Seismic evaluation of the Flemish Cap and Goban Spur pre-rift relationship prior to the opening of the North Atlantic, with support from plate reconstruction

Yang, Pei; Welford, J. Kim

doi:https://doi.org/10.5194/egusphere-2023-2524

Preprints

https://doi.org/10.5194/egusphere-2023-2524

Preprints

28 Nov 2023

| 28 Nov 2023

Seismic evaluation of the Flemish Cap and Goban Spur pre-rift relationship prior to the opening of the North Atlantic, with support from plate reconstruction

Pei Yang and J. Kim Welford

Abstract. Recent geophysical investigations of the NE Newfoundland-Irish Atlantic rifted margin pair (North Atlantic) have called into question the previously assumed conjugate relationship and rift-perpendicular extension between the Flemish Cap and Goban Spur. In this study, we present multichannel seismic reflection profiles across the margins of the Flemish Cap, Porcupine Bank, and Goban Spur, and define their structural domains (proximal, necking, hyperextended, and/or exhumed mantle domains), which display varying degrees of asymmetry along strike. Observed intra-crustal reflectivity patterns are interpreted to be related to Paleozoic orogeny and/or orogenic collapse prior to the major Mesozoic rifting, consistent with this rift system having been strongly influenced by inherited Appalachian-Caledonian and Variscan structures. Reflective features within each structural domain are strikingly different across both margins, however similarities are most pronounced for the necking domains of the Porcupine Bank and Flemish Cap, which is consistent with a connection between the Porcupine Bank and Flemish Cap during Early Jurassic rifting. This inference is compatible with recently published deformable plate reconstruction models, which are used herein to relocate and reconstruct the representative seismic sections back through time to the onset of rifting. The changes of paleo-positions and geometric shapes of the seismic sections in deformable plate reconstruction models over time further show complicated 3D plate kinematics for the NE Newfoundland-Porcupine Atlantic margins, highlighting interplay of inherited structures, oblique extension, and poly-phase margin evolution between the Porcupine Bank, Goban Spur, and Flemish Cap and their intervening rift basins during the southern North Atlantic opening.

Received: 30 Oct 2023 – Discussion started: 28 Nov 2023

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Pei Yang and J. Kim Welford

Status: closed

RC1:
'Comment on egusphere-2023-2524', Frank Zwaan, 08 Feb 2024
Manuscript Review BRE-151-2023 (Yang et al.)
The submitted manuscript presents a study about how the Flemish Cap and Goban Spur were linked prior to North Atlantic rifting. I found the manuscript quite interesting. However, there are some important aspects that need attention. Please find my comments in the text below. I hope the authors will find these helpful and wish them success revising the manuscript.
Kind regards,
Frank Zwaan

General comments
Overall, I have read the text multiple times, and had quite some trouble following things, as there seems to be no clear distinction between methods, results, and discussion. As a result, everything seems to be a bit mixed up, and I had no clear idea of what data is really new, and what was already existing. For instance, Fig. 2 seems to be a result from a new analysis, but it is not explained how that is done, only the map is given so how can we know that it is reliable? Another thing is that the authors present the 4 lines, but it is really not that clear why these are chosen as conjugate sets (as the reconstructions are only shown later in the manuscript, so I got a bit lost there --> they are conjugates right?).
The authors should really reorder their manuscript in such a way that there is a clear distinction and a logical order between these parts.
A clear method section is needed

Would it not be more logical to first do the plate reconstruction in order to show what lines are the right ones to look at? (see also later comments on what the sections may tell us)

NB: now I reread the abstract + intro once more, the idea is quite clear and nice, it just doesn’t come through well in the subsequent text, I fear (as a result of the general issues I am pointing out here)

The paper is also rather short. I feel that various things could be expanded and explained in more detail, so that the text is clearer and a bit more accessible.
Perhaps some added figures can also help to illustrate specific points addressed in the paper. Think of the rifting history derived from the sections, and perhaps some schematic summary figure to highlight the main findings.

The figures need some work (see detailed comments below)

Detailed comments

Section 2 (crustal architecture or methods?) --> see general comment on mixing
Line 98: somehow this seems the start of the methods?

Line 100: why not to Late Jurassic (the start of North Atlantic rifting as mentioned earlier)?

Line 119: bit of nitpicking, but is the Orphan Basin really that massive?

Line 149: this dashed line (MOHO) is very poorly visible

Line 140-162: I found it very hard to follow this as things are poorly visible in the sections, but I think this can be easily improved (see comments on Fig. 3).

Line 170-172: it is not clear to me why the previously proposed relationship is challenged. Perhaps the differences need to be made clearer. Why should both margins look the same (asymmetry happens all the time in rift systems, and sediment patterns can easily be different on two sides of a basin)? I guess the sections look different, but these are also different surveys, so to be expected? Also note that this is discussion, after which a new analysis with results kicks off  see comments on structure.
Question: if these 4 selected lines are not a good fit, which ones are? (should they not be shown as well?)

Check also the comments on Fig. 3  perhaps the concepts are just not clear enough shows in these figures. Otherwise, the only clear evidence (to me) that the margins do not fit as previously thought stems from the newer plate reconstructions (it’s quite neat to see how the sections would have some strange overap when considering the new reconstruction, which also suggest some massive rotation of the sections  this is something that is of great importance for our interpretations of seismic lines/rifted margins)

Line 187: from here on, new methods are described it seems?  see comments on the need for a clear methods section. Otherwise it seems discussion (see comments on structure)

Line 203: how can lines be points? Perhaps “series of points” is meant here?

Discussion:
Lines 234-246: this reads like motivation, which should be put in the introduction I would say

Line 246-248: not clear where this inheritance is shown, perhaps I missed the evidence for inheritance in the sections?  this should be clearly indicated in the figures and mentioned in the results.

Line 260-262: this part could use some attention in the results (see general comments)

Line 264-265: it is not directly clear to me why these sections would indicate that 2D extension is not tenable.

Line 281-283: only line PAD95-13 is shown in Fig. 4 I believe? Please add PAD95-15 to support these statements (and please make sure that it is already mentioned in the results).

Line 285-287: why is this more reasonable? Please explain.

Figures
Fig. 1
Panel (a) The red lines indicating the Variscan fronts are very poorly visible on the green background (at least to me, I have slight red-green colorblindness), as is the “C34” (and the red of the dotted line it indicates) Please use some other colors
Somehow the indications (text) of the location of panels (b) and (c) are also a bit unclear  perhaps put them in a white box linked to the outline of the areas of interest?

Also the pink lines in panels (b) and (c), these are not well visible.

Some of the annotation is cross-cut by lines and therefore poorly visible.

Fig. 2
Also here, the red “M0” is barely visible.

It may be useful to indicate the locations of the seismic lines here?

Some of the annotation is cross-cut by lines and therefore poorly visible.

Ireland and Newfoundland are indicated in green, suggesting exhumed mantle

Fig. 3
The sections are really very small, can they be made larger? (e.g. rotate 90˚ to cover a whole page and/or split into two figures if needed).

The color hues used to indicate domains are rather vague, perhaps there is some other way of doing this? (clearer, more distinct colors, or perhaps just indicate the extent with horizontal double arrows or so?). I found it really hard to make out what is what here, so I am not sure if I fully followed the text.
Note that to me, the pink syn-rift is hardly distinguishable from the greyish post-rift.

It would be useful to annotate specific important observations to help the reader out (e.g. the landward dipping faults in F5 or the chaotic necking domain)

The labelling of panels (e) and (f) seems shifted
Same for panels (k) and (l)

Most of the sections miss TWT scales
Panels (i), (j), (k) and (l) do have a vertical scale, but it is only a relative scale

Personal preference, I would not use pink/violet for the dotted outlines in panels (a-h), or for the outline of panels (i-l)

Fig. 4
Please avoid poorly visible red annotation

Also the green and blue arrows in (b) are not that well visible (I only noticed them later on)

I strongly suggest using another colorscale for crustal thickness, i.e. one that goes from a bright to a dark color, as the current bright color seens to suggest a zero-value (unless that is the intention?)

Could a length scale be added? (plus a north arrow?)

Perhaps add headers indication which type of model each column represents? (easy distinction).

Can the dark grey background be removed? It is quite dominant and distracts a bit from the key information.
Citation: https://doi.org/10.5194/egusphere-2023-2524-RC1
RC2: 'Comment on egusphere-2023-2524', Anonymous Referee #2, 10 Mar 2024

Review of manuscript entitled:
“Seismic evaluation of the Flemish Cap and Goban Spur pre-rift relationship prior to the opening of the North Atlantic, with support from plate reconstruction
Pei Yang and J. Kim Welford

General comments:
The manuscript combines seismic data with a previously published plate reconstruction of the conjugate Newfoundland-Irish Atlantic margin. However, even after a second reading of the manuscript, the objectives of the manuscript remain unclear, as do the scientific questions addressed in this manuscript. The present version of the manuscript is not focussed and lacks a clear structure. Furthermore, the seismic interpretations are in great need of improvement. In the current version, it is not only difficult to recognise the geometric relationships and to follow the description, but there are also many interpretations that are difficult to understand and need much more description. Examples of this are the interpretations of the reflections in the basement. The structural interpretation of the rift structures is also unclear, and it is not clear how the crustal thinning and associated accommodation can be explained by the faults shown in the sections. Furthermore, the authors do not describe the methods they used for their kinematic model. Although the kinematic model has already been published, it is important to provide at least a brief description of the model so that the reader can understand it. It is also not clear how conjugate sections can be compared to blocks that rotate during rifting. This needs to be better explained. Last but not least, the discussion section is not connected to the previous part of the manuscript. The discussion on inheritance is not based on observations nor is the variability of the structures along strike described (at least I cannot find it in the manuscript or in the figures). There are many shortcuts and inaccuracies in this manuscript that need to be corrected, along with a complete reorganisation of the manuscript before resubmission. The main changes that need to be made are: 1) defining the objectives of the manuscript, 2) adding a methods section, 3) improving the seismic interpretations (the current interpretations are inadequate and inconclusive), and 4) the discussion section needs to be rewritten and link the main questions and the main observations (both are currently missing) with the discussion section. Therefore, I regret that I cannot recommend publishing this manuscript as it stands.

