New Mexico Geological Society Annual Spring Meeting — Abstracts

A recently discovered locality in the Trujillo Formation, Chinle Group, south of Lamy, Santa Fe County, New Mexico (T12N, R11E), yields a remarkably well-preserved Upper Triassic paleoflora. The fossil plants come from two stratigraphic levels in an ~1-m-thick bed of muddy, micaceous fine-grained sandstone and siltstone. Locally, the Trujillo Formation is ~24 m thick, and the plant levels are ~18 m below its contact with the overlying Petrified Forest Formation. We interpret the plant-bearing bed as a shallow lacustrine deposit that developed on the floodplain surface between Trujillo channel courses. The paleoflora is dominated by carbonized compressions of two taxa, the palmate fern Phlebopteris smithii (Daugherty) (including complete, monopodial palmate leaves) and the bennettitalean Otozamites powelli (Fontaine). Much less common plants include the fern Todites fragilis Daugherty and the horsetail Neocalamites. The quality of preservation of this macroflora is exceptional, encompassing epidermis, sporangia and spores. This paleoflora is characteristic of the Dinophyton floral zone, yet it is stratigraphically high for an occurrence of this floral zone. Thus, the overlying Sanmiguelia floral zone normally is found in Trujillo Formation strata. Nevertheless, near Las Vegas in San Miguel County, Sanmiguelia has been found below the Trujillo Formation, in the uppermost Garita Creek Formation. The Lamy locality thus adds to evidence that there is a stratigraphic overlap between the Dinophyton and the Sanmiguelia floral zones in the middle part of the Chinle Group.