Hybrid turbidite-drift channel complexes: An integrated multiscale model

Abstract

The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution seafloor data, and near-bed current measurements from two sites where eastward-flowing gravity flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, deposited over a period of ∼20 m.y. (Upper Cretaceous to Paleocene). High-resolution modern seafloor data from offshore Mozambique reveal similar asymmetric channel geometries, which are related to northward-flowing near-bed currents with measured velocities of up to 1.4 m/s. Higher sediment accumulation occurs on the downstream flank of channel margins (with respect to bottom currents), with inhibited deposition or scouring on the upstream flank (where velocities are highest). Toes of the drift deposits, consisting of thick laminated muddy siltstone, which progressively step back into the channel axis over time, result in an interfingering relationship with the sandstone-dominated channel fill. Bottom-current flow directions contrast with those of previous models, which lacked direct current measurements or paleoflow indicators. We finally show how large-scale depositional architecture is built through the temporally variable coupling of these two globally important sediment transport processes. Our findings enable more-robust reconstructions of past oceanic circulation and diagnosis of ancient hybrid turbidite-drift systems.

Contourite characterization and its discrimination from other deep‐water deposits in the Gulf of Cadiz contourite depositional system

“…The range of depositional processes described here suggests that the middle slope of the Gulf of Cadiz has been affected by numerous processes and therefore the sedimentary stacking pattern of a contourite drift and contourite channel was not only built up by pure contourite facies. The frequency and amount of sediment input and the relative persistence and strength of bottom currents is determinant for the predominance of one or another deposit (Fuhrmann et al, 2020), including sediment reworking and winnowing.…”

“…The interest in distinguishing among contourites, turbidites and hemipelagites based on: (i) the role of mixed turbiditic-contouritic systems in deep-water petroleum plays (Sansom, 2018;Fonnesu et al, 2020); (ii) implications for mineral resources and for the judicial determination of a continental shelf´s outer limits since contourites shape continental shelf morphology (Rebesco et al, 2014;Mosher et al, 2017); (iii) the environmental impact of bottom current deposits in the accumulation of microplastics (Courtene-Jones et al, 2019;Kane et al, 2020); (iv) the close link between contourites and deep-water ecosystems (Hebbeln et al, 2016;L€ udmann et al, 2016;Lozano et al, 2020); and (v) slope stability and other geohazards (Laberg & Camerlenghi, 2008;Miramontes et al, 2018). Despite this interest, there is still no clear criteria for contourite characterization and its discrimination from other deep-water deposits.…”

Distribution of contourite drifts on convergent margins: Examples from the Hikurangi subduction margin of New Zealand

“…Variations in oceanic stratification in terms of density (i.e. related to temperature and salinity) and in oxygenation in proximity to the continental slope are known to be associated with different water masses [for example, the Argentine margin (Preu et al ., 2013); South China Sea (Chen et al ., 2014); Gulf of Cadiz (Hernández‐Molina et al ., 2014); Alboran Sea (Ercilla et al ., 2016); Mozambique (Fuhrmann et al ., 2020)]. Through linking prior mapping of bottom currents to observed depositional and erosional features, this study attempts to correlate drifts with the physical properties of specific water masses and the boundaries between them ( sensu Preu et al ., 2013; Rebesco et al ., 2013; Hernández‐Molina et al ., 2014).…”

“…When turbidite systems are present, contour currents can modify them to different degrees, ranging from reworking turbidite bed tops to complete erosion and redistribution to form stand‐alone contourites (e.g. Locker & Laine, 1992; Howe et al ., 1994; Masse et al ., 1998; Mulder et al ., 2008; Brackenridge et al ., 2013; Sansom, 2018; Fonnesu et al ., 2020; Fuhrmann et al ., 2020). Contourites constitute high‐resolution, semi‐continuous sedimentary records of past oceanic circulation and climate change with implications for palaeoceanography, palaeoclimatology and geohazard studies (Mulder et al ., 2002; Toucanne et al ., 2007; Knutz, 2008; Laberg et al ., 2016; Miramontes et al ., 2018).…”

Neogene to recent evolution of the Southern Gulf of Mexico basin: Tectonic controls on deep‐water sediment dispersal systems

“…Generally speaking, important end‐member morphological distinctions in describing these bedforms are (a) symmetrical versus asymmetrical, (b) up‐slope (into current) migrating versus down‐slope (with current) migrating, and (c) net‐aggradational versus non‐aggradational (purely migratory) versus net‐erosional (Cartigny et al., 2011; Covault et al., 2014; Wynn & Stow, 2002). Underlying current drivers can be bottom (contour) currents, down‐slope or levee‐overbanking turbidity currents, or hybrids between these deep‐water processes (Fuhrmann et al., 2020; Wynn & Stow, 2002). Understanding the generative processes behind specific occurrences of these bedforms is a crucial component of understanding local and regional basin evolution.…”