Genesis of Argillic Horizons in Ochraqualfs Derived from Fine Textured Till Deposits of Northwestern Ohio and Southeastern Michigan

Abstract

Abstract Chemical, physical, mineralogical, macro‐ and micro‐morphological data are presented for Bt and C horizons of Nappanee profiles (Aeric Ochraqualfs); three of which were sampled in the lake plain region of Ohio and the fourth on the Defiance Moraine in Michigan. Calcareous till deposits are similar across the study area: lake plain sites average 36% clay vs. 40% for the Michigan site; carbonate equivalents average 24%, with 20% of the total consisting of carbonate clays; and calcite/dolomite ratios average 2.5. Bt/C total clay and Bt fine/coarse clay ratios average 1.3 and 0.7, respectively, for these profiles. A lithological break was identified between the Ap and argillic horizon of all profiles which negates the use of A/B clay ratios in establishing argillic horizons in these soils. Under such conditions B/C total and/or fine clay ratios would be more appropriate as supporting criteria of an argillic horizon. Maximum fine clay gain usually occurs in upper Bt horizons. The Michigan profile has strong continuous illuviation argillans along conducting voids, but profiles of the lake plain exhibit only striated illuviation and stress cutans. More strongly expressed illuviation features of the former are attributed to the higher frequency of wetting‐drying cycles on the older, more strongly dissected Defiance Moraine. The Michigan Nappanee profile is similar to the Blount soils of Ohio in its argillic horizon expression but lacks the degradation in the upper Bt horizons characteristic of the Blount.