HR: 1340h
AN: GP43A-0928    [Abstracts]
TI: Magnetostratigraphy of Plio-Pleistocene Lake Sediments from Armenia
AU: Kirscher, U
EM: uwe.kirscher@campus.lmu.de
AF: Ludwig-Maximilians-Universität München, Theresienstrasse 41, M 80333, Germany
AU: * Bachtadse, V
EM: valerian@lmu.de
AF: Ludwig-Maximilians-Universität München, Theresienstrasse 41, M 80333, Germany
AU: Bruch, A
EM: abruch@senckenberg.de
AF: Senckenberg Research Institute and Natural History Museum, Senckenberganlage 25, Frankfurt, 60325, Germany
AU: Scharrer, S
EM: sscharrer@senckenberg.de
AF: Senckenberg Research Institute and Natural History Museum, Senckenberganlage 25, Frankfurt, 60325, Germany
AU: Abdul Aziz, H
EM: haziz@geo.uu.nl
AF: TNO Built Environment and Geosciences, Princetonlaan 6, Utrecht, 3584 CB, Netherlands
AB: The Pleistocene geology of Armenia is dominated by the widespread occurrence of lake sediments which testify rapid changes of the environmental conditions during the last 2 million years. These sediments are perfectly suited for paleoenvironmental studies and yield various fossil remains, which allow to reconstruct flora and fauna as well as climatic conditions during dispersal of early man like homo georgicus (1.8 Ma) into Eurasia. Unfortunately, however, precise dating of these sequences is still a matter of debate and absolute ages for basalts directly overlying the lacustrine diatomites range from 1.2 to 0.935 Ma. Addressing the age debate, a detailed magnetostratigraphic study has been carried out in the Vorotan river area near the town of Sisian. A total number of 250 oriented drill cores have been obtained from 5 sections covering 75 meters in stratigraphic thickness. First results demonstrate the high quality of the sampled material and, after removal of a present day overprint at demagnetization temperatures of around 150° C, a stable component of magnetization can be identified in the majority of the samples. Magnetizations of both normal and reverse polarities have been determined. In cases where the magnetic spectrum could not be resolved due to overlapping blocking spectra, great circle analysis was applied successfully to identify the characteristic direction of the NRM. The resulting mean direction for both polarity components plots slightly to the west of the direction of the present day magnetic field at the sampling site and has an inclination value of 55° . A positive reversal test suggests the primary character of these magnetizations. Plotting the characteristic directions in stratigraphic order reveals that the lowermost 50m of the composite profile are of inverse polarity, followed by 20m of normal and 5m of inverse polarity. Based on these preliminary results, and in combination with existing radiometric data, we interpret the zone of normal polarity as the Olduvai normal subchron (1.778 - 1.945 Ma according to the Astronomically Tuned Neogene Time Scale, ATNTS04) within the Matuyama chron. These results provide an important correlation tool for the region and furthermore improve the dating accuracy of the sedimentary sequences in the Vorotan river area.
DE: 1520 Magnetostratigraphy
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting