Comparison of Basin-Floor Deposits Along a Proximal to More Distal Transect: Upper and Middle Kaza Groups, British Columbia, Canada

Viktor Terlaky, Hugues Longuépée, Kelsey Privett, Greg van Hees, and R. William C. Arnott
University of Ottawa, Ottawa, ON, Canada

The stratigraphy and architecture of proximal (Upper Kaza Group) and more distal (Middle Kaza Group) basin floor strata show many similarities, but also a number of important differences that might have significant impact on estimating reservoir continuity and connectivity. The most obvious similarity between proximal and more distal deposits is their “sheet-like” morphology when observed at large (several 100’s meters) scale. Strata consist generally of 5-35 m thick “sheets” of mostly stacked normally-graded coarse sandstone. Sandstone sheets commonly overlie a unit of medium-bedded, matrix-rich, structureless sandstone (“harbinger beds”), and in turn are overlain by thinly-bedded, fine-grained turbidites up to 35 m thick.

The most significant difference is that coarse sandstone and fine-grained turbidite intervals are thicker in more distal deposits. Furthermore, in proximal strata, sandstones invariably become increasingly interstratified with thin-bedded turbidites upward, a trend not always observed in more distal strata. In addition, net-to-gross ratio of more distal deposits change little laterally, compared to proximal deposits where values commonly change by 20-40% over 100-200 m laterally. Major scours, albeit uncommon in proximal strata (confined to a single observation), are absent in more distal deposits. Muddy debrites too are absent in more distal deposits, but present in proximal strata.

Collectively these observations suggest that although vertical connectivity is significantly better in sand-rich proximal basin floor reservoirs, their lateral continuity may be less compared to seemingly similar sand-rich units deposited in more distal settings.

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