Equilibrium and response to climatic and tectonic forcing: a study of alluvial sequences in the Devonian Munster Basin, Ireland

The Upper Palaeozoic Munster Basin is characterised by thick (>6 km), Late Devonian alluvial successions (the Old Red Sandstone) that were well exposed throughout southwest Ireland. These represent the deposits of large-scale, complex terminal fan systems which operated under a semi-arid climate. The application of the estimated sediment accumulation rate to the three most prominent cycle thicknesses (31-175 m) and the assessment of relative frequencies has been used to establish the approximate cycle periodicities, all of which appear to lie within the Milankovitch Band. It is suggested that these features represent the stratigraphic expression of climatic perturbations related to orbital forcing (particularly eccentricity variation). It is further suggested that the recognition of these cycles throughout the basin-fill may, in future, form the basis of high resolution relative timescale and allow the correlation of proximal and distal sections through the basin-fill at scales comparable to the high frequency cyclicities (c. 40 m). -from Authors