Fern Macroflora Identified in the Basal Danian of the Raton Formation Supports Palynological Signal of a Widespread “Postdisaster” Fern Flora

Abstract

Premise of research. From a purely palynological perspective, lowest Danian fern-dominated assemblages of the Williston Basin (North Dakota and southwestern Saskatchewan) and the Raton Basin (northeastern New Mexico and southeastern Colorado) appear indistinguishable, although this perspective has yet to be corroborated by macrofloral studies across this same region. No ferns have been collected from the lowest Danian barren series of the Raton Formation in more than a century, and this section remains sparsely sampled. Methodology. New collections of fossil ferns from the basal portion of the barren series or informal middle member of the Raton Formation, which directly overlies the K/Pg boundary, are compared with contemporaneous assemblages in other North American depositional basins. Pivotal results. Dennastra sorimarginata McIver and Basinger (Dennstaedtiaceae Lotsy) and Woodwardia arctica (Heer) Brown (Blechnaceae Newman) that produce Cyathidites diaphana (Wilson and Webster) Nichols and JL Brown and Laevigatosporites haardtii (Potonié and Venitz) Thomson and Pflug, respectively, are recognized as characteristic ferns in the basal portion of the barren series, in addition to Osmunda macrophylla Penhallow. Conclusions. In accordance with palynological perspectives, lowest Danian fern macrofossil assemblages from the Raton Basin support the concept of a geographically widespread “postdisaster” pteridophyte flora represented predominantly by Dennstaedtiaceae and Blechnaceae, with other minor components of more northern assemblages. The enigmatic hypothesis of a landscape dominated by anemiaceous or schizaeaceous ferns is rejected on the basis of this new evidence, which suggests that Cyathidites diaphana–producing dennstaedtiaceous ferns were the K/Pg boundary “disaster taxon” and among those that flourished in the Raton Basin.