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Depositional Architecture Along the Transition from Basin Floor To Slope, Neoproterozoic Passive-Margin Windermere Turbidite System, Canada

Lilian Navarro
University of Ottawa, Department of Earth Sciences, Ottawa, Ontario, Canada; [email protected]

Outstanding outcrops of Neoproterozoic metasedimentary units of the Upper Kaza Group and Isaac Formation, located in the Cariboo Mountains in east central British Columbia, have a unique value for studying an ancient transition from basin floor to slope. These units were deposited in the Windermere turbidite system developed on the western passive margin of Laurentia.

In a 600 m-thick section of the Kaza-Isaac transition interval, five key architectural elements have been recognized, showing distinctive lithofacies, morphology and stacking patterns: (1) Proximal Lobe complexes comprise several coalesced “sheet-like” sandstone units consisting of broad, very shallow channels, deposited most likely close to the main feeder channels; (2) Channel-levee and Channel complexes composed of vertically-stacked, multistory channels filled by highly-amalgamated, fine conglomerate and coarse sandstone; (3) Mudstone-dominated sheets characterize by laterally-extensive, thin-bedded turbidites; (4) Large-scale, shallow scours formed as a result of bypass currents that transited deepwater transitional areas; and (5) Mass-transport complexes consist of slide and debris-flow deposits linked to recurring periods of slope failures. Furthermore, the uppermost part of the section is distinguished by a thick and widespread succession, the Lower Isaac Carbonate, of carbonate and mixed carbonate-siliciclastic turbidites.

The upward evolution in the Kaza-Isaac interval reflects the interplay of major controls, such as sediment supply, sea level fluctuations, seafloor topography, slope gradient, and flow properties. Therefore, this interval represents an extraordinary ancient analogue for characterization and modeling of similar deepwater reservoirs.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid