Sedimentology and palaeogeography of the Upper Old Red Sandstone in the Scottish Border Basin

Abstract

Synopsis The Upper Old Red Sandstone of the southern Scottish Borders is a wholly fluviatile succession. The basal unconformity with the Silurian shows evidence of exhumed, ?pre-Upper O.R.S. topography. Facies association 1 comprises fining-up cycles of sandstone and siltstone deposited by high sinuosity stream systems. Facies association 2 comprises fining-up cycles deposited by low sinuosity streams which may have been braided or non-braided. Facies association 3 comprises conglomerates, pebbly sandstones and sandstones deposited by low sinuosity, braided stream channels. Facies association 4 comprises thick sequences of thinly bedded sandstones, siltstones and conglomerates laid down in persistent flood basins. Palaeocurrents show persistent stream flow from south west to north east and grain and pebble compositions are consistent with igneous and sedimentary sourcelands in Galloway. A gross upward trend to coarser, braided channel facies may have resulted from isostatic uplift in the hinterlands. The southern Border streams formed part of an interior drainage basin (Border Basin) with its centre to the north west of the present day Cheviot hills.