HR: 15:00h
AN: GP43A-05 INVITED     [Abstracts]
TI: Gilbert-Gauss geomagnetic reversal recorded in Pliocene volcanic sequences from Lesser Caucasus: Revisited
AU: * Gogichaishvili, A
EM: avto@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria, s/n, Mexico, 04510, Mexico
AU: Cervantes, M A
EM: miguelg@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria, s/n, Mexico, 04510, Mexico
AU: Rathert, M C
EM: mcalvo@ubu.es
AF: Departamento de Fisica, Universidad de Burgos, Av. Cantabria, s/n, 09006 Burgos, Burgos, Spain
AU: Camps, P
EM: camps@dstu.univ-montp2.fr
AF: ISTEEM, Université Montpellier 2 , Montpellier, 34095, France
AU: Sologashvili, J
EM: avto@geofisica.unam.mx
AF: Tbilisi State University, 3, Tshavtshavadze Av., Tbilissi, 380064, Georgia
AU: Maissuradze, G
EM: avto@geofisica.unam.mx
AF: Geology Institute, 9, Alexidze St, Tbilissi, 380009, Georgia
AB: We carried out a detailed paleomagnetic, rock-magnetic and Thellier paleointensity study of a ~ 3.6 My Pliocene lava flow succession from southern Georgia. Previous study (Camps et al. 1996, PEPI, vol. 96, pp. 41-59) revealed that several consecutive lava flows record an intermediate polarity direction at the base of the section followed by a thick reverse polarity zone. The transitional field was interpreted as an excursion within chron 2Ar or an upper Cochiti-Gilbert reversal. New paleomagnetic data reported in present study are obtained from nearby lava successions. This allowed the better knowing the nature and morphology of geomagnetic record. In total about 140 standard paleomagnetic cores belonging to 23 consecutive lava flows were obtained during the 2006 sample collection campaign. Rock-magnetic experiments show that the remanence is carried by Ti-poor titanomagnetite in most of cases. The fraction of grains with multidomain magnetic structure does not seem to be important. Characteristic remanent magnetization is successfully determined on all samples. The direct correlation with original (Thoki) sequence and field observations allowed to establish a new magnetic stratigraphy. The lower part of section is characterized by intermediate magnetic polarity followed by thick reversely magnetized lavas. The upper sequence, represented by 11 consecutive flows yielded normal magnetic polarity. The mean paleointensity of the intermediate field is 12.8 (2.7) microT (10 flows). The reverse polarity paleointensity is higher with a mean 27.3 (9.3) microT (22 flows) while normal polarity yielded in average 34.2 (6.8) microT. Considering all available radiometric ages and new paleomagnetic data it may be speculated that Gilbert-Gauss (R-N) reversal is recorded at the upper part of sequence. Lower intermediate polarity flows possibly represent a kind of precursor of this reversal similarly to Matuyama-Brunhes geomagnetic transition.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
DE: 1535 Reversals: process, timescale, magnetostratigraphy
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly