Quaternary Science Advances最新文献

Slope failures are a significant natural geohazard in hilly and mountainous regions, often resulting in loss of life and infrastructure damage. The Muketuri-Alem Ketema road in Ethiopia is particularly vulnerable to landslides due to colluvial deposits on steep slopes from the higher northeastern plots to the lower Jemma River valley. This study investigates the characteristics of colluvial soil and evaluates the stability of slopes prone to landslides. It combines geophysical data, penetrometer tests, laboratory analyses, Google Earth images, and detailed field visits to assess the soil and bedrock composition and structure. Numerical methods, including limit equilibrium (Bishop, Janbu, Spencer, and Morgenstern-Price methods) and finite element methods, were used to analyze slope sections under various saturation conditions and simulate different rainfall patterns. The results indicate that the Bishop, Morgenstern-Price, and Spencer methods produce similar safety factors with minimal differences (<0.3%), while the Janbu method shows more significant variation (1.5%–5.6%). Safety factor differences for sections A-A and B-B range from 5.26% to 9.86% and 3.5%–4.7%, respectively. Simulations reveal that short-term saturation significantly reduces the stability of the upper slope layer by 20%–46.76%, and long-term saturation decreases the entire slope section by 26.81%–46.76% compared to dry conditions due to increased pore water pressure and self-weight. Long-term saturation effects, combined with dynamic loads, can further reduce colluvial soil stability by over 50% compared to a dry static state. The finite element method predicts larger failure zones than limit equilibrium methods, emphasizing the need for accurate predictions to characterize slope behavior during failure and inform stabilization decisions. This study provides crucial data for maintaining and planning the Muketuri-Alem Ketema Road, highlighting slope performance over time and the effectiveness of stabilization techniques.

Phytolith content and its preservation in soils form a robust tool for paleoecological reconstruction. Post-depositional processes, however, influence the preservation of phytolith assemblages in soils thus making the paleoecological inferences biased. Here we evaluated the preservation of phytoliths in a Late Quaternary loess-paleosol sequence (LPS) from Kashmir Valley, northwest Himalaya. The soil micromorphological study, physicochemical parameters, phytolith morphometry, and phytolith translocation rates were employed to assess phytolith preservation and absence (not recorded) in the various litho-units of the Wanihama LPS. The comparison of phytolith content and soil physio-chemical parameters including pH, electrical conductivity, available N, P, K, organic carbon, extractable Fe, Zn, Mn and Cu do not show any significant correlation. This suggests that soil physicochemical parameters have a minor role in regulating the preservation of phytoliths in the LPS. The depth distribution of phytoliths exhibits an inconsistent pattern and phytolith content doesn't decrease systematically with depth. The phytolith content usually follows the loess-paleosol stratigraphy, with low concentrations in loess units and high concentrations in paleosols indicating that phytolith assemblages in the LPS have not been altered or translocated as a result of pedogenic processes. The micromorphological observations suggest weak pedogenesis and the sequence does not seem to be significantly mixed by bioturbation activities. This is augmented by the low translocation rate of <18%, and phytolith morphometry suggesting well-preserved phytoliths with minimum morphological alterations along the depth. The absence of phytoliths at certain stratigraphic units in the LPS thus suggests that climatic conditions rather than physicochemical parameters determine the phytolith preservation and their content in the Kashmir LPS.

Individual niche variation occurs when individuals within a population adopt unique behavioural or ecological traits, giving the population a distinct niche structure. Although widespread amongst natural populations, most of niche theory and its applications in ecological and palaeoenvironmental contexts remains focused on species level patterns, treating variation within the population as noise. Using serial stable isotope profiles sampled along teeth of herbivore fossils recovered from the Mid-Pleistocene site of Kathu Pan 1, Northern Cape (South Africa), enabling partitioning of isotopic niche variation into between- and within-individual components. Stable carbon isotope data revealed significant dietary differences between-individuals within most of the taxa sampled, but no dietary differences between taxa. By contrast, stable oxygen isotope compositions were more consistent amongst individuals, but varied across taxa. In both isotope systems, as well as in bivariate space, most taxa comprised individuals with both narrow and broad isotope niches, indicating flexibility in dietary strategies. These results indicate sufficient opportunity for individual level specialization within the Kathu palaeocommunity, afforded by a palaeoenvironment that provided a consistent supply of resources year-round. Given the herbivore sample is strongly associated with fossil hominin activities, our results imply that hominins in these landscapes would have profited from year-round accessibility to resources, accounting for the record of occupancy of Kathu Pan I during the Mid-Pleistocene.

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.

Lipid biomarkers are valuable proxies for reconstructing paleoclimate and paleoenvironmental changes as well as human impact. However, little attention has been paid on evaluating how the combination of biomarkers can be used to reconstruct various aspects of local paleoenvironmental conditions. This study presents a suite of lipid biomarker records from a sediment core from Lake Höglwörth, southern Germany, covering the past 400 years. Compound-specific hydrogen isotopic compositions (δD) of terrestrial n-alkanes (n-C_29-alkane) and n-alkanoic acids (n-C_30-acid) indicate minor changes in isotopic composition of precipitation. The δD of n-C_22-acid is interpreted to record the isotopic composition of the lake water and evaporative enrichment, which drops after 1700 CE, coinciding with the construction of a mill and the related rerouting of a creek into Lake Höglwörth. The δD of n-C_25-alkane is also enriched but decoupled from the reconstructed isotopic composition of precipitation and lake water. Therefore, we suggest that δD of n-C_25-alkane reflects the leaf water isotopic composition of Sphagnum, which is present in the catchment and undergoes transpirative enrichment. Both short-chain compounds have become more enriched over the last century, maybe related to increasing temperature associated with anthropogenic climate warming. The faecal biomarkers record the changes in human population, partly related to the history of the local Monastery, the World Wars I and II as well as the intensive farming after the mid-20th century. Polycyclic aromatic hydrocarbons (PAHs) reveal a significant change in combustion activities associated with human activities such as the industrial revolution, biomass burning, and environmental cleanup as well as the implementation of emission standards. Our study demonstrates that the combination of plant wax compounds, faecal biomarkers, and PAHs from lacustrine sediment serves as a valuable tool to reconstruct and distinguish various aspects of paleoclimate and paleoenvironmental changes including human impacts.

Ethiopia is currently emphasizing the construction of micro dams to enhance agricultural productivity and assure food security. The Upper Guder Dam, situated in the West Shoa Zone, Central Ethiopia, is one such project. However, the dam faces challenges due to complex geological and structural conditions, including leakage and slope instability. Hence, this study focuses on addressing the abutment slope stability and watertightness condition of this dam. Accordingly, the study employed discontinuity surveying, Seismic Refraction Tomography (SRT), Rock Quality Designation (RQD), and Lugeon testing to assess the water tightness. Additionally, kinematic analysis and the Limit Equilibrium Method (LEM) were used to evaluate abutment slope stability. Results from surface geological mapping and core drilling showed that the dam site is constituted by quaternary soil, tuff, and basalt. The Lugeon test results indicate that the left abutment of the dam is susceptible to leakage down to a depth of 40 m, which suggests that the permeable zone extends deeper than the results revealed by the SRT. Furthermore, this test demonstrated that the dam's right and central foundations are susceptible to leakage to the drilled depths. The SRT revealed that the central foundation, right, and left abutments of the dam are susceptible to leakage to the depth of 35 m, 30 m, and 34 m, respectively. Moreover, the kinematic analysis revealed that a section of the left abutment of the dam is susceptible to wedge mode of failure due to the intersection of JS1 and JS2. The LEM modeling of the right abutment of the dam also depicted that this section of the dam is unstable under saturated conditions which illustrates the importance of precipitation as the major slope destabilizing factor in the study area. Based on the study findings, this study recommended the use of curtain grouting to address the water tightness issue and slope angle reduction to mitigate the slope instability problem.