Cornstone (Fossil Caliche): Its Origin, Stratigraphic, and Sedimentological Importance in the New Red Sandstone, Western Scotland

An examination of more than 200 cornstone (concretionary carbonate) profiles of New Red Sandstone age, in western Scotland, confirms that these carbonate accumulations are analogues to the caliche of semi-arid areas. New evidence of laminated, pisolitic and brecciated textures from the cornstone "caprock" strongly suggests that downward percolating water and non-tectonic fracturing were important during subaerial diagenesis. The cornstones occur preferentially in floodplain deposits, and particularly within the upper parts of alluvial, fining-upwards cyclothems. The occurrence of cornstones in this part of the cyclothems and their persistence through such cyclothemic sequences suggest, contrary to a commonly accepted hypothesis, that climatic controls are important in the formation of such alluvial sequences. The cornstones are stratigraphically more significant than the associated rock types in the monotonous New Red continental sequences. In particular, thick, mature cornstones indicate condensed sequences and are also a useful palaeoclimatic index, such caliche normally forming in semi-arid regions.