A palaeomagnetic and palaeointensity study of the Mauchline lavas, south-west Scotland

The Mauchline lavas of SW Scotland erupted close to the Carboniferous-Permian boundary and near the middle of the Permo-Carboniferous Reversed Superchron (PCRS). Rock magnetic studies have identified mixed magnetite-hematite assemblages; both minerals record reversed components of magnetisation. A fold test is not diagnostic but the mean remanence recovered in 23 stable samples at five sites (D/I = 192.5/-26.1 degrees, alpha(95) = 14.3 degrees) accords with the regional field at the time of eruption and the pole position (346.8 degrees E, 47.2 degrees S) is coincident with late Carboniferous-Early Permian poles. A palaeointensity study of 15 samples employing the modified Thellier-Thellier method yields nine acceptable estimates of ancient field intensity with a mean value of 13.6 +/- 4.5 mu T from four lava flows. The corresponding virtual dipole moment of 3.3 x 10(22) Am-2 is approximately 40% of the present day value. This result supports recent studies from western Europe which suggest that the geomagnetic field strength was low during the PCRS but is in conflict with Russian data which suggest that the field strength was close to, or slightly higher than the present day value.