Pollen taphonomy of cave sediments: What does the pollen record in caves tell us about external environments and how do we assess its reliability?

Abstract

Cave sediments may contain important long-term records of past environments and human activity. Pollen provides key evidence, since it disperses widely and is relatively durable. We still know relatively little about the dispersal of pollen into caves, and its preservation within cave sediments, compared with our relatively detailed knowledge of pollen taphonomy in other sedimentary environments. Pollen taphonomy in caves is dependent on a variety of transport pathways and seems to be very contingent on local circumstance. The airfall component of cave pollen assemblages often seems comparable with airfall spectra in the landscape outside the cave, but bees, birds and bats may transport considerable quantities of pollen into caves, and the entrance-flora may also be significant. Cave sediments are rarely waterlogged and pollen within them can be subject tomicrobial and chemical degradation. Sedimentation in caves is often episodic, with episodes of storage and deposition, sometimes redeposition of sediment, which means that biostratinomic, preservational, factors become very significant. Comparison with sequences outside caves is difficult because few caves are found in landscapes where there are comparable pollen records from lakes and bogs. Here we review the factors affecting cave pollen taphonomy and hence the reliability of palynological analysis of sediments from caves, with suggestions for future investigation.