The Bohai Sea is a semi-closed sea in northern China which is known to have thick and continuous Quaternary sediments. Many studies on the geological and environmental evolution around the Bohai coast have been carried out on these Quaternary sediments (Yi
During the Holocene, significant geomorphological changes took place in the Bohai coastal area due to coastline migration (sea level change) and fluvial sediment input. These sediments showing the Holocene transgressive phase are widely distributed, especially in three bays of the Bohai Sea with flat landforms. The regional sea level in Bohai rose to the highest sea level at 5–7 ka, and then oscillated slightly and fell to the present level gradually (Xue, 2009; Xue and Ding, 2008; Xu, 1994; Zhao
In the past decades, luminescence dating methods have been significantly improved and applied widely to establish chronologies of various sedimentary archives of the late Quaternary, especially after the development of a single aliquot regenerative dose (SAR) protocol (Murray and Wintle, 2000, 2003). The optically stimulated luminescence (OSL) signal from quartz and the infrared stimulated luminescence (IRSL) signal from feldspar are the two main signals that are used for dating. Although there are still challenges (e.g. relatively large uncertainties from insufficient luminescence sensitivity, overestimation caused by thermal transfer, and incomplete bleaching; Madsen and Murray, 2009), the quartz OSL dating using the SAR protocol has been successfully carried out to date young sediments from different environments (e.g. marine deposits: Madsen
We study a well-preserved sand dune and the underlying marsh sediment situated in the Lower Liao Plain, the north coastal area of the Bohai Sea. Our aim is two-fold; first, we apply OSL dating to sand-sized quartz grains extracted from a well-preserved sand dune and marsh sediment to establish the chronology of these deposits. On the basis of coastline changes in historical documents, the timing of sand accumulation and the possible forcing mechanisms of the sand deposition are discussed. Our second aim is to investigate the effects of the residual dose in the pIRIR dating of young sediments. The pIRIR150 protocol is applied on K-feldspar fraction for all samples and the results are compared with the quartz ages to determine the applicability of the protocol for the young dune sediments.
The Lower Liao Plain (LLP) is an alluvial plain located in northeastern China (Fig. 1). To the north of the LLP, the Horqin dune field is located, which is one of the four biggest dune fields in China (Fig. 1A). South of the LLP is the Liaodong Bay, which is the northern part of the Bohai Sea. As a consequence of continuous subsidence during the Quaternary (Allen (A) The location of the study area in NE China. (B) Map showing the geological setting (Lower Liao River plain, local drainage streams and adjacent mountain areas) and coastline changes (sea level in Holocene, coastlines in 1905 AD, 1932 AD, 1950 AD and present, Fu, 1988; Chen et al., 2010). The location of the sampling site is also shown. (C)–(E) Typical sand deposits in the LLP. (C) is a photo of studied PJ sand dune.Fig. 1
The position of the coastline has changed significantly since the late Pleistocene widely along the Bohai coast. Several marine layers were found in cores drilled in the LLP; these have been correlated to transgressions (IOCAS, 1985). The uppermost transgressive phase is widely distributed along the Bohai coast and constrained to the Holocene climate optimum (IOCAS, 1985). The regional sea level highstand in the Liaodong Bay occurred at 5–7 ka and reached to the area of 50 km inland from the modern coastline (Fu, 1988). Afterwards, the sea level oscillated and fell to the present-day level. Historical documents and remote sensing were applied to examine the coastline changes in the LLP over the last hundred years (Chen
At the present surface, fluvial, alluvial, aeolian, and coastal sediments can be recognized in the LLP. Aeolian sediments in the LLP are mainly reworked sand dunes, which are mobile under strong wind force (e.g. Fig. 1C, IOCAS, 1985). Although the sand deposits are distributed extensively, it is difficult to map the distribution as most of the comparatively large sand dunes and ridges are disturbed by human activities (e.g. agricultural movement: residual sand dune in farmland, Fig. 1D). The sand deposits at small scales are covered by vegetation and cannot be identified from satellite images (Fig. 1E).
The entire region is affected mainly by the East Asian monsoon. The mean annual temperature is 5–10°C, with the mean temperature at 27–31°C in summer and the mean temperature at –5–18°C in winter. The mean annual precipitation is 634 mm, while annual evaporation reaches 1670 mm. During the winter seasons, the wind direction is north-western, whilst the summer seasons is dominated by south or south eastern wind from the Pacific (BGMRL, 1989).
The sampling site is located in the Panjin (PJ) forest park within the elapsed marine-terrestrial interacted area (Fig. 1), where the PJ sand dune is well preserved. Four sedimentary sections (S1-S4; Fig. 2B) were investigated and sampled. The sediments can be divided into four units (Fig. 2): Unit A contains homogenous yellowish fine sand with a thickness of ca. 4.5 m, covered by vegetation. The sediments are well to moderately sorted. Several roots were found in this layer. Unit B consists of grey fine sand with a thickness of 0.5–0.6 m. The grey sands are moderately to poorly sorted with organic matter. Unit C is a blackish sandy soil layer, consisting of poorly sorted sandy silt and clayey silt with organic-rich matter and soil aggregates. Clear boundaries can be distinguished between the different units. Additionally, at S2, a grey silt layer (Unit D) was found under the blackish sand layer which is not exposed in other sections. Unit A and B are relatively homogenous sands deposited above the sandy silt layer containing organic matter. The darker colour of unit B represents the anoxic condition due to the ground water above the impermeable soil layer.
(A) Investigated profile and its description. The positions of OSL samples are shown in the profile. (B) Stratigraphy of the PJ dune showing the positions of four investigated sections and sampling depths.Fig. 2
Eight OSL samples (LUM3191 to LUM3198) were taken by hammering steel tubes (10 cm long cylinders with a diameter of 4 cm) into freshly prepared vertical sections from S1 and S4. The cylinders were fully filled with sediments to make sure that there is no mixing during transportation. The tubes were then covered and sealed with black plastic sheets and tapes to prevent light exposure and moisture loss. Two samples were taken from S1 (LUM3197 and LUM3198) and six samples were taken from S4 (LUM3191 to LUM3196), covering the three sedimentary units A-C.
The preparation of sand-sized samples was conducted under the subdued red light in the luminescence laboratory at Leibniz Institute for Applied Geophysics. Materials of the outer 2 cm from both ends of the tubes were removed and discarded. For the upper six sand samples (LUM3191-3194, LUM3197-3198), the remaining nonlight exposed material was dry-sieved to collect grains of 100–150 μm in diameter. With diluted hydrochloric acid (HCl) for two hours, sodium oxalate (Na2C2O4) for one day and hydrogen peroxide (H2O2) for two hours, the samples were treated to remove carbonate, mineral aggregates and organic matter, respectively. For the lower two sandy soil samples (LUM3195-3196), chemical treatment was carried out first because the grains can be hardly dispersed and dry-sieved. Subsequently, the remaining material was dry-sieved to extract grains 63–100 μm in diameter. Three steps density separations were performed using heavy liquid to extract quartz grains (2.62 < ρ < 2.70 g/cm−3) and K-feldspar grains (ρ < 2.58 g/cm−3). The quartz extracts were subsequently treated with 40% hydrofluoric acid (HF) for 1 hour and to remove the remaining feldspar grains and etch quartz grains to eliminate the effect of the alpha-irradiated outer layer. The etched samples were finally treated with HCl and resieved to ensure the grains smaller than 100 μm for sand samples and 63 μm for sandy soil samples were removed.
The quartz and feldspar grains were mounted on stainless steel discs with a diameter of 6 mm and 2.5 mm respectively using silicone oil as adhesive. Luminescence measurements were carried out with an automated Ris⊘ TL/OSL system (DA-15) equipped with a calibrated 90Y/90Sr beta source. For quartz measurements, blue light-emitting diodes (LEDs, 470 ± 30 nm) were employed for stimulation, and the quartz OSL signals were detected through a 7.5mm Hoya U-340 filter. The feldspar signals were detected through a combined blue filter pack (Schott BG-39 and Corning 7-59) stimulated by infrared LEDs (870 ± 40 nm).
A single-aliquot regenerative dose (SAR; Murray and Wintle, 2003) protocol was applied for pre-tests and equivalent dose (
SAR protocol applied for equivalent dose determination.
Step | Quartz OSL | K-feldspar post-IR IRSL150 | |||
---|---|---|---|---|---|
Treatment | Observed | Step | Treatment | Observed | |
1 | Give dose | 1 | Give dose | ||
2 | Preheat for 60 s at 180°C | 2 | Preheat for 60 s at 180°C | ||
3 | IR stimulation | 3 | IR stimulation for 100 s at 50°C | ||
4 | Stimulation for 40 s at 125°C | 4 | IR stimulation for 200 s at 150°C | ||
5 | Give test dose, | 5 | Test dose, Dt | ||
6 | Heat to 160°C | 6 | Preheat for 60 s at 180°C | ||
7 | Stimulate for 40 s at 125°C | 7 | IR stimulation for 100 s at 50°C | ||
8 | Return to 1 | 8 | IR stimulation for 200 s at 150°C Return to 1 | ||
9 | Return to 1 |
The pIRIR150 protocol (Table 1) was applied for K-feldspar
For dose rate determination, additional 50 g of dried sample material were filled in plastic containers and stored at least four weeks before gamma spectrometry measurements to secure equilibrium between radon and its daughters. The concentrations of uranium (U), thorium (Th) and potassium (K) of the surrounding sediment were calculated from the activity of these nuclides measured by high-resolution gamma spectrometry. Each sample was measured over a period of two to three days. Bulk samples were weighed before and after drying the samples at 130°C for one day to determine the natural water content. The median water content value of six sand samples with an error which can cover the range of all water contents, 6 ± 4%, was assumed for the water content of sand sediment in antiquity. The water content of the two soil samples was estimated to be 13 ± 3% according to the observed water content. The cosmic dose rate was calculated for each sample as a function of depth, altitude and geomagnetic latitude according to Prescott and Hutton (1994). The conversion factors of Guérin
Dose rate determination
SampleID | Depth (cm) | Grain size Interval (μm) | U (ppm) | Th (ppm) | K (%) | Water content (%) | Dose rate(Gy/ka) | |
---|---|---|---|---|---|---|---|---|
K-feldspar | quartz | |||||||
LUM3197 | 80 | 100–150 | 0.96 ± 0.06 | 2.63 ± 0.14 | 2.85 ± 0.14 | 6 ± 4 (1.7) | 4.02 ± 0.17 | 3.24 ± 0.24 |
LUM3198 | 149 | 100–150 | 1.06 ± 0.06 | 2.82 ± 0.15 | 2.91 ± 0.15 | 6 ± 4 (2.1) | 4.10 ± 0.17 | 3.31 ± 0.24 |
LUM3191 | 380 | 100–150 | 1.00 ± 0.05 | 2.66 ± 0.14 | 2.79 ± 0.14 | 6 ± 4 (2.6) | 3.96 ± 0.17 | 3.13 ± 0.23 |
LUM3192 | 434 | 100–150 | 0.91 ± 0.05 | 2.72 ± 0.14 | 2.83 ± 0.14 | 6 ± 4 (4.2) | 3.92 ± 0.16 | 3.15 ± 0.24 |
LUM3193 | 462 | 100–150 | 1.13 ± 0.06 | 3.27 ± 0.17 | 2.87 ± 0.14 | 6 ± 4 (6.6) | 4.05 ± 0.17 | 3.26 ± 0.24 |
LUM3194 | 480 | 100–150 | 1.31 ± 0.07 | 4.30 ± 0.22 | 2.82 ± 014 | 6 ± 4 (9.5) | 4.12 ± 0.17 | 3.32 ± 0.24 |
LUM3195 | 511 | 63–100 | 1.88 ± 0.10 | 6.95 ± 0.35 | 2.61 ± 0.13 | 13 ± 3 (14) | 4.14 ± 0.17 | 3.20 ± 0.22 |
LUM3196 | 532 | 63–100 | 2.24 ± 0.12 | 8.01 ± 0.41 | 2.34 ± 0.12 | 13 ± 3 (15) | 4.07 ± 0.17 | 3.10 ± 0.20 |
To determine the most appropriate preheat temperature for the Results of quartz OSL pre-tests. (A) Measured/given ratio (dose recovery test), (B) equivalent dose and (C) thermal transfer at different preheat temperatures for sample LUM3192. (D)–(F) show the results of the same set of tests for sample LUM3196.Fig. 3
Aliquots out of the acceptable ranges (0.9–1.1) of the recycling ratio, recuperation (Wintle and Murray, 2006) and OSL IR depletion ratio (Duller, 2003) were rejected prior to the
Typical decay and dose response curves for both sand sample (LUM3191) and sandy soil sample (LUM3196) are shown in Fig. 4. A clear decay of natural quartz OSL signal for each sample was observed. All the samples yielded detectable quartz OSL signal. The dose response curves of upper six samples were fitted by a linear function, and those of two sandy soil samples were fitted by one single saturating exponential function. The distributions of Quartz decay curve, dose response curve and De distribution for sample LUM3191–(A) and (B); for sample LUM3196–(C) and (D). De distributions are presented using abanico plots (Dietze et al., 2016). Result of OSL datingFig. 4
Feldspar LumNo. Depth (cm) Quartz pIRIR150 IR50 (cm) Dose rate (Gy/ka) De (Gy) Age (a) σOD (%) Dose rate (Gy/ka) De (Gy) Age (a) Corrected age (a) De (Gy) Age (a) Corrected age (a) 3197 80 3.24±0.23 0.28±0.01 87±7 6.3 4.02±0.17 0.81±0.05 0.99±0.38 202±15 214±21 0.34±0.01 8.38±0.59 85±4 145±13 3198 149 3.31±0.24 0.28±0.01 85±7 4.4 4.10±0.17 0.88±0.06 1.96±0.41 215±18 243±26 0.35±0.01 9.23±0.64 86±5 159±18 3191 380 3.13±0.23 0.34±0.01 110±9 6.6 3.96±0.17 0.68±0.03 0.38±0.28 173±10 177±14 0.38±0.01 9.18±0.52 96±5 178±17 3192 434 3.15±0.23 0.36±0.01 115±9 5.9 3.92±0.16 0.74±0.03 1.11±0.39 189±12 203±17 0.39±0.01 9.30±0.54 100±4 187±17 3193 462 3.26±0.24 0.37±0.01 114±9 12.5 4.05±0.17 0.66±0.03 0.44±0.31 164±9 168±13 0.39±0.01 9.36±0.74 96±5 181±21 3194 480 3.31±0.24 0.42±0.01 128±10 6.7 4.12±0.17 0.60±0.05 0.62±0.42 145±13 151±17 0.46±0.03 7.80±0.74 111±8 186±25 3195 511 3.19±0.22 4.69±0.14 1470±110 12.3 4.14±0.17 5.77±0.24 0.25±0.41 1390±80 1430±120 4.28±0.18 4.99±0.26 1040±60 1500±120 3196 532 3.08±0.21 15.3±0.3 4970±350 10.1 4.07±0.17 22.1±1.7 0.80±0.28 5420±470 5760±620 14.1±0.4 4.45±0.19 3480±180 4950±350
The quartz ages are calculated by dividing the
Representative decay curves and dose response curves of two samples are shown in Fig. 5. The dose response curves of the young sand samples are fitted by linear function, and those of the two sandy soil samples are fitted by single saturating exponential function. Recycling ratios of all aliquots are satisfactory within the acceptable range (0.9–1.1), and almost all of the recuperation values are below 6%. The IR50 and pIRIR150 K-feldspar IR50 and pIRIR150 decay curve, growth curve and De distribution for sample LUM3191–(A) and (B), for sample LUM3196–(C) and (D).Fig. 5
The applicability of the pIRIR150 protocol on the samples in this study was checked utilizing dose recovery and residual dose tests. Six aliquots of each sample were bleached for 4 hours in the Hönle SOL2 solar simulator. Three aliquots were measured using the pIRIR150 protocol after given a beta dose close to the equivalent dose from Dose recovery ratio and residual dose for IR50 and pIRIR150 for each sample. Summary of predicted residual dose and measured residual dose (4 h SOL2 bleaching).Fig. 6
Sample pIRIR150 IR50 Predicted Measured Predicted Measured residual residual residual residual 3197 0.48 ± 0.07 0.13 ± 0.02 0.00 ± 0.06 0.03 ± 0.00 3198 0.57 ± 0.08 0.16 ± 0.02 0.14 ± 0.06 0.04 ± 0.01 3191 0.26 ± 0.06 0.09 ± 0.01 0.12 ± 0.05 0.03 ± 0.01 3192 0.32 ± 0.06 0.11 ± 0.01 0.12 ± 0.04 0.04 ± 0.00 3193 0.21 ± 0.06 0.07 ± 0.01 0.11 ± 0.05 0.04 ± 0.02 3194 0.09 ± 0.09 0.05 ± 0.01 0.12 ± 0.07 0.02 ± 0.00 3195 -0.19 ± 0.06 0.11 ± 0.01 -0.18 ± 0.06 0.03 ± 0.00 3196 2.91 ± 0.09 0.34 ± 0.02 0.87 ± 0.05 0.08 ± 0.01
A fading test following Auclair Fading rate (g2ays-value) of IR50 and pIRIR150 signals for one representative sample LUM3191.Fig. 7
The comparison of ages from quartz OSL, feldspar IR50 and pIRIR150 signals are shown in Fig. 8A and 8B. In Fig. 8A, the apparent IR50 ages for the six sand samples are consistent with quartz ages, whereas the fading corrected IR50 ages are much older than the associated quartz ages. However, two sandy soil samples shown in Fig. 8B yielded the opposite results. The fading corrected IR50 ages are in agreement with quartz ages, while the apparent IR50 ages underestimated the quartz ages. The fading rates obtained from the fading experiment demonstrate that the sand samples (LUM3191-LUM3194, LUM3197-LUM3198) faded more significantly ( Ages from different luminescence signals and the comparison of the predicted and measured residual doses. A shows the comparison for the sand samples, B shows the comparison for two sandy soil samples. C demonstrates the comparison of the predicted residual dose and measured dose for all samples (See details in text).Fig. 8
Compared with the pIRIR signals with high thermal treatment (stimulated at 225 or 290°C), the pIRIR150 signal has an advantage of faster bleaching for dating some young deposits during the Holocene (Reimann
We conducted the reverse derivation to simulate the natural growth of the pIRIR150 and the associated IR50 signals concerning the anomalous fading using the reference (quartz) age, the feldspar dose rate and the fading rate (Kars
The measured residual doses are generally smaller than the predicted residual doses except sample LUM3195, indicating that the natural exposure was less than the equivalent time to 4 h of SOL2 bleaching. The offsets obtained from the difference between the predicted and the measured pIRIR150 residual doses are ~0.04–0.40 Gy (~10–100 a) for sand samples and ~2.57 Gy (~630 a) for the sandy soil sample LUM3196, which should cause the overestimation of several tens of percent for sand samples and of ~10% for the old sandy soil sample, if the measured residual dose is subtracted from the
All OSL ages were calculated in years (a) before 2015 (Table 2). All ages derived from the OSL samples are stratigraphically consistent taking uncertainty into account. In the profile a clear boundary between yellowish and grey sand can be identified, but two samples above and below the boundary, LUM3192 and LUM3193, gave almost identical ages (115 ± 9 a and 114 ± 9 a, respectively), indicating the PJ sand dune accumulated successively in a short time interval. The high sedimentation rate for sand deposits and low sedimentary rate for sandy soil layer are observed (Fig. 9). Our results are consistent with the mid-Holocene chronostratigraphy presented by Li Depth-age relationship of the PJ sand dune and sandy soil layer with a graphic log and all sample codes.Fig. 9
