Age and controls of ironstone deposition (Ordovician) North Wales

Trythall, R. J. B.; Eccles, Charles; Molyneux, Stewart G.; Taylor, William E.

doi:10.1002/gj.3350220505

Cited by 17 publications

(9 citation statements)

References 25 publications

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“…They are known to extend from the middle part of the Upper Cambrian (Martin and Dean 1988;Volkova 1990;Parsons and Anderson 2000) to the Ordovician. Cymatiogalea has been reported up to the Llanvirn (Servais 1991) and Stelliferidium up to the Llandeilo (Turner 1985;Trythall et al 1987). Acanthodiacrodium has also been reported from the Llandeilo (Turner 1985, as Actinotodissus) and also in the Ashgill (Molyneux et al 1996, as Actinotodissus).…”

Section: Samples Pb99/068 and Pb99/070mentioning

confidence: 98%

Acritarchs from the Lower Palaeozoic succession on the south County Wexford coast, Ireland: new age constraints for the Cullenstown Formation and the Cahore and Ribband Groups

Bruck

Vanguestaine

2004

Geological Journal

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Lower Palaeozoic sediments crop out on the southern coast of County Wexford, Ireland, comprising three distinctive lithostratigraphical units: from west to east the Cahore Group, the Blackhall Formation of the Ribband Group and the Cullenstown Formation. The three units are largely devoid of macrofossils and thus their ages have to date been uncertain and, in the case of the Cullenstown Formation, speculative. In the Cahore Group, a diverse assemblage of acritarchs composed of seventeen species has been recorded indicating a middle Early Cambrian age. This is similar to the age of the lithologically identical Bray Group to the north, in County Wicklow. In the Ribband Group, two very distinct assemblages have been noted. Both are poorly preserved, but diagnostic species have been determined giving a biostratigrapical range of early Mid‐Cambrian to Llanvirn. Palynomorphs have been recorded for the first time from the Cullenstown Formation allowing comparison with eastern Newfoundland where a similar, less diverse assemblage has been recorded. The age indicated is latest Mid‐Cambrian to early Late Cambrian. Overall, despite generally poor preservation of the organic matter, some 45 acritarch species have been distinguished, among which one new combination is proposed: Retisphaeridium postae instead of Cymatiosphaera postae. Copyright © 2004 John Wiley & Sons, Ltd.

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Section: Samples Pb99/068 and Pb99/070mentioning

confidence: 98%

Acritarchs from the Lower Palaeozoic succession on the south County Wexford coast, Ireland: new age constraints for the Cullenstown Formation and the Cahore and Ribband Groups

Bruck

Vanguestaine

2004

Geological Journal

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“…These horizons are penecontemporaneous with other ironstone beds in eastern North America, southwestern Europe and North Africa (Young, 1989;Young et al, 1989;Woodcock, 1990;Young, 1992;Young et al, 2002;Todd et al, 2019), which also accumulated along the margins of the Rheic Ocean. Research herein focuses on the Darrwilian Hen-dy-Capel Ironstone Member of the Tygarn Formation (Figure 3; Trythall et al, 1987;Young et al, 2002) because it provides the clearest window into ironstone depositional processes. Unlike other ironstone horizons in Wales, the Hen-dy-Capel Ironstone Member is well-exposed in old mining adits and quarries.…”

Section: General Geology and Stratigraphymentioning

confidence: 99%

“…In upwelling-related ironstone, the absence of a diverse assemblage of carbonate-producing organisms and abundance of sponges with siliceous spicules is consistent with this relationship. In the Welsh Basin, sponges, phosphatic brachiopods, and trilobites (Trythall et al, 1987) apparently flourished in waters too acidic to support a healthy carbonate community. The absence of carbonate skeletons in nutrient-rich environments may also reflect a dysoxic seafloor and dissolution associated with the microbial respiration of accumulating organic matter (James et al, 2005).…”

Section: Paleozoic Ironstone Ocean Chemistry and Evolutionmentioning

confidence: 99%

Middle Ordovician Upwelling-Related Ironstone of North Wales: Coated Grains, Ocean Chemistry, and Biological Evolution

et al. 2021

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Middle Ordovician phosphatic ironstone of the Welsh Basin provides new insight into the paleoenvironmental significance of ironstone and Ordovician ocean chemistry. Deposition occurred in a back-arc basin along the southern margin of Avalonia as the Rheic Ocean opened to the south. Ironstone is interpreted to have accumulated as part of an aggradational parasequence on a storm-dominated shelf with coastal upwelling. This parasequence has a laminated pyritic mudstone base that grades upward into variably bioturbated mudstone and coated grain-rich, intraclastic ironstone, which is overlain in turn by cross-stratified grainstone composed entirely of coated Fe grains. A coarser clastic parasequence composed of more proximal lithofacies rests conformably above and suggests the contact between the two parasequences is a maximum flooding surface marking the onset of highstand conditions. Lithofacies associations suggest that sustained coastal upwelling created a wedge of nutrient-rich, ferruginous seawater on the middle shelf that stimulated high surface ocean productivities. Large, coated Fe grains (granule size) composed of discontinuous and concentric carbonate fluorapatite, hematite, and chamosite cortical layers record fluctuations in pore water Eh that are interpreted to have been related to changes in upwelling intensity and intermittent storm reworking of the seafloor. Results support an emerging model for Ordovician ironstone underpinned by the development of ferruginous bottom water that was periodically tapped by coastal upwelling. Expanding, semi-restricted seaways such as the Rheic Ocean were ideal locations for the ponding of this anoxic, hydrothermally enriched seawater, especially during the early Paleozoic when the deep ocean was variably and inconsistently oxygenated. The coincidence of ironstone depositional episodes with graptolite diversification events suggests that, in addition to Fe, the sustained supply of upwelling-related P may have driven the radiation of some planktonic ecosystems during the Great Ordovician Biodiversification Event. Concomitant minor extinctions of benthic trilobites occurred as these ferruginous waters impinged on the shelf.

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“…1) and Micrhystridium aff. acuminosum (18) (Molyneux 1987;Molyneux & Rushton 1988;author's unpublished data).…”

mentioning

confidence: 99%

“…G . MOLYNEUX recognized (Molyneux 1987). However, stratigraphical coverage has to be improved to ascertain the range of each assemblage and to determine whether additional assemblages are present.…”

mentioning

confidence: 99%