In the frame of the ICDP project ‘PALEOVAN’, a deep drilling campaign and geophysical downhole logging has been executed in summer 2010. The objectives are to enhance the understanding of the paleoclimatic and paleoenvironmental conditions for more than 550,000 years of the Middle East. An international scientific team investigates the sediments with geophysical, geological, mineralogical and paleoecological measurements. The PALEOVAN project is executed by eight groups from Germany, Switzerland and Turkey.
What is special about Lake Van?
Lake Van is a terminal lake, located in eastern Anatolia. It is assumed as excellent archive for more than 550,000 years and thus, covers several glacial-interglacial cycles. The tectonic setting is controlled by its location at the collision zone of the Arabian- and the Anatolian/Eurasian plate. Lake Van is surrounded by several volcanoes which are sources of tephra deposits in the lake sediments. Dating of volcanic events and evaluation of its environmental impact is possible by study of tephra layers. Geological investigations (seismic, shallow coring) have led to identification of suitable drilling locations with undisturbed sediments. The unique geological conditions predestine Lake Van as a high resolution climate archive in the Middle East.
Results of borehole geophysics
The acquired downhole logging data (spectral gamma ray, magnetic susceptibility, resistivity, dipmeter and partly sonic (vp)) data was analyzed by means of cluster analysis. Extensive tests have shown best results by adding of additional data from core analysis (elemental intensities from XRF scanning).
The lithological record (lacustrine clayey silts and tephra deposits from different volcanic sources) has contrasting physical and chemical properties. Stunning are the differences between the volcanic deposits for spectral gamma ray, susceptibility as well as intensities of calcium and zirconium. Together with other working groups, the statistical tephra units from cluster analysis were linked to the dominant volcanic composition. It spans from basaltic to rhyolitic composition and depth trends were observed. Basaltic tephra prevails at the lower part of the drilled sediments whereas rhyolitic deposits increase gradually towards the top.
The results of several working groups were submitted to Quaternary Science Reviews for publication as special issue (PALEOVAN).
Further, cyclostratigraphic analysis of uranium contents from spectral gamma ray was performed. The lacustrine sediments were spectral analyzed and high amplitudes were correlated with Milankovitch cycles. Based on this correlation, sedimentation rates and the time of deposition were calculated as 593,000 years down to a depth of 220 m below lake floor.
A Swiss scientific group correlated core material with orbital climate proxies and estimated the time of deposition at about 600,000 years, which is in good agreement with the results from spectral analysis.