Post-depositional bone destruction in cave sediments: a micromorphological study of the MIS 5a-d cave bear strata of Bisnik Cave, Poland

摘要

Accumulations of cave bear bones are common in Pleistocene cave sediments. The reasons for the deposition are usually clear, and believed to be associated with the hibernation behavior of bears. Although they are common, little is known about the post-sedimentary processes that affect the assemblages. The cave bear bone accumulations from the Lower Weichselian layers of Bisnik Cave, Poland, represent an interesting case of intensive post-depositional bone destruction. Bones are highly fragmented and rounded, although no traces of water currents have been detected in the stratigraphic series. In this paper we use the case of Bisnik Cave as an example of cave bear strata, to describe the taphonomic features of the abraded-like bones and to recognize the underlying processes. We present a micromorphological study of rounded bones and surrounding sediments to increase knowledge of the depositional context in the cave environment. Micromorphological analysis of the sediments indicated in situ disintegration of bones rather than abrasion. The factor responsible here was internal stress, as opposed to the external pressure of mineral grains in the case of abrasion. We indicate frost action as a possible factor responsible for the post-depositional bone disintegration.