A record of a stable transitional VGP in a Pliocene lava flow sequence from the Lesser Caucasus

Abstract

A paleomagnetic and paleointensity study has been performed on 28 basaltic flows from a sequence in the Lesser Caucasus. Two radiometric determinations yielded 3.45 ± 0.23 Ma in its lower and 3.43 ± 0.19 Ma in its upper part. Paleomagnetic determinations in the lower section (14 flows) yielded an anomalous direction D = 252.8°, I = 43.1°, (α95 = 3.7°), reflecting a transitional record. In the upper section (14 flows), a reverse polarity direction D = 185.8°, I = − 53.1°, (α95 = 2.3°) was obtained. Analysis of the scatter in paleomagnetic directions suggests that the stable anomalous direction observed throughout the lower section might have persisted for several centuries. Thellier–Coe paleointensity experiments on 165 specimens produced only 7 successful determinations. Very low paleointensity values below 10 μT were obtained in the lower, and stronger ones (35 and 50 μT) in the upper flows. Application of a pTRM-check correction to the data resulted in an important increase of successful determinations (78) and a significant intra- and inter-flow coherence of results, confirming very low paleointensities in the lower section and stronger ones in the upper flows. 20 paleointensity determinations with the multispecimen method produced results in 16 samples (13 flows). A multimethod analysis combining results of both methods yielded paleointensities between 5.4 and 12.5 μT in the lower flows, reflecting a transitional field. The upper flows produced a mean paleointensity B = 40.9 ± 9.4 μT. The sequence seems to record the C2An.3n–C2An.3r (Gauss–Mammoth) reversal at 3.330 Ma.