Abstract
Studies of near-seabed datasets show that salt tectonics controls the distribution and architecture of deep-water reservoirs in many salt-influenced basins. It is typically difficult, however, to study the distribution and stratigraphic evolution of depositional systems preserved at deeper, economically significant depths, reflecting poor seismic imaging of steeply dipping strata flanking high-relief salt structures. 3D seismic and borehole data from the Santos Basin, offshore Brazil allow us to identify a range of depositional elements that form the building blocks of three main tectono-stratigraphic phases. During the first phase, channel systems and lobes were confined within updip minibasins and to the hangingwalls of salt-detached faults. During the second phase, channel systems and lobes filled updip minibasins to bypass sediment downslope, with coarse clastic deposition then occurring in downdip minibasins, >100 km from the coeval shelf margin. Syndepositional seafloor relief caused: (i) channel system deflection and diversion around salt-cored highs; (ii) channel system uplift and rotation on the flanks of rising salt structures; (iii) lateral and frontal confinement of channel systems. During the final phase, rising salt walls dissected previously deposited deep-water systems, with MTCs deposition becoming increasingly important. Our results have important implications for post-salt prospectivity in the Santos Basin and other salt-influenced sedimentary basins, with a range of reservoirs and trapping styles present in this underexplored interval. More specifically, we show that large volumes of clastic sediment were not trapped behind the ‘Albian Gap’, a salt-controlled depocenter dominating the north-western basin margin, but were instead delivered further basinward.
Highlights
Understanding the spatial distribution and temporal evolution of deep-water depositional systems relative to the style and evolution of seafloor relief is key to improving the ability to predict reservoir presence, architecture and hydrocarbon trapping styles along deep-water slopes
By integrating 3D seismic reflection and borehole data we here show that: (i) deep-water systems of the Itajai-Acu Formation were deposited on the São Paulo Plateau, some distance seaward of the Albian Gap and the coeval Late Cretaceous shelf edge; and (ii) large thickness variations occur within the Marambaia Formation due to continue salt diapirism, and the emplacement of relatively small, intra-minibasin and larger, shelf-derived mass transport complexes (MTCs)
We propose that the salt-related controls observed in the central deep-water Santos Basin led to changes in the geometry, distribution and potential structural and stratigraphic trapping of reservoir-prone units
Summary
Understanding the spatial distribution and temporal evolution of deep-water depositional systems relative to the style and evolution of seafloor relief is key to improving the ability to predict reservoir presence, architecture and hydrocarbon trapping styles along deep-water slopes. Booth et al, 2003; Gee and Gawthorpe, 2006, 2007; Jackson et al, 2010; Mayall et al, 2010; Oluboyo et al, 2014; Sylvester et al, 2015; Doughty Jones et al, 2017; Wang et al, 2017) Overall, these studies suggest that the style of salt sediment interaction is a result of; i) the nature (e.g. grain-size, erosive power, etc) and temporal evolution of deep-water depositional systems; ii) downdip changes in salt-related structural style (i.e., from predominantly thin-skinned extensional styles near the updip basin margins, to thin-skinned contractional styles towards the basin center), with a key control being the orientation, scale and growth rate of structures relative to the incoming deep-water systems; and iii) the timing of sediment deposition relative to the formation, growth and decay of salt-induced seafloor relief. This study improves our current understanding of the distribution of and controls on, depositional systems along salt-influenced deep-water slopes, providing new insights into the tectono-stratigraphic evolution of this salt-dominated basin
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