Tectonic subsidence history and thermal evolution of the Orange Basin

Abstract

The Orange Basin offshore southwest Africa appears to represent a classical example of continental rifting and break up associated with large-scale, transient volcanism. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension.We present results of a combined approach using subsidence analysis and basin history inversion models. Our results show that a classical uniform stretching model does not account for the observed tectonic subsidence. Moreover, we find that the thermal and subsidence implications of underplating need to be considered. Another departure from the uniform stretching model is renewed sub-crustal thinning and linked to that uplift in the Cenozoic that is necessary to reproduce the observed phases of erosion and the presentday depth of the basin. The dimension of these events has been examined and quantified in terms of tectonic uplift and sub-crustal thinning. Based on these forward models we predict the heat flow evolution not only for the available real wells but also for virtual wells over the entire study area. Finally, the hydrocarbon potential and the temperature evolution is presented and shown in combination with inferred maturation of the sediments for depth intervals which comprise potential source rocks.

Coupled thermo-mechanical 3D subsidence analysis along the SW African passive continental margin

“…Similar conclusions were derived from a previous study by Hirsch et al (2010) centered on the Orange Basin. According to their subsidence analysis, the observed tectonic history and maturation of organic matter could not be reproduced by assuming uniform stretching of the lithosphere.…”

“…Bauer et al 2000;Gladczenko et al 1998;Maystrenko et al 2013;Paton et al 2008), post-breakup vertical movements Japsen et al 2012), sedimentation history and tectonic evolution for specific areas (e.g. Hirsch et al 2007Hirsch et al , 2009Hirsch et al , 2010Stewart et al 2000;Broad et al 2006;Uenzelmann-Neben et al 2007;Brown et al 1995). However, apart from some recent efforts Rouby et al 2013), these studies usually neglected to consider thermo-mechanical feedback effects on the subsidence and uplift processes along the continental margin.…”

Interaction of crustal heterogeneity and lithospheric processes in determining passive margin architecture on the southern Namibian margin

“…The lower transitional megasequence includes the emplacement of SDRs as well as the extrusion of more extensive volcanics across the basin that cap the syn-rift half-graben fills. The distribution of volcanics is often associated with lower crustal bodies (Hirsch et al 2010). As these bodies are considered to be emplaced at the time of rifting it is likely that these lower crustal bodies represent the remnants of the magma chambers that fed the surface volcanics.…”

Reconstruction of the southwestern African continental margin by backward modeling

“…This implies that the density of the crystalline crust does not change during the post-rift phase, but was established syn-rift. Table 1 Names, lithologies, ages and physical properties of the individual units used in this study for "backstripping" as well as for the calculation of the thermal subsidence (after Broad et al, 2006;Hirsch et al, 2007Hirsch et al, , 2010Holtar and Forsberg, 2000;Maystrenko et al, 2013;Paton et al, 2007 andSclater andChristie, 1980 Throughout the sedimentary succession clastic sediments such as sandstone, siltstones, claystones dominate as well as a few shales and subordinate limestones ( Table 1). The set of properties considered for the different sedimentary units is consistent with previous stratigraphic investigations of Holtar and Forsberg (2000) for the Walvis Basin and with studies by Brown et al (1995), Hirsch et al (2007) and Paton et al (2007) for the southern area, especially the Orange Basin.…”

“…Bauer et al, 2000;Bauer et al, 2003;Fern andez et al, 2010;Gladczenko et al, 1998;Hartwig et al, 2012;Koopmann et al, 2013;Kuhlmann et al, 2010;Weigelt and Uenzelmann-Neben, 2007), (2) potential field modeling (Hirsch et al, 2007(Hirsch et al, , 2009; Maystrenko et al, 2013;Stewart et al, 2000), (3) dating of vertical movements by sequence stratigraphy and geochemical dating methods (Broad et al, 2006;Brown et al, 1995;Holtar and Forsberg, 2000;Kuhlmann et al, 2011;Light et al, 1993;McMillan, 2003;Paton et al, 2007;Trumbull et al, 2007), (4) kinematic analysis or (5) a combination of several techniques (e.g. : Hirsch et al, 2010;Paton et al, 2008).…”