Submarine-Channel Pathways and Reservoir Architecture in Response to Sedimentation and Salt-Related Structural Deformation

Abstract

In continental margins affected by salt tectonics, structural deformation can promote the development of complex, dynamic slope topography, which can exert a fundamental control on the trend of submarine-channel systems and their sediment-dispersal patterns. We use a Kirchhoff pre-stack depth-migrated, high-resolution (~10 m tuning thickness) 3-D seismic-reflection volume (courtesy of Petroleum Geo-Services, PGS) covering ~2000 sq. km of the Campos basin, offshore Brazil, to investigate the response of submarine-channel evolution to salt-related structural deformation. A network of salt-withdrawal minibasins initiated at the northeast edge of a structural high called the Campos salient during the Late Cretaceous, and Cenozoic deformation established a template across which submarine-channel systems developed. Numerous laterally offset Miocene channel systems filled minibasins that formed between salt diapirs. We interpret that sedimentation eventually outpaced subsidence of the minibasins, which led to the development of a dominantly northwest-southeast-sloping seafloor. Pliocene-Quaternary channel deposits vertically stacked to form a single ~400 m-thick northwest-southeast-trending system that overrode some diapirs that had been buried by sediment. Miocene-Quaternary channel-migration patterns are dominated by downstream translation (i.e., sweep), likely as a result of a combination of basin confinement and tilting, which promoted the development of distinctive counter-point bar geometry (i.e., remnant channel deposits with concave bends). We evaluate the influence of basin confinement and tilting on the trend of channel systems and their sediment-dispersal patterns with a surface-based stratigraphic forward model. The evolution of these submarine-channel deposits reflects a balance between sedimentation and structural deformation. Preserved submarine-channel pathways and stratigraphic architecture do not necessarily reflect the present locations of salt structures. In the Campos basin, multiple syndepositional diapirs influenced the development of numerous laterally offset channel systems in a network of minibasins; when sedimentation outpaced subsidence, channel deposits vertically stacked in the direction of steepest descent across the slope.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018