Architectural Hierarchy, Processes and Reservoir Implications of Channel-Mouth Lobe Complexes in the Transition from Basin Floor to Base-of-Slope Strata, Neoproterozoic Windermere Supergroup, Canada

Lilian L. Navarro and R. William C. Arnott
Earth Science and Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, ON, Canada

Superb exposures of Neoproterozoic basin floor (Upper Kaza Group) and base-of-slope (Isaac Formation) strata in the Cariboo Mountains provide an excellent opportunity to study ancient deep-water lobe complexes. A hierarchy of architectural elements showing a characteristic stacking pattern has been identified that illustrates recurring spatial and sequential relationships of lobe complexes in the transition from slope to basin floor.

Lobe complexes are 20-30 m thick and appear to be sheet-like sandstone units. Internally, however, they consist of several (at least 3) coalesced lobeforms that locally are truncated by low-relief channels or scours. Lobeforms are 2-5 m thick, and composed of multiple lobes. Each lobe consists of amalgamated, medium to coarse sandstone (with localized channelized features) gradationally overlain by sheet-like, non-amalgamated sandstone and mudstone. Commonly observed at the base of lobate deposits are sandstone sheets that consist of matrix-rich sandstone deposited by precursor, unconfined sandy flows. Subsequently, lobes were deposited by moderately confined to unconfined flows, downflow of the channel mouth. Depending to the degree of lobe switching, sediment caliber or seafloor topography, single or multiple lobes were formed.

Fine-grained sheets comprise thin-bedded turbidites, and occur as laterally continuous layers that separate lobe complexes or as laterally discontinuous layers within lobeforms. In addition, large-scale scours and low-relief, channels are observed to erode part of not only fine-grained sheets, but also the lobeforms. Collectively, these observations have important implications concerning reservoir continuity and compartmentalization.

Insights into the internal complexity and development of lobe complexes are essential in order to understand this environment.

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