the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Oct 2021
Low-latitude climate change linked to high-latitude glaciation during the Late Paleozoic Ice Age: evidence from the terrigenous detrital kaolinite
Abstract. The Late Paleozoic Ice Age (LPIA; ca. 360–260 million years ago) was one of the most significant glacial events in Earth history that records cycles of ice advance and retreat in southern high-latitude Gondwana and provides a deep-time perspective for climate-glaciation coevolution. However, climate records from the LIPA are poorly understood in low latitudes, particularly in the North China Plate (NCP) on the eastern Palaeo-Tethys. We address this through a detailed mineralogical study of the marine-continental sedimentary succession in the Yuzhou Coalfield from the southern NCP in which we apply Zircon U-Pb dating, biostratigraphy, and high-resolution clay mineral composition to reconstruct latest Carboniferous to early Permian chronostratigraphy and climate change. The Benxi, Taiyuan, and Shanxi formations in the study area are assigned to the Gzhelian, Asselian-Artinskian, and Kungurian-Roadian stages respectively and the Carboniferous Permian lithostratigraphy across NCP recognized as widely diachronous. Detrital micromorphology of kaolinite under scanning electron microscopy and illite crystallization indicates kaolinite contents to be a robust proxy for palaeoclimate reconstruction. Kaolinite data show alternating warm-humid and cool-humid climate conditions that are roughly consistent with the calibrated glacial-interglacial successions recognized in high-latitude eastern Australia, including the glaciations P1 (Asselian-early Sakmarian) and P2 (late Sakmarian-early Artinskian), as well as the climatic transition to glaciation P3 (Roadian). Our results indicate a comparatively cool-humid and warm-humid climate mode in low-latitude NCP during glacial and interglacial periods, and this is a significant step toward connecting climate change in low-latitudes to high-latitude glaciation during the LPIA.
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RC1: 'Comment on cp-2021-108', Anonymous Referee #1, 13 Oct 2021
Title: Low-latitude climate change linked to high-latitude glaciation during the Late Paleozoic Ice Age: evidence from the terrigenous detrital kaolinite Author(s): Peixin Zhang, Jing Lu, Minfang Yang, Longyi Shao, Ziwei Wang, and Jason Hilton MS No.: cp-2021-108
Recommendation: Rejected
The paper is well written and presents interesting results concerning past climate conditions for North China. However I identified a fundamental issue requiring clarification. Indeed the authors investigate local climate conditions without presenting and discussing the geological setting of the area. In the absence of data highlighting the geological evolution of this site, most of statements presented in the discussion (4.2) remain too speculative to support authors’ conclusions. I encourage the authors to resubmit their article after significant rewriting of the manuscript, with a full description of the continental environment and its temporal evolution (which explains why I recommend “rejected” rather than “major revision”).
In addition here is a list a suggestions to improve the manuscript
- One major issue is the determination of the paleolatitude of the site through time with good precision. In principle, local paleomagnetic data could decide this issue because from them paleolatitude can be estimated. Moreover, authors used a unique reconstruction (Blakey 2011) for a period extending over 30 myr (300-270Ma) without discussing most recent reconstructions with finer time slices (for details, see https://www.earthbyte.org/category/resources/data-models/paleogeography/). Because the hydrological cycle (thus the weathering) depends on the Hadley cell in low latitudes this point must be solved in order to discuss the accuracy of findings in term of Earth's climate.
- lines 195-200: the time-correlation deserves more attention. Based on the fig.9, the atmospheric pCO2 for S-II and S-IV overcomes the one for S-3 while this state appears as “warm and humid”.
Citation: https://doi.org/10.5194/cp-2021-108-RC1 -
AC1: 'Reply on RC1', Jason Hilton, 30 Oct 2021
Dear reviewer,
Thank you for your assessment of our paper “Low-latitude climate change linked to high-latitude glaciation during the Late Paleozoic Ice Age: evidence from the terrigenous detrital kaolinite". The points raised are valid so the review provides us with the opportunity to expand our manuscript to address them comprehensively. However, we disagree with the recommendation of rejecting the manuscript because of the points raised as (i) the information is readily available and has now been incorporated into the revised manuscript, and (ii) this does not alter any of our results or conclusions in any way. Below we address each point individually and consider them fully resolved.
In the submission system, we cannot upload the revised manuscript. Therefore, we outline the changes we have made as indicated on the updated version of the manuscript showing marked changes (see below). These are provided in full in the attached pdf file.
We hope you find these changes agreeable.
Yours faithfully and on behalf of co-authors,
Jason Hilton
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AC2: 'Reply on AC1', Jason Hilton, 30 Oct 2021
Detailed responses to reviewer #1's comments:
Reviewer #1:
- The paper is well written and presents interesting results concerning past climate conditions for North China. However I identified a fundamental issue requiring clarification. Indeed the authors investigate local climate conditions without presenting and discussing the geological setting of the area. In the absence of data highlighting the geological evolution of this site, most of statements presented in the discussion (4.2) remain too speculative to support authors’ conclusions. I encourage the authors to resubmit their article after significant rewriting of the manuscript, with a full description of the continental environment and its temporal evolution (which explains why I recommend “rejected” rather than “major revision”).
Response: We thank the reviewer for their comments here. We added the contents about the geological background and environmental evolution of the study area in section 4.2, and we have added additional figures to demonstrate this.
The details are as follows: “Changes in continental plate position, land-sea distributions, ice extent in Gondwana, atmospheric CO2 and monsoonal rainfall are considered the main factors controlling climate change in low latitudes during the LPIA (Tabor and Poulsen, 2008; Cao et al., 2017). In the study area, local paleomagnetic data demonstrate that no large-scale plate motion occurred from the early to late Early Permian (Zhu et al., 1996). Through this time interval, the region remained in an equatorial humid climate zone (Zhu et al., 1996) on the southern margin of the North China Plate (NCP) in proximity to the sea (Fig. 9). Following regression of the epicontinental sea in the earliest Permian (Fig. 9a, b), sedimentary environments gradually developed from coastal tidal flat deposition to a series of shallow-water delta sedimentary systems comprising fluvial and tidally influenced offshore peat-bearing deposits (Zhu et al., 1996; Yang and Lei, 1987; Fig. 9). Fossil plants were widespread and abundant, comprising stable, tropical, ever-wet communities dominated by lycophytes, equisetophytes, marattialean ferns and pteridosperms (Zhu et al. 1996; Yang and Lei, 1987; Yang, 2006; Hilton and Cleal, 2007). Collectively, this information builds a picture of stability in continental plate position and land-sea distributions. The sedimentary record provides no evidence of monsoons. Consequently, we consider that waxing and waning of ice sheets in high latitude Gondwana and changes in global atmospheric CO2 were the main factors affecting climate change in the study area through the LPIA.”
[Please see pdf for revised figure]
Figure 9. Lithofacies palaeogeograpy map from late Bashkirian to Wordian in the North China Plate (modified from Shao et al., 2014).
We collected palaeomagnetic data from the Dafengkou section in Yuzhou coalfield from early to late Early Permian. These data show that from the early to late Early Permian, the paleolatitude change in the study area is between 11.0°N and 11.4°N, that is, it is within the equatorial humid climate zone (Zhu et al., 1996).
Table 1 Permian ancient geomagnetic parameters and latitude in Dafengkou section
Period
sampling point
mean direction of magnetization
α95
stability valuation
Paleomagnetic pole position
Paleolatitude position
D (°)
I (°)
K (°)
Plat.(°N)
Plong.(°N)
Dp
Dm
P21
6
143.2
-21.2
12.9
19.4
R
-49.2
177.4
10.7
20.4
11.0
P11
3
124.9
-22.0
82.1
13.7
R
-35.1
192.5
7.7
14.5
11.4
P1
9
136.9
-21.7
16.1
13.2
-44.6
183.4
7.4
14.0
11.2
[Please see pdf for revised figure]
Figure 11. Comparison of climate change, glaciations, d18O, and pCO2 records from the Gzhelian Stage of the Carboniferous to the Roadian Stage of the Permian. Age stratigraphic framework from Shen et al. (2019); a, Climate stages interpreted from the studied section; b, Interpreted climatic records with blue representing intervals of climate cooling while yellow represents climatic warming based on fluctuating climate signals from kaolinite content from the studied section, and climate type interpreted from the studied section. c, Records of glaciation events in Australia from Fielding et al. (2008), Frank et al. (2015), and Garbelli et al. (2019); d, Oxygen isotope values from Korte et al. (2005) and Grossman et al. (2008); e, Global pCO2 concentration from Montañez et al. (2007), Foster et al. (2017) and Richey et al. (2020). Note: the red line from Foster et al. (2017), the black line comes from Richey et al. (2020). Abbreviations: Gzh. = Gzhelian; Sak. = Sakmarian; Cli. S. = Climate stage; Clim. type = Climate type; 21# = Coal 21 seam; Temp. = Temperature.
References:
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Cecil, C. B., Dulong, F. T., West, R. R., Stamm, R., Wardlaw, B. and Edgar, N. T.: Cliamte controls on the stratigraphy of a Middle Pennsylvanian cyclothem in North America, in Climate Controls on Stratigraphy, pp. 151–180, SEPM (Society for Sedimentary Geology)., 2003.
Clapham, M. E. and James, N. P.: Paleoecology Of Early-Middle Permian Marine Communities In Eastern Australia: Response To Global Climate Change In the Aftermath Of the Late Paleozoic Ice Age, Palaios, 23(11), 738–750, doi:10.2110/palo.2008.p08-022r, 2008.
Frank, T. D., Shultis, A. I. and Fielding, C. R.: Acme and demise of the late Palaeozoic ice age: A view from the southeastern margin of Gondwana, Palaeogeogr. Palaeoclimatol. Palaeoecol., 418, 176–192, doi:10.1016/j.palaeo.2014.11.016, 2015.
Koch, J. T. and Frank, T. D.: The Pennsylvanian-Permian transition in the low-latitude carbonate record and the onset of major Gondwanan glaciation, Palaeogeogr. Palaeoclimatol. Palaeoecol., 308(3–4), 362–372, doi:10.1016/j.palaeo.2011.05.041, 2011.
Lowry, D. P., Poulsen, C. J., Horton, D. E., Torsvik, T. H. and Pollard, D.: Thresholds for Paleozoic ice sheet initiation, Geology, 42(7), 627–630, 2014.
Montañez, I. P. and Poulsen, C. J.: The Late Paleozoic Ice Age: An Evolving Paradigm, Annu. Rev. Earth Planet. Sci., 41(1), 629–656, doi:10.1146/annurev.earth.031208.100118, 2013.
Montañez, I. P., Tabor, N. J., Niemeier, D., DiMichele, W. A., Frank, T. D., Fielding, C. R., Isbell, J. L., Birgenheier, L. P. and Rygel, M. C.: CO2-Forced Climate and Vegetation Instability During Late Paleozoic Deglaciation, Science (80-. )., 315(5808), 87–91, doi:10.1126/science.1134207, 2007.
Poulsen, C. J., Pollard, D., Montañez, I. P. and Rowley, D.: Late Paleozoic tropical climate response to Gondwanan deglaciation, Geology, 35(9), 771–774, doi:10.1130/G23841A.1, 2007.
Powell, M. G.: Latitudinal diversity gradients for brachiopod genera during late Palaeozoic time: links between climate, biogeography and evolutionary rates, Glob. Ecol. Biogeogr., 16(4), 519–528, doi:10.1111/j.1466-8238.2007.00300.x, 2007.
Richey, J. D., Montañez, I. P., Goddéris, Y., Looy, C. V, Griffis, N. P. and DiMichele, W. A.: Influence of temporally varying weatherability on CO2-climate coupling and ecosystem change in the late Paleozoic, Clim. Past, 16(5), 1759–1775, doi:10.5194/cp-16-1759-2020, 2020.
Roy, D. K. and Roser, B. P.: Climatic control on the composition of Carboniferous-Permian Gondwana sediments, Khalaspir basin, Bangladesh. Gondwana Res., 23, 1163–1171. doi: 10.1016/j.gr.2012.07.006, 2013.
Stemmerik, L.: Influence of late Paleozoic Gondwana glaciations on the depositional evolution of the northern Pangean shelf, North Greenland, Svalbard, and the Barents Sea, Resolv. Late Paleoz. Ice Age Time Sp., 441, 205, 2008.
Tabor, N. J. and Poulsen, C. J.: Palaeoclimate across the Late Pennsylvanian-Early Permian tropical palaeolatitudes: A review of climate indicators, their distribution, and relation to palaeophysiographic climate factors, Palaeogeogr. Palaeoclimatol. Palaeoecol., 268(3–4), 293–310, doi:10.1016/j.palaeo.2008.03.052, 2008.
Waterhouse, J. B. and Shi, G. R.: Evolution in a cold climate, Palaeogeogr. Palaeoclimatol. Palaeoecol., 298(1–2), 17–30, doi:10.1016/j.palaeo.2010.08.022, 2010.
Yang, G.: The Permian cathaysian flora in western Henan province, China-Yuzhou flora., 1–76, 2006.
Yang, Q. and Lei, S.: Depositional Environments and Coal-forming Characteristics of Late Palaeozoic Coal Measures in Yuxian, Henan Province., 1987.
Zhu, H., Yang, G. and Sheng, A. X.: A study on palaeomagnetism of Permian strata in the Dafengkou section, Yuzhou, Henan Province, Acta Geol. Sin., 70(2), 121–128, 1996.
Citation: https://doi.org/10.5194/cp-2021-108-AC2 - The paper is well written and presents interesting results concerning past climate conditions for North China. However I identified a fundamental issue requiring clarification. Indeed the authors investigate local climate conditions without presenting and discussing the geological setting of the area. In the absence of data highlighting the geological evolution of this site, most of statements presented in the discussion (4.2) remain too speculative to support authors’ conclusions. I encourage the authors to resubmit their article after significant rewriting of the manuscript, with a full description of the continental environment and its temporal evolution (which explains why I recommend “rejected” rather than “major revision”).
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AC2: 'Reply on AC1', Jason Hilton, 30 Oct 2021
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AC1: 'Reply on RC1', Jason Hilton, 30 Oct 2021
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RC2: 'Comment on cp-2021-108', Anonymous Referee #2, 30 Oct 2021
Clay mineralogy is well outside my area of expertise so my comments are confined to the paleogeography and general aspects of chronostratigraphic correlations which are essential in reaching conclusions about climate responses across latituide in the Late Paleozoic Ice Age.
The paleogeographic context is inadequate. Fig. 1a is a cartoon with virtually no documentation of how the North China Block was positioned in the Early Permian, e.g., Liu1990 cited is a one-page comment/reply and Blakely2011 has no quantitative analysis fordetermination of paleolatitude, whereas Yang+Lei1987 and Zhou2002 are not readily accessible and would need to be described here for a broader audience. The authors state that the NCP was located at ~5-15°N but there could be a huge lithostratigraphic consequence between being in the tropical humid belt (5°) and the arid belt (15°). Unless the authors have alternative methods, paleolatitudes are based on paleomagnetism and hence the authors might consult references to the modern paleomagnetic literature and syntheses for the NCB and Tethyan environs in papers like Torsvik+2012 ESR or Kent+Muttoni2020 Palaeo3.
There is a bewildering array of regional and global stage names and fossil zonations for the Late Paleozoic but one would have to be a real aficionado to decipher from Fig. 1c where in the geologic column all the names are supposed to be: Early Permian? A very rudimentary paleogepographic map (Fig. 1b ), which should at least show lines of paleolatitude, is labeled Cisuralian but that time-stratigraphic interval is not indicated in the stratigraphic column in Fig. 1b.
Two U-Pb dates are quoted as 270.7 Ma and 299.4 Ma based on 5-11 zircons selected from an astonishing number (1000 to 1500!) grains extracted from two levels. The technique is not described (presumably laser-ablation ICPMS) nor how the 1:100 grains were selcected, or what was done with the remaining zircon grains (were they measured?). What about potential lead-loss? These dates are extremely important for the chronostratigraphy and correlation to the wider world and must be described in much more detail; the reportage of Gehrels+2020 Geochro may provide a useful example.
A thckness-age plot (with cumulative thickness scales and not simply scale also shown in the stratigraphic diagrams in Figs. 1c, 4, 8,) would be useful to access temporal resolution of stages and fossil zonations.
In summary, ihe authors should take the opportunity to provide a broader and deeper context for their results, including more detailed map and stratigraphic charts with explicit proposed tie-lines to standard columns, especially when so much of the literature is so difficult to obtain let alone read by most of us outside of China. As it stands, the spatiotemporal and this climate significance of the work remains unfortunalety superficial.
My suggestion is that majpr revisions are needed before the paper can be reconsidered.
Citation: https://doi.org/10.5194/cp-2021-108-RC2 -
AC3: 'Reply on RC2', Jason Hilton, 06 Nov 2021
Detailed responses to reviewer #2's comments:
Dear Editor,
Thank you very much for reviewing our paper “Low-latitude climate change linked to high-latitude glaciation during the Late Palaeozoic Ice Age: evidence from the terrigenous detrital kaolinite" and giving very valuable comments. The points raised are valid so the review provides us with the opportunity to expand our manuscript to address them comprehensively. Below we address each point individually and consider them fully resolved.
In the submission system, we cannot upload the revised manuscript. Therefore, we outline the changes we have made as indicated on the updated version of the manuscript showing marked changes (in red) as an attachment here.
We hope you find these changes agreeable and we look forwards to hearing from you in the future.
Yours sincerely and on behalf of co-authors,
Jason Hilton
Reviewer #2:
Overall, reviewer 2 makes some detailed comments on the geological context of the study but nothing that impacts the results or conclusions presented. We will reply to their comments individually below.
1. The paleogeographic context is inadequate. Fig. 1a is a cartoon with virtually no documentation of how the North China Block was positioned in the Early Permian, e.g., Liu1990 cited is a one-page comment/reply and Blakely2011 has no quantitative analysis for determination of paleolatitude, whereas Yang+Lei1987 and Zhou2002 are not readily accessible and would need to be described here for a broader audience. The authors state that the NCP was located at ~5-15°N but there could be a huge lithostratigraphic consequence between being in the tropical humid belt (5°) and the arid belt (15°). Unless the authors have alternative methods, paleolatitudes are based on paleomagnetism and hence the authors might consult references to the modern paleomagnetic literature and syntheses for the NCB and Tethyan environs in papers like Torsvik+2012 ESR or Kent+Muttoni2020 Palaeo3.
Response: We disagree with the overall sentiment here – the information is provided is coparable to other papers on the topic utilizing similar appraches, but if the reviewer wants us to provide additional context, we can do that. We note this does not change the results or conclusions presented.
We have reviewed palaeomagnetic data from the Dafengkou section in the Yuzhou coalfield from the early to late Early Permian (including the Taiyuan, Shanxi, and Shangshihezi formations). These data show that from the early Early Permian to late Early Permian, the palaeolatitude change in the study area is between 11.0°N and 11.4°N, that is, it is within the equatorial humid climate zone (Zhu et al., 1996).
Table 1 The Characteristic remanent magnetization directions, palaeomagnetic pole, and palaeolatitude of Permian of Dafengkou profile in Yuzhou, Henan Province
Period
sampling point
mean direction of magnetization
α95
stability valuation
Palaeomagnetic pole position
Palaeolatitude position
D (°)
I (°)
K (°)
Plat.(°N)
Plong.(°N)
Dp
Dm
P21
6
143.2
-21.2
12.9
19.4
R
-49.2
177.4
10.7
20.4
11.0
P11
3
124.9
-22.0
82.1
13.7
R
-35.1
192.5
7.7
14.5
11.4
P1
9
136.9
-21.7
16.1
13.2
-44.6
183.4
7.4
14.0
11.2
According to palaeomagnetic data from the Dafengkou section in the Yuzhou Coalfield during the early Early Permian (P1) to late Early Permian (P21) (Table 1; see below), we determined the exact location of the study area through time and have modified this in the geological background section. We have revised figure 1, and replaced “Blake’s paleogeographic map (Fig. 1a)” with the “generalized tectonic map of present-day China”, and also replaced the “Palaeofacies map of the NCP during the Cisuralian (modified from Liu, 1990) (Fig. 1b)” with the “Simplified tectonic map of the present-day NCP (modified from Liu et al., 2013)”. In these maps, we have added modern latitude and longitude (Figs. 1a, 1b; see below). However, this information does not affect the geological background in our manuscript. We have added a map of the the facies and palaeogeographic evolution of the NCP over time from the late Bashkirian to the Wordian (~318 Ma – 265.1 Ma) in the revised manuscript (Figure 9) to provde full context on this.
The revised figure 1 is attached to this reply.
2. There is a bewildering array of regional and global stage names and fossil zonations for the Late Paleozoic but one would have to be a real aficionado to decipher from Fig. 1c where in the geologic column all the names are supposed to be: Early Permian? A very rudimentary paleogepographic map (Fig. 1b ), which should at least show lines of paleolatitude, is labeled Cisuralian but that time-stratigraphic interval is not indicated in the stratigraphic column in Fig. 1b.
Response: We have added the names of geological periods (e.g., Carboniferous and Permian) in the geological column in Figure 1c (Fig. 1c; see Response 1). We have replaced the “Palaeofacies map of the NCP during the Cisuralian (modified from Liu, 1990)(Fig. 1b)” with a“Simplified tectonic map of the present-day NCP showing the location of the study area (modified from Liu et al., 2013)”, but this did not affect the geological background in our manuscript. We have also added a map of the evolution of the NCP (see above) over time from late Bashkirian to Wordian (~318 Ma – 265.1 Ma) in the manuscript (Figure 9), and added the paleolatitude based on the previous palaeomagnetic data (Zhu et al., 1996; Table 1).The new figure 9 is attached to this reply.
3. Two U-Pb dates are quoted as 270.7 Ma and 299.4 Ma based on 5-11 zircons selected from an astonishing number (1000 to 1500!) grains extracted from two levels. The technique is not described (presumably laser-ablation ICPMS) nor how the 1:100 grains were selected, or what was done with the remaining zircon grains (were they measured?). What about potential lead-loss? These dates are extremely important for the chronostratigraphy and correlation to the wider world and must be described in much more detail; the reportage of Gehrels+2020 Geochro may provide a useful example.
We have revised the text in the manuscript to read: “After crushing, grinding, sieving, and heavy liquid and magnetic separation, euhedral zircon crystals with clear oscillatory zoning under cathodoluminescence (CL) microscope were selected for U-Pb zircon isotope analysis. U-Pb dating was conducted at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing). Laser sampling was performed using a Coherent’s GeoLasPro-193nm system. A Thermo Fisher’s X-Series 2 ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas. Argon was used as the make-up gas and mixed with the carrier gas. All data were acquired on zircon in single spot ablation mode at a spot size of 32 μm with 6 Hz frequency in this study. Standard material SRM610 from National Institute of Standards and Technology (NIST) of America was used to optimize the ICP-MS instrument, and as an external standard for determination of trace elements. Zircon 91500 was used as an external standard for U-Th-Pb isotopic ratios (Wiedenbeck et al., 1995, 2004). Plešovice Zircon was used as a monitoring standard for each analysis (Sláma et al., 2008). Time-dependent drifts of U-Th-Pb isotopic ratios were corrected using a linear interpolation (with time) for every five analyses according to the variations of 91500 (i.e., 2 zircon 91500 + 5 samples + 2 zircon 91500). Each analysis incorporated a background acquisition of approximately 20s (gas blank) followed by 50s data acquisition from the sample. Off-line selection and integration of background and analyte signals, and time-drift correction and quantitative calibration for trace element analyses and U-Pb dating were performed by ICPMSDataCal (Liu et al., 2008). Data reduction and concordia diagram was carried out using the Isoplot 3.0 (e.g., Lu et al., 2021a, b)”.
and
“In this study, zircon U-Pb age distributions are displayed and analyzed with probability density diagram, which is based on the individual ages and measured uncertainties from each sample (Fig. 3; Table S2). Sedimentary age interpretations are based on the main clusters of youngest zircon ages, with less emphasis on ages that do not belong to youngest clusters given the possibility that they are unreliable due to Pb loss, inheritance, analysis of inclusions, high common Pb, or unusual Pb–U fractionation due to ablation along with fractures (e.g., Gehrels, 2014; Gehrels et al., 2020)”.
4. A thickness-age plot (with cumulative thickness scales and not simply scale also shown in the stratigraphic diagrams in Figs. 1c, 4, 8,) would be useful to access temporal resolution of stages and fossil zonations
Response: We revised Figure 1c (see Response 1), 4 and 8 (see below), and added the cumulative thickness of the sedimentary stratigraphic time stages. This does not alter the results or conclusions of the work.
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Schmitz, M. D., Pfefferkorn, H. W., Shen, S. Z. and Wang, J.: A volcanic tuff near the Carboniferous–Permian boundary, Taiyuan Formation, North China: Radioisotopic dating and global correlation. Rev. Palaeobot. Palynol., 104244. doi:10.1016/j.revpalbo.2020.104244, 2020.
Shao, L., Dong, D., Li, M., Wang, H., Wang, D., Lu, J., Zheng, M. and Cheng, A.: Sequence-paleogeography and coal accumulation of the Carboniferous-Permian in the North China Basin, J. China. Coal. Soc., 39(8), 1725–1734, doi:10.13225/j.cnki.jccs.2013.9033, 2014.
Sláma, J., Košler, J., Condon, D. J., Crowley, J. L., Gerdes, A., Hanchar, J. M., Horstwood, M. S. A., Morris, G. A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M. N. and Whitehouse, M. J.: Plešovice zircon — A new natural reference material for U–Pb and Hf isotopic microanalysis, Chem. Geol., 249(1–2), 1–35, doi:10.1016/j.chemgeo.2007.11.005, 2008.
Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W. L., Meier, M., Oberli, F. v, Quadt, A. von, Roddick, J. C. and Spiegel, W.: Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses, Geostand. Newsl., 19(1), 1–23, doi:10.1111/j.1751-908X.1995.tb00147.x, 1995.
Wiedenbeck, M., Hanchar, J. M., Peck, W. H., Sylvester, P., Valley, J., Whitehouse, M., Kronz, A., Morishita, Y., Nasdala, L., Fiebig, J., Franchi, I., Girard, J.-P., Greenwood, R. C., Hinton, R., Kita, N., Mason, P. R. D., Norman, M., Ogasawara, M., Piccoli, P. M., Rhede, D., Satoh, H., Schulz-Dobrick, B., Skår, O., Spicuzza, M., Terada, K., Tindle, A., Togashi, S., Vennemann, T., Xie, Q. and Zheng, Y.-F.: Further Characterisation of the 91500 Zircon Crystal, Geostand. Geoanalytical Res., 28(1), 9–39, doi:10.1111/j.1751-908X.2004.tb01041.x, 2004.
Wu, Q., Ramezani, J., Zhang, H., Wang, J., Zeng, F., Zhang, Y., Liu, F., Chen, J., Cai, Y., Hou, Z., Liu, C., Yang, W., Henderson, C. M. and Shen, S.: High-precision U-Pb age constraints on the Permian floral turnovers, paleoclimate change, and tectonics of the North China block. Geology, 49, 677-681. doi: 10.1130/G48051.1, 2021.
Yang, G. X.: The Permian Cathaysian Flora in Western Henan province, China - Yuzhou Flora. Geological Publishing House, Beijing, pp. 1–76, 2006.
Yang, G. X., Wang, H. S.: Yuzhou flora - a hidden gem of the Middle and Late Cathaysian Flora. Sci. China Earth Sci., 55, 1601–1619. doi: 10.1007/s11430-012-4476-2, 2012.
Yang, Q. and Lei, S.: Depositional environments and coal-forming characteristics of Late Palaeozoic Coal Measures in Yuxian, Henan Province. Geological Publishing House, Beijing, pp. 1–87, 1987.
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Zhu, H., Yang, G. and Sheng, A. X.: A study on palaeomagnetism of Permian strata in the Dafengkou section, Yuzhou, Henan Province, Acta Geol. Sin., 70(2), 121–128, 1996.
Zhou, W. M., Wan, M. L., Yan, M. X., Cheng, C. and Wang, J.: The succession sequence of early Permian wetland vegetational communities in the Shanxi Formation of the Wuda Coalfield, Inner Mongolia. Acta Palaeontol. Sin., 54, 66-83. doi: CNKI:SUN:GSWX.0.2015-01-005, 2015.
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AC3: 'Reply on RC2', Jason Hilton, 06 Nov 2021
Status: closed
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RC1: 'Comment on cp-2021-108', Anonymous Referee #1, 13 Oct 2021
Title: Low-latitude climate change linked to high-latitude glaciation during the Late Paleozoic Ice Age: evidence from the terrigenous detrital kaolinite Author(s): Peixin Zhang, Jing Lu, Minfang Yang, Longyi Shao, Ziwei Wang, and Jason Hilton MS No.: cp-2021-108
Recommendation: Rejected
The paper is well written and presents interesting results concerning past climate conditions for North China. However I identified a fundamental issue requiring clarification. Indeed the authors investigate local climate conditions without presenting and discussing the geological setting of the area. In the absence of data highlighting the geological evolution of this site, most of statements presented in the discussion (4.2) remain too speculative to support authors’ conclusions. I encourage the authors to resubmit their article after significant rewriting of the manuscript, with a full description of the continental environment and its temporal evolution (which explains why I recommend “rejected” rather than “major revision”).
In addition here is a list a suggestions to improve the manuscript
- One major issue is the determination of the paleolatitude of the site through time with good precision. In principle, local paleomagnetic data could decide this issue because from them paleolatitude can be estimated. Moreover, authors used a unique reconstruction (Blakey 2011) for a period extending over 30 myr (300-270Ma) without discussing most recent reconstructions with finer time slices (for details, see https://www.earthbyte.org/category/resources/data-models/paleogeography/). Because the hydrological cycle (thus the weathering) depends on the Hadley cell in low latitudes this point must be solved in order to discuss the accuracy of findings in term of Earth's climate.
- lines 195-200: the time-correlation deserves more attention. Based on the fig.9, the atmospheric pCO2 for S-II and S-IV overcomes the one for S-3 while this state appears as “warm and humid”.
Citation: https://doi.org/10.5194/cp-2021-108-RC1 -
AC1: 'Reply on RC1', Jason Hilton, 30 Oct 2021
Dear reviewer,
Thank you for your assessment of our paper “Low-latitude climate change linked to high-latitude glaciation during the Late Paleozoic Ice Age: evidence from the terrigenous detrital kaolinite". The points raised are valid so the review provides us with the opportunity to expand our manuscript to address them comprehensively. However, we disagree with the recommendation of rejecting the manuscript because of the points raised as (i) the information is readily available and has now been incorporated into the revised manuscript, and (ii) this does not alter any of our results or conclusions in any way. Below we address each point individually and consider them fully resolved.
In the submission system, we cannot upload the revised manuscript. Therefore, we outline the changes we have made as indicated on the updated version of the manuscript showing marked changes (see below). These are provided in full in the attached pdf file.
We hope you find these changes agreeable.
Yours faithfully and on behalf of co-authors,
Jason Hilton
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AC2: 'Reply on AC1', Jason Hilton, 30 Oct 2021
Detailed responses to reviewer #1's comments:
Reviewer #1:
- The paper is well written and presents interesting results concerning past climate conditions for North China. However I identified a fundamental issue requiring clarification. Indeed the authors investigate local climate conditions without presenting and discussing the geological setting of the area. In the absence of data highlighting the geological evolution of this site, most of statements presented in the discussion (4.2) remain too speculative to support authors’ conclusions. I encourage the authors to resubmit their article after significant rewriting of the manuscript, with a full description of the continental environment and its temporal evolution (which explains why I recommend “rejected” rather than “major revision”).
Response: We thank the reviewer for their comments here. We added the contents about the geological background and environmental evolution of the study area in section 4.2, and we have added additional figures to demonstrate this.
The details are as follows: “Changes in continental plate position, land-sea distributions, ice extent in Gondwana, atmospheric CO2 and monsoonal rainfall are considered the main factors controlling climate change in low latitudes during the LPIA (Tabor and Poulsen, 2008; Cao et al., 2017). In the study area, local paleomagnetic data demonstrate that no large-scale plate motion occurred from the early to late Early Permian (Zhu et al., 1996). Through this time interval, the region remained in an equatorial humid climate zone (Zhu et al., 1996) on the southern margin of the North China Plate (NCP) in proximity to the sea (Fig. 9). Following regression of the epicontinental sea in the earliest Permian (Fig. 9a, b), sedimentary environments gradually developed from coastal tidal flat deposition to a series of shallow-water delta sedimentary systems comprising fluvial and tidally influenced offshore peat-bearing deposits (Zhu et al., 1996; Yang and Lei, 1987; Fig. 9). Fossil plants were widespread and abundant, comprising stable, tropical, ever-wet communities dominated by lycophytes, equisetophytes, marattialean ferns and pteridosperms (Zhu et al. 1996; Yang and Lei, 1987; Yang, 2006; Hilton and Cleal, 2007). Collectively, this information builds a picture of stability in continental plate position and land-sea distributions. The sedimentary record provides no evidence of monsoons. Consequently, we consider that waxing and waning of ice sheets in high latitude Gondwana and changes in global atmospheric CO2 were the main factors affecting climate change in the study area through the LPIA.”
[Please see pdf for revised figure]
Figure 9. Lithofacies palaeogeograpy map from late Bashkirian to Wordian in the North China Plate (modified from Shao et al., 2014).
We collected palaeomagnetic data from the Dafengkou section in Yuzhou coalfield from early to late Early Permian. These data show that from the early to late Early Permian, the paleolatitude change in the study area is between 11.0°N and 11.4°N, that is, it is within the equatorial humid climate zone (Zhu et al., 1996).
Table 1 Permian ancient geomagnetic parameters and latitude in Dafengkou section
Period
sampling point
mean direction of magnetization
α95
stability valuation
Paleomagnetic pole position
Paleolatitude position
D (°)
I (°)
K (°)
Plat.(°N)
Plong.(°N)
Dp
Dm
P21
6
143.2
-21.2
12.9
19.4
R
-49.2
177.4
10.7
20.4
11.0
P11
3
124.9
-22.0
82.1
13.7
R
-35.1
192.5
7.7
14.5
11.4
P1
9
136.9
-21.7
16.1
13.2
-44.6
183.4
7.4
14.0
11.2
[Please see pdf for revised figure]
Figure 11. Comparison of climate change, glaciations, d18O, and pCO2 records from the Gzhelian Stage of the Carboniferous to the Roadian Stage of the Permian. Age stratigraphic framework from Shen et al. (2019); a, Climate stages interpreted from the studied section; b, Interpreted climatic records with blue representing intervals of climate cooling while yellow represents climatic warming based on fluctuating climate signals from kaolinite content from the studied section, and climate type interpreted from the studied section. c, Records of glaciation events in Australia from Fielding et al. (2008), Frank et al. (2015), and Garbelli et al. (2019); d, Oxygen isotope values from Korte et al. (2005) and Grossman et al. (2008); e, Global pCO2 concentration from Montañez et al. (2007), Foster et al. (2017) and Richey et al. (2020). Note: the red line from Foster et al. (2017), the black line comes from Richey et al. (2020). Abbreviations: Gzh. = Gzhelian; Sak. = Sakmarian; Cli. S. = Climate stage; Clim. type = Climate type; 21# = Coal 21 seam; Temp. = Temperature.
References:
Cao, W., Williams, S., Flament, N., Zahirovic, S., Scotese, C. and Muller, R. D.: Palaeolatitudinal distribution of lithologic indicators of climate in a palaeogeographic framework, Geol. Mag., 156(2), 331–354, doi:10.1017/S0016756818000110, 2019.
Cecil, C. B., Dulong, F. T., West, R. R., Stamm, R., Wardlaw, B. and Edgar, N. T.: Cliamte controls on the stratigraphy of a Middle Pennsylvanian cyclothem in North America, in Climate Controls on Stratigraphy, pp. 151–180, SEPM (Society for Sedimentary Geology)., 2003.
Clapham, M. E. and James, N. P.: Paleoecology Of Early-Middle Permian Marine Communities In Eastern Australia: Response To Global Climate Change In the Aftermath Of the Late Paleozoic Ice Age, Palaios, 23(11), 738–750, doi:10.2110/palo.2008.p08-022r, 2008.
Frank, T. D., Shultis, A. I. and Fielding, C. R.: Acme and demise of the late Palaeozoic ice age: A view from the southeastern margin of Gondwana, Palaeogeogr. Palaeoclimatol. Palaeoecol., 418, 176–192, doi:10.1016/j.palaeo.2014.11.016, 2015.
Koch, J. T. and Frank, T. D.: The Pennsylvanian-Permian transition in the low-latitude carbonate record and the onset of major Gondwanan glaciation, Palaeogeogr. Palaeoclimatol. Palaeoecol., 308(3–4), 362–372, doi:10.1016/j.palaeo.2011.05.041, 2011.
Lowry, D. P., Poulsen, C. J., Horton, D. E., Torsvik, T. H. and Pollard, D.: Thresholds for Paleozoic ice sheet initiation, Geology, 42(7), 627–630, 2014.
Montañez, I. P. and Poulsen, C. J.: The Late Paleozoic Ice Age: An Evolving Paradigm, Annu. Rev. Earth Planet. Sci., 41(1), 629–656, doi:10.1146/annurev.earth.031208.100118, 2013.
Montañez, I. P., Tabor, N. J., Niemeier, D., DiMichele, W. A., Frank, T. D., Fielding, C. R., Isbell, J. L., Birgenheier, L. P. and Rygel, M. C.: CO2-Forced Climate and Vegetation Instability During Late Paleozoic Deglaciation, Science (80-. )., 315(5808), 87–91, doi:10.1126/science.1134207, 2007.
Poulsen, C. J., Pollard, D., Montañez, I. P. and Rowley, D.: Late Paleozoic tropical climate response to Gondwanan deglaciation, Geology, 35(9), 771–774, doi:10.1130/G23841A.1, 2007.
Powell, M. G.: Latitudinal diversity gradients for brachiopod genera during late Palaeozoic time: links between climate, biogeography and evolutionary rates, Glob. Ecol. Biogeogr., 16(4), 519–528, doi:10.1111/j.1466-8238.2007.00300.x, 2007.
Richey, J. D., Montañez, I. P., Goddéris, Y., Looy, C. V, Griffis, N. P. and DiMichele, W. A.: Influence of temporally varying weatherability on CO2-climate coupling and ecosystem change in the late Paleozoic, Clim. Past, 16(5), 1759–1775, doi:10.5194/cp-16-1759-2020, 2020.
Roy, D. K. and Roser, B. P.: Climatic control on the composition of Carboniferous-Permian Gondwana sediments, Khalaspir basin, Bangladesh. Gondwana Res., 23, 1163–1171. doi: 10.1016/j.gr.2012.07.006, 2013.
Stemmerik, L.: Influence of late Paleozoic Gondwana glaciations on the depositional evolution of the northern Pangean shelf, North Greenland, Svalbard, and the Barents Sea, Resolv. Late Paleoz. Ice Age Time Sp., 441, 205, 2008.
Tabor, N. J. and Poulsen, C. J.: Palaeoclimate across the Late Pennsylvanian-Early Permian tropical palaeolatitudes: A review of climate indicators, their distribution, and relation to palaeophysiographic climate factors, Palaeogeogr. Palaeoclimatol. Palaeoecol., 268(3–4), 293–310, doi:10.1016/j.palaeo.2008.03.052, 2008.
Waterhouse, J. B. and Shi, G. R.: Evolution in a cold climate, Palaeogeogr. Palaeoclimatol. Palaeoecol., 298(1–2), 17–30, doi:10.1016/j.palaeo.2010.08.022, 2010.
Yang, G.: The Permian cathaysian flora in western Henan province, China-Yuzhou flora., 1–76, 2006.
Yang, Q. and Lei, S.: Depositional Environments and Coal-forming Characteristics of Late Palaeozoic Coal Measures in Yuxian, Henan Province., 1987.
Zhu, H., Yang, G. and Sheng, A. X.: A study on palaeomagnetism of Permian strata in the Dafengkou section, Yuzhou, Henan Province, Acta Geol. Sin., 70(2), 121–128, 1996.
Citation: https://doi.org/10.5194/cp-2021-108-AC2 - The paper is well written and presents interesting results concerning past climate conditions for North China. However I identified a fundamental issue requiring clarification. Indeed the authors investigate local climate conditions without presenting and discussing the geological setting of the area. In the absence of data highlighting the geological evolution of this site, most of statements presented in the discussion (4.2) remain too speculative to support authors’ conclusions. I encourage the authors to resubmit their article after significant rewriting of the manuscript, with a full description of the continental environment and its temporal evolution (which explains why I recommend “rejected” rather than “major revision”).
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AC2: 'Reply on AC1', Jason Hilton, 30 Oct 2021
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AC1: 'Reply on RC1', Jason Hilton, 30 Oct 2021
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RC2: 'Comment on cp-2021-108', Anonymous Referee #2, 30 Oct 2021
Clay mineralogy is well outside my area of expertise so my comments are confined to the paleogeography and general aspects of chronostratigraphic correlations which are essential in reaching conclusions about climate responses across latituide in the Late Paleozoic Ice Age.
The paleogeographic context is inadequate. Fig. 1a is a cartoon with virtually no documentation of how the North China Block was positioned in the Early Permian, e.g., Liu1990 cited is a one-page comment/reply and Blakely2011 has no quantitative analysis fordetermination of paleolatitude, whereas Yang+Lei1987 and Zhou2002 are not readily accessible and would need to be described here for a broader audience. The authors state that the NCP was located at ~5-15°N but there could be a huge lithostratigraphic consequence between being in the tropical humid belt (5°) and the arid belt (15°). Unless the authors have alternative methods, paleolatitudes are based on paleomagnetism and hence the authors might consult references to the modern paleomagnetic literature and syntheses for the NCB and Tethyan environs in papers like Torsvik+2012 ESR or Kent+Muttoni2020 Palaeo3.
There is a bewildering array of regional and global stage names and fossil zonations for the Late Paleozoic but one would have to be a real aficionado to decipher from Fig. 1c where in the geologic column all the names are supposed to be: Early Permian? A very rudimentary paleogepographic map (Fig. 1b ), which should at least show lines of paleolatitude, is labeled Cisuralian but that time-stratigraphic interval is not indicated in the stratigraphic column in Fig. 1b.
Two U-Pb dates are quoted as 270.7 Ma and 299.4 Ma based on 5-11 zircons selected from an astonishing number (1000 to 1500!) grains extracted from two levels. The technique is not described (presumably laser-ablation ICPMS) nor how the 1:100 grains were selcected, or what was done with the remaining zircon grains (were they measured?). What about potential lead-loss? These dates are extremely important for the chronostratigraphy and correlation to the wider world and must be described in much more detail; the reportage of Gehrels+2020 Geochro may provide a useful example.
A thckness-age plot (with cumulative thickness scales and not simply scale also shown in the stratigraphic diagrams in Figs. 1c, 4, 8,) would be useful to access temporal resolution of stages and fossil zonations.
In summary, ihe authors should take the opportunity to provide a broader and deeper context for their results, including more detailed map and stratigraphic charts with explicit proposed tie-lines to standard columns, especially when so much of the literature is so difficult to obtain let alone read by most of us outside of China. As it stands, the spatiotemporal and this climate significance of the work remains unfortunalety superficial.
My suggestion is that majpr revisions are needed before the paper can be reconsidered.
Citation: https://doi.org/10.5194/cp-2021-108-RC2 -
AC3: 'Reply on RC2', Jason Hilton, 06 Nov 2021
Detailed responses to reviewer #2's comments:
Dear Editor,
Thank you very much for reviewing our paper “Low-latitude climate change linked to high-latitude glaciation during the Late Palaeozoic Ice Age: evidence from the terrigenous detrital kaolinite" and giving very valuable comments. The points raised are valid so the review provides us with the opportunity to expand our manuscript to address them comprehensively. Below we address each point individually and consider them fully resolved.
In the submission system, we cannot upload the revised manuscript. Therefore, we outline the changes we have made as indicated on the updated version of the manuscript showing marked changes (in red) as an attachment here.
We hope you find these changes agreeable and we look forwards to hearing from you in the future.
Yours sincerely and on behalf of co-authors,
Jason Hilton
Reviewer #2:
Overall, reviewer 2 makes some detailed comments on the geological context of the study but nothing that impacts the results or conclusions presented. We will reply to their comments individually below.
1. The paleogeographic context is inadequate. Fig. 1a is a cartoon with virtually no documentation of how the North China Block was positioned in the Early Permian, e.g., Liu1990 cited is a one-page comment/reply and Blakely2011 has no quantitative analysis for determination of paleolatitude, whereas Yang+Lei1987 and Zhou2002 are not readily accessible and would need to be described here for a broader audience. The authors state that the NCP was located at ~5-15°N but there could be a huge lithostratigraphic consequence between being in the tropical humid belt (5°) and the arid belt (15°). Unless the authors have alternative methods, paleolatitudes are based on paleomagnetism and hence the authors might consult references to the modern paleomagnetic literature and syntheses for the NCB and Tethyan environs in papers like Torsvik+2012 ESR or Kent+Muttoni2020 Palaeo3.
Response: We disagree with the overall sentiment here – the information is provided is coparable to other papers on the topic utilizing similar appraches, but if the reviewer wants us to provide additional context, we can do that. We note this does not change the results or conclusions presented.
We have reviewed palaeomagnetic data from the Dafengkou section in the Yuzhou coalfield from the early to late Early Permian (including the Taiyuan, Shanxi, and Shangshihezi formations). These data show that from the early Early Permian to late Early Permian, the palaeolatitude change in the study area is between 11.0°N and 11.4°N, that is, it is within the equatorial humid climate zone (Zhu et al., 1996).
Table 1 The Characteristic remanent magnetization directions, palaeomagnetic pole, and palaeolatitude of Permian of Dafengkou profile in Yuzhou, Henan Province
Period
sampling point
mean direction of magnetization
α95
stability valuation
Palaeomagnetic pole position
Palaeolatitude position
D (°)
I (°)
K (°)
Plat.(°N)
Plong.(°N)
Dp
Dm
P21
6
143.2
-21.2
12.9
19.4
R
-49.2
177.4
10.7
20.4
11.0
P11
3
124.9
-22.0
82.1
13.7
R
-35.1
192.5
7.7
14.5
11.4
P1
9
136.9
-21.7
16.1
13.2
-44.6
183.4
7.4
14.0
11.2
According to palaeomagnetic data from the Dafengkou section in the Yuzhou Coalfield during the early Early Permian (P1) to late Early Permian (P21) (Table 1; see below), we determined the exact location of the study area through time and have modified this in the geological background section. We have revised figure 1, and replaced “Blake’s paleogeographic map (Fig. 1a)” with the “generalized tectonic map of present-day China”, and also replaced the “Palaeofacies map of the NCP during the Cisuralian (modified from Liu, 1990) (Fig. 1b)” with the “Simplified tectonic map of the present-day NCP (modified from Liu et al., 2013)”. In these maps, we have added modern latitude and longitude (Figs. 1a, 1b; see below). However, this information does not affect the geological background in our manuscript. We have added a map of the the facies and palaeogeographic evolution of the NCP over time from the late Bashkirian to the Wordian (~318 Ma – 265.1 Ma) in the revised manuscript (Figure 9) to provde full context on this.
The revised figure 1 is attached to this reply.
2. There is a bewildering array of regional and global stage names and fossil zonations for the Late Paleozoic but one would have to be a real aficionado to decipher from Fig. 1c where in the geologic column all the names are supposed to be: Early Permian? A very rudimentary paleogepographic map (Fig. 1b ), which should at least show lines of paleolatitude, is labeled Cisuralian but that time-stratigraphic interval is not indicated in the stratigraphic column in Fig. 1b.
Response: We have added the names of geological periods (e.g., Carboniferous and Permian) in the geological column in Figure 1c (Fig. 1c; see Response 1). We have replaced the “Palaeofacies map of the NCP during the Cisuralian (modified from Liu, 1990)(Fig. 1b)” with a“Simplified tectonic map of the present-day NCP showing the location of the study area (modified from Liu et al., 2013)”, but this did not affect the geological background in our manuscript. We have also added a map of the evolution of the NCP (see above) over time from late Bashkirian to Wordian (~318 Ma – 265.1 Ma) in the manuscript (Figure 9), and added the paleolatitude based on the previous palaeomagnetic data (Zhu et al., 1996; Table 1).The new figure 9 is attached to this reply.
3. Two U-Pb dates are quoted as 270.7 Ma and 299.4 Ma based on 5-11 zircons selected from an astonishing number (1000 to 1500!) grains extracted from two levels. The technique is not described (presumably laser-ablation ICPMS) nor how the 1:100 grains were selected, or what was done with the remaining zircon grains (were they measured?). What about potential lead-loss? These dates are extremely important for the chronostratigraphy and correlation to the wider world and must be described in much more detail; the reportage of Gehrels+2020 Geochro may provide a useful example.
We have revised the text in the manuscript to read: “After crushing, grinding, sieving, and heavy liquid and magnetic separation, euhedral zircon crystals with clear oscillatory zoning under cathodoluminescence (CL) microscope were selected for U-Pb zircon isotope analysis. U-Pb dating was conducted at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing). Laser sampling was performed using a Coherent’s GeoLasPro-193nm system. A Thermo Fisher’s X-Series 2 ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas. Argon was used as the make-up gas and mixed with the carrier gas. All data were acquired on zircon in single spot ablation mode at a spot size of 32 μm with 6 Hz frequency in this study. Standard material SRM610 from National Institute of Standards and Technology (NIST) of America was used to optimize the ICP-MS instrument, and as an external standard for determination of trace elements. Zircon 91500 was used as an external standard for U-Th-Pb isotopic ratios (Wiedenbeck et al., 1995, 2004). Plešovice Zircon was used as a monitoring standard for each analysis (Sláma et al., 2008). Time-dependent drifts of U-Th-Pb isotopic ratios were corrected using a linear interpolation (with time) for every five analyses according to the variations of 91500 (i.e., 2 zircon 91500 + 5 samples + 2 zircon 91500). Each analysis incorporated a background acquisition of approximately 20s (gas blank) followed by 50s data acquisition from the sample. Off-line selection and integration of background and analyte signals, and time-drift correction and quantitative calibration for trace element analyses and U-Pb dating were performed by ICPMSDataCal (Liu et al., 2008). Data reduction and concordia diagram was carried out using the Isoplot 3.0 (e.g., Lu et al., 2021a, b)”.
and
“In this study, zircon U-Pb age distributions are displayed and analyzed with probability density diagram, which is based on the individual ages and measured uncertainties from each sample (Fig. 3; Table S2). Sedimentary age interpretations are based on the main clusters of youngest zircon ages, with less emphasis on ages that do not belong to youngest clusters given the possibility that they are unreliable due to Pb loss, inheritance, analysis of inclusions, high common Pb, or unusual Pb–U fractionation due to ablation along with fractures (e.g., Gehrels, 2014; Gehrels et al., 2020)”.
4. A thickness-age plot (with cumulative thickness scales and not simply scale also shown in the stratigraphic diagrams in Figs. 1c, 4, 8,) would be useful to access temporal resolution of stages and fossil zonations
Response: We revised Figure 1c (see Response 1), 4 and 8 (see below), and added the cumulative thickness of the sedimentary stratigraphic time stages. This does not alter the results or conclusions of the work.
Reference:
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AC3: 'Reply on RC2', Jason Hilton, 06 Nov 2021
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