PALEOECOLOGY OF LATE CRETACEOUS FOSSIL WOODS FROM CHACO CULTURE NATIONAL HISTORICAL PARK

During the Cretaceous, fossil evidence supports the expansion of flowering plants into habitats previously dominated by gymnosperm and pteridophyte floras. In an effort to better understand the paleoecological dynamics of this expansion, well-preserved and sampled plant fossils with paleoenvironmental data are essential. In this study, over sixty silicified wood specimens of in situ trunks and logs were collected from several exposures of the early Campanian Menefee Formation within Chaco Culture National Historical Park in northwestern New Mexico. Thin sections of samples were prepared and examined using light microscopy. Over 65% of the wood assemblage consists of a few different gymnosperms withCupressinoxylon as the most common. Several different angiosperm woods were identified with basal angiosperm families represented, such as Lauraceae, as well as those having affinities with core eudicots, and some new xylotypes. Three different conifer specimens contain extensive termite galleries. Growth rings and interruptions were identified in both gymnosperm and angiosperm woods and may be due to changes in water availability or other short-term disturbances. Generally, this assemblage is similar to other gymnosperm-dominated wood sites of Late Cretaceous age in North America. However, when comparing the wood character traits and paleoenvironmental data within the assemblage to other localities, trends in the co-occurrence of xylotypes and particular character traits will be discussed. Correcting for the influence of sampling and natural variability in wood anatomy within these settings requires modern analogue datasets. By gathering data on the settings and assemblages that supported more diverse forest habitats, we can gain insight into the expansion of angiosperm tree forms into different environmental niches.