Glacially redeposited pollen in tills of southern Ontario, Canada

Abstract

According to published opinion based on analytical data, the secondary pollen of subglacial till in the eastern Baltic region of Europe reflect the pollen assemblages of the preceding interstadial or interglacial sediment, including abundant thermo-philous pollen. Tills and glaciolacustrine sediments from 10 sites in southern Ontario, including the Don Valley Brickyard section at Toronto, where polynologically investigated to compare the pollen content in glacigenic deposits of various ages. Only one site (upper Bradtville till) contained a secondary pollen assemblage with abundant deciduous pollen, like those found in a Yarmouthian interglacial deposit in Indiana. In all the others, pine (Pinus) pollen dominate. This phenomenon is explained by glacial incorporation of sediments enriched in overproduced Pinus pollen, which had accumulated during either (i) a lengthy cool transitional period between the warm phase of the Sangamonian Interglacial and the first major Early Wisconsinan glacial advance, (ii) the interstadial Middle Wisconsinan, or (iii) the cool nonglacial episode of Illinoian and pre-Illinoian time. Therefore, the northern European model for distinguishing tills of different ages by their secondary pollen assemblages is applicable to southern Ontario only in exceptional cases. Pollen in the glaciolacustrine Early Wisconsinan Sunnybrook Drift sediments resembles those of Sunnybrook till, but are more variable in their preservation and composition and contain more pre-Quaternary palynomorphs.