Basal Mixing Zones in Loesses of Louisiana and Idaho: II. Formation, Spatial Distribution, and Stratigraphic Implications
1988
Miller, B. J. | Schumacher, B. A. | Lewis, G. C. | Rehage, J. A. | Spicer, B. E.
Basal mixing zones of loess with different underlying materials in Louisiana and Idaho have been identified. Formation of basal mixed zones occurs when loess is deposited on a pedogenically active surface and becomes incorporated into the underlying stratigraphic unit through bioturbation and pedoturbation processes. Factors influencing basal mixed zone formation include climate, nature of stratigraphic materials underlying the loess deposits, and rate of loess deposition. The warm, humid climate in Louisiana is more conducive to the formation of thicker basal mixed zones than the cool, semiarid climate of Idaho. In Louisiana, thicker basal mixing zones were found where loess was underlain by coarse textured, unconsolidated materials than where underlain by unconsolidated materials with similar or finer textures. Amount and distribution of precipitation in Idaho appears to override the influence of underlying materials on basal mixed zone formation. A progressive thickening of basal mixing zones and thinning of the unmixed loess mantle was found as distance from the loess source increased until a point was reached where all loess was incorported or lost through erosion and the basal mixed zone occurred at the soil surface. Implications of the existence of basal mixed zones with respect to loess stratigraphy are discussed. approved for publication by the director of the Louisiana Agric. Exp. Stn. as manuscript number 87-09-1320. Contribution of the Agronomy Dep., LA Agr. Exp. Stn., Louisiana State Univ., Agr. Center, Baton Rouge, LA 70803.
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