Aspects of the palaeoecology and palaeoenvironmental setting of Waulsortian carbonate buildups in Ireland

Abstract

The aim of this project has been to elucidate further aspects of the palaeoecology and palaeoenvironmental setting of the Waulsortian facies which developed in Ireland during the late Dinantian. Various techniques have been employed to this end, although work has tended to focus on the sedimentological characteristics of the limestones and the vast wealth of palaeoecological information which is recorded by the fauna associated with these carbonate buildups. In particular, the taphonomy of those organisms actually preserved has provided valuable information concerning the likely surface conditions which would have been present during the accumulation of typical Waulsortian buildups. The development of the Waulsortian facies in Ireland has been investigated and this appears to have been closely associated with cyclically rising sea levels which transgressed the southern margin of the Laurussian continent during the Tournaisian. Conodont biozonation has shown that the northward passage of this transgression is reflected in the diachronous initiation of the facies across Ireland. In most places growth was restricted to the late Tournaisian, although the facies appears to have been slighdy longer-lived in the south and southwest of Ireland, where it clearly extended into the Viséan. It has been suggested that the development of a microbial mud-mound facies at this time may have represented a disaster form which filled the frame-building role during a period of reduced metazoan competition, following an apparent reduction in the availability of many previously important framework reef taxa during the latter stages of the Devonian.