Terrestrial responses of low-latitude Asia to the Eocene–Oligocene  climate transition revealed by integrated chronostratigraphy

Li, Y. X.; Jiao, W. J.; Liu, Z. H.; Jin, J. H.; Wang, D. H.; He, Y. X.; Quan, C.

doi:https://doi.org/10.5194/cp-12-255-2016

Articles | Volume 12, issue 2

https://doi.org/10.5194/cp-12-255-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/cp-12-255-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 2

Research article

|

11 Feb 2016

Research article |

| 11 Feb 2016

Terrestrial responses of low-latitude Asia to the Eocene–Oligocene climate transition revealed by integrated chronostratigraphy

Y. X. Li, W. J. Jiao, Z. H. Liu, J. H. Jin, D. H. Wang, Y. X. He, and C. Quan

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Final revised paper (published on 11 Feb 2016)
Supplement to the final revised paper
Preprint (discussion started on 08 Jul 2015)

Interactive discussion

Status: closed

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

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- Supplement

RC C1123: 'Comments', Alexis Licht, 21 Jul 2015
- AC C1353: 'Responses to Reviewer Dr. Licht', Yong-Xiang Li, 16 Aug 2015
RC C1701: 'Interactive comment on cp-2015-62', Christian Rolf, 17 Sep 2015
- AC C1874: 'Responses to Reviewer Dr. Rolf', Yong-Xiang Li, 02 Oct 2015
RC C1877: 'Review', Luigi Jovane, 02 Oct 2015
- AC C1899: 'Responses to Reviewer Dr. Jovane', Yong-Xiang Li, 05 Oct 2015

Peer-review completion

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

ED: Reconsider after major revisions (09 Oct 2015) by Hugues Goosse

AR by Yong-Xiang Li on behalf of the Authors (18 Nov 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Nov 2015) by Hugues Goosse

RR by Alexis Licht (14 Dec 2015)

Suggestions for revision or reasons for rejection

The revised version of Li et al.'s manuscript is much clearer and easier to read than the first draft. The authors have been doing a great job simplifying their discussion. The introduction and geological context are now well explained, and all the important details that were lacking about the sedimentology, biostratigraphy, and the previous work in the area are present in the manuscript. However, I still have major concerns about critical issues that were not addressed during the first round of revision. I will focus my comments on the sedimentological part and on the discussion (I am not competent to discuss magnetic properties matters).

The sedimentological part of the manuscript (section 4.1) is still very weak.

1) There is still a mix of description and interpretation throughout the entire section. Please separate both.

2) Most of the sedimentological description is still based on colors (lines 21-30 page 7). You need to use lithofacies (including the description of grain-size, sedimentary figure and texture, thickness and size of the beds etc...). You can not base paleoenvironmental interpretations on descriptions that are mainly based on sediment color.

3) The 'log' in Fig. 2 is not a sedimentary log. Please make a standard sedimentary log with varying grain-size and displaying sedimentary textures. If your red layers are finer grained than the rest of the section, describe them as fine-grained and display them as finer-grained on Fig. 2. You have partly based your correlations on grain-size consideration. You must provide (at least qualitative) grain-size data in your log!

4) You argue that there are cyclic red beds in the Huangniuling Fm, but a) you do not provide any frequency data for this unit; b) your log from the Huangniuling Fm is incomplete and has no scale (please provide a real log for this unit, not a schematic one); c) the ~30 m log of the base of the Huangniuling Fm that is provided in Fig. 8 does not display any clear cyclic pattern.

5) Stop using evidence for orbital forcing in other Eocene sections as a justification for orbital forcing in yours! (pages 9 and 14). You can find sections with evidence of orbital forcing for every geological period, it has nothing to do with the late Eocene. Actually, most of these other sections do not display the same kind of orbital forcing (for instance, in Xining -the closest late Eocene section, obliquity is the prominent orbital parameter in the record). This should be discussed.

6) You keep using the word 'parasequence' without describing them. If you have identified parasequences in your section, make them clear. Evidence of parasequence IS NOT evidence for orbital forcing, as discussed during the previous round of comments.

Their preferred correlation for the GPTS is still poorly justified.
Note that I think that the correlation chosen by the authors might be right, because I would expect a major hydrological disturbance at the EOT. However, nothing in the present manuscript has convinced me of the accuracy of their choice. All the scientific arguments that are brought by the authors to justify their choice are either controversial or fallacious.

1) As I already discussed during the previous round of revision, increase in grain-size does not imply increase in sedimentation rate. The authors argue "the sedimentation rate for mudstone is generally slower than that of sandstone". This is a big mistake. There is no room here for a lengthy lesson on sedimentology, but I invite the authors to read Miall's books about deposition dynamics in continental setting or any general book about continental sedimentology basics. The coarsening upward trend in grain-size that you observed in your section likely reflects the shift from lacutrine to deltaic setting. If you want to show that there is a major change in erosion dynamics and a potential increase of sedimentation rate at the transition between both geological units, you need to show that the increase of grain-size is basin-wide, and provide logs from different parts of the basin.

2) The reply of the authors about accumulation rates in lacustrine context is not satisfying. Accumulation rates are just 2-3 times higher in hypothesis 5 compared to hypothesis 6. This is nothing compared to the actual range of accumulation rates in lacustrine environments. The authors argue that hypothesis 6 is more relevant because it has sedimentation rates that are closer to mid-Cretaceous oil shales from the same area. But I do not see why those mid-cretaceous oil shales can be use as analog; as I already noted last time, accumulation rates in lakes are highly variable, in profundal or nearshore setting.

3) I acknowledge that the authors have made a great effort in describing the paleontological context of the basin. However, their biostratigraphic considerations are based on one single taxon (Lunania) found only in two other basins. Though one taxon is better than no taxon at all, this is still too weak to make this a key argument for the correlation.

After this first round of revision, almost all the other chronostratigraphic hypotheses still look as pertinent as the one that is eventually proposed.

The paleoclimatic discussion is still weak. The authors do not discuss the meaning of obliquity forcing in their section (cf, for ideas of interpretation: Zachos et al., 2008, Nature; Abels et al., 2011, Paleo3; Xiao et al., 2010, CotP). They do not explain the reasons of a potential increase of aridity at the EOT. Is it related to summer or winter rainfall, to monsoonal dynamics? e.g. Huber and Goldner, 2012 JAES, Licht et al., 2014, Nature. What about the increase of accumulation rates: how does it compare with other Asian records? e.g. Peter Clift's paper in the South China sea, Metivier's paper in southeast Asia and Tibet.

Finally, the scientific English writing is for me comprehensible, but there are many repetitions throughout the paper and a few paragraphs that are particularly unclear (cf the legend of Fig. 2).

After this round of revision, my feelings have not changed and I think that this study needs more biostratigraphic or geochronological data to constrain the chronology of the section. I am clearly not convinced by the current set of arguments brought by the authors.

Alexis Licht

Referee Report: PDF

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RR by Christian Rolf (16 Dec 2015)

RR by Luigi Jovane (21 Dec 2015)

Suggestions for revision or reasons for rejection

The manuscript improved very much in this version both in terms of science that in the discussion.
However, there are still some minor changes that are needed before complete acceptance of the manuscript:

1- Spectral analyses need to specify: which method is used (they cited a book not the method; a method is periodogram or blackman-tukey or evolutive etc); number of points and lags used for the spectral analyses; bandwidth; confidence level; have performed re-sampling, interpolation and trend removal?; is it taped? It is fundamental to know those information because without those the spectral analyses do not have meaning.

2- It is still not clear which is the phase relation. There should be a relation such as a geological process that relates the insolation oscillation to the changes in color in the lake. This is fundamental in terms of defining the cycles in the section. I.e. is there any relation between the insolation and the precipitation pattern or winds or erosion...?

3- They continue to endorse the ensemble 6 as the only one possible. I think that also ensembles 4 and 5 as reasonably possible.
Ensemble 6 actually shows a C13r (R2) very short in comparison to C15n (N2) which is not realistic if the sedimentary rate is constant inside the Youganwo Fm. Ensemble 6 also shows sedimentary rates too low also for a deep marine basin and seems to me reasonably impossible for a continental section.
Ensample 5 shows a strong change in sedimentary rate at the Youganwo and Huangniuling boundary Fm. C15n (N1) and C15r (R2) which should have the same length are very different in the section meaning that the Huangniuling Fm have a sedimentary rate 3-4 time higher that the Youganwo Fm.
Ensemble 4 would be possible assuming very high sedimentary rates without major changes along the section.
But the main problem is that they assume that the major climate change of the EOT happens at the EO boundary. This is very wrong because the EOT is not one event and do not coincide with the EO boundary and even more with major changes in sedimentations in the oceans. Almost everywhere in the world there is first a strong change in the lithology (i.e. Scaglia Variegada to Scaglia Cinerea Fm), then the EO boundary and then the EOT. In this view, it would be much more reasonable that the Youganwo and Huangniuling boundary Fm occur inside the C15 like in the Ensemble 5.

4 - In the text they speak about grain-size changes along the section (page 14 line 5/6). I have not seen those data in the figures. It is fundamental to see those data because it is the main Indication of continuous deposition between the Youganwo and Huangniuling boundary Fm.

Minor:
-Fig 1 - It would really help to understand the section to have the topography in this maps.

-Table 1- For ensemble 5 and 6 the polarity zone R1 should be R2.

-Fig 8 - I do not think that the marine isotope curve is needed here. Alternatively they can use the final figure of Jovane et al., 2009, which show the E-O GSSP with stable isotopes and magnetostratigrapy and lithological changes.

-Please, remove the reference Brown et al., 2009. This is a grad-student thesis with very bad quality that for 3-4 years have been around trying to be accepted in various journals and at the end the editors/authors have published in their own volume because they was able to bias the review. So, I would like that Authors and Editors do not use this reference because is not scientifically reliable.

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ED: Publish subject to minor revisions (review by Editor) (31 Dec 2015) by Hugues Goosse

AR by Yong-Xiang Li on behalf of the Authors (10 Jan 2016) Author's response Manuscript

ED: Publish as is (14 Jan 2016) by Hugues Goosse

AR by Yong-Xiang Li on behalf of the Authors (18 Jan 2016) Manuscript

Short summary

An integrated litho-, bio-, cyclo-, and magnetostratigraphy constrains the onset of a depositional environmental change from a lacustrine to a deltaic environment in the Maoming Basin, China, at 33.88 Ma. This coincides with the global cooling during the Eocene-Oligocene transition (EOT) at ~ 33.7–33.9 Ma. This change represents terrestrial responses of low-latitude Asia to the EOT. The greatly refined chronology permits detailed examination of the late Paleogene climate change in southeast Asia.