An Ordovician age for the Muggort's Bay Lower Palaeozoic inlier, County Waterford, Ireland—the southernmost exposure of the Irish Caledonides

Abstract

The most southerly exposed Lower Palaeozoic strata in Ireland occur on the southwest coast of County Waterford along a 2.5 km long coastal section at Muggort's Bay where they are surrounded by Devonian rocks. Five formations can be distinguished which, in ascending order, are: the Ballycurreen, Carrickbrean, Rathnameenagh, Moanbrack and Killinoorin formations. The total thickness of the succession is over 1800 m. No macrofossils are present, but the lithologies are largely fine-grained turbidites and subordinate volcanic rocks which closely resemble the Ribband Group seen elsewhere in southeast Ireland and have previously therefore been classified with it. Palynological analysis was undertaken on 25 samples collected from Muggort's Bay, of which eight were productive. Diagnostic microfossils, comprising acritarchs, chitinozoans and scolecodonts, indicate an Early to Middle Ordovician age for both the Rathnameenagh and the Moanbrack formations. These ages confirm that the strata are part of the Ribband Group which elsewhere has been biostratigraphically dated as ranging from Mid-Cambrian to Mid-Ordovician. Reworked mid-Middle Cambrian acritarchs occur in the Moanbrack Formation and reworked late Middle to early Late Cambrian acritarchs in the Rathnameenagh Formation. Despite generally poor preservation of the organic matter, some 20 acritarch species have been distinguished. Among these, three species belong to the herein revised genus Retisphaeridium for which an emended diagnosis is proposed together with two new combinations, Retisphaeridium capsulatum (Jankauskas, 1976) Vanguestaine nov. comb. and Retisphaeridium pusillum (Moczydlowska, 1998) Vanguestaine nov. comb.

The Carbon Isotope Organic Geochemistry of Early Ordovician Rocks from the Annascaul Formation, County Kerry

“…Four other acritarch genera isolated from the Annascaul Formation, specifically Caldariola, Coryphidium, Cymatiogalea, and Stelliferidium, have been found in North African Ordovician sediments (Stricanne and Servais 2002;Todd et al 2000). One notes that, while this study revealed a marine origin for the palynomorph isolates of the Annascaul Formation, the technique employed here could be used to look for the first chemical evidence of terrestrial spores within palynomorph assemblages, possibly within the Middle or Late Ordovician sediments that are also abundant within Ireland (e.g., Bruck and Vanguestaine 2005).…”

Organic‐walled microfossils from the Kistedalen Formation, Norway: acritarch chronostratigraphy of the Baltic Miaolingian and evolutionary trends of placoid acritarchs

“…Forms with sutures without ornamentation included in Retisphaeridium are R. dichamerum , R. lechistanium , R. striatum , R. rugulatum and R. minimum . We have not followed the revision of Retisphaeridium by Brück &Vanguestaine (2005) because it does not discuss the problem of flattened species as taphonomic artefacts, which is especially important in Retisphaeridium .…”

“…5, figs 18, 19.2004 Retisphaeridium dichamerum Staplin, Jansonius & Pocock; Brück & Vanguestaine, p. 209, fig. 6, 3.2005 Retisphaeridium postae (Jankauskas) Brück & Vanguestaine; Brück & Vanguestaine, p. 533, fig. 6:1, 2.2008 Cristallinium ovillense (Cramer & Díez) Martin; Ghavidel‐Syooki & Vecoli, p. 103, pl.…”

“…4, figs 2, 8–16.2004 Cristallinium cambriense (Slavíková) Vanguestaine; Brück & Vanguestaine, p. 207, fig. 6, 1–2.2005 Cristallinium cambriense (Slavíková) Vanguestaine; Brück & Vanguestaine, p. 529, fig. 6, 1, 2.2006 Cristallinium cambriense (Slavíková) Vanguestaine; Albani et al ., p. 50, pl.…”

“…Furongian occurrences are generally represented by scarce and problematic material and based on a small number of samples. The great abundance of C. cambriense in the Miaolingian makes it especially sensitive to reworking, as evidenced by Brück & Vanguestaine (2005) in the Lower–Middle Ordovician rocks of the Rathnameenagh and Moanbrack formations in Ireland. We therefore conclude that although C. cambriense has been reported from the Lower Ordovician (Moczydłowska 1998) it cannot be ruled out that those are reworked forms.…”