An interdisciplinary investigation of a recent submarine mass transport deposit at the continental margin off Uruguay

Abstract

[1] Assessing frequency and extent of mass movement at continental margins is crucial to evaluate risks for offshore constructions and coastal areas. A multidisciplinary approach including geophysical, sedimentological, geotechnical, and geochemical methods was applied to investigate multistage mass transport deposits (MTDs) off Uruguay, on top of which no surficial hemipelagic drape was detected based on echosounder data. Nonsteady state pore water conditions are evidenced by a distinct gradient change in the sulCopyright 2011 by the American Geophysical Union 1 of 19 fate (SO 4 2− ) profile at 2.8 m depth. A sharp sedimentological contact at 2.43 m coincides with an abrupt downward increase in shear strength from ∼10 to >20 kPa. This boundary is interpreted as a paleosurface (and top of an older MTD) that has recently been covered by a sediment package during a younger landslide event. This youngest MTD supposedly originated from an upslope position and carried its initial pore water signature downward. The kink in the SO 4 2− profile ∼35 cm below the sedimentological and geotechnical contact indicates that bioirrigation affected the paleosurface before deposition of the youngest MTD. Based on modeling of the diffusive re-equilibration of SO 4 2− the age of the most recent MTD is estimated to be <30 years. The mass movement was possibly related to an earthquake in 1988 (∼70 km southwest of the core location). Probabilistic slope stability back analysis of general landslide structures in the study area reveals that slope failure initiation requires additional ground accelerations. Therefore, we consider the earthquake as a reasonable trigger if additional weakening processes (e.g., erosion by previous retrogressive failure events or excess pore pressures) preconditioned the slope for failure. Our study reveals the necessity of multidisciplinary approaches to accurately recognize and date recent slope failures in complex settings such as the investigated area.

Lake sediments as natural seismographs: A compiled record of Late Quaternary earthquakes in Central Switzerland and its implication for Alpine deformation

“…As for the latter, many studies have investigated the sedimentary record of lakes and continental margins to link sea bed scarps, soft‐sediment deformation, subaquatic landslides and turbidites with historical earthquake records (e.g. Sims, ; Siegenthaler et al ., ; Niemi & Ben‐Avraham, ; Chapron et al ., ; Nakajima & Kanai, ; Gràcia et al ., ; Monecke et al ., ; Guyard et al ., ; Noda et al ., ; Henkel et al ., ; Sakaguchi et al ., ). Since the pioneering work by Sims () and Kastens (), more recent studies have taken advantage of rapidly developing techniques to efficiently survey, sample and monitor marine and lacustrine sedimentary systems.…”

Sulfur Cycling in an Iron Oxide-Dominated, Dynamic Marine Depositional System: The Argentine Continental Margin

“…Predominantly terrigenous material, delivered from the numerous fluvial tributaries along the coast of Argentina and Uruguay (Iriondo, 1984;Piccolo and Perillo, 1999), is transported downslope from the continental shelf via gravity-controlled mass flows, including turbidity currents and density flows (Biscaye and Dasch, 1971;Klaus and Ledbetter, 1988;Sachs and Ellwood, 1988;Romero and Hensen, 2002;Hensen et al, 2003;Henkel et al, 2011Henkel et al, , 2012Gruetzner et al, 2012;Voigt et al, 2013). These mass flows also transport reworked organic matter further downslope, resulting in burial of refractory organic carbon (Hedges and Keil, 1995) in the deeper parts of the basin.…”

“…Rapid overall sedimentation is sometimes interrupted by phases of sediment winnowing caused by ocean currents. Episodic mass wasting processes can lead to instantaneous sediment accumulation (e.g., Hensen et al, 2003;Riedinger et al, 2005;Henkel et al, 2011Henkel et al, , 2012. These changes cause non-steady state conditions in the subsurface sediment/pore-water system (e.g., Kasten et al, 2003).…”

“…Shielded from sulfidic conditions in the upper sediment column due to rapid burial-and in the presence of mostly reworked, unreactive organic matter-those oxidized reactive iron phases are then preserved in deeper subsurface sediments März et al, 2008;Riedinger et al, 2014). The continental margin off Uruguay and Argentina is characterized by such highly dynamic depositional conditions (e.g., Riedinger et al, 2005;Henkel et al, 2011Henkel et al, , 2012Krastel et al, , 2013, and these locations are likely to be representative of environments that are common throughout the world along continental margins.…”

Constraining the Age and Evolution of the Tuaheni Landslide Complex, Hikurangi Margin, New Zealand, Using Pore‐Water Geochemistry and Numerical Modeling

“…The pore‐water record is very sensitive to recent perturbations such as changes in methane flux, organic carbon rain rate, and rapid sedimentary events (e.g., Chen et al, 2019; de Lange, 1983; Fischer et al, 2013; Henkel et al, 2011; Henkel et al, 2012; Hensen et al, 2003; Luo et al, 2015; Zabel & Schulz, 2001). In dynamic depositional settings, pore‐water species involved in early diagenetic processes can exhibit transient‐state features that hold a historical record of sediment perturbations.…”