Fertile organs and in situ spores of ferns from the late Triassic Chinle Formation of Arizona and New Mexico, with discussion of the associated dispersed spores

Abstract

The fertile structures of four late Triassic leptosporangiate fern species are described, as are their isolated spores. The spores are compared both with in situ spores of other known fertile species of the same genera and with the most similar dispersed spores of the Chinle Formation palynoflora. The species included in this study are Todites fragilis Daugherty emend. Ash (family Osmundaceae), Wingatea plumosa (Daugherty) Ash (family Gleicheniaceae?), Phlebopteris smithii (Daugherty) Arnold emend. Ash et al. (family Matoniaceae), and Clathropteris walkeri Daugherty emend. Ash (family Dipteridaceae). The fluvial and lacustrine, calcareous, bentonitic silstones of the Petrified Forest and Monitor Butte Members of the late Triassic Chinle Formation, from which these fern specimens were collected, bear an abundant and diverse dispersed palynoflora containing Brodispora striata, Camerosporites secatus, Enzonalasporites vigens, Granulatisporites infirmus, Ovalipollis pseudoalatus, Patinasporites densus, Pyramidosporites traversei, Pseudoenzonalasporites summus, Vallasporites ignacii, and other species. The presence of these species suggests a mid-to-late Carnian age for these strata, as was previously reported by several authors. It may be possible to place the assemblage more precisely in the late Carnian (Tuvalian substage), based on the presence of Brodispora striata and Pseudoenzonalasporites summus, the absence of Carollina, and the almost complete absence of striate bisaccate forms. In these characteristics this assemblage is similar to that in strata of the Dockum Group of the southwestern United States, parts of the “Newark Supergroup” of the eastern United States, and portions of the late Triassic of Europe.