Citation: https://doi.org/10.5194/egusphere-2023-2524-RC2

Status: closed

RC1:
'Comment on egusphere-2023-2524', Frank Zwaan, 08 Feb 2024
Manuscript Review BRE-151-2023 (Yang et al.)
The submitted manuscript presents a study about how the Flemish Cap and Goban Spur were linked prior to North Atlantic rifting. I found the manuscript quite interesting. However, there are some important aspects that need attention. Please find my comments in the text below. I hope the authors will find these helpful and wish them success revising the manuscript.
Kind regards,
Frank Zwaan

General comments
Overall, I have read the text multiple times, and had quite some trouble following things, as there seems to be no clear distinction between methods, results, and discussion. As a result, everything seems to be a bit mixed up, and I had no clear idea of what data is really new, and what was already existing. For instance, Fig. 2 seems to be a result from a new analysis, but it is not explained how that is done, only the map is given so how can we know that it is reliable? Another thing is that the authors present the 4 lines, but it is really not that clear why these are chosen as conjugate sets (as the reconstructions are only shown later in the manuscript, so I got a bit lost there --> they are conjugates right?).
The authors should really reorder their manuscript in such a way that there is a clear distinction and a logical order between these parts.
A clear method section is needed

Would it not be more logical to first do the plate reconstruction in order to show what lines are the right ones to look at? (see also later comments on what the sections may tell us)

NB: now I reread the abstract + intro once more, the idea is quite clear and nice, it just doesn’t come through well in the subsequent text, I fear (as a result of the general issues I am pointing out here)

The paper is also rather short. I feel that various things could be expanded and explained in more detail, so that the text is clearer and a bit more accessible.
Perhaps some added figures can also help to illustrate specific points addressed in the paper. Think of the rifting history derived from the sections, and perhaps some schematic summary figure to highlight the main findings.

The figures need some work (see detailed comments below)

Detailed comments

Section 2 (crustal architecture or methods?) --> see general comment on mixing
Line 98: somehow this seems the start of the methods?

Line 100: why not to Late Jurassic (the start of North Atlantic rifting as mentioned earlier)?

Line 119: bit of nitpicking, but is the Orphan Basin really that massive?

Line 149: this dashed line (MOHO) is very poorly visible

Line 140-162: I found it very hard to follow this as things are poorly visible in the sections, but I think this can be easily improved (see comments on Fig. 3).

Line 170-172: it is not clear to me why the previously proposed relationship is challenged. Perhaps the differences need to be made clearer. Why should both margins look the same (asymmetry happens all the time in rift systems, and sediment patterns can easily be different on two sides of a basin)? I guess the sections look different, but these are also different surveys, so to be expected? Also note that this is discussion, after which a new analysis with results kicks off  see comments on structure.
Question: if these 4 selected lines are not a good fit, which ones are? (should they not be shown as well?)

Check also the comments on Fig. 3  perhaps the concepts are just not clear enough shows in these figures. Otherwise, the only clear evidence (to me) that the margins do not fit as previously thought stems from the newer plate reconstructions (it’s quite neat to see how the sections would have some strange overap when considering the new reconstruction, which also suggest some massive rotation of the sections  this is something that is of great importance for our interpretations of seismic lines/rifted margins)

Line 187: from here on, new methods are described it seems?  see comments on the need for a clear methods section. Otherwise it seems discussion (see comments on structure)

Line 203: how can lines be points? Perhaps “series of points” is meant here?

Discussion:
Lines 234-246: this reads like motivation, which should be put in the introduction I would say

Line 246-248: not clear where this inheritance is shown, perhaps I missed the evidence for inheritance in the sections?  this should be clearly indicated in the figures and mentioned in the results.

Line 260-262: this part could use some attention in the results (see general comments)

Line 264-265: it is not directly clear to me why these sections would indicate that 2D extension is not tenable.

Line 281-283: only line PAD95-13 is shown in Fig. 4 I believe? Please add PAD95-15 to support these statements (and please make sure that it is already mentioned in the results).

Line 285-287: why is this more reasonable? Please explain.

