Tectonic control on sedimentation during transgression: a case study from Silurian successions in Ireland and Scotland

Abstract

The Silurian succession of North Galway is relatively well constrained in terms of environmental analysis and, in its lower half, palaeontologically. The initiation of a late Llandovery marine transgression can be demonstrated over fluviatile red sandstones. The deposition of shallow-water conglomerates at the base of a turbidite sequence within the succession indicates the long-lived presence of a channel system that was probably fault controlled. The back-stripping method allows a subsidence curve to be constructed for this succession. It demonstrates an initial period of rapid rift-related subsidence followed by a short-lived hiatus that may be due to the cessation of subduction in this part of the Caledonides. A comparison of the Galway subsidence curve with that of the Silurian succession at Girvan in Scotland shows strong, but diachronous, similarities. This tends to support an earlier suggestion that they formed part of a single but partitioned basin throughout most of the Silurian period. Although the eustatic fall in sea level at the Llandovery–Wenlock boundary can be recognized, the influence of tectonic regime and sedimentation rates were the controlling factors in determining relative sea levels.