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Article

Late-Middle Pleistocene Sedimentary Environment and Climate Variation in North Hebei Plain, China: Evidence from the SHBZK-1 Core

by
Zhirong Liu
1,2,*,
Jun Shen
1,2,
Xunye Dai
1,2 and
Xuankai Jiao
1,2
1
Hebei Key Laboratory of Earthquake Dynamics, Institute of Disaster Prevention, Langfang 065201, China
2
Department of Earth Sciences, Institute of Disaster Prevention, Langfang 065201, China
*
Author to whom correspondence should be addressed.
Atmosphere 2023, 14(3), 575; https://doi.org/10.3390/atmos14030575
Submission received: 7 February 2023 / Revised: 10 March 2023 / Accepted: 15 March 2023 / Published: 17 March 2023
(This article belongs to the Section Climatology)
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Abstract

:
Thick Quaternary alluvial and floodplain sediments in north Hebei Plain provide important information for understanding local paleoenvironmental and paleoclimatic variations. A 120.8 m drilled core (SHBZK-1) was recovered to determine the late Pleistocene climatic fluctuations, sedimentary environment and their coevolutionary relationship. Laboratory analysis, including grain size distribution, magnetic susceptibility, and optical stimulated luminescence dating, was carried out. Lithofacies and grain size showed that the sediments are of fluvial origin and contain two subfaces: river sand bar and flood plain. The good correlation between magnetic susceptibility and grain size show that climate change is the main factor controlling the variation of sedimentary environment in Hebei Plain, rather than tectonic factors. Furthermore, variations of the magnetic susceptibility and lithofacies reflect the intensity and fluctuations of Asian monsoons and couple well with glacial-interglacial cycles, suggesting that the variation of ice volume in the Northern Hemisphere drives climate change in the Hebei Plain, which, in turn, regulates the variation of the sedimentary environment and facies through controlling precipitation changes, as well as the input amount of magnetic minerals. This research provides a useful continental archive for understanding the late Pleistocene environmental and climatic variation and suggests the prevalence of climate-driven environmental change.

1. Introduction

The east Asian monsoon circulation was formed early in the late Miocene, due to the rapid uplift of the Tibetan Plateau and changes in land-sea distribution [1,2], and regulated the precipitation of the east Asian continent. Influenced by this tectonic geomorphic pattern and climate environment, the Quaternary strata in eastern China developed two main sedimentary types: fluvial lacustrine strata and eolian deposits [2]. These sediments provide important archives for the study of paleoclimate and environmental variations. The eolian deposits are widely used as a typical continental sequence to study the evolution mechanism of East Asian monsoons, as these are considered to be continuous [3,4,5,6,7,8,9,10]. In contrast, research on the continental fluvial sediments has not been widely accepted, due to its complexity and possible discontinuity. However, accompanied by the uplift of the north Yanshan mountains and west Taihang mountains since the Cenozoic, the Hebei Plain was characterized by ongoing subsidence and was filled by quasi-continuous thick fluvial and lacustrine sediments [2,11], thereby providing valuable paleoclimate proxies. Meanwhile, fluvial systems have been proven to be excellent indicators of paleoenvironmental variations due to their rapid response to climate changes [12,13,14]. Therefore, as an area highly sensitive to the East Asian monsoon system [1,15], the Quaternary fluvial deposits in north Hebei Plain are potentially valuable archives for the study of the variation of climate systems and the interaction between the climate and environment.
Over recent decades, therefore, the Quaternary evolution of paleoenvironment and paleoclimate in north Hebei Plain has been carried out using organic carbon isotopic composition [16], major and trace elements [17,18], grain size [19,20,21], and magnetic susceptibility (MS) [19,21,22,23]. Then, the climate fluctuations, such as the millennial-scale Henrich events, the Dansgaard–Oeschger oscillations, the glacial-interglacial cycles, and the East Asian monsoon signals were identified from the sediments in north Hebei Plain [16,18,19,21,23,24]. Nevertheless, the driving factors of climate variation, the response mechanism of sedimentary environment to climate change, and the co-evolution relationship between different sedimentary environmental parameters are still unclear. Therefore, a late Pleistocene sequence was drilled in north Hebei Plain to explore the coevolutionary mechanism of environmental and climatic changes, as well as the relationship between various parameters based on quantitative analysis within a reliable stratigraphic and chronological framework.
Grain size, as one common physical property used as a proxy for environmental and climatic change, is closely related to the transport medium, mode, energy, and genetic type [25,26,27,28,29] and widely used in various paleoenvironmental reconstruction [5,20,30,31,32,33]. In addition, MS in alluvial and fluvial sediments has been successfully employed as a climate proxy to explore climate changes [9,29,34]. A detailed investigation of the grain size distribution and MS is a useful approach to assess the paleoenvironment and the driving climatic factors during deposition [32,33,34,35,36]. In this paper, a high-resolution analysis of stratum, grain size, and MS is introduced to identify facies changes, delineate the paleoclimate stages, and discuss the response of the environment to climate change.

2. Regional Geology

Hebei Plain is bounded by the Yellow River in the south, Yanshan Mountains in the north, Taihang Mountains in the west, and Bohai Sea in the east (Figure 1). It is composed mostly of alluvial deposits from the Yellow River and the Haihe River, and its terrain is flat and low with large area of depressions and small lakes. It has a warm temperate seasonal climate variation. In summer, the summer monsoon transports heat and moisture from the equatorial oceans to the Hebei Plain, resulting in hot and rainy weather. In winter, the winter monsoon transports cold and dry air from the northwest, leading to cold and dry weather [37]. The annual mean precipitation and temperature are 590 mm and 12 °C, respectively. Two sets of NNE and NW faults formed a series of depressions and uplifts in the Hebei Plain and regulated its paleogeographic environment, sedimentation, volcanism, and seismic activity during the Quaternary [38]. During the Quaternary, the tectonic movement in the Hebei Plain was characterized by a continuous subsidence and was filled by quasi-continuous fluvial sequences. However, the sediments are characterized by variable thickness, weak lateral continuity, and unstable sedimentary facies, due to the different tectonic background [39].
The topography of the northern Hebei plain is not undulating, tilting from the relative high north to low south (Figure 1). The Chaobai river, the Yongding River, and the Wenyu River shaped the north Hebei plain [18]. The studied area is located at the alluvial plain of Chaobai River. This river flows through north Hebei Plain, sculpting the surface morphology. However, the erosion, transportation, and deposition of Chaobai River have weakened since 1960, due to the construction of the upstream Miyun Reservoir. At present, the runoff of Chaobai River is small, and the channel is almost fixed. Neotectonic movements have led to various thickness from 100 m to 500 m sediments in different geological tectonic units, since the late Pleistocene [40,41,42]. Therefore, the north Hebei Plain is an ideal region to carry out studies on stratigraphic sequence, paleoenvironment, paleoclimate, and chronology. Nevertheless, there are no apparent features on the surface left by the ancient Chaobai River system, owing to human farming.

3. Materials and Methods

The sequence we used in this study was derived from the SHBZK-1 drilled core (N 39°57′39.93″, E 116°47′43.72″, H 29 m) in north Hebei Plain (Figure 1). The shortest straight distance from the SHBZK-1 core to the present channel of Chaobai River is about 2~3 km. The rate of core recovery was 98%. The Quaternary sediments of the core were mainly Chaobai River alluvial deposits, including clay, silty clay, clayey silt, silt, fine sand, medium sand, coarse sand, gravelly medium-coarse sand, and a gravel layer with calcareous nodules, carbonaceous particles, and rust spots locally (Figure 2a). Altogether, 58 layers were distinguished from the 120.8 m SHBZK-1 core, according to the lithology, color, texture, sedimentary structures, and biological content.
After removing the surface regolith, we collected total 2065 grain size samples with an average sampling interval of 5.5 cm from the drill core. The sampling intervals differed according to various lithologies. Generally, the sample interval was less than 5 cm clay and silt, while most sampling intervals for coarse sediments were larger, most from 5~15 cm, up to 95 cm. The samples were measured by a Malvern Mastersizer 3000 with the grain size range of 0.01–3500 um. Grain size samples and 9 optically stimulated luminescence (OSL) samples were prepared and analyzed in the neotectonic geochronology Laboratory of Institute of Disaster Prevention.
The mean size (Mz), standard deviation (σ), skewness (Sk), and kurtosis (KG) of each sample were calculated using moment statistical calculation [43,44,45,46]. The grain size of each sample was transferred to phi (Φ) using the formula “Φ = −log2D” [47], where D is the grain diameter in millimeters. The sediment composition was divided into gravel (<−1Φ), coarse sand (−1~1Φ), medium sand (1~2Φ), fine sand (2~4Φ), silt (4~8Φ), and clay (>8Φ), according to the Udden–Wentworth grain size classification of Terrigenous sediments [47].
Fine-grained quartz from 4~11 um was extracted using the simple multiple aliquot-regenerate dose (SMAR) method [24,48,49,50,51,52] to test the equivalent dose (De); the instrument used was the Risø TL/OSL DA-20 thermoluminescence optical luminescence instrument produced by Risø Laboratory in Denmark. The content determination of U, Th, and K elements was completed in the Beijing Institute of Nuclear Industry Geology, with a NexION300D plasma mass spectrometer (U, Th) and Z-2000 graphite furnace atomic absorption analyzer (K).
MS measurements were performed with a 0.05 m interval using the GeoVista comprehensive logger, which can identify the contained magnetite with concentrations ranging from 0.005% to 100%. A total of 2023 MS samples were collected from 1~102.5 m. The default output data χ is the volumetric MS (SI), which is a dimensionless parameter.

4. Results

4.1. Chronology

OSL data (Table 1) of the SHBZK-1 core indicate that the age value gradually increases from the top to the bottom, agreeing with the law of stratigraphic deposition. The average sedimentation rate of the depth from 1.98 m to 47.32 m was approximately 33.44 cm/ka, according to the data in Table 1, and a depth-age equation (y = 2.79x + 9.84, R2 = 0.95) was derived using linear interpolation. According to the equation, we inferred that the SHBZK-1 core strata was deposited between 9.84 to 346.87 ka during the middle-to-late Pleistocene. Bayesian age-depth model analysis [53,54] using the Bacon package implemented in R suggest the deposition process is between 9.58 to 302 ka. The Bayesian analysis method improves the age accuracy above 16 m, due to the OSL age constraints; however, the error gradually increases with depth below 16 m because of the age limitation of 14C calibration curve and the lacking of extrapolation calculation above 55 ka. Then, the average age error at the deepest 120.8 m of the borehole can reach 66 ka. The following research is based on the comprehensive consideration of the two methods.

4.2. Grain Size

Most of the mean size of the SHBZK-1 core ranged from 2~8Φ (Figure 2b), with a maximum value of 10.5Φ and a minimum 1.65Φ (Figure 2c). Most of σ were between 1~3, with a maximum of 4.5 and a minimum of 0.78 (Figure 2d), indicating a poorly sorted environment with moderately sorted and very poorly sorted parts. Sk varied greatly, with a maximum of 2.8 and a minimum of −2.4 (Figure 2e). The maximum of KG was 11.5 and the minimum was 1.2, and most of the values were between 2~6 (Figure 2f).
Five distinct sedimentary processes of the core can be distinguished (Table 2), based on lithology (Figure 2a), contour map of grain size distribution (Figure 2b), Mz (Figure 2c), σ (Figure 2d), Sk (Figure 2e), KG (Figure 2f), frequency distribution curves (Figure 3b,e,h,k,n), probability accumulation curves (Figure 3c,f,i,l,o), and grain size composition percentage triangle (Figure 3d,g,j,m,p).
The I-segment sediments, from the depth of 0 m to 26.72 m, with a corresponding age from 0 ka to 84.4 ka, were silt and clay (Figure 2a,b), with Mz of 4~8Φ (Figure 2c), σ of 1.1~3.6 (Figure 2d), Sk of −2~2 (Figure 2e), and KG > 1.8 (Figure 2f). The frequency distribution curves are mainly bimodal negative and peak at 4Φ (Figure 3b). The probability accumulation curves are two-stage for the majority of suspended components (Figure 3c). Therefore, the sedimentary environment was interpreted as floodplain with thin-layer channel deposition.
The II-segment is between 26.72 m and 44.04 m in depth, and its corresponding geological age is between 84.4 ka and 132.7 ka. It has a grain size of 1~4Φ (Figure 2b), Mz of 2~6Φ (Figure 2c), σ of 1.5~2.8 (Figure 2d), Sk of 0~2 (Figure 2e), and KG > 2 (Figure 2f). The frequency distribution curves are bimodally positive, with a high proportion of medium to coarse sand (Figure 3e). The probability accumulation curves are of the two-stage type with a well-sorted jumping component (Figure 3f). The grain size composition percentage triangle shows that this segment is composed mainly of sand (Figure 3g). Consequently, it was considered to be river sand bar deposit under strong hydrodynamic conditions (Table 2).
The III-segment, with a depth from 44.02 m to 61.76 m and an age range between 132.7 ka to 182.1 ka, has similar grain size characteristics (Figure 2b–f and Figure 3h–j) to the I-segment.
The grain size of the IV-segment (Figure 2b–f and Figure 3k–m), with a depth from 61.76 m to 92.02 m and a corresponding age from 182.1 ka to 266.6 ka, is comparable to that of the II-segment, suggesting an analogous sedimentary environment.
The grain size parameters of the V-segment, in the depth of 92.02 m to 120.8 m, with a corresponding age between 266.6 ka to 346.9 ka, are similar to those of the I- and III-segments. However, the frequency distribution curves are unimodal or bimodal with a negative bias (Figure 3n), and the probability accumulation curves are two-stage with the suspended component content above 80% (Figure 3o). Therefore, the sediments of this part mainly consist of silt and clay (Figure 3p), belonging to floodplain lacustrine deposits.
We suggest that the sediments of the SHBZK-1 core were deposited in a fluvial environment with cyclic sedimentary characteristics. The sand at the bottom of each cycle indicates stronger hydrodynamic conditions, while the silt and clay at the top represent weaker hydrodynamic conditions.

4.3. Magnetic Susceptibility (MS)

The χ(SI) values of the SHBZK-1 core at different depth vary greatly (Figure 4a). The maximum is 8.21, the minimum is −9.91, and the average is −6.51. The apparent variations suggest the climate experienced significant shifts during deposition.
The MS of the SHBZK-1 core (Figure 4a) was contrasted with different grain size distributions (Figure 4b–d) to determine their relationship. High percentages of medium sand (1~2Φ) and fine sand (2~3Φ) (Figure 4c) were in phase with high MS values, and low MS values had synchronous variations with the proportion of clay and silt (Figure 4b). However, the coarse sand (0~1Φ) and very coarse sand (−1~0Φ) had no discernible relationship with MS (Figure 4d).
Using linear normalization, the percentages of clay, silt, fine sand, medium sand, and coarse sand, as well as the MS of the SHBZK-1 core, were recalculated to investigate the link between different grain size and MS. MS showed a negative correlation with the clay and silt content, with correlation coefficients of −0.37 or −0.43, respectively (Figure 5). In contrast, MS was positively correlated with the content of fine sand and medium sand, and the correlation coefficients were 0.31 and 0.40, respectively (Figure 5). The correlation coefficient between MS and coarse sand was 0.029, with no obvious correlation.

5. Discussion

5.1. The Relationship between MS and Grain Size

Magnetic minerals are abundant in sediments with different grain sizes in various environments, due to the diversification of provenance and sedimentary environment. In general, coarser grains with fewer magnetic minerals accumulated during colder periods, while finer grains with more magnetic minerals deposited in warmer periods in typical loess-paleosol sediments [6,7,55]. Therefore, the paleosol is dominated by clay with fine grain size and high MS values, indicating a warm and humid interglacial period strongly related to weathering and pedogenesis; loess is characterized by silt with relatively coarse grain size and low MS values, implying a cold and dry glacial period [3,7,8,10].
However, the relationship between MS and grain size in fluvial sediments is perceived differently. Most studies consider that high MS is positively correlated with coarse grains under warm and humid climates, and low MS values are negatively correlated with fine-grained deposits under dry and cold conditions, supporting the detrital origin of magnetic minerals [19,21,22,34,56]. Nevertheless, there are contradictory opinions that high MS is positively connected with fine-grained sediment concentration and inversely correlated with coarse-grained content in fluvial sediments [24,57]. All investigations on the grain size and MS of fluvial systems concur that magnetic minerals are exogenous and derived from detrital origins.
Visual linear comparison (Figure 4) and quantitative correlation coefficient analysis (Figure 5) of the SHBZK-1 core indicate that MS exhibited a strong coupling with grain size. High MS values in sediments are coupled with a high proportion of coarse sediments (1~3Φ), while low MS values are accompanied by a high concentration of fine sediments (>4Φ). The grain size of fluvial sediments is closely related to hydrodynamic conditions and geomorphological locations, and the MS value is dependent on the quantity of magnetic minerals transported into the fluvial system; therefore, the MS of fluvial sediments in subsidence tectonic settings has a strong relationship with grain size and can be used as a proxy for sedimentary hydrodynamic conditions. Since MS is successfully employed as a climate proxy in alluvial and fluvial sediments to explore climate and environmental changes [9,32,33,34,57,58], the correlation between MS and grain size seems to confirm that climate change is the main factor controlling the fluvial sedimentary process in the north Hebei Plain.

5.2. Paleoclimate Evolution of the North Hebei Plain

The grain size distribution of fluvial sediments is mostly a consequence of river load capacity (speed and river flow) [20,25,26]. Generally, coarser grains deposit when the flow rate and water volume are high, whereas finer grains accumulate under the conditions of slow flow rate and small amounts of water. The SHBZK-1 core was divided into five segments based on grain size changes (Figure 2 and Figure 3, Table 2). The finer sediments of the I, III, and V segments indicate a weaker hydrodynamic environment in colder and drier periods, whereas the coarser sediments of the II and IV segments reflect stronger hydrodynamic conditions during warmer and wetter eras. Meanwhile, the high MS values of the SHBZK-1 core have a strong positive correlation with the content of medium and fine sand, but an inverse association with the concentration of silt and clay. Therefore, we suggest that climate change mainly regulates the cyclic change of grain size and MS.
The correlation between the MS of the SHBZK-1 (Figure 6a) core and the MS of Luochuan loess (Figure 6b) may be weakened by the missing sediments or dating error. However, the subsiding background and the fine-grain size sediments illustrate that the erosion can be ignorable. So, regardless of the dating error, their similarity shows that the sediments in north Hebei Plain also recorded monsoon signals. Four stages, with corresponding depths of 72.9~92.02 m, 61.76~70.65 m, 26.72~44.02 m, and 0~1.5 m, accumulated during the summer monsoon, represented as S3, S2, S1, and S0 in the Luochuan section (Figure 6b), respectively. Increasing precipitation during the summer monsoon would have enhanced runoff energy and result in the deposition of more comparatively coarse-grained debris rich in magnetic minerals. During the four periods, the sedimentary subfacies were river sand bar (Table 2). The winter monsoon is strengthened at the stages of 92.02~101 m, 70.65~72.9 m, 44.02~61.76 m, and 1.5~26.72 m, represented as L4, L3, L2, and L1 in the Luochuan section, respectively (Figure 6b). Additionally, low precipitation in cold weather reduces erosion and the input of exogenous magnetic minerals. The corresponding sedimentary subfacies are flood plains with low MS values. Therefore, MS and its correlation with typical loess sections, combined with grain size, reveals that the East Asian monsoon oscillations are the most important form of climate change controlling surface hydrodynamic conditions and the input of magnetic minerals in the north Hebei Plains.
Anchored by OSL ages in Table 1, we have developed a timescale for the SHBZK-1 core by matching the MS (Figure 6a) curve to the MS curve of the Luochuan loess stratum profile (Figure 6b) [4,8] using AnalySeries [59]. The timescale (Figure 6c) shows that the sediments of the SHBZK-1 core were formed within 9.68 ka to 356.7 ka before the present, with an average sedimentation rate of 28.88 cm/ka. The accumulation rate is comparable to that of the late Pleistocene sedimentation in other areas of the north Hebei Plain [20,22,42,60], indicating the stability of the regional sedimentary environment.
The time domain MS series (Figure 6c) correlates well with the Northern Hemisphere ice sheet volume [61] (Figure 6d) and the stacked benthic δ18O [62] (Figure 6e), which confirms that the glacial-interglacial cycles are the most important form of climate change affecting the deposition process of north Hebei Plain. Therefore, the sediment in the north Hebei Plain shows the same 100 ka monsoon cycle recorded by the ocean [62] and the loess [4,8], indicating that there is an obvious coupling relationship between the sedimentary environment and the ice volume variation in the Northern Hemisphere. It is shown that, when the ice volume decreases (MIS3, MIS5, MIS7, MIS9), the climate becomes warm, the summer monsoon strengthens, and the weathering enhances. Consequently, the grain size of the sediment becomes coarser, the input of magnetic minerals increases (Figure 6c), and the sedimentary environment becomes mainly river sandbar. Conversely, when the ice volume in the Northern Hemisphere increases, the climate becomes colder, the winter monsoon increases, and the weathering weakens. Therefore, the precipitation decreases, the grain size of the sediment becomes finer, and the input of magnetic minerals decreases, so the sedimentary environment is dominated by floodplain deposits. In a word, climate changes drive the alterations of the late Pleistocene sedimentary environment in the northwest Hebei Plain and control the input of magnetic minerals.
Atmosphere 14 00575 g006 550
Figure 6. Linkage between MS of the SHBZK-1 core and different targets; (a) MS of the SHBZK-1 core in depth domain (①–⑨ are the OSL ages of Table 1); (b) MS of Luochuan section from [4,8]; (c) MS of the SHBZK-1 core in time domain; (d) the Northern Hemisphere (NH) ice volume [61]; (e) the stacked benthic δ18O record [62].
Figure 6. Linkage between MS of the SHBZK-1 core and different targets; (a) MS of the SHBZK-1 core in depth domain (①–⑨ are the OSL ages of Table 1); (b) MS of Luochuan section from [4,8]; (c) MS of the SHBZK-1 core in time domain; (d) the Northern Hemisphere (NH) ice volume [61]; (e) the stacked benthic δ18O record [62].
Atmosphere 14 00575 g006
However, there is a discrepancy at the depth of 61.76–92.02 m. The sediments of this stage were interpreted as river sand bar with strong hydrodynamic conditions, spanning the S3, L3, and S2 phases of monsoon cycles. The low sedimentation rate and short time duration of L3 (245–270 ka) [3] resulted in a quite thin layer of silt and clay. Thus, this layer was too thin to be separated from the upper and lower strata in the sedimentary environmental analysis.

6. Conclusions

Grain size and MS studies of the SHBZK-1 core in north Hebei Plain allow for quantitative investigation into the sedimentary environment and climate variation. The sedimentary facies of the SHBZK-1 core are identified as fluvial facies, which can be subdivided into periodic fluctuations of flood plain and river bar subfacies. The SHBZK-1 core was separated into five segments based on the Mz, σ, Sk, KG, frequency distribution curves, probability accumulation curves, and grain size composition percentage triangles. The contrast between the percentages of different grain sizes and MS suggests the magnetic minerals in the studied sediments are exogenous.
Comparing the MS of the SHBZK-1 core and the Luochuan section based on the OSL ages revealed a strong correlation between the two sections. Three monsoon cycles are observed, which we interpret as a rapid response of the fluvial environment to monsoon variation in Hebei Plain through variations in runoff energy constrained by hydrology. Higher MS concentrations and coarse grain size agree with a warm period, during which the summer monsoon is intensified with increasing runoff energy and a subsequent increasing of exogenous magnetic minerals. Lower concentrations of MS and relatively fine grain size are consistent with the cold epoch, during which the winter monsoon predominate with decreasing precipitation and fewer foreign magnetic minerals.
The sedimentary environment and climate changes in north Hebei Plain are consistent with the glacial-interglacial cycles recorded by loess and ocean deposition, which testify that the sediments in Hebei Plain completely record the climate change process at high latitudes in the Northern Hemisphere. Meanwhile, it also confirms that fluvial sediments deposited in a subsidence background can be used as an archive to perform climate study.

Author Contributions

Conceptualization, methodology, formal analysis, writing—review, editing and original draft preparation, Z.L.; investigation, X.J. and Z.L.; funding acquisition, resources, writing—review, J.S.; laboratory experiment, X.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Institute of Disaster Prevention (grant number ZY20180105), the National Natural Science Foundation of China (grant number 42172253), and the Langfang Science and Technology Bureau (grant number 2021013078).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing is not applicable to this article.

Acknowledgments

We would like to thank all the developers and maintainers of Generic Mapping Tools (GMT), OriginLab, and Adobe Illustrator. We also are grateful to Jonathan Yuan and three reviewers for the very thorough and constructive review.

Conflicts of Interest

The authors declare no conflict of interest.

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Atmosphere 14 00575 g001 550
Figure 1. Map showing the location of Hebei plain and the SHBZK-1 core (the red dot).
Figure 1. Map showing the location of Hebei plain and the SHBZK-1 core (the red dot).
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Figure 2. Stratigraphic histogram, grain size contour map, and grain size parameters of the SHBZK−1. (a) Stratigraphic histogram; (b) grain size contour map; (c) mean size (Mz); (d) standard deviation (σ); (e) skewness (Sk); (f) kurtosis (KG).
Figure 2. Stratigraphic histogram, grain size contour map, and grain size parameters of the SHBZK−1. (a) Stratigraphic histogram; (b) grain size contour map; (c) mean size (Mz); (d) standard deviation (σ); (e) skewness (Sk); (f) kurtosis (KG).
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Figure 3. Grain size distribution curves and composition of five different segments (✩ in (a) is the grain size analysis samples location). (a), Stratigraphic histogram; (b,e,h,k), frequency distribution curves; (c,f,i,l,o), probability accumulation curves; (d,g,j,m,p), grain size composition (b–d) are the same sample of the I-segment; (e–g) are the same sample of the II-segment; (h–j) are the same sample of the III-segment; (k–m) are the same sample of the IV-segment; (n–p) are the same sample of the V-segment).
Figure 3. Grain size distribution curves and composition of five different segments (✩ in (a) is the grain size analysis samples location). (a), Stratigraphic histogram; (b,e,h,k), frequency distribution curves; (c,f,i,l,o), probability accumulation curves; (d,g,j,m,p), grain size composition (b–d) are the same sample of the I-segment; (e–g) are the same sample of the II-segment; (h–j) are the same sample of the III-segment; (k–m) are the same sample of the IV-segment; (n–p) are the same sample of the V-segment).
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Figure 4. Comparison diagram between MS and grain size of the SHBZK-1 core. (a) MS curve; (b) silt (4~8Φ) curve; (c) sand (1~4Φ) curve; (d) coarse sand (−1~1Φ) curve.
Figure 4. Comparison diagram between MS and grain size of the SHBZK-1 core. (a) MS curve; (b) silt (4~8Φ) curve; (c) sand (1~4Φ) curve; (d) coarse sand (−1~1Φ) curve.
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Figure 5. Correlation coefficients between different grain size and MS.
Figure 5. Correlation coefficients between different grain size and MS.
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Table
Table 1. OSL data of the SHBZK-1 core in north Hebei Plain.
Table 1. OSL data of the SHBZK-1 core in north Hebei Plain.
SampleDepth
(m)		U-238
(ppm)		Th-232
(ppm)		K-40
(%)		H2O
(%)		Saturated H2O (%)Dose Rate
(Gy/ka)		De
(Gy)		Age
(ka)
①1.9832.2 ± 1.640.1 ± 4.8755.2 ± 15.113.12939.7383.3 ± 0.339.9 ± 1.612.1 ± 0.6
②4.9030.4 ± 2.835.0 ± 4.2788.8 ± 15.822.84636.9003.0 ± 0.352.4 ± 2.817.6 ± 1.0
③1633.8 ± 2.249.4 ± 5.9695.5 ± 13.921.88839.5072.8 ± 0.3141.8 ± 7.449.9 ± 2.9
④22.1129.1 ± 1.238.5 ± 2.3766.6 ± 15.313.66536.81572.9 ± 0.3265.0 ± 12.192.5 ± 4.8
⑤30.4729.5 ± 3.135.8 ± 3.6826.1 ± 16.514.95328.36073.2 ± 0.3309.3 ± 9.696.1 ± 3.8
⑥32.442.7 ± 1.947.1 ± 4.7776.9 ± 15.524.827353.3 ± 0.3358.9 ± 15.2108.2 ± 5.3
⑦38.723.4 ± 3.024.9 ± 2.51011.9 ± 20.216.07934.2053.2 ± 0.3349.1 ± 32.9109.6 ± 10.7
⑧43.63.2 ± 1.127.3 ± 2.81095.3 ± 98.619.17728.2683.1 ± 0.3364.9 ± 12.5117.8 ± 5.1
⑨47.327.3 ± 1.045.6 ± 4.6824.4 ± 16.516.0097322.7 ± 0.3400.7 ± 23.6147.7 ± 9.4
Table
Table 2. Five distinct sedimentary processes of the SHBZK-1 core in north Hebei Plain.
Table 2. Five distinct sedimentary processes of the SHBZK-1 core in north Hebei Plain.
The I-SegmentThe II-SegmentThe III-SegmentThe IV-SegmentThe V-Segment
Depth (m)0~26.7226.72~44.0244.02~61.7661.76~92.0292.02~120.8
Age (ka)0~84.484.4~132.7132.7~182.1182.1~266.6266.6~346.9
Grain size (Φ)3~61~43~91~34~10
Mz (Φ)4~82~64~82~44~8
σ1.1~3.61.5~2.81.1~2.81.2~2.41.2~3.5
Sk−2~20~2−2.3~1.61~3negative
KG>1.8>2>2>2---
Frequency distribution curvesbimodal positive typebimodal positive typebimodal typebimodal positive biasbimodal negative bias
Probability accumulation curvestwo-stage with high skipped componentstwo-stage type with high jumping components; well sortedthree-stage type with high suspended componentstwo-stage type with high jumping componentstwo-stage and three-stage type with high suspended components
Grain size compositionmainly siltmainly sandmainly siltmainly sandmainly silt
Sedimentary environmentflood plain with a few thin-layer river barriver sand barflood plainriver sand barflood plain intercalated with river bar
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Liu, Z.; Shen, J.; Dai, X.; Jiao, X. Late-Middle Pleistocene Sedimentary Environment and Climate Variation in North Hebei Plain, China: Evidence from the SHBZK-1 Core. Atmosphere 2023, 14, 575. https://doi.org/10.3390/atmos14030575

AMA Style

Liu Z, Shen J, Dai X, Jiao X. Late-Middle Pleistocene Sedimentary Environment and Climate Variation in North Hebei Plain, China: Evidence from the SHBZK-1 Core. Atmosphere. 2023; 14(3):575. https://doi.org/10.3390/atmos14030575

Chicago/Turabian Style

Liu, Zhirong, Jun Shen, Xunye Dai, and Xuankai Jiao. 2023. "Late-Middle Pleistocene Sedimentary Environment and Climate Variation in North Hebei Plain, China: Evidence from the SHBZK-1 Core" Atmosphere 14, no. 3: 575. https://doi.org/10.3390/atmos14030575

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