The role of mass-transport deposits and turbidites in shaping modern lacustrine deepwater channels

Abstract

a b s t r a c tSubaquatic canyons are an important pathway for sediment transport into oceanic and lacustrine basins. Understanding the mechanisms governing their geomorphological evolution is a key to predict the sediment distribution patterns through these sediment conduits as well as to implement geo-hazard assessments. Submerged channels developed in large lacustrine basins offer a small-scale natural laboratory to understand the sedimentological processes operating in submarine channels. For this reason, a multidisciplinary research initiative -including time-lapse, high-resolution bathymetric surveys, innovative coring using submersibles, in situ geotechnical tests, and geophysical and sedimentological analyses-was applied to unravel the factors controlling the geomorphological evolution of the Rhone delta channels in Lake Geneva during the last decades. The morphology of the lacustrine Rhone Delta consists of a freshwater delta system deeply incised by nine canyons (C1eC9). Geotechnical measurements in proximal areas and sediment cores retrieved in the distal fans at the end of each canyon revealed complex sediment dynamics. No turbidity current events have occurred in the easternmost canyons (C1eC4) during the last decades while the western canyons sediment record (C5eC9) indicated repeated flushing events during the 20 th century. The main "active" canyon C8 has been dominated by turbidite activity on the canyon floor with frequent overspill events along the levees. A large 6.2 Â 10 6 m 3 Mass-Transport Deposit (MTD) that resembles a debrite in its upper section was found in the distal area of the active channel. The MTD was dated at 1998e2000 CE and most likely originated from proximal delta areas affected by frequent slope failures of the steep channel walls. In situ geotechnical tests on the modern proximal channel floor showed an unconsolidated soft top-layer that might have served as a low-friction surface favouring the MTD long run-out distance to the distal part of the channel. The MTD has had a major effect morphological evolution of the distal channel by filling the existing conduit, indirectly promoting the formation of a new channel. The role of MTD emplacement in subaquatic channels has important implications for hydrocarbon exploration as they control channel avulsion processes and the location of sand-prone deposits. This study gives a detailed insight on poorly investigated short-term sedimentological dynamics that affect the long-term evolution of turbidite systems and channel migration processes. This detailed model of a river-dominated deep-lacustrine depositional system can be used as an analog for similar modern and ancient deep-water systems.

The Role of Mass Wasting In the Progressive Development Of Submarine Channels (Espírito Santo Basin, Se Brazil)

“…They evacuate large volumes of sediment and are capable of changing seafloor topography, ultimately controlling the distribution of turbiditic sandstones which comprise important reservoirs for hydrocarbons (e.g., Pickering and Corregidor 2005;Armitage et al 2009;Jackson and Johnson 2009;Joanne et al 2010;Olafiranye et al 2013;Ortiz-Karpf et al 2015;Turner 2015;Kneller et al 2016;Corella et al 2016).…”

“…To better understand accommodation space as a function of MTD geometry and internal structure, the interaction between MTDs and turbidity currents has been documented in a number of studies based on outcrop analogues (e.g., Shultz et al 2005;Lucente and Pini 2008;Jackson and Johnson 2009), seismic data (e.g., Kertznus 2009;Bernhardt et al 2012;Masalimova et al 2015;Ortiz-Karpf et al 2015;Kneller et al 2016), bathymetric data (Corella et al 2016), well and core data (Eggenhuisen et al 2010;Corella et al 2016), and numerical models (Stright et al 2013). These studies have shown that turbidity flows can deposit upstream and above MTDs (e.g., Bernhardt et al 2012;Ortiz-Karpf et al 2015;Corella et al 2016), or, instead, can be erosive to create large-scale scours above MTDs (e.g., Shultz et al 2005).…”

“…These studies have shown that turbidity flows can deposit upstream and above MTDs (e.g., Bernhardt et al 2012;Ortiz-Karpf et al 2015;Corella et al 2016), or, instead, can be erosive to create large-scale scours above MTDs (e.g., Shultz et al 2005). Furthermore, turbidity flows can be diverted by topographic highs created by MTDs, leading to the generation of new sediment routes (Hansen et al 2013;Masalimova et al 2015;Kertznus 2009;Corella et al 2016).…”

“…Previous studies focused mainly on the location and pathways of channels influenced by MTDs (e.g., Kertznus 2009;Hansen et al 2013;Masalimova et al 2015;Kneller et al 2016;Corella et al 2016), but less attention has been paid to the initiation and development submarine-channels affected by MTD-related topography. The presence of MTDs at the base of channel systems has been documented on both seismic (e.g., Deptuck et al 2003;Mayall et al 2006) and outcrop data (e.g., Macauley and Hubbard 2013;Bain and Hubbard 2016), leading some authors to suggest that seafloor roughness produced by mass-wasting processes can capture and accelerate turbidity flows, facilitating the formation of channels (e.g., Deptuck et al 2003;Gee et al 2007;Abdurrokhim and Ito 2013).…”

Sedimentary characteristics of hyperpycnites in a shallow lacustrine environment: A case study from the Lower Cretaceous Xiguayuan Formation, Luanping Basin, Northeast China

“…Relatively dense fluvial discharges entering an oceanic or lacustrine basin commonly result in a subaqueous extension of the fluvial channels in deep-water locations (Xian et al, 2018;Zavala et al, 2006). Such flows are common in modern sedimentary records (Corella et al, 2016;Soyinka & Slatt, 2008;Yang et al, 2017;X. Zhang & Scholz, 2015).…”