--> --> Conjugate Margin Chronostratigraphy – Comparison of Cretaceous-Tertiary Petroleum Systems in Namibia and Uruguay

2018 AAPG International Conference and Exhibition

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Conjugate Margin Chronostratigraphy – Comparison of Cretaceous-Tertiary Petroleum Systems in Namibia and Uruguay


Extensive offshore areas of the South Atlantic eastern and western margins remain underexplored. Offshore Brazil, Uruguay and Argentina host multiple underexplored basins south of the salt provinces. Exploration wells drilled on the conjugate Namibian margin suggest a petroleum system is present in this area as well. Offshore basins containing Early Cretaceous through Tertiary strata along the South Atlantic margins host significant recent hydrocarbon discoveries in near-shore shelf carbonates to deep-water siliciclastic reservoirs. The recent discoveries reveal functioning petroleum systems on both sides of the conjugate margin and provide data to address the potential for future discoveries. We develop detailed chronostratigraphy of the sedimentary section of the Uruguayan and Namibian conjugate margins. We evaluate the geo-chronologic timing of syn- and post-rift fill sequences including the enigmatic seaward-dipping reflector (SDR) packages. Long-offset seismic profiles from the South Atlantic rifted margins provide a comparison of basin-fill, sedimentation and SDR chronostratigraphy by comparison of seismic facies and stratal architecture of both margins. The margins share a similar geologic history until Early Cretaceous rifting initiated their separation. Post-rifting, the margins also show synchronous, symmetrical sedimentary section development and evolution, with tectonics driving variable sedimentation episodes between the margins. The zone composed of SDR packages links the crustal processes driving magmatic rifting/stretching of the continental crust and formation of oceanic crust to sedimentation (including extrusive volcanic) patterns observed along the rifted margins. Therefore the SDR packages are included at the end of the syn-rift fill sediments which fill early mini-grabens overlying continental crust, and show similar timing on opposing sides of the Atlantic. These observations facilitate our evolving understanding of petroleum systems on both margins and provide a joint stratigraphic framework for depositional history and identification of play types and models. Our comparison predicts that Uruguay has a potential post-Cretaceous play which may also exist in Namibia, and that the Cenomanian-Turonian may be a viable source interval on both margins. This interpretation is supported by seismic facies analysis of stratal architecture and geobody distribution observed across both margins.