Stratigraphy, palaeoenvironments and geochemistry across the Triassic-Jurassic boundary transition at Carnduff, County Antrim, Northern Ireland

The latest Triassic to earliest Jurassic transition has been widely studied due the occurrence of a major global extinction associated with a global hyperthermal event in this interval. Furthermore, a number of distinct geochemical events in the global carbon cycle can be recognised in the stable-isotope record across this boundary interval at many localities. Two fully-cored boreholes from East Antrim in Northern Ireland (Carnduff-1 and Carnduff-2) have penetrated sediments of latest Triassic to Early Jurassic age (Rhaetian to Early Sinemurian). Ammonites, foraminifera, ostracods and palynomorphs provide a robust chronology as well as insights to palaeoenvironmental conditions during this period. The sedimentary and palynological evidence support a largely marginal-marine setting for the sediments of the Triassic Penarth Group while a range of palaeontological evidence shows that the Early Jurassic Waterloo Mudstone Formation represents shallow-marine, shelf conditions that represent generally well-oxygenated bottom waters, with little evidence for dysoxia. Detailed ammonite biostratigraphy (ammonites first occur about 7.5 m up from the base of the Lias Group) indicates that the cores represent largely continuous sedimentation through the Hettangian and earliest Sinemurian (to Turneri Chronozone, Birchi Subchronozone). Stable-isotope analysis of both carbonate and organic carbon show a distinct carbon isotope excursion (CIE) in both fractions through the Cotham and Langport members (Lilstock Formation, Penarth Group, latest Triassic) which are considered to correlate with the distinctive 'Initial' CIE witnessed in SW England and probably the GSSP and other sites across the world. (C) 2020 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.

Automated summary

The passage discusses the major global extinction event associated with a global hyperthermal event during the Triassic to Jurassic transition, as well as distinct geochemical events in the global carbon cycle. It also highlights the paleontological evidence from fully-cored boreholes in Northern Ireland, providing insights into the sedimentary environments and continuous sedimentation through different geological periods.