Bulletin No. 42. Lower Upper Cretaceous Plant Microfossils from Minnesota

Spores and pollen from the pre-marine Cretaceous clays and lignites of Minnesota indicate that the probable age of these deposits is Cenomanian. Forests of conifers appear to have been the main type of vegetation; however, these forests contained a diversity of species that do not occur in modern conifer forests of the State. Many of the conifer pollen species found appear to be referable to the Podocarpaceae, a family of Eastern Asiatic, Mexican, and Southern Hemispheric distribution. Dicotyledonous angiosperms were present in the flora, but their pollen is seldom abundant in the Cretaceous deposits of Minnesota. The morphological simplicity and lack of diversity of the angiosperm pollen in these rocks indicate that the angiosperms were at a lower stage of evolution than that often ascribed to them on the basis of leaf impressions from the same rocks. The physiognomy of the flora reflected by the spores, pollen, and previously described leaf impressions can be reconciled with the physiognomy of floras that occur in moist, warm-temperate areas such as Seattle, Washington. A moist, warm-temperate climate, in an area of little relief, is postulated to have prevailed in Minnesota during Cenomanian time