The stratigraphy of latest Devonian and earliest Carboniferous rocks in Ireland
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ORIGINAL PAPER
The stratigraphy of latest Devonian and earliest Carboniferous rocks in Ireland John R. Graham 1 & George D. Sevastopulo 1 Received: 27 May 2020 / Revised: 20 August 2020 / Accepted: 8 September 2020 # Senckenberg Gesellschaft für Naturforschung and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Thick successions of latest Devonian and early Carboniferous siliciclastic rocks of fluviatile and shallow marine origin are well exposed in numerous coastal sections in the south of Ireland. Correlations based on palynostratigraphy demonstrate that an overall northward transgression, in detail consisting of several fluctuations of relative sea level, resulted in the replacement of fluvial coastal plain environments by shallow marine conditions. The most conspicuous lithological record of transgression occurred at or close to the base of the Carboniferous, when a regionally distributed mudstone deposited in a shallow sea, replaced the generally sandy strata that had prevailed in the latest Devonian. There is no evidence for very large glacioeustatic changes of sea level related to the coeval western Gondwanan glaciation. Of the three horizons for a new GSSP for the base of the Carboniferous currently under review, the base of the Protognathodus kuehni Zone/basal Siphonodella sulcata Zone and coastal plant extinction is the most easily applied in Ireland and can be identified using palynology and corresponds to an easily recognised, extensively developed lithological change in the south of the country. Keywords Palynostratigraphy . Glaciation . Sea level . Hangenberg . Famennian . Tournaisian
Introduction Latest Devonian and earliest Carboniferous rocks are well exposed along the rocky coastline of south and southwest Ireland. They are also seen in inland natural exposures and quarries and have been proved in boreholes further north. Research on the stratigraphy, sedimentology and biostratigraphy of these sections over the past 60 years, summarised by Clayton et al. (1981), Graham (2009a) and Sevastopulo and Wyse Jackson (2009), has established that the successions in the south of Ireland are exceptionally thick in comparison with coeval successions elsewhere in western Europe; that the rocks represent fluviatile and shallow marine environments; and that despite high levels of organic maturation (Clayton 1989), a well-resolved palynological biostratigraphical framework provides correlations that allow detailed analysis of the This article is a contribution to the special issue “Global review of the Devonian-Carboniferous Boundary” * George D. Sevastopulo [email protected] 1
Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland
changing palaeoenvironments. These exceptionally thick successions provide an opportunity to analyse the far-field effects of the Late Devonian glaciation reported from western Gondwana (Caputo 1985; Isaacson et al. 1999, 2008; Caputo et al. 2008) in terrestrial/shallow marine settings and to evaluate the changes in sea level
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