Stratigraphic record in the transition from basin floor to continental slope sedimentation in the ancient passive‐margin Windermere turbidite system

Abstract

Well-exposed, vertically dipping, glacially polished outcrops of the Neoproterozoic Windermere Supergroup in the southern Canadian Cordillera include basin-floor deposits of the Upper Kaza Group overlain by slope channel complexes of the Isaac Formation. Within the 2Á5 km thick Kaza and Isaac succession is an up to 360 m thick interval composed of diverse deep-water stratal elements including scour and interscour deposits, distributary channels, finegrained turbidites, terminal splays, mass-transport deposits, erosional and lev eed channels and avulsion splays, which collectively were formed during the development of an ancient passive-margin channel-lobe system. The proportion and vertical and lateral arrangement of stratal elements reveal three distinct complexes. The lower complex, consisting mostly of distributary channels and small and large scours, is interpreted to represent the detachment of lobes from an upflow lev eed channel, wherein a well-developed channel-lobe transition zone was formed by efficient, siliciclastic flows during a period of sustained transport bypass and limited deposition coincident with the onset of falling relative sea level. The middle, comparatively thicker and more sandstone-rich complex, comprises distributary channel fills, fine-grained turbidites and lesser terminal splays that are interspersed with small scours, capped by a slope lev eed channel filled with coarser-grained siliciclastic sediment. The abundance of basin-floor elements suggests negligible separation between the lev eed channel and lobe, and therefore a poorly-developed channel-lobe transition zone, resulting from inefficient, siliciclastic-rich depositional flows that became dominant during lowstand and/or ensuing transgression. The stratal makeup of the upper complex resembles the lower detached complex, suggesting a return to efficient flows, and an abrupt change to mixed carbonate-siliciclastic sediments associated with highstand conditions. Accordingly, the stratigraphic architecture and stacking pattern of the Kaza-Isaac interval, which relate to the formation of multiple channel-lobe transition zones, were controlled by temporal changes in sediment supply and flow characteristics during the long-term progradation of the Laurentian continental margin.

Sole marks reveal deep-marine depositional process and environment: Implications for flow transformation and hybrid-event-bed models

“…The SGF deposits in Units 1, 3, and 7 were thicker and the erosional scours were less common than in the channel-lobe transition zone successions described by Brooks et al (2018) and Hansen et al (2019). This may indicate that the channels and lobes in the studied part of the Aberystywth Grits Group were not separated by a pronounced zone of bypass and hydraulic jumps (Mutti and Normark 1987;Dorrell et al 2016;Cunha et al 2017;Navarro and Arnott 2020).…”

Submarine Channel Mouth Settings: Processes, Geomorphology, and Deposits

“…Classically, this tract is characterised by lags and scours immediately downdip of the channel with a range of forms and degree of coalescence, passing into areas dominated by sediment waves, before lobes. Reported dimensions of CLTZs range from a few kms to 10s of km in widths and lengths (e.g., Morris et al, 1998;Wynn et al, 2002a;Navarro and Arnott, 2020). However, this configuration can be dynamic, and can expand, contract, and migrate (Brooks et al, 2018).…”

“…There is a growing literature on CLTZs interpreted from ancient outcrops (see compilation by Navarro and Arnott, 2020), with recognition criteria proposed to support links between sedimentary processes and deposits (e.g., Bravo and Robles, 1995;Ito, 2008;Pyles et al, 2014;Hofstra et al, 2015;Pemberton et al, 2016;Postma et al, 2016;Brooks et al, 2018;Hofstra et al, 2018;Postma et al, 2021). Preserved stratigraphic successions of interpreted CLTZs range from thick successions of aggradational beds in close association with scour-fill features (e.g., Pemberton et al, 2016;Brooks et al, 2018;Mansor and Amir Hassan, 2021;Brooks et al, 2022) to single surfaces that separate lobes from overlying channel-levee systems (e.g., Gardner et al, 2003;Hodgson et al, 2016).…”

“…Preserved stratigraphic successions of interpreted CLTZs range from thick successions of aggradational beds in close association with scour-fill features (e.g., Pemberton et al, 2016;Brooks et al, 2018;Mansor and Amir Hassan, 2021;Brooks et al, 2022) to single surfaces that separate lobes from overlying channel-levee systems (e.g., Gardner et al, 2003;Hodgson et al, 2016). The wide range of expressions and dimensions (Navarro and Arnott, 2020) point to a number of parameters and configurations that control the transfer, and preservation, of channel mouth settings into the rock record.…”

Provenance of the Incipient Passive Margin of NW Laurentia (Neoproterozoic): Detrital Zircon from Continental Slope and Basin Floor Deposits of the Windermere Supergroup, Southern Canadian Cordillera

“…In the eastern part of the outcrop belt, upper slope deposits, including submarine canyons filled with coarse clastic sediment flanked by fine-grained continental slope deposits crop out (Arnott and [24]). Toward the northwest, and over distances of hundreds of kilometers, these strata pass into slope and base-of-slope deposits populated locally by thickly developed (up to ~200 m thick) leveed-channel complexes, and then sheetlike, sandstone-rich basin-floor strata in the northwest part of the outcrop belt [25]. Above the slope, facies are carbonate and siliciclastic strata that were deposited in shallow marine environments (e.g., [26]) (Figures 2 and 3).…”