Stratigraphic and Depositional Architecture of a Slope Channel System: Isaac Channel 5, Castle Creek South, Isaac Formation, Windermere Supergroup, British Columbia, Canada

Abstract

A detailed architectural analysis was conducted on Isaac Channel 5 in the Castle Creek area (east-central British Columbia, Canada, Figure 1). Isaac Channel 5 developed within a Neoproterozoic slope turbidite system along the passive western margin of North America where debris flows and mass movements were common (see Arnott and Ross, Chapter 22, this volume). Isaac Channel 5 crops out across a 3.5-km (2.1-mi)-long section oriented oblique to mean paleoflow (toward the northwest) and represents an enduring transport and depositional pathway that accumulated ~100 m (~330 ft) of mostly sand sediment (Figures 2, 3). It consists of three stacked, high net-to-gross channel-complex fills (each 8–30 m [25–100 ft] thick) that correspond to shorter term flow conduits (C1, C2, and C3; Figures 2, 3). Channel complexes are multistory units that consist mainly of thick-bedded, Bouma Ta and Tab divisions, mudstone-clast breccia, and medium-bedded, dune cross-stratified sandstone. Granule conglomerate to medium-grained sandstone is the most common grain-size range. Five different channel-fill elements were identified within the channel complexes. Each consists of a different assemblage of facies, stratal patterns, and/or lateral dimensions, and unique reservoir characteristics (Figure 12). The development of channel-fill elements is linked to specific combinations of flow and sediment flux conditions that controlled aggradation and erosion within channels. Channel complexes are capped by siltstone-rich, thin-bedded units (T3 and T4; Figures 2, 3) that represent intervening episodes of overbank and levee sedimentation (local channel-complex deactivation). Additionally, debrite deposits (D1 and D2), which occur typically at the base of channels and channel complexes, are the result of cohesive sediment-gravity flows during channel/channelcomplex initiation. These siltstone- and mudstone-rich units, which separate channel complexes and extend across the full outcrop (>3 km [>2 mi] long), represent the most important potential impediments to intrastratal fluid flow. Strata of Isaac Channel 5 document the stratigraphic complexity, in terms of evolution and reservoir characterization, that can be expected in slope turbidite channel systems, developed in passive margins. Further, it is a potential analog for similar systems developed in continental margin basins that are mostly known from subsurface data (e.g., offshore Brazil, Egypt, Gulf of Mexico, and West Africa).