Stratigraphic Architecture of the Transition from Basin Floor to Slope, Hadrynian Passive-Margin Windermere Turbidite System, Canada

Lilian Navarro and R. William(Bill) C. Arnott
Earth Science, University of Ottawa, Ottawa, ON, Canada

The Windermere turbidite system was developed on the Hadrynian passive margin of western North America. At Castle Creek, a 2.5 km-thick x 8 km-wide succession of basin floor (Upper Kaza Group) to base-of-slope and slope (Isaac Formation) rocks are well exposed. A representative 350 m-thick, stratigraphic section was studied with the aim to elucidate spatial and temporal changes that occur in the transition from basin floor to slope strata.

Several architectural elements were recognized and observed to stack in a consistent pattern: (1) Frontal Splay/ Lobe complexes are up to 30 m thick and consist commonly of intermediate to high net-to-gross, lobe-shaped sandstone units with broad, shallow scours and channels, suggesting deposition close to the main feeder channels; (2) Channel and channel-levee complexes, in contrast, are 14-25 m thick, formed of multistory, vertically-stacked channels filled mostly with amalgamated, coarser sandstone and conglomerate (the highest net-to-gross ratios); (3) Mudstone-dominated sheets are 5-12 m thick, laterally continuous and composed of thin-bedded turbidites; (4) Large-scale scours, generally incised mudstone sheets, were formed by bypass currents that transited the transitional zone; and (5) Slide and debris-flow complexes, up to 21 m thick, occur indicating slope instability and failure.

Upward changes from lobe to channel complexes in addition to the occurrence of erosional and instability elements, suggest progradation of the depositional system related to changes in sediment supply, slope gradient, sea level fluctuations and flow properties.

Observations based on this ancient deep-water succession appear comparable to seismically-defined features described from transitional zones of some submarine fans. Accordingly, subseismic-scale data obtained from Kaza-Isaac outcrops can be used to refine corresponding reservoir models.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery