Bulletin 028

Bulletin 028

BUL 028

Lower Cretaceous Microfloras of the Peace River Area, Northwestern Alberta

Author(s) Singh, C. Date 1971-01-01

Eight sections of Lower Cretaceous rocks exposed along the Peace and Smoky Rivers in northwestern Alberta were sampled for palynological study. The rocks comprise a succession of interbedded shaly and arenaceous units of predominantly marine origin, encompassing the upper part of the Loon River Formation, the Peace River Formation Notikewin, Harmon, Cadotte, and Paddy Members), and the lower part of the Shaftesbury Formation, dated as Albian on the basis of faunal content.

The microflora recovered from these strata contains 94 genera and 202 species of microspores and pollen, 7 genera and 13 species of megaspores, and 47 genera and 114 species of microplankton. Of these, 1 genus and 31 species of microspores and pollen, 1 genus and 1 species of megaspores, and 20 species of microplankton are new. The oldest microflora, from the upper part of the Loon River Formation, is essentially similar to the nonangiospermous upper Mannville microflora (middle Albian) of central Alberta. Angiosperm pollen make their main entrance in the Peace River Formation in the upper part of the Harmon Member, and show marked evolutionary diversification in the overlying beds. Many of these angiosperm species are known to make their entrance in strata of middle and late Albian age in other parts of North America The microflora of the Harmon and Cadotte Members is dated as middle Albian and that of the overlying Paddy Member provisionally as late Albian. The lower part of the Shaftesbury Formation (from the base of the formation to just above the 'Fish-scale' marker bed) contains microfloral species of late Albian age.

The microfloral evidence indicates that the Loon River Formation is correlative with the upper Mannville strata of central Alberta. The Harmon Member is older than the Joli Fou Formation and presumably correlative with part of the erosional interval between the Mannville Group and Joli Fou Formation in central Alberta. The Cadotte Member is partly correlative with the Joli Fou Formation. The microfloral evidence for correlation of the Paddy Member with the Viking Formation of central Alberta is inconclusive but the overlying Shaftesbury Formation is approximately correlative with the post-Viking shales in the lower part of the Colorado Group.

There is an increase in the representation of microplankton and a decline in that of megaspores in the shaly Loon River, Harmon, and Shaftesbury units, indicative of an offshore environment of deposition. This trend is reversed in the silty and sandy beds of the Cadotte and Paddy Members, which represent nearshore to continental depositional facies.

Singh, C. (1971): Lower Cretaceous microfloras of the Peace River area, northwestern Alberta; Research Council of Alberta, RCA/AGS Bulletin 28, 586 p.