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North-Central Section - 37th Annual Meeting (March 24–25, 2003)

Paper No. 3
Presentation Time: 8:00 AM-12:00 PM

A LATE PLEISTOCENE ROCK-MAGNETIC STRATIGRAPHY FROM GARFIELD HEIGHTS, OHIO


PECK, John, Office for Terrestrial Records of Environmental Change, Department of Geology, Univ. of Akron, Akron, OH 44325-4101, MULLEN, Andrea and SZABO, John, jpeck@uakron.edu

At Garfield Heights, OH, an exposed sediment section spans (from top to bottom) the Late Wisconsinan (till, loess, lacustrine sediment, upper loess), Middle Wisconsinan (lower loess, paleosol accretion-gley), and Illinoian (gravel having a B3 Sangamonian soil at the upper surface). Prior studies of this site have provided important insight on Wisconsinan stadial-interstadial stratigraphy and paleoenvironmental conditions. We revisited this classic site for the purpose of assessing if rock-magnetic measures of magnetic concentration, grain-size and mineralogy could be used to delineate sedimentary units and provide paleoenvironmental information.

The rock-magnetic parameters display pronounced variations corresponding to the major lithologic unit boundaries. The magnetically coarsest-grained units are the loesses. These intervals also have the smallest percentage of clay in the < 2 mm fraction. Conversely, as clay content of the < 2 mm fraction increases, the magnetic grain size decreases, thus magnetic grain size generally reflects the bulk sediment (< 2 mm) grain size. Rock-magnetic parameters also provide insight on paleoenvironmental conditions. For example, the Middle Wisconsinan paleosol accretion-gley is characterized by large amounts of extremely fine-grained (superparamagnetic), low-coercivity minerals (e.g., magnetite, maghemite). This magnetic mineral assemblage is characteristic of pedogenic enhancement and thus supports the paleosol accretion-gley interpretation for this unit. The top most 20 cm of the Middle Wisconsinan lower loess unit is leached silt having low concentrations of coarse-grained, high-coercivity minerals (hematite, goethite) suggestive of intense weathering before the accumulation of the upper loess unit (Late Wisconsinan).

This study demonstrates that rock-magnetic measurements can provide additional information useful in defining interstadial/stadial lithostratigraphy and for understanding paleoenvironmental conditions.

Session No. 19--Booth# 3

T5. Quaternary Geology of the U.S. Midwest (Posters)
Tuesday, 25 March 2003: 8:00 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 35, No. 2, February 2003, p.54
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