Mineralogy of Petrified Wood from Costa Rica
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors- The introduction part is too simplistic. It fails to introduce the research progress of peat in the study area, the existing problems, and the unique aspects of your research. The citation of references is rather crude.
- The geological background part is a bit lengthy and not concise enough. Only a reference is cited at the beginning, and then there are several paragraphs without any individual citation of references.
- The discussion part mainly consists of your own elaboration, with too few references cited. Please make corrections.
- The introduction part is too simplistic. It fails to introduce the research progress of peat in the study area, the existing problems, and the unique aspects of your research. The citation of references is rather crude.
- The geological background part is a bit lengthy and not concise enough. Only a reference is cited at the beginning, and then there are several paragraphs without any individual citation of references.
- The discussion part mainly consists of your own elaboration, with too few references cited. Please make corrections.
Author Response
Comments and Suggestions for Authors
- The introduction part is too simplistic. It fails to introduce the research progress of peat in the study area, the existing problems, and the unique aspects of your research. The citation of references is rather crude.
Reply: Thanks for your recommendations. We have rewritten the introduction, added details about the history of peat research, and added additional references.
- The geological background part is a bit lengthy and not concise enough. Only a reference is cited at the beginning, and then there are several paragraphs without any individual citation of references.
Reply: The geology background has been revised, with additional references.
- The discussion part mainly consists of your own elaboration, with too few references cited. Please make corrections.
Reply: Thanks, we have rewritten the discussion and conclusions. Please see the revised manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsI recommend major revisions to improve the clarity and accuracy of the paper. Overall, the authors should provide a more thorough description and discussion of their results and present sufficient evidence to support their conclusions.
Line 41: Could you also state the geologic age?
Line 48: Parenthesis is missing.
Line 55: Dot is missing.
Line 61: Could you please elaborate on “ready source for dissolved silica”?
Line 84-86: Please provide reference(s).
Line 102-103: Please elaborate on specific examples of taxa in Costa Rica and on the Pleistocene plant communities and their significance.
Line 105-122: Divide this paragraph into multiple ones according to the techniques used and explain the scope for each technique.
Line 109: Which are the other analytical techniques, and which is the scope for all of them including the density measurement by hydrostatic weighing?
Line 110-118: Which is the purpose of using different microscopes? Please remove the links.
Line113: Which is the thickness of the sections? How were they prepared?
Line 119-122: Provide more details on the SEM imaging. Working distance, thickness of coating? Sputter coating instrument? Type of imaging (SE, BSE)? Are the samples being polished?
Line 121: Write diameter instead of “dia”.
Line 126: How do you discriminate “microcrystalline quartz, and megacrystalline quartz” by XRD? This info should be indicated in the spectra as well. Which are the size ranges for each quartz group? Could you also provide the miller indices of the crystallographic phases and add in SI information spectra of control samples/databases confirming the existence of these minerals.
Line 130: What the presence of heulandite indicates?
Line 139: Please provide reference(s).
Line 143: Please provide all the EDS spectra confirming the description provided in Figure 6. Use also, abbreviations and/or arrows indicated where the tephra is, the silicified wood specimen, plagioclase minerals and heulandites crystals. Otherwise, is hard to understand what has been shown in the SEM images. Provide also low magnification images of the actual specimens from where these images were taken.
Line 148: How have you identified the presence of “tuffaceous matrial.” Correct also the word matrial.
Line 152: Where the different coloring in panels of Figure 7 contribute to? Are there differences within the cells of Figures 7A and 7B. Elaborate on the observations.
Line 160: It is hard to see the quartz within the fractures. Which method was utilized? Please provide the data showing the presence of quartz within the fractures.
Line 164: Indicate on SEM images the silicified fungal hyphae. How have you identified the presence of fungal hyphae and fungal spores? Please explain.
Line 168-169: Indicate the given description in the Figure 9. Correct the numbering of images.
Line 181: Use higher magnification to indicate chalcedony. It is hard to distinguish from these images.
Line 183: What is the difference between Figure 10G and 10H. Where the central region refers to?
Line 196: What extra information is shown in Figure 10C (right panel) compared to the left one?
Line 204: Would be interesting to indicate the crystallographic planes exposed in SEM images of Figure 12.
Line 210-216: Please provide reference(s).
Line 224: Provide Figure number showing it is opal-CT.
Line 229: Do you mean cell walls or cell voids?
Line 320-331: Please provide references.
Line 341: Provide evidence that justify this observation (charcoalification).
Line 345: Indicate with arrows the organic matrix area and the data showing its presence.
Line 351-352: Please write eH and pH.
Line 378: Please remove the Acknowledgments section if there is no information to provide.
Line 380: Correct the reference numbering.
Author Response
I recommend major revisions to improve the clarity and accuracy of the paper. Overall, the authors should provide a more thorough description and discussion of their results and present sufficient evidence to support their conclusions.
Reply: Thanks, we are striving to improve these aspects of the presentation. We appreciate your careful review and many helpful suggestions for the manuscript’s improvement.
Line 41: Could you also state the geologic age?
Reply: Thanks, age has been added.
Line 48: Parenthesis is missing.
Line 55: Dot is missing.
Reply: Thanks for catching these small errors
Line 61: Could you please elaborate on “ready source for dissolved silica”?
Reply: Thanks, I have added to the text, and cited two references.
Line 84-86: Please provide reference(s).
Line 102-103: Please elaborate on specific examples of taxa in Costa Rica and on the Pleistocene plant communities and their significance.
Reply: There is extensive literature and Pleistocene and Holocene plant communities in Costa Rica, but these reports don’t have much relevance for petrified wood, which is predominately Miocene. However, we have added information regarding these investigations.
Line 105-122: Divide this paragraph into multiple ones according to the techniques used and explain the scope for each technique. Line 109: Which are the other analytical techniques, and which is the scope for all of them including the density measurement by hydrostatic weighing?
Reply: Thanks, I have divided the paragraph, and added additional details regarding methods.
Line 110-118: Which is the purpose of using different microscopes? Please remove the links.
Reply: As a microscopist, I strive to use the instruments that provide the best images. The minimum requirements are a petrographic microscope for transmitted light illumination (including polarized light), and a lower-power reflected light microscope. However, I use several other microscopes in order to achieve the widest possible range for depth of field and magnification. The links to suppliers are required by the journal.
Line113: Which is the thickness of the sections? How were they prepared?
Reply: We used standard 30 micron thick sections, prepared using a Wards Science thin section machine at the Western Washington University petrography lab, with System Three epoxy resin used as a mounting material and for attaching coverslips. I will be happy to add those details to the text, but there is nothing special about the thin section making process.
Line 119-122: Provide more details on the SEM imaging. Working distance, thickness of coating? Sputter coating instrument? Type of imaging (SE, BSE)? Are the samples being polished?
Reply: I have added those details to the methods section
Line 121: Write diameter instead of “dia”.
Reply: Change has been made
Line 126: How do you discriminate “microcrystalline quartz, and megacrystalline quartz” by XRD? This info should be indicated in the spectra as well. Which are the size ranges for each quartz group? Could you also provide the miller indices of the crystallographic phases and add in SI information spectra of control samples/databases confirming the existence of these minerals.
Reply: microcrystalline quartz and megacrystalline quartz are indistinguishable in XRD patterns. Crystal sizes are recognizable by optical microscpy and SEM. As for the size ranges, I discussed this phenomenon in detail in a paper “Mineralization of Fossil Wood with Macrocrystalline Quartz: A Microscopic Investigation”.That paper was recently published online in Minerals 15.225, the same special issue that will include the Costa Rica paper. Therefore it seems redundant to repeat the crystallographic discussion in this manuscript.
Line 130: What the presence of heulandite indicates?
Reply: Thanks, we will clarify that,but the presence of heulandite is evidence of diageneic alteration of the volcanoclastic matrix for the silicified wood.
Line 139: Please provide reference(s).
Line 143: Please provide all the EDS spectra confirming the description provided in Figure 6. Use also, abbreviations and/or arrows indicated where the tephra is, the silicified wood specimen, plagioclase minerals and heulandites crystals. Otherwise, is hard to understand what has been shown in the SEM images. Provide also low magnification images of the actual specimens from where these images were taken.
Reply: I have added images of the specimens, and arrows showing tephra. In the interest of space-saving, I am not eager to include EDS spectra, but I will consider that option if I can get SEM time before the deadline for returning the revised manuscript. Our main point is simply that Costa Rica wood commonly occurs in association with volcanoclastic pryroclastic deposits, and the matrix material typically shows evidence of diagentic alteriation, a process that may be related to the release of silica for wood petrifaction.
