Tumbling effects on bone surface modifications (BSM): An experimental application on archaeological deposits from the Barranc de la Boella site (Tarragona, Spain)

Tumbling is defined as a process in which hyper-concentrated flows alter bone remains, producing changes in their morphology and original structure. Although the process is well known, little experimental research has focused on describing the effects this process has on bone surface modifications (BSM), which can subsequently be applied to the fossil record. Water currents may have played an important role in altering the surfaces of bones from Barranc de la Boella, which were deposited in a deltaic fan context. Striae of undetermined origin have been documented on bones at the la Mina locality, and possible cut marks found on bones at Pit 1 locality. In our experiments, both fresh and dry bones with reproduced trampling striae and cut marks were tumbled in a tumbling machine, combining different types of movement and proportions of water to sediment. The bones were examined after each of the five cycles of the modification process, which lasted 30′, 30′, 1 h, 2 h, and 4 h. Our results show a considerable diminishing of trampling striae, while the majority of cut marks were preserved. The marks on fresh bones were more severely altered than those on dry bones. Based on the results of this experiment, the marks from Pit 1 appear to be morphologically close to the experimentally altered cut marks, while the majority of those from la Mina are more similar to the altered trampling striae.