The environmental significance of some faunal changes in the Upper Ardmillan succession (upper Ordovician), Girvan, Scotland

Summary A series of discrete, distinctive faunules has been established for the Upper Ardmillan succession in the Girvan district. The faunules, collected from a diverse suite of clastic sedimentary rocks in a well defined stratigraphical framework, belong to the Whitehouse Group, the Shalloch Formation, the Drummuck Group, and the High Mains Formation; these rock units range in age from late Caradoc (Onnian) to late Ashgill (Hirnantian). The brachiopod associations identified within each faunule are outlined; few are considered indigenous. The series of faunal changes is fundamental to the assessment of the depositional environment of the sequence. The changing composition and structure of the brachiopod associations appear to reflect deposition in a predominantly unstable and often turbulent offshore continental slope environment. The faunal and sedimentary evidence supports the existence of a submarine fan throughout at least much of Upper Ardmillan times at Girvan.