GEOCHEMISTRY AND MINERALOGY OF A SOIL CHRONOSEQUENCE ON FLUVIAL TERRACES, FOUR MILE CREEK, SOUTHWESTERN OHIO

A soil chronosequence is valuable to understanding landscape evolution because it is possible to infer the relative length of time a geomorphic surface has been exposed. Multiple soil profiles were examined on fluvial terraces that range in age from historic to ~20,000 years old to determine the best methods of quantifying soil development in this area. The fluvial overbank parent material in Four Mile Creek is primarily reworked glacial outwash and glacial till of Wisconsin age. Bulk samples were collected in 10cm intervals from excavated trenches and river outcrops, air dried, and analyzed with a portable XRF analyzer to determine the elemental concentration with depth. The mineralogy at the base and surface of the profile was determined with powder XRD. Fe:Ca ratios were calculated from the elemental data to quantify weathering of the profile. Ti:Zr ratios were also calculated to determine if there was any variation in parent material with depth, as Titanium and Zirconium are immobile and retain the signature of the parent material.

The most notable changes in soil mineralogy and chemistry with age is the loss of carbonate minerals, a decrease in Ca concentrations, and the accumulation of Fe oxides. Soils older than ~15 ka contain <1% Ca above a depth of 1m and reach ~4% Fe at depth, with dominant minerals quartz, orthoclase, and albite at the surface with quartz and potassium feldspar at depth. The Fe:Ca values of these older soils were ~5 at the surface and increased to as high as 11 at depth. Latest Holocene and historic soils contain up to 7% Ca above a depth of 1m and ~2-3% Fe, with dolomite, quartz, and albite dominant at the surface and calcite, potassium feldspar, quartz, and dolomite at depth. The Fe:Ca values were relatively stable in these young soils, recording values ~1 throughout the profile. Therefore, initial results suggest that Fe:Ca and Ti:Zr ratios , in conjunction with mineralogy, are powerful tools to quantify soil development in this region.