Date of Award

4-1979

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Dr. William Harrison III

Second Advisor

Dr. W. Thomas Straw

Third Advisor

Dr. Richard Passero

Access Setting

Masters Thesis-Open Access

Abstract

The depositional and ecological history of Oakland Bog, a relic Wisconsinan (16,500+300 years B.P.) lake site is interpreted from pollen stratigraphy, molluscan faunal assemblages and sediment facies. The lake basin, which probably formed after the melting of a late Wisconsinan buried ice block in the Kalamazoo Moraine Complex, is irregular, steep-sided and floored by glacial till. The till is overlain by as much as 7.6 meters of lacustrine marls which extend over an area of nearly 0.5 km2. Basal marls are characteristically medium gray, clayey, and contain abundant calcified stem fragments of charophytes; however, the overlying marls display alternating pale carbonate-rich and darker organic-rich laminae separated by massive or graded unlaminated beds.

The molluscan faunal assemblages occur in vertically restricted associations that probably reflect changing environmental conditions influencing the local habitat. The oldest molluscan assemblage is interpreted to record a pioneering stage because it is characterized by low species diversity and low intra-specific frequency. The pioneering stage was associated with a creek or intermittent ponded setting that was rapidly transformed to a relatively silt-free, permanent waterbody with a soft substrate and considerable vegetation in the shallow areas.

There is no evidence in either the pollen record or the molluscan assemblages to indicate any reversals in the general trend of climatic warming. Throughout late-glacial and early post-glacial time, the climate of southwestern Michigan appears to have been cool and relatively continental with no clear record of temperature oscillations correlative with ice margin movements. The tripartite nature of the pollen record strongly resembles that of other Great Lake region pollen stratigraphies. Differential migration rates may help to explain the basic pattern of postglacial vegetation succession. Ecotones of mollusks and vegetation appear to have a south to north zonation which is time transgressive.

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