DIFFERENTIAL PRESERVATION AND PERMINERALIZATION OF FOSSIL WOOD IN THE EARLY EOCENE CHICKALOON FORMATION

Fossilized wood is abundant in the floodplain facies of the early Eocene Chickaloon Formation of south-central Alaska. We studied numerous samples of fossil wood from several fossil localities in the Chickaloon Formation to better understand the permineralization history of the samples and to link this process to the depositional environment. Wood anatomical features of these samples indicate they are assignable to the form genus Taxodioxylon Hartig emend. Gothan, that is anatomically similar to modern Metasequoia glyptostroboides wood. We utilized bulk geochemical analyses, the study of petrographic thin-sections and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX) to characterize the mineralogy of permineralization at the scale of individual tracheids and annual increments. The dominant permineralizing materials were carbonates, with the carbonate phase ranging from siderite to ferroan calcite and dolomite depending on stratigraphic interval within some localities. Permineralization of some wood by silica was also detected in localized sections of the fossil wood collected from certain strata. Distortion of wood anatomical features and disruption of tree ring structure that resulted in poor wood structure preservation was apparently caused by the force of crystallization from an increase in authigenic crystal volume. An examination of relict carbonate textures and the quality of organic preservation in both carbonate and silica phases within individual samples, argues for late stage recrystallization of the carbonates in some specimens which may influence the interpretation of isotopic ratios of these carbonates.