Holocene uplift and vegetation history along the northern shore of Lake Michigan

Author

William H. Petty

Date of Award

8-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Paul A. Delcourt, Hazel R. Delcourt

Committee Members

Thomas W. Broadhead

Abstract

Radiocarbon dates from organic material exposed in a river cutbank and basal sediments from Elbow Lake, Mackinac Co., Michigan, indicate a maximum age of a high stand of Lake Michigan at 6900 ¹⁴C yr B.P. (radiocarbon years Before Present), during the late-Chippewa transgression of Lake Michigan. Basal radiocarbon dates from beach swales and a second lake site (Beaverhouse Lake, Mackinac Co.) provide geomorphic evidence for a subsequent high stand between 5600 and 5400 ¹⁴C yr B.P., prior to the classically recognized Nipissing I high stand from 5000 to 4500 ¹⁴C yr B.P. Basal radiocarbon dates from a transect of sediment cores, along with tree-ring data, and General Land Office Surveyor notes of a shipwreck, circa A.D. 1846, reveal an average rate of regression of 3.1 m/century (10 ft/century), over the past 5400 ¹⁴C years. Based on the elevation and age of these sites, a differential isostatic rebound rate of 22.6 cm/100 radiocarbon years (0.74 ft/100 radiocarbon years) was calculated for the northern shore of Lake Michigan, relative to the Lake Michigan-Lake Huron outlet at Sarnia, Ontario. Changes in the pollen record, sediment stratigraphy, and sediment accumulation rates document that this mid- to late-Holocene retreat of the shoreline due to isostatic rebound was punctuated by periodic high stands resulting in progressive development over the past 5400 ¹⁴C yr of 75 pairs of dune ridges and swales each formed over an interval of 72 years.

A sediment core, spanning the past 8000 years in time, was collected in June of 1993 from Elbow Lake. Analysis of fossil pollen preserved in radiocarbon-dated sediments of Elbow Lake indicates changes in Holocene vegetation following deglaciation. These vegetational changes are related to climatic variation and proximity to the Lake Michigan shoreline. Pollen percentages for hemlock (Tsuga canadensis) and American beech (Fagus grandifolia) both reached >1% by 5500 ¹⁴C yr B.P., indicating that coastal terraces along the northern shore of Lake Michigan provided suitable mesic habitat for these tree species to invade. This mid-Holocene establishment of beech near the shore of Lake Michigan was associated with a coastal rise in water table on relict lakeshore terraces. The invasion of beech on the clayey till soils of the coastal uplands around Elbow Lake occurred 2000 years earlier than its late-Holocene expansion into the interior of Michigan's Upper Peninsula around 3400 ¹⁴C yr B.P. (Futyma, 1982). This coastal establishment of beech by 5500 ¹⁴C yr В.Р. supports the idea that climate, rather than dispersal, limited the mid-Holocene expansion the beech into the Upper Peninsula's interior.

By 2200 ¹⁴C yr B.P., pollen percentages of mesic hardwoods, such as beech and sugar maple (Acer saccharum) along with hemlock, increased to their modern levels, associated with coastal paludification of two lowland sites suggesting more mesic conditions within the area. The late-Holocene increase of beech pollen values to modern levels probably represents an expansion of existing outlying populations (such as near Elbow Lake) rather than subsequent waves of recolonization from the more southerly seed source of Michigan's lower peninsula.

Recommended Citation

Petty, William H., "Holocene uplift and vegetation history along the northern shore of Lake Michigan. " Master's Thesis, University of Tennessee, 1994.
https://trace.tennessee.edu/utk_gradthes/11651