Magnetostratigraphy of Plio-Pleistocene Lake Sediments from Armenia (Magnetostratigraphie Plio-Pleistozäner Seesedimente aus Armenien)
Final Report Abstract
The Pleistocene geology of Armenia is dominated by the widespread occurrence of lake sediments testifying repeated rapid and drastic changes of the environmental conditions during at least the last 2 million years. These sediments contain a huge variety of various fossil remains in turn providing valuable information on fauna and flora as well as the climatic conditions during the last 2 Ma. Since findings of Homo georgicus at Dmanisi, dated as 1.8m.a. in age, reconstruction of the paleoenvironment of the Caucasus region at this time has become critical for our understanding of early hominin migration along a corridor connecting Eastern Africa and Eurasia via the Middle East and the Caucasus region. However, whereas the Dmanisi findings seem to be well dated on both, radiometric and magnetostratigraphic data, the situation in Armenia is less clear. At the start of the project, only one absolute age was available for the diatomite sequences at Vorotan despite the fact that absolute ages are of crucial importance for a reliable reconstruction of climate evolution during time. This age has been derived from a basalt flow overlaying the lacustrine diatomites and ranges from 1.2 to 0.935 Ma according to different authors. No absolute age data were available for the underlying diatomites themselfes opening the door to various interpretations of their absolute age. Addressing this age debate, a detailed magnetostratigraphic study has been carried out in the Vorotan river area near the town of Sisian, where approximately 500 orientated one inch drill cores, have been obtained. Sampling covered 6 sections with roughly 170 meters in total stratigraphic thickness. A detailed paleomagnetic analysis reveals the presence of a zone of normal polarity within the sequence which is dominated by inverse magnetizations. The zone of normal magnetization, in five of the eight sections studied is interpreted to represent the Jaramillo subchron of positive polarity within the Matuyama chron of inverse polarity. Thus this work represents a major step forward in assigning absolute ages to the sequence. In addition, the extremely high quality of the material provides important contributions for correlation of these sediments on regional and global scales. Furthermore, detailed studies of the Normal to Reverse and Reverse to Normal transitions yielded valuable information with regards to the structure of the Earth's magnetic field shortly before, during and shortly after field reversals. A major outcome of this part of the project is the identification of rather high relative paleoinstensities of the Earth Magnetic Field during the reversal itself in combination with massive fluctuations in intensity as well as direction. This behavior has been identified in all sections studied AND is independent of the magnetic mineral inventory suggesting that we are dealing with a real geomagnetic phenomenon. However, the causes of these anomalously high relative intensities are not understood at all. Unfortunately, however, one of our original goals, to use rockmagnetic parameters as proxies for climate (change) could not be achieved.
Publications
- (2007) Magnetostratigraphy of Plio-Pleistocene Lake Sediments from Armenia American Geophysical Union, Fall Meeting 2007, abstract #GP43A-0928
Kirscher, U., Bachtadse, V., Bruch, A., Scharrer, S., Abdul Aziz, H.
- (2008) Early Pleistocene climate and vegetation change in Armenia based on pollen, leaves, fruits and seeds - the environment of early men in the Caucasus. Joint 12th International Palynological Congress and 8th International Organisation of Palaeobotany Conference, Bonn, Germany (Sept 2008), Terra Nostra 2008/2: 246-247
Scharrer, S., Bruch, A.A., Gabrielyan, I., Kirscher, U., Bachtadse, V.
- (2008) High Resolution Magnetostratigraphy from Plio-Pleistocene Sediments, Armenia, American Geophysical Union, Fall Meeting 2008, abstract #GP21A-0773
Kirscher, U.; Bachtadse, V.; Bruch, A. A.; Gabrielyan, I.
- (2011) Early Pleistocene climate and environmental change in Armenia – reconstructing temporal corridors of early human expansions. Geophysical Research Abstracts Vol. 13, EGU2011-286, 2011
Bruch, A.A., Scharrer, S., Gabrielyan, I.
- (2011) Magnetostratigraphy and Reversal Pattern of Pleistocene Lake Sediments from Armenia, American Geophysical Union, Fall Meeting 2011, abstract #GP23A-1031
Kirscher, U., Bachtadse, V., Bruch, A. A., Gabrielyan, I.
