Biostratinomic study of bones immersed in marine water: Preliminary results and inferences from the Delta Project bone assemblages

Abstract

In this paper, we present the preliminary results of a biostratinomic study of bones submerged in sea water with the aim to identify patterns that may help us to understand the diagenetic processes that took place in the assemblages of two historical shipwrecks (16th and 17th centuries) located in the Bay of Cádiz (Spain). The faunal assemblage of these shipwrecks was composed by 122 NISP of cattle, caprine, suid, cat, chicken and probably cetaceous species that were recovered with different taphonomical characteristics (cut marks, stains, erosion and fouling) and, probably, different origins (refuse from the ships or from the slaughterhouses located around the bay). In order to understand the taphonomic characteristics and to attempt to reconstruct the origin of the shipwreck bone assemblages we collaborated with the ARQUEOMONITOR Project during its final year. The main objective of this project was to document the alteration of different submerged materials at two sites within the Bay of Cádiz. The reference bone materials used in the experiment were cattle tibia and femur, half of them boiled before immersion to remove the collagen. These samples were then retrieved at different times over a one-year period in order to study the macroscopic taphonomy produced by the marine sediments and biota. The preliminary results enable us to define differences between boiled and raw bones during the first 6 months of the trial, although after this time alterations are similar in both samples. Furthermore, we are able to understand the fouling of the archaeological bones from the shipwrecks as modern bioerosion. We also present the initial results of microanalysis using SEM (scanning electron microscopy) and EDX (energy dispersive X-ray spectroscopy) for the study of microerosion and chemical changes in bone structure.