MINERALOGICAL ANALYSIS OF A GUMMI BED FROM THE MIDDLE DEVONIAN

Numerous bentonite beds have been found in the Devonian sequences of the Appalachian Basin. These beds typically have a gummi or soapy feel because of the presence of water saturated clays. One of these gummi beds was found at a Devonian section at Hannacroix Creek. This gummi bed was determined through mineralogical and microscopic analyses not to contain the typical characteristics of bentonite beds such as, illite/smectite mixed layer clays, and igneous phenocrysts (biotite, zircon, amphibole, apatite, quartz and sanidine). The bed may still be the remnants of an ash bed that underwent reworking and/or other preservational processes through which some of the bentonite characteristics may have been loss.