^PSThe Application of High Resolution Chemostratigraphy to Differentiate between Low Accommodation Incised Valley Systems in a Foreland Basin Setting: The Lower Cretaceous Basal Colorado and Basal Quartz of the Western Canadian Sedimentary Basin

By

A.M. Wright¹, B.A. Zaitlin², R. Walker³, and K.T. Ratcliffe⁴

Search and Discovery Article #30041 (2006)

Posted July 20, 2006

*Poster presentation at AAPG Annual Convention, Houston, Texas, April 9-12, 2006

Click to view poster presentation in PDF format.

Poster 1 (8.4 mb)               Poster 2 (1.8 mb)               Poster 3 (1.9 mb)

¹Chemostrat Inc., Houston, Texas ([email protected])

²Suncor Energy Inc., Calgary, Alberta ([email protected])

³Roger Walker Consulting Inc., Calgary, Alberta ([email protected])

⁴Chemostrat Ltd., Llanfyllin, Powys, United Kingdom

Abstract 

The Lower Cretaceous Basal Quartz (BQ) and Basal Colorado (BCS) sequences are prolific hydrocarbon producers within the Western Canadian Sedimentary Basin. Due to the low accommodation and predominantly fluvial nature of these incised valley system (IVS) deposits, traditional stratigraphic characterization and correlation of the reservoir sequences is problematic. Whole rock geochemistry is used here to characterize between: 1) the IVS fill sequences of the BQ and BCS; 2) between internal units of the BQ IVS (Horsefly, BAT and Ellerslie); and 3) between BCS and Upper Mannville deposits. 

The Basal Quartz system is chemically differentiated from the BCS system by changing Na/K and Cs/Al values within silty-claystone lithologies, indicating that the two depositional systems were sourced from different provenances, and deposited under differing palaeoclimate conditions. 

Within the BQ three lithostratigraphic units are identified, and are differentiated by changes in clay mineralogy, heavy mineralogy, feldspar contents and the degree of volcanogenic input, all of which can be geochemically modeled. The component units of the BCS are differentiated by changes in Ti/Nb and K/Na ratio values that indicate the

Lower Basal Colorado and Upper Basal Colorado IVS sandstones were derived from different provenances. 

With the greater understanding of the component units of the IVS sequences afforded by combining chemostratigraphy with heavy mineral analysis, it is possible the better to explore for and exploit these types of reservoirs.

Selected Figures 

Conclusion 

1. Chemostratigraphy provides a means to:

i)                    Clearly differentiate silty claystones associated with Basal Quartz incised valley systems from silty claystones associated with Upper Mannville and Basal Colorado Incised valley systems;

ii)                   Characterise and differentiate Basal Quartz component units (Horsefly Unit, BAT Unit and Ellerslie Unit).

iii)                 Characterise and differentiate channel fill sandstones and associated claystones of the Upper Mannville Formation from the Basal Colorado and Viking formations.

iv)                 Clearly differentiate Lower Colorado and Upper basal Colorado channel systems.  

2. By using chemostratigraphic information in conjunction with heavy mineral analyses it is possible to identify major and more subtle changes in sediment provenance. 

3. By combining current depositional models for the Basal Quartz and Basal Colorado Sandstone systems, with information on sediment provenance derived from geochemical and heavy mineral analysis, it is possible to understand the timing of major provenance changes terms of basin evolution.