General comments

In this paper, Xing and coauthors present a thermochronological study in the western margin of the Ordos Basin with the aim to reveal its uplift and cooling history.  In particular, the result of the work shows that different zones of the Ordos Basin underwent cooling at different times, demonstrating the complex tectonic history of the fold-and-thrust belt of which it is part of. Anyway, I think that the concepts reported in this contribution appear to be disconnected from each other, making it hard to give conceptual and scientific continuity to what is meant to be said. Therefore, I suggest a more homogeneous writing style. There are also several major errors in terminology and nomenclature related to tectonic structures and geological timescales (e.g. Early Cretaceous (130-30 ma) at line 367).

#Introduction

The introduction focuses on the tectonic history of the study area and the general objectives of the work. However, the concepts are explained in a confusing and, sometimes, repetitive manner. Moreover, they are always expressed in a general way, never going into detail.

#Geological setting

The geological setting is focused on describing the tectonic events that have characterized the study area over time. However, there is a complete lack of stratigraphic setting and description of the outcropping deposits with their respective ages. This information is not only important to make the geological framing more complete, but also to better correlate the thermochronological data and resetting conditions of the samples. Moreover, a key aspect that makes this section difficult to read is the complete disconnection from Figure 1 in which the different areas within the Ordos Basin does not follow what is shown in the figure.

#Sampling strategy and methodology

The sampling strategy and methodology paragraph lacks two tables (one for the apatite fission-track and one for the (U-Th)/He data) with information related to:

AFT:

• Geographic coordinates of samples;
• N° of counted mounts;
• N° of counted grains for each samples;
• Ns, Ni, ρd, ρi, ρs;
• Central ages.

AHe:

• Rs;
• Age ± error;
• U, Th, Sm content;
• eU correlation and content (eU= U+(0,24 x Th)).

#Discussion

The discussion section should be written more thoroughly as it is currently a report of the results obtained with few considerations about tectonic implications with respect to the long-term orogenic history. There is a lack of reference to the figures, which makes it difficult to read the data and, consequently, to interpret them. There are also many errors regarding the ages of the different uplift phases, of which it would be important to indicate the numerical value to understand what is mean for “slow,” “rapid,” and “intermediate,” also with respect to the correlation made with the events reported in the literature. Referring to “Late” and “Early Mesozoic,” it seems that the related tectonic phases are diversified from those described of Jurassic and Cretaceous ages, creating much confusion. Moreover, as pointed out in the text, the term “Late” and “Early” Palaeozoic is not right terminologically according to ICS (International Chronostratigraphic Chart).

Specific comments (line-by-line)

Line 23: Lower Cretaceous- Oligocene.

Line 24: Late Jurassic-Early Cretaceous.

Line 25: Early Cretaceous- Oligocene.

Line 27: How much does the exhumation rate vary numerically?

Line 47-50: “…and developed since the Mesozoic as a residual intra-cratonic basin”.

Line 53: please describe which kind of sedimentary strata.

Line 57-59: are you sure that these are tectonic units?

Line 62: since the Mesozoic or Phanerozoic?

Line 64: which tectonic units? Please specify.

Line 67-68: I think that the study area is in the western margin of the Ordos Basin.

Line 71: Are you talking about the Ordos Basin or about the belt of which it is part of?

Line 72:  ...previous published papers investigated the structural framework…

Line 74: western margin of what? The belt? The Ordon Basin?

Line 87: …“south, central and northern”. It is not reported in Fig.1. Maybe it is necessary to explain these concepts with another figure.

Line 107: Which geological evidence? Not clear.

Line 118:  ..”large composite”. What do you mean?

Line 122-128: please modify “,” with “;”.

Line 133: “part”. It is not reported in any figure.

Line 137: “… and surrounding areas. The red rectangle mostly evidences the Yinchuan Basin…”.

Line 138: western or south-western sector.

Line 140-143: d-f) W-E oriented simplified geological cross-sections (modified from Zhou, 2015; Zhao, 2006 and Ma, 2019, respectively).

Line 150: Why only westward?

Line 156: What do you mean?

Line 161: Yinchuan Basin.

Line 161-162: please, explain more deeply this concept.

Line 163-165: If you are referring to the geological cross-section of Fig. 1 (1f) the thrusts are both W- and E-dipping. I also think that it is necessary to modify the dip-angle of these structures as it is too high.

Line 165: What do you mean?

Line 166-170: This information is not reported in Fig.1. In addition, I think that the name that you gave are referred to single thrusts, not thrust sheets. Maybe, it is necessary to revise the terminology used. Furthermore, the structure that is represented in the geological cross-section in Fig.1f is not an anticline.

Line 173: It is necessary to find a name that make sense from a geological/geographical of structural point of view.

Line 182: Tianshuibao city.

Line 183: fission-track (please correct it within all the text).

Line 185: “The ages obtained through the apatite fission-track analysis…”.

Line 185: from 189.6 to 3.1 Ma.

Line 186: From 192 to 105.4 Ma.

Line 195: please modify the last part of the sentence as “thermochronological data in the study area”.

Line 196: What does it mean? Please, clarify. 

Line 201: which kind of geochronological methods?

Line 206-207: This is not a consequence of the temperature to which the apatite grains are sensitive. Please, delete.

Line 214: It is not necessary to repeat it every time. Just use “study area”.

Line 221: It is necessary to ass information about the stratigraphic setting of the study area. Otherwise, all the consideration are useless.

Line 222-223: Put the sentence in the next paragraph.

Line 256: peak ages.

Line 256-257: These ages do not correspond to what it is reported in Fig. 4b.

Line 258: How much is the error?

Line 259: Which kind of tectonic event?

Line 279: “…in this region from Late Jurassic to Eocene (Fig. 4c).

Line 289: Is the age referred to sample Z2-11?

Line 295-296: Is the relation with eU direct or inverse?

Line 313: Please, specify the parameters.

Line 316-317: It is a repetition, please integrate as a single sentence from line 314 top 318.

Line 333-334: You should specify how many lengths did you measure for each sample to check if there are enough for modelling.

Line 359: Jurassic belongs to the Mesozoic.

Line 361: How did you calculate the average uplift rate?

Line 367: See the comment at line 359.

Line 368: What do you mean by “slow cooling”?

Line 379: The uplift is faster respect to what?

Line 381: What do you mean by “intermediate uplify?”

Line 382: Which analyses?

Line 395: See the comment at line 367.

Line 407: 95 Ma is Upper Cretaceous.

Line 443: Please, indicate the age of sediments.

Line 444: To indicate the first part of Palaeozoic you cannot you the capital letter. You should write “early Palaeozoic”.

Line 450: See comment at line 444.

Line 450-453: As written, it seems that the fluvial and deltaic deposits are shallow water sediments.

Line 455: Which kind of event of faulting?

Line 456; See comment at line 444.

Line 461: Which kind of tectonic event?

Line 468: sedimentary succession?                        

Line 480: Which kind of unconformity?

Line 532: What are you referring to by “this existing structure”?

Comments to figure

Figure 1: (general comment) I think that it is necessary to revise the figure in a deeply way. In particular:

• Lacks a stratigraphic column indicating the outcropping fms and their age;
• I do not see the localisation of the samples used for the study;
• Differentiate the samples used for the study and those in Gao 2014 in a way that is more graphically evident;
• Switch the order of the figures or letters shown above. It is not intuitive to see figure 1c as first;
• Increase figure resolution;
• Put the scale in Fig.1c;
• Unify the style of the geological cross-sections;
• The bedding symbology is completely missing, so it is difficult to understand if the geologic structures indicate on the map correspond to the reality.

In Fig. 1c:

• The bedding symbology is completely missing;
• Specify the symbology of faults to differentiate the tectonic structures. I think that the right orientation of the thrust faults is NNW-SSE;
• Indicate the North-South Tectonic Belt of China (as indicate in the text (line 64).

In Fig. 1d: 

• Put the faults in the legend;
• Fault displacement is inverted with respect to the direction of slip indicated by the arrows;
• Review the nature of the contact reported on the flanks of the anticline.

In Fig. 1e:

• Put in the legend the symbology of faults;
• What do the double arrows at the hanging wall of faults indicate? Do they refer to a tectonic inversion?

Figure 3: It is necessary to try to report the data in a more visible way. Currently, both radial plots and labels are too small, making it difficult to read the data and the sample to which it belongs clearly enough to interpret it.

Figure 4: Again, it is necessary to enlarge the labels in the figure. Specify what the coloured dots in the legend indicate. Does it refer to the stratigraphic age?

Figure 6: Boxes are missing to understand what geological parameters are used (stratigraphic age, known tectonic events, etc.). Do the modelled ages refer to AFT, AHe data, or both? This information is important to understand how constrained the model is. Also, linked to the model, there is a missing table indicating the stratigraphic age of the sample, number of model interactions, path constraints, randomizer style and halve. Report in the same table or directly on the models the number of total, acceptable and good pathways.

Figure 7: As represented now, the data reported in the thermal model do not allow a clear correlation. It would be appropriate to report only the weighted mean paths for each sample. As highlighted in Fig.6, the model lacks the boxes indicating the main constraints. 

Figure 8: Explain what the red arrows connecting the “lithostratigraphy” column to the “chronostratigraphy” column indicate. Also, what do the abbreviations in panels a and b indicate? In the “chronostratigraphy” column replace “Paleocene” with “Paleogene”.

Summary

The study presented here by Xing and co-authors seeks to reconstruct the uplift and thermal history of the central-northern section of the western margin of Ordos Basin in mainland China. To do so, the authors have utilized the apatite fission track and apatite (U-Th)/He methods on samples collected from three different areas within the studied region, and have also reviewed already published data. The authors conclude that in each of the areas uplift rates varied with time and that the uplift history also varies from one area to the other.

General comments

Despite the interesting topic, the manuscript lacks consistency, precision, meaningful discussion and clear structure, and thus it makes it difficult for the reader to follow up or gain a clear conclusion on the findings. For example: 1) there is a lot of repetition of information, such as on the formation and evolution of the Ordos Basin; 2) information given on the uplift rates is incomplete and vague – the rate is described qualitative (e.g. slow uplift) but there are no quantitative rates to back up the statement; 3) there are whole paragraphs that need repositioning (e.g. from the results part to methodology), and the references lack consistency in their presentation (both in the text and the list). An improvement to the terminology used and scientific writing is also needed (e.g. use the word central and not middle when referring to geographic locations)

#Introduction

There is a lot of repetition on the occurring of various tectonic events that caused deformation and there are no details about these deformation events. There are also a lot of locations/structures named in the text that are not appearing in Fig. 1 and a reader wouldn’t be able to place them if they are not familiar with the region. For example, the Qinling Orogenic Belt, Tectonic Belt of China etc. are not represented in Fig. 1. Furthermore, Fig. 1 has too many details making it very difficult to decipher the different locations or structures, is too small (and/or has not great resolution) and is difficult to connect it to the text. I would suggest you make a bigger more general map showing the location of the structures (as named in lines 57 to 66) and a different map focusing on the studied region with the locations of the samples and the three areas.

#Sampling strategy and methodology

Here you need to clearly name the different samples collected for the three different areas (names of the samples). Also, references are needed for the apatite separation methods used in this study and the dating. You also need to state the criteria for acceptable data (which you briefly mention later on the results section as you exclude samples) and the acceptable error range.

You also need to transfer part of the section 4.2 (lines 310 to 325) in the methodology section. Along these lines you set up the methodology you follow in order to evaluate thermal simulation results from your inversed modelling, and you do not really present any real results.

#Results

The section lacks a presentation of the inverted time-temperature paths you have simulated. Could you please expand in the text on what you graphically show on Fig. 6? What do all these graphs in Fig. 6 mean? What samples (out of the total 16) have been used and from which of the three areas. These details need to be presented here.

#Discussion

The discussion part needs to be more precise and to the point. You qualitative express your results but there are scarcely any values given on the uplift and cooling rates. How slow is a “slow rate”, how fast a “fast rate”? What are you comparing with (e.g. average global uplift rates)? There is also barely a mention on the cooling rates. However, since you have already simulated these values you should present them here and discuss their meaning.

A more structured style of writing is needed in section 5.2. The authors jump between tectonic areas making it very difficult to follow up. Try to write all the information available about one area (e.g. Tibetan Plateau) before you move to the next (e.g. Alxa block). Furthermore, as the Indosinian orogeny is older than the Yanshanian it would make more sense to start describing the impact of this orogeny to the area first.

There is lack of discussion on how the samples collected by the authors compare to the samples evaluated from the existing literature. There is only a mention of assessing of already published data in the methodology section but we do not read anything about them after that. How do these pre-existing data fit/not fit with your results? And how do they fit into your proposed tectonic evolution of the area?

#Figures

In general all figures presented on this manuscript are very busy, with very small fonts and difficult to see (even when zooming in in the pdf version, which might also mean a poor image resolution). Authors are advised not to use a font size smaller than 9pt for the figures, use a larger area for the figures when necessary and if allowed and use a key below the figure to save more space for the actual image.

#References

There is no consistency in the presentation of references in the manuscript, both in the text and the reference list. Also there are references in the text that are not reported on the list (see technical comments) and references reported with different publication years in the text and on the list. Whatever style you choose to use for the references please be consistent throughout. The following rules apply: 1) when only one author use the surname and the year of publication (in the text); 2) when two authors then use both their surnames and the year of publication (in the text); 3) when more than two authors then use the surname of the first author followed by “et al.” and the year of publication; 4) names of authors are not reported in the text; 5) you need to name all the authors involved in a paper when you present this paper on the reference list, no matter how many there are (e.g. reference no. 1 after the third author there is an “et al.”. You should not use that here, but instead present the full author list; 6) when you have more than one papers from the same first author published in the same year you need to identify them with letters (e.g. a, b, c…). For example references no. 79, 80 and 81 are all from the same author, but which is which (in the text you cite them as 2007a, 2007b, 2007c)? 7) when you have authors with the same surname you have to be able to separate them between the two in the text (e.g. references no. 33 and 34. Which is which?).

Technical comments

Line 17: “central” and not “middle” for geographic locations (the same for lines 19, 31 and throughout the text where necessary)

Line 21: add a space between the words “Mountain” and “(Mt.)”

Line 22: add a space between “160” and “Ma”; repeat for all the other cases too

Line 32: instead of “and” use “while”

Lines 33-34: “…multiple stages/events of the Yanshanian orogeny…”?

Lines 43-44: “…since 1.8 Ga years…” or “…from 1.8 Ga years ago…”

Line 53: you mean “Craton” instead of “region”?

Line 64: where is the North-South Tectonic Belt of China in Fig. 1?

Line 94: where is well LS1 in Fig. 1?

Line 94: remove the word “well” after LS1, T1 and TS1

Line 95: refer to Fig. 1c at the end of the sentence

Lines 96-98: needs referencing

Lines 109-113: “The research … the Mesozoic”; repetition

Line 119: what do you mean by “…extents…”?

Line 128: do you mean “basin” instead of “significant”?

Line 131: “In order to define more precisely…”

Line 132: “stages” instead of “processes”

Line 137: “Shi et al., 2020” is not in the reference list

Line 143: “E-F” instead of “C-D”

Line 158: explain how the structural characteristics differ

Lines 166-167: remove the “thrust sheet” after Weizhou, Qinglongshan and Shigouyi

Line 168: “…thrust sheets.”

Line 182: “…specifically from the area between…”

Lines 185-186: present the dates from older to younger

Line 190: delete “fission tracks”

Line 190: “…at 78 and 101 Ma, and at 153 Ma respectively.”

Line 196: “Myr” instead of “Ma”

Lines 201-202: what do you mean by “lack of chronological methods”?

Line 207: delete “valuable”

Line 224: “…using the apatite…”

Line 233: “…for all collected samples of the studied area”

Lines 233-234: “(WHM-5…this paper)”: I don’t even understand what that means

Line 235: “…following three criteria…”, but you present only two. Which is the third?

Line 239: “The dating” instead of “This experiment”

Line 247: what are central ages?

Line 249: “. All of them are significantly…”

Line 252: “…13.3±1.7μm, respectively, all of…”

Line 258: name the error range

Lines 258-262: “The age of…Cretaceous”: unnecessary, please remove

Line 284: “…part, respectively.”

Line 286: “…sweet spot…”?? please remove (you can say a location of interest instead)

Lines 298-299: Caption of Fig. 5, you need to present b before c and d

Lines 310-325: “Due to … good match.” This part belongs to the methodology section

Line 341: “studied areas” instead of “sample sections”

Line 346: which one is the “northern part”? Name it

Line 349: which one is the “southern part”? Name it

Line 360: “This phase marks…”

Line 367: “Early Cretaceous (130 Ma – 30 Ma)”. Be careful of the terminology you use, 30 Ma is not Early Cretaceous. Same in line 395

Line 396: “(ca. 30 Ma – present?)”

Line 398: name the error range

Line 405: what is a spatial pattern?

Line 442: “…covered by stratigraphic…”. What does that mean? Be careful of the terminology you use

Line 448: “…between Ordovician…”

Line 449: “strata” instead of “systems”

Lines 449-453: are you sure about the succession of transition? Marine deposits refer to deposits of saltwater seas or oceans

Lines 454-455: “Since the … faulting.” I though uplift occurred already at Jurassic times?

Lines 476-481: “During the…2001)”: this paragraph needs to be placed before the Yanshanian orogeny part

Line 491: “…of the Mongol-Okhotsk…”. Same in lines 524 and 563

Line 497: “Yang et al., 1999” not in the reference list

Line 506: “…northern section”: northern section of what?

Line 517: “this time” instead of “the Early Cretaceous”

Line 537: “…of the mountains,”. Which mountains?

Line 557: “…and Himalayan orogenies…”

Lines 557-560: “The Indosinian…field.”. This should be merged with the paragraph about the Indosinian orogeny earlier on the section

Lines 560-563: “The tectonic…Ocean.”. This should be merged with the paragraph about the Yanshanian orogeny earlier on the section

Lines 571-572: “The main source…the study area.” What do you mean by the Tethys tectonic domain?? What about the movement of the Indian Plate towards the Eurasian plate. This is the primary cause of the closure of the Tethys Ocean and responsible for the stresses applied in the region