FLORAS FROM THE PREHISTORIC TRACKWAYS NATIONAL MONUMENT, PENNSYLVANIAN-PERMIAN BOUNDARY, SOUTHERN NEW MEXICO

Fossil floras, exclusive of fossilized wood, have been identified within or in the immediate vicinity of the Prehistoric Trackways National Monument, Robledo Mountains, Doña Ana County, NM. The floras range in age from near the Pennsylvanian-Permian boundary into the Lower Permian, occurring in the Community Pit, Robledo Mountains and Apache Dam formations. The oldest, from the Community Pit Formation (CPF) occur in micritic mudstones preserved in a small, possibly submarine, paleovalley. The flora is dominated by voltzialean conifers (the oldest reported occurrence of this lineage), Dichophyllum moorei, and calamitalean foliage. Several assemblages occur in rocks of the Robledo Mountains Formation (RMF), a partial equivalent of the Lower Permian Abo Formation, which crops out extensively to the north. The most extensive of these RMF floras is dominated almost exclusively by walchian conifers, preserved in interbedded siltstones and claystones with evidence of periodic subaerial exposure. Small collections from other sites are dominated by conifers, and include callipterids and Taeniopteris, or by the gigantopterid seed plant Gigantopteridium, extremely rare in Abo and equivalent rocks, or by Supaia, locally abundant elsewhere in the Abo. A single occurrence of Taeniopteris was recorded in the Apache Dam Formation, in a deposit that appeared to be intermittently flooded and repeatedly re-colonized by plants. The RMF floras are typical for rocks of the Early Permian Abo red beds and occur in facies similar to those found elsewhere in the Abo throughout central and southern New Mexico. The CPF flora, however, is unique compositionally and in terms of the facies in which it is preserved. It appears to be coastal vegetation that includes elements typical of younger (Missourian-Kasimovian) and older (late Leonardian-Kungurian) floras elsewhere in equatorial Pangea.