New Mexico Geological Society Annual Spring Meeting — Abstracts

New fossil sites near Placitas, New Mexico, yield a diverse array of vertebrate bone, teeth, footprints, insects and other invertebrate fossils, and plant macrofossils. This and the nearly complete Lower Permian stratigraphic section provide a unique opportunity to reconstruct past climate and paleoecology for this critical period in earth history. Plant remains commonly occur in the typically brick red to maroon sandstones of the lower Permian Abo Formation but consist nearly exclusively of impressions of branch fragments of the early conifer Walchia. The monodominance of walchian conifers probably reflects a taphonomic bias toward preserving these robust and heavily cutinized three dimensional branch systems in a coarse-grained sediment. The discovery of a dark gray shale lens near the top of the Abo Formation (NMMNH locality 3922), bearing abundant plant reamins, offers a rare glimpse of co-occurring floral elements that are not preserved in most cases. In addition to conifer branch fragments, these floral elements include the peltasperms Rhachiphyllum schenkii and Autunia conferta, cordaite leaf fragments, the seed genus Samaropsis sp. and small seeds of unknown affinity, pecopterid frond fragments, and charcoalified wood. The fragmentary nature of the plant remains indicates that they either underwent transport or experienced some biological degradation pror to burial. This allochthonous assemblage provides valuable information on overall diversity, because it may represent sampling over a broader geographic area and possibly greater diversity of habitats. Although occurring gradually in time, the Permo-Carboniferous transition represents a period of global scale climate change of unusually great overall magnitude. The Wolfcampian Placitas flora, in conjunction with the older Kinney Brick and the Carrizo Arroyo floras, provides possibly time ordered documentation of unique regional aspects of the transition to the drought tolerant sclerophyllous floras that originated in the Late Carboniferous and persisted to comprise the dominant floras of the Permian.