Original paper

New occurrences of the controversial Late Triassic plant fossil Sanmiguelia Brown and associated ichnofossils in the Chinle Formation of Arizona and Utah, USA

Ash, Sidney R.; Hasiotis, Stephen T.


Fragments of the rare and distinctive palm-like leaves of the controversial Late Triassic plant Sanmiguelia have been discovered recently in both Petrified Forest National Park, Arizona and Arches National Park, Utah. Although, the new specimens do not clarify the classification of this intriguing fossil, they do confirm that it occurs in all members of the Chinle Formation except for the very lowest units, the Shinarump, Mesa Redondo, and Temple Mountain members. Furthermore, their discovery in Petrified Forest National Park extends the known geographical distribution of the fossil into east-central Arizona and demonstrates that it is a characteristic member of the Late Triassic flora of the American southwest and requires a revision of the Chinle floral zone scheme proposed and revised earlier by Ash (1980). In Petrified Forest National Park the leaves are associated with several types of ichnofossils including Scoyenia, Arenicolites, Cylindrichum, cf. Scolicia, cf. Beaconites, Selenchnites, and other trace fossils in open nomenclature. These trace fossils suggest that Sanmiguelia was preserved in high moisture, imperfectly drained, water-margin setting inhabited by phytosaurs, snails, horseshoe crabs, and a variety of arthropods such as beetles and dipteran larvae and record high water table conditions punctuated by flooding and overbank deposition. The findings reported here generally support and improve on previous interpretations of the paleoenvironment inhabited by the Sanmiguelia plant.


sanmiguelia lewsiiscoyenianorianchinle formationplant fossilscontinental ichnologyarizonautah