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

Abstract

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 Biśnik 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 Biśnik 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.

Frontiers of the Lower Palaeolithic expansion in Europe: Tunel Wielki Cave (Poland)

“…Layer F exhibits typical micromorphological features of sediments deposited in the low-energy environment of a cave floor: massive structure, silty clay grain size composition and the presence of numerous bone and tooth fragments, which correlates with data from other sites [50][51][52] . It is also characterized by periglacial or frost-actionrelated micro-structures (see Supplement Data S7).…”

“…Quite a similar effect was also observed for bones in Biśnik Cave. There, it was explained rather by tension due to frost weathering than compression 50 , although the main factor was still frost processes. The edge damage is believed to be an effect of tension due to pressure from swelling and shrinking sediments within a periglacial environment 55 .…”

Pre-LGM loess deposits in caves of Polish Jura – occurrence and stratigraphic importance

“…Such studies were limited in the pre-LGM cave loess, as well as in caves of the Polish Jura in general. A few exceptions are micromorphological studies of Layer 12 in Biśnik Cave (Krajcarz and Krajcarz 2019) and Layer E in Tunel Wielki Cave (Kot et al 2022a), conducted by the author of this paper. These analyses revealed the presence of lamination, clay balls and isolated aggregates of loamy material, and separation of sand and silt.…”