40Ar/39Ar geochronology of ICDP PALEOVAN drilling cores

• Main Author: Engelhardt, Jonathan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2018
• Subjects: ddc:550; Institut für Geowissenschaften; Greenland; Greenland ice cores; ice core
• Online Access: https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/index/index/docId/42953; https://nbn-resolving.org/urn:nbn:de:kobv:517-opus4-429539; https://doi.org/10.25932/publishup-42953; https://publishup.uni-potsdam.de/opus4-ubp/files/42953/engelhardt_diss.pdf

The scientific drilling campaign PALEOVAN was conducted in the summer of 2010 and was part of the international continental drilling programme (ICDP). The main goal of the campaign was the recovery of a sensitive climate archive in the East of Anatolia. Lacustrine deposits underneath the lake floor of ‘Lake Van’ constitute this archive. The drilled core material was recovered from two locations: the Ahlat Ridge and the Northern Basin. A composite core was constructed from cored material of seven parallel boreholes at the Ahlat Ridge and covers an almost complete lacustrine history of Lake Van. The composite record offered sensitive climate proxies such as variations of total organic carbon, K/Ca ratios, or a relative abundance of arboreal pollen. These proxies revealed patterns that are similar to climate proxy variations from Greenland ice cores. Climate variations in Greenland ice cores have been dated by modelling the timing of orbital forces to affect the climate. Volatiles from melted ice aliquots are often taken as high-resolution proxies and provide a base for fitting the according temporal models. The ICDP PALEOVAN scientific team fitted proxy data from the lacustrine drilling record to ice core data and constructed an age model. Embedded volcaniclastic layers had to be dated radiometrically in order to provide independent age constraints to the climate-stratigraphic age model. Solving this task by an application of the 40Ar/39Ar method was the main objective of this thesis. Earlier efforts to apply the 40Ar/39Ar dating resulted in inaccuracies that could not be explained satisfactorily. The absence of K-rich feldspars in suitable tephra layers implied that feldspar crystals needed to be 500 μm in size minimum, in order to apply single-crystal 40Ar/39Ar dating. Some of the samples did not contain any of these grain sizes or only very few crystals of that size. In order to overcome this problem this study applied a combined single-crystal and multi-crystal approach with different crystal fractions from ...