Bulletin 044

Author(s) Date 1982-12-31

Four outcrop sections and three subsurface cores were sampled for palynological study of the Cenomanian rocks in northwestern Alberta. The rocks comprise marine shales of the upper Shaftesbury and lower Kaskapau Formations, with a wedge of deltaic to prodeltaic sediments of the Dunvegan Formation between the two units.

Only the upper Shaftesbury and Dunvegan Formations contain ufficiently well preserved and diverse microflora for establishing a reliable microfloral succession. Most of the microflora in the lower Kaskapau Formation and the sections in the western region close to he Rocky Mountain Foothills has been destroyed by organic metamorphism. However, a large number of megaspores were recovered, which seem to have survived the thermal effects in this area.

Of the 416 microfloral species present in the Cenomanian strata of northwestern Alberta, 225 continue from the underlying Albian deposits. The remaining 191 microfloral species appear in the Cenomanian strata for the first time. These consist of 30 genera and 2 species of microspores and gymnosperm pollen, 19 genera and 41 species of angiosperm pollen, 13 genera and 27 species of megaspores, and 54 genera and 81 species of microplankton. Of these, 5 species of microspores and gymnosperm pollen, 1 genus and 22 species of angiosperm pollen, 10 species of megaspores, and 2 genera and 25 species of microplankton are new.

The upper Shaftesbury microflora is of early Cenomanian age and reflects an open marine environment of deposition. It contains many species of dinoflagellates which make their entrance in strata of latest Albian (Vraconian) or younger age. Angiosperm pollen consisting of small, psilate, triangular, tricolporates and permanent tetrads, which mark the Albian-Cenomanian boundary in North America, are also present in the upper Shaftesbury Formation. This unit further contains a few species of megaspores which occur only in strata of Cenomanian or younger age.

The Dunvegan Formation is of middle Cenomanian age and was deposited under deltaic to prodeltaic conditions. Megaspores are abundant in this unit and consist of Ariadnaesporites, Molaspora, and distinctive species like Paxillitriletes dakotaensis which characterize strata of Cenomanian age in North America. Large, tricolporate, angiosperm ollen with thick, reticulate to tectate-perforate, foveolate exines, and dark, costate colpi become well established in the Dunvegan Formation. Morphologically similar angiosperm pollen are known to ake their entrance in strata of middle Cenomanian age in the United States. The angiosperm tetrads diversify in the Dunvegan Formation and are represented by species with three different types of exine sculpture. Some of these species have a worldwide distribution and make their first appearance in strata of Cenomanian age. Additional species of angiosperm pollen comparable to those recorded from the Cenomanian strata of the eastern United States are also present in the Dunvegan Formation. However, the triporate Normapolles genera, which make their entrance during middle Cenomanian time in the eastern United States do not occur in the Dunvegan Formation. It seems that the Late Cretaceous epeiric sea in North America served as a partial barrier to the westward migration of the Normapolles flora, which was introduced into eastern North America from Europe. As a result, it makes a late appearance and is sparser in the region to the west of the Late Cretaceous seaway.

There are indications of three shallow marine incursions in the middle and upper parts of the Dunvegan Formation. These marine intervals are dominated by dinoflagellates, some of which make their entrance in Cenomanian strata in other parts of the orld.Palaeohystrichophora infusorioides makes its first appearance near the top of the Dunvegan Formation. This is in accord with its middle to upper Cenomanian entrance level in the Western Interior of North America.P. infusorioides appears earlier in Europe and Australia in beds of Vraconian (latest Albian) age. The appearance of two new species of Trithyrodinium and one species of Alterbia near the top of the Dunvegan Formation is also stratigraphically significant.

NTS Keywords

Singh, C. (1983): Cenomanian microfloras of the Peace River area, northwestern Alberta; Alberta Research Council, ARC/AGS Bulletin 44, 338 p.