Organic Matter Source, Fluid Migration, and Geological Significance of Stylolites in Organic-Lean Carbonate Rocks: A Case from the Sichuan Basin
Round 1
Reviewer 1 Report
This is an original study that provides essential data on stylolites and the organic matter within them. This work shed lights on petroleum migration along these structures and emphasized the importance of stylolites for expelling hydrocarbons. The manuscript is generally well written but requires minor corrections before being accepted.
(1) Line 15-16, “common thin section observation, thin section observation under fluorescent light”. It seems to be redundant.
(2) Provide details on fluorescence measurements, specifically, excitation and emission wavelength bins.
(3) Pleases introduce standard reference materials were used to check the programmed pyrolysis and TOC accuracy and precision?
(4) The format of Tables 4 and 5 is problematic. Note the underlines, the bond and the caption.
(5) Improve the resolution of fig. 10; the caption of Fig. 8 forgets (C).
(6) It should note that the difference in minerology may affect the oil cracking and thus the oil compositions. The clay minerals which are more abundant in stylolites can catalyze the oil-cracking (Please refer to the following reference). The authors should considered.
Qi, Y.; Cai, C.; Sun, P.; Wang, D.; Zhu, H. Crude oil cracking in deep reservoirs: A review of the controlling factors and estimation methods. Petroleum Science. 2023. https://doi.org/10.1016/j.petsci.2023.03.006.
Author Response
(1) Line 15-16, “common thin section observation, thin section observation under fluorescent light”. It seems to be redundant.
Response: Thank you for the comment and feedback. We have carefully reviewed and revised.
(2) Provide details on fluorescence measurements, specifically, excitation and emission wavelength bins.
Response: Blue fluorescence was used to observe the organic matter of different samples, with an excitation wavelength ranging from 420nm to 485nm and a emission wavelength of 515nm. These details have been added to Section 3.2.2 Petrographic analyses.
(3) Pleases introduce standard reference materials were used to check the programmed pyrolysis and TOC accuracy and precision?
Response: The standard sample used for TOC is LOT NO.0602 (CARBON% = 0.691±0.006), and for Rock-Eval Pyrolysis are IFP 160000 and Chinese standard reference materials. These details have been added to Section 3.2.1 TOC and Rock-Eval experiments.
(4) The format of Tables 4 and 5 is problematic. Note the underlines, the bond and the caption.
Response: Thank you for your feedback，We have revise the tables.
(5) Improve the resolution of fig. 10; the caption of Fig. 8 forgets (C).
Response: Thank you for your feedback on the clarity of the image. The image was not as clear as we had intended, as this may have been due to the compression. We will provide an original high-resolution image separately upon submitting the revised manuscript.
(6) It should note that the difference in minerology may affect the oil cracking and thus the oil compositions. The clay minerals which are more abundant in stylolites can catalyze the oil-cracking (Please refer to the following reference). The authors should considered.
Response: Thank you very much for your suggestions. We have revise in the manu, see Line 310.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This work attempts to reveal the enrichment mechanism of organic matter and establish the geofluid migration mode for the stylolites developed in carbonate rocks. However, there are some obvious issues that must be addressed before acceptance.
1) Inappropriate title. "Organic matter source, fluid migration and geological significance for stylolites in organic-lean carbonate rocks: a case from the Sichuan Basin" might be more appropriate.
2) When the S2 content is low, Tmax will be distorted (such as sample 5-Msr with S2 = 0.16 mg/g while Tmax = 600℃), and the relevant explanations are not convincing.
3) The format of the References is very chaotic.
4) The organic matter of the suture is not sedimentary organic matter, but its TOC can be up to 27 times higher than that of the surrounding rock (samples 5-Ssr and 5-Msr; Table 2). How to explain this? The pre-treatment process of TOC samples requires a detailed introduction. Besides, please provide the typical pyrolysis curve results (samples 1-Ssr and 1-Msr; samples 5-Ssr and 5-Msr).
5) Assuming that there are only EOM, pyrobitumen and bitumen in the stylolites, why is the Tmax difference so significant (373~500℃)? Does it mean that there are other types of organic matter that have not been observed? For example, insoluble organic matter (kerogen).
English is very difficult to understand/incomprehensible, including the Abstract, Conclusions, Acknowledgments, and References.
Author Response
1) Inappropriate title. "Organic matter source, fluid migration and geological significance for stylolites in organic-lean carbonate rocks: a case from the Sichuan Basin" might be more appropriate.
Response: Thank you very much for your suggestions. The title has been revised.
2) When the S2 content is low, Tmax will be distorted (such as sample 5-Msr with S2 = 0.16 mg/g while Tmax = 600℃), and the relevant explanations are not convincing.
Response: Thank you very much for your suggestions. In this paper, Tmax is not used to discuss the maturity of source rocks, because the S2 value of carbonate rocks with low organic matter abundance is very low, so Tmax will be inaccurate. In this paper, the source of organic matter in stylolites is analyzed, which mainly comes from secondary organic matter, so the Tmax value of sutures is smaller than that of surrounding rocks, so the analysis of Tmax in this paper mainly describes the difference between sutures and surrounding rocks.
3) The format of the References is very chaotic.
Response: Thank you very much for your suggestions. The references have been corrected.
4) The organic matter of the suture is not sedimentary organic matter, but its TOC can be up to 27 times higher than that of the surrounding rock (samples 5-Ssr and 5-Msr; Table 2). How to explain this? The pre-treatment process of TOC samples requires a detailed introduction. Besides, please provide the typical pyrolysis curve results (samples 1-Ssr and 1-Msr; samples 5-Ssr and 5-Msr).
Response: a) According to the analysis in this paper, stylolites are the dominant hydrocarbon migration channel and storage space in tight carbonate rocks. Therefore, many hydrocarbons will accumulate in stylolites, leading to more enriched organic matter in stylolites.
- b) The pre- treatment process of TOC analysis has been described in the paper. Line 137-142.
- c) Since the pyrolysis experiment was completed in 2016, the pyrolysis curve can no longer be found. We will pay attention to this problem in future work.
5) Assuming that there are only EOM, pyrobitumen and bitumen in the stylolites, why is the Tmax difference so significant (373~500℃)? Does it mean that there are other types of organic matter that have not been observed? For example, insoluble organic matter (kerogen).
Response: Through petrology and SEM observation, no primary organic matter was observed in the stylolites, and the large difference in Tmax value was mainly due to the large difference in S1 value in the stylolites.
Author Response File: Author Response.pdf
Reviewer 3 Report
the manuscript (Stylolite in organic-lean carbonate rocks, implications for organic matter source, fluid migration and geological significance) has potential to be published after some modification.
the novelty is not clear in the introduction, the authors have to strengthen this part.
the reference can be updated with recent papers discussed stylolite in carbonate (here some https://scholar.google.pl/scholar?hl=en&as_sdt=0%2C5&q=radwan+STYLOLITE&btnG=)
samples, some details are missed, how many thin sections, cored section status, references for classification
no references for methods, you have to add it.
4.2. Petrographic analyses are poorly written; it should be rewritten as standard petrographic sedimentology,
Diagenesis has not been discussed! Stylolite’s has not been given priority in the results?
Figure 1 add lat and long and north direction, 1b figure is not clear
What is the evident supporting figure 10 model and what is the limitations?
revise English language.
need improvement
Author Response
the novelty is not clear in the introduction, the authors have to strengthen this part. the reference can be updated with recent papers discussed stylolite in carbonate (here some https://scholar.google.pl/scholar?hl=en&as_sdt=0%2C5&q=radwan+STYLOLITE&btnG=)
Response: Thanks for your comments, this section has been rewritten and recent references have been added.
samples, some details are missed, how many thin sections, cored section status, references for classification
Response: Thanks for your suggestion, this part has been added in the sample introduction section.
no references for methods, you have to add it.
4.2. Petrographic analyses are poorly written; it should be rewritten as standard petrographic sedimentology, Diagenesis has not been discussed! Stylolite’s has not been given priority in the results?
Response: In this paper, we will not discuss the genesis, diagenesis, and sedimentary process of sutures. We focus on the occurrence of organic matter in sutures. So these aspects you mentioned are ignored in this part. We will devote ourselves to this area in our future work.
Figure 1 add lat and long and north direction, 1b figure is not clear
Response: Thanks for your suggestion, Figure 1 has been modified
What is the evident supporting figure 10 model and what is the limitations?
Response: Based on our analysis, the organic matter within stylolites originates from the migration of crude oil from the matrix, and through petrological and scanning electron microscope observations, we have found that pores and microfractures within the stylolites are more extensively developed, providing excellent pathways for fluid migration. Additionally, in a study by Liu et al. in 2020, molecular geochemistry demonstrated that during the migration process from matrix to stylolites, a fractionation effect occurs, with this effect being particularly pronounced along the stylolites.
revise English language.
Response: Thanks for your suggestion, we have repolished the language in the article.
Author Response File: Author Response.pdf
Reviewer 4 Report
I am recommending that this article is rejected, as I have serious concerns as to whether this paper actually represents a new contribution. The main problem here is that the work presented seems to be very similar to work published previously by some of these same authors (and, by authors from the same institutions), in a 2020 article in the Journal of Petroleum Science and Engineering titled "Implications of organic matter source and fluid migration from geochemical characteristics of stylolites and matrix in carbonate rocks: A case study from the Carboniferous and the Ordovician in the Sichuan Basin, SW China." As far as I can tell, this 2020 study was on samples from the exact same location, investigates almost identical questions, and reaches very similar conclusions as this article submitted to Processes.
If the authors object to my assessment, I would ask that they please very clearly address how the present study represents a new contribution that is distinct (investigating new questions, presenting new data and analyses, and arriving at distinct, novel conclusions) from their 2020 paper on the same topic. They should address this both in their reply to my review, and within the text of any resubmitted manuscript itself, clearly stating how any new paper contributes and advances upon their previous 2020 study.
This paper needs some grammatical editing and correction throughout.
Author Response
I am recommending that this article is rejected, as I have serious concerns as to whether this paper actually represents a new contribution. The main problem here is that the work presented seems to be very similar to work published previously by some of these same authors (and, by authors from the same institutions), in a 2020 article in the Journal of Petroleum Science and Engineering titled "Implications of organic matter source and fluid migration from geochemical characteristics of stylolites and matrix in carbonate rocks: A case study from the Carboniferous and the Ordovician in the Sichuan Basin, SW China." As far as I can tell, this 2020 study was on samples from the exact same location, investigates almost identical questions, and reaches very similar conclusions as this article submitted to Processes.
If the authors object to my assessment, I would ask that they please very clearly address how the present study represents a new contribution that is distinct (investigating new questions, presenting new data and analyses, and arriving at distinct, novel conclusions) from their 2020 paper on the same topic. They should address this both in their reply to my review, and within the text of any resubmitted manuscript itself, clearly stating how any new paper contributes and advances upon their previous 2020 study.
Response: In the study by Liu et al. (2020), molecular geochemistry was predominantly employed to demonstrate that hydrocarbons generated in the matrix tend to accumulate within sutures. Moreover, this process undergoes migration fractionation, with notable differentiation in fractionation effects observed during migration along the sutures. However, the present study seeks to establish that organic matter within sutures primarily originates from secondary organic materials such as light oil, intermediate-stage asphalt, and solid bitumen. Furthermore, through a combination of petrological and isotopic geochemical methods, this study substantiates the permeation and accumulation characteristics of sutures. These findings notably extend beyond the scope of Liu et al.'s 2020 research. Additionally, several analogous viewpoints in this study are grounded in references to Liu et al.'s 2020 work.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The quality of the revised paper has significantly improved. Only make the following minor modifications to be accepted.
（1）Suggest supplementing 2 latest literature in the Line 44, namely Hu et al., 2022 and He et al., 2023 .[Hu, T., Pang, X., Jiang, F., Zhang, C., Wu, G., Hu, M., Jiang, L., Wang, Q., Xu, T., Hu, Y., Jiang, S., Wang, W., Li, M., 2022. Dynamic continuous hydrocarbon accumulation (DCHA): Existing theories and a new unified accumulation model. Earth-Science Reviews 232, 104109. https://doi.org/10.1016/j.earscirev.2022.104109ï¼›He, T.-H., Li, W.-H., Lu, S.-F., Yang, E.-Q., Jing, T.-T., Ying, J.-F., Zhu, P.-F., Wang, X.-Z., Pan, W.-Q., Zhang, B.-S., Chen, Z.-H., 2023. Quantitatively unmixing method for complex mixed oil based on its fractions carbon isotopes: A case from the Tarim Basin, NW China. Petroleum Science 20, 102–113. https://doi.org/10.1016/j.petsci.2022.07.010]
（2）Some English literature lacks DOI information, such as Line 406-410.
Author Response
It has been modified according to your requirements and has been marked in red letters in the text.
Reviewer 3 Report
authors addressed comments.
Author Response
It has been modified according to your requirements and has been marked in red letters in the text.
Reviewer 4 Report
Thanks for the opportunity to read this interesting study. Please see and address/incorporate the attached suggestions and comments. Once these minor revisions are made, I believe this manuscript could be ready for publication in Processes.
Comments for author File: Comments.pdf
Minor grammar and syntax corrections needed throughout the manuscript. I have made some examples of such required corrections in the Abstract, but the entirety of the manuscript should be subjected to careful grammar correction.
Author Response
It has been modified according to your requirements and has been marked in red letters in the text.
