PALEOMAGNETIC AND GEOCHRONOLOGICAL STUDY OF A GEOMAGNETIC-FIELD REVERSAL OR EXCURSION RECORDED IN PLIOCENE VOLCANIC-ROCKS FROM GEORGIA (LESSER CAUCASUS)
P. Camps et al., PALEOMAGNETIC AND GEOCHRONOLOGICAL STUDY OF A GEOMAGNETIC-FIELD REVERSAL OR EXCURSION RECORDED IN PLIOCENE VOLCANIC-ROCKS FROM GEORGIA (LESSER CAUCASUS), Physics of the earth and planetary interiors, 96(1), 1996, pp. 41-59
A 250-m thick volcanic sequence of some 63 Pliocene lava flows from Ge
orgia (Akhalkalaki plateau) which was previously thought to record the
Gauss-Matuyama reversal was re-studied in detail. About 400 oriented
cores were sampled along four sub-vertical sections partially overlapp
ing each other. At the base of the section, 16 consecutive lava flows
were found to record intermediate directions. The overlying flows are
all reversely magnetized. With the exception of the upper part of the
sequence, four groups of three to 11 consecutive lava flows with stric
tly the same paleodirection can be recognized. The location of the int
ermediate virtual geomagnetic poles (VGPs) does not correspond to that
of the VGP clusters previously proposed as indicating a long lasting
near dipole configuration during reversals. The field paleointensity i
s close to one fifth of the present field at the bottom of the section
and tends to increase uphill. Age determination (Ar-40/Ar-39) provide
s an estimate of 3.6 +/- 0.06 Ma, which leaves us with two possible in
terpretations: the transitional vectors could correspond either to an
excursion within chron 2Ar or to the upper (N-R) Cochiti-Gilbert rever
sal.