Palynology of a short sequence of the Lower Devonian Beartooth Butte Formation at Cottonwood Canyon (Wyoming): Age, depositional environments and plant diversity

The Beartooth Butte Formation hosts the most extensive Early Devonian macroflora of western North America. The age of the flora at Cottonwood Canyon (Wyoming) has been constrained to the Lochkovian-Pragian interval, based on fish biostratigraphy and unpublished palynological data. We present a detailed palynological analysis of the plant-bearing layers at Cottonwood Canyon. The palynomorphs comprise 32 spore, five cryptospore, two prasinophycean algae and an acritarch species. The stratigraphic ranges of these palynomorphs indicate a late Lochkovian - Pragian age, confirming previous age assignments. Analyses on samples from three different depositional environments of the plant-bearing sequence – layers with in situ lycophyte populations, flood layers that buried those populations and an organic matter accumulation zone within a flood layer – demonstrate distinct palynofacies. Comparisons between palynomorph and plant macrofossil diversity reveal some discrepancies. Whereas zoste...