Results of the Study of Epigenetic Changes of Famennian–Tournaisian Carbonate Rocks of the Northern Marginal Shear Zone of the Caspian Syneclise (Kazakhstan)

Round 1

Reviewer 1 Report

Review of the paper “Results of the Study of Epigenetic Changes of Famennian- Tournaisian Carbonate Rocks of the Northern Margnal Shear Zone of the Caspian Syneclise (Kazakhstan)”

This work presents the results of  the study of the material composition and reservoir properties of the Famennian-Tournaisian carbonate rocks the Chinarevskoye oil and gas condensate deposit (ChD) from the northern border zone of the Caspian syneclise are presented. To diagnose carbonates, a method of staining carbonates in a thin section with alizarin red was used, which makes it possible to distinguish calcite from dolomite. Instrumental methods  (X-ray, DTA, TGA and probe microanalysis) were used to study carbonates-X-ray diffractometry and thermal analyses. The elemental and oxide composition of many samples was carried out using  the method of radiometric probe microanalysis.

The conducted research allowed to observe the peculiarities of the composition and structure of the crystalline matrix, the size and shape of secondary minerals filling the voids, as well as to assess the morphology and type of fracturing of reservoir rocks. The results’ measurements made it possible to identify thermally inert formations of calcium, magnesium, silicon, iron and other compounds in the composition of carbonates.

The authors concluded that the final formation of the reservoir properties of carbonate rocks occurs as a result of the development of tectonic fracturing and diagenetic processes of leaching and secondary mineral formation. Based on the results of X-ray diffractometry (X-ray), thermal analysis (DTA, TGA), probe microanalysis and complex microscopic study carbonate rocks of the ChD, their mineral and material composition has been determined.  The rocks are composed mainly of forms of calcite having different degrees of perfection of their crystalline lattices, dolomites with moderately ordered structures and magnesites with underdeveloped bonds of carbon dioxide in the intermolecular space.  Mineral formations with intermediate thermochemical properties mainly between calcites and dolomites were found in a several samples. Based on these carbonate formations, as well as based on mono-mineral calcites and dolomites (according to thermogravimetric data), kinetic parameters (EA) of the decomposition of their crystalline structures were obtained.

The results of X-ray, DTA and TGA measurements and data of probe microanalysis  made it possible to identify thermally inert formations in the composition of carbonates as oxides of calcium, magnesium, silicon, iron and other compounds accumulated during the conversion of carbonates.

The paper is of good scientific level and practical interest. The structure of the article is well organized, the text is clear, the drawings are made with high quality, experimental studies are used correctly.

There are a small remarks:

1. for Fig.1, you need to show the coordinates, scale and inset with a small geographical scheme, where it is shown by the position of Fig.1.;

2. for Fig.2. decipher ChD;

3. Conclusions need divided by 1, 2, 3....

The paper can be published in its present form taking into account the indicated minor remarks.

Comments for author File: Comments.pdf

Author Response

Thank You for the professionally made comments, they are objective and constructive. It was nice to work with You.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript shows a very interesting case study. The authors spent many paragraphs describing what was done using traditional methods. However, some high-level statements are missing. For example, why is this work important? What’s the purpose of this research? What are the potential applications of the results? What is the novelty of this study?

Introduction

-       What is the research gap? What is the logic flow of this manuscript?

Discussion

-       The discussion section is only limited to the observations in this study. Can the authors compare them with other studies in this area? How will those be different from the authors’ findings?

-       Some grammar errors are found. For example, in Lines 477-479: “Establish the type of reservoirs and identify the morphology of voids and the influence of epigenetic processes on the formation and change of reservoir properties of carbonate rocks.”

Conclusions

-       What are the most important findings?

-       How can the results be applied further? What are the implications and significance of the work?

Author Response

Thank you for your professional approach and constructive comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article of the authors is devoted to an important and topical issue related to the comprehensive study of carbonate rocks using modern methods. Identification of the factors that affect the properties of rocks in specific sections makes it possible to develop reliable geoecological methods for predicting the prospects for their productivity based on the use of mineral geochemical characteristics as diagnostic features, indicators, and criteria. The solution of these urgent problems, geoecological control of the variation of mineral associations, physical and mineralogical modification of rocks of successive units of terrigenous strata is the most important task of assessing the geoecological characteristics of the geoecological section of rocks. The studies presented in the paper are undoubtedly of interest to readers in the field under consideration.

However, it would be necessary to clarify a number of comments that are available to the article:

1. Interesting data are presented in Table 2 and Figure 7. It would be useful to summarize the results and show their applicability in similar conditions in other regions of the world.

2. The data on chemical elements presented in tables 5, 6, 7 should have been presented in figures for greater perceptibility by the readership, and the tables themselves should have been excluded from the article.

3. The explanation of the difference in the mineral composition of rocks according to the data of various analyzes presented in Figure 8 and Table 8 is not entirely clear.

4. In the article, it was possible to carry out mathematical modeling of the influence of the content of various chemical elements on the entire structure of the rocks under consideration. And then there are a lot of tables and graphs that need to be summarized in the conclusions in more detail, possibly with mathematical models.

5. The article should have paid more attention to the prospects of ongoing research in terms of considering the possible oil and gas content of the areas under consideration, which at present seems to be a very topical issue.

6. It is not entirely clear from the article whether it is planned to issue a patent for the analysis technique used and to what extent it can be tested under similar conditions?

7. The research methods used by the authors have been used in a number of publications by other authors, which confirms the relevance and significance of the work. A link to the following article could be added to the bibliography: Bosikov I. I., Klyuev R. V., Tekiev M. V. Analysis of spatial distribution of chemical elements of apatite-stafelite ore. Geologiya I Geofizika Yuga Russia = Geology and Geophysics of Russian South. (in Russ.). 2021. 11 (2): 137 – 157. DOI: 10.46698/VNC. 2021.62.10.010.

8. We should dwell on further prospects for conducting these interesting studies, including taking into account the new realities in the world

Author Response

Thank You for Your cooperation and the attention You paid to our humble work.

Author Response File: Author Response.pdf

Reviewer 4 Report

The article contains the results of the study of rocks by modern optical and physical methods, which is important for replenishing the arsenal of study methods. The results of measurements supplement the existing base of ideas about inert formations of calcium, magnesium, silicon, iron and other components of carbonates. The importance of the results obtained lies in the refinement of the knowledge base on the mutual influence of tectonic fracturing and mineral leaching processes. Studies using modern methods have obtained the kinetic parameters of the formation of crystalline structures, which makes it possible to identify inert formations in the composition of carbonates and use them to improve the production of commercial products and other purposes.

The article is of undoubted interest for the study of minerals and the processes of their formation, but does not contain at least an indication of the directions of the new knowledge gained in the branches of production, which reduces its value without preventing publication.

Author Response

Thank You for Your comments, which will be taken into account in our further research activities.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thanks to the authors’ efforts in improving the manuscript. However, after detailed looking through the new version, I still feel the revised manuscript doesn’t meet my expected quality for publication.

The paper is still obscure in the significance of the method and the description of the technical

details. It is hard for me to list out all my comments before the paper is sufficiently clear in

notations and contributions, and smooth/concise enough in writing.

Specifically, here are additional items that the author can consider more modification: 

- This manuscript is more like a review report instead of a scientific paper. 

- The response to comments is too general to follow. The readers would be more interested to see how this can be further applied in their research. One example is, the authors spent several paragraphs describing other researchers' work at the end, but how are their results compared with yours? They used the same method, so why is your work significant?

Author Response

Thank You for the careful detailed study of our article and the comments made, which were taken into account in the edited version of the article. And also Your comments will be taken into account in our future activities.

Author Response File: Author Response.docx