Journal of Quaternary Science最新文献

Turbidites, deposited by sub-aqueous gravity flows, are common in sedimentary archives worldwide and present a unique challenge and opportunity when reconstructing past vegetation through pollen analysis. When sampling pollen from a sediment core for palaeovegetation records, it is common practice to target background sediments (i.e. pelagic sediment) and avoid sampling turbidites, as they are presumed to portray a misleading picture of past vegetation. This assumption stems from our limited understanding of pollen abundance and distribution through turbidites, meaning that palynologists overlook deposits that could potentially be used to reconstruct past vegetation and climate. We present pollen assemblage and sedimentological data from four recent (<150 years) deep marine turbidite deposits from the Hikurangi Subduction Margin, Aotearoa-New Zealand, with the aim of understanding the abundance and distribution of pollen in fine-grained turbidites. We find that pollen is diluted in the bases of turbidites, but despite this dilution, the proportions of different pollen taxa remain consistent through each turbidite. These results confirm that pollen can be sampled from turbidites for palaeovegetation reconstructions and that sampling the fine-grained upper parts of turbidites will provide the best pollen recovery.

The stratigraphy and dating of lacustrine sediments and loess derivatives from Rodderberg, a crater of the East Eifel Volcanic Field in Germany, is based on luminescence dating and incorporates radiocarbon ages, fingerprinting of key tephra layers of the East Eifel Volcanic Field (Rieden Tephra, Hüttenberg Tephra, Laacher See Tephra), pollen stratigraphy, varve counting data, and a correlative age–depth model. These methods yield a robust age–depth model for the last 258 ka. Beyond this, luminescence ages differ from tephra-derived ages. In light of the apparent presence of the Rieden Tephra, the lowermost interglacial is assigned to Marine Isotope Stage (MIS) 11 or 420 ka. This provides a high-resolution record of environmental conditions representing an analogue for the Holocene, characterized by a warming planet. However, new luminescence ages may indicate a younger age for basal sediments, with the lowermost interglacial representing MIS 9. Both age–depth models constrain regional environmental changes during the Middle Pleistocene controlled by global climate variations. For the hydrologically closed nature of the Rodderberg crater, with limited pathways for sediment inflow and erosional export, these results shed new light on the continuity of long Middle Pleistocene records.

Soil erosion across South Africa's drylands occurs widely in the form of gullies and badlands (locally termed dongas) that have developed in colluvium and in valley fills along incised rivers. This erosion has commonly been attributed to land mismanagement, particularly since European settlement, but natural factors such as soil properties, local base level fall and climate change have also been invoked. To disentangle human and natural factors, we use optically stimulated luminescence (OSL) dating, supported by documentary and archaeological evidence, to constrain the timing and causes of donga formation at three widely spaced sites across interior South Africa. At all three sites, the exposed stratigraphy indicates that hillslopes and floodplains underwent net sediment accumulation during most of the late Quaternary, and that present-day deep erosion is of a magnitude unprecedented probably within at least the past 100 ka. OSL ages indicate that the onset of erosion at each site significantly pre-dates European incursion and instead was broadly coincident with abrupt climatic changes that occurred during the Medieval Climatic Anomaly (MCA, ~ad 900–1300) and Little Ice Age (LIA, ~ad 1300–1800). Based on correlation with palaeoclimate proxy records, we propose that erosion was triggered by abrupt hydroclimatic oscillations during the MCA, and continued during the LIA in response to climate-driven, large floods. At these sites, soil type and local base level falls exert secondary controls on the specific locations, processes, rates and depths of erosion. In other areas of South Africa, clear links between land mismanagement and soil erosion have been demonstrated, but for sites where detailed investigations have yet to be undertaken, these findings challenge an often default assumption that soil erosion is necessarily attributable to human factors. Our findings have significant implications for soil erosion control strategies and assessment of South African dryland landscape response to future climate changes.

Studies of the Last Interglacial (ca. 129 to 116 ka BP) provide an opportunity to study the impact of high-latitude warm temperatures on the Earth system. To build an accurate spatio-temporal picture of climate and environmental variability during the Last Interglacial, building robust chronologies, through which the patchwork of terrestrial, marine, and ice core archives can be correlated, is paramount. In this review, we briefly evaluate the most common approaches used to date climate and environmental archives from the Last Interglacial, as well as the chronostratigraphic tools available for direct correlation between sequences, with a focus on terrestrial archives. We then present a case study on the use of pollen biostratigraphy for correlating sequences in NW Europe, highlighting its strength as a local correlation tool, and the challenges this approach presents in comparing sequences to global records of climate and environmental change. A move towards consistently dated sequences will improve our understanding of environmental responses to Last Interglacial climate variability across different elements of the global climate system and the rates at which different elements of the climate system respond to changes in global temperatures.

The Late Pleistocene Marine Isotope Stage (MIS) 5 – MIS 4 transition (at ca. 75 ka) is globally known to correspond to a period of strong cooling and sea-level lowering. Terrestrial records indicate the transition had a large impact on terrestrial environments, but the impact on coastal and shallow-marine areas is poorly documented due to a lack of well-dated, continuous archives caused by erosion during succeeding glacial lowstands. The extensive offshore deposits of the Brown Bank Formation in the southern North Sea yield a valuable record of this transition in a shallow-marine environment. We show that the southern North Sea experienced subarctic marine conditions with a high input of terrestrial material during the MIS 5–4 transition. These continued marine conditions, which have not been described earlier for northwestern Europe, show that sea level remained relatively high, and lagged cooling on land inferred from lipid-biomarker palaeothermometry. The time-lag between terrestrial cooling and sea-level fall created a sediment preservation window during the onset of MIS 4 in a shallow-marine environment. Our record captures changes in both the terrestrial and shallow-marine environments, and allows for linking terrestrial and marine records of the MIS 5–4 transition in NW Europe.

The Early Upper Paleolithic Level 497D of Cova Gran (Pre-Pyrenees, Spain) comprises large assemblages of lithics, fauna, hearths, ash accumulations and well-preserved refitting sequences. This provides exceptional information to analyze spatial patterns and deepen our understanding of the socio-economic behavior of these human groups. This large interdisciplinary dataset has allowed us to carry out a detailed spatial study based on density analysis, geostatistics, fabric analysis and orientation techniques, revealing a structuring of the activities performed within the rock shelter. The distribution and accumulation of lithic artifacts, fauna and refits, and their association with the 10 hearths and ash accumulations, show that different types of activities were developed at the site, as well as showing the different uses of the hearths. 497D is a palimpsest where several short-term occupations and/or activities could have occurred in a relatively short period of time, avoiding prolonged exposure to biotic and abiotic post-depositional factors that could have significantly disturbed this well-preserved assemblage. This level shows a place visited several times in relation to the development of specific activities, with movements throughout the landscape for the exploitation of local and regional resources, and less so its use as a domestic space. This implies that the central settlement, or dwelling space, would have been located somewhere other than Cova Gran.