Borehole logging and seismic data from Lake Ohrid (North Macedonia/Albania) as a basis for age-depth modelling over the last one million years

Abstract

Robust age-depth models are essential for developing sophisticated interpretations of the sedimentological history in lake basins. In most cases, such models are created using an integrated geoscientific approach, including biostratigraphy, magnetostratigraphy and radiometric dating. In this study, we present an approach to construct age-depth models based on integrating downhole logging and seismic survey data when there are no samples available for dating. An example of this method is shown using data from Lake Ohrid (North Macedonia/Albania).First, we interpret seismic data and correlate downhole logging data from three sites - DEEP, Pestani and Cerava - to the LR04 benthic stack. We cross-check the resulting age-depth models using cyclostratigraphic methods, which deliver sedimentation rates that are on the same order of magnitude. The maximum age of the investigated sediments is based on lacustrine seismic marker horizons and is approximately 1 million years at DEEP/Pestani and 0.6 million years at Cerava.In the second step, we construct an artificial lithological log based on cluster analysis using the physical properties of the sediments and integrate it with the age-depth model. This allows an initial interpretation of the sedimentological history at Cerava and Pestani.Our methodological approach cannot substitute classical sediment core investigations, but we suggest that this two-step approach be applied to future projects of the International Continental Scientific Drilling Program. It can rapidly provide preliminary results on age and sediment type and is particularly useful when datable material is not available.