Mass-Transport Deposit Surface Topography and Its Impact on Overlying Turbidite Systems, Paganzo Basin, NW Argentina: Implications for Hydrocarbon Exploration

Mass-transport deposits (MTD) are virtually ubiquitous on the modern seafloor and in ancient slope successions. They are formed by resedimentation of slope sediments, and commonly remould originally flat seafloor creating accommodation in the form of surface topography. This topography may confine and pond turbidity currents, forming distinct thick deposits of sand that are potential hydrocarbon reservoirs. In these situations, both the form of the basal contact and the internal architecture of the deposit are important in determining the nature of a potential reservoir; they are determined by the scale of the MTD surface topography and the filling style of the turbidite system, respectively. A common model for the internal architecture of turbidites in topographically complex settings is the fill-and-spill model. This produces a characteristic fill-and-spill style with sand-to-shale ratio increasing progressively with infill. We have assessed the applicability of this model using a seismic-scale outcrop in the syn- to post-glacial succession of the Carboniferous-age Paganzo Basin, NW Argentina.

Preliminary results show that MTD surface topography is organised into a scaled hierarchy with shorter wavelength and smaller amplitude ‘basins’ being superimposed upon larger wavelength and amplitude ‘basins’. These vary considerably in scale from 200 to >6500m and are overfilled; their associated amplitudes are of 10 - 100m and thus range from seismic to sub-seismic for typical reservoir depths.

We present an alternative filling mechanism/model for MTD surface topography where five turbidite units with different filling styles can be identified, illustrating that not all scales of MTD topography fill-and-spill, and thus do not show fill-and-spill sand/shale trends. The nature of the boundaries between the turbidite units, and their spatial variation further demonstrate that MTD topography is neither static nor instantaneous, but is generated over time, contemporaneously with turbidite deposition. It is suggested that this is as a result of post-depositional creep and/or heterogeneous compaction.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California