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Cenozoic Shelf to Slope Transition along a Passive Continental Margin: Demerara Rise, Suriname, South America

Goss, Shawn 1; Mosher, David 2; Kean, Allan 3; Wach, Grant 1
1 Dalhousie University, Halifax, NS, Canada.
2 Geological Survey of Canada, Dartmouth, NS, Canada.
3 RepsolYPF, The Woodlands, TX.

The Demerara margin off Suriname, South America is highly prospective in light of hydrocarbon exploration and production successes to the south, off Brazil and to the north off Venezuela and Trinidad. Regional 2D seismic reflection data and a few offshore wells set the stage for the latest phase of exploration activity. A 3D volume bridging the shelf to slope transition allows for detailed investigation of Cenozoic stratigraphy, to improve understanding of shelf to slope linked depositional systems. Understanding forcing functions, sediment pathways and depositional processes are expected to provide insights into exploration models for passive clastic margins.

Exploration seismic data off Suriname show sedimentary sequences of subsidence infill and overall progradation. Early post-rifting conditions were highly anoxic, resulting in a thick (~90 m) interval of Cretaceous black shale that provides excellent hydrocarbon source rock. Several significant regional deep water unconformities indicate episodes of extensive erosion, such as during the Mid-Miocene. Outboard, the Cenozoic section is thin as a result, yet on the upper slope, the section is expanded with classic shelf-to-slope progradational architecture. Based on the position of the shelf-to-slope hinge line, it is apparent that progradation slowed during the Paleogene. In the Neogene, a regional Pliocene unconformity marks the return to rapid progradation that continued into the Quaternary. Although sea level is no doubt a primary control on establishing the broad stratigraphic framework, lack of major erosional phases creating canyons and channels on the upper continental slope during the Cenozoic suggests other sedimentation processes dominate between major sea level excursions. Rapid Pliocene progradation, for example may be related to increased sediment supply, due to uplift of the Andes, outpacing relative sea-level rise and increasing accommodation space in the basin. Rapid progradation and sediment loading on the shelf, presumably lead to over-steepening of unconsolidated sediments at the critical location of the shelf -slope transition zone. Extensive faults with seafloor offsets, in some cases paralleling the shelf edge, may be a consequence of such loading. Gullies along the shelf edge, probably cut by turbidity currents and the shallow margin-parallel faults suggests seafloor instability and mass-transport processes are responsible for moving sediment to deep water.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009