Meteoric Water Incursion, Crude Oil Degradation and Calcite Cementation of an Upper Cretaceous Reservoir in the Zagros Foreland Basin (Kurdistan Region of Iraq)

Round 1

Reviewer 1 Report

 

General Comments:

 

I recommend moderate changes be made before publication of this manuscript.  In particular, Figures 4 and 5, and to a lesser extent Figures 6 and 7, need to be better labelled so that the reader can see what is referred to in the text.  Also, the explanation as to why the d18O values of the columnar calcite are lower than expected is a bit unsatisfactory, although they clearly indicate the involvement of meteoric water, which was the objective.

 

Specific Comments:

 

Line 27 – by “nil salinity” I assume you mean no salt crystals, yes?  Also, can you be more specific when you say “low temperatures.

 

Line 37 – I’m sure what you mean by “unsaturated meteoric water”.  What chemical/compound is unsaturated?

 

Line 46 – rewrite as follows “with low API gravity (< X°) have frequently”

 

Lines 82 to 88 – refer to Figure 2 and Figure 3 in this paragraph.

 

Line 99 – it is unclear how you used the filters in this method. What is being filtered?

 

Line 105 – mention that the units are per mill and you need to give the precision of this analysis.

 

Line 128 – start a new paragraph when you begin talking about strontium.  Also, you need to make it clear that you are talking about the Sr isotopic composition of the carbonate.  Finally, how were these sample prepared for the analysis?

 

Line 148 – What do you mean by “a loss of 9.3%”?

 

Line 151 – You mention C24 tetracyclic terpane is noticeable.  Which figure are you referring to?

 

Line 153 – What is Tm in the equation?  Also, you refer to Figure 5 but have not labelled Ts or Tm on the chromatogram.

 

Line 156 and lines 159 to 160 – You refer to steranes, diasteranes, pregnane and homopregnane in the text but these are not labelled in Figure 6.

 

Lines 177 to 180 – It would be useful to have better photos showing these different phases.  Also clearly state the paragenetic sequence (i.e., the order of formation of these diagenetic phases).  Perhaps Figure 11 should appear earlier in the paper.

 

Lines 183 to 187 – It might be useful to show the data for the saddle dolomite and vug/fracture filling calcite on Figures 8 and 9.  Also, the range in C and O isotope values of the saddle dolomite is not much narrower than the columnar calcite.  However, both of these exhibit a narrower range than the vug/fracture filling calcite, which has a huge range.  I wonder if there is more than 1 generation of vug/fracture filling calcite.

 

Lines 181 to 183 – Why are the Sr isotope data for the columnar calcite reported to 6 digits when the dolomite and vug/fracture filling calcite only to 5 digits?

 

Lines 192 to 193 – I assume these measured Tmice refer to the dolomite, yes?

 

Line 193 – This is the first time you have mentioned “equant calcite”.  You did not mention it on lines 177 to 180.  Is this the vug/fracture calcite you mentioned before?  If not, why is this carbonate not shown in Figures 10 and 11.

 

Lines 194 to 195 – Make it clear you are referring to the equant calcite.

 

Lines 196 to 198 – Are these the only inclusion that contain oil?  You should make this fact clear.

 

Line 204 – Is it possible that the degradation of the oil has modified the isotopic composition?

 

Line 209 – What lack of n-alkanes.  Isn’t Figure 4 (bottom) showing that n-alkanes are present?

 

Line 211 – What are Pr/n-C17 and Ph/n-C18?

 

Lines 221 to 222 – So you are saying that Ts/(Ts+Tm) ratio is low because these are carbonate source rocks?  Please clarify.

 

Line 226 – What other evidence do you have suggesting that it was a restricted environment?

 

Line 235 (also see line 331) – Here you say there is a terrigenous component but back on line 205 you say the input of terrigenous material is limited.  It cannot be both.  Please clarify.

 

Line 248 – I am not sure what you mean by “high resistivity to biodegradation”.  Do you mean biodegradation was probably limited?  Also “most depositional and diagenetic conditions” is a rather broad statement to make.

 

Lines 251 to 253 – So, what is this telling us about the biodegradation of the hydrocarbon?

 

Lines 255 to 257 – Remove the discussion of the stable isotopes from this paragraph because you discuss this data later in Section 5.2.  It is also a little confusing (e.g., I don’t see the correlation between d13C and d18O, unless you remove the three most negative values and then maybe).  Only talk about Sr and move this discussion/paragraph to after the stable isotope discussion. This would mean swapping Figures 9 and 10.

 

Lines 270 to 274 – Can you think of no other reason why the d18O might be lighter than you expect.  What if you assumption of the meteoric water composition is wrong or the temperature.  I think you need to investigate this a bit more.

 

Lines 275 to 280 (also lines 305 and 335) – Interestingly, the d13C values, which only vary by 7.3 per mill (not that large) of the columnar calcite are what you would expect for meteoric calcite it presumably formed from (see Figure 8).  Why is it necessary to invoke explanations as to why it is lighter than Cretaceous limestone?

 

 

Edits:

 

Line 20 – rewrite as “(GC-MS) and stable carbon isotope analysis of bitumen…”

 

Line 25 – add space between d13C and VPDB

 

Line 26 – add space between d18O and VPDB

 

Line 27 – remove “as well as”

 

Line 38 – missing a bracket after toluene

 

Line 49 – the f of “Formation” should not be capitalized (also see lines 53, 71, 83, 84)

 

Line 54 – add a comma after calcite (e., dolomite, calcite, and bitumen…)

 

Lines 54 to 56 – Move the sentence that starts with “Heavy oil in several recent discoveries…” to the end of the previous paragraph.

 

Line 56 – replace “The current study..” with “This current study…”

 

Line 57 – add a comma after oil (e.g., heavy oil, and the…)

 

Line 62 – remove (Ghia Gara Formation)

 

Line 65 – rewrite as follows “covering all of what is now Iraq,…”

 

Line 70 – need a capital “L” on Late (i.e., Late Cretaceous)

 

Line 73 – remove the “s” from margins

 

Line 75 – add “a” before “clastic” (e.g., within a clastic starved…)

 

Line 76 – replace “at” with “within” (e.g., The Bekhme Formation lies with the ….)

 

Line 77 – add a comma after (e.g., short-lived (29 my), and….)

Line 81 – missing a bracket after [22]

 

Line 86 – replace “and” with “that” (e.g., fragments that alternate with…)

 

Line 95 – replace “at” with “in” (e.g., an outcrop in the Bekhme Gorge”

 

Line 97 – remove “the” and add an “s” to vein (e.g., and in large veins…)

 

Line 100 – rewrite as follows “…and asphaltenes using the SARA method [4].

 

Line 101 – replace “determination on” with “composition of”

 

Lines 102 and 103 – DeltaC or Delta-C

 

Line 104 – replace “saccharose” with “sucrose”

 

Line 105 – replace “refers to” with “relative to”

 

Line 106 – start a new paragraph for the GC-MS method description

 

Line 115 – do not start a new paragraph here because you are still talking about the GC-MS analysis

 

Line 123 – add a hyphen (i.e., Twenty-three)

 

Line 125 – the 3 and 4 in H2PO4 should be subscripts

 

Line 128 – remove “standard” after (VPDB)

 

Line 128 – start a new paragraph for the strontium isotope discussion

 

Line 132 – start a new paragraph for the fluid inclusion method

 

Lines 139 to 141 – You describe this on page 4 (lines 96-98) so remove it from here.  This also solves the problem of a one sentence paragraph.

 

Line 150 – missing a bracket after “(Figure 4)”

 

Lines 163 to 164 – add a space between d13C and VPDB and I think you mean whole bitumen and the four fractions.  Also, refer to Table 1 at the end of the sentence.

 

Line 181 – Add a space between d18O and VPDB, d13C and VPDB, and d18O VSMOW.  Also, see lines 183, 184, 186, 255, 247, 265, 269, 272, 275, 277, 278, and 280.

 

Line 182 – elsewhere in the text you have spelled out Figure rather than using Fig.  Pick one and use it consistently throughout the text.

 

Line 214 – do not start a new paragraph

 

Line 218 – missing a “t” on “the”

 

Line 221 to 222 – rewrite as follows “According to Peters et al. [10] … “

 

Line 226 – replace the word corroborates” with “suggests”

 

Line 233 – replace “The” at the start of the sentence with “There are” (e.g., There are relatively high amounts…)

 

Line 242 – no new paragraph needed here.

 

Line 250 – remove “the” before “other four”

 

Line 260 – fix spelling of elevated

 

Line 266 – remove semicolon after “50°C”

 

Line 270 – replace “be of” by “range from” (e.g., inferred to range from -12.1‰ to ….)

 

Line 299 – use a comma after Orogeny

 

Line 300 – use brackets around the statement starting with i.e.,

 

Line 302 – the degree sign needs to be a superscript, do not start a new sentence before meteoric-water, and it should be influx, not flux

 

Line 305 – replace “12C-rich” with “isotopically light d13C”

 

Line 321 – fix spelling of carbonate

 

 

Figures:

 

Figure 1 – In the caption, please explain what the colors represent.  Also, the top figure should be labeled a and the bottom figure b).  Finally, indicate the location of the study site in some way (e.g., a star).

 

Figure 2 – The resolution of 2a (Chronostratigraphic column) is very poor.  I cannot read the formation names or the legend. In the figure caption, replace “Samples location from” with “Sampling location of the…”.  Finally, in 2c it is hard to tell bitumen from shadow.

 

Figure 3 – It is difficult to see the columnar nature of the calcite crystals in these photos.  Do you have better / higher resolution photos?

 

Figure 4 – These two figures should be labelled “a” and “b” and make sure you refer to Figure 4a and Figure 4b in the text.  Label the important peaks like you did in Figure 6.  For example, in Figure 4 you should label the tricyclics and pentacyclics since you mention them in the text (line 151).  Also, you refer to the bottom figure as ion m/z 57 but the figure is also labelled n-Alkanes.  This causes some confusion.  Perhaps it is better just to say n-alkanes (e.g., line 208).

 

Figure 5 – As per figure 4, you need to label these two figures “a” and “b” and refer to them in the text.  Also label the gammacerane you mention on line 226.

 

Figure 8 – Fix typo in the figure caption (columnar) and indicate the pink box represents calcite precipitated from Cretaceous seawater (e.g., (pink box [60]).  Plot the figure like Figure 10 so that the axes can be labelled properly and use the units per mill.  Also, VPDB are not subscripts.  Fix this in Figures 9 and 10 as well.

 

Figure 10 – In the caption you mention the flux of hydrothermal brines.  Please provide the reference here.

 

Figure 12 – remove space between Strike- Slip

 

Table 1 – Rewrite the title as “Isotopic values for whole bitumen and all SARA fractions”. Also, the columns need headers (e.g., column 1 is the Sample, column 2 is the d13C (per mil vs VPDB) and column 3 is the fraction).  Finally, use periods rather than commas in the numbers (e.g., -27.9 … not -27,9).

 

 

 

The quality of the English is quite good.  Just a few typos and punctuation errors to fix.

Author Response

Thank you for your kind comments

all modifications done 

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, the Incursion, Crude-Oil Degradation and Calcite Cementation of an Upper Cretaceous Reservoir have been studied by bitumen composition, C-O-Sr isotopes and fluid inclusions. It's an interesting article. But there are still many deficiencies that need to be further modified. The main problem is that the sample analysis results are not comprehensive enough. It is suggested to supplement the detailed sample description and results data.

 

Some comments are as follows:

1.      The Abstract need to be rewrite.

2.      The upper and lower scripts of some chemical formulas need to be revised, such as δ13CVPDB, H3PO4 , etc.  

3.      Table 1 need to be revised

4.      In 4.2, some data such as C O isotope and fluid inclusions result are from other references, please indicate the test results for in article. If the data is referenced, analyze it in the discussion section.

5.      It is also recommended to make a data table to present the text data and reference data

6.      The discussion section need to be furtherly revised.

7.      Fig. 9 and 10 Lack of references

8.      Fig. 12, the Burial history curve need to be furtherly revised according to the results.

 

Author Response

Thank you for your kind comments

all modifications are modified in the new version

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

 

Lines 2 and 3 – use “in” before “the” (e.g., in the Zagros Basin) and my preference would be to remove the second “the” and put Kurdistan Region of Iraq in brackets.  For example “in the Zagros Foreland Basin (Kurdistan Region of Iraq)”.

 

Table 1 – the per mil sign is not needed since you wrote “per mil vs VPDB” and remove the extra vertical line in column 3

 

Figure 1 caption – Rewrite as follows “Geological map of northern Iraq showing the distribution of the Bekhme Formation (green) and Bekhme Anticline (red line) in the Kurdistan Region after [14].”

 

Figure 2 caption – Rewrite as follows “(A) chronostratigraphic column for the study are (after [15]); (B) Sampling location in the Bekhme Gorge, Kurdistan Region of northern Iraq; (C) Outcrop showing the thick bitumen seeping out of the Bekhme Formation.”

 

Lines 111 to 115 – You still need to state the precision of the bitumen d13C analysis.  Standards of some type must have been run.

 

Line 141 – Rewrite this because it sounds like you leached the sample using a mass spectrometer and the “l” in HCl should be small (e.g., 0.2 N HCl and then analyzing the solution using an ….”)

 

Line 232 You still need to define what Pr and Ph stand for (i.e., Pristane and Phytane, respectively).

 

Lines 287 to 290 – This needs to be a new sentence (e.g., Evidence shows that bitumen postdates the crystallization of saddle dolomite, whereas ….)

 

Figure 8 caption – Rewrite the last sentence of the figure caption as follows “Note the positive correlation between carbon and oxygen isotopic values of the columnar calcite if the three outliers with unusually low d18O values are removed.”

 

 

Author Response

responses in the attached file

Author Response File: Author Response.docx

Reviewer 2 Report

The article has been improved a lot after revision. But there are still some minor problems that need further revision,sucha as:

1. Line 32   Columnar calcite cementation

2. Traces of modification have not been removed, it is very messy to read, it is recommended to upload the final version.

3. a lot of minor mistakes, such as line 81-82; Recommend checking yourself.

4. It would be better to add some instructions under the figure caption.

Author Response

Reponses in the attached file

Author Response File: Author Response.docx