Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head

Abstract

The evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides, can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub‐bottom profiles, high‐resolution sediment core analyses (X‐ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine‐grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro‐scale and micro‐scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross‐laminations and fining‐upward successions, which are attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross‐cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re‐establishment of benthos and associated biogenic structures, supporting the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.

Evolution and architecture of an overbank in an ocean-facing canyon-fill.

“…ITDs resemble SGF deposits that have been reworked by internal tides (May and Warme, 2007;He et al, 2011;Maier et al, 2019;Normandeau et al, 2024). The structureless divisions within ITD beds support deposition from waning turbidity currents.…”

“…The structureless divisions within ITD beds support deposition from waning turbidity currents. However, their sharp tops, grain-size breaks and upper divisions of cyclical laminated and banded bundles (rhythmites) suggest reworking by internal tidal currents (Normandeau et al, 2024). The grain-size breaks at the top of sharp-topped beds might indicate bypass of the fine-grained fraction of a sediment gravity flow downslope (Stevenson et al, 2013), or by internal tides either preventing the fine-grained tail of turbidity currents from settling, or subsequently winnowing the turbidite after deposition (Soutter et al, 2024).…”

“…Flame structures at the bases of sandstone beds are representative of syn-or post-depositional dewatering (Stow and Johansson, 2000). Mud clasts are interpreted as lag deposits, suggesting prolonged erosion (Kneller, 1995) Confined overbank, characterised by turbidity currents (Bouma, 1962;Mutti, 1992), combined flows (Tinterri, 2011), turbulence-modulated transitional flows (Baas et al, 2009) and internal-tides (Normandeau et al, 2024). HDTs record channel-unconfined flows, and LDTs record flows that were stripped or overspilled from channelised high-to lowmagnitude turbidity currents, depositing hummock-like bedforms which indicate flows that deflected off steep canyon walls (Tinterri et al, 2022).…”

“…In fact, their interpretation has long been contested (e.g., Shanmugam and Wang, 2014), due to a previous lack of studies that link direct flow monitoring of modern internal tides to cored deposits. However, this is no longer the case as recent studies have successfully verified sedimentological observations from sediment traps and cores with direct measurements of internal tides from the Whittard Canyon, NE Atlantic margin (Soutter et al, 2024); Monterrey Canyon, California (Maier et al, 2019); and Logan Canyon, Eastern Canada (Normandeau et al, 2024). Attempts can now be made to interpret internal tide deposits from ancient canyon-fills to support palaeoenvironmental reconstructions.…”

“…Within the steep walls of canyons, internal tides can become focussed, amplified (van Haren et al, 2022), and strong enough to transport, erode and inhibit deposition of sediment (Petruncio et al, 1998;Hall et al, 2017;Li et al, 2019;Maier et al, 2019). Despite their ubiquity in modern canyons (Wain et al, 2013;Maier et al, 2019;Normandeau et al, 2024), there is a paucity of documented internal tide deposits in ancient deposits (e.g. May and Warme, 2007;He et al, 2011), partly due to an interpretive bias towards SGF deposits in the rock record (Zhenzhong and Eriksson, 1991;Shanmugam, 2003;Dykstra, 2012), or their poor preservation potential, given the erosive power of SGFs within canyon axes that may remove previously deposited layers (Maier et al, 2019;Talling et al, 2023).…”