Stratal composition and stratigraphic organization of stratal elements in an ancient deep‐marine basin‐floor succession, Neoproterozoic Windermere Supergroup, British Columbia, Canada

Abstract

Stratal composition and stratigraphic organization of stratal elements in an ancient deep-marine basin-floor succession, Neoproterozoic Windermere Supergroup, British Columbia, Canada ABSTRACT Despite a globally growing seismic and outcrop analogue data set, the detailed (centimetre to decametre) internal stratal make up of deep-marine basin-floor 'channelized-lobe' strata remain poorly known. An ancient analogue for modern, mixed-sediment, passive margin, deep-marine basin-floor fans is the wellpreserved Neoproterozoic Upper and Middle Kaza groups in the southern Canadian Cordillera. This succession is a few kilometres thick and comprises six sedimentary facies representing deposition from different kinds of sediment-gravity flows. Representative lateral and vertical assemblages of one or more of these facies comprise six stratal elements, including: isolated scours, avulsion splays, feeder channels, distributary channels, terminal splays, and distal and off-axis fine-grained turbidite units. The internal characteristics of the various stratal elements do not differ from more distal to more proximal settings, but the relative abundance of the various stratal elements does. The difference in relative abundance of stratal elements in the kilometre-scale stratigraphy of the Kaza Group results in a systematic upward change in architecture. The systematic arrangement of the stratal elements within the interpreted larger bodies, or lobes, and then lobes within the basin-floor fan, suggests a hierarchical organization. In this article a hierarchy is proposed that is based on avulsion but, also importantly, the location of avulsion. The proposed avulsion-based hierarchical scheme will be a useful tool to bridge the scalar gap between outcrop and seismic studies by providing a single stratigraphic framework and terminology for basin-floor stratal elements.

Turbidite, debrite, and hybrid event beds in submarine lobe deposits of the Palaeocene to middle Eocene Kapit and Pelagus members, Belaga Formation, Sarawak, Malaysia

“…This interpretation is consistent with our observations in the Belaga Formation. The shallow channelized turbidite beds are interpreted as representing the down‐dip termination of distributary channels (Johnson et al, ; Terlaky, Rocheleau, & Arnott, ). There is increasing evidence that gravity flow transformations, from turbidity flow to cohesive and laminar flow, are the dominant bed type in the distal ends of submarine fan systems and the fringes of individual lobes (e.g., Barker, Haughton, McCaffrey, Archer, & Hakes, ; Fonnesu et al, ; Grundvåg et al, ; Haughton et al, , ; Hodgson, ; Ito, ; Kane & Pontén, ; Lowe & Guy, ; Pierce et al, ; Spychala, Hodgson, & Lee, ; Sylvester & Lowe, ; Talling et al, ).…”

“…Hybrid event beds of the Belaga Formation are relatively rich in mud and sandstone clasts, which appear to have a local origin. Mud clast entrainment in proximal locations leading to the development of proximal HEBs has been attributed to enhanced turbulence in the channel‐lobe transition zone due to loss of confinement and flow expansion (e.g., Ito, ; Terlaky et al, ). For example, the coarse‐grained sand‐rich Bordighera turbidite system of NW Italy displays an abundance of HEBs in axial/proximal lobe deposits, which have been interpreted to be a product of entrainment of basin floor mud at the channel‐lobe transition zone by unconfined jet flows (Mueller et al, ).…”

“…This interpretation is consistent with our observations in the Belaga Formation. The shallow channelized turbidite beds are interpreted as representing the down-dip termination of distributary channels (Johnson et al, 2001;Terlaky, Rocheleau, & Arnott, 2016).…”

“…There is increasing evidence that gravity flow transformations, from turbidity flow to cohesive and laminar flow, are the dominant bed type in the distal ends of submarine fan systems and the fringes of individual lobes (e.g., Barker, Haughton, McCaffrey, Archer, & Hakes, 2008;Fonnesu et al, 2018;Grundvåg et al, 2014;Haughton et al, 2003Haughton et al, , 2009Hodgson, 2009;Ito, 2008;Kane & Pontén, 2012;Lowe & Guy, 2000;Pierce et al, 2017;Spychala, Hodgson, & Lee, 2017;Sylvester & Lowe, 2004;Talling et al, 2004). However, they are not exclusively restricted to the distal parts and can also be present in proximal areas of lobes, where they are interpreted as the product of enhanced erosion and flow deceleration due to processes occurring in the channel-lobe transition and due to basin confinement (e.g., Fonnesu et al, 2018;Haughton et al, 2009;Ito, 2008;Jackson et al, 2009;Mueller et al, 2017;Patacci et al, 2014;Sylvester & Lowe, 2004;Terlaky et al, 2016;Vinnels, Butler, McCaffrey, & Lickorish, 2010).…”

Integrating outcrop and subsurface data to assess the temporal evolution of a submarine channel–levee system

“…Many studies have documented the highly organized nature of deep-water deposits, suggesting a regular, ordered set of controls on the development of stratal architecture (e.g., Beaubouef et al, 1999;Gardner et al, 2003;Hodgson et al, 2006Hodgson et al, , 2011Hodgson et al, , 2016Pyles, 2008;Flint et al, 2011;Terlaky et al, 2016). This stratigraphic organization has enabled the development of a hierarchical approach to both confined and unconfined parts of deepwater systems.…”