Marine Geophysik und Hydroakustik

Lake Van, Turkey

 

Summary

Lake Van in Eastern Anatolia (Turkey) is the fourth largest terminal lake in the world with a surface area of 3,574 km², a volume of 607 km³, a maximum depth of 450 m, and a maximal length of 130 km WSW-ENE (Wong and Degens, 1978). Over 1500 km of multi-channel seismic reflection profiles in combination with ICDP drilling and bathymetric data from Lake Van, eastern Turkey, allow to reconstruct stratigraphic evolution of the lake basin. Three major basins (Tatvan, Deveboynu and the Northern basin) are separated from each other by Ahlat and Northern ridges. mehr

map
Bathymetry map of Lake Van basin and tracks of seismic surveys acquired in 2004 and 2012.

 

Seismic Interpretation of the sedimentary history

The sedimentary history of the lake was subdivided into19 distinct phases reflecting major environmental and depositional changes. Five major regressive and fourteen transgressive phases have been identified. Interpretation of seismic reflection and drill data from Lake Van reveal extensive details about the structure, stratigraphy, lake level fluctuations, and the evolution of the lake basin. Seismic data reveals the main structural features inside the lake, including the Northern basin, Tatvan basin, Ahlat sub-basin, and Deveboynu basin. These basins are separated by basement ridges such as Northern and Ahlat ridges. Seventeen seismic sequence boundary including the top of the acoustic basement (SB1 to SB17 from oldest to youngest) in the deep basin were interpreted and mapped. Time-structure maps were converted into depth using the time-depth relationship constructed from seismic-to-well tie at the Ahlat ridge well. The structure maps of the sequence boundaries exhibit tilting to west, suggesting that the sequences were deposited with greater subsidence in the west. NE-trending normal faults are dominant; E-W oriented thrust faults are seen locally.

seismic

Seismic Equipment used in 2004 for the Pre-site Seismic Survey for the deep Drilling Campaign PALEOVAN.

Lake level fluctuations

Five lake lowstands have been dated as follows: (Phase 1) ~580 ka; (Phase 5) ~ 355-341 ka; (Phase 7) ~ 320-210 ka; (Phase 12) ~ 170-140 ka; and (Phase 18) ~ 30-16 ka. Estimated paleolake levels (below present lake level) at the end of each phase are; 610 m for Phase 1, 560 m for Phase 5, 470 m for Phase 7, 310 m for Phase 12, and 210 m for Phase 18. The sediment infill history of Lake Van over the ~580 ka is characterized five types of sedimentary facies.

  1. Uniform 'well-stratified' lacustrine deposits (alternating organic muds and fine grained turbidites and tephra) formed under quiescent lake level conditions characterize the deeper parts of the basin.
  2. Chaotic 'mass-transport' deposits characteristics of the southern parts of the lake have likely resulted from mass-transport process possibly triggered by ongoing tectonic activity along the lake margins.
  3. Oblique or complex-oblique shaped 'deltaic' deposits have formed on the eastern/southeastern shelf and slope areas most likely due to accumulation of large volumes of clastic material derived from adjacent rivers.
  4.  Non-uniform 'fluvial' deposits characterizing the shelves are interpreted to have mainly deposited by fluvial processes when the shelf was subaerially exposed.
  5. Chaotic 'volcaniclastic' deposits that fill local basins (Northern basin) are probably due to volcanic mass flows such as pyroclastic flows.

In summary, our data show that sedimentation in the basins was mainly controlled by tectonic, climatic, and volcanic factors. The effect of climate was more pronounced in sedimentary phases rather than other factors as suggested by repeated patterns of lake level fluctuations. Such lake level fluctuations which reflected in clinoforms in seismic data are also documented as morphological features (channels, terraces) in bathymetric data.

model

Model of the lake level history and its fluctuations for the Lake Van basin constructed by Deniz Cukur (now at KIGAM, Korea)

On average channels are V-shaped, 5-25 m deep, 40-500 m wide, and extending water depth of 200 m where approximately the shelf breaks occur (Fig. 3). Previous studies describe these morphological depressions as a karst-like morphology, braided channel system, and pockmarks. Mapping the spatial distribution of these depressions using multibeam bathymetry leaves us no doubt that they represent channels.

 

Ansprechpartner: Sebastian Krastel

Forschungsfahrten:

  • 2014 Bathymetric and seismic survey
  • 2012 Postdrilling Seismic Reflection Survey
  • 2010 ICDP Deep drilling campaign PALEOVAN
  • 2004 Pre-Site Seismic Survey

 

Publikationen

  • Cukur, D., Krastel, S., Çağatay, M.N., Damcı, E., Meydan, A.F., Kim, S.-P., 2015. Evidence of extensive carbonate mounds and sublacustrine channels in shallow waters of Lake Van, eastern Turkey, based on high-resolution chirp subbottom profiler and multibeam echosounder data. Geo-Marine Letters 35, 329-340.
  • Cukur, D., Krastel, S., Demirel-Schlüter, F., Demirbağ, E., Imren, C., Niessen, F., Toker, M., 2013. Sedimentary evolution of Lake Van (Eastern Turkey) reconstructed from high-resolution seismic investigations. International Journal of Earth Sciences 102, 571-585.
  • Cukur, D., Krastel, S., Schmincke, H.U., Sumita, M., Tomonaga, Y., Namık Çağatay, M., 2014. Water level changes in Lake Van, Turkey, during the past ca. 600 ka: climatic, volcanic and tectonic controls. Journal of Paleolimnology 52, 201-214.
  • Cukur, D., Krastel, S., Schmincke, H.-U., Sumita, M., Çağatay, M.N., Meydan, A.F., Damcı, E., Stockhecke, M., 2014. Seismic stratigraphy of Lake Van, eastern Turkey. Quaternary Science Reviews 104, 63-84.
  • Cukur, D., Krastel, S., Tomonaga, Y., Schmincke, H.-U., Sumita, M., Meydan, A.F., Çağatay, M.N., Toker, M., Kim, S.-P., Kong, G.-S., 2016. Structural characteristics of the Lake Van Basin, eastern Turkey, from high-resolution seismic reflection profiles and multibeam echosounder data: geologic and tectonic implications. International Journal of Earth Sciences (Geologische Rundschau) 106, 239-253.
  • Litt, T., Anselmetti, F.S., Cagatay, M.N., Kipfer, R., Krastel, S., Schmincke, H.-U., Sturm, M., 2011. A 500,000-year-long sediment archive drilled in eastern Anatolia. Eos, Transactions American Geophysical Union 92, 477-479.
  • Litt, T., Krastel, S., Sturm, M., Kipfer, R., Örcen, S., Heumann, G., Franz, S.O., Ülgen, U.B., Niessen, F., 2009. ‘PALEOVAN’, International Continental Scientific Drilling Program (ICDP): site survey results and perspectives. Quaternary Science Reviews 28, 1555-1567.

 

studentische Arbeiten

  • Anke Neupert (2013) Seismische Stratigraphie des Nördlichen Beckens im Vansee, Ostanatolien (Diplomarbeit)