INVITED: ARCHITECTURE AND STRATIGRAPHIC HISTORY OF THE EDMONTON GROUP (UPPER CRETACEOUS), SOUTHERN ALBERTA PLAINS, CANADA

A complex stratigraphic history for the Upper Cretaceous Edmonton Group (southern Alberta, Canada) can be inferred from lithostratigraphic, sedimentologic, and paleontologic data that provide evidence for changes in (1) regional tectonism, (2) accommodation, (3) sea level, and (4) climate. In ascending order the Edmonton Group consists of the Horseshoe Canyon, Whitemud, Battle, and Scollard formations. The Horseshoe Canyon consists of five sub-units: Unit 1 (150-160 m) marks a marine-to-nonmarine transition characterized by vertically-aggraded parasequences; Unit 2 (30 m) shows a reduction in bed thickness, has few organic horizons, and records a significant transgressive event; Unit 3 (10-20 m) consists of stacked alluvial sandstones with minor paludal/lacustrine beds and is interpreted as a HST; Unit 4 (25 m) remains non-coaly but marks a return to sub-equal paleochannel-overbank bed thicknesses and non-amalgamated channel deposits, indicating increased accommodation; Unit 5 (20 m) is characterized by coals and lags of extraformational pebbles and cobbles, indicating a tectonic influence. Vertebrate fossil assemblages indicate a climatic cooling trend upward through units 1-4, and a possible warming event in Unit 5.

The Whitemud comprises mature sediments, indicating a reduction in accommodation and sediment supply. The Battle-Whitemud contact is a significant unconformity characterized by channel-scale relief, and intense rooting and weathering on the Whitemud. Channel fills at the base of the Battle yield palynomorphs previously unrecognized in the area, and very rare dinoflagellates. Most of the Battle consists of altered volcanic ash with thin siliceous (weathered) zones. The ancient Whitemud and Battle landscape was dominated by cool-temperature, sediment-starved paludal/lacustrine environments.

The Battle passes conformably up into an organic rich interval with palynological affinities to the Scollard. Amalgamated channel sandstones with worn vertebrate fossils and extrabasinal clasts characterize the lower Scollard. Upsection, there is a return to sub-equal channel/overbank ratios, and increased numbers of paleosols. Coals appear just below the K-T boundary where there is a notable shift from low- to high-sinuosity paleochannels.