Periglacial Slope Deposits Research Articles

Quantification of the effect of loess admixture on soil hydrological properties in sandy slope deposits

The admixture of loess in soils formed in sandy parent materials has considerable impact on pedogenesis and soil ecological functions. This study aimed to evaluate these effects on soil hydrology by quantifying the relationships between loess content and soil hydrological properties in a sandstone landscape covered by Pleistocene periglacial slope deposits in central Europe. Studied properties were saturated soil water capacity, field capacity, permanent wilting point, available water capacity, macro-porosity, matrix porosity and saturated hydraulic conductivity. The effect of loess addition on soil hydrological properties differed between topsoil (pedogenic A horizons) and subsoil (pedogenic B and C horizons). In the subsoil, the studied soil hydrological properties were mainly controlled by loess content. By contrast, in the topsoil the effects of loess content on soil hydrological properties were largely masked by the effects of soil organic matter (reflected by soil organic carbon, SOC). The enhancing effect of SOC on soil hydrological properties was most prominent for saturated soil water capacity and was also significant for all other parameters except permanent wilting point. After the effects of SOC were accounted for, the residual effects of loess on soil hydrological properties were the same in both topsoils and subsoils, with one exception: Saturated hydraulic conductivity decreased with increasing loess content for subsoils, but not for topsoils. This study highlighted the ecohydrological significance of loess admixture in coarse-textured soils, especially for subsoils with low SOC contents. However, for coarse-textured topsoils, SOC content plays the dominant role in affecting soil hydrological properties.

Investigation of subsurface connectivity and subsurface stormflow in low mountain ranges—Findings from the two research catchments Obere Brachtpe and Bohlmicke (Germany)

AbstractThe two small research catchments Obere Brachtpe (2.6 km2; 50.989986, 7.752013) and Bohlmicke (1 km2, 51.079319, 7.892988) are located in the Rhenish Massif, a low mountain range in Germany. Land use in both catchments is dominated by pasture land, spruce stands and mixed forests. Mean annual temperature is 9.1°C, and mean annual total precipitation is 1250 mm, with 15%–20% of the annual precipitation falling as snow. The geology is characterized by sandy silty clay shale from the Lower and Middle Devonian. Loamy Cambisols derived from periglacial slope deposits, complemented by Leptosols and Stagnosols, are the most prominent soils in the catchments. Long‐term hydrological datasets of precipitation, throughfall, discharge, groundwater levels and soil moisture (at different soil depths) in a high temporal and spatial resolution are available for further scientific analysis. Both catchments were monitored within the time period 1999 and 2009, in order to understand how the antecedent soil moisture, stratified soils (periglacial cover beds) and topography (slope form) impacted the subsurface connectivity, and the subsurface stormflow generation ‐ a dominant runoff generation process in humid mountainous catchments. Detailed physically based investigations on runoff processes were carried out, and the obtained results helped to better understand subsurface stormflow generation and subsurface connectivity dynamics. The process knowledge gained, which was presented at several conferences, as well as publications, was the basis for the discussion of open questions within the scientific network ‘Subsurface Stormflow ‐ A well‐recognized, but still challenging process in Catchment Hydrology’ (2016–2021), and the research unit ‘Fast and invisible: conquering subsurface stormflow through an interdisciplinary multisite approach’ (2022–2025), both financed by the German Research Foundation (DFG).

Loess in Pleistocene periglacial slope deposits and Holocene colluvium of European low mountain ranges: Mixing processes and spatial variations

Loess, as an allochthonous material, plays a significant role in the formation of Pleistocene periglacial slope deposits (PPSD), and thus also for Holocene soil formation, in the central European low mountain range. Although the differing loess proportions in different layers of the PPSD have been well recognized, quantitative distribution and mixing processes of loess in PPSD are still not fully understood. Detailed particle-size distribution was applied for quantifying loess proportions in PPSD in a sandstone area in central Germany. The bimodal pattern of the particle-size distribution curves clearly reflected loess and sandstone-weathering material as two components of the loess-affected layers, which allowed for the quantification of these two components by applying a two-endmembers unmixing model. By inspecting variations of particle-size distribution curves both vertically and spatially, we gained insights into the mixing processes of loess in PPSD and Holocene colluvium. Our results suggest that the loess component in upper layers most likely results from the incorporation of preexisting loess. Holocene colluvium and upper layers were thoroughly homogenized by various earth-surface processes. Radiocarbon dating of charcoal indicated strong human impact during historic times. Close correlation between the overall thickness of loess-containing layers and the depth-weighted loess content pointed to the erosional-depositional history at each site. Our research demonstrates the utility of detailed particle-size data for detecting and interpreting geomorphological processes and landscape evolution. It shows that the spatial distribution patterns of loess are subjected not only to topographic factors controlling primary loess deposition, but also to erosional-depositional histories and anthropogenic impact.

Pedosedimentary and geoarcheological archives from clay-dominated sinkhole infillings in Middle Franconia, Germany

Sinkholes in the karstified Middle Keuper gypsum of Middle Franconia, Germany reveal numerous archeological findings and contain unique pedosedimentary records of landscape development and human-environment interaction during the Holocene. Mudstone-derived high clay contents result in a unique set of sedimentary and pedogenic properties of these archives in that all units exhibit vertic properties. Since the horizons have a polygenic history, detailed field and micromorphological observations, together with laboratory analyses (grain-size, color, iron-pedochemistry) are the basis for a classification of the pedosediments. 14C dating provides a chronological framework for geomorphological stability phases and thus, identified soil-forming processes. The first anthropogenic colluvial sediments of the studied archive date to the Early Bronze Age and accumulated in an initial karst depression. Water saturation caused iron reduction of these early infillings. In the pedosediments above, oxidation and iron release are largely related to changes in the parent material. Here, the soil material contains coarse silt indicating an admixture of nearby periglacial slope deposits. Furthermore, fossil root traces point to a longer time with stable conditions, which we interpret as absence of humans or at least an extended period of fallow land. The superimposed sediments from the Urnfield period are more inhomogeneous and consist of material from the eroded agricultural soils of the surrounding. The characteristics of these pedosediments point to intensified human land use. Pedogenic processes such as iron release, reduction of iron, swelling-shrinking, and short-distance translocation of clay intensively overprinted all soil sediments. In this context, micromorphology proved to be an essential tool for the characterization of polygenesis in terms of soil-forming as well as redepositional processes that lead to the formation of these complex archives. The present study reflects a multi-methodological approach to a rather disregarded type of polygenic terrestrial records. It constitutes an example for the investigation of clayey pedosediments in karstic environments under moderate climate in the frame of a prehistoric geoarcheological setting.

Short Communication. Quantification of loess proportions in Pleistocene periglacial slope deposits and Holocene colluvium using grain‐size data by laser diffractometry

AbstractLoess proportions in slope deposits have rarely been quantified, due to the lack of quantification methods. In this study, we used laser granulometry to analyze grain‐size distributions in slope deposits of a Buntsandstein landscape in central Germany. The consistent loess contents obtained from two independent models corroborate the validity of the calculated loess proportions and the applicability of the new R package EMMAgeo. Yet, some limitations in transferability need to be considered.

Chronostratigraphy of silt-dominated Pleistocene periglacial slope deposits on Mt. Ślęża (SW, Poland): Palaeoenvironmental and pedogenic significance

Slope deposits with aeolian silt admixture are a widespread parent material of soils in the temperate zone but may be neglected when rates of soil production are quantified. The concept of periglacial cover beds differentiates slope deposits with or without aeolian silt admixture; yet there is a remaining debate on processes and the timing of their formation. A previous study done by us at Mt. Ślęża, SW Poland, concluded that slope deposits with variable aeolian silt admixture, or its lack, have a significant influence on the pathway of soil formation. The present work builds upon this finding, by adding further granulometric and micromorphological data from three representative profiles along a toposequence, in order to refine our understanding of local slope deposits and soil formation. Additionally, seven numerical ages using luminescence dating provide a chronological framework for our reconstructions and allow linking the forming processes of these pedosedimentary records to regional palaeoenvironmental conditions. The oldest aeolian deposits are of Middle Pleistocene age (>280 ± 19 ka) with interlayered palaeosol (marine isotope stage [MIS] 9 or older). Late Pleistocene slope deposits encompass the maximum loess thickness and are dated to MIS 2. Luminescence ages from the upper layers indicate shallow reworking, which we tentatively correlate to the Younger Dryas (YD). Two profiles with thick loess mantles have strong clay illuviation features, presumably formed during the Holocene. However, weak clay illuviation in the third profile with a thin loess mantle (having an age of YD) over granite regolith seems to have occurred before the Holocene, as only fragmented clay coatings (probably MIS 2 pedogenesis) could be found.

