The sedimentology of sandstone formations within the Upper Old Red Sandstone and lowest Calciferous Sandstone Measures west of Stirling, Scotland

Synopsis Between Stirling and Fintry the beds between the Lower Old Red Sandstone and the Clyde Plateau Lavas fall naturally into four lithological formations named, from below upwards, the Gargunnock Sandstones, the Cornstone Beds, the Ballagan Beds and the Downie’s Loup Sandstones. All of these formations except the Ballagan Beds consist dominantly of sandstone and are thought to be fluvial deposits. The Ballagan Beds are alternating thin dolomites and mud-stones and are not dealt with in this paper. The Gargunnock Sandstones rest unconformably upon the Lower Old Red Sandstone. Apart from the basal conglomerates they are uniform, brick-red sandstones with few argillaceous beds and may possibly be the deposits of braided streams which carried detritus from a source area of wind blown sand. The Cornstone Beds and Downie’s Loup Sandstones closely resemble each other despite their being separated by a considerable thickness of Ballagan Beds. Both formations comprise a series of ‘fining-upwards’ cycles, each with a lower sandstone member which is commonly white and an upper siltstone or mudstone member which is commonly red and contains caliche-like cornstones. It is thought that these formations were deposited by meandering streams. Cross-strata dip samples from each formation show that all three were laid down by currents flowing dominantly from the north and west. Statistical tests—chi-squared and Steinmetz’s (1962) method—show that only the sample s from the lower two formations are likely to belong to a single population.