Multi-Element Imaging of a 1.4 Ga Authigenic Siderite Crystal
Round 1
Reviewer 1 Report
It appears that the only new data in this paper are elemental maps for Fe, Mn, Zn, Al, and Si, on only one crystal of siderite, obtained by LA-ICP-MS. These data are of low precision and low resolution. Much more precise data at higher resolution, and also for more elements,. could be quickly and easily obtained by electron microprobe. Such better data on a number of crystals would be required to justify detailed speculation about formation conditions.
Author Response
Point 1: It appears that the only new data in this paper are elemental maps for Fe, Mn, Zn, Al, and Si, on only one crystal of siderite, obtained by LA-ICP-MS. These data are of low precision and low resolution. Much more precise data at higher resolution, and also for more elements could be quickly and easily obtained by electron microprobe. Such better data on a number of crystals would be required to justify detailed speculation about formation conditions.
Response 1: Besides the multi-element imaging data, we provide the carbon isotopic values and element contents of 9 bulk samples. These data are useful to discuss the role of dissimilatory iron reduction (DIR) during the siderite formation. The LA-ICP-MS mapping data are only used to reveal the element distribution within the siderite, while other evidence consistently indicates the role of DIR during the formation of the Xiamaling siderite. Though more experimental data are always encouraged, we believe that the data we present in this study are sufficient to prove our interpretation.
Reviewer 2 Report
The is an interesting topic, a nice study, and a well prepared paper. I recommend that it be accepted.
I only had a few minor comments:
1) What is the / in table 2 mean? There is no indication and there are also other places where nothing is listed (neither a value or a /).
2) The negative d13C siderite values are certainly interesting. The role of iron reduction as an explanation is also interesting. Beyond saying that it was quite vigorous, can it be translated into rates of iron reduction?
3) Mentioning siderite oxidation later on was a bit confusing because you are showing siderite deposition and preservation. Where this would be happening could be clarified.
Author Response
Point 1: What is the / in table 2 mean? There is no indication and there are also other places where nothing is listed (neither a value or a /).
Response 1: “/” denotes no data, which has been added in the revised table caption.
Point 2: The negative d13C siderite values are certainly interesting. The role of iron reduction as an explanation is also interesting. Beyond saying that it was quite vigorous, can it be translated into rates of iron reduction?
Response 2: Thanks for the comment. The negative δ13Ccarb almost exclusively indicate the involvement of dissimilatory iron reduction Though it is hard to determine the rate of iron reduction quantitatively, we believe that the reaction rate cannot be very slow because the formation of siderite should be restricted just below the sediment-water interface with relative short time for growth.
Point 3: Mentioning siderite oxidation later on was a bit confusing because you are showing siderite deposition and preservation. Where this would be happening could be clarified.
Response 3: To avoid disputes, these discussions have been deleted.
Reviewer 3 Report
The manuscript seems to be interesting for the readers. It is revealing some short period of the Earth history related to formation of sedimented rocks and theirs iron content. The authors have been properly taken advantage of the investigation methods to form their conclusions. In my opinion, the manuscript can be published in the present form.
Author Response
Point 1: The manuscript seems to be interesting for the readers. It is revealing some short period of the Earth history related to formation of sedimental rocks and theirs iron content. The authors have been properly taken advantage of the investigation methods to form their conclusions. In my opinion, the manuscript can be published in the present form.
Response 1: Thanks for your suggestion. In accordance with the suggestions of other reviewers, we have also made appropriate revisions.
Reviewer 4 Report
Comments: (1) The coordinate data in figure 4 is not clear, please use clear images. (2) For figure 4 and figure 5, please divide into group diagrams, such as (a) (b) (c)……. (3) In conclusion section, Line337-339, the citation of references is forbidden, because it is focused on summarizing. (4) Line 87 and Line 174, add a space between the data and the unit. Please check throughout the manuscript.Author Response
Point 1: The coordinate data in figure 4 is not clear, please use clear images.
Response 1: It has been revised.
Point 2: For figure 4 and figure 5, please divide into group diagrams, such as (a) (b) (c)…….
Response 2: It has been revised.
Point 3: In conclusion section, Line337-339, the citation of references is forbidden, because it is focused on summarizing.
Response 3: The text has been deleted.
Point 4: Line 87 and Line 174, add a space between the data and the unit. Please check throughout the manuscript.
Response 4: They have been revised.
Reviewer 5 Report
It is a good work to explore the crystallization and formation 15 mechanisms of siderite. However, the paper lacks innovation. Some aspects should be taken into account.
- The manuscript needs editing by someone with expertise in technical English editing paying particular attention to English grammar, spelling, and sentence structure so that the goals and results of the study are clear to the reader.
- Too much sample description of phenomena, lack of in-depth explanation of data in the study.
- The experimental process and instruments should be described in more detail.
- How to ensure the representativeness of samples?
- The chemical composition of the siderites is complex. What are the effects of multi elements on growth of the siderite crystal?
Author Response
Point 1: The manuscript needs editing by someone with expertise in technical English editing paying particular attention to English grammar, spelling, and sentence structure so that the goals and results of the study are clear to the reader.
Response 1: The manuscript has been carefully edited.
Point 2: Too much sample description of phenomena, lack of in-depth explanation of data in the study.
Response 2: We believe that detailed background and description of the sample is important to the discussion. The elemental and isotopic evidence has been fully discussed which delineates the role of dissimilatory iron reduction during siderite formation.
Point 3: The experimental process and instruments should be described in more detail.
Response 3: All the experimental processes in detail can be found in our previous papers. We also gave references and briefly description. According to the reviewer’s request, some detailed descriptions have been added.
Point 4: How to ensure the representativeness of samples?
Response 4: We agree that our LA-ICP-MS imaging evidence is limited, and siderite formations through other processed are not precluded. However, observation by optical microscope shows that most siderite is rhombohedral structure with good crystallinity and uniform size, indicating suitable water environment for the crystallization and growth of siderite. In this case, a well-preserved crystal can record all crystallization and growth processes. Uniform carbon isotope data for the samples from different depths also indicate the representativeness of samples. These data consistently indicate that the activity of dissimilatory iron reduction was vigorous during the formation of the Xiamaling IF.
Point 5: The chemical composition of the siderites is complex. What are the effects of multi elements on growth of the siderite crystal?
Response 5: They can change the microenvironment of the pore water. Some elements (e.g., Zn, Mn) mixed into the crystal can reduce its purity and even stop its growth. The detailed mechanism, however, is not the aim of this article. Here, we focus on the proving of dissimilatory iron reduction activity during the formation of the siderite. Further studies are needed to fully understand the role of multi elements on the growth of siderite crystal.
Round 2
Reviewer 1 Report
Although the text has been changed considerable the basic shortcoming has not. The LA-ICP-MS technique used is not the best way to characterize the major element zoning in the carbonate crystals. Important elements like Mg and Ca were not determined. Therefore the analysis data is of little value.
Perhaps the carbon isotope data is of independent value.
