Baltimore Ecosystem Study Institute of Ecosystem Studies

2014 BES Annual Meeting Presentation and Poster Abstracts

Investigating geochemical weathering of regolith and bedrock in Dead Run watershed
Gau, Samuel
Co-Authors: Dr.Joel Moore, Dr.Claire Welty, Dr. Dan Bain

Abstract: In order to study geochemical weathering rates in Dead Run, we collected core samples from the regolith (soil and saprolite) overlying two geologic formations in the watershed: the Mt. Washington amphibolite (amphibolite rock forming minerals are primarily horneblende, plagioclase, and epidote) and the Hollofield layered ultramafite (formation made of the minerals in amphibolite, actinolite, and serpentinite). We analyzed regolith chemistry using X-ray Fluorescence. To interpret chemical changes, we normalized the concentration data to zirconium, an element that is chemically immobile in most weathering profiles, to determine elemental depletion or enrichment in the regolith profiles. The following major elements Na, Mg, Ca, Ti, Mn, Fe, Al, Si, and P were all depleted from 0.29-1.13m depth in the profile indicating the boundary between the chemically altered, but physically undisturbed saprolite and the chemically and physically altered soil layer. In both locations, however, the regolith was considerably enriched with silicon, aluminum, and iron oxides relative to the bedrock. In the amphibolite concentrations of magnesium and calcium are substantially lower than they are in the bedrock. This most likely indicates that the regolith is composed of secondary clay and Fe-oxide minerals and that the weathering of primary minerals (those present in the bedrock) occurs at a deeper location near the bedrock interface. It is important to identify these features in the profiles as these features reveal how weathering works and affects the ecology in surrounding areas.