Composition and Weathering of Loess Mantled Wisconsin‐ and Illinoian‐age Terraces in Central Ohio

Abstract

AbstractElemental and mineralogical evidence indicate that both loess and outwash deposits on relatively high Illinoian‐age terraces are more intensively weathered than comparable units of lower level Wisconsin‐age terraces. The Illinoian site, particularly in the outwash paleosol, has lower weight percentages of heavy minerals; lower hornblende contents; lower elemental Fe, K, and Ca contents; and more pronounced pedogenic transformation of micas to partially or fully expandable 14Å components. Subtle weathering trends of elemental Ca, even in the Illinoian paleosol, are attributed to its occurrence in more resistant plagioclase‐feldspars. The 50‐20µ light mineral fraction (sp. gr. < 2.86) in both loess and outwash units contains appreciably higher quantities of Ti, Zr, and Fe than was originally anticipated. From 50–70% of the Ti, 20–45% of the Zr, and 85–90% of the total Fe occurs in light minerals. Essentially all of the K and 70–90% of the Ca also occurs in this isolate. Loci of Fe, Ti, and Zr in light minerals have not been established but are postulated to be either micro occlusions of primary minerals in host framework silicates or proxy for other metallic cations in these structures.