The Ashgill Series near Welshpool, North Wales

Cave, R.; Price, David

doi:10.1017/s0016756800036864

Cited by 8 publications

(4 citation statements)

References 15 publications

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“…The assemblages at generic level undoubtedly reflect a variety of neritic ecosystems, but at specific level their correlation potential in Britain has already been demonstrated (e.g. McNamara, 1979 a, b;Cave & Price, 1978;Price, 1973aPrice, , b, 1977Price, , 1980Price, , 1981.…”

Section: B Cautleyan Stagementioning

confidence: 95%

A revision of Ordovician series and stages from the historical type area

et al. 1995

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This paper is a revision of the standard chronostratigraphy of the Ordovician of the historical type area in England and Wales. The revision is a response to the need for more precise definitions of series and stages, especially for practical international correlation. In some cases this has entailed moving horizons for Series bases away from those in the classical sections. The scheme will be used as the standard for a forthcoming revision of the Correlation Chart of the British Ordovician System. The Ordovician is divided into five series: Tremadoc, Arenig, Llanvirn, Caradoc and Ashgill. The Llanvirn is extended to include part of the classical Llandeilo Series, which is included within it as a stage. Where stage subdivisions of standard series have not yet been defined, as in the Tremadoc, they are proposed in this paper. However, Bancroft’s fine stadial divisions of the Caradoc, which have been criticized for their brevity and local utility, are combined into four new stages, which will have wider application. The former Caradoc subdivisions are retained as substages for the purposes of regional correlation.

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Section: B Cautleyan Stagementioning

confidence: 95%

A revision of Ordovician series and stages from the historical type area

et al. 1995

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“…At Welshpool (Fig. In a re-examination of the Welshpool sequence Cave & Price (1978) named the Cautleyan mudstone unit and confirmed the stratigraphic break separating it from the underlying Pen-y-garnedd Shale. Graptolites are not abundant in the Caradoc area, Shropshire, but according to Dean (in Williams et al 1972, p. 40) the Actonian Stage and most, if not all, of the Onnian Stage belong to the D. clingani Biozone.…”

Section: Ashgill Series (A Dw)mentioning

confidence: 81%

Definition of the Tremadoc Series and the series of the Ordovician System in Britain

Whittington¹,

Dean²,

Fortey

et al. 1984

Geol. Mag.

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The Tremadoc Series and series of the Ordovician System are widely used in international correlations, and this review explains and summarizes how the base ofeach of these series is recognized in Britain. No type section in which the base of any one of them is displayed has ever been selected and formally designated, hence the basal horizon of each series is a matter of general understanding rather than precise.definition. This general understanding is of particular biozones, or of assemblages of fossils and their relative ages. The geographical separation between type sections of series, and differences in facies, complicate the understanding of relative ages of biozones. Brachiopod and trilobite faunas of the Llandeilo, Caradoc and Ashgill Series have been studied in detail in recent years, and biozones proposed. These biozones have proved difficult or impossible to recognize outside their type areas in Britain, and brachiopod-trilobite faunas of the Tremadoc, Arenig and Llanvirn Series are likewise highly provincial. Thus for correlation within and outside Britain attention has been focused on the ' standard' graptolite biozones, particularly since such conodont faunas as have been found have not proved useful. Yet there are problems associated with these 'standard' biozones; for example, the Tetragraptus approximatus Biozone is unknown in Wales or England, the relationship between the base of the Glyptograptus teretiusculus Biozone and the earliest Llandeilo shelly faunas requires clarification, and at what level the base of the Caradoc Series may lie in the Nemagraptus gracilis Biozone is unknown.Thus to bring precision to definitions of Ordovician Series in Britain the identification of continuous, fossiliferous sequences that will serve as stratotypes, is required. Such a section for the basal portion of the Tremadoc Series has recently been .proposed. Systematic studies related to particular biozones are needed, for example early Caradoc and-early Ashgill brachiopods, and graptolites of the Didymograptus bifidus and Glyptograptus teretiusculus Biozones. The stratigraphical ranges and abundances of species in particular sections require documentation, so that the type of biozone (assemblage, acme, concurrent-range, etc.) may be recognized. Such work could lead towards chronostratigraphy, the provision of a standard stratigraphical scale in Britain for the Tremadoc Series and Ordovician series.

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“…1). Since the Nod Glas contains a mid-Onnian (Upper Caradoc) shelly fauna at Welshpool and is also overlain by Rawtheyan rocks (Cave & Price, 1978), the presence of a substantial non-sequence between the Nod Glas and Broad Vein formations has been inferred, which at Corris could encompass the lower part of the Ashgill (Fig. 2).…”

Section: Stratigraphymentioning

confidence: 99%

The Nod Glas décollement of the Welsh Basin

Pratt

1991

Geol. Mag.

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Structural, petrographic and metamorphic evidence is presented for localized end-Caledonian (Acadian) décollement within a ‘black shale’ formation in the central Welsh Basin, close to the Caradoc–Ashgill boundary. Similar detachments are probably widespread in other parts of the, paratectonic Caledonides with upright folds and cleavage, particularly in sequences with strong viscosity contrasts.

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The Ashgill Series near Welshpool, North Wales

Cited by 8 publications

References 15 publications

A revision of Ordovician series and stages from the historical type area

A revision of Ordovician series and stages from the historical type area

Definition of the Tremadoc Series and the series of the Ordovician System in Britain

The Nod Glas décollement of the Welsh Basin

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