Petrography and Facies of Some Upper Visean (mississippian) Limestones in North Wales

Observations on Late Mississippian strata are summarized including: the Brigantian Cefn Mawr Limestone and Minera formations; and the Namurian Pentre Chert and Cefn-y-Fedw Sandstone formations. Many of those observations relate to transitory, commercial quarry exposures, especially in the Cefn Mawr Limestone Formation. During the Late Mississippian, the area was located in proximity to an unstable northeast-facing platform edge and slope on which earlier workers postulated a megaslide, probably related to the Nant Figillt Fault zone and affecting the Cefn Mawr Limestone and Pentre Chert formations. This study reinforces that general model and highlights new evidence indicative of mass wastage along the platform margin including: synsedimentary faults, slides and slumps. Penecontemporaneous submarine crevassing occurred in the Pentre Chert Formation. Limestone beds previously described as tidal or storm-related sand bars in the Cefn Mawr Limestone Formation are instead considered as gravity-driven resedimented deposits. Channelling in relatively deep water facies of the Cefn Mawr Limestone, Pentre Chert, and Cefn-y-Fedw Sandstone formations occurred.

Section: Stratigraphymentioning

confidence: 75%

Mass collapse and resedimentation on a Brigantian–Early Namurian platform margin, Halkyn–Mold area, North Wales, UK

Kirkham¹

2021

“…The lithologic units were mapped and correlated with the already known stratigraphy. The nomenclature used to describe the limestones was devised (Banerjee 1959) before the publication of new terminologies by Folk (1959). The original nomenclature is given here with the equivalent term of Folk in brackets.…”

Section: Introductionmentioning

confidence: 99%

“…The original nomenclature is given here with the equivalent term of Folk in brackets. The reconstruction of the depositional environments is dealt with only briefly, as it was examined in detail earlier (Banerjee 1959). The conclusions of this paper are based on mapping on a scale of 1 : 10,560 and the study of 205 thin sections.…”

Section: Introductionmentioning

confidence: 99%

Carboniferous lithofacies, rhydymwyn to erryrys, North Wales

Banerjee¹

1969

Carboniferous lithofacies, Halkyn Mountain, North Wales

Oldershaw

1969

A brief description of the carboniferous succession on Halkyn Mountain, North Wales, together with a map illustrating the areal distribution of upper Vistan carbonate and Namurian noncarbonate lithologies, is presented. The upper Vistan carbonates have been divided into four major units termed in ascending order: A1 (pelsparites and biopelsparites); A2 (alternating biopelmicsparites, non-argillaceous biomicrites and micrites); B1 (argillaceous calcite siltstones); B2 (alternating non-argillaceous and argillaceous biomicrites and micrites). Analysis of the distribution of microfacies within each unit indicates that during upper V i s h times, deposition of shallow water, off-shore, carbonate sand banks alternated with, and finally gave way to, the deposition of in-shore, lagoonal carbonate muds. The presence of an erosional surface at the top of Unit B2 suggests that a period of emergence took place prior to the deposition of the succeeding Namurian bedded cherts. The,cherts can be differentiated into three major lithologies which exhibit characteristics that are consistent with cyclic deposition in a marginal, restricted basin.Une description brtve de la succession Carboniftre de Halkyn Mountain, nord du Pays de Galles, est prtsentte avec une carte illustrant la distribution gtographique des lithologies carbonates du VisQn suptrieur et des lithologies non-carbonates du Namurien. Les carbonates du Viseen suptrieur ont bte divists en quatre unitis principales appeltes en ordre ascendant: Al (pelsparites et biopelsparites), A2 (en alternance biopelmicsparites, non-argileux biomicrites et micrites), B1 (grts fines calcites et argileuses), B2 (en alternance biomicrites et micrites non-argileux et argileux). Une analyse de la distribution de microfacits a I'interieur de chaque unite indique qu'aux temps du Visten suptrieur des depots de bancs de sable calcaire en eau peu profonde au large, alternaient avec des dep6ts de vase calcaire en lagunes prts des rives. La presence d'une surface d'trosion en haut de ]'unit6 8 2 laisse penser qu'une ptriode d'emergence eut lieu avant les dtp6ts des assises de silex come Namuriennes suivantes. On peut difftrencier les assises silicienses entre trois lithologies principales qui montrent des caracttristiques constquentes avec dCpBt cyclique dans un bassin marginal restreint.Es wird eine kurze Beschreibung der Karbonschichten des Halkyn Mountain, North Wales vorgelegt, sowie eine Karte, die die ortliche Verteilung der hoheren Vise Karbonat-und Namur Nichtkarbonatgesteine erlautert. Die hoheren Vist Karbonate sind in vier Haupteinheiten eingeteilt und in aufsteigender Ordnung wie folgt bezeichnet: A1 (Belsparite und Biopelsparite); A2 (abwechselnd Biopeimiksparite mit tonfreien Biomikriten und Mikriten); B1 (tonige Kalzit Feinsandsteine); B2 (abwechselnd tonfreie und tonige Biomikrite und Mikrite). Die Analyse der Verteilung der Mikrofazies innerhalb jeder Einheit weist darauf hin, dal3 wahreng der hoheren Vist-Epoche Ablagerungen von kiistenfernen Karbonatsandbanken in flachem Wasser...