham Member is sharp but conformable.…”

Section: Lilstock Formationmentioning

confidence: 99%

Sea-level change and facies development across potential Triassic–Jurassic boundary horizons, SW Britain

Hesselbo

Robinson

Surlyk

2004

JGS

179

167

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The Late Triassic to Early Jurassic aged succession of SW Britain (the Penarth and lower Lias Groups) comprises mudstone, sandstone and limestone strata deposited in a variety of marine to non-marine environments. Faunal and floral characteristics of these successions have led to the proposal that one location in SW England, St Audrie's Bay, should serve as the Global Stratotype Section and Point (GSSP) for the base of the Hettangian Stage and, thus, for the Triassic-Jurassic (Tr-J) boundary. The sections of SW Britain have also been used previously to infer sea-level change history and relate this to potential kill mechanisms associated with the Tr-J boundary mass extinction. Chemostratigraphic, biofacies and lithofacies data are used here to suggest alternative models of sea-level change in relation to possible Tr-J boundary horizons in the sections of SW Britain. A sea-level lowstand surface of erosion is inferred to occur within the Cotham Member of the Lilstock Formation, a unit deposited in an environment that was often subaerially exposed. In contrast to previous interpretations, the top surface of the overlying Langport Member (here inferred to be deposited on a carbonate ramp of depositional or tectonic origin) represents a drowning event of at least regional extent. All horizons regarded as plausible levels at which to place the Tr-J boundary based on fossil distributions lie within strata deposited during relative sea-level rise. However, it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and, additionally, there is no positive evidence that sea-level fall had any relation to the genesis of proposed Tr-J marker horizons. It is unlikely that sea-level fall played a significant role in the Tr-J boundary extinctions in either a local or a global context.

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A review of the nature and outcrop of the ‘White Lias’ facies of the Langport Member (Penarth Group: Upper Triassic) in Britain

Cited by 25 publications

References 22 publications

Sedimentology of the Triassic-Jurassic boundary beds in Pinhay Bay (Devon, SW England)

Sedimentology of the Triassic-Jurassic boundary beds in Pinhay Bay (Devon, SW England)

A marine vertebrate fauna from the Late Triassic of Somerset, and a review of British placodonts

Sea-level change and facies development across potential Triassic–Jurassic boundary horizons, SW Britain

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