TRANSFORMATION OF MODERN WOOD IN THE DUNE ENVIRONMENT

Investigation into the development of holes in the Mt. Baldy Dune at Indiana Dunes National Lakeshore indicates that in-place decay of buried trees is responsible for void formation. To understand the decay process, wood samples from several holes were analyzed using organic petrographic and micro-FTIR techniques. Megascopically, wood samples varied from relatively unaltered to moderately transformed by fungi and insects. Evidence for fungal activity includes brown- and cream-colored fungal hyphae and distinctive patterns of white-rot decay. Insect damage is inferred from borings and frass-laden holes in the wood. Petrographically, the wood is largely unaltered, although gelification of cell-fill materials has begun. Adjacent to areas of fungal decay, there are regions with delaminated cell walls and reduced fluorescence. Melanized hyphae occur in many cell lumens. These hyphae appear white in cross section and are morphologically identical to those described from Miocene and modern wood. Armillaria-type fungal hyphae display linear structures similar to those observed in some etched telinites; this may indicate that some textures interpreted as woody in the fossil record are of fungal origin. Frass is present in many samples; its size and morphology is consistent with that of Bess beetles, and it has the overall appearance of finely macerated oak wood. Chemically, relatively unaltered wood is characterized by distinct aliphatic stretching bands (2800-3000 cm^-1 region), a prominent aromatic carbon band (peak at ~1604 cm^-1), aliphatic bands in the bending mode (1300-1500cm^-1), and distinct bands that are assigned to cellulose and lignin (1000-1300 cm^-1). Especially prominent is a high-intensity cellulose band (peak at 1118 cm^-1) and a lower-intensity lignin band (1218 cm^-1). The main chemical difference between the hyphae and the wood is the absence of a cellulose band at 1118 cm^-1 in the former and the appearance of a large 1080 cm^-1 band assigned to the –C-O-C cm^-1 band in lignin. Wood that is affected by fungal activity shows increases in intensity of lignin bands compared to the cellulose. Frass is chemically similar to the wood, although the intensity of aliphatic stretching and aliphatic bending modes is lower and, like the hyphae, there is a lack of a cellulose band in favor of a lignin band at 1083 cm^-1.