DOI

10.17077/etd.q2f2com5

Document Type

Thesis

Date of Degree

Fall 2013

Degree Name

MS (Master of Science)

Degree In

Geoscience

First Advisor

Bettis, E Arthur, III

First Committee Member

Ward, Adam

Second Committee Member

Weirich, Frank

Abstract

The processes that generated the distinctive landscape of the Iowa Erosion Surface (IES) of northeastern Iowa have been debated for over a century. A number of researchers have concluded that the IES experienced a periglacial environment and was underlain by continuous permafrost during the last glacial maximum. Ubiquitous throughout the IES is a stone zone that lies 60-100cm below the surface. Several explanations for the genesis of the stone zone have been proposed, including a lag concentrate, biomantle processes, and cryogenesis. We utilized a combination of coring and trenching, ground penetrating radar and resistivity to investigate the 3D distribution of the stone zone, overlying "pedisediment" and the underlying contact with dense till across a 100m2 area on a typical IES hillslope in east-central Iowa .

Our preliminary results indicate that the stone zone occurs in the basal few decimeters of pedisediment that rests uncomformably and abruptly on eroded, dense till. Ice wedge casts extend from the stone zone into the underlying till. The depth of the stone zone below the modern surface increases downslope and the stone zone dissipates and eventually is replaced by relatively thick loamy sand beneath the footslope. These relationships argue against the stone zone being of biogenic origin. The occurrence of ice wedge casts associated with the stone zone and systematic changes in the thickness and texture of the pedisediment suggest to us that stone zone on the IES was formed by a combination of cryogenic and active zone erosive processes during the full glacial period.

Keywords

Biomantle, Cryogenesis, Geophysics, Iowa Erosion Surface, Lag Concentrate, Stone Zone

Pages

viii, 126 pages

Bibliography

Includes bibliographical references (pages 124-126).

Copyright

Copyright 2013 Jeffrey Alan Matzke

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