Formation and alteration of magnesite nodules from Kunwarara, Queensland, Australia, as an analogue to Mg-carbonate formation on Mars

Comment #257 Kamilla Dyreborg Hansen @ 2025-12-05 00:03

Thank you for sharing this interesting and detailed study. I appreciate the work that has gone into the field observations, analytical methods, and microtextural characterization. The comments below are offered in the spirit of constructive feedback, with the hope of strengthening the clarity and overall impact of the manuscript.

In general…
1) Given that the title and abstract emphasize Kunwarara as an analogue for Mg-carbonates observed in Jezero crater, the manuscript would benefit from a more explicit synthesis connecting the detailed mineralogical and textural results to the geological context of Jezero. In particular, it would be helpful to clarify which of the documented formation pathways (e.g., pedogenic, diagenetic, or groundwater-driven precipitation) are considered plausible under Martian conditions, and how these processes compare with current rover-based interpretations of Mg-carbonate formation.
Section 5 is relatively brief compared to the depth of the earlier results. Expanding the discussion to highlight how specific microtextures, mineral assemblages, and alteration trends in Kunwarara correspond to proposed scenarios for Mg-carbonate formation in Jezero crater (such as low-temperature diagenesis, subsurface groundwater interactions, or CO₂–H₂O weathering) would greatly strengthen the Mars relevance of the study. A clearer linkage would help readers understand why these terrestrial observations matter for interpreting Mg-carbonates on Mars.

2) The samples appear to have been collected from a naturally exposed vertical profile rather than from core material. It may help readers if the manuscript briefly clarifies the exposure history of the section and whether near-surface alteration (e.g., weathering, biological activity, erosion, or material displacement) could have influenced the observed textures. This information would make it easier to distinguish primary features from those related to post-exposure processes.
If the profiles represent undisturbed stratigraphy despite being exposed slopes, a short note on how exposure conditions and potential disturbance (including natural or human activity) were accounted for during sampling would greatly improve clarity for readers who are not familiar with the field area.

3) Because the figures are placed at the end of the manuscript rather than near their first mention in the text, it becomes difficult to follow the narrative—especially for SEM and XRD results, which are visually essential. It would greatly improve readability (particularly in the preprint format) if figures were embedded closer to the relevant sections.

4) The abbreviation ‘bgs’ (below ground surface) appears without definition. Although common in some subfields, you might consider defining it at first use for readers from adjacent disciplines.

5) I would like to suggest that you either include the depth information for each horizon directly in the text or add an explicit reference to where the information can be found (e.g., Table S1).

Section 1 Introduction page 4.
Word missing???: ” Groundwater calcrete, in turn, form when Ca-rich waters ascend from the groundwater table through evapotranspiration and capillary action, forming extensive carbonate cement horizons with nodular facies towards the top of the ??? (Alonso-Zarza, 2003)”

Section 3.1 Composition and textural relationships of Kunwarara sediments. Page 7
The manuscript alternates between present and past tense, sometimes within the same paragraph. For clarity and consistency with conventional scientific style, you may consider using past tense for observational results and reserving present tense for figure descriptions or general statements.

This section includes both the core observations directly relevant to Mg-carbonate formation dolomite/ magnesite textures, vertical trends) and a number of additional SEM observations (e.g., Mn-oxides, cerianite, fungal hyphae). For clarity, you might consider separating these into two subsections—one focused on results that underpin your interpretation of Mg-carbonate genesis, and one summarizing ancillary mineralogical findings. This would help maintain the narrative focus while still documenting the full range of observations.

Section 3.2 Composition and occurrence of the Kunwarara magnesite nodules. Page 8
As multiple Mg-carbonate phases are described in this section (magnesite, dolomite, etc.), the plural construction “magnesium carbonates occur…” may be clearer than the singular “magnesium carbonate occurs…”

The phrasing ‘XRD analyses determined that…’ sounds slightly awkward in scientific English. It may read more naturally as ‘XRD analysis showed that…’ or ‘XRD results indicate that…’, depending on whether one or multiple analyses are meant.

There appears to be a formatting or typesetting error: ‘Mg-carbonate=’. This likely should be “Mg-carbonate is” or “Mg-carbonates are…”.
Additionally, the phrase “contain 100 µm to centimeter-scale glaebules that are light gray” reads somewhat awkwardly; a clearer construction might be “contain light gray glaebules ranging from ~100 µm to centimeter scale.”
Finally, the clause “multiple types of glaebules … or micronodules” is difficult to parse grammatically. It may help to clarify whether micronodules are a distinct category or a subtype of glaebules.

Section 3.2 Composition and occurrence of the Kunwarara magnesite nodules. Page 9
Original sentence: “Amorphous silica and chalcedony also line pores in magnesite aggregates.”.
Suggested sentence: “Amorphous silica and chalcedony occur as pore-lining phases within the magnesite aggregates, indicating late-stage silicification.”

I look forward to seeing how future observations from Mars rovers and returned samples may provide the presently missing pieces.

