Does the syn- versus post-rift thickness ratio have an impact on the inversion-related structural style?
Abstract. Many extensional basins worldwide are modified by subsequent compressional episodes, which lead to inverted structures. The structures associated with the reactivation of preexisting faults play are critically important in forming suitable subsurface traps for hydrocarbons. Major concerns regarding inverted structures are trap integrity and fault seal. In general, the preferred structures have simple four-way closures as the result of only mild to moderate inversion.
Five physical sandbox models, coupled with Particle Image Velocimetry (PIV) analysis, have been performed to address the influence of the syn- versus post-rift thickness ratio (Mode I and II) and the degree of positive inversion on the style of fault propagation into and overall deformation of the post-rift cover. The results of these experiments are broadly comparable with natural data examples from New Zealand, Israel and Turkey. The main control on the development of mild to moderate inversion structures is the degree of inversion, and the style of deformation within the post-rift sequence appears to be different due to the amount of displacement accommodated by the inherited listric fault and the thickness of the post-rift cover (Mode I and II inverted structures). These observations do have a direct impact on the understanding of the geo-energy systems associated with inverted structures.
Alexandra Tamas et al.
Status: open (until 06 Apr 2023)
- RC1: 'Comment on egusphere-2023-280', Hamed Fazlikhani, 14 Mar 2023 reply
- RC2: 'Comment on egusphere-2023-280', Piotr Krzywiec, 20 Mar 2023 reply
Alexandra Tamas et al.
Alexandra Tamas et al.
Viewed (geographical distribution)
Comments on the egusphere-2023-280 “Does the syn- versus post-rift thickness ratio have an impact on the inversion-related structural style?” by Tamas et al.
This study uses analogue sand box models designed to test the influence of syn- versus post-rift thickness ratio (Mode I and II) and the amount of postrift shortening/compression on the style of fault propagation and the inversion-related deformation. Authors then compare the results of the experiments with four natural cases. The experiments are nicely presented and described in the text, as are the natural cases. Please see my main comments below and the annotated pdf document for more detailed comments.
My main comment is regarding the main controlling factor in the vertical propagation of the inverted fault observed in the experiments versus presented natural cases. Authors conclude (line 384-397) that in the experiments the amount of shortening/compression controls the upward propagation of the inverted fault, while in the presented natural cases a higher syn vs. postrift ratio “tend to inhibit the propagation of thrust fault up-section”.
As I understand, authors aim to present natural cases for comparison with observations from the experiments. However, in the conclusions (line 384-397) authors state that further experiments (with larger syn to postrift ratio) are needed to fully reproduce geometries observed in presented natural cases. In my opinion if the authors give some information/estimation about the amount of shortening/compression in the presented natural cases, comparison between the experiment and the natural cases will be easier.
Abstract: Please consider stating the influence of the postrift vs. synrift thickness clearly, as this appears to be the main parameter to be tested in this study and is the question asked in the title.
Post-rift versus post-inversion: I am not entirely sure, but post-inversion is also part of the post-rift, right? Basically, all units deposited after the cessation of rifting are post-rift including syn and post inversion. I understand that when authors compare the thickness of units in Mode I and II, they are referring to the syn-inversion sequence of the post-rift. However, to avoid confusion, please consider clarifying this early on in the text.
Fault geometry effect: listric fault (sub-horizontal fault geometry at depth) vs. more planar fault. In the experiments, as nicely shown, main bounding fault is a listric master fault which dips to sub-horizontal at depth. It is very interesting to see what the inversion structure would look like if the main fault was not listric (sub-horizontal at depth) and rather had more planar geometry at depth developing graben and half graben structures as it is shown in all presented natural cases. Perhaps the fault geometry has not a major influence on the inversion structure, but I think it is worth mentioning.
Natural case studies: The results of the presented experiments suggest that the main parameter controlling the inversion structures and fault propagation is the amount of shortening/compression during tectonic inversion and the syn vs. postrift ration has a minor influence. However, the natural cases presented are discussed only in terms of their syn versus postrift thickness ratio. I would suggest that the authors consider adding some sentences on the amount of shortening/compression for each natural cases presented (also mentioned above). Please also consider shortening the geological history of the presented cases.
In my opinion, adding information about the amount of shortening/compression for each natural case (as much as possible/available) will establish a stronger link between the experiments and the natural cases. Please note that I am only commenting on the points where I think it could be improved, of course there are many interesting results and nice figures presented in this nice work. Please let me know if are there any questions or concerns regarding my comments, I am happy to discuss further.