Paleoenvironmental Reconstruction of the AAR

Paleoenvironmental Reconstruction

The use of benthic organisms and other microfossils have provided a record of the regional paleoenvironment during the Lake Stanley lowstand phase of Lake Huron. Isotopic studies using ostracods and other bivalves in Lake Huron (Rea et al., 1994; Macdonald & Longstaffe, 2008) note variation in both the carbon and oxygen isotope record from the northern and southern basins, likely related to the mid-lake position of the Ridge. Especially during lowstand events, the Ridge would have acted as a barrier to water movement between the different basins within Lake Huron, allowing for different trophic conditions within the isolated basins to develop.

The most common means of reconstructing paleoenvironments in and around the Lake Huron basin is the utilization of pollen and testate amoebae analysis. The pollen phases in Lake Huron that are relevant to the Lake Stanley lowstand include Phase 1 (prior to 10,000 cal. yr B.P.) which records the post-glacial landscape of spruce and tundra, Phase 2 (10,000–8000 cal. yr B.P.) showing the shift to a pine-dominated boreal forest environment, and Phase 3 (after 8000 cal. yr B.P.) where the establishment of more modern mixed-forest environments begins (McCarthy et al., 2007).

Phase 2 pollen assemblages are synchronous with the Lake Stanley lowstand and also recorded along with Phase 2 pollen assemblages are low diversity testate amoebae assemblages dominated by Centropyxis species, which are tolerant of brackish conditions. These brackish conditions during the Phase 2 pollen assemblages provided additional evidence of closed basin conditions during the Lake Stanley lowstand (McCarthy & McAndrews, 2012).

References Cited

Macdonald, R.A., & Longstaffe, F.J. (2008). The late quaternary oxygen-isotope composition of Southern Lake Huron. Aquatic Ecosystem Health, & Management, 11, 137–143.

McCarthy, F., McAndrews, J., Blasco, S., & Tiffin, S. (2007). Spatially discontinuous modern sedimentation in Georgian Bay, Huron Basin, Great Lakes. Journal of Paleolimnology, 37, 453–470.

McCarthy, F., & McAndrews, J. (2012). Early Holocene drought in the Laurentian Great Lakes basin caused hydrologic closure of Georgian Bay. Journal of Paleolimnology, 47, 411–428.

Rea, D.K., Moore Jr., T.C., Lewis, C.F.M., Mayer, L.A., Dettman, D.L., Smith, A.J., & Dobson, D.M. (1994). Stratigraphy and paleolimnologic record of lower Holocene sediments in northern Lake Huron and Georgian Bay. Canadian Journal of Earth Sciences, 31, 1586–1605.