Line 148: How have you identified the presence of “tuffaceous matrial.” Correct also the word matrial.
Reply: The tuffaceous nature of the volcaniclastic matrix is very evident at Costa Rica volcaniclastic deposits. It’s easy to see in hand specimens and in thin sections. SEM images are useful for observing the diagenetic alteration that produces zeolites, glass devitrification textures, and intact phenocrysts of minerals like plagioclase.
Line 152: Where the different coloring in panels of Figure 7 contribute to? Are there differences within the cells of Figures 7A and 7B. Elaborate on the observations.
Reply: I was hesitant to elaborate on the origin of color because it means self-citing a paper, but I am happy to have the suggestion to provide an explanation.
Line 160: It is hard to see the quartz within the fractures. Which method was utilized? Please provide the data showing the presence of quartz within the fractures.
Reply: Quartz in voids and fractures are evident in polarized light views of thin sections, where the birefringence is a distinguishing characteristic. At high magnification, the euhedral shapes of quartz crystals can be seen. I have added to photos.
Line 164: Indicate on SEM images the silicified fungal hyphae. How have you identified the presence of fungal hyphae and fungal spores? Please explain.
Reply: Thanks, I have added arrows to the image. As for the identifications, they are based on morphology. For a microbiologist, the recognition of fungal hyphae and spores is not much different from recognizing a life for as a tree because of the presence of a trunk and a leaf crown. Although I ended up working half a century as a geologist/geochemist, as an undergraduate I studied microbiology and biochemistry. Fungal traces are pretty common in fossil wood. I could include references to some published examples, but editors give me a hard time for self-citations.
Line 168-169: Indicate the given description in the Figure 9. Correct the numbering of images.
Reply: Thanks, I think the image numbering is now ok, but that’s an issue that always gets resolved during production editing. The MDPI editors are perfectionists.
Line 181: Use higher magnification to indicate chalcedony. It is hard to distinguish from these images.
Reply: Thanks, I have added a plate that shows some high magnification images of chalcedony/
Line 183: What is the difference between Figure 10G and 10H. Where the central region refers to?
Reply: The “central region” refers to the vessel lumen, and I have changed to that wording. The main reason for including two photos is to balance the composition of the plate.
Line 196: What extra information is shown in Figure 10C (right panel) compared to the left one?
Reply: The left image shows that preservation of cell architecture is rather patchy. Some areas show longitudinal cells, other areas are relatively featureless. The right image shows the replacement of cells with microcrystalline quartz. I have expanded to caption.
Line 204: Would be interesting to indicate the crystallographic planes exposed in SEM images of Figure 12.
Reply: It would be possible to describe these planes as Miller Indices, but I am not sure that the information would be useful to most readers. Mineralogists will have no trouble visualizing the geometry for these quartz crystals, but paleobotanists are not likely to care.
Line 210-216: Please provide reference(s).
Line 224: Provide Figure number showing it is opal-CT.
Line 229: Do you mean cell walls or cell voids?
Line 320-331: Please provide references.
Reply: I am having some trouble with review comment that refer to line numbers because the manuscript I receive from the editors does not contain line numbers, and when I try to add them the numbering sequence is somewhat different from the version that went to reviewers. However, I believe that I have accommodated the above recommendations. Additional references have been cited.
Line 341: Provide evidence that justify this observation (charcoalification).
Reply: Not much room for doubt here, when material is black, low density, and shows huge carbon peaks in EDS spectra.
Line 345: Indicate with arrows the organic matrix area and the data showing its presence.
Reply: Matrix is marked “M”. In these images, the matrix is readily visually discernable because of its granular texture. The volcanoclastic composition is also evident from SEM/EDS spectra, but I don’t see the matrix identification as being controversial, and I prefer not to use page space for additional data.
Lines 1-352: Please write eH and pH.
Reply: Thanks, this has been done.
Line 378: Please remove the Acknowledgments section if there is no information to provide.
Reply: Acknowledgements have been added. There was a bit of delay because the editors require that authors need to have permission from people that they wish to acknowledge.
Line 380: Correct the reference numbering.
Reply: Thanks, I have that goal, but this another instance where the MDPI production editors do very careful checking of reference citation prior to final acceptance.
Round 2
Reviewer 1 Report
Comments and Suggestions for Authorsaccept
Reviewer 2 Report
Comments and Suggestions for Authorspg. 378: The reference 69 appears twice
