The Unified Theory of Fragipan Genesis.

The fragipan subsoil horizon is one of the most land use limiting soil horizons worldwide due to its ability to perch water and limit deep rooting.  Multiple theories of fragipan genesis have been proposed for discrete parent materials with little agreement in processes, but general agreement to common properties and geography.  How a soil horizon with such similar characteristics occurs over such a broad geographic range with contrasting major land resource areas and geological history is still a perplexing issue in pedology.  We present a new, more unifying hypothesis explaining the distribution of fragipans and show that the fragipan horizon’s dominant characteristics of high bulk density and prismatic macro-structure were polygenetic, derived in the late Wisconsinan, and that eolian influence was necessary for genesis.   We postulate that a unifying theory of fragipan genesis consists of: a) a transported parent material that has density imparted to it via desiccation and consolidation (producing coarse prismatic structure);  b) containing 30 – 70% silt, and approximately 5-35% clay; and c) that the deposit be all or in part derived from eolian sources.  The importance of this new theory to other Geoscience fields is significant since the fragipan’s extent is intimately tied to eolian deposition.  Fragipans may be considered an indicator of climate change.  Its ephemeral nature, degrading over time to the point where other soil horizons engulf the fragipan, supports this hypothesis.