Abstract
Submarine landslides can generate complicated patterns of seafloor relief that influence subsequent flow behaviour and sediment dispersal patterns. In subsurface studies, the term mass transport deposits (MTDs) is commonly used and covers a range of processes and resultant deposits. While the large-scale morphology of submarine landslide deposits can be resolved in seismic reflection data, the nature of their upper surface and its impact on both facies distributions and stratal architecture of overlying deposits is rarely resolvable. However, field-based studies often allow a more detailed characterisation of the deposit. The early post-rift Middle Jurassic deep-water succession of the Los Molles Formation is exceptionally well-exposed along a dip-orientated WSW-ENE outcrop belt in the Chacay Melehue depocentre, Neuquén Basin, Argentina. We correlate 27 sedimentary logs constrained by marker beds to document the sedimentology and architecture of a >47 m thick and at least 9.6 km long debrite, which contains two different types of megaclasts. The debrite overlies ramps and steps, indicating erosion and substrate entrainment. Two distinct sandstone-dominated units overlie the debrite. The lower sandstone unit is characterised by: 1) abrupt thickness changes, wedging and progressive rotation of laminae in sandstone beds associated with growth strata; and 2) detached sandstone load balls within the underlying debrite. The combination of these features suggests syn-sedimentary foundering processes due to density instabilities at the top of the fluid-saturated mud-rich debrite. The debrite relief controlled the spatial distribution of foundered sandstones. The upper sandstone unit is characterised by thin-bedded deposits, locally overlain by medium-to thick-bedded lobe axis/off-axis deposits. The thin-beds show local thinning and onlapping onto the debrite, where it develops its highest relief. Facies distributions and stacking patterns record the progradation of submarine lobes and their complex interaction with long-lived debrite-related topography. The emplacement of a kilometre-scale debrite in an otherwise mud-rich basinal setting and accumulation of overlying sand-rich deposits suggests a genetic link between the mass-wasting event and transient coarse clastic sediment supply to an otherwise sand-starved part of the basin. Therefore, submarine landslides demonstrably impact the routing and behaviour of subsequent sediment gravity flows, which must be considered when predicting facies distributions and palaeoenvironments above MTDs in subsurface datasets.
Highlights
IntroductionOlistostromes (Flores, 1955), or Mass Transport Deposits (MTDs) (Nardin et al, 1979), are sedimentary bodies that have been translated downslope from high to low gradient slopes as a result of mass failure and gravitational processes (Hampton et al, 1995; Moscardelli and Wood, 2008; Ogata et al, 2012; Festa et al, 2016; Kneller et al, 2016)
As submarine landslides travel across the seafloor, they exert shear stress on the substrate, coupled with significant overpressure (Bull et al, 2009; Hodgson et al, 2019; Payros and Pujalte, 2019)
The stress applied to the substrate during the emplacement is accommodated by both stratigraphic intervals consisting of deformed packages and interfaces consisting on a plane (Alves and Lourenço, 2010), such as the discrete basal shear zone located in upper Unit 1
Summary
Olistostromes (Flores, 1955), or Mass Transport Deposits (MTDs) (Nardin et al, 1979), are sedimentary bodies that have been translated downslope from high to low gradient slopes as a result of mass failure and gravitational processes (Hampton et al, 1995; Moscardelli and Wood, 2008; Ogata et al, 2012; Festa et al, 2016; Kneller et al, 2016). Megaclasts within MTDs are sourced either from headwall areas or entrained from the substrate (Festa et al, 2016; Ogata et al, 2019) These features, accompanied by synand post-depositional faulting (Dykstra, 2005; Dykstra et al, 2011), generate the topographically irregular upper surfaces of MTDs (Moscardelli et al, 2006; Bull et al, 2009). The interaction between the initial topographic relief of MTDs, dewatering processes, post-depositional deformation and subsequent sediment gravity flows (and their deposits) is highly dynamic and inherently complex Detailed field-based studies can help to bridge the resolution gap
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
