TRIASSIC–JURASSIC STRATA OF THE COLORADO SPRINGS REGION AND ASSOCIATED PALYNOFLORA

The Triassic Lykins Formation, a succession of red sandstone and shale, overlies Permian–Triassic eolian deposits of the Lyons Formation in the Colorado Springs region. These dominantly terrestrial deposits contain one to two 45–79 cm thick stromatolite beds and associated minor intraclast conglomerate. Above the Lykins lies strata of uncertain stratigraphic affinity, a 15.7 m thick unit of silty shale, fine sandstone, and thick crystalline gypsum layers, locally up to 10.7 m thick. At two localities, the top of this unit contains a thin (<1 m) well-known chert-bearing unit mapped extensively in the central and western U.S. as the base of the Morrison Formation. This bed, recognized for first time in the Colorado Springs area, marks a significant shift in facies from restricted marine basin deposits to freshwater terrestrial strata of the overlying strata that consist of gray sandstone, shale, carbonate mudstone, and up to three, 24-45 cm thick, stromatolitic lacustrian limestone beds. We correlate the latter to similar beds on the Comanche National Grasslands, ~250 km to the southeast. The carbonate beds at that locality include oolitic grainstone, freshwater ostracods, and dinosaur bones and footprints. Thin layers of organic rich shale to poorly developed coal in the uppermost beds of the evaporite succession have yielded pollen and sparse dinoflagellates. This is the first report of palynomorphs from this member. The low-diversity palynoflora is dominated by two species of fern spores, Ischyosporites marburgensis (Schizaeaceae) and Cyathidites minor (possibly the tree fern family Cyatheaceae), and the extinct conifer taxon Classopollis. Other rare taxa include Araucariacites spp. (representing the southern hemisphere family Araucariaceae) Exesipollenites tumulus (?Taxodiaceae), and bisaccates (?Pinaceae), as well as the dinoflagellates Spiniferites and Odontochitina. The assemblage resembles others previously recovered from elsewhere in the Morrison Formation, except for its much lower diversity. Classopollis is often indicative of drier conditions, but the abundance of two spore types (as well as the presence of coal) suggests wetter conditions, perhaps a local wetland with input from drier adapted plants occupying interfluves.