A palaeointensity study of Lower Carboniferous transitional geomagnetic field directions: the Cockermouth lavas, northern England

Abstract

Palaeomagnetic and palaeointensity results are reported from a thin succession of lavas erupted in Lower Carboniferous times (ca. 355 Ma) in northern England. Characteristic magnetisations were apparently acquired at the time of eruption but the stable (normal) field direction is recovered from only two sites out of seven. The remainder are not compatible with younger overprinting and are interpreted as thermo remanent magnetisations (TRMs) recording transitional fields. Palaeointensity studies employing the Shaw method identify main field intensities averaging 20.8 μT within the range of estimates of the Lower Carboniferous field intensity from studies elsewhere. In contrast, the lavas recording transitional field directions yield palaeointensity estimates which fall mostly between 10 and 20% of this value. Hence it is inferred that Palaeozoic field inversions were, like Recent examples, characterised by a general decline in the intensity of the field.