Open File Report 2011-07

Open File Report 2011-07

OFR 2011-07

Measured Outcrop Section T27-R17W4-01 of the Bearpaw and Horseshoe Canyon Formations, Dorothy, Red Deer River Valley, Southern Alberta (NTS 72P/08)

Measured outcrop section T27-R17W4-01, located 34 km southeast of Drumheller on the southwest side of the Red Deer River valley opposite the village of Dorothy, includes the upper part of the Bearpaw Formation and the lowermost part of the Horseshoe Canyon Formation.

This report includes a graphic log of the measured section with an outcrop gamma curve; and a detailed description of the section (avoiding lithofacies interpretation, but detailing stratigraphic context where appropriate) with selected photos.

The Bearpaw Formation interval includes the upper part of the Dorothy sandstone at the base of the section and the Dorothy bentonite. The bioturbated contact of the Dorothy sandstone with overlying mudstone is marked by the sharpest increase in gamma-ray counts in the measured section. Gamma-ray counts and observed lithofacies for the Bearpaw Formation interval above the Dorothy sandstone define a series of coarsening-upward packages. Mean gamma-ray counts for the basal part of each coarsening-upward cycle are progressively lower up through the section. In the two best-defined of these cycles, grey-brown mudstone passes gradationally up into intervals dominated by hummocky cross-stratified, fine-grained sandstone units. The 11.9 m thick Dorothy bentonite shows relatively uniform gamma-ray counts in the middle range of values for the measured section. The base of the Horseshoe Canyon Formation is placed at the base of a thick (9.5 m exposed) swaley cross-stratified sandstone interval at the top of the measured section.