Analogue modelling of basin inversion: the role of oblique kinematics and implications for the Araripe Basin (Brazil)
Abstract. Basin inversion is a process that takes place when a sedimentary basin is subjected to compressional stresses and may result in the reactivation of pre-existing faults and/or the localization of deformation along new reverse faults. The Araripe Basin (NE Brazil) is an example of a Cretaceous intracontinental aborted rift with its sedimentary infill found at ca. 1000 m altitude in the present day. Post-rift basin inversion is proposed as the cause of this topographic high, however how inversion mechanisms affected this basin is a matter of debate with two end member scenarios: reactivation of pre-existing normal faults leading to local uplift, or regional tectonic uplift. In this study, we conducted analogue models of basin inversion to test these scenarios. We present two series of crustal-scale brittle-viscous experiments: i) extension followed by compression without sedimentation, with a variation of rifting and inversion directions (orthogonal or 45° oblique) and ii) extension and compression with syn-rift sedimentation, with the same variation in rifting and inversion directions. We used a seed representing a structural weakness that was applied at the base of the brittle layer to localize deformation along the model axis. We found that orthogonal rifting without sedimentation forms through-going border faults, whereas oblique rifting creates initial en-echelon faults that eventually link up creating large border faults. Rift basins with syn-rift sedimentation evolved in a similar fashion, however sedimentary loading increased subsidence. During inversion, most deformation is accommodated along new low angle reverse faults. Within that framework, significant intra-graben fault reactivation occurred in models without sedimentation. By contrast, syn-rift sedimentation caused only minor reactivation of rift faults in oblique inversion since the sediments acted as a buffer during compression; no rift fault reactivation occurred in orthogonal compression situations. Comparing the existing scenarios for inversion in the Araripe Basin with our model results and field data show that these scenarios do not fully explain the natural example. Therefore, we propose an alternative scenario based on our models, involving oblique compression and the development of low angle reverse faults, which better explains inversion in the Araripe Basin.
Pâmela Cristina Richetti et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2022-1251', Fernando Ornelas Marques, 02 Dec 2022
- AC1: 'Reply on RC1', Pamela Richetti, 10 Mar 2023
RC2: 'Comment on egusphere-2022-1251', Ioan Munteanu, 14 Dec 2022
- AC2: 'Reply on RC2', Pamela Richetti, 10 Mar 2023
- EC1: 'Comment on egusphere-2022-1251', Ernst Willingshofer, 13 Mar 2023
Pâmela Cristina Richetti et al.
Pâmela Cristina Richetti et al.
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Report on “Analogue modelling of basin inversion: the role of oblique kinematics and implications for the Araripe Basin (Brazil)” by Richetti et al.
Assessment: the topic of the ms. is relevant for geosciences, and therefore suitable for EGUsphere, but not in its present form. The ms. needs major revision before matching the high standards of the journal. Based on their experimental results, the authors conclude that the scenario proposed by Marques et al. (2014) for the inversion of the Araripe Basin is not viable. This is wrong because they did not test the arguments used by Marques et al. (2014), which are much lower angle between shortening direction and graben strike (<45º), and fault lubrication by injected soft clays. Therefore, all the authors may conclude is that 45º are not enough to explain the amount of inversion in the Araripe Basin. This is the main problem that the authors have to solve. The authors should read more carefully what previous authors have said about the mechanics of inversion of normal faults (e.g. Sibson 1985; Brun and Nalpas, 1996; Marques and Nogueira, 2008), in particular what Marques et al. (2014) proposed for the Araripe Basin.
Richetti et al. say in lines 497-499, and I quote: “However, although we observed some fault reactivation in our oblique inversion models, this reactivation did never lead to full inversion of the graben normal faults (Figs. 9 and 10), which contradicts the Marques et al. (2014) scenario”. No, it does not contradict. We proposed a much lower angle between shortening direction and graben strike (you can check in Fig. 6B). Besides, we also considered fault weakening as a mechanism that can promote inversion (read text upfront in the Abstract, and look at Fig. 11 for a field example) as experimentally shown by Marques and Nogueira (2008), which you should cite when discussing mechanisms of normal fault inversion and the Araripe Basin.
Richetti et al. further say in lines 514-515, and I quote: “We thus find that neither of the two end-member scenarios seems to fully explain the inversion observed in the Araripe Basin area.”. This is simply wrong, for two reasons: (1) you did not test Peulvast and Bétard's hypothesis; (2) you did not test what Marques et al. (2014) proposed for the Araripe inversion, which is low inversion angle and fault lubrication.
Many comments, main and minor, can be found in the attached annotated PDF.
The text is in many cases sloppy. Although not being my job, I carried out the revision of the ms. that should have been done by author and co-authors. I did not revise everything, therefore there is still need for a more thorough revision of the text and English. For instance, verb tenses are mostly inconsistent throughout the text. Position of commas (mostly absence) are also a problem.
References that should be cited by the authors:
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Fernando Ornelas Marques