Experimental abrasion of water submerged bone: the influence of bombardment by different sediment classes on microabrasion rate

Data presented here demonstrates the utility of quantitative analysis of sediment-induced microabrasion on bone's surface. Fresh sheep (Ovis aries) bone, acting as a human analogue, was bombarded by mobile sediments from silt, sand and gravel classes (ranging 20 μm–3.35 mm) in a series of flume-based experiments. Controlled bombardment produced unique abrasion patterns on bone which were recordable using scanning electron microscopy. Imaging abrasion at both × 100 and × 1000 magnifications allowed quantitative and qualitative distinction to be made concerning the sediment class that the bone was abraded by; bombardment by gravel classes caused abrasion to advance through cyclical cracking, whereas smoothing of bone's surface occurred more frequently in sand and silt classes. A stepwise multi-linear regression model identified changes in sediment grain size (p < 0.001), duration of exposure to abrasion (p < 0.001), sphericity of the abrasive (p = 0.002), and T value (abrasive force) (p = 0.013) respectively, as the strongest rate limiting factors controlling microabrasion propagation. The methodology presented herein demonstrates analytical value by allowing diagnostic modifications to bone's surface to be correlated with specific taphonomic processes. Data developed from flume-based experimentation was applied in four separate case studies; abrasion data recorded on bones recovered from different aquatic contexts, was linked to hydrological and marine seabed sediment data to demonstrate how documented microabrasion can reflect the different sedimentary contexts bone has passed through. In light of these results we suggest that a quantitative approach to analysing abrasion on bone retrieved from water has potential to allow remains' submersion times and transport pathways to be established with a higher degree of resolution than is currently possible. The development of improved methodologies for the interpretation of submerged human bone is vital due to the increasing risks posed by flooding and coastal erosion to archaeological sites.