High-amplitude lake-level changes in tectonically active Lake Issyk-Kul (Kyrgyzstan) revealed by high-resolution seismic reflection data

Gebhardt, Andrea Catalina; Naudts, Lieven; De Mol, Lies; Klerkx, Jan; Abdrakhmatov, Kanatbek; Sobel, Edward R.; De Batist, Marc

doi:https://doi.org/10.5194/cp-13-73-2017

Articles | Volume 13, issue 1

https://doi.org/10.5194/cp-13-73-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/cp-13-73-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 1

Research article

|

18 Jan 2017

Research article |

| 18 Jan 2017

High-amplitude lake-level changes in tectonically active Lake Issyk-Kul (Kyrgyzstan) revealed by high-resolution seismic reflection data

Andrea Catalina Gebhardt, Lieven Naudts, Lies De Mol, Jan Klerkx, Kanatbek Abdrakhmatov, Edward R. Sobel, and Marc De Batist

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Final revised paper (published on 18 Jan 2017)
Preprint (discussion started on 18 Jan 2016)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review Gebhardt et al, Lake Lake Issyk-Kul', Anonymous Referee #1, 19 Feb 2016
RC2: 'Review of Gebhardt et al', Anonymous Referee #2, 20 Feb 2016
RC3: 'Comments to Authors', Anonymous Referee #3, 22 Feb 2016
AC1: 'Answer to the comments by reviewers 1, 2, and 3', Catalina Gebhardt, 03 May 2016
EC1: 'Editor comment', Volker Rath, 24 May 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (24 May 2016) by Volker Rath

AR by Catalina Gebhardt on behalf of the Authors (08 Jul 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (02 Aug 2016) by Volker Rath

RR by Anonymous Referee #2 (13 Sep 2016)

Suggestions for revision or reasons for rejection

After my evaluation of the initial submission, this here is my second review of this manuscript. I welcome very much the changes as they addressed basically all raised issues. The new figures contribute also significantly to the quality of the paper, well done. I still have minor comments to be considered, see below, but recommend acceptance after these minor issues have been dealt with. I look forward for the final and published version.

Comments with page numbers and lines:

p.3/l. 2: Lake XY is located in Country Z, and all other sentences with '...is located....': I would not make a single-sentence statement here for the country, just put the country in () after you mention the lake. But it is politically not correct to place Lake Lisan entirely in Israel; there is the Jordan and a Palestine part of modern Dead Sea, thus also of the higher-level Lake Lisan - may be just say '...in the Levant...'

p.5/l.14: 'uplifted terraces' could also be caused by higher lake level! This feeds in discussion on early p.15, where terraces are only discussed in terms of lake level and not anymore of tectonics! It is finally mentioned on p.15/l.19 (uplifted) p.16/l.12, but I would open this section and stating the two endmember options (hydrology-induced lake-level changes vs. uplift/subsidences at the beginning of this section.

p.8 and other parts: I repeat my statement of the initial review: On seismic data, you only see reflections (not reflectors). Reflections are (apparently) truncated, not reflectors.

p.10/l.8: I also would indicate that 1500 m/s is truly a minimal velocity for such sediments: Coarse-grained deposits such as sand and gravel will be significantly faster. One should mention that thus the thicknesses are also from this perspective minimal values.

Fig. 9: The curve with the lake-level reconstruction: if the lake level would evolve in the fashion shown with the red line, it would not form delta sequences. Each delta represents, as stated in the paper elsewhere, a stillstand or slowdown of lake level. I suggest that is schematically shown in Figure 9 by making the red line step-shaped, i.e. between subsequences of 7 (falling) or all subsequences of 1 (rising).

p. 14/l.15-20: I also would mention the increased compaction in deeply buried sediments here, that will reduce the apparent sedimentation rate (apparent in contrast to mass-accumulation rate).

p.20/l.23-25: These mentioned sequence boundaries do not represent times of strong or weak Siberian highs, but they represent times of shifts: The high is strong or weak within the sequence with overall changed lake level, but the boundary indicates onset if changes, establishment of a new depositional sequence due to new climate regime.

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RR by Anonymous Referee #1 (02 Nov 2016)

Suggestions for revision or reasons for rejection

The revised manuscript ‘An extended history of high-amplitude lake-level changes in tectonically active Lake Issyk-Kul (Kyrgyzstan), as revealed by high-resolution seismic reflection data’ by Gebhardt et al is greatly improved. All comments of the first review are included and if not, the authors deliver good arguments for not following the suggestions. Especially the inclusion of the additional seismic profile makes the main conclusion of the manuscript more convincing. Figures are improved as well.
I only have a few remaining minor comments:

1) Page 6, Line 10: You mention that it is not possible to trace sequence boundaries between the eastern and western delta complexes but it was still possible to identify the same sequences in both areas due to similar TWT depth. This is a weak argument as tilting may have occurred due to tectonic activity. Can you provide other arguments? Maybe the succession of sedimentary units with similar characteristics identified in both areas supports this statement and should be mentioned. Perhaps you have additional arguments for this statement.
2) Page 8, Line 5: I do not understand this sentence: Erosion truncates older strata hence form toplaps or onlaps onto the erosional discordance. What is eroded and what form toplaps and onlaps? Toplap is a termination against an upper boundary caused by non-deposition. Hence, they cannot be toplap onto the erosional surface. Check also caption for Fig. 3 where you have the identical sentence. I cannot follow your nomenclature in Fig. 3b and 3c. Some of your downlaps seem to be onlaps (blue lines on Fig. 3b). The red labels are onlaps and toplaps but toplap is against an upper boundary and onlap against a lower boundary. Check and clarify.
3) Mark the profiles shown in the manuscript much clearer on Fig. 1
4) You show seismic line 49 on Fig. 3 and 5. Is it possible to combine these two figures?
5) Page 9, Line 20. You mention that the sequence boundary between S3 and S4 could not be identified. What does it mean? Is this unit comprising both S3 and S4 or only one of these units? I understand your text in that way, that S5 is the same sequence on both profiles (Fig. 5 and 6) but you used different colours for Unit S5 on the Figs. 5 and 6. Use same colours. Also use similar colours for S3 and S4 on Fig. 5, which is only one Unit on Fig. 6.
6) Page 9, Line 24: Should be issyk049 not issyk0149.
7) My impression is that you see delta sediments in S6 on the most western part of Fig. 6, which are not marked on the figure. Do you agree? If yes, please mark them.
8) Page 11, Line 25: lines 26 and 27: Repetition from the previous paragraph.
9) Line 12, Line 7 and following: You state that S3 is deposited during a lake level rise. The boundary to S2 may be erosive in parts but seem to be non-erosive in other parts. In the previous section you state that S3 cannot be distinguished from S3 or it is completely eroded. If S3 is deposited during a rising lake level and you do not have very clear signs of erosion at the boundary between S2 and S3, I cannot see, how S3 should have been eroded in the eastern part of the lake. In addition, a few lines up you state that S3 is mostly transparent in the eastern part. This would imply that S3 is indeed deposited which is questioned in the previous paragraph. Clarify.
10) Page 17, Line 16: The anticlinal structures are not mentioned in the text before but only shown on Fig. 1. This is a bit confusing. I am aware that you decided to delete the part with the anticlinal structure but if you need them for the discussion, you have to introduce them somewhere. I think you can delete the remark on the anticlinal structures. Just mention that similar depths of the deltas in the western and eastern part do not support the idea that both areas experienced significantly different histories.
11) Page 21, Line 10: Not really still stands but times of relatively constant lake levels.

I am not a native English speaker; hence, I have not made any language corrections.

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ED: Publish subject to minor revisions (review by Editor) (10 Nov 2016) by Volker Rath

AR by Catalina Gebhardt on behalf of the Authors (14 Nov 2016) Author's response Manuscript

ED: Publish as is (21 Nov 2016) by Volker Rath

AR by Catalina Gebhardt on behalf of the Authors (21 Nov 2016) Author's response Manuscript

Short summary

Seismic profiles from the western and eastern deltas of Lake Issyk-Kul were used to identify lake-level changes of up to 400 m. Seven stratigraphic sequences were identified, each containing a series of delta lobes that were formed during former lake-level stillstands. Lake-level fluctuations point to significant changes in the strength and position of the Siberian High and the mid-latitude Westerlies. Their interplay is responsible for the amount of moisture that reaches this area.