Palaeomagnetism of the Sarclet Sandstone (Orcadian Basin): age perspectives

Abstract

Synopsis Palaeomagnetic results from the Sarclet Sandstone Formation, stratigraphically positioned near the base of the Old Red Sandstone (ORS) sequence of Caithness, suggest the presence of two different axes of magnetization, with Dec. 211, Inc. 33 and Dec. 191, Inc. 6 respectively. The most steeply inclined magnetization is in correspondence with results from Scottish Lower Old Red Sandstone volcanics indicating that the age of the Sarclet Sandstone dates from the topmost Silurian-lowermost Devonian. The abundant clasts of basalts in the underlying Sarclet Conglomerate give further substance to the notion that the Lower Old Red Sandstone volcanics, which have a wide distribution in central and southern regions of Scotland, also occurred in the Caithness/Moray Firth area. It is concluded therefore that the Orcadian Basin developed concurrently with the ORS basins of the Midland Valley and the Scottish Borders. It is inferred that the second magnetization (with shallow inclination) was imposed at around Middle Devonian, but owing to a relatively early silica cementation the Sarclet Sandstone was not susceptible to acquiring the “Permian” magnetization overprint that is strongly developed in the higher stratigraphic units of the Caithness Old Red Sandstone.