RESEARCH: OUTCOMES, VIEWPOINTS & PERSPECTIVES

Taphonomical research of pollen assemblages from cave surfaces

Both depositional and preservational features of the pollen spectra inside caves are uneven and clearly influenced by the cave morphology and sedimentary types. Stochastic and episodic forms of particle influx, such as transport by animals, periodic flooding and human activities, may also influence pollen deposition inside caves in proportion that are unique to each site.

Caves with multiple entrances, or streams that bring sediments in from the cave exterior may pose additional interpretative problems. Such factors result in a complex interacting series of taphonomical effects which differ in rate across the cave. Caves with large entrances and isodiametric chambers present fewer problems of alteration in the pollen spectra and are likely to have higher pollen influxes than caves with smaller entrances. Caves in which the dominant type of pollen transfer from the external environment is airborne will often show a decrease in pollen deposition with increasing distance into the cave. Generally, in these cases, the highest concentrations of pollen and spores are observed in the cave entrance areas, and the lowest at the rear of the cave. But this is not an universal rule. Sometimes, when biotic or aquatic pollen transfer is dominant, pollen deposition increase toward the rear caves.

Sediments associated to dry depositional and post-depositional conditions are the most reliable materials for environmental reconstruction from pollen analysis in cave sites, independent of the vegetation context and the external source area to be considered. Aridity is the most desirable property for cave as sources of palaeoenvironmental information as it enhances preservation and minimizes bioturbation. Contrastingly, speleothems and wet or carbonated sediment samples have been demonstrated to be less suitable for pollen analysis, often containing altered pollen spectra and low concentration. The potential may still exist if the speleothems lie close to the cave openings.

Sediments from caves contain pollen assemblages that may reflect the vegetation of local and regional catchment areas. Globally considered, pollen spectra inside caves are similar to those obtained in the exterior environment.

We recommend that sampling is undertaken on the basis of a multiple-profile strategy, if possible not very close to parietal and rear areas and avoiding zones of actual moisture, or areas where old hydromorphic processes can be detected from sedimentological features. It is also of vital importance to use all the available information (pollen percentages, concentration, diversity and preservation) to establish a robust taphonomical model. This might facilitate the isolation of abnormal inputs, i.e. over-representation of some taxa, allowing a more reliable ecological interpretation of the data. From this strategy, as applied to every set of contemporary pollen spectra across temporal sequences, it would follow a more realistic picture of the external vegetation and its variation through time.

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NAVARRO, C., CARRIÓN, J.S., PRIETO, A.R. & MUNUERA, M. 2001. Modern cave pollen and its application to describe the palaeorecords in an arid environment. Complutum 13: 7-18

NAVARRO, C., CARRIÓN, J.S., NAVARRO, J., MUNUERA, M. & PRIETO, A.R. 2000. An experimental approach to the palynology of cave deposits. Journal of Quaternary Science 15: 603-619