Heavy Mineral Variability in the Yellow River Sediments as Determined by the Multiple-Window Strategy

Round 1

Reviewer 1 Report

In their article, entitled " Heavy Mineral Discrimination of the Yellow River Sediment by “Wide-Window Strategy", the Authors combine grain-size and heavy-mineral data on fluvial sediments in the lower tract of the Yellow River (Huang He) with the principal goal to investigate intersample and intrasample variability in this huge river system.

Although the amount of data that the Authors provide is considerable, the organization of the article and English expressions are not invariably optimal, and in some places awkward and confused. Most important, the fundamental concepts of hydraulic-sorting and settling-equivalence analysis of sediments are too often expressed with insufficient clarity. The article is therefore in need of major revision before it can be accepted for publication.

Let us start first with clear definition of basic concepts that the Authors should clarify from the start in the Introduction section, beginning with the title. They have used a multiple-window strategy in their study (as indicated at Lines 120-121), which is in fact an excellent approach.

The title should thus read: HEAVY-MINERAL VARIABILITY IN YELLOW RIVER SEDIMENTS AS DETERMINED BY MULTIPLE-WINDOW STRATEGY.

ANALYTICAL APPROACHES

Narrow-window strategy: Several Authors still believe that analysing heavy minerals in a single size class (e.g., 63-125 mm or 125-250 mm) or even in a single subclass (e.g., 125-180 mm) maximizes consistency. Conversely, such an approach is demonstrated to maximize bias (see Figure 1 in Garzanti et al., 2009).

Wide-window strategy: Analytical bias is instead minimized by expanding the size window analysed (we routinely use the 4f wide 15-500 mm size window or the 5f-wide 32-500 mm size window), and eliminated altogether if the sample is analysed in bulk. In this case, however, point-counting is required in order to obtain real volume percentages.

Multiple-window strategy: This strategy implies analysing all size classes separately in each sample. Although quite time-consuming, this is by far the most complete way to investigate mineralogical variability in a sedimentary system. Moreover, grains within each size class (or better size subclass) can be considered as all of the same size, and when this requirement is fulfilled real volume percentages can be obtained by grain counting. Point counting is no longer required.

 MINERALOGICAL VARIABILITY

Intrasample mineralogical variability: Difference in mineralogical composition among different size classes within the same sample.

Intersample mineralogical variability: Difference in mineralogical composition among different samples.

Other points of concern are discussed here below:

1)                  Presumed mineral stabilities and relationships with hydraulic sorting

In different parts of the manuscript the Authors claim that a group of minerals (i.e., zircon, tourmaline, rutile, apatite, and garnet) are “stable”, and have a common physical behaviour (e.g., Lines 19-20; 191-192; 202-205; 336-342; 358-360; 426-428). These statements have no firm basis, because these minerals have different durabilities depending on the characteristics of the chemical environment. Both garnet and apatite can be extremely labile during climate-controlled chemical weathering (see Morton and Hallsworth, 2007, and Garzanti et al., 2013 J.Geol., especially Figure 9C). Moreover, zircon, rutile, and garnet are high-density to ultra-high density heavy minerals, whereas tourmaline and apatite are low-density heavy minerals. As a consequence, these two groups of presumed “stable” heavy minerals respond very differently to hydraulic processes.

2)                  Definition of heavy minerals

Defining heavy minerals is not straightforward, and different Authors use the term differently. My preference goes to restricting the definition to terrigenous transparent minerals only, thus excluding micas, glaucony, phosphates, pyrite, and limonite. The Authors are free to choose differently (e.g., Line 272), but including micas and limonite enhances noise substantially (see Lines 334-335 or 422-425).

3)                  Subsection 4.4

I would suggest to supress the entire subsection 4.4. Heavy mineral indices such as ATi and GZi have been introduced for the study of ancient sandstones, where heavy-mineral assemblages are strongly depleted and commonly limited to a few durable species only. This is not a very useful approach to the heavy-mineral study of modern sediments, where other indices can be used (see Table 1 in Andò et al. 2014 Geol. Soc. London SP386).

Lines 361-364 at the end of subsection 5.1 can also be beneficially eliminated.

4)                  Subsection 5.3.

The whole subsection needs careful reconsideration. Following from the definitions and statements provided at the beginning of this document, the question at Lines 377-378 is out of place, as the conclusion at Lines 415-416 and Lines 429-431. There is no specific size fraction to be selected for analysis! No 1f-wide class can provide unbiased results. The choice is between analysing each size class in each sample separately (multiple-window approach), which is indeed time-consuming, and to analyse the sample in bulk if well sorted or a size window as wide as possible if poorly sorted  (e.g., 15-500 mm or 32-500 mm).

5)                  Meaningless decimals

Two digits are used for compositional figures throughout the manuscript (e.g., subsections 4.2, 5.1). In most cases decimals are not meaningful, and centesimals even less. Eliminating meaningless decimals and centesimals will make reading easier.

6)                  Referencing and English expressions

Referencing is locally inaccurate, with lack of correspondence between text and reference list. As an example, Laura and Yani 2018 should be cited in the text as Fielding et al. 2018, and the correct reference is Fielding, L., Najman, Y., Millar, I., Butterworth, P., Garzanti, E., Vezzoli, G., Barfod, D. and Kneller, B., 2018. The initiation and evolution of the River Nile. Earth and Planetary Science Letters, 489, 166-178.

Many English expressions are awkward. This is fully understandable and excusable, because the Authors are all Chinese and if I were supposed to write in Chinese then I would not know where to begin. Improving the language in many parts of the manuscript is nevertheless required (e.g., Line 74: anatomically; Line 98: magmatite rock; Line 130: difficult under these grains; Line 137: difficult to identification; Line 143: shows that the Yellow estuarine sediments mainly composed; Line 148: presents double peak; Line 186: wide grains; Line 189: coarse particle of >3f); Line 281: wide window grains.

Moreover: Lines 257-264 are particularly difficult to read. Lines 285-292 are utterly confusing and better eliminated altogether. Lines 315-329 are awkward and contain many confuse statements.  Lines 339-342 are also in need of clarification, as are Lines 390-400.

MORE SPECIFIC POINTS:

Line 162: I would define heavy-mineral concentration in Yellow River sediments as “moderately rich” rather than “low”.

Line 175: please explain what do you mean by “complex”.

Lines 177 vs. 180: choose one between “more than 20” and “about 30”.

Line 179: particles -> size classes

Line 182: oblique zoisite -> clinozoisite

Line 332: into -> together with

Line 349: very high heavy-mineral concentration in coarse sediment appears contradictory with previous statements.

Line 365: there is no subsection 5.2.

Line 406: superior –> complementary

Line 356: chart –> plots

Lines 372-375: according to the definitions provided at the beginning of this document, the strategy described here is the “multiple-window” strategy and not the “wide window” strategy.

Faithfully yours,

Author Response

Dear Reviewer1,

We express our sincere thanks to you for your constructive suggestions. According to the revision comments and suggestions, this manuscript (Minerals-430432) has been revised carefully. Our responds are listed with red mark in the Word version.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

I read you manuscript with pleasure and have to commend you on writing up a very interesting paper. 

The paper focus on the importance of grain-size to control heavy mineral assemblages using an example from the Yellow River in China.

Overall, the manuscript is well-structured and well written. Nevertheless, there are several parts of the text that are colored in yellow and the authors must remove it.

In my opinion, the abstract should be rewritten, in particular the sentence staring with "Similarity analysis reveals that similarity value..." No need to repeat words.

I believe the introduction to the theme and the works referred in the text are correct and offer the reader a good perspective into the problem.

Again, I also enjoyed reading methodology and the results section. Both are clear, concise and easy to follow. Results are interesting and provide insights for lithological and sediment dynamic interpretations.

The authors wrote a superb discussion and made my life easier as a reviewer because I felt they focused on several topics very throughly. My only observation is that they do not explore the different indexes presented on chapter 4.4.

I strongly recommend they add a couple of paragraphs in the discussion to establish the relevance of this indexes and what can be inferred from them in this case study.

Overall, a nice manuscript. Therefore, I recommend this manuscript to be accepted for publication after minor changes.

Regards

Author Response

Dear Reviewer 2,

We express our sincere thanks to you for your profesional suggstions. According to your revision comments and suggestions, this manuscript (Minerals-430432) has been revised carefully. Our responds are listed with red mark.

Author Response File: Author Response.docx