With kind regards
Kamilla Dyreborg Hansen

Comment #256 Kamilla Dyreborg Hansen @ 2025-12-05 00:01

Thank you for sharing this interesting and detailed study. I appreciate the work that has gone into the field observations, analytical methods, and microtextural characterization. The comments below are offered in the spirit of constructive feedback, with the hope of strengthening the clarity and overall impact of the manuscript.

In general…
1) Given that the title and abstract emphasize Kunwarara as an analogue for Mg-carbonates observed in Jezero crater, the manuscript would benefit from a more explicit synthesis connecting the detailed mineralogical and textural results to the geological context of Jezero. In particular, it would be helpful to clarify which of the documented formation pathways (e.g., pedogenic, diagenetic, or groundwater-driven precipitation) are considered plausible under Martian conditions, and how these processes compare with current rover-based interpretations of Mg-carbonate formation.
Section 5 is relatively brief compared to the depth of the earlier results. Expanding the discussion to highlight how specific microtextures, mineral assemblages, and alteration trends in Kunwarara correspond to proposed scenarios for Mg-carbonate formation in Jezero crater (such as low-temperature diagenesis, subsurface groundwater interactions, or CO₂–H₂O weathering) would greatly strengthen the Mars relevance of the study. A clearer linkage would help readers understand why these terrestrial observations matter for interpreting Mg-carbonates on Mars.

2) The samples appear to have been collected from a naturally exposed vertical profile rather than from core material. It may help readers if the manuscript briefly clarifies the exposure history of the section and whether near-surface alteration (e.g., weathering, biological activity, erosion, or material displacement) could have influenced the observed textures. This information would make it easier to distinguish primary features from those related to post-exposure processes.
If the profiles represent undisturbed stratigraphy despite being exposed slopes, a short note on how exposure conditions and potential disturbance (including natural or human activity) were accounted for during sampling would greatly improve clarity for readers who are not familiar with the field area.

3) Because the figures are placed at the end of the manuscript rather than near their first mention in the text, it becomes difficult to follow the narrative—especially for SEM and XRD results, which are visually essential. It would greatly improve readability (particularly in the preprint format) if figures were embedded closer to the relevant sections.

4) The abbreviation ‘bgs’ (below ground surface) appears without definition. Although common in some subfields, you might consider defining it at first use for readers from adjacent disciplines.

5) I would like to suggest that you either include the depth information for each horizon directly in the text or add an explicit reference to where the information can be found (e.g., Table S1).

Section 1 Introduction page 4.
Word missing???: ” Groundwater calcrete, in turn, form when Ca-rich waters ascend from the groundwater table through evapotranspiration and capillary action, forming extensive carbonate cement horizons with nodular facies towards the top of the ??? (Alonso-Zarza, 2003)”

Section 3.1 Composition and textural relationships of Kunwarara sediments. Page 7
The manuscript alternates between present and past tense, sometimes within the same paragraph. For clarity and consistency with conventional scientific style, you may consider using past tense for observational results and reserving present tense for figure descriptions or general statements.

This section includes both the core observations directly relevant to Mg-carbonate formation dolomite/ magnesite textures, vertical trends) and a number of additional SEM observations (e.g., Mn-oxides, cerianite, fungal hyphae). For clarity, you might consider separating these into two subsections—one focused on results that underpin your interpretation of Mg-carbonate genesis, and one summarizing ancillary mineralogical findings. This would help maintain the narrative focus while still documenting the full range of observations.

Section 3.2 Composition and occurrence of the Kunwarara magnesite nodules. Page 8
As multiple Mg-carbonate phases are described in this section (magnesite, dolomite, etc.), the plural construction “magnesium carbonates occur…” may be clearer than the singular “magnesium carbonate occurs…”

The phrasing ‘XRD analyses determined that…’ sounds slightly awkward in scientific English. It may read more naturally as ‘XRD analysis showed that…’ or ‘XRD results indicate that…’, depending on whether one or multiple analyses are meant.

There appears to be a formatting or typesetting error: ‘Mg-carbonate=’. This likely should be “Mg-carbonate is” or “Mg-carbonates are…”.
Additionally, the phrase “contain 100 µm to centimeter-scale glaebules that are light gray” reads somewhat awkwardly; a clearer construction might be “contain light gray glaebules ranging from ~100 µm to centimeter scale.”
Finally, the clause “multiple types of glaebules … or micronodules” is difficult to parse grammatically. It may help to clarify whether micronodules are a distinct category or a subtype of glaebules.

Section 3.2 Composition and occurrence of the Kunwarara magnesite nodules. Page 9
Original sentence: “Amorphous silica and chalcedony also line pores in magnesite aggregates.”.
Suggested sentence: “Amorphous silica and chalcedony occur as pore-lining phases within the magnesite aggregates, indicating late-stage silicification.”

I look forward to seeing how future observations from Mars rovers and returned samples may provide the presently missing pieces.

With kind regards
Kamilla Dyreborg Hansen