First calibration site for Schmidt hammer exposure-age dating (SHD) in Türkiye and an experimental approach on ultramafic rocks

Schmidt hammer exposure-age dating (SHD) estimates the age of rock surfaces by measuring their hardness through rebound values, which are influenced by weathering. It is a low-cost, quick, and straightforward calibrated-age dating method. Calibration curves are used to correlate rebound values with known surface exposure-ages. However, accuracy of SHD is highly sensitive to various factors, making it susceptible to external influences. Lithology plays a critical role in the reliability of this method, while environmental factors also exert significant control over the results. This is because obtaining robust outcomes relies heavily on the rebound value (R-value) derived directly from simple measurements on rock surfaces using the Schmidt hammer. In this study, we applied the SHD method to date moraine boulders composed of serpentinized harzburgite, a lithology known for its complex mineralogical structure, in order to obtain consistent R-values. We adopted an approach that diverges from the “established” SHD methodology, aiming to minimize potential misinterpretations and inaccuracies arising from lithologic variations. We designed a sampling strategy by pairing moraine boulders with established TCND ages (control boulders) to those with unknown ages (test boulders) and comparing their R-values. This approach aimed to evaluate the consistency of R-values within each pair and minimize issues related to lithologic variations in the R-value – exposure-age relationship. Our primary objective was to evaluate the consistency of the SHD method in a formerly glaciated area dominated by ultramafic lithology. We also evaluated factors that could influence R-value results and developed an SHD-based glacial chronology. This first SHD application in Türkiye was conducted on Mt. Sandıras, in the westernmost section of the Taurus Mountains. Surface exposure-ages from Kartal Lake Valley and Northwest Valley have been previously determined using terrestrial cosmogenic ³⁶Cl nuclide dating (TCND) and served as control points in the SHD application. Despite the limited sampled moraine boulders and challenging lithology, a glacial chronology has been established. Glacial landform ages ranging from 19.4 ± 1.1 ka (Last Glacial Maximum) to 13.1 ± 1.2 ka (Late-glacial) have been determined. With this study, not only was the first SHD chronology in Türkiye established, but the methodological application to different lithologies was also expanded.