WOOD ASSEMBLAGES FROM WESTERN NORTH AMERICA: COMPOSITION AND PALEOECOLOGY OF EARLY CAMPANIAN PLANT COMMUNITIES FROM THE MENEFEE FORMATION

Silicified wood specimens are invaluable because they contribute evolutionary and paleoecological information not preserved in other types of floral remains. Furthermore, they provide confirmation that plants with significant secondary growth and tree stature defined the landscape as primary producers within the terrestrial paleoenvironment. In this study, over eighty well-preserved samples of in situ trunks and scattered logs were collected from several exposures of the early Campanian Menefee Formation in northwestern New Mexico. Specimens were analyzed using thin-section and cellulose-acetate peel techniques with light and scanning electron microscopy. Gymnosperms dominate the assemblage with specimens consisting of a few xylotypes including Cupressinoxylon and Araucarioxylon. Angiospermous woods include those with possible Lauraceae and Anacardiaceae affinities, Palmoxylon, and some new xylotypes. Other features preserved in the wood include two conifer samples with extensive termite galleries, and growth rings and interruptions in some specimens. Mean sensitivity and vulnerability indices indicate some seasonality or short-term disturbances of the otherwise mesic environment and are consistent with other geologic evidence of a deltaic and coastal plain setting. Some of the trunks are relatively large, up to 60 cm in diameter, with most identified as coniferous. The composition is similar to other assemblages of Late Cretaceous woods, especially in North America, and characterized as gymnosperm dominated woodlands. Additional evidence of plant community structure along different landscapes and paleolatitudes is essential to developing a better understanding of the evolutionary and ecosystem dynamics at play during this critical time of angiosperm ecological expansion.