Late Maastrichtian paleovalley systems in west-central Alberta: Mapping the Battle Formation in the subsurface

Abstract

Abstract The Maastrichtian Battle Formation forms an important stratigraphic marker in the nonmarine Upper Cretaceous succession across a wide area of west-central Alberta. This mudstone-dominated unit, with a maximum thickness of 18.0 m, is distinctive both at outcrop and in down-hole geophysical well logs. New stratigraphic picks for the top and base of the Battle Formation in 8935 wells, together with data-points from a further 608 wells in which the Battle Formation is absent, were used to generate a regional isopach map. In combination with closely spaced well-log cross-sections, the isopach map allows delineation of a series of paleovalley systems incised into the Battle Formation and filled by sandy fluvial deposits of the overlying Scollard Formation. Across wide areas within the paleovalleys, the Battle Formation has been completely removed and Scollard Formation strata rest directly on the underlying Horseshoe Canyon or Wapiti formations. Paleovalley trends appear to have been broadly similar to those of major present-day river systems in the region. A paleo-Athabasca River system with a main trunk valley up to 30 km across trends southwest to northeast in the area between Edson and Whitecourt. Farther south, a well-defined paleovalley system with a main valley up to 10 km wide trending northwest to southeast in the area between Red Deer and Drumheller can be considered as a precursor to the present Red Deer River drainage system. A less well-defined paleovalley trends northwest to southeast in the area of the present Bow River to the east of Calgary.