Chemical and Mineralogical Cementing Agents in Fragipans from Pennsylvania Parent Materials

The fragipan diagnostic subsurface horizon is identified in soils on diverse landscapes throughout the world. In Pennsylvania, fragipans have been identified as having formed in aeolian, alluvial, glacial, peri-glacial (colluvial), and residual (including numerous geologies) parent materials. Fragipans are also identified in soils of varying age in Pennsylvania; in inceptisols, alfisols, and ultisols. Numerous theories abound as to the formation of the fragipan and what are the binding agents for this dense, root and hydraulically restrictive subsurface horizon. We collected soil samples of fragipans in Eastern and Central Pennsylvania that formed in a variety of parent materials and geologies. Pedogenic opaline silica was quantified by tiron extraction and crystalline and amorphous Fe and Mn structures via citate dithiotnite and acid ammonium oxalate. Structures and cementing agents within fragipan horizons were examined utilizing a Focused Ion Beam (FIB) and Transmission Electron Microscope (TEM).