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High Resolution Magnetostratigraphy and Radio-Isotope Dating of Early Pleistocene Lake

Kirscher, Uwe, Angela A. Bruch, Iwan Gabrielyan, S. Scharrer, K. Kuiper, and V. Bachtadse (2014), High Resolution Magnetostratigraphy and Radio-Isotope Dating of Early Pleistocene Lake, Quaternary Internationa, 328-329, 31-44, doi:10.1016/j.quaint.2013.06.010.

Abstract
The Pleistocene geology of Armenia is dominated by widespread occurrence of sediments recording
recurring rapid and drastic changes of the environmental conditions during at least the last 2 million
years. These sediments, predominantly diatomites, contain a huge variety of various fossil remains,
allowing the reconstruction of flora, fauna as well as the climatic conditions especially during dispersal of
early man into Eurasia 1.8 Ma. Radio isotope dating of pumice levels as well as a detailed magneto-
stratigraphic study have been carried out in Syunik Province near the town of Sisian, southern Armenia,
in order to establish a temporal correlation of all major outcrops of paleo-lake sediments and to provide a
timeframe for paleoenvironmental studies within this lake sediment succession.
A total of 455 oriented drill cores was sampled at six large and four short sections with a sampling
resolution between 5 and 20 cm. Detailed paleomagnetic experiments reveal the presence of a char-
acteristic remanent magnetization (ChRM) pointing either to the north and down or south and up. A
positive reversal test suggests the primary character of this magnetization component. Combining the
normal and reverse polarity directions results in an overall sample mean direction of D 1⁄4 354.8 , I 1⁄4 51.5
with a Fisherian precision parameter k of 14.6 and the associated a95 of 2.9 , combining demagnetization
data of 169 samples. In addition, ash layers were sampled for 40Ar/39Ar geochronology at five of the
sections studied paleomagnetically and three additional small outcrops. The resulting ages range be-
tween 1.31 Ma and 1.08 Ma, with two samples yielding w1.65 and 1.90 Ma. The latter are characterized
by extremely low abundances of radiogenic 40Ar, suggesting that the mineral system has not been closed
since the time of eruption, leading to substantial loss in Ar. Integration of these radio-isotope dates with
the polarity data suggests that the normal polarities can be linked to the Jaramillo subchron within the
Matuyama reversed polarity chron. Based on the longest interval of normal polarity identified at
Ashotavan-2, a lower limit for the sedimentation rate of w37 cm/ky can be estimated. Therefore, we infer
the duration of lake sedimentation as w350 ky, starting at w1.4 Ma.
BibTeX
@article{id1976,
  author = {Uwe Kirscher and Angela A. Bruch and Iwan Gabrielyan and S. Scharrer and K. Kuiper and V. Bachtadse},
  journal = {Quaternary Internationa},
  pages = {31-44},
  title = {{High Resolution Magnetostratigraphy and Radio-Isotope Dating of Early Pleistocene Lake}},
  volume = {328-329},
  year = {2014},
  doi = {10.1016/j.quaint.2013.06.010},
}
EndNote
%0 Journal Article
%A Kirscher, Uwe
%A Bruch, Angela A.
%A Gabrielyan, Iwan
%A Scharrer, S.
%A Kuiper, K.
%A Bachtadse, V.
%D 2014
%V 328-329
%J Quaternary Internationa
%P 31-44
%T High Resolution Magnetostratigraphy and Radio-Isotope Dating of Early Pleistocene Lake
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Printed 12. Dec 2019 06:27