Incorporation of substrate blocks into mass transport deposits: Insights from subsurface and outcrop studies

Abstract

Mass movements are common on the continental slope, affecting not only the subsequent sea floor morphology but often substantially modifying the underlying deposits. Various styles of substrate interaction have been recognised, representing the various degrees of involvement of the underlying material and its incorporation into the mass movement. This work presents a new style of basal interaction not previously described. Based on the morphology of the basal surface of a mass transport deposit, this can be recognised both in seismic data and in an outcrop analogue. A subsurface example, from an ca 100 m thick mass transport deposit located in Santos Basin, offshore Brazil, displays a basal surface with spoon-shaped scours or scoops. These scoops are of the order of tens up to 400 m in maximum dimension, where masses of underlying sediment have been removed and incorporated into the mass movement. Outcrops used for this work are located in La Rioja Province, Western Argentina, where the study involves a well-exposed ca 200 m thick mass transport deposit that crops out continuously over 7 km. Its basal surface is incised irregularly into the underlying sandstones, incorporating the blocks of sandstone into the mass movement. The striking similarities observed between outcrop examples and the northern Santos Basin suggest that they can be effective analogues, facilitating a comprehensive understanding of mass transport deposit dynamics across diverse basin environments.