Frozen in Motion: a Controlled in Vitro Freeze-Thaw Experiment on Object Displacement and Microscopic Surface Alterations of Lithics

Artifact displacement caused by freeze-thaw cycles has been documented at Pleistocene sites, like at Quinçay in France, yet the extent of lithic movement and microscopic surface alterations remain underexplored. Distinguishing frost-induced wear from use-wear traces is particularly challenging. Building on prior experiments, we tested the effects of freeze-thaw cycles on experimentally produced lithics across different sediments. Lithics were exposed to 42, 330 and 600 cycles in a climatic chamber within five sediment types: clay, sandy-silt sediment (Quinçay), fine and coarse sand, and clay with gravel. Variables such as temperature, sediment volume and water saturation were controlled. We included unused flakes and cut blocks as well as experimentally produced scrapers, bladelets and Châtelperronian-type points comparable to Quinçay artifacts. Results show major displacement and rotation of lithics buried in fine-grain sediments after 330 cycles, while lithics in sandy deposits experienced limited movement. Moreover, some lithics rotated and moved downwards after 600 cycles, while smaller flakes deposited in a lower depth remained stable after both 330 and 600 cycles. Micro-wear analysis showed alteration polish due to freeze-thaw cycles likely influenced by sediment type. Our study provides new evidence on the effects of sequential freeze-thaw cycles on lithic displacement and microscopic surface alterations. It establishes an explicit reference collection of lithics exposed to long-term freeze-thaw conditions, providing systematic documentation through micro-wear analysis. These results enhance a better understanding of site formation processes and the effects of frost-related phenomena on Pleistocene archaeological contexts and the embedded material.