Aeolian sediments in the late Devonian of the Scottish Midland Valley

Abstract

The late Devonian and early Carboniferous strata of Central Scotland have recently been reclassified by Paterson and Hall (1986). Following their nomenclature, the term Stratheden Group (Figs. 1,2) is applied to strata above the basal unconformity and below the cornstone-bearing beds (Kinnesswood Formation) that mark the base of the succeeding Inverclyde Group. The Stratheden Group thus includes the lower and middle divisions of the Upper Old Red Sandstone of Bluck (1978, fig. 12) but excludes the upper division, sandstones-with-cornstones, which equates with the Kinnesswood Formation. In the new classification, as in the old, the units are lithostratigraphical and their boundaries are not time-planes. There is an implication, however (Paterson and Hall 1986, p. 7), that the onset of the cornstone-bearing facies took place near the Devonian-Carboniferous boundary, and that the Stratheden Group is therefore of late Devonian age. The palaeogeography of late Devonian times is generally considered to have been dominated by eastward-flowing rivers, with some aeolian input from outside the depositional basin (Bluck 1978, fig. 15: lower and middle divisions; Read and Johnson 1967, p. 264). However, the relative importance of the aeolian component in this concept has been increased by the recognition that the highest unit of the Stratheden Group in Fife (Knox Pulpit Formation) is of aeolian origin (McAlpine 1978, pp. 259–64; Mader and Yardley 1985, pp. 213–18), not shallow marine as had previously been supposed (Chisholm and Dean 1974, p. 24). In the Knox Pulpit Formation Mader and Yardley recognised the presence of cross-bedded . . .