Compressional Structures (Patterned Ground) in Devonian Pedogenic Limestones

Abstract

The Old Red Sandstone (Devonian) of Wales and the Welsh Borderland abounds in carbonate-rich rocks loosely named cornstones. These are typically associated with thick red siltstones which commonly add to the upper fine-grained members of fining-upward cyclothems^1–5. Fluviatile conditions explain the cyclothems⁶, the fine-grained members denoting a range of floodplain environments, and the lower coarse-grained members the channels. Here I draw the attention of geologists and soil scientists to the strong likelihood that the carbonate-rich rocks are pedogenic (palaeosols), comparing with carbonate-rich (calcretized) horizons in certain soils of modern sub-humid to arid regions, and point out that some of the beds, like a number of their modern counterparts, show forms of patterned ground (? gilgai). Very probably the Old Red Sandstone accumulated in hot sub-humid to arid climates under conditions of strongly seasonal rainfall.