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

DYKSTRA, M, GARYFALOU, K., KERTZNUS, V., KNELLER, B., MILANA, J.P., MOLINARO. M., SZUMAN, M., AND THOMPSON, P.

Mass Transport Deposits

SEPM

Lugar: Tulsa; Año: 2009;

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 from which to assess the likely fluid flow behavior of mass-transport deposits. Seismic-scale outcrops and high-resolution seismic data bridge this scale gap. We are using exceptional outcrops of large mass transport deposits to develop strategies to relate core- and seismic scale observations for the purposes of sub-surface 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 debris flow of Carboniferous age in NW Argentina, which we have studied in detail; the other is an approximately 300 m thick slide complex of Jurassic-Cretaceous age in Antarctica, for which we use published and unpublished data from Butterworth and Macdonald. We record differences in internal structure, and in the seismic expression of the deposits based on forward modeling of the outcrop architecture. Topography on the tops of the mass-transport deposits is defined by very localized (few meters wavelength and amplitude), localized (few tens of meters wavelength, few meters to ~ 10 m amplitude), and sub-regional (kilometers in wavelength, 10s meters in amplitude) ‘ponding’ or partial confinement of turbidite beds on the surface of the mass-transport deposits. Strain histories and strain distributions are complex and variable from one part of a deposit to another, implying that inferences based on limited well data are likely to yield incorrect conclusions regarding the movement direction and slope orientation. This is clearly illustrated by the non-coaxial deformation visible in high-resolution seismic data.