AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Turbidite-Contourite Interactions on Continental Margins: New Insights From the Cretaceous Uruguayan Margin


Globally, there is an increasing catalogue of turbidite reservoirs worldwide hosting anomalous reservoir qualities and not conforming to typical end-member models. While gross-depositional architectures may host the primary characteristics of one process, medium- to small-scale seismic and sedimentological characteristics may show traits of two or more sedimentary processes. These ‘mixed-depositional system’ have been shown to be fundamental in controlling the morphology and the sedimentary stacking pattern of continental margins, though the nature and consequences of both along- (bottom-current) and down-slope processes are still relatively unknown. Using a combination of regional 2D seismic with a 3D datacube we aim to: (1) characterise the Cretaceous mixed-drift system, (2) evaluate the conceptual implications for the interaction of deep-marine sedimentary processes and (3), propose new depositional models for mixed-systems. Four large (>25 km wide and up to 100 km long) asymmetric channel-drifts have been identified propagating obliquely (90 – 120o) from the middle slope, before terminating after about 40 km on the lower slope. Individual drifts have over 1km of localised relief over adjacent depressions which amalgamate towards the SE following underlying basement topography. Internally, drifts are characterised by a series of convex-up, low to medium amplitude reflections which prograde away from the slope, and prograde/aggrade laterally towards the south-west. Basal reflections can be traced across multiple drifts, though later, these terminate into adjacent depressions or pinch-out against internal discontinuities and scarps formed by MTDs across stoss-slopes. Similar drifts have been recognised across the Weddell Sea, Antarctic Peninsula and Eastern Greenland. In all examples, sediment availability appears fundamental in controlling the growth of channel-drifts, with prominent growth correlating to highest sediment supply due to the continental margin progradation or glaciation, coinciding with the intensification of ocean circulation following the opening of tectonic gateways. Under these conditions, bottom-currents pirate fine-grained material from turbidite plumes to build muddy-drifts and leave ‘cleaned’ channel-sands of primary interest in hydrocarbon exploration. Despite this, the fundamental mechanics behind their depositional processes and associated sedimentological consequences are still relatively unknown and significant work is needed.