The geomorphology – sediment distribution – soil formation nexus on the northeastern Qinghai-Tibetan Plateau: Implications for landscape evolution

The interactions between geomorphology, sediment distribution and soil development in alpine regions are poorly understood. In this study, we analyzed the spatial variations of different sediment types and corresponding soils in 15 pedosedimentary profiles across three major geomorphic units in an alpine ridge-valley basin of the Qilian Mountains, northeastern Qinghai-Tibetan Plateau. Particle size distribution was used to trace the sediment types. Inorganic and organic carbon concentrations were included as metrics of soil processes. Aeolian silts from both distant and proximal sources cover floodplains, hillslopes and some positions on alluvial fans, while the distribution of fluvial sediments and periglacial slope deposits are much more limited due to the coverage of loess. The soils vary in response to sediment types and climatic conditions under the influence of their geomorphic settings. The vertical distribution patterns of carbonates in soil profiles show considerable differences among different geomorphic units, reflecting their contrasting water balance and migration pathways. Soil organic carbon accumulates most extensively in aeolian silts with sufficient water supply. A special pedogenic soil horizon – the mattic epipedon is formed primarily in loessial sediments in Kobresia ecosystems. The complex entanglement of fine earths and massive grassroots make the mattic epipedon extremely resilient, which helps to preserve the soils and to shape the landscapes. By integrating geomorphology, sedimentology, ecology and pedology, the outcomes of this study promote the understanding of the evolution of typical landscapes and ecosystems of the northeastern Qinghai-Tibetan Plateau and many other periglacial settings.

Field Trip D (27 September 2018): characteristics and development of the Mesozoic–Tertiary weathering mantle and Pleistocene periglacial slope deposits in the Hintertaunus mountainous region

Abstract. The Devonian slates and sandstones of the Rhenish Massif were subject to deep and intensive weathering under (sub)tropical climate conditions during the Cretaceous, the Paleogene and the Neogene, which caused the development of a weathering mantle (regolith) >100 m thick, consisting of kaolinitic saprolite and paleosols as well as correlated sediments. Especially the tectonic uplift of the Rhenish Massif and climate change during the Neogene and the Pleistocene led to a vast denudation of the weathering mantle. Only in less uplifted areas of the mountainous region did thick remnants of saprolites remain, and they were covered by Neogene sediments as well as Quaternary periglacial slope deposits. As the kaolinitic weathering products serve as raw materials for the clay industry, unique exposures are available in the Hintertaunus which offer impressive insights into the landscape development of the past ∼80 million years: the excursion proceeds from Giessen to Limburg and further south and southwest to the eastern and western Hintertaunus area. At site 1 near the village of Langhecke, characteristics and properties of the fresh, unweathered slates will be demonstrated. Excursion sites 2 and 3 are situated near the village of Eisenbach. In two open-cast clay mines, both a terrestrial and a semi-terrestrial saprolite from silt slate, covered by periglacial layers, are exposed. Properties and genesis will be discussed on the basis of morphological characteristics and mineralogical and geochemical analyses, as well as isovolumetric elemental mass balances. At site 4 a former basalt quarry near the village of Biebrich exposes a Paleogene Plinthosol above saprolite. The autochthonous paleosol was preserved below Upper Oligocene basalt tuff and periglacial layers. Site 5 is situated within a huge pit for mining of Upper Oligocene to Miocene quartz gravel near the village of Wasenbach. A Miocene Plinthosol developed from alluvial sediments on top of the gravel beds and was covered by periglacial slope deposits. At nearly all sites the basal layers of the periglacial cover beds consist of kaolinitic paleosol/saprolite material, which has an important influence on the site properties of the Holocene soils.

Chronostratigraphic interpretation of intermediate layer formation cycles based on OSL-dates from intercalated slope wash sediments

Stratified periglacial sediments extensively cover the slopes of central European low mountain areas. Periglacial cover beds and loess-like sediments as most abundant strata influence many near-surface processes, forming an important component of the Earth's critical zone.The present study focusses on the analysis of a complex sequence of periglacial slope deposits with multiple intermediate layers and intercalated slope wash sediments in order to determine and date periods of intermediate layer formation.Since luminescence dating often provides inconsistent data for cover beds, there is need to reconsider the numerical dating strategy. This study hence places stronger emphasis on numerical dating of interbedded, sufficiently bleached slope wash sediments. The gained OSL-ages are more reliable and consistent and thus, provide a temporal framework for relative dating of intermediate layer formation cycles. In combination with paleosol relics the numerical ages allowed a chronostratigraphic interpretation of Late Pleistocene paleoenvironmental dynamics and slope evolution.Our findings not only prove multiple phases of intermediate layer formation in the study area during the last glacial period but also enabled the correlation of single intermediate layers with specific time spans, including Early and Middle Weichselian as well as the Late Glacial. Remnants of the Eemian soil in the studied sequence even indicate a Saalian age for the lowermost intermediate layer.The present study shows that luminescence dating of intercalated slope wash deposits instead of cover beds is a promising numerical dating strategy for the chronostratigraphic interpretation of cover bed sequences. The findings further illustrate that complex, fanned out periglacial sediment sequences form despite their scarcity important paleoenvironmental archives for Late Pleistocene periglacial landscape dynamics in central European low mountain areas.

