Mass-transport deposits: combining outcrop studies and seismic forward modeling to understand lithofacies distributions, deformation, and their seismic expression

Mass-transport deposits may act as barriers or baffles to fluid flow in the subsurface, or may conduct fluids via internal structures or lithological connectivity. Conventional seismic and borehole data present radically different scales of observation to assess the likely fluid-flow behavior of mass-transport deposits. Seismic-scale outcrops and high- resolution seismic data bridge this scale gap. Exceptional outcrops of large mass- transport deposits are used to develop strategies to relate core- and seismic-scale observations for the purposes of subsurface prediction of reservoir, baffle, or seal potential, and for prediction of fluid flow through mass-transport deposits in the subsurface. We present here an outline of our approach, and some preliminary results based on two systems of contrasting styles. One is a ›120-m-thick debrite of Carboniferous age in northwest Argentina; the other is an approximately 300-m-thick slide complex of Jurassic-Cretaceous age in Antarctica. Differences in these two systems are assessed by evaluating the internal structure and seismic expression of the deposits, based on forward modeling of the outcrop architecture. Topography on the top surface of mass- transport deposits is defined by very localized (a few meters wavelength and amplitude), localized (a few tens of meters wavelength, a few meters to ~10 m amplitude), and subregional (kilometers in wavelength, tens of meters in amplitude) "ponding" or partial confinement of turbidite beds immediately above the masstransport deposits. Strain histories and strain distributions are complex and variable within deposits, implying that inferences based on limited well data are likely to yield incorrect conclusions regarding direction of movement and slope orientation. This observation is clearly illustrated by the non-coaxial deformation, which is visible in high- resolution seismic data.