Early Devonian (pre‐Acadian) magnetization directions in Lower Old Red Sandstone of south Wales (UK)

Abstract

Two components of magnetization have been resolved from the Lower Old Red Sandstone of south Wales. All 39 sampled sites lie north of the Variscan front, and all but three are largely unaffected by Variscan folding. Thirteen sites yield a high unblocking temperature magnetization component which pre‐dates Acadian (mid‐Devonian) folding. The site mean direction for this component (Dec.: 232.2°, Inc.: 31.9°, α95: 8.5°) yields a pole position (Lat.: 7.3°S, Long.: 306.7°E) which can be assigned an Early Devonian age. A lower unblocking temperature component is present at 38 of the sampled sites. This component post‐dates both the Acadian and Variscan folding, has reversed polarity and a mean direction (Dec.: 193.8°, Inc.: −7.2°, α95: 2.6°) which corresponds to a pole position (Lat.: 40.4°S, Long.: 338.0°E) consistent with a latest Carboniferous or early Permian age. The Early Devonian pole position confirms the existence of a Siluro‐Devonian inflexion in the apparent polar wander path (APWP) for southern Britain which coincides with an inflexion in the APWP for Scotland (Britain north of the Iapetus suture), indicating the closure of the Iapetus Ocean by Siluro‐Devonian time. The Early Devonian palaeolatitude (17°S ± 5°) is consistent with an Early Devonian configuration in which Gondwana, Laurentia, Baltica and Avalonia were part of a single supercontinent. Copyright © 1992, Wiley Blackwell. All rights reserved