Quaternary pollen taphonomy: examples of differential redeposition and differential preservation

Pollen assemblages are affected by a variety of processes between dehiscence and recovery. Here, two examples from western Canada illustrate two of the most important biases affecting pollen assemblages after production and initial dispersal. A site in Canadaʹs Yukon Territory provides evidence of selective redeposition of penecontemporaneous pollen grains, which is detectable only through paired coring. A deposit on the floor of a kettle depression shows trends in the ratios of extra-local pollen types, which are opposed to the trends shown in a core taken from the slope of the same depression. This is explained as a trend to reduced mobility of saccate grains with time due to increased permeability of the substrate on the kettle slope. A study of the differential degradation of Populus pollen illustrates the complexities of pollen preservation. Populus pollen is generally recognized as more susceptible to corrosion than are most other pollen types. The poor preservation of this pollen type is attributed largely to its lack of harmomegathic adaptation and low sporopollenin content. This real susceptibility is compounded by the pollen grainʹs lack of distinctive surface ornamentation, inhibiting recognition of damaged grains. At least part of the general impression of poor preservation of Populus pollen may be due to a recent increase in the abundance of Populus on the landscape in western Canada. Early studies in this region may have sampled sediments from before the increase in Populus, and compared their pollen spectra with post-Populus increase vegetation.