New charophyte flora from the Pine Hollow and Claron formations (southwestern Utah). Taxonomic, biostratigraphic, and paleobiogeographic implications

Abstract

Paleogene non-marine deposits of the Pine Hollow and Claron formations (southwestern Utah, USA) provided a rich microfossil assemblage composed of charophytes, freshwater gastropods and ostracods. Charophytes were extracted from a ca. 450-m-thick section, especially from floodplain deposits belonging to the Claron and the Pine Hollow formations. The samples from the Pine Hollow Formation includes small and recrystallized populations of Psilochara sp., Peckichara sp. and Harrisichara sp. The occurrence of these genera suggests that this unit is Paleogene in age. The richer charophyte assemblage was recovered from the Claron Formation and is dominated by Microchara cristata, Microchara cf. punctata and Peckichara torulosa (here synonymized with the well-known Eurasian species Peckichara varians), along with Lychnothamnus sp. and Dughiella sp. Based solely upon charophyte Euroasiatic biostratigraphic ranges of M. cristata, M. punctata and P. torulosa, the basal/middle part of the Claron Formation is probably Danian in age. However, recent biostratigraphic studies based on mammals indicate that the middle part of the Claron Formation (unit 7) is early Eocene in age. The correlation of charophytes with mammals and the lack of significant unconformities in this formation suggest that these species could live longer in North America than Eurasia. The lack of North American charophyte studies, along with the long biostratigraphic ranges of the dominant taxa, M. cristata and P. torulosa, makes precise relative dating, solely on the basis of charophytes, difficult. This study also provides valuable data about Eurasian charophyte species and genera discovered for the first time in North America.