A LATE CRETACEOUS CONIFEROUS WOODLAND FROM THE SAN JUAN BASIN, NEW MEXICO

The Fossil Forest Research Natural Area (FFRNA) in New Mexico is the site of an exceptionally preserved fossil forest of Campanian age. This study combines paleoecological, taxonomic, and sedimentological analysis, together with GIS mapping of 68 fossil tree stumps and nine fossil logs, in order to provide a detailed description of this forest. Wood analysis of stumps illustrates that the forest is almost exclusively composed of conifers most likely related to the Cupressaceae. Reconstruction of the forest indicates that the conifers were mature and widely spaced, creating an open canopy woodland; however, leaf litter directly associated with the fossil woodland has not been preserved, so the detailed composition of its understory remains enigmatic. Analysis of the substrate in which the stumps were rooted suggests that trees grew in a gley soil under wet floodplain conditions. Mean sensitivity analysis of growth rings in the stumps indicates that small-scale environmental disturbances on the floodplain, such as periodic flooding, or regional environmental disturbances, such as volcanism, disrupted wood production. The death of the woodland was probably due to waterlogging and burial by suspended sediment associated with flooding. Despite the presumed dominance of angiosperms in disturbed, riparian environments during the Late Cretaceous, this study indicates that conifers were still dominant in some subenvironments at this time and could form mature open canopy woodlands on wet unstable floodplains.