Age-depth model derived from borehole logging and seismic data – sedimentological evolution of Lake Ohrid (North Macedonia/Albania) for the last 1 million years

To understand the evolution of lake basins, a robust age-depth model is essential. Usually, such model is created based on core material using various dating techniques (e.g. radiometric dating, magnetostratigraphy, tephra dating/identification, biostratigraphy etc.). However, suitable core material is not always available and other less direct methods have to be applied. In this study, we present an approach to develop an age-depth model based on integrating downhole logging data and seismic survey data from Lake Ohrid to obtain a rough but representative model before core opening. Logging data was acquired during an International Continental Scientific Drilling Program campaign in 2013 and seismic data is from pre-site surveys conducted in 2007 and 2008. First, the interpretation of seismic data and the use of cyclostratigraphic methods on downhole logging data lead to development of age-depth models derived from direct correlation to the LR04 benthic stack (Lisiecki and Raymo, 2005) at three drill sites at the Lake Ohrid. Based on seismic surveys data, marker horizons are interpreted to support our understanding of accumulation rates. Additional information on sedimentation processes is provided by the evaluation of eccentricity related amplitude modulations using Meyers' timeOptTemplate method (2015, 2019). The use of various, independent methods and the comparison of their age estimations ensures a robust verification of obtained age-depth models. In a second step, we apply cluster analysis to the physical properties of the sediments, construct artificial lithology logs and integrate them into the age-depth models. This step makes first interpretations of the sedimentological evolution possible.