Irish Carboniferous conodonts record maturation levels and the influence of tectonism, igneous activity and mineralization

Abstract

ABSTRACT Organic maturation patterns in the Lower Carboniferous of Ireland have been determined from conodont colour alteration indices (CAI) for some 750 localities. Onshore Ireland conodonts record increasing maturation in the Carboniferous rocks from the oil‐window rocks of the north‐east, southwards to the greenschist meta‐argillite regime of the Munster Basin. In detail the Caledonoid trend has a marked influence in the Midlands, whilst in the south sharp variations in CAI are interpreted as being caused by thrusting of the Variscan Orogeny. In the south‐east low maturities in the Wexford Half‐graben indicate that the region was shielded from orogenic stresses, probably by the Leinster Massif. Igneous centres such as the Carlingford Complex and Croghan Hill produce local sites of increased palaeotemperature. Significant CAI variations have also been noted in proximity to major base‐metal orebodies. The CAI results highlight north‐east Ireland and the Wexford Half‐Graben as areas with hydrocarbon potential.