The Silurian of North Galway and South Mayo

Silurian rocks are present in three successor basins that have no spatial and probably no temporal overlap. The southernmost Killary Harbour-Joyce country succession everywhere masks the contact between the Ordovician rocks of the South Mayo Trough and the Connemara Dalradian. It was deposited in c 5 m.y. from mid-Telychian (Late Llandovery) to Sheinwoodian (mid-Wenlock). The succession shows rapid deepening from terrestrial through shallow marine to a deeper water turbidite dominated package and then a subsequent shallowing. There are significant provenance changes throughout the succession and detrita that relate to source areas that are no longer extant. The Croagh Patrick succession was deposited on Ordovician rocks of the South Mayo Trough that had already been folded to form the open Mweelrea-Partry Syncline. This quartzose succession of Laurentian provenance is poorly dated but is probably Llandovery. It is of shallow marine origin with some indications of more offshore conditions to the west and is strongly deformed. The northernmost Louisburgh-Clare Island succession is non-marine and rests unconformably on the Clew Bay Complex and is in faulted contact with the Croagh Patrick succession. The lower part is of Ludlow or Pridoli age. It is not currently possible to delimit the geometry or extent of any of the depositional basins in which these three disparate successions formed.