Impacts of a capillary barrier on infiltration and subsurface stormflow in layered slope deposits monitored with 3-D ERT and hydrometric measurements

Abstract. Identifying principles of water movement in the shallow subsurface is crucial for adequate process-based hydrological models. Hillslopes are the essential interface for water movement in catchments. The shallow subsurface on slopes typically consists of different layers with varying characteristics. The aim of this study was to draw conclusions about the infiltration behaviour, to identify water flow pathways and derive some general interpretations for the validity of the water movement on a hillslope with periglacial slope deposits (cover beds), where the layers differ in their sedimentological and hydrological properties. Especially the described varying influence of the basal layer (LB) as an impeding layer on the one hand and as a remarkable pathway for rapid subsurface stormflow on the other. We used a time lapse 3-D electrical resistivity tomography (ERT) approach combined with punctual hydrometric data to trace the spreading and the progression of an irrigation plume in layered slope deposits during two irrigation experiments. This multi-technical approach enables us to connect the high spatial resolution of the 3-D ERT with the high temporal resolution of the hydrometric devices. Infiltration through the uppermost layer was dominated by preferential flow, whereas the water flow in the deeper layers was mainly matrix flow. Subsurface stormflow due to impeding characteristic of the underlying layer occurs in form of organic layer interflow and at the interface to the first basal layer (LB1). However, the main driving factor for subsurface stormflow is the formation of a capillary barrier at the interface to the second basal layer (LB2). The capillary barrier prevents water from entering the deeper layer under unsaturated conditions and diverts the seepage water according to the slope inclination. With higher saturation, the capillary barrier breaks down and water reaches the highly conductive deeper layer. This highlights the importance of the capillary barrier effect for the prevention or activation of different flow pathways under variable hydrological conditions.

Genesis and evolution of regoliths: Evidence from trace and major elements and Sr-Nd-Pb-U isotopes

Regoliths encompass different materials from the fresh bedrock to the top of the organic horizons. The occurrence and evolution of these materials are determined by deposition, erosion and weathering processes that are specific for each region. The origin and interaction of the regolith layers are still important issues in the study of critical zone functioning. Studies that attempt to understand the processes responsible for the structure and the evolution of regoliths often focus either on the soil or on the bedrock compartment, and often from a narrowly focused approach using just a single tool such as major element patterns or mineralogy. This limits the understanding of the complete regolith composition and evolution. The present study proposes the combination of mineralogy, major and trace element concentrations, and Sr-Nd-Pb-U isotopes as an extremely useful procedure for tracking the spatial and temporal origin of regolith materials and understanding their stratification. This multi-tracer approach was applied on a regolith profile from the south-western edge of the Rhenish Massif, which is characterised by the occurrence of slate bedrocks and overlying Pleistocene Periglacial Slope Deposits (PPSD). The data allowed the differentiation of three compartments within the regolith: 1) the organic compartment, where low 206Pb/207Pb and 87Sr/86Sr isotopic ratios reflected the impact of atmosphere-derived components; 2) the PPSD compartment, whose upper horizons were characterised by the presence of atmosphere-derived particles rich in Cd, Sn, Sb, Hg and Pb and by relatively low 206Pb/207Pb and 87Sr/86Sr ratios, whereas the lower horizons showed Nb enrichments in their matrix and a mineralogical composition pointing to ancient volcanic events; and 3) the weathered slate compartment, whose weathering progression and genetic relationship with the PPSD were particularly well tracked with 87Sr/86Sr and 143Nd/144Nd isotope ratios, (234U/238U) activity ratios and positive Ce anomalies. The results prove the efficiency of radiogenic isotope measurements combined with the analysis of major and trace elements to complete regolith studies. Moreover, these isotopes and elements are shown to be potential geochemical tracers of exchange processes at the water-mineral interface. This approach allows for the first time the description of an evolution scheme of a complete slate regolith, which covers a large part of the Rhenish Massif.

Macro‐ and Micromorphologic Interpretation of Relict Periglacial Slope Deposits from the Holy Cross Mountains, Poland

AbstractRelict periglacial slope cover deposits in the Holy Cross Mountains of Poland are composed of material derived from bedrock, loess and sand of polygenic origin. The aim of this study was to interpret the processes that deposited three massive coarse‐grained diamictons near the base of gentle hillslopes. Based on macroscopic and microscopic sedimentological analyses, the diamictons are attributed to deposition by three processes – active‐layer detachment, solifluction and high‐energy overland flow – due to climatic and geomorphologic factors. