Characterization of McMurray Formation Strata Utilizing Palynofloral Assemblages, Surmont Lease and Immediate Surrounding Areas

Thomas D. Demchuk¹, Graham Dolby², Daniel Michoux³, John R. Suter⁴, and Alain Lejay^3
1 ConocoPhillips Inc, Houston, TX
² G. Dolby and Associates, Calgary, AB
³ Total, Pau, France (4) ConocoPhillips, Houston, TX

Palynofloral assemblages can be extremely useful in discerning paleoenvironments and confirming sequence stratigraphic system tracts. In marginal marine and transitional paleoenvironments, palynofloral assemblages are of greater significance in that they span the terrestrial/marine realm and relative percentages of terrestrially-derived pollen/spore versus “marine” dinoflagellates can be used to discern paleosalinities and the location of the paleoshoreline. In the McMurray Fm. of northern Alberta, palynofloral assemblages are abundant and diverse with a mix of pollen/spore, dinoflagellates and other algae. Relative percentages of these palynofloral components can aid in characterizing the nature and paleoenvironments of the associated argillaceous strata, and in turn can aid in determining the paleoenvironments of the McMurray Formation reservoirs placing them in their sequence stratigraphic context.

Palynofloral assemblages from McMurray Fm. particularly from the Surmont Lease are dominated by terrestrially-derived pollen and spore, including abundant bisaccate pollen. Such domination indicates that paleoenvironments throughout the McMurray were dominated by freshwater input, with significant fluvial systems in proximity. Sporadic abundance of algae (Schizosporis spp., Pediastrum spp.) and freshwater dinoflagellates (e.g. Hurlandsia spp.) suggest that lacustrine paleoenvironments were present in the general vicinity. Dinoflagellates of low-salinity affinity (Nyktericysta spp., Vesperopsis spp., Balmula spp., Pseudoceratium spp.) are present, sometimes in significant abundances indicating possible brackish influence on the deposition of McMurray Fm. strata. In one example from the Surmont Lease, such low-salinity dinoflagellates are most abundant in thick argillaceous strata of the middle member of the McMurray Fm. These occurrences decrease within the upper member, suggesting an overall regressive nature to the deposition of the McMurray Fm. at this locality. Other examples from the Surmont Lease indicate sporadic abundances of low-salinity dinoflagellates throughout, suggesting periodic incursions and proximity of marine waters to the region. Future detailed palynological study of the argillaceous strata from McMurray Fm. will further characterize these paleoenvironments.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005