The possible depositional ages for the top and bottom of the sand dune were assumed by extrapolating the fitted age-depth relationship shown in Fig. 10. The results after the extrapolation show that the PJ sand dune accumulated from ca.120 a (1890 AD) to ca. 70 a (1940 AD). Although there are only two data points available, the age of the top of sandy soil was also estimated by an extrapolation, resulting in Comparison of different proxies. (A) The precipitation variations in northern China revealed by the δ18O data from the Shihua Cave stalagmites record (Li et al., 1998; orange solid line). (B) Temperature change in Liaoning Province (Sun and Zhao, 2002; green solid line). (C) Population change in Northeastern China from 1812 to 1911 AD (blue solid line) summarized by Zhao (2004). (D) Quartz OSL ages for the sand deposits.Fig. 10
The Holocene transgression in the Liaodong coastal area was recorded by marine sediments with buried thicknesses of 6–15 m (Fu, 1988) and 7.85 m (Bing
More direct evidence is available from historical records of coastline migration (Lin, 1991) and research on recent coastline evolution over the past hundred years conducted by Chen
Previous studies on the Little Ice Age (LIA) in China showed that the last sub-cooling period of the LIA occurred during 1840–1870 AD according to Zhu (1973) and 1830–1890 AD according to Wang and Wang (1990). Several sand deposits worldwide were correlated to the cold period in the last millennium based on accurate OSL chronology (e.g. Tamura
A well-preserved sand dune in elapsed marine-terrestrial interacted area in northeastern China is studied in this paper. Based on the results, we conclude:
Using OSL ages of quartz, the chronology of the PJ sand dune and underlying sandy soil layer based on quartz ages was established: The sandy soil sediments deposited after 5.0 ± 0.4 ka at an extremely low sedimentary rate. The PJ sand dune accumulated from c.120 a (1890 AD) to c.70 a (1940 AD) at a high sediment accumulation rate. There is no major hiatus between sand dune and sand soil layer. The quartz OSL chronology shows that the sandy soil layer formed after the sea level highstand in the Holocene. The sandy soil layer is recognized as a marsh deposition based on the characteristics of the containing organic-rich matter and soil aggregate. Combined with historical coastline change, the PJ sand dune is an inland sand dune instead of a coastal sand dune. Under a humid and warm climate period, the PJ sand dune was very likely impacted by human activity at the end of Qing dynasty but not due to the climate change. The IR50 fading rates for six sand samples are between ~5 - 10%/decade, whilst he pIRIR150 fading rates are generally negligible. The fading corrected IR50 and pIRIR150 ages are overestimated for six sand samples, and consistent with the quartz ages for two sandy soil samples. The predicted residual doses obtained from the quartz OSL ages are generally larger than the measured residual doses for our samples. The use of the measured residual dose for correction is not appropriate, because the true residual dose is highly dependent on the natural bleaching condition. The pIRIR150 dating is generally applicable for samples older than ~1000 a when the effect of residual dose becomes insignificant.