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Correlation of Mississippian (Upper Visean) foraminiferan, condonont, miospore and ammonoid zonal schemes, and correlation with the Asbian-Brigantian boundary in northwest Ireland

Cozar, P.; Somerville, I.D.; Mitchell, W.I.; Medina-Varea, P.. 2006 Correlation of Mississippian (Upper Visean) foraminiferan, condonont, miospore and ammonoid zonal schemes, and correlation with the Asbian-Brigantian boundary in northwest Ireland. Geological Journal, 41 (2). 221-241. 10.1002/gj.1036

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Abstract/Summary

The microbiota of the upper Viséan (Asbian-Brigantian) rocks in the Lough Allen Basin in northwest Ireland is analysed. The Middle Mississippian sequence studied extends from the upper part of the Dartry Limestone/Bricklieve Limestone formations of the Tyrone Group to the Carraun Shale Formation of the Leitrim Group. The rocks have been traditionally dated by ammonoid faunas representing the B2a to P2c subzones. The Meenymore Formation (base of the Leitrim Group) also contains conodont faunas of the informal partial-range Mestognathus bipluti zone. The upper Brigantian Lochriea nodosa Conodont Zone was recognized by previous authors in the middle of the Carraun Shale Formation (Ardvarney Limestone Member), where it coincides with upper Brigantian ammonoids of the Lusitanoceras granosus Subzone (P2a). Foraminifera and algae in the top of the Dartry Limestone Formation are assigned to the upper Cf6 Foraminifera Subzone (highest Asbian), whereas those in the Meenymore Formation belong to the lower Cf6 Foraminifera Subzone (lower Brigantian). The Dartry Limestone Formation-Meenymore Formation boundary is thus correlated with the Asbian-Brigantian boundary in northwest Ireland. For the first time, based on new data, a correlation between the ammonoid, miospore, foraminiferan and conodont zonal schemes is demonstrated. The foraminiferans and algae, conodonts and ammonoids are compared with those from other basins in Ireland, northern England, and the German Rhenish Massif. Historically, the Asbian-Brigantian boundary has been correlated with several levels within the P1a Ammonoid Subzone. However, the new integrated biostratigraphical data indicate that the Asbian-Brigantian boundary in northwest Ireland is probably located within the B2a Ammonoid Subzone and the NM Miospore Zone, but the scarcity of ammonoids in the Tyrone Group precludes an accurate placement of that boundary within this subzone

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1002/gj.1036
Programmes: BGS Programmes > Geological Survey of Northern Ireland
ISSN: 0072-1050
Additional Keywords: Visean, foraminiferans, algae, ammonoids, conodonts, miospores, biostratigraphy, Mississippian, late Viséan, Asbian-Brigantian boundary, NW Ireland
NORA Subject Terms: Earth Sciences
Date made live: 21 Aug 2007 16:12
URI: http://nora.nerc.ac.uk/id/eprint/184

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