Researching Holocene Sediments at Bac Lieu Offshore, Vietnam with Insights from Near-Surface 2D Reflection Seismic Data

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper has value by providing a case study of applying high-resolution shallow seismic data to interpret lithology near sea bed. I suggest some revisions to improve the presentation.

 

1.       The title is misleading. “Seismic” alone commonly means low-frequency subsurface data for hydrocarbon exploration. Add “near surface” or “shallow”.

2.       Your manuscript reads like a project report, not a research paper. If purely for engineering/economics, submit to a domestic trade journal. This is an international science journal, and authors should have an international perspective.

3.       Please rewrite introduction; add reference review for current status in this field, hot issues, unsolved problems, and your research questions.

4.       Fig 1: please outline Vietnam in map.

5.       “Seismic attributes” is a general term and have to be specific (e.g., amplitude, phase, etc.) when used in text or figs.

6.       English has room for improvement.

Comments on the Quality of English Language

English has room for improvement.

Author Response

Our response to the comments of the Reviewer 1:
Thank you for your feedback.
In the response file, we have carefully copied each sentence from your comment content. We are pretty sure that we tried our best to answer all the questions. We deeply acknowledge the supports of the reviewer according to big amounts of time and efforts that you spent on my works.
In this new revision, we have rewritten paragraphs and added new figures for clarity.
Once again, thank you for considering our paper and we believe it is significantly improved.

Point-by-point response to Comments and Suggestions for Authors

Comments 1: The title is misleading. “Seismic” alone commonly means low-frequency subsurface data for hydrocarbon exploration. Add “near surface” or “shallow”.
Response 1: Yes, thank you. We have updated the title. The new title: Researching Holocene sediments at Bac Lieu offshore, Vietnam with insights from near surface 2D reflection seismic data. 

Comments 2: Your manuscript reads like a project report, not a research paper. If purely for engineering/economics, submit to a domestic trade journal. This is an international science journal, and authors should have an international perspective.
Response 2: Thank you for your comments. We have updated our paper to make it suitable to the international science journal. Our paper focuses on (i) using seismic attributes to delineate seismic boundaries and match seismic patterns with sediment types, (ii) new seismic interpretation with the support of prior geological information and drill holes for understanding the sand deposit in Bac Lieu offshore, Vietnam. Moreover, Geosciences (ISSN 2076-3263) is a peer-reviewed, open-access journal that publishes a variety oof research including original papers, short communications, technical notes, reviews, and discussions. Therefore, we believe that our updated version matches well with the theme of the journal.

Comments 3: Please rewrite introduction; add reference review for current status in this field, hot issues, unsolved problems, and your research questions.
Response 3: Yes, thank you. We have updated the introduction.

Comments 4: Fig 1: please outline Vietnam in map.
Response 4: Yes, thank you. We added a figure having Vietnam in map (Figure 1).

Comments 5:  “Seismic attributes” is a general term and have to be specific (e.g., amplitude, phase, etc.) when used in text or figs.
Response 5: Yes, I added specific information as the term “amplitude” in our paper.

Comments 6: English has room for improvement.
Response 6: Yes, thank you. We have updated our paper.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor and authors,

I send you my comments and observations on the manuscript geosciences-3449726. I hope that my comments will useful to the authors.

Comments

The manuscript "Researching Holocene sediments at Bac Lieu offshore, Vietnam with insights from high resolution 2D seismic data" presents a case study in which amplitude and other seismic attributes are used to differentiate shallow seabed sedimentary lithologies for future exploitation. The manuscript is well written and clearly details the applied methodology. The methodology applied is interesting and can be used in other studies. My recommendation is that the manuscript be accepted after minor corrections. The aspects that should be clarified and/or completed are detailed below:

The introduction is clear and contains sufficient information and references.

In the methodology section please could the authors detail how the filtering time windows have been selected. They talk about a 51 ms window in profile A15, in each profile the windows are different or they have used the same for all of them.

Line 113 “... an important parameter as demonstrated by [14].” before the reference, complete the text as it is not adequate.

In line 139 the authors refer to figure 5 instead of figure 4, please clarify.

In the methodology described in section 2.2, could the authors illustrate it with an example of their own processing?

In figure 8 delimitation colors, fill sediment is not well identified.

In figure 12 the profile names and lengths are missing, which appear in previous figures.

Best regards,

Author Response

Our response to the comments of the Reviewer 2:
Thank you for your feedback.
In the response file, we have carefully copied each sentence from your comment content. We are pretty sure that we tried our best to answer all the questions. We deeply acknowledge the supports of the reviewer according to big amounts of time and efforts that you spent on my works.
In this new revision, we have rewritten paragraphs and added new figures for clarity.
Once again, thank you for considering our paper and we believe it is significantly improved.

Point-by-point response to Comments and Suggestions for Authors

Comments 1: In the methodology section please could the authors detail how the filtering time windows have been selected. They talk about a 51 ms window in profile A15, in each profile the windows are different, or they have used the same for all of them.
Response 1: Yes, Thank you. For the running average filter, the filtering time windows were selected as 51 ms for all the 2D seismic profiles. This number came directly from the seismic equipment ‘s capabilities. The seismic machine is designed to have bottom penetration of up to 40 meters in marine sediment environment (https://geo-matching.com/products/stratabox). Therefore, with the average propagation velocity 1550 m/s, the maximum recorded time is calculated around 51 ms. Therefore, the time 51 ms can capture the entire signal range.

Comments 2: Line 113 “... an important parameter as demonstrated by [14].” before the reference, complete the text as it is not adequate.
Response 2: Thank you. We updated it.

Comments 3: In line 139 the authors refer to figure 5 instead of figure 4, please clarify.
Response 3: Yes, Thank you. We updated it.

Comments 4: In the methodology described in section 2.2, could the authors illustrate it with an example of their own processing?
Response 4: Yes, Thank you. OpendTect is a closed software which helps us to calculate seismic attributes from seismic data input and some parameters. The software operates as a “black box”, meaning it does not give any intermediate output except the final result, seismic textures. To improve the clarity of our methodology, we updated Section 2.2. Calculating seismic attributes and add a new figure for better understanding how the textural attributes are computed.

Comments 5:  In figure 8 delimitation colors, fill sediment is not well identified.
Response 5: Yes, thank you. We updated the image (Figure 8 now changes to Figure 9).

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript under review describes the results of offshore seismic surveys for the exploration of sedimentary deposits of construction materials. To a certain extent, the topic of the article corresponds to the Geoscience journal and can be published after some revision. The main observations and recommendations to the authors are summarized below.

1. In the introduction, the authors provide very rudimentary information on the physics of seismic wave propagation. This topic should either be removed from the introduction or expanded upon with references to fundamental publications that describe in more detail the phenomena that cause the formation of acoustic reflectors in the seafloor.
2. The authors used a portable StrataBox HD TM technique designed for shallow water sediment studies. It should be noted that a large amount of other equipment of this type is known in modern marine geophysics. I would recommend the authors to give a comparative characterization of such technologies in the introduction and to note the advantage of the equipment used for the task at hand.
3. The authors' use of seismic attributes in processing and interpretation of seismic data is to be welcomed. However, this section requires a more thorough description.
4. Figure 2 is very simplified. If the authors want to show the principle of the seismic wave reflection method, their propagation under the seabed should be shown.
5. The quality of FIG. 3 should be improved.
6. Reflection horizons were identified using Drill hole VC1, located onshore at a distance of approximately 20 km from the nearest seismic profile. Fig.12 shows a very schematic section of the borehole. However, it is not clear on what basis the reflectors of the seismic profiles (profile A23) and the well are compared. Also there is no information about the velocities of seismic wave propagation and, accordingly, about the real depth of horizons in the seismic sections.
7. For a clearer understanding of the results of the study it is desirable to present a geologic map of the area and bathymetric scheme of the proposed field.
8. Lines 333-334. The authors write of a new view of the spatial distribution of Holocene sediments, including “silt, sand, and clay layers, both horizontally and vertically.” However, the VC1 well column (Fig. 12) shows only Pleistocene horizons conventionally (lacking lithology and detailed stratigraphy). In addition, there are no clays in the borehole section. It should be noted on what basis the clays appeared on the seismic profiles.

Author Response

Our response to the comments of the Reviewer 3:
Thank you for your feedback.
In the response file, we have carefully copied each sentence from your comment content. We are pretty sure that we tried our best to answer all the questions. We deeply acknowledge the supports of the reviewer according to big amounts of time and efforts that you spent on my works.
In this new revision, we have rewritten paragraphs and added new figures for clarity.
Once again, thank you for considering our paper and we believe it is significantly improved.

Point-by-point response to Comments and Suggestions for Authors

The manuscript under review describes the results of offshore seismic surveys for the exploration of sedimentary deposits of construction materials. To a certain extent, the topic of the article corresponds to the Geoscience journal and can be published after some revision. The main observations and recommendations to the authors are summarized below.

Comments 1: In the introduction, the authors provide very rudimentary information on the physics of seismic wave propagation. This topic should either be removed from the introduction or expanded upon with references to fundamental publications that describe in more detail the phenomena that cause the formation of acoustic reflectors in the seafloor.
Response 1: Yes, thank you. We improved the paragraphs and deleted it.

Comments 2: The authors used a portable StrataBox HD TM technique designed for shallow water sediment studies. It should be noted that a large amount of other equipment of this type is known in modern marine geophysics. I would recommend the authors to give a comparative characterization of such technologies in the introduction and to note the advantage of the equipment used for the task at hand.
Response 2: Yes, thank you. We updated it thanks to your comment (please see Section 1. Introduction, line 40-45)

Comments 3: The authors' use of seismic attributes in processing and interpretation of seismic data is welcomed. However, this section requires a more thorough description.
Response 3: Yes, thank you. We updated it (please see Section 2.2. Calculating seismic attributes).

Comments 4: Figure 2 is very simplified. If the authors want to show the principle of the seismic wave reflection method, their propagation under the seabed should be shown.
Response 4: Yes, thank you. We updated Figure 2.

Comments 5:  The quality of FIG. 3 should be improved.
Response 5:  Yes, thank you. We improved quality of Figure 3.

Comments 6:  Reflection horizons were identified using Drill hole VC1, located onshore at a distance of approximately 20 km from the nearest seismic profile. Fig.12 shows a very schematic section of the borehole. However, it is not clear on what basis the reflectors of the seismic profiles (profile A23) and the well are compared. Also there is no information about the velocities of seismic wave propagation and, accordingly, about the real depth of horizons in the seismic sections.
Response 6: Yes, thank you. We also added two more drill holes published in the work of Nguyen, Do [1] for better comparison the drill holes and the seismic data (Reference: Nguyen, T.T., et al., Depositional sequences of the Mekong river delta and adjacent shelf over the past 140 kyr, southern Vietnam. Journal of Asian Earth Sciences, 2021. 206: p. 104634). The main reflector of the seismic profiles and the drill holes are the boundary between Holocene and Pleistocene layers. We also updated Section 3. Result and Discussion for clarity.

Comments 7:  For a clearer understanding of the results of the study it is desirable to present a geologic map of the area and bathymetric scheme of the proposed field.
Response 7: Yes, thank you. We updated Figures 1, 8 and 13 which include geologic map of the area. The seabed was calculated from the seismic data in Bac Lieu offshore, Vietnam (see Figure 11a).

Comments 8:  Lines 333-334. The authors write of a new view of the spatial distribution of Holocene sediments, including “silt, sand, and clay layers, both horizontally and vertically.” However, the VC1 well column (Fig. 12) shows only Pleistocene horizons conventionally (lacking lithology and detailed stratigraphy). In addition, there are no clays in the borehole section. It should be noted on what basis the clays appeared on the seismic profiles.
Response 8: Yes, thank you. We updated Figures 1 and 13 which include geologic map of the area and existence of clay. We also included two new drill holes which consists of clay sediment information (see Figures 13 and 14). The two new drill holes were investigated in the work of Nguyen, Do [1] for better comparison the drill holes and the seismic data (Reference: Nguyen, T.T., et al., Depositional sequences of the Mekong river delta and adjacent shelf over the past 140 kyr, southern Vietnam. Journal of Asian Earth Sciences, 2021. 206: p. 104634).

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I'm satisfied to see the significant improvements.