Geochemical Characteristics of the Lower Cretaceous HengTongshan Formation in the Tonghua Basin, Northeast China: Implications for Depositional Environment and Shale Oil Potential Evaluation

Round 1

Reviewer 1 Report

This paper shows an accurate and detailed study of rocks from cores, achieving good results that can be of high economic interests, apart from the mere scientific interest. 

I recommend, however, to the Authors to carefully review the present written form, that suffer of unnecessary repetition throughout the text. The following are some suggestions of simplifications.

Lines 26-30   “The organic matter in the Hengtongshan Formation has the characteristics of lacustrine or special bacteria-influenced facies. Overall, the source material in the source rock in the Hengtongshan Formation is a mixture of aquatic organisms (algae and bacteria) and higher plants, and there may be some marine organic components present in some strata.”

• What “special” means? Explain or remove
• “the source material in the source rock” is confusing. Are you meaning “the provenance of organic matter in the source rocks”
• In general, is there a repetition in the above outlined sentences?

Lines 30-31    “The organic matter was deposited and preserved in a saline reducing environment, which was conducive to the enrichment and preservation of organic matter.”

Here too, it sounds to be a repetition… please simplify.

Line 33   “and the lake may have experienced a short-term transgression that led to an increase in the salinity of the lake water.”

Can be changed in: “and the lake may have experienced a short-term marine ingression with the increase in the salinity.”

Line 73   “the high-precision organic geochemistry of the Hengtongshan Formation is studied”

Can be changed in: “a highly detailed organic geochemistry study of the Hengtongshan Formation is carried on”

Line 87 “in the quiet period of basin development” What means this sentence? In a quite period, meaning no significant tectonic events acting?

Line 89   “Hercynian movement and the Mesozoic Yanshan movement” movement stays for contractional tectonic events?

Line 98 “cut and transform the surface” What is for “transform”? Dissecting, offsetting, folding?

Lines 408-411  “According to previous studies, during the depositional period of the Hengtongshan Formation, there was no large-scale strong volcanic activity in the Tonghua Basin, resulting in a basin-wide quiescent stage, and sediments were deposited under a humid and warm climate, with only occasional small-scale volcanic activity occurring near the faults in the basin (Zhao et al., 1996; Li et al., 1998).”

Apparently contradicting sentence. May be you can change in “According to previous studies, during the depositional period of the Hengtongshan Formation, only occasional small-scale volcanic activity occurred near the faults in the Tonghua Basin, resulting in a basin-wide, relatively quiescent stage, and sediments were deposited under a humid and warm climate.”

Line 413  “basin, which stratified the water there”  may be changed in “basin, causing stratification of water masses”

Lines 415-416  “which is conducive to the accumulation of organic matter by stimulating microorganisms at the bottom of the lake basin.” May be changed in: “stimulating the growth of microorganism at the bottom of the lake and, therefore, increasing the accumulation of organic matter” Is this the sense?

Lines 444-448  “According to the oil and gas evidence observed during drilling, the oil and gas generated in the source rock may have migrated to units with high porosities. Considering the formation depth of the discovered oil and gas and the geochemical test results for source rocks at various depths, the range of shale oil migration was likely very short.” These sentences are not well understandable. Did a migration of oil and gas occur?

Line 449 “range of natural gas migration may have been relatively long.” Relatively long? Or Relatively high?

Figures

Fig1 c - A caption for the stratigraphic column is lacking. Please add the keys for the symbols and colours!

Fig 1 b – the figure as it is is barely redable due to its size. Too small!

Author Response

Dear reviewer: I'm glad to receive your suggestions and comments . These suggestions are highly scientific and professional, and detailed, which will definitely help to improve the quality of papers. After studying your comments carefully, I made in-depth thinking to analyze the problems and solve them under your guidance. Here is my reversion to each question. 1.Lines 26-30   “The organic matter in the Hengtongshan Formation has the characteristics of lacustrine or special bacteria-influenced facies. Overall, the source material in the source rock in the Hengtongshan Formation is a mixture of aquatic organisms (algae and bacteria) and higher plants, and there may be some marine organic components present in some strata.”What “special” means? Explain or remove；“the source material in the source rock” is confusing. Are you meaning “the provenance of organic matter in the source rocks”In general, is there a repetition in the above outlined sentences? Wentong：modified to“The provenance of organic matter in the source rocks in the Hengtongshan Formation is a mixture of aquatic organisms (algae and bacteria) and higher plants, and there may be some marine organic components present in some strata.” 2.Lines 30-31 “The organic matter was deposited and preserved in a saline reducing environment, which was conducive to the enrichment and preservation of organic matter.”Here too, it sounds to be a repetition… please simplify. Wentong：modified to“The organic matter was deposited and preserved in a saline reducing environment.” 3.Line 33   “and the lake may have experienced a short-term transgression that led to an increase in the salinity of the lake water.”Can be changed in: “and the lake may have experienced a short-term marine ingression with the increase in the salinity.” Wentong：modified to“and the lake may have experienced a short-term marine ingression with the increase in the salinity.” 4.Line 73 ：“the high-precision organic geochemistry of the Hengtongshan Formation is studied”.Can be changed in: “a highly detailed organic geochemistry study of the Hengtongshan Formation is carried on” Wentong：modified to“a highly detailed organic geochemistry study of the Hengtongshan Formation is carried on” 5.Line 87 “in the quiet period of basin development” What means this sentence? In a quite period, meaning no significant tectonic events acting? Wentong：modified to“The target layer studied in this paper is the Lower Cretaceous Hengtongshan Formation, which was mainly formed under humid and warm climate conditions after volcanic activity” Line 89   “Hercynian movement and the Mesozoic Yanshan movement” movement stays for contractional tectonic events? Wentong：The cited literature does not indicate how the late Paleozoic Hercynian movement and the Mesozoic Yanshan movement affected the geological structural evolution of the Tonghua basin.So delete it. Line 98 “cut and transform the surface” What is for “transform”? Dissecting, offsetting, folding? Wentong：modified to“NW faults extend to the surface and produce visible faults on the surface.” 8.Lines 408-411  “According to previous studies, during the depositional period of the Hengtongshan Formation, there was no large-scale strong volcanic activity in the Tonghua Basin, resulting in a basin-wide quiescent stage, and sediments were deposited under a humid and warm climate, with only occasional small-scale volcanic activity occurring near the faults in the basin (Zhao et al., 1996; Li et al., 1998).”Apparently contradicting sentence. May be you can change in “According to previous studies, during the depositional period of the Hengtongshan Formation, only occasional small-scale volcanic activity occurred near the faults in the Tonghua Basin, resulting in a basin-wide, relatively quiescent stage, and sediments were deposited under a humid and warm climate.” Wentong：modified to“According to previous studies, during the depositional period of the Hengtongshan Formation, only occasional small-scale volcanic activity occurred near the faults in the Tonghua Basin, resulting in a basin-wide, relatively quiescent stage, and sediments were deposited under a humid and warm climate.” 9.Line 413  “basin, which stratified the water there”  may be changed in “basin, causing stratification of water masses” Wentong：modified to“may be changed in “basin, causing stratification of water masses” 10.Lines 415-416  “which is conducive to the accumulation of organic matter by stimulating microorganisms at the bottom of the lake basin.” May be changed in: “stimulating the growth of microorganism at the bottom of the lake and, therefore, increasing the accumulation of organic matter” Is this the sense? Wentong：modified to“stimulating the growth of microorganism at the bottom of the lake and, therefore, increasing the accumulation of organic matter” 11.Lines 444-448  “According to the oil and gas evidence observed during drilling, the oil and gas generated in the source rock may have migrated to units with high porosities. Considering the formation depth of the discovered oil and gas and the geochemical test results for source rocks at various depths, the range of shale oil migration was likely very short.” These sentences are not well understandable. Did a migration of oil and gas occur? 12.Line 449 “range of natural gas migration may have been relatively long.” Relatively long? Or Relatively high? Wentong：Previously, it was considered that the migration range of shale oil may be very short because the components of shale oil samples collected through drilling are similar to those of shale extract, so the migration distance is relatively short. However, the reason is not sufficient and is not the main focus of the paper, so we decided to delete it. Figures 13.Fig1 c - A caption for the stratigraphic column is lacking. Please add the keys for the symbols and colours! Fig 1 b – the figure as it is is barely redable due to its size. Too small! Wentong：Figures 1-B and 1-C have been adjusted. And I edited the modified Manuscript by English editing service. Thank you very much for your guidance, if there are still deficiencies and need to be corrected, please correct, thank you again! Best regards, Wentong He

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors

this study concerns the Geochemical characteristics of the Lower Cretaceous Hengtongshan Formation in the Tonghua Basin, Northeast China: Implications for Depositional Environment and Shale Oil Potential Evaluation

The manuscript is very interesting but in some parts unclear.

The Authors would separate the mineralogy from the lithology and make a paragraph mineralogy, therefore I recommend making only one paragraph 4.2

The figures and tables are not always clear and some are not well explained in the text.

The References are complete and all significantly useful in the text.

I think the paper is not suitable to be published in the current form, but only with major revisions.

Please check also the attached pdf where are reported the suggestions of modification.

Best regards

Comments for author File: Comments.pdf

Author Response

Dear reviewer: I'm glad to receive your suggestions and comments . These suggestions are highly scientific and professional, and detailed, which will definitely help to improve the quality of papers. After studying your comments carefully, I made in-depth thinking to analyze the problems and solve them under your guidance. Here is my reversion to each question. 1.Line 115：I don’t understand what you mean. Wentong：modified to“13 representative samples were selected to observe the lithology, kerogen organic matter and vitrinite reflectance (RO), and the whole rock minerals were analyzed.102 source rock samples were selected for organic element analysis and rock pyrolysis experiments.32 source rock samples were extracted.” 2.Line 176：Figure 4 should be explained in detail in the text. Wentong：Each part of Figure 4 will be covered in the following related discussion and marked. 3.Line 181：The data reported in Tab 1 should be discussed first and then the XRD data in Tab. 2, then I would separate the mineralogy from the lithology and make a paragraph mineralogy. Wentong：The text has been revised. 4.Line 183：In Tab 2 you should insert an average column because otherwise it is not easy to read. Wentong：Have inserted an average column. 5.Line 189：4.2 Please insert the paragraph Mineralogy. Wentong：The text has been revised. 6.Line 190：4.3 Bulk geochemical parameters. Wentong：The text has been revised. 7.Line 205：Tab 1 is difficult to read and needs to be reorganized better…. Wentong：I divided Table 1 into sections by page for easy reading. 8.Line 227：In Tab 3 an average column should be inserted because otherwise it is not easy to read Wentong：Have inserted an average column. 8.Line 234：4.5 Wentong：The text has been revised. 10.Line 239：Fig.7 does not read should be improved Wentong：I enlarge the font in the picture. 11.Line 246：4.5.1 Wentong：The text has been revised. 12.Line 273：4.5.2. Wentong：The text has been revised. 13.Line 280：the figures are difficult to follow, because they do not follow the order of the numbering in the text Wentong：The positions of Figures 7 and 8 have been adjusted. 14.Line 320：4.5.3 Wentong：The text has been revised. Figure: 15.Line 628：I suggest the Authors to explain the figure well in the text Wentong：The explanation of Figure 3 is added in the paper. 16.Line 631：figures e-h: the size bar and the magnification at which the photographs were taken under the microscope must be inserted. Wentong：I have modified the content of the map and added the size bar and the magnification at which the photographs were taken under the microscope. 17.Line 633：figures c-d are not understood. Wentong：Explanation of this figure has been added. 18.Line 643：the figure is difficult to read. Wentong：I have revised the contents of the map and enlarged the font And I edited the modified Manuscript by English editing service. Thank you very much for your guidance, if there are still deficiencies and need to be corrected, please correct, thank you again! Best regards, Wentong He

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear Authors

the manuscript has been significantly improved and is may be accepted in this form for publication on Applied Sciences.

Best regards