Date of Award

4-2018

Degree Name

Doctor of Philosophy

Department

Geosciences

First Advisor

Dr. Alan E. Kehew

Second Advisor

Dr. Robb Gillespie

Third Advisor

Dr. William A. Sauck

Fourth Advisor

Dr. Walter L. Loope

Abstract

Pictured Rocks National Lakeshore is among the most popular parks in Michigan, yet prior to this study, it was the only National Park that lacked a detailed surficial geology map characterizing the distribution of sediments and landforms. Additionally, much of the landscape remained unexplored. These factors prevented thorough interpretations of landscape development and evolution. This research aims to map and further explore the relationship of glacial sediments and landforms throughout Pictured Rocks to refine and expand the current understanding of glacial events that shaped this landscape.

A new, detailed (1:24,000-scale) surficial geology map of the ten 7.5-minute quadrangles that contain Pictured Rocks was developed as part of this study. Sediments were classified below the surface soil horizons throughout the mapped area. Additionally, the horizontal-to-vertical spectral ratio (HVSR) passive seismic method was employed throughout the greater Pictured Rocks region to estimate glacial sediment thickness and subsurface bedrock topography. Optically Stimulated Luminescence (OSL) dating was performed on two samples chosen from specific landforms of interest to help develop a chronological framework for this region. However, insufficient sediment bleaching yielded ambiguous OSL results. Field investigations were combined with several additional, preexisting datasets to produce the final surficial geology map of the Pictured Rocks area.

Mapping reveals notable regional differences in sediment and landform distribution. The western portion of Pictured Rocks consists of subtle subglacial and ice-marginal landforms that appear to have been segmented by subsequent proglacial outwash deposition. These features are largely underlain by undifferentiated thin sediment accumulations above shallow bedrock. The east displays thicker accumulations of glaciofluvial sediments consisting of various outwash units. Collectively, the surficial geology in the west and east areas of Pictured Rocks create a landform suite that is characteristic of actively receding glaciers in temperate climate conditions. Several buried bedrock valleys were also discovered and/or confirmed throughout the study area, which are interpreted as southern extensions of the glacial tunnel valley network carved into the floor of the Lake Superior basin north of Pictured Rocks. Sediments deposited during the final stages of deglaciation buried the southernmost segments of many of these valleys.

The surficial geology map and subsurface findings serve as primary resources to guide landform interpretations throughout the study area. These interpretations are integrated into a newly-proposed reconstruction of glacial events that occurred from the late Pleistocene through final deglaciation of the Pictured Rocks region during the early Holocene. This research has revealed greater detail of sediment-landform assemblages and the subsurface bedrock topography, which has led to a more comprehensive analysis of the glacial processes that shaped the Pictured Rocks landscape.

Access Setting

Dissertation-Open Access

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