The Application of Chemostratigraphy to Understanding Play Systems in Low Accommodation Settings

Gemma V. Hildred¹, Kenneth T. Ratcliffe¹, Amelia M. Wright¹, and Brian A. Zaitlin^2
1Chemostrat Inc, Houston, TX
²Suncor Energy Inc, Calgary, AB, Canada

Chemostratigraphy, a technique that enables sequences to be subdivided and correlated using variations in their inorganic geochemistry is here applied to the Lower Cretaceous Basal Quartz (BQ) of Southern Alberta. The BQ, a prolific hydrocarbon producing unit in the Western Canada Sedimentary Basin, was deposited in a low accommodation fluvial-estuarine setting, draining towards the Northern Boreal Sea. Regional studies south of the Vulcan Low have shown that the BQ was deposited in two sub-parallel valley systems, the easterly Whitlash valley and the westerly Taber-Cutbank valley.

Whole rock inorganic geochemical analyses using ICP-OES/MS were carried out on core samples from the BQ in both the Whitlash and Taber-Cutbank valleys. Analyses were undertaken on three of the informal units within the Basal Quartz, namely the Horsefly, BAT and Ellerslie. The Horsefly was sampled in both valley systems in order to determine whether lateral variations in whole rock geochemistry within a single unit are of a greater magnitude than the vertical variations between stratigraphic units.

The Horsefly, BAT and Ellerslie each have distinctive whole rock geochemical compositions that reflect marked changes in sediment provenance and paleoclimate. The Horsefly shows no significant geochemical variations longitudinally within a valley system. However, its geochemical composition varies significantly between the two sub-parallel valley systems. This variation between the two valley systems reflects relatively subtle changes in sediment provenance and variations in residence time at the surface between valley forms. By combining the chemostratigraphic interpretations with valley geometry data, it is postulated that the Whitlash valley may be a southward flowing tributary of the overall northward flowing Taber-Cutbank valley system, with the confluence occurring in Northern Montana.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas