Continental drift triggered the Early Permian aridification of North China

Domain: earth_science
Published: 2025-01-04
Editorial outcome: minor_revision

Abstract
The boundary between wet and arid climate zones in the Tethys Ocean remains challenging to trace, complicating our understanding of global aridification pattern during the Late Carboniferous to Early Permian transition.
The North China Block (NCB), situated in the Tethys Ocean, underwent a transition from humid to arid climate during the Early Permian, providing a rare opportunity to trace this climate boundary across this region. Here, we present paleomagnetic evidence indicating that the NCB underwent rapid northward drift between 290 and 281 million years ago. The NCB’s movement from a tropical wet to a subtropical arid zone corresponds to a lithological change from coal-bearing to red-bed deposits, demonstrating tectonic drift into a subtropical arid zone as the main driver of aridification in the NCB during this period. This drift also delineates the wet–dry boundary over the Tethys Ocean, consistent with modern climatic zonation patterns.

Introduction
During the Late Carboniferous to the Early Permian transition period, the Pangea supercontinent began to undergo significant aridification1,2, with most the low-latitude regions transitioning to arid environments3. This environmental change led to the collapse of tropical rainforests near-equatorial Pangea4 and a transition in the deposition of climate-sensitive sediments. For example, indicators of a humid tropical paleoclimate (e.g., coal, laterite, and bauxite) are common in Pennsylvanian strata, but are replaced by indicators of a dry climate (e.g., calcrete and evaporite) in Lower Permian strata. Previous studies have suggested that the large-scale aridification of Pangea’s low latitudes was closely related to the migration of the Intertropical Convergence Zone (ITCZ)2,5. It is well-established that the ITCZ was unstable over Pangea during the climate transition, with its migration influenced by the deglaciation of Gondwana1,2. However, the impact of this instability on the Tethys Ocean remains unclear.

Interestingly, while much of low-latitude Pangea began to experience an arid climate, several microcontinents in the Tethys Ocean continued to experience a tropical rainforest climate1,3,6. This marked climatic disparity between low-latitude Pangea and the Tethys Ocean presents challenges in tracking the continuity of climate zones from continental to oceanic regions, resulting in an incomplete understanding of global climate pattern during this climate transition period.

The North China Block (NCB; Fig. 1a), situated within the Tethys Ocean domain, underwent a climatic transition from a tropical rainforest to an arid environment during the Artinskian of the Early Permian1,7,8. This transition offers a rare opportunity to delineate the boundary between tropical wet and subtropical arid climatic zones in the Tethys Ocean. However, paleomagnetic data from the NCB during the Early Permian remain sparse, primarily derived from the clastic rocks9,10, and are constrained by imprecise dating and insufficient inclination hallowing corrections. These limitations have hindered the development of high-resolution paleogeographic reconstructions for this period, further leading to divergent interpretations of the mechanisms driving the NCB’s aridification.

Some researchers have proposed that the paleogeographic position of the NCB remained relatively stable during the Early Permian, attributing its aridification to orogenic uplift11–13 or the exhaust of large igneous provinces14,15. However, these hypotheses cannot explain the spatial heterogeneity in the NCB’s climate during this period, characterized by arid conditions in the north and wet conditions in the south. Consequently, greater support has been directed toward the prevailing hypothesis that the NCB’s aridification was driven by its northward drift from a tropical wet climate zone to a subtropical arid zone in the Tethys Ocean6,16,17. Nevertheless, this hypothesis has yet to be substantiated by reliable Early Permian paleomagnetic data.

In this work, we report two key paleomagnetic data from well-dated (ca. 290 and ca. 281 million years ago; Ma) units in the northern NCB, which reveal a rapid northward motion of the NCB between 290 and 280 Ma. This movement establishes a clear linkage between the NCB’s tectonic drift and its transition to arid conditions. The new data provide high-resolution constraints for Early Permian paleogeographic reconstructions, enabling us to trace the boundary between tropical wet and subtropical arid zones in the Tethys Ocean. These findings not only elucidate the mechanisms driving regional climatic changes in the NCB but also shed light on the contrasting climatic patterns between the Pangea supercontinent and the Tethys Oceanic domain.

Results
Paleomagnetic investigations were carried out in the Siziwangqi (Fig. 1b) and Chifeng (Fig. 1c) areas, near the northern margin of the NCB (Fig. 1a). In Siziwangqi, the Lower Permian Dahongshan Formation (DF; >665 m thick) consists mainly of andesitic and rhyolitic lavas with interbedded volcanoclastic rocks, and is unconformably overlain by molasse facies deposits of the middle Permian Naobaogou Formation and underlain by terrestrial clastic rocks of the upper Carboniferous Shuanmazhuang Formation (Fig. 1d; ref. 18). In the western Yangpanshan Basin, an andesite flow sampled near the top of the DF yields a zircon U–Pb age of 277±1.4 Ma19. In this study, we collected 183 oriented samples for paleomagnetic analysis comprising andesitic and rhyolitic rocks from 21 sites (DT01–DT21) in the lower member of the DF, along with 155 andesitic and sandstone samples from 15 sites (LT01–LT15) in the upper member, near the village of Datan in southern Siziwangqi (Fig. 1b and Supplementary Fig. 1a). The attitudes of the lava flows were measured from interbedded volcanoclastic rocks (Supplementary Fig. 1b–i). In addition, fresh andesite (NL-DT01 and NL-LT02) and rhyolite (NL-DT02 and NL-LT01) samples collected from the top and bottom of the two paleomagnetic sampling sections were subjected to zircon U–Pb dating (Fig. 1d and Supplementary Fig. 1a). In Chifeng, the volcanic–sedimentary rocks of the lower Permian Qingfengshan Formation (QF) are conformably overlain by sedimentary rocks of the Suolun Formation and unconformably underlain by clastic rocks of the upper Carboniferous Jiujuzi Formation (Fig. 1d; ref. 18). The ~3000 m thick QF is divided into three members18, of which member 1 (1000-m thick) consists of conglomerates, red siltstones, and tuffaceous interbeds and is the focus of our study. We collected 112 red siltstone samples for paleomagnetic analysis from member 1 at 15 sites (AQ01–AQ21) across an outcrop located ~8 km northwest of the village of Anqing in northeast Chifeng (Fig. 1c and Supplementary Fig. 1j–l). A tuff sample (NL-AQ03) was collected near paleomagnetic sampling site AQ06 for zircon U–Pb geochronology (Fig. 1c and Supplementary Fig. 1m).

Zircon U–Pb geochronological results
Zircon grains from the andesite (NL-DT01) and rhyolite (NL-DT02) samples from the lower member of the DF are typically 30–80 μm wide and 80–150 μm long, subhedral to euhedral, prismatic, and have clear oscillatory zoning (Supplementary Fig. 2a, d). Their Th/U ratios (0.46–1.30; Supplementary Table 1) suggest a magmatic origin20. Thirty-eight analyses of sample NL-DT01 yielded concordant ages (Supplementary Fig. 2b) with a weighted mean 206Pb/238U age of 291.7±1.7 Ma (MSWD=1.10; Supplementary Fig. 2c), which is interpreted as the crystallization age. Eighteen analyses of sample NL-DT02 yielded concordant ages (Supplementary Fig. 2e), with a weighted mean 206Pb/238U age of 288.2±1.5 Ma (MSWD=0.23; Supplementary Fig. 2f). Therefore, the age of the lower member of the DF and the corresponding paleomagnetic sampling section is 291.7–288.2 Ma (late Sakmarian–early Artinskian).

Zircons from the rhyolite (NL-LT01) and andesite (NL-LT02) samples from the upper member of the DF are typically 30–110 μm wide and 80–150 μm long, subhedral to euhedral, prismatic, and have clear oscillatory zoning (Supplementary Fig. 2g, j). Their Th/U ratios (0.45–1.42; Supplementary Table 1) indicate a magmatic origin20. Twenty-one analyses of sample NL-LT01 yielded concordant ages (Supplementary Fig. 2h), with a weighted mean 206Pb/238U age of 281.3±1.6 Ma (MSWD=0.21; Supplementary Fig. 2i), which we interpret as the crystallization age. Twenty analyses of sample NL-LT02 yielded concordant ages (Supplementary Fig. 2k), with a weighted mean 206Pb/238U age of 279.9±0.9 Ma (MSWD=0.45; Supplementary Fig. 2l). Therefore, the age of the upper member of the DF and the corresponding paleomagnetic sampling section is 281.3–279.9 Ma (early Kungurian).

Most zircon grains in the tuff sample (NL-AQ03) from the lower member of the QF are colorless and transparent. Their euhedral and prismatic morphology implies they are well preserved. The zircons are typically 20–60 μm wide and 60–120 μm long, and they exhibit highly luminescent oscillatory zoning when subject to cathodoluminescence imaging (Supplementary Fig. 2m). Their Th/U ratios (0.66–2.28) indicate a magmatic origin20. Only euhedral, prismatic zircons were chosen for U–Pb analysis. Nine analyses on twelve zircons yielded concordant ages (Supplementary Fig. 2n) and a weighted mean 206Pb/238U age of 281.0±1.6 Ma (MSWD=1.08; Supplementary Fig. 2p). Therefore, member 1 of the QF at the paleomagnetic sampling site was deposited during the early Kungurian (ca. 281 Ma).

Rock magnetic results
Andesite, rhyolite, and sandstone samples from sites DT1-4, DT7, DT10-19, and LT01-15 in the DF were subjected to stepwise thermal demagnetization of the three orthogonal isothermal remanent magnetization (IRM) components21. The results show that the soft (0.12 T) and intermediate (0.4 T) IRM components have similar unblocking temperatures of ~580°C (Supplementary Fig. 3a, c), suggesting that the remanent magnetism in these specimens is carried principally by magnetite.

Stepwise thermal demagnetization of the three orthogonal IRM components21 in the andesites from sites DT5-6, DT8-9, and DT20-21 in the DF suggests that the IRM intensity is dominated by the soft component (0.12 T). The IRM intensity decreased to zero at ~580°C (Supplementary Fig. 3b). The hard (2.4 T) and intermediate (0.4 T) components were unblocked at 675°C (Supplementary Fig. 3b). These results are consistent with the presence of both magnetite and hematite in the andesites.

Stepwise thermal demagnetization of the three orthogonal IRM components21 in specimens from the red bed (AQ01–AQ21) in the lower member of the QF show that the IRM intensity is dominated by the hard (2.4 T) and intermediate (0.4 T) components. Both IRM intensities decreased rapidly at ~675°C (Supplementary Fig. 3d), suggesting that hematite is the predominant magnetic carrier in the red beds.

Paleomagnetic results of the lower member of the DF (290 Ma)
Thermal demagnetization of 155 andesite and rhyolite specimens from 21 sites in the lower member of the DF yields stable magnetic signals (Supplementary Table 2 and Supplementary Fig. 4a–f). The in situ low temperature components (LTCs), mostly removed below 300°C, are distributed around the local recent geomagnetic field (RGF; Supplementary Fig. 5a) and represent a viscous remanent magnetization (VRM) of the RGF. The stable high-temperature components (HTCs) carried by magnetite and hematite are typically isolated from 500 to 580°C (site DT1-4, DT7, and DT10-19) and from 560 to 680°C (site DT5-6, DT8-9, and DT20-21), respectively. This is consistent with the results of rock magnetism experiments (Supplementary Fig. 3a, b).

All site-level HTCs yield uniformly reversed polarity, pointing southeast and upward after tilt correction (Fig. 2a and Supplementary Table 2). All HTCs pass the fold tests of McElhinny22 and McFadden23 at the 95% and 99% confidence levels (Supplementary Table 2) and the “k” parameter reaches a maximum at 98.2% unfolding in a stepwise unfolding test (Fig. 2d; ref. 24). The earliest folding of this formation in the Siziwangqi region occurred during the latest early Permian–Middle Triassic18,19, indicating that the HTCs are primary magnetization that was incorporated prior to folding and before the latest early Permian.

Nine volcanic breccia specimens from the lower member of the DF (Supplementary Fig. 7a–c) have stable magnetic signals (Supplementary Fig. 7d). The in situ LTCs, removed below 300°C, are distributed around the local RGF (Supplementary Fig. 7e) and represent a VRM of the RGF. The stable HTCs decay toward the origin near unblocking temperatures of 550–580°C. The HTC directions from the different pebbles are randomly distributed (Supplementary Fig. 7f, g), and those from the same pebble are consistent (e.g., DT22A and DT22B; DT22E and DT22F; Supplementary Fig. 7a, c). A random distribution test gives an R value of 3.39 (n=9), which is significantly lower than the critical R-values of 4.76 and 5.61 at the 95% and 99% confidence levels, respectively25, indicating a positive conglomerate test. Therefore, these robust fold and conglomerate tests show that the HTCs reflect primary magnetization.

Remanent magnetization was acquired at 291.7‒288.2 Ma during the Permian‒Carboniferous Reversed Superchron (318–262 Ma; Fig. 1d; ref. 26). Three lines of evidence suggest that paleosecular variation has been time-averaged in the volcanic rocks, as follows: (1) Twenty-one paleomagnetic sites from more than ten different rhyolitic and andesitic lava flows cover a long interval (291.7–288.2 Ma) and are interbedded with many layers of sedimentary rock. (2) The virtual geomagnetic pole (VGP) scatters (SB = 13.7°) for 21 reversed polarity sites are consistent with the PCRS predicted values of the best-fit “Model G” of de Oliveira et al.27. (3) The value of A95 obtained from the VGP of 155 lava specimens is 2.9, within an N-dependent A95 envelope with a 95% confidence interval (1.6, 3.4), as proposed by Deenen et al.28,29. Therefore, given the time-integrated nature of our results, we averaged all of the site-level VGPs determined in the ca. 290 Ma lower member of the DF and obtained a pole at 41.5°N/5.4°E (A95 = 5.8°; Supplementary Table 2).

Paleomagnetic results of the upper member of the DF (281 Ma)
A total of 133 andesite and sandstone specimens from 15 sites in the upper member of the DF yield stable magnetic signals during thermal demagnetization (Supplementary Table 2; Supplementary Fig. 4g–i). The in situ LTCs, removed primarily below 300°C, are distributed around the local RGF (Supplementary Fig. 5b) and represent a VRM of the RGF. The stable HTCs carried by magnetite and hematite are typically isolated from 500 to 580°C, consistent with the results of rock magnetism experiments (Supplementary Fig. 3c). All site-level HTCs exhibit uniformly reversed polarity, directed south-southeast and upward after tilt correction (Fig. 2b; Supplementary Table 2). All HTCs pass the fold tests of McElhinny22 and McFadden23 at the 95% and 99% confidence levels (Supplementary Table 2), with the “k” parameter reaching a maximum at 103% unfolding in a stepwise unfolding test (Fig. 2e; ref. 24), suggesting that the HTC reflects primary magnetization acquired prior to folding. Eleven paleomagnetic specimens from volcanic breccias in the upper member of the DF (Supplementary Fig. 8a, b) also yield stable magnetic signals (Supplementary Fig. 8c). The in situ LTCs, removed below 300°C, are distributed around the local RGF (Supplementary Fig. 7d), representing a VRM of the RGF. The stable HTCs decay toward the origin near unblocking temperature of 550–580°C. HTC directions from different pebbles show a random distribution (Supplementary Fig. 8e, f), while those from the same pebble are consistent (e.g., LT16D and LT16E; LT16H, LT16I, and LT16J; Supplementary Fig. 8a, b). A random distribution test yields an R value of 2.21 (n=11), lower than the critical R-values of 5.29 and 6.25 at the 95% and 99% confidence levels, respectively25, indicating a positive conglomerate test. Therefore, these robust fold and conglomerate tests confirm that the HTC reflect primary magnetization. The fact that similar results were obtained from the volcanic rocks and sandstones suggests that they represent a long interval (279.9–281.3 Ma) over which we can average out paleosecular variation. Consequently, we averaged all site-level VGPs determined from the ca. 281 Ma upper member of the DF, resulting in a pole at 66.0°N/332.8°E (A95 = 3.3°; Supplementary Table 2).

Paleomagnetic results of member 1 of the QF (281 Ma)
Thermal demagnetization results from the 112 red siltstone specimens collected from 15 sites (AQ01-AQ21) in member 1 of the QF revealed stable magnetic signals (Supplementary Fig. 4j–p; Supplementary Table 2). The in situ LTCs were largely removed below 250°C and are clustered around the RGF direction (Supplementary Fig. 5c); these represent a VRM of the RGF. Stable HTCs had unblocking temperatures up to 680°C and indicate that hematite is the main magnetic carrier, which is consistent with results of rock magnetism experiments (Supplementary Fig. 3d). All HTCs have dual-polarity directions (Fig. 2c and Supplementary Table 2) that pass a reversal test30 at the 95% confidence level (Class B). The angle between the two averages is γ = 3.7 < γcritical = 5.5. The results of our geochronological analyses indicate that remanent magnetizations were acquired at ca. 281 Ma (the early Kungurian stage of the early Cisuralian) during a short period of normal polarity at 282‒280 Ma (CI2; Fig. 1d; ref. 26). These data account for the documented dual-polarity at our sampling site. The HTCs also pass fold tests22,23 at 95% and 99% confidence levels, and the “k” parameter reaches a maximum at 99.3% unfolding in the stepwise unfolding test (Fig. 2f; ref. 24). Thus, these robust tests indicate that the HTC represents pre-folding primary magnetization. For the hematite-bearing red beds, we analyzed the Fisher distribution of the site-level VGPs and applied the widely accepted elongation/inclination (E/I) method of Tauxe and Kent31 to correct for the 112 sample directions. The f value was 0.7 and inclination was corrected from 29.5° to 37.1°, with the 95% confidence interval between 31.2° and 42.8° (Supplementary Fig. 6). According to the palaeomagnetic criteria suggested by Meert et al.32, the paleomagnetic inclination (after flattening correction) of the red beds from member 1 of the QF is consistent with that of the coeval volcanic rocks in the upper member of the DF, indicating that the flattening correction is valid. We obtained a pole at 68.1°N/323.6°E (A95 = 2.5°) by averaging all of the site-level VGPs in the ca. 281 Ma member 1 of the QF. Furthermore, since both the red beds in member 1 of the QF and the volcano-sedimentary rocks of the upper member of the DF yield similar paleomagnetic results (with their VGPs passing a significance test; Supplementary Table 2), we obtained a pole for the northern margin of the NCB at ca. 281 Ma of 67.1°N/328.4°E (A95 = 2.1°) by averaging all 30 site-level VGPs.

Methods
Zircon U‒Pb
Zircon grains were separated from whole rock samples using conventional heavy liquid and magnetic techniques at the Institute of the Hebei Regional Geology and Mineral Survey in Langfang, China. More than 500 representative zircon grains were hand-picked under a binocular microscope from each sample. Both unknowns and zircon standards were then mounted in epoxy and polished to expose the internal structures of each grain. The morphologies and internal structures of the zircons were studied using transmitted and reflected light microscopy and cathodoluminescence imaging.

Zircon U–Pb geochronology was conducted using laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) at the Chinese Academy of Geological Sciences, Beijing, China, for sample NL-DT01, at the Mineral Laser Microprobe Analysis Laboratory of China University of Geosciences, Beijing, China, for samples NL-DT02 and NL-AQ03, and at the Gengxin Geological Service Company Limited, Langfang, Hebei Province, China, for samples NL-LT01 and NL-LT02. Procedures followed those described by Liu et al.47. Data reduction was performed using ICPMSDataCal 10.2 (ref. 47) for off-line analyses and ComPbCorr#3‒151 (ref. 48) for common Pb correction. Zircon ages with >10% discordance were excluded from the final dataset. Uncertainties on individual analyses are reported with 1σ errors; weighted mean ages are reported at the 95% confidence level. Concordia diagrams were plotted and weighted mean ages were calculated using Isoplot 4.15 (ref. 49).

Paleomagnetic Laboratory Techniques and Measurements
A total of 400 paleomagnetic samples (6–13 cores per sampling site) were collected using a water-cooled portable driller. Samples were oriented using both a magnetic compass and a sun compass. Because the difference in declination between these two methods was <2°, corrections for local magnetic disturbances can be neglected.

All oriented core samples were cut into 2.2-cm long and 2.5-cm diameter specimens for rock-magnetic and paleomagnetic analyses. The specimens were processed and measured in the Paleomagnetism and Environmental Magnetism Laboratory of the China University of Geosciences, Beijing, China. First, thermal demagnetization of the three-axis IRMs21 was performed on typical specimens to identify ferromagnetic minerals and select the most appropriate demagnetization approach. Fields of 2.4, 0.4, and 0.12 T were successively applied using the IM10–30 pulse magnetizer along the z, y, and x-axes of the specimens, respectively. Then, stepwise thermal demagnetization to 680°C was performed and measured using an AGICO JR‒6A spinner magnetometer. Based on the results of rock-magnetism assessments, all specimens were then subjected to stepwise thermal demagnetization using an ASC TD‒48 Oven (residual magnetic field <10 nT). All remanent magnetizations were measured using a 2G 755‒4K cryogenic magnetometer and an AGICO JR-6A spinner magnetometer. All thermal demagnetization and remanence measurements were performed in a mu-metal shielded room with residual fields of less than 200 nT. Remanent magnetization directions of all specimens were determined using principal component analysis50. The site-mean directions were calculated using the statistics of Fisher51. All paleomagnetic data were analyzed using the computational packages of Enkin52 and Cogné53.

Monte Carlo simulation for the calculation of plate movement rates
Monte Carlo simulations were used to determine the uncertainty in the rates of plate movement between pairs of latitudes. Prior to each Monte Carlo simulation, the rate of plate motion as defined by mean latitudes, and mean ages were calculated using:

Raw rate = (mean latitude_young - mean latitude_old) / (mean age_young - mean age_old) (1)

Raw data can be found in Supplementary Table 4. Both plate latitudes and their ages have associated errors, so a Monte Carlo simulation was performed to best estimate of the rate of plate motion incorporating this uncertainty. For this approach, a large number of random ages and latitudes were selected from a Gaussian distribution to allow the 95% confidence interval of the estimate to be determined. The procedure used is as described below.

First, each latitude and age entry were resampled 10,000 times to generate new subsets of data (Supplementary Figs. 9–11). For example, as shown in Supplementary Fig. 9a, after the Monte Carlo simulation, the seven entries of the NCB were represented in seven discrete datasets, with each dataset containing 10,000 data points.

Second, the rate of plate motion was calculated for each subset, using:

rate = (latitude_young - latitude_old) / (age_young - age_old) (2)

where latitude_young is the location of the plate at the younger age, and latitude_old is the location of the plate at the older age. Northern latitudes are positive and southern latitudes negative. age_young and age_old are young and old ages (Ma), respectively.

Third, estimation of the rates of plate motion used a Monte Carlo simulation. We calculated the rate of plate motion 10,000 times. For each calculation, one data point from the dataset containing older plate positions and another from the dataset containing younger plate positions were sampled. A total of 10,000 calculations yielded a distribution containing 10,000 assessments of the rate of plate motion. The mean, median (50 percentile), 2.5 percentile, and 97.5 percentile of the distribution were calculated (Supplementary Table 5). In the case that data define a strictly normal distribution, the mean, mode, and median of the data should be similar. However, in cases where data are skewed, the mode and median may be more representative. In this study, the median is used to best represent the rate of plate motion, as it is not affected by outliers. Rates from degrees per million years converted to centimeters per year using the factor 11.1 (cm/yr)/(°/Myr).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Review of manuscript “New paleomagnetic evidence constrained tectonic drift to trigger the Early\nPermian aridification of North China” by Ren et al. for publication in Nature Communications.\nThis manuscript presents new paleomagnetic and U-Pb geochronology results from 2 Permian\nsection in North China. The authors then use the obtained age and paleolatitude constraints to\nestablish a paleolatitude sequence and argue for tectonic explanations for the observed climatic\nshifts in North China compared to Pangea. Furthermore, using a Monte Carlo simulation the\nauthors argue for rapid northward motion that caused the aridification in the area.\nWhile I do generally agree with the authors that the data is of high quality and the conclusions are\ncertainly based on the data, I do find some problems in the presentation and argumentation, which\nshould be addressed before the paper can be published.\nI will focus on the paleomagnetic data and implications, because this is what I know best. I am not\na particular expert for the Permian climatic evolution, especially the differences between North\nChina and Pangea. After reading this manuscript, I do agree that the topic is important and of great\ninterest. However, it sounds more like the authors strengthen a former hypothesis with new high-\nquality data. This does not address the complexity in climatic evolution between an island and a\nneighbouring supercontinent including a more or less confined ocean basin. So I am not sure if the\npresented story is rightly placed at Nature Communications. Having said that, I do believe that\nrobust data is always good especially for controversial topics like this.\nRegarding the general presentation, I would suggest the authors get some native English speaker\nwith knowledge of geology to correct the English language. The text sounds often very strange to\nme, which makes it at times hard to understand (e.g. l.63: “It provides important a unique…”).\nSecondly, I am very sceptical that the fold test of the Qingfengshan Fm is correct. Fig. 2c shows the\nfold test for the Dahongshan Fm, which has some high scatter before untilting and far less scatter\nafter untilting. There the picture in Fig.2c is very likely. However, the directions of Qingfengshan are\nvery similar, which should not result in such a graph, but a much flatter one. Doing a fold test\nmyself, I got a vey different result with an almost flat line (the maximum is still around 100%).\nMaybe I missed something, but the authors should definitely check this. I am not arguing against\nprimary origin, which is also shown by the reversal test, but the presentation should be consistent.\nFinally, and most importantly, I do have some problems with the arguments for the high plate\nvelocity. Generally, the arguments by the authors makes sense, and it is very justified to argue for\nclimatic changes related to latitudinal changes. However, I have some points of criticism in the\nauthors argumentation: (1) why do the authors not use data from the same section with maybe the\nsame lithology? In Siziwangqi for example, there is an age of 277 not far above the sampling with\nsimilar volcanic rocks, which would be a good target as well? Seeing the latitudinal changes in one\nsection would be more convincing, since both areas are also represented by different lithologies.\nThis leads to my second point (2) the inclination shallowing correction is very well carried out, while\n112 samples are sufficient but on the lower end (Tauxe and Kent are proposing to use more than\n100), but the uncertainty of this analysis is quite large. This is related to the lack of elongation\nand to the method itself. In my experience, this technique is very susceptible to outliers, so it is not\nvery stable with this low amount of samples. In any case, the uncertainties of this analysis should be\ntaking into account, which the authors don’t do. In the study, if I understand it correctly, the authors\nuse the resulting inclination with the corresponding alpha95 value, which is very small. Only\nusing this values the authors get a high shift in latitudes. Taking the uncertainties into account would\nonly require a very low latitudinal shift between the two results when taking the low end of the EI\nuncertainty interval. Again, I do believe the data is of very high quality and this is a good story, but I\nthink some more discussion should be presented to take the data seriously.", "reviewer_2": "This is a clear and interesting study arguing for the primary trigger of the late Paleozoic to early\nMesozoic aridification of North China by paleomagnetism, which yields two seemingly robust Early\nPermian paleomagnetic poles from the northern margin of the North China Block (NCB), indicating\na fast-northward drift from the tropical humid to subtropical arid zones during the period between\n~290 and ~281 Ma. Although the topic, rapid-northward drift of the NCB triggered the aridification of\nNorth China, could be traced back at least more than two or three decades ago (e.g., Wu, HN et al.,\nChinese J Geophys. 1990; Cope et al., Inter. Geol. Rew. 2005), and the comprehensive review of the\npublished late Paleozoic to early Mesozoic paleomagnetic poles shows the rapid latitudinal\nmovement of the NCB (from ~10°N to >20°N) was occurred around the Permian-Triassic boundary\n(i.e., ~260-240 Ma, Figure 3 of Huang et al., Earth Sci. Rev. 2018), the new Early Permian robust\npaleomagnetic results from this study provide more robust evidence to constrain the northward\ndrift history of the NCB, which might be the primary trigger for the aridification of North China\nduring the late Paleozoic to early Triassic times.\nFirstly, the first Early Permian paleomagnetic pole (~290 Ma) is isolated from a suit of lava flow with\nrobust field tests supporting its high quality for paleogeographic reconstruction. Whilst another\nEarly Permian pole was identified from a clastic sequence, of course, with some tuff interbeds\nproviding absolute geochronological dating age around ~281 Ma. Both dual polarities and positive\nfold test result indicate the characteristic remanent magnetization (ChRM) was very likely the\nprimary romance acquired during the formation of the member I of the Qingfengshan Formation\n(~1000-m thick). Although either the ~290 Ma pole from the volcanic rocks or the ~281 Ma pole from\nthe siltstones yield a comparable paleolatitude of around ~13°N-16°N at reference site (42.5°N,\n119.5°E) for the NCB during the period of ~290-281 Ma, the authors prefer to use the E/I method to\nperform an inclination shallowing correction for the clastic rocks and then yields a much higher\npaleolatitude (~22°N) for the member I of the Qingfengshan Formation. Considering the late\nPaleozoic volcanic and clastic rocks from the North China, South China and North Qiangtang\nblocks (Zhao et al., 1990; Huang et al., 2018; Cheng et al., 2013; Supplementary Table 3) yielded\ncompatible paleomagnetic results, which indicating none or no significant inclination shallowing\nwas observed from these clastic rocks in these blocks, I wonder if the ~281 Ma clastic rocks are\nreally suffered from significant inclination shallowing? If so, the main finding of this study (very fast\nnorthward drift of the NCB during the Early Permian) should be a missense. For this issue, I suggest\nthe authors to do further studies such as the anisotropy of high-field IRM (hf-AIR, Billardello &\nKodama, 2009) to confirm if the suspicion is correct. In addition, noting that Meert et al. (2020)\nstate that “… any poles based on flattening corrections will not meet the R5 criterion unless the\ninclinations are corroborated by paleomagnetic data from either intercalated volcanic rocks that\nhave a similar R-value or other sedimentary rocks within the same sequence that do not require\nflattening corrections (Section 3.5, page 10)”, I do not think the ~281 Ma clastic flattening-corrected\npole (this study) is a robust evidence for the very fast northward drift history of the NCB during the\nlate Paleozoic to early Mesozoic.\nSecondary, noting that paleomagnetic calculation of plate drift rate is strongly depend on the age of\npaleomagnetic pole, the estimated age uncertainty of the selected paleomagnetic poles\n(Supplementary Table 4) should be a key point for the discussions. I note that the authors give a age\nerror of 1.6 Ma for the ~281 Ma clastic pole; however, this age error is a geochronological dating\nerror for the tuff layer in the middle of the sampling section (Figure 1d) rather than the duration of\nthe sampled siltstone sequence (i.e., the member I of the Qingfengshan Formation), which was\nconformably covered by the member II and member III of the Qingfengshan Formation with two\ngeochronological ages of ~257 to 254 Ma in the top of the member III and of ~273 Ma in the bottom\nof the member II (Figure 1d). Considering the three members of the Qingfengshan Formation have\ncomparable thickness of ~1000 m, the member I of the Qingfengshan Formation may have a\nduration around 10 million years, and if taking this age uncertainty into account, estimation of the\nnorthward drift rate of the NCB during the Permian should be quite different. Anyway, for this issue,\nthe authors need to provide details about the age-error in the calculation.\nThirdly, the authors use the distribution of coal seams and red bed deposits to be the climate\nindicators for the tropical humid and subtropical arid zones of the NCB, respectively, and conclude\nthat the NCB’s transition from the tropical humid to subtropical arid zone is diachronous ranging\nfrom the Early Permian in the western and northern parts to the Late Permian in the southern\nmargin of the NCB (Figures 3-4 and Supplementary Figure 11). This view might be valid; however,\nwhether a suit of red rocks indicates an arid sedimentary environment also depends on its lithology\nand sedimentary facies. For example, it was well known that Permian rocks in North China\nbasically began to turn red from the Lower Shihhotse Formation (Cisuralian), while the\nsandstone actually turned red from the Shiqianfeng/Sunjiagou Formation (Lopingian). The Lower\nShihhotse and Upper Shihhotse (Cisuralian, Wu Q et al., Geology 2021) formations of North China\nbasically developed in delta plain environment, where sediments were deposited above the sea\nlevel, in distributary channel or flood plain facies. In this sedimentary environment, the Lower\nShihhotse and Upper Shihhotse sandstones, developed in distributary channel facies, actually does\nnot show red color, while the flood plain facies mudstone, exposed in the air and experienced\nlong-term oxidation after sedimentation, generally displays red color. In other words, the red\nmudstone in the flood plain facies probably does not represent a totally arid\nenvironment. Instead, the assemblage of red mudstones and yellowish sandstones in\ndelta plain environment might reflect a transitional subhumid to subarid environment.\nGenerally, colors of terrestrial sandstones developed in fluvial facies or distributed\nchannel facies, having not been long-termly exposed to the air after sedimentation,\ncould be more reliable indicator of an arid environment. In North China, it was not until\nthe latest Permian (the upper part of the Lopingian Shiqianfeng/Sunjiagou Formation) that the\nstrata sequence was actually transformed into a fluvial facies red bed. In addition, Wu Q et al.\n(Geology 2021) proposed a tectonism-related sedimentary unconformity of ~20 million years from\nthe late Cisuralian to Guadalupian (~280–260 Ma) between the Upper Shihhotse and Sunjiagou\nformations, based on high resolution CA-ID-TIMS U-Pb dating. Regardless of whether the\nunconformity is of general significance in North China, they clearly pointed out that the Upper and\nLower Shihhotse formations in central North China belong to the humid to subhumid zone, and only\nevolved into an arid climate during the formation of the Lopingian Sunjiagou Formation. Thus, the\ntransition from tropical humid to subtropical arid environments was more likely a step-by-step\nprocess.\nFinally, even if the timing of the rapid northward migration of the NCB (from tropical humid to\nsubtropical arid zone) constrained by paleomagnetic data coincides well with the timing of the\naridification of the most of North China, whether the rapid migration of North China from tropical\nhumid to subtropical arid zone is the triggering mechanism or the primary factor of aridification in\nNorth China still needs further studies. As concluded by Wu Q et al. (2021), “similarities in the floral\nand climate shift histories between Euramerica and North China suggest that aside from the\nregional tectonic controls and continental movement, extensive volcanism during the Cisuralian\nmay have played a major role in the global warming and aridification in the aftermath of the late\nPaleozoic ice age (LPIA)”. In other words, current study may provide robust evidence for the rapid\nnorthward migration of the NCB from the tropical humid to subtropical arid zones during the late\nPaleozoic; but its significance and originality to the aridification of North China as well as the global\nclimate change after the LPIA is open to debate."}, "author_response": "Dear Reviewers,\nThanks very much for taking your time to review this manuscript. We really\nappreciate all your comments and suggestions. We have carefully revised our\nmanuscript according to your comments and suggestions. The changes are marked in\nred words in the revised manuscript. The following is our point-by-point response to\nthe comments and suggestions.\nReviewer #1:\nPoint 1: I will focus on the paleomagnetic data and implications, because this is what\nI know best. I am not a particular expert for the Permian climatic evolution, especially\nthe differences between North China and Pangea. After reading this manuscript, I do\nagree that the topic is important and of great interest. However, it sounds more like the\nauthors strengthen a former hypothesis with new high-quality data. This does not\naddress the complexity in climatic evolution between an island and a neighbouring\nsupercontinent including a more or less confined ocean basin. So I am not sure if the\npresented story is rightly placed at Nature Communications. Having said that, I do\nbelieve that robust data is always good especially for controversial topics like this.\nAnswer: Thanks for the comment. The internal aridity of Pangea is likely influenced\nby the interaction of several factors, including the Hercynian orogeny, rising\natmospheric CO levels, and deglaciation (Tabor & Poulsen, 2008; Montañez &\nLPIA), the North China Block (NCB), an island block in the Tethys Ocean, rapidly\ndrifted towards the Pangea continent. This mode of aridification differs markedly from\nthat of the inner Pangea supercontinent. Additionally, the other Tethyan island blocks\nin low-latitude regions, such as the South China and Indochina blocks, underwent rapid\nnorthward motion. However, only the NCB traversed multiple climatic zones, resulting\nin progressive intra-plate aridification from north to south, while the other blocks\nmaintained a tropical humid environment near the equator (Fig. 4). If North China had\nnot undergone rapid latitudinal drift from the tropics to the arid zone, it likely would\nhave remained in a humid environment, similar to other low-latitude Tethyan island\nblocks. We therefore conclude that the rapid drift of North China was the key driver of\nits gradual spatiotemporal aridification. The results provide unique insights into the\nmechanisms driving regional climate change in the context of global aridification. We\nbelieve that our study on regional climate changes driven by plate tectonics offers\nsignificant insights into the co-evolution of Earth's surface systems.\nTo enhance readers' understanding of the complex climatic evolution of the NCB\nrelative to Pangea and the other Tethyan island blocks, we have expanded the\ndiscussion in lines 305–311.\nPoint 2: Regarding the general presentation, I would suggest the authors get some\nnative English speaker with knowledge of geology to correct the English language. The\ntext sounds often very strange to me, which makes it at times hard to understand (e.g.\nl.63: “It provides important a unique…”).\nAnswer: We sincerely apologize for any language shortcomings in the initial\nsubmission. We have since consulted with a native English speaker who has expertise\nin geology to thoroughly review and improve the language throughout the manuscript.\nWe hope that the quality of the language has been significantly enhanced in this revised\nversion.\nPoint 3: Secondly, I am very sceptical that the fold test of the Qingfengshan Fm is\ncorrect. Fig. 2c shows the fold test for the Dahongshan Fm, which has some high scatter\nbefore untilting and far less scatter after untilting. There the picture in Fig.2c is very\nlikely. However, the directions of Qingfengshan are very similar, which should not\nresult in such a graph, but a much flatter one. Doing a fold test myself, I got a vey\ndifferent result with an almost flat line (the maximum is still around 100%).\nMaybe I missed something, but the authors should definitely check this. I am not\narguing against primary origin, which is also shown by the reversal test, but the\npresentation should be consistent.\nAnswer: Thanks for the suggestion. We have re-examined the data carefully. Since\nfolding occurred after inclination shallowing, we opted to use the data prior to the E/I\ncorrection. This pre-correction dataset was analyzed using the stepwise unfolding\nmethod in the PMGSC software. It is important to note that before running the analysis,\nthe polarity of the data must be unified; otherwise, the software is unable to recognize\nit. Please refer to the figure below for further clarification.\nPoint 4: Finally, and most importantly, I do have some problems with the arguments\nfor the high plate velocity. Generally, the arguments by the authors makes sense, and it\nis very justified to argue for climatic changes related to latitudinal changes. However,\nI have some points of criticism in the authors argumentation: (1) why do the authors\nnot use data from the same section with maybe the same lithology? In Siziwangqi for\nexample, there is an age of 277 not far above the sampling with similar volcanic rocks,\nwhich would be a good target as well? Seeing the latitudinal changes in one section\nwould be more convincing, since both areas are also represented by different lithologies.\nThis leads to my second point (2) the inclination shallowing correction is very well\ncarried out, while 112 samples are sufficient but on the lower end (Tauxe and Kent are\nproposing to use more than 100), but the uncertainty of this analysis is quite large. This\nis related to the lack of elongation and to the method itself. In my experience, this\ntechnique is very susceptible to outliers, so it is not very stable with this low amount of\nsamples. In any case, the uncertainties of this analysis should be taking into account,\nwhich the authors don’t do. In the study, if I understand it correctly, the authors use the\nresulting inclination with the corresponding alpha95 value, which is very small. Only\nusing this values the authors get a high shift in latitudes. Taking the uncertainties into\naccount would only require a very low latitudinal shift between the two results when\ntaking the low end of the EI uncertainty interval. Again, I do believe the data is of very\nhigh quality and this is a good story, but I think some more discussion should be\npresented to take the data seriously.\nAnswer: Thank you for your valuable suggestions. With your important reminder, we\nwere able to collect 155 paleomagnetic samples (andesites and sandstones) and two\ngeochronology samples from the upper member of the Dahongshan Formation (near\n~277 Ma section; Li et al., 2018) in the Siziwangqi area in August. We obtained an\neruption age of ~281.3–279.9 Ma (Fig. S2), which is consistent with the age of the\nQingfengshan Formation.\nIn terms of paleomagnetic results, we conducted stepwise thermal\ndemagnetization on 133 samples from 15 sites, successfully isolating stable high-\ntemperature components (HTCs). These HTCs passed both fold and conglomerate tests,\nconfirming that they represent primary magnetization. Since the data come from\ninterbedded volcanic and clastic rocks with similar paleomagnetic directions (see Meert\net al., 2020), they effectively rule out the influence of paleosecular variation and\ninclination shallowing.\nAdditionally, there is no significant difference between the ~281 Ma new\npaleomagnetic direction and that of the red beds of the Qingfengshan Formation from\na similar time period. The virtual geomagnetic poles (VGPs) from both formations\npassed significance testing (see figure below), further supporting the reliability of the\nE/I correction for the red beds of the Qingfengshan Formation.\nWe have included a new sketch of the Dahongshan Formation section in\nSiziwangqi and incorporated descriptions of the new results from the upper member of\nthe Dahongshan Formation in the main text.\nReviewer #2 (Prof. Baochun Huang):\nPoint 1: Firstly, the first Early Permian paleomagnetic pole (~290 Ma) is isolated from\na suit of lava flow with robust field tests supporting its high quality for paleogeographic\nreconstruction. Whilst another Early Permian pole was identified from a clastic\nsequence, of course, with some tuff interbeds providing absolute geochronological\ndating age around ~281 Ma. Both dual polarities and positive fold test result indicate\nthe characteristic remanent magnetization (ChRM) was very likely the primary\nromance acquired during the formation of the member I of the Qingfengshan Formation\n(~1000-m thick). Although either the ~290 Ma pole from the volcanic rocks or the ~281\nMa pole from the siltstones yield a comparable paleolatitude of around ~13°N-16°N at\nreference site (42.5°N, 119.5°E) for the NCB during the period of ~290-281 Ma, the\nauthors prefer to use the E/I method to perform an inclination shallowing correction for\nthe clastic rocks and then yields a much higher paleolatitude (~22°N) for the member I\nof the Qingfengshan Formation. Considering the late Paleozoic volcanic and clastic\nrocks from the North China, South China and North Qiangtang blocks (Zhao et al.,\n1990; Huang et al., 2018; Cheng et al., 2013; Supplementary Table 3) yielded\ncompatible paleomagnetic results, which indicating none or no significant inclination\nshallowing was observed from these clastic rocks in these blocks, I wonder if the ~281\nMa clastic rocks are really suffered from significant inclination shallowing? If so, the\nmain finding of this study (very fast northward drift of the NCB during the Early\nPermian) should be a missense. For this issue, I suggest the authors to do further studies\nsuch as the anisotropy of high-field IRM (hf-AIR, Billardello & Kodama, 2009) to\nconfirm if the suspicion is correct. In addition, noting that Meert et al. (2020) state that\n“… any poles based on flattening corrections will not meet the R5 criterion unless the\ninclinations are corroborated by paleomagnetic data from either intercalated volcanic rocks that\nhave a similar R-value or other sedimentary rocks within the same sequence that do not require\nflattening corrections (Section 3.5, page 10)”, I do not think the ~281\nMa clastic flattening-corrected pole (this study) is a robust evidence for the very fast\nnorthward drift history of the NCB during the late Paleozoic to early Mesozoic.\nAnswer: Thanks for your thoughtful comment. We agree with your observation that\nthe most robustly studied paleomagnetic sections are those containing interlayers of\nvolcanic and clastic rocks. Following the reviewers' valuable suggestions, we were able\nto collect 155 paleomagnetic samples (andesites and intercalated sandstones) and two\ngeochronology samples from the upper member of the Dahongshan Formation (near\n~277 Ma section; Li et al., 2018) in the Siziwangqi area this summer. The obtained\neruption age of ~281.3–279.9 Ma (Fig. S2) is consistent with the age of the\nQingfengshan Formation.\nRegarding paleomagnetism, we successfully isolated stable high-temperature\ncomponents (HTCs) from 133 samples across 15 sites using stepwise thermal\ndemagnetization. The HTCs passed both the fold and conglomerate tests, confirming\nthat they represent primary magnetization. Given that these data originate from\ninterbedded volcanic and clastic rocks with similar paleomagnetic directions (see Meert\net al., 2020), they effectively rule out the influence of paleosecular variation and\ninclination shallowing.\nMoreover, there is no significant difference between the newly obtained directions\nand those from the red beds of the Qingfengshan Formation of a similar age (~281 Ma).\nThe virtual geomagnetic poles (VGPs) for both formations passed a significance test\n(see figure below), further confirming the reliability of the E/I correction applied to the\nred beds of the Qingfengshan Formation.\nWe have also included a new sketch section of the Dahongshan Formation in\nSiziwangqi, and the description of the new results from the upper member of the\nDahongshan Formation has been incorporated into the main text.\nPoint 2: Secondary, noting that paleomagnetic calculation of plate drift rate is strongly\ndepend on the age of paleomagnetic pole, the estimated age uncertainty of the selected\npaleomagnetic poles (Supplementary Table 4) should be a key point for the discussions.\nI note that the authors give a age error of 1.6 Ma for the ~281 Ma clastic pole; however,\nthis age error is a geochronological dating error for the tuff layer in the middle of the\nsampling section (Figure 1d) rather than the duration of the sampled siltstone sequence\n(i.e., the member I of the Qingfengshan Formation), which was conformably covered\nby the member II and member III of the Qingfengshan Formation with two\ngeochronological ages of ~257 to 254 Ma in the top of the member III and of ~273 Ma\nin the bottom of the member II (Figure 1d). Considering the three members of the\nQingfengshan Formation have comparable thickness of ~1000 m, the member I of the\nQingfengshan Formation may have a duration around 10 million years, and if taking\nthis age uncertainty into account, estimation of the northward drift rate of the NCB\nduring the Permian should be quite different. Anyway, for this issue, the authors need\nto provide details about the age-error in the calculation.\nAnswer: We appreciate the valuable suggestion. In the revised manuscript, we have\nincorporated new paleomagnetic and geochronologic data from the upper member of\nthe Dahongshan Formation. This includes two age determinations from the top and\nbottom of the paleomagnetic section, allowing for tighter age constraints. Furthermore,\nthis new data aligns well with the paleomagnetic and chronological data from the red\nbeds of member I of the Qingfengshan Formation. As a result, we are confident in using\nthe new data from the upper member of the Dahongshan Formation for the next phase\nof Monte Carlo simulations and plate motion rate discussions. Importantly, our\nconclusion regarding the rapid latitudinal movement of the plate remains unchanged.\nPoint 3: Thirdly, the authors use the distribution of coal seams and red bed deposits to\nbe the climate indicators for the tropical humid and subtropical arid zones of the NCB,\nrespectively, and conclude that the NCB’s transition from the tropical humid to\nsubtropical arid zone is diachronous ranging from the Early Permian in the western and\nnorthern parts to the Late Permian in the southern margin of the NCB (Figures 3-4 and\nSupplementary Figure 11). This view might be valid; however, whether a suit of red\nrocks indicates an arid sedimentary environment also depends on its lithology and\nsedimentary facies. For example, it was well known that Permian rocks in North China\nbasically began to turn red from the Lower Shihhotse Formation (Cisuralian), while the\nsandstone actually turned red from the Shiqianfeng/Sunjiagou Formation (Lopingian).\nThe Lower Shihhotse and Upper Shihhotse (Cisuralian, Wu Q et al., Geology 2021)\nformations of North China basically developed in delta plain environment, where\nsediments were deposited above the sea level, in distributary channel or flood plain\nfacies. In this sedimentary environment, the Lower Shihhotse and Upper Shihhotse\nsandstones, developed in distributary channel facies, actually does not show red color,\nwhile the flood plain facies mudstone, exposed in the air and experienced long-term\noxidation after sedimentation, generally displays red color. In other words, the red\nmudstone in the flood plain facies probably does not represent a totally arid\nenvironment. Instead, the assemblage of red mudstones and yellowish sandstones in\ndelta plain environment might reflect a transitional subhumid to subarid environment.\nGenerally, colors of terrestrial sandstones developed in fluvial facies or distributed\nchannel facies, having not been long-termly exposed to the air after sedimentation,\ncould be more reliable indicator of an arid environment. In North China, it was not until\nthe latest Permian (the upper part of the Lopingian Shiqianfeng/Sunjiagou Formation)\nthat the strata sequence was actually transformed into a fluvial facies red bed. In\naddition, Wu Q et al. (Geology 2021) proposed a tectonism-related sedimentary\nunconformity of ~20 million years from the late Cisuralian to Guadalupian (~280–260\nMa) between the Upper Shihhotse and Sunjiagou formations, based on high resolution\nCA-ID-TIMS U-Pb dating. Regardless of whether the unconformity is of general\nsignificance in North China, they clearly pointed out that the Upper and Lower\nShihhotse formations in central North China belong to the humid to subhumid zone,\nand only evolved into an arid climate during the formation of the Lopingian Sunjiagou\nFormation. Thus, the transition from tropical humid to subtropical arid environments\nwas more likely a step-by-step process.\nAnswer: Thanks for the comment. We agree that different sedimentary facies may yield\nrocks of varying colors. Based on regional geological data from North China (Wu et al.,\n2021; Shen et al., 2022), there is no significant lithofacies selectivity associated with\nclimatic changes during the interval of 295–280 Ma across the region. The Lower\nShihhotse and Upper Shihhotse formations are predominantly composed of fluvial\nsediments (see Supplementary Information in Wu et al., 2021, Geology), indicating that\nthe observed black-red transition is not influenced by regional lithofacies.\nThe disappearance of the 290–280 Ma coal seams in North China marks the\ntransition from a humid to an arid environment, encompassing a brief semi-humid to\nsemi-arid phase, which is an important period of environmental drought. The coal\nseams in the lower part of the Upper Shihhotse Formation have vanished, and fluvial\nred beds have begun to appear. Additionally, drought-tolerant species such as Ginkgo\nbiloba and conifers emerged during the early stages of the Upper Shihhotse Formation,\ngradually occupying more competitive ecological niches (Liu et al., 2015; Shen et al.,\n2022). These findings collectively indicate a notable increase in aridity in North China\nduring this period, though the degree of aridification was not as pronounced as that\nobserved in the Shiqianfeng Formation. Furthermore, North China may have been\ninfluenced by the rain shadow effect resulting from the uplift of the northern mountains,\ncompounded by global warming, which exacerbated overall drying during the\nShiqianfeng Formation. To clarify the geological manifestations of aridity in North\nChina, we have added a discussion in lines 273–281 of the revised manuscript.\nPoint 4: Finally, even if the timing of the rapid northward migration of the NCB (from\ntropical humid to subtropical arid zone) constrained by paleomagnetic data coincides\nwell with the timing of the aridification of the most of North China, whether the rapid\nmigration of North China from tropical humid to subtropical arid zone is the triggering\nmechanism or the primary factor of aridification in North China still needs further\nstudies. As concluded by Wu Q et al. (2021), “similarities in the floral and climate shift\nhistories between Euramerica and North China suggest that aside from the regional\ntectonic controls and continental movement, extensive volcanism during the Cisuralian\nmay have played a major role in the global warming and aridification in the aftermath\nof the late Paleozoic ice age (LPIA)”. In other words, current study may provide robust\nevidence for the rapid northward migration of the NCB from the tropical humid to\nsubtropical arid zones during the late Paleozoic; but its significance and originality to\nthe aridification of North China as well as the global climate change after the LPIA is\nopen to debate.\nAnswer: Good comment. We agree that the background of global warming at the end\nof the LPIA may have influenced the arid climate in North China, although quantifying\nthis impact is challenging. During this period of global warming, several Tethyan island\nblocks in low latitudes, such as the South China and Indochina blocks, did not transition\nto arid environments (Fig. 4). If North China had not undergone rapid latitudinal drift\nfrom the tropics to the arid zone, it likely would have remained a wet environment,\nsimilar to these low-latitude Tethyan island blocks. Therefore, we conclude that the\nrapid drift of the North China Block serves as the primary mechanism triggering the\ngradual spatiotemporal aridity. The subsequent severe aridity in North China may be\nattributed to both global warming and the rain shadow effect resulting from the uplift\nof the high mountains along the northern margin. Of course, we agree that the\ncontribution of these factors to the Permian aridity of North China is still worthy of\nfurther study. To better articulate the relationship between North China and global\nclimate change, we have added a discussion in lines 305–311 of the revised manuscript.\nWe would like to express our sincere gratitude to the reviewers for your\nconstructive comments and suggestions. We have made every effort to revise the\nmanuscript in accordance with your recommendations and to enhance its quality to\nmeet the journal’s publication standards."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors did a great job in improving the paper at the data side. All my concerns were addressed\nand I think the high quality dataset is in an even better shape now, leaving no room of speculation\nthat the conclusions of the authors are supported by the data.\nI still do think the paper needs some improvement in making the global significance better\nunderstandable. The abstract was barely changed, and it concludes that “the tectonic drift of the\nNCB into a subtropical arid zone between 290 and 280 Ma was the main driver of regional\naridification.” So what is the global significance of the results? It sounds like the results support the\nshifts seen in North China are related to motion of the NCB. That is a nice result, but why should\nsomeone who studies e.g. climate evolution in the Permian or climate related to supercontinents or\nsomeone else care about these results? I don’t quite follow the argumentation in the discussion: I\nthought the results fit with models of where the arid belts etc. are, so how can this help to constrain the\n“climate zone of the Paleo-Tethys”, wasn’t this used as a reason for shifts in sediment type? In\nline 318 the authors write that “rapid paleogeographic changes in the Tethyan demain may have\nbeen the primary reason for the sudden decrease in terrestrial and marine biodiversity”? This has to\nbe further explained! I remember a talk by Celal Sengor (e.g. Paleo-Tethys, Permian extinction, and\nstratabound copper-sulfide deposits of the Cimmerides, Arizona Geological Digest 22, 2008) that\nthe closure of the Paleotethys caused the Permian mass extinction, is this something the authors\nwant to imply? I am no expert there, so I don’t know the recent publications in this topic, but that\nwould be the only reason I could see in making the paleogeographic motions of the NCB globally\ninteresting. I think this is needed to put the unquestionable great paleomagnetic results in a global\nperspective apart from regional climatic changes due to motion through climate zones.", "reviewer_2": "The authors seem to have addressed all the issues raised by the reviewers, but some substantive\nissues (such as: the influence of the error/uncertainties of the paleomagnetic data as well as their\nage constraints on the rapid change of the paleoposition of the North China Block (NCB) in\nPermian; whether the rapid change of the paleoposition of North China was the trigger/primary\nfactor of aridification at the end of the Permian in North China; why does the newly obtained ~280\nMa paleomagnetic pole almost overlap with the Triassic paleomagnetic poles from the Ordos Basin\nof western NCB?) seem to be no better explanation or solution. In conclusion, the paleomagnetic\ndata in this paper looks be of high quality and reliable. However, the originality and regional/global\nsignificance of the scientific questions discussed are debatable."}, "author_response": "Dear Reviewers,\nThank you very much for taking the time to review our manuscript again. We\ngreatly appreciate all your comments and suggestions. In response, we have carefully\nrevised the manuscript, incorporating your feedback. The changes are marked in red\nwords in the revised manuscript. The following is our point-by-point response to\nthe comments and suggestions.\nReviewer #1:\nPoint 1: The abstract was barely changed, and it concludes that “the tectonic drift of\nthe NCB into a subtropical arid zone between 290 and 280 Ma was the main driver of\nregional aridification.” So what is the global significance of the results? It sounds like\nthe results support the shifts seen in North China are related to motion of the NCB. That\nis a nice result, but why should someone who studies e.g. climate evolution in the\nPermian or climate related to supercontinents or someone else care about these results?\nAnswer: Thanks for your insightful comment. Previous studies based on\npaleogeographic reconstructions have suggested that the widespread aridity of the\nPangea supercontinent might be linked to the equatorward migration of arid climatic\nzones due to shifts in the Intertropical Convergence Zone. However, due to the\ndifficulty in precisely delineating climate zone boundaries, the implications for the\nTethys Ocean domain remain unclear. The North China Block (NCB), drifted in the\nTethys Ocean domain underwent a climatic transition from a tropical rainforest to an\narid environment during the Early Permian. This transition provides offers a unique\nopportunity trace the boundary between tropical wet and subtropical arid climatic zones\nin the Tethys Ocean. Our paleomagnetic data reconstruct the paleogeographic positions\nof the NCB at 290 and 280 Ma. Combined with the distribution of climate-sensitive\nsediments, we reconstructed the Tethys Oceanic climate zone showing that the\nboundary between the tropical wet belt and the subtropical arid belt across the central\nNCB at ~280 Ma (~15–25°N; Fig. 4). This spatial arrangement is comparable to modern\nclimatic zonation patterns. These findings suggest that the Tethys oceanic regions\nexhibited greater climatic stability compared to the Pangea supercontinent during the\nEarly Permian.\nWe greatly appreciate your suggestion to place North China within the global\nclimatic zonation framework. This perspective has enhanced the quality of our\nmanuscript. We have incorporated these insights into the abstract, introduction (lines\n36-46), and discussion (lines 261–268 and 318–322). To better illustrate the global\nsignificance, we replace the 3D projection in Figure 4 with the Mollweide projection.\nPoint 2: I don’t quite follow the argumentation in the discussion: I thought the results\nfit with models of where the arid belts etc. are, so how can this help to constrain the\n“climate zone of the Paleo-Tethys”, wasn’t this used as a reason for shifts in sediment\ntype?\nAnswer: Thank you for pointing out the error in this expression. Integrating these\npaleomagnetic data with evidence from climate-sensitive sediments, we reconstruct the\npaleogeographic locations of the NCB, identifying the boundary between the Tropical\nWet Belt and the Subtropical Arid Belt across its central region. This provides strong\nevidence for tracing this boundary in the Tethys Ocean. We have modified it in lines\n261-268.\nPoint 3: In line 318 the authors write that “rapid paleogeographic changes in the\nTethyan demain may have been the primary reason for the sudden decrease in terrestrial\nand marine biodiversity”? This has to be further explained! I remember a talk by Celal\nSengor (e.g. Paleo-Tethys, Permian extinction, and stratabound copper-sulfide deposits\nof the Cimmerides, Arizona Geological Digest 22, 2008) that the closure of the\nPaleotethys caused the Permian mass extinction, is this something the authors want to\nimply? I am no expert there, so I don’t know the recent publications in this topic, but\nthat would be the only reason I could see in making the paleogeographic motions of the\nNCB globally interesting. I think this is needed to put the unquestionable great\npaleomagnetic results in a global perspective apart from regional climatic changes due\nto motion through climate zones.\nAnswer: Thanks for your suggestions. In revision, we put the NCB in a global\nperspective. Our high-resolution paleogeographic reconstruction of Early Permian\nNorth China combined with climate-sensitive sediments enables us to accurately trace\nthe boundary between wet and arid climate zones over the Tethys Ocean. By comparing\nthe climate zone patterns within the Pangea supercontinent, we can fully understand the\nglobal climate zone patterns during the aridification period.\nAdditionally, we have elaborated on the primary causes of the sudden decrease in\nterrestrial and marine biodiversity in lines 308–316. First, the northward drift of the\nNCB reduced the area of Tethyan landmasses in the tropics (Fig. 4), likely decreasing\nsilicate weathering, which in turn elevated atmospheric pCO levels and contributed to\n2\nglobal warming during the Sakmarian–Artinskian. Second, the rapid convergence of\nlow-latitude Tethyan landmasses toward Pangea triggered intense volcanic activity, as\nevidenced by detrital zircon age peaks at 290–280 Ma (Fig. 3c). The resulting massive\nvolcanic emissions likely exacerbated global warming during the Early Permian. Thus,\nthe combined effects of intense volcanic emissions from Tethyan plate convergence\nand the NCB’s rapid passage through various climatic zones likely drove sudden global\nwarming, ultimately causing a dramatic decline in both terrestrial and marine\nbiodiversity.\nReviewer #2 (Prof. Baochun Huang):\nPoint 1: the influence of the error/uncertainties of the paleomagnetic data as well as\ntheir age constraints on the rapid change of the paleoposition of the North China Block\n(NCB) in Permian.\nAnswer: In our research, we accounted for errors in both plate latitudes and ages, which\nare overlooked by simple arithmetic averaging methods, making the calculated plate\nmotion rates less reliable. To address this, we employed the Monte Carlo simulation\nmethod, which has gained wide acceptance in recent studies (e.g., Swanson-Hysell et\nal., 2019-GSAB; Fu et al., 2022-SA). This approach, based on statistical principles, is\ncurrently the best method for estimating plate motion rates while incorporating these\nuncertainties. This methodological approach is a key feature of our study. We have\nprovided detailed descriptions of the methods in the Methods section at the end of the\ntext and have clarified our intentions in the Discussion section (lines 241–244).\nPoint 2: whether the rapid change of the paleoposition of North China was the\ntrigger/primary factor of aridification at the end of the Permian in North China\nAnswer: Thanks for the comment. This study focuses on the rapid northward\nmovement of North China during the Early Permian (290-280 Ma) and its role in\ntriggering aridification during that period. However, the aridification at the end of the\nPermian (~255 Ma) occurred approximately 30 million years later. The NCB had\nbecome part of the Pangea supercontinent at the end of the Permian, and its climate was\npredominantly influenced by the supercontinental climate system. The mechanisms\ndriving aridification at the end of the Permian are more complex and multifaceted,\ninvolving global climatic shifts and tectonic processes. Currently, we lack definitive\nevidence to confirm whether the earlier rapid paleogeographic changes of the NCB\nwere a trigger or a primary factor contributing to its later aridification.\nPoint 3: why does the newly obtained ~280 Ma paleomagnetic pole almost overlap\nwith the Triassic paleomagnetic poles from the Ordos Basin of western NCB?\nAnswer: Thanks for the question. The robust paleomagnetic tests have proved the\nreliability of our 280 Ma data. The reliability of our 280 Ma paleomagnetic data has\nbeen confirmed through robust paleomagnetic tests. Even if it may overlap with the\nEarly Triassic (T1) paleopole, this could suggest unobvious plate movement between\nthese periods. To explore this further, we compared our 280 Ma paleomagnetic pole\nwith the Early Triassic poles (reviewed in Huang et al., 2018, ESR; see Figure below).\nOur analysis shows that, despite similar latitudes between the 280 Ma data and the\nOrdos Early Triassic data, there are notable differences in declination. Importantly, the\ntwo 280 Ma consistent paleomagnetic data were obtained from two very far apart\nsections, reinforcing its representativeness of the stable NCB. The declination\ndifferences between the 280 Ma data and the Ordos T1 paleomagnetic data reflect a\nvariation in the paleo-azimuth of the entire NCB. Moreover, the T1 paleomagnetic data\nfrom Ordos are based on clastic rock samples, which have been shown to exhibit\nsignificant inclination shallowing, with a correction factor (f) of approximately 0.6\n(Zhou et al., 2018). After applying the E/I correction, the mean pole of these T1\npaleomagnetic data (Zhou et al., 2018) diverges significantly from our 280 Ma\npaleomagnetic pole (see Figure below). We have added the discussion in\nSupplementary text.\nWe would like to express our sincere gratitude to the reviewers for your\nconstructive comments and suggestions. We have carefully revised the manuscript in\nresponse to your feedback and have made every effort to improve its quality to meet\nthe journal's publication standards."}]

Decision letter