Flora of the Ravenscrag Formation of the Big Muddy Valley, Willow Bunch Lake map area (72H), Saskatchewan

Abstract

Paleocene aged beds of the Ravenscrag Formation exposed in the Big Muddy Valley of Southern Saskatchewan produce numerous plant fossils. Studies into these fossils last occurred in the 1930s. Studies into the contemporaneous Ravenscrag Butte flora of southwestern Saskatchewan have shown that the flora of these beds needed updating. Collections of specimens and stratigraphic sections were taken from the area.

Forty species, including two new species and seven unknowns were identified. Elatocladus megasequoiae n.sp. and Corvirupestrobus adrielensis n.sp. are both Conifers, and Corvirupestrobus is also a new genus. Many species were previously unknown in Ravenscrag Formation floras, including cf.Lygodium sp., Thelypteris sp., Sparganium sp., Paloreodoxites plicata (Lesquereux) Knowlton, Carya antiquorum Newberry and Nordenskioldia borealis Heer. Two new combinations are proposed, transferring Quercus praegroenlandica Berry to Fagopsiphyllum praegroenlandicum (Berry) n. comb. and Harmsia hydrocotoloidea McIver and Basinger to Harmsvernia hydrocotoloidea (McIver and Basinger) n. comb., with Harmsvernia a new genus.

Three sub-floras are recognized for this flora. Sub-flora 1 is a conifer dominated swamp sub-flora, common to many Paleocene localities. Sub-flora 2 is a conifer dominated sub-flora suspected of being from a drier environment than florule 1. Elements of sub-flora 1 appear in sub-flora 2 and vice versa, but relative abundances differ. There is little taxonomic overlap between sub-floras 1 and 2 with sub-flora 3. Sub-flora 3 is more typical of contemporaneous localities to the south such as those of the Bear Den Member of the Golden Valley Formation (Hickey 1977), whereas sub-floras 1 and 2 are more typical of northern localities, like the Genesee locality (Chandrasekharam 1974) and Koryak Formation (Golovneva 1994). The Big Muddy Valley occurs at the ecotone between the Arctic floras and the floras of the South.

The taxonomy of Glyptostrobus from the Paleocene is revised as an appendix, written as a separate report. This revision is more extensive than for the other taxa of this study, utilizing materials from numerous other localities, including the Joffre Bridge Roadcut localities (Hoffman and Stockey 1999), the Smokey Tower localities (Christophel 1976) and the Buchanan Lake Formation (Basinger 1991).