Abstract

Vitrinite reflectivities from Lower Old Red Sandstone (ORS) sediments of the Strathmore region in the Midland Valley of Scotland give values of 1.2% for the Stonehaven Group (Kincardineshire), 0.9% for the Arbuthnott Group (Angus) and 1.3% for the Strathmore Group (Perthshire). These values are corroborated by clay mineral diagenesis studies. The Stonehaven Group reflectivity values are considerably lower than expected under the 9 km thickness of sediments aggregated for the Lower Old Red Sandstone of Kincardineshire and demonstrate a maximum burial of some 3 to 5 km. These results together with detailed vitrinite reflectivity measurements in the Dundee Formation, consideration of post-Devonian burial history and kinetic burial modelling, show that the present level of Lower ORS thermal maturation results from Late Carboniferous maximum burial. This is confirmed by comparison with a vitrinite reflectivity gradient from the Strathclyde Group of Fife.

To reconcile the vitrinite reflectivity data with the stratigraphy and structure of the Lower Old Red Sandstone, burial models invoking structural repetition, depocentre migration and structurally assembled stratigraphy are considered. It is concluded that the Lower Old Red Sandstone is a structurally assembled series of basins with the Cowie Formation of the Stonehaven Group being part of a separate depositional succession and structurally juxtaposed into its present position as part of an apparently contiguous sequence.

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