The evolution of a thick shallow marine succession, the South Munster Basin, Ireland

The relatively fine-grained Late Devonian to Early Carboniferous 'Cork Beds' succession of the South Munster Basin includes continuous sections of paralic facies that are over 1000 m thick and individual sandstone units over 300 m thick. However, the succession does not reflect prolonged phases when facies belts were stationary, but rather multiple stacking of small-scale, high-frequency sequences, each associated with pronounced migration of shorelines. What seems to have been unusual about the South Munster Basin succession was that the geographical positioning of these high-frequency sequences was fixed. This resulted from an unusual combination of tectonics, shelf hydrodynamics, sedimentation rates and the textural maturity of the sediment within the basin. Of these, tectonics was probably most critical, particularly the juxtaposition of rapid subsidence in basinal areas and a basin margin zone (to the north) that was sufficiently up-standing to pin the maximum extent of transgression during repeated highstands of sea-level, yet not so upstanding as to have diverted the major regional drainage system. The embayed palaeogeography of the area may also have been influential.