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AAPG Bulletin, Preliminary version published online Ahead of Print 15 May 2023.

Copyright © 2023. The American Association of Petroleum Geologists. All rights reserved.


Carbonate platform or volcanic mound? Seismic characterization of a syn-rift build-up along the outer high of the Lüderitz Basin, Namibia

N. Rochelle-Bates1 , G. Calvès2 , M. Huuse1 , and S. Schröder1

1 Department of Earth and Environmental Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK
2 Université Toulouse III, GET-OMP, 14 Avenue Edouard Belin, 31400 Toulouse, France

Ahead of Print Abstract

Prospect B is one of the largest Cretaceous sag-phase build-ups yet identified along the outer high of Namibia’s Atlantic volcanic-rifted margin. These enigmatic build-ups constitute a potential new carbonate play offshore Namibia and South Africa. However, no unambiguous carbonate geometries have been reported to date, and they sit atop a highly volcanic sedimentary sequence. In the absence of well data, it is thus prudent to examine these build-ups carefully using all available data and analogs, to test their carbonate vs. igneous origin and therefore their potential as hydrocarbon reservoirs.

This study used 3D seismic data to extract detailed depositional information for Prospect B. The analysis included assessment of the build-up’s external morphology and internal seismic facies, measuring the dip and dip direction of inclined reflectors, making horizon slices, mapping internal surfaces onto which seismic attributes were extracted (RMS amplitude, spectral decomposition), and creating thickness maps to show build-up evolution through time. These data were then evaluated against known and published observations made on volcanic and carbonate systems (continental and marine). Architectural elements like vents, igneous flows and complex clinoform geometries suggest that a large portion of the build-up is likely volcanic in origin. Though it has carbonate-like features, no definitive carbonate geometries were identified. Thus, Prospect B is more likely to be dominated by igneous materials such as hyaloclastites. Contrary to existing interpretations, Prospect B and its equivalents probably represent a late, waning phase of regional volcanism, and are an important bathymetric record of the South Atlantic’s formation.

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Please cite this AAPG Bulletin Ahead of Print article as:

N. Rochelle-Bates , G. Calvès , M. Huuse , S. Schröder: Carbonate platform or volcanic mound? Seismic characterization of a syn-rift build-up along the outer high of the Lüderitz Basin, Namibia, (in press; preliminary version published online Ahead of Print 15 May 2023: AAPG Bulletin, DOI:10.1306/12202220205.