Figures
Fig. 1
Panel (a) The red lines indicating the Variscan fronts are very poorly visible on the green background (at least to me, I have slight red-green colorblindness), as is the “C34” (and the red of the dotted line it indicates) Please use some other colors
Somehow the indications (text) of the location of panels (b) and (c) are also a bit unclear  perhaps put them in a white box linked to the outline of the areas of interest?

Also the pink lines in panels (b) and (c), these are not well visible.

Some of the annotation is cross-cut by lines and therefore poorly visible.

Fig. 2
Also here, the red “M0” is barely visible.

It may be useful to indicate the locations of the seismic lines here?

Some of the annotation is cross-cut by lines and therefore poorly visible.

Ireland and Newfoundland are indicated in green, suggesting exhumed mantle

Fig. 3
The sections are really very small, can they be made larger? (e.g. rotate 90˚ to cover a whole page and/or split into two figures if needed).

The color hues used to indicate domains are rather vague, perhaps there is some other way of doing this? (clearer, more distinct colors, or perhaps just indicate the extent with horizontal double arrows or so?). I found it really hard to make out what is what here, so I am not sure if I fully followed the text.
Note that to me, the pink syn-rift is hardly distinguishable from the greyish post-rift.

It would be useful to annotate specific important observations to help the reader out (e.g. the landward dipping faults in F5 or the chaotic necking domain)

The labelling of panels (e) and (f) seems shifted
Same for panels (k) and (l)

Most of the sections miss TWT scales
Panels (i), (j), (k) and (l) do have a vertical scale, but it is only a relative scale

Personal preference, I would not use pink/violet for the dotted outlines in panels (a-h), or for the outline of panels (i-l)

Fig. 4
Please avoid poorly visible red annotation

Also the green and blue arrows in (b) are not that well visible (I only noticed them later on)

I strongly suggest using another colorscale for crustal thickness, i.e. one that goes from a bright to a dark color, as the current bright color seens to suggest a zero-value (unless that is the intention?)

Could a length scale be added? (plus a north arrow?)

Perhaps add headers indication which type of model each column represents? (easy distinction).

Can the dark grey background be removed? It is quite dominant and distracts a bit from the key information.
Citation: https://doi.org/10.5194/egusphere-2023-2524-RC1
RC2: 'Comment on egusphere-2023-2524', Anonymous Referee #2, 10 Mar 2024

Review of manuscript entitled:
“Seismic evaluation of the Flemish Cap and Goban Spur pre-rift relationship prior to the opening of the North Atlantic, with support from plate reconstruction
Pei Yang and J. Kim Welford

General comments:
The manuscript combines seismic data with a previously published plate reconstruction of the conjugate Newfoundland-Irish Atlantic margin. However, even after a second reading of the manuscript, the objectives of the manuscript remain unclear, as do the scientific questions addressed in this manuscript. The present version of the manuscript is not focussed and lacks a clear structure. Furthermore, the seismic interpretations are in great need of improvement. In the current version, it is not only difficult to recognise the geometric relationships and to follow the description, but there are also many interpretations that are difficult to understand and need much more description. Examples of this are the interpretations of the reflections in the basement. The structural interpretation of the rift structures is also unclear, and it is not clear how the crustal thinning and associated accommodation can be explained by the faults shown in the sections. Furthermore, the authors do not describe the methods they used for their kinematic model. Although the kinematic model has already been published, it is important to provide at least a brief description of the model so that the reader can understand it. It is also not clear how conjugate sections can be compared to blocks that rotate during rifting. This needs to be better explained. Last but not least, the discussion section is not connected to the previous part of the manuscript. The discussion on inheritance is not based on observations nor is the variability of the structures along strike described (at least I cannot find it in the manuscript or in the figures). There are many shortcuts and inaccuracies in this manuscript that need to be corrected, along with a complete reorganisation of the manuscript before resubmission. The main changes that need to be made are: 1) defining the objectives of the manuscript, 2) adding a methods section, 3) improving the seismic interpretations (the current interpretations are inadequate and inconclusive), and 4) the discussion section needs to be rewritten and link the main questions and the main observations (both are currently missing) with the discussion section. Therefore, I regret that I cannot recommend publishing this manuscript as it stands.

Citation: https://doi.org/10.5194/egusphere-2023-2524-RC2

Pei Yang and J. Kim Welford

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https://doi.org/10.5194/egusphere-2023-2524-supplement

Pei Yang and J. Kim Welford

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Short summary

This study challenged previous understanding of the conjugate relationship between the Goban Spur and Flemish Cap, and supports the conjugate relationship between the Porcupine Bank and Flemish Cap instead from a seismic perspective, which is further illustrated in different deformable plate reconstruction models, revealing complex 3D kinematics during the orogenic, orogenic collapse, and oblique extension stages between both margin sides.


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