The Dinosaur Park Formation of the Upper Cretaceous Judith River (Belly River) Group, subsurface of southern Alberta

Abstract

Regional subsurface correlation of the upper Judith River /Belly River clastic wedge confirms that the Dinosaur Park Formation can be distinguished and mapped in the subsurface throughout southern and central Alberta. The formation generally thins to zero to the south due to depositional thinning. The sediments of the Dinosaur Park were derived from the northwest, whereas those of the underlying Oldman and Foremost formations were derived from the west and southwest. This change likely represents a reorientation of paleogeography, during Judith River time, related to an increase in rate of subsidence in southern Alberta. Thickness variation of the Dinosaur Park in southern Alberta is characterized by relatively narrow, linear trends, generally oriented WNW /ESE, which fan out from locii near Rocky Mountain House and Calgary, and result primarily from localized erosional geometry at the base of the formation. Linear trends are sharp-based, and are overlain by multi-storied individual fining-upward channel sandstone units, interpreted as composite incised valley fills. Corresponding clean sandstone trends (potential reservoir rock), are up to 40 m thick. Included maps are intended as guides: for practical application, more detailed mapping of individual sandstone bodies is necessary. The regionally-consistent upward sequence of facies from erosional base, to sandstone-dominated, to sandstone/mudstone-dominated, to Lethbridge Coal Zone, to Bearpaw marine transgression (from the southeast) can also be interpreted to represent a fundamental reorientation of paleogeography related to an increasing rate of basin subsidence, and consequent transgressive pressure, in southern Alberta. The Dinosaur Park Formation encloses 145 gas pools of the 1384 pools known from the Judith River Group, scattered through 60 different fields, and totalling 6806 x 106 cubic metres of gas reserves. Large areas of thick, clean sandstone, with no designated pools, are present throughout the play area, suggesting further exploration possibilities.