Using Microfossils to Observe the Occupancy of Pre-Historic Peoples: the Value of Non-Pollen Palynomorphs

English Abstract:

Microfossils, particularly pollen grains, have been used to address archaeological questions since the early 1900’s. Their use has expanded beyond their original application to date archaeological remains. A classic example is the response of various microfossil groups (diatoms, rotifers, fungal spores, dinoflagellate cysts and pollen) to several periods of human occupation around Crawford Lake, Ontario. While Euro-Canadian land clearing, farming and logging (identified by abundant ragweed pollen) added nutrients to the lake, the Iroquois occupation (identified by cultivar pollen and spores of their pathogenic fungi) had the greatest impact on the lake ecosystem. These higher abundances are observed more than once between ~A.D.1286–1486, indicating cycles of habitation of the village. Similarly, the distribution of palynomorphs (acid resistant microfossils) in small lakes on the Penetanguishene Peninsula and in Severn Sound, Ontario reveals distinct Euro-Canadian and Wendat (Huron - ~A.D.1450–1650) occupation zones, both characterized by an increase in algal microfossils (particularly eutrophic taxa) as well as non-arboreal pollen. Ongoing studies in Lake Simcoe have identified evidence of Wendat occupation in the Orillia region, where the palynological signature is supported by measurements of increased nutrient and heavy metal concentrations in pre-European sections of the core. The abundance of algal palynomorphs in our samples clearly records cultural eutrophication, but because most pollen analysts use acetolysis to “clean up their preparations”, the more susceptible non-pollen palynomorphs are destroyed. Analysis of samples from Smith’s Bay (Lake Simcoe) pre- and post- acetolysis treatment show a loss of most desmid species (particularly Staurastrum spp.) and small, thin-walled dinoflagellates, for instance, whereas Pediastrum appear to be unaffected. Geoarcheologists are urged to avoid acetolysis and examine the non-pollen palynomorphs in their “pollen” slides, thus getting broader insights into anthropogenic impact than by relying on the pollen alone.