Quaternary Science Advances最新文献

In this study, we investigated the past hydroclimate and its controlling factors over East Asia by reconstructing hydroclimate variability during the middle-to-late Holocene using rainfall-driven sedimentary features in the Gaho paleolake, Hapcheon County on the southern Korean Peninsula. Based on radiocarbon dates, median grain sizes, and elemental ratios of strontium (Sr), titanium (Ti), and zirconium (Zr) measured by high-resolution X-ray fluorescence core scanning, we tested potential indicators of past heavy rainfall. During the past 7000 years, temporal changes in median grain size and elemental ratios (Sr/Ti and Zr/Ti) were found to be similar to those in the Asian monsoonal precipitation index and sea surface temperature (SST) in the western North Pacific region, suggesting that periods with increased elemental ratios may have been influenced by intensified regional rainfall events and higher SSTs. During the past 2000 years, time series of Sr/Ti and Zr/Ti ratios in the paleolake sediments appeared to covary with a megadrought period (AD 1593–1698; 357-252 cal BP), flooding events in the 1500s, and the collapse of ancient nations in Korea and other parts of East Asia. This similarity between sedimentary records and historical events suggests considerable potential for the dating of elemental ratios in lake sediments as high-resolution analogs of past hydrological events to support historical records.

Landslides are prevalent in the Ethiopian highlands, particularly in the east Gojjam zone, which is highly affected by landslide problems. This research was carried out in the east Gojjam zone, northwestern Ethiopia. The study area is part of an economically important area in the country, and it is the main source of water for the Grand Ethiopian Renaissance Dam (GERD). The main objective of this work was to undertake a detailed inventory of past landslide locations and prediction of present and future landslide hazards, as well as the preparation of a landslide zonation map in the East Gojjam zone by using the Analytical Hierarchy Process (AHP) with the GIS technique. The parameters used for this study were slope degree, slope aspect, land use and land cover, road proximity, rainfall, lithology, altitude, and river proximity. The various causative parameters were collected from the field, and suitable modifications were made to the thematic maps. Finally, the ratings for various parameters were used as the basis to prepare the LHZ map in GIS windows. The landslide susceptibility and inventory mapping were produced in the GIS environment. The results of the study show that the main driving factors for the landslide hazards in the area were river proximity, rainfall, and manmade activities. Validation of this LHZ map revealed that more than 80% of past landslides match within the "high hazard zone" and reasonably accepted the rationality of the adopted methodology. The considered parameters, as well as their evaluation of the production of LHZ-Map, were confirmed. The produced landslide inventory map is very important for urban planners, agricultural studies, environmentalists, and future landslide hazardous prevention and mitigation strategies.

Slope failure is a prominent and recurring geohazard in numerous parts of Ethiopia, including Adama City, which is located in the Northern Main Ethiopian Rift (NMER). The city is surrounded by two ridges oriented in the NNE-SSW direction, which are susceptible to slope instability. Thus, this study is aimed at modeling slope stability along these two ridges using Finite Element Method (FEM) and Limit Equilibrium Method (LEM). The modeling was carried out on slopes of multifaceted geometry composed of eluvium soil, pumice, and moderately to highly-weathered ignimbrites. Critical slope sections were identified using satellite imagery and field manifestations such as slope toe condition and slope face tilting. Their geometries were then inferred from detailed geological cross-sections based on field data. Input parameters for the modeling, such as cohesion, friction angle, and elastic modulus, were calculated via Back Analysis using the Hoek-Brown criterion while unit weight and Poisson ratio were determined from empirical equations. For soil formations, the parameters were determined via standard laboratory experiments. The modeling was then carried out under different conditions, including dry, saturated, static, and dynamic conditions. Results from both LEM and FEM models revealed that three of the four analyzed slope segments were unstable under dynamic and saturated conditions, highlighting the influence and importance of precipitation and seismicity as triggering variables. Results from both methods tend to agree when the critical slip surface passes through a single geological material in both models. However, notable differences arise when the slip surface involves multiple geological materials. Under such conditions, LEM tends to yield higher FOS values compared to FEM. The results also showed that all unstable slopes were associated with the NNE-SSW striking fault of the study area, as inferred from failure surfaces generated from both models and field data. The study concluded that unstable slopes pose a serious risk to nearby residents and infrastructure, and as a remedy, it designed and recommended coupled benching and slope flattening.

The directly dated RRMarch2021 age model (Roberts et al., 2021) for the ∼293 m long composite core from Chew Bahir, southern Ethiopia, has provided a valuable chronology for long-term climate changes in northeastern Africa. However, the age model has limitations on shorter time scales (less than 1–2 precession cycles), especially in the time range <20 kyr BP (kiloyears before present or thousand years before 1950) and between ∼155 and 428 kyr BP. To address those constraints we developed a partially orbitally tuned age model. A comparison with the ODP Site 967 record of the wetness index from the eastern Mediterranean, 3300 km away but connected to the Ethiopian plateau via the River Nile, suggests that the partially orbitally tuned age model offers some advantages compared to the exclusively directly dated age model, with the limitation of the reduced significance of (cross) spectral analysis results of tuned age models in cause-effect studies. The availability of this more detailed age model is a prerequisite for further detailed spatiotemporal correlations of climate variability and its potential impact on the exchange of different populations of Homo sapiens in the region.

The present study aims to investigate the palaeoenvironmental changes around Sattal Lake, Kumaun Lesser Himalaya spanning the last 1670 years. Based on multi proxy analysis (i.e., grain size, mineral magnetism, clay mineralogy, Total Organic Carbon (TOC) and carbon isotopes), supported by a robust radiocarbon chronology, three major environmental phases were identified. Warm, wet phases occurred between 1,150–650 cal yr BP and 260 cal yr BP to the present. These phases coincide closely with the Medieval Climatic Anomaly (MCA) and modern warming, respectively. These warm/wet events were due to elevated precipitation, resulting in high lake levels and an expansion of the lake margin, which were marked by lower δ¹³C values, comparatively higher sand concentration, TOC values and magnetic susceptibility (χ_lf). The inference of a modern warm phase is supported by high resolution instrumental data. The MCA, which is marked by elevated amounts of coarse grained (sand) detrital material, is inferred to be an interval of strengthened of monsoonal intensity, which correlates with available monsoon records from various continental paleoclimate archives. Following the MCA a cold and dry phase was observed to occur between 610 and 260 cal yr BP, corresponding to the Little Ice Age (LIA). The LIA, which was characterized by high silt and clay concentration, high δ¹³C, low TOC and reduced magnetic susceptibility (χ_lf), is inferred to represent an interval of low lake levels, likely reflecting an episode of weakened monsoonal intensity.

The authigenic ¹⁰Be/⁹Be dating method presents a valuable tool for reconstructing depositional chronologies in sedimentary environments, requiring only ubiquitous mud for sampling. Nevertheless, studies elucidating the variability of the ¹⁰Be/⁹Be record preserved in epicontinental successions are lacking, despite the essential nature of such knowledge for the application of authigenic ¹⁰Be/⁹Be in geochronology. In this study, we investigate the variability of measured natural ¹⁰Be/⁹Be ratios in sediment cores recovered from the Holocene Po River delta plain in Northern Italy, aiming to unveil the influence of changing sedimentary environments and provenance on the beryllium isotopic signature. We identified significant variations in the authigenic ¹⁰Be/⁹Be ratios across parasequences, which correlates with a provenance change from the Eastern Alps to the Po River. The observed variation would cause an age offset of ∼1 Myr if unrecognized in a dated succession. Our analysis revealed consistent ratios between the delta plain (primarily represented by swamp) and delta front consisting of proximal prodelta facies, suggesting a prevalent riverine signature in the proximal prodelta, likely maintained by hyperpycnal flow deposition. Statistical assessments based on random sampling and bootstrapping highlighted the importance of a sample size of n > 10. Furthermore, a standard deviation of the observed variability indicates a necessity of an additional 9% uncertainty in authigenic ¹⁰Be/⁹Be dating studies if the sample size is smaller. Overall, our findings emphasize that the normal regressive highstand settings of a deltaic system maintain relatively stable beryllium isotopic fluxes, which are favourable for the authigenic ¹⁰Be/⁹Be dating application, if provenance changes are known.

Recently, radiocarbon (¹⁴C) dating methods using fossil pollen extracted from sediments with a flow cytometer (cell sorter) are under development. Technical limitations experienced by previous studies required extraction of grains <80 μm in diameter. Thus, obtaining a sufficient mass of carbon for dating requires extracting a very large number (∼10⁵) of grains. Another challenge faced by earlier work was preventing contamination by exotic carbon during the extraction process. Here we present a novel solution to this problem by using a cell sorter with a newly designed pretreatment method and an improved extraction method. This enables us to extract large pollen fossils than was previously possible. By using grains, >100 μm in diameter, such as Pinus sp., we have reduced the number of grains for required for ¹⁴C dating by an order of magnitude, particularly when considering the recent advances in measure ultra-small carbon masses on a single-stage accelerator mass spectrometer at the Atmosphere and Ocean Research Institute, University of Tokyo. We then apply this method to sediments recovered from Lake Motosu, which already has a very robust chronology, to evaluate the new method. Results indicate the method is successful and reveal temporal radiocarbon reservoir effects that appear related to the changes in the depositional environment and/or hydroclimate. The method presented here is widely applicable across multiple environments.

Unraveling how Global Mean Sea Level (GMSL) fluctuated during past warm periods can improve our understanding of linkages between sea-level fluctuations, orbital forcing, and ice-sheet dynamics. Current estimates of GMSL for Marine Isotope Stages (MIS) 5a and 5c — two warm intervals following the relatively well-documented MIS 5e — contain meters of uncertainty and fewer data due to several challenges. These challenges include concealment of datable in-situ coral facies by MIS 1 deposits and inaccessibility due to submergence by modern sea level. We present a comprehensive dataset based on U–Th dating and stratigraphic correlation of 23 cores totaling over 170 m of recovered coral-reef deposits across the tectonically stable Florida Keys Reef Tract (FKRT). Following detailed facies descriptions, 34 in-situ, minimally altered aragonitic coral samples (≤2.7% calcite) below the Holocene-Pleistocene boundary were targeted for U–Th geochronology. Fourteen closed-system coral U–Th ages from MIS 5a include the commonly used sea-level indicator Acropora palmata, but also the massive coral taxa Pseudodiploria strigosa, Siderastrea siderea, Orbicella spp., and Porites astreoides. Dating yielded ages in the range of 88–81 ka (average 2σ uncertainty of less than 200 years). These ages suggest MIS 5a reef initiation at ∼88 ka BP, a peak near 83 ka with minimum elevations between −6.0 ± 0.5 and −5.6 ± 0.5 m MSL (2σ uncertainty and subsidence-corrected), and reef termination and sea-level fall by ∼81 ka BP. Notably, the range of peak MIS 5a relative sea-level estimates of −6.5 to −5.1 m MSL are more than 2 m shallower (higher) than previous estimates of −11 to −9 m. Our higher resolution regional sea-level reconstruction across four subregions of the Florida Keys reef tract aligns with changes in July insolation at 65° N: a trend that most other records, such as deep-sea sediments, do not have the accuracy and precision to resolve. Three massive coral samples from MIS 5c, consisting of Pseudodiploria clivosa, and Orbicella spp., yielded ages in the range of 104 to 99 ka (average 2σ uncertainty less than 200 years); however, because only one sample met the closed-system criteria, our ability to estimate MIS 5c sea level is relatively limited. More empirical estimates of sea-level from the MIS 5a and MIS 5c intervals based on numerical dating of reliable local sea-level constraints are critical for GMSL calculations and relating changes in sea-level amplitude and timing to global ice volume modeling and glacio-isostatic effects, all of which can improve predictions of future sea-level changes in coastal regions.

This paper examines the interplay of environmental change and human demographic shifts among late Pleistocene and Holocene populations in the hyper-arid context of the Central Namib Gravel plains, Western Namibia. This paper applies a structural equation modeling (SEM) approach to arid-zone hunter-gatherer mobility patterns and settlement systems based on variability among ethnographically and historically observed groups. It then applies this model in examining issues related to the Middle-to-Later Stone Age transition at the sites of Erb Tanks and the Mirabib rock shelter. This model suggests that, among modern arid-zone foragers, population density is by far the strongest factor influencing mobility and settlement systems, with higher population densities favoring longer residential site usages and shorter residential moves within smaller territories. In contrast, environmental variables having to do with annual rainfall, rainfall seasonality, and effective temperature affect mobility and settlement systems in ambiguous and statistically insignificant ways. This paper closes by arguing that regional-scale population increases signaled by various features of Later Stone Age archaeological patterning led to local population expansions in the Central Namib Desert, and that this in turn caused a range of recognizable cultural shifts that were strongly linked with adaptations to aridity.

This research focuses on analyzing paleosols, major and trace element geochemistry, organic carbon levels, and geo-archaeological aspects of Quaternary deposits investigated in two sedimentary successions located in the east-central Barind region of NW Bangladesh. Several factors that influence the paleosol development can be used to decipher the paleoenvironment and paleoclimatic conditions of the study area. Sedimentary succession of the studied sections have been grouped into two broad categories i.e., Gray unit/Newer Alluvium (NA) of Late Holocene and Red unit/Older Alluvium (OA) of Early Pleistocene age. Some geoarchaeological evidences have been found at the bottom of the gray unit and the top of the red unit in Durgadaha (DD) section indicating the existence of paleo-settlement at about ∼1300 years BP. The age is determined by the relative dating of several artifacts found at the paleo-settlement surface. Interpretation of several field characteristics and geochemical parameters i.e., clayeyness, salinization, base loss, calcification, leaching (Ba/Sr), aeolian input (Zr/Al), CIA, CIW, CIA-K, etc. revealed that the paleosols in gray unit are weakly developed; whereas, paleosols in red unit are relatively moderate, strong to very strongly developed. In the red unit, the MAP and MAT range from 1000 ± 181 mm to 1478 ± 181 mm and 9° ± 4.4°–14° ± 4.4 °C respectively. On the other hand, MAT ranges from 23.1° ± 0.6 °C to 28.3° ± 0.6 °C in gray unit paleosols. Depending on the depositional pattern and estimated MAT, five short-term climatic cycles (i.e., alternating phases of dry and wet) have been recognized in gray/newer alluvium units during the last 1300 years. The demise of paleo settlement (1300 years BP) due to the abrupt climatic change towards a dry and cooler phase where the MAT was estimated as 23.1° ± 0.6° which is at least 3 °C lower than the present. This study also revealed that the estimated MAP and MAT are more analogous to paleoclimatic records of the Asian regions.