A Geophysical Survey of the Kentland Crater Formation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is an interesting manuscript that is well written, though one wonder why it was not sent to a more meteor impact based journal. The only major issue is that the gravity data should be modelled properly. Some minor comments also follow below;

It is not necessary to describe the basic reduction of gravity data.

RBA: display the figures as images not 3D surface. Give the equation of the ‘linearly interpolated background’; it is clearly not a simple bilinear polynomial. State the grid interval here as well. I think what the authors mean is that they have fitted a high order polynomial using linear regression, which is not the same in general as fitting a linear function (although it can be).

Gravity data; this dataset looks to be of good quality and needs to be modelled in 3D. The RBA boundaries will probably be outside of the associated geological boundaries. Computing the zero contour of the second vertical derivative of the data (if noise levels permit) can provide a useful starting estimate for the geological boundaries.

Section 3; don’t mention the gravity gradiometry or MT surveys if the results were not used.

Figure 1; a map showing the location of the crater within America would be useful, as would a dtm.

 

Figures 2 and 3 should show exactly the same area, for comparison. Show the outline of the seismic array on Figure 2.

 

Figure 4; label the frequency peaks with the associated interpreted depths.

Figure 6,7,8,9; state the grid interval and the gridding method in the caption.

Why does every figure use a different colourmap ? (figs 6-9) ? I suggest either a single grayscale or a single rainbow colourmap throughout.

References; ‘Koeverl’ should be ‘Koeberl’

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article topic is part of a revival interest for past impact of Earth with celestial bodies. It includes two important geophysical methods (seismic and gravity), not a variety as stated in the Abstract, but unfortunately missing the magnetic one, relevant in many such analyses.

The study geophysical was well conducted but the interpretation of gravity anomalies should be reconsidered and improved.

There are not enough geological information of the subserface structures, in terms of lithology, structural particularities and density of Pennsylvanian and Mississippian formations.

Comments:

• Abstract: a central peak high gravity anomaly is quite common for complex impact craters, not uncommon.
• Materials and Methods: the value of 2.7 g/cc density for limestone is normally high, since calcite mineral has 2.67 g/cc and limestone structures are usually affected by karst phenomena.
• Results: Gravity gradient data, measured or computed, should be employed in this study, not preserved. Vertical gravity gradient map would be very useful for locating the impact crater infrastructure. The Bouguer residual gravity anomaly was nor properly separated, a high gravity component being preserved from the NE-SW trending high anomaly, probably associated to the deep geological structure. More of that, the residual possibly cumulates the effect of the central peak with the crater marginal rim, both high density features. The central peak, even fractured, would not generate a Bouguer gravity low contrasting with low density till and post-impact crater filling.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors, I found the article interesting and well-organized overall, I really appreciate the availability of the data for future studies. I’ve suggested some changes in the attached file that I think could improve your work. I think some information can be included in the supplementary document without too many changes to the main paper already done. The only issue you should resolve before publishing the article—and the one I want to draw your attention to—is the citation and discussion of the results from article [36], which has only been submitted to date (I tried searching for the paper, and it hasn’t been published yet). You cite it along your paper, further you discuss its results: if you had access to these researchers’ data in any way, you must make this explicit and add, for example, “personal communication”. However, in any case,  that paper it is not yet available to readers, and we do not know when it will be, so it is essential that the “Discussion” section report only your own results without direct comparisons to that work. Try to solve this issue.

Again congratulations for your research, and all the best with your work.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Unfortunately the authors have not made the majority of the necessary changes to their manuscript, probably because of the limited time that they had to perform the revision.

 

There is still no gravity modelling, and the zero contour of the 2VD is still not overlain on Figures 10 and 12.

 

Why was the highly unusual natural neighbour gridding method used  in Figure 7 ? The standard approach is to use minimum curvature gridding or Kriging. All the gravity figure captions still need the grid interval and gridding method information.

 

The ‘red-dashed’ circle overlain on Figure 12 is a solid line, not a dashed line.

 

The manuscript still changes colourmaps at random. These images show different aspects of the impact structure and readers will want to compare them (even the gravity data is displayed sometimes in blue and sometimes and in brown). I strongly suggest that they choose a single colourscheme (eg a more standard rainbow colourmap) and stick to it throughout.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The study deserves to be continued, using the experience gained writing this article and possibly involving new geophysical methods (e.g., Magnetics) and new petrophysical data (real rock densities). 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors, thanks for considering and following my suggestions. In my opinion, your very interesting paper is now complete, well written and ready to be published (please only check line 238, there is a repetition)

All the best

Author Response

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Author Response File: Author Response.pdf