Triassic sand supply to the Slyne Basin, offshore western Ireland—new insights from a multi-proxy provenance approach

To assess provenance data and derive basin infill models with a higher level of certainty it is vital to understand how minerals used in sedimentary provenance behave in the sedimentary system. A multi-proxy methodology helps ensure rigour in how provenance data are interpreted. U–Pb geochronology of refractory zircon, relatively less stable apatite, and Pb isotopic analysis of labile K-feldspar, are employed in this study to re-assess the provenance of Triassic sandstones in the Slyne Basin, offshore western Ireland. This approach aims at reducing the potential bias in each method, producing a complementary dataset. U–Pb zircon and apatite geochronology yields Archaean– Palaeoproterozoic ages, Caledonian ages and previously unrecognised Permo-Triassic ages. Pb isotopic analysis of K-feldspar does not identify the Permo–Triassic as a source. The detection of Permo–Triassic aged detritus may suggest that volcanism was more widespread than previously recognised. These results support the hypothesis of a Triassic drainage divide between the basins offshore western Ireland versus those onshore Great Britain and in the Irish Sea. Sand supply was dominantly from the north, with significant input from the flanks of the basin, and previously unrecorded sources, such as Permian-aged rocks, playing an important role. The provenance signal is consistent and homogenised throughout the sampled sequence indicating that the drainage system was long-lived.