Needle in a Haystack or a Stack Full of Needles: Distinguishing Pedogenic Gypsum From Parent Materials Rich in Gypsum.

The identification and distinction of pedogenic gypsum from gypsum that occurs in the parent material is important for understanding pedogenic processes and for use in  Soil Taxonomy.  Recognition of pedogenic gypsum in soils that have formed from parent materials which are predominantly gypsum  can prove extremely difficult or impossible in the field.  This research is focused on studying the processes of pedogenesis related to gypsum movement and transformation in a soil that has formed from a parent material  composed of greater than 95% gypsum.  Soils selected for study were located in Culberson and Hudspeth counties in West Texas and formed from gypsic bedrock (Permian, Castile Formation).  Thin sections, SEM analysis, XRD, along with features observable in hand specimen were utilized in order to ascertain the processes of formation which occur. Preliminary analysis of thin sections showed an alteration of the crystal structure and habit from the parent material, which appears to undergo a discernible series of changes as pedogenesis progresses.   For soils forming on the Castile Formation, the dissolution of interlocking crystals and the formation of lenticular gypsum crystals, which are commonly associated with pedogenic processes, were observed to occur in soils that had greater degrees of pedogenesis.