A foreland basin on the southern margin of Iapetus

The Windermere Group basin was situated on the northwestern margin of Eastern Avalonia, dose to the suture with Laurentia. Sediment accumulation rates within the basin, estimated using a graptolite time-scale, show a history of accelerating subsidence through the mid- to late Silurian, with rates exceeding 1mm per year in the Ludlow. The characteristic subsidence curve, high sedimentation rate, and lack of syndepositional extensional faulting or basic magmatism indicate a foreland basin. The basin was generated by subduction of Avalonian continental crust beneath Laureutia from the mid-Wenlock onwards, which resulted in a slowing of continental convergence. Further slowing occurred towards the end of the Silurian.