Evolution of an ancient (Lower Cretaceous) marginal‐marine system from tide‐dominated to wave‐dominated deposition, McMurray Formation

Abstract

Regionally extensive parasequences in the upper McMurray Formation, Grouse Paleovalley, north‐east Alberta, Canada, preserve a shift in depositional processes in a paralic environment from tide domination, with notable fluvial influence, through to wave domination. Three stacked parasequences form the upper McMurray Formation and are separated by allogenic flooding surfaces. Sediments within the three parasequences are grouped into three facies associations: wave‐dominated/storm‐dominated deltas, storm‐affected shorefaces to sheltered bay‐margin and fluvio‐tidal brackish‐water channels. The two oldest parasequences comprise dominantly tide‐dominated, wave‐influenced/fluvial‐influenced, shoreface to bay‐margin deposits bisected by penecontemporaneous brackish‐water channels. Brackish‐water channels trend approximately north‐west/south‐east, which is perpendicular to the interpreted shoreline trend; this implies that the basinward and progradational direction was towards the north‐west during deposition of the upper McMurray Formation in Grouse Paleovalley. The youngest parasequence is interpreted as amalgamated wave‐dominated/storm‐dominated delta lobes. The transition from tide‐dominated deposition in the oldest two parasequences to wave‐dominated deposition in the youngest is attributed mainly to drowning of carbonate highlands to the north and north‐west of the study area, and potentially to relative changes in accommodation space and deposition rate. The sedimentological, ichnological and regional distribution of the three facies associations within each parasequence are compared to modern and Holocene analogues that have experienced similar shifts in process dominance. Through this comparison it is possible to consider how shifts in depositional processes are expressed in the rock record. In particular, this study provides one of few ancient examples of preservation of depositional process shifts and showcases how topography impacts the character and architecture of marginal‐marine systems.

Shoreline migration paths and depositional architecture of early–mid Miocene deltaic clinoforms in response to sea‐level changes in the north‐eastern shelf margin, South China Sea

“…12D, E and G), along with a series of beach-ridge set-pairs (Fig. 10), suggests the environments of wave-dominated shorelines/delta front (Olariu & Bhattacharya, 2006;Hansen & MacEachern, 2007;Uroza & Steel, 2008;Coates & MacEachern, 2009;Vakarelov et al, 2012;Weleschuk & Dashtgard, 2019). According to previous studies, the along-strike elongated beach ridges are likely to be attributed to the longshore currents that redistributed the sediments fed by the distributary channels in the river mouth (Nanson et al, 2013;Bourget et al, 2014;Ainsworth et al, 2019).…”

“…The upward‐coarsening nature with trough cross‐stratification, wave oscillation ripples and marine trace fossils supports a depositional interpretation of FA3 as a delta front environment. The presence of trough cross‐stratification and wave oscillation ripples that may be deposited in the environment where sediments were affected by the orbital motion of wind‐driven waves, suggests wave processes (shoaling waves, breaking or spilling waves) operating at the river mouth (Komar, 1976; Garza & Bhattacharya, 2008; Frey & Dashtgard, 2011; Vakarelov & Ainsworth, 2012; Weleschuk & Dashtgard, 2019; Fig. 12D and F).…”

Resolving stratigraphic architecture and constraining ages of paralic strata in a low‐accommodation setting, Firebag Tributary, McMurray Formation, Canada

“…Recent research suggests at least some interpreted incised valleys are more akin to contemporaneous fluvial or fluvio-tidal channel belts that are genetically related to regional DUs (Baniak & Kingsmith, 2018;Château et al, 2019;Weleschuk & Dashtgard, 2019). Furthermore, stratigraphic relationships are partially obscured by syndepositional subsidence associated with salt dissolution in the Devonian Prairie Evaporite Formation (Barton et al, 2017;Broughton, 2014).…”

“…The formation comprises a wide array of sedimentary deposits, including cross‐stratified sandstones, coals and pedogenically altered mudstones, and a variety of heterolithic facies (Carrigy, 1959; Keith et al, 1988; Mossop & Flach, 1983; Rinke‐Hardekopf et al, 2019). From the bottom to the top of the stratigraphic succession of the McMurray Formation, heterolithic deposits preferentially exhibit sedimentary structures characteristic of fluvial, tidal and wave influence (Château et al, 2021; Hayes et al, 2017; Hein & Cotterill, 2006; Timmer et al, 2016; Weleschuk & Dashtgard, 2019). The ichnology and palynology of McMurray Formation strata also indicate deposition in freshwater through to brackish‐water environments (Baniak & Kingsmith, 2018; Fustic et al, 2012; Gingras et al, 2016; Harris et al, 2016; Hubbard et al, 2011; La Croix et al, 2019, 2020; Mossop & Flach, 1983; Pemberton et al, 1982; Ranger & Pemberton, 1997; Shchepetkina et al, 2016).…”

“…Depositional units are ca 10 m thick and were partially removed by channel‐belt migration and/or subsequent valley incision, some of which have been attributed to major base‐level falls (Alberta Energy and Utilities Board, 2003; Château et al, 2019, 2020, 2021; Hein & Cotterill, 2006; Hein et al, 2013; Horner et al, 2018, 2019; Ranger & Pemberton, 1997). Recent research suggests at least some interpreted incised valleys are more akin to contemporaneous fluvial or fluvio‐tidal channel belts that are genetically related to regional DUs (Baniak & Kingsmith, 2018; Château et al, 2019; Weleschuk & Dashtgard, 2019). Furthermore, stratigraphic relationships are partially obscured by syndepositional subsidence associated with salt dissolution in the Devonian Prairie Evaporite Formation (Barton et al, 2017; Broughton, 2014).…”