Biostratigraphy, sequence stratigraphy and gamma-ray spectrometry of the Tournaisian-Viséan boundary interval in the Dublin Basin

摘要

A study of three carbonate and carbonate-siliciclastic sections at the Tournaisian-Viséan (Tn-V) boundary in the Dublin Basin (Ireland), has been carried out using high resolution foraminiferal biostratigraphy and gamma-ray spectrometry. The aim was to identify the Tn-V boundary and trace correlatable log patterns in different environmental settings of the Dublin Basin. The foraminiferal fauna in the heterozoan and mixed heterozoan-photozoan (foramderm and bryonoderm extended) late Tournaisian shallow ramp facies and its calciturbidite products is taxonomically impoverished and resembles the similar impoverished foraminiferal associations of western Canada interpreted as reflecting upwelling zones. The increase of photozoan bioclasts which occurs in the latest Tournaisian is accompanied by the entry of important foraminiferal guides of the Tn-V boundary interval. The combination of biostratigraphic and spectral gamma-ray data proved to be a useful tool for the identification of the sequence boundary just below the Tn-V boundary across the different environmental settings of the Dublin Basin. The recognized sea-level fall is correlatable across the London Brabant Massif from western Ireland through to England, South Wales and Belgium.