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| Titel |
Holocene paleoenvironmental records of Lake Van (eastern Turkey) from mineral magnetic analysis |
| VerfasserIn |
Ozlem Makaroglu, Naci Orbay, Namik Cagatay, Lauri J. Pesonen, Sena Akçer Ön, Umut B. Ulgen, Mumtaz Hisarli |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053268
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| Zusammenfassung |
| We present the results of mineral magnetic measurements (Ï, SIRM, ARM, NRM) and
geochemical XRF Core Scanner elemental analysis from four cores located in water depths of
60-80 m in different parts of Lake Van, eastern Turkey. Lake Van is the fourth largest terminal
Lake in the world by volume (607 km3). It is 460 m deep and has a salinity of 21.4 per
mil and a pH of 9.81. It is located on the East Anatolian Plateau with present day
water level of 1648 m.a.s.l., and surrounded by Quaternary Volcanoes (Nemrut and
Süphan) to the west and north, and the Bitlis metamorphic rocks to the south. It
has accumulated varved-sediments with tephra units, which all provide important
paleoenvironmental records. The sediments extending back to 14570 a BP have been
previously dated by varve counting (Landman et al., 1996). We have correlated our
cores with the varve-dated cores of Landmann et al (1996) using the tephra units.
Our cores extend back to 9.5 ka BP (varve years). We also obtained 10 AMS C-14
ages from total organic carbon in our cores, which indicate reservoir ages ranging
from 2600 to 4275 a; the reservoir ages generally increase with the varve age of the
sediments.
Downcore profiles of all magnetic properties are highly correlatable between different
cores, suggesting that the magnetic records are related to basinwide environmental changes
rather than local effects. The magnetic properties of the cores are predominantly controlled
by detrital paramagnetic minerals, with some contribution from small amount of
ferrimagnetic minerals, all of which are derived from the catchment area. The tephra layers
originating from Nemrut and Süphan volcanoes are characterized by strong ferrimagnetic
minerals and high Zr, K, Si and Zn values. Downcore variation of magnetic properties and
some geochemical elemental profiles (e.g., Fe, Ti, Zr, Ni, Ca) show good correlation
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The SIRM/Ï and Mn profiles show wide variation during the last 3.5 ka suggesting
significant redox changes. During the same period, high HIRM and ÏARM/SIRM values
indicate an increase in delivery of fine-grained detrital material. Low HIRM values and high
ÏARM/SIRM values during period 7.2-3.5 ka BP, show further decrease in the grain size of
magnetic minerals. There is sharp change in the in all magnetic properties, but especially in
HIRM and ÏARM/SIRM, before 7.2 ka BP, indicating drastic increase in coarse magnetic
minerals, which correlates well with high Zr and Ni values during the same interval. These
results indicate high, but variable lake levels during the last 3.5 ka; still higher
lake levels during 7.2-3.5 ka BP, and considerably low lake levels prior to 7.2 ka
BP.
This work was supported by Scientific Research Projects Coordination Unit of Istanbul
University. Project numbers: 1228 and 2475.
Referances:
Landmann, G., Reimer, A., Lemcke, G., Kempe, S., 1996b. Dating Late Glacial abrupt
climate changes in the 14,570 yr long continuous varve record of Lake Van, Turkey.
Palaeogeography, Palaeoclimatology, Palaeoecology 122, 107–118. |
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