Mineralogical Evidence of Peoria Loess Addition to Soils of the Green Bay LobeShane Degen, Secondary Education & Peter Jacobs (mentor), Geography and Geology.

Typical thin loess mantle in south central Wisconsin. (representative photo)

90 cm Peoria Loess mantles

The purpose of this study is to demonstrate the mineralogical evidence of loess addition to soils on the Green Gay Lobe surface; specifically we compare mineralogical properties of a soil with an obvious loess cap with those of a soil typically interpreted as being derived from glacial sediment.

Genge 1 SiteSoil with an obvious loess cap

Hake Drumlin SiteSoil lacking an obvious loess cap

Genge 1

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Fine Earth Cumulative Percent (+ CF)

Dep

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sand

clay

C. Frags

Particle fraction analysis by sieve and pipet. Note high silt content of loess-derived upper horizons that grade into the sandy glacial sediment, indicating mixing.

Quantification of clay mineral composition in the Hake profile. Expandable clay minerals are a distinctive signature of Peoria Loess and indicate much the chemical reactivity can be attributed to a loessial input to this soil.

Hake MgAD

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Cumulative %D

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expandables illite kaolinite

We wish to acknowledge support for this research from the Provost’s Summer Research Scholars program, the UWW Undergraduate Research Program, and Dr. Joe Mason, UW-Madison for use of his laser particle size analyzer.

High resolution particle fraction analysis demonstrates a strong modal particle size in the silt fraction of the loess-derived horizons, and mixing with the glacial sediment.

Dodge County drumlin hillslope cross section. Note how major soil genetic horizon (Bt) thickness appears to be controlled by loess thickness as identified in the field. (■ = sampling sites)

Genge East Transect

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Distance (m)

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Base of loess

Base of Bt

Glacial sediment

Typical south central Wisconsin soil mapped as being derived from glacial sediment. (representative photo)

Hake

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Diameter (mm)

A 0-12cm

AE 12-18cm

E 18-35cm

BE 35-43cm

Bt1 43-53cm

Bt2 53-69cm

Bt3 69-80cm

BC 80-90cm

C 90-115+cm

High resolution particle fraction analysis demonstrates a strong modal particle size characteristics of loess is only in the uppermost horizons. Sand from the glacial sediment has been thoroughly mixed to the surface.

Hake VFS Weathering Ratio

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P/Q

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Ratios of weatherable to resistant minerals in the very fine sand fraction determined by x-ray diffraction. Ratios of potassium feldspar (K) to quartz (Q) are nearly uniform with depth, indicating no significant chemical weathering and depletion of potassium feldspars in the soil. Plagioclase feldspar (P) to quartz are more erratic, but do not indicate significant depletion of P. Minimal weathering of minerals that could supply clays indicate that loessial input of clays is critical to the ecosystem productivity of these soils.

Gathering samples in the field

stony glacial sediment

Expandable clay minerals are a signature of Peoria Loess across the midcontinent. (E = expandable, I = illite, K = kaolinite, and Q = quartz)

E

IK

Q

Loess derived horizon

Glacial sediment

Particle fraction analysis by sieve and pipet. Note high sand content throughout the soil, which soil surveyors interpreted to indicate the soil is derived from sandy glacial sediment.

Sand Silt Clay

Stack of x-ray diffractograms of clay fraction in all horizons of the Hake profile. Note high content of the expandable minerals throughout all soil horizons, indicating much of the critically reactive clay fraction in these soils can be attributed to loess input, even though the soil composition is dominated by sand from the glacial sediment.

E I K

Genge 1 profile clay fraction x-ray diffractograms. Note high content of the expandable minerals throughout all soil horizons, indicates much of the critically reactive clay fraction in these soils can be attributed to loess input, even into horizons dominated by sandy glacial sediment.

E I K