Carbon isotopes, ammonites and earthquakes: Key Triassic-Jurassic boundary events in the coastal sections of south-east County Antrim, Northern Ireland, UK

Abstract

A continuous succession of marine and marginal-marine sediments of Rhaetian (Late Triassic) and Hettangian (Early Jurassic) age is present in the Larne Basin in Northern Ireland. These strata cover a period in Earth's history that included the emplacement of the Central Atlantic Magmatic Province (CAMP), the End Triassic Mass extinction (ETE), the Triassic–Jurassic Boundary (TJB), and major perturbations in the global carbon cycle. The Waterloo Bay section in the Larne Basin offers a well exposed sedimentary succession that spans this interval, and it has previously been proposed as a candidate GSSP for the base of the Jurassic System. A high-resolution δ13Corg and organic carbon record for this locality is presented here, with these new data tied to previous stratigraphic descriptions, ammonite biostratigraphy, atmospheric carbon dioxide concentration (pCO2) estimates, and nearby borehole sections that do not suffer from the thermal alteration that has affected the Waterloo Bay section. Several new exposures, unaffected by thermal metamorphism, are described that could provide future palynological and micropalaentological studies across this important boundary interval. Correlation is established between the well-studied sections in north Somerset and the likely position of the TJB in the Larne Basin, and records of soft sediment deformation, synsedimentary fault movement, relative sea-level change and their likely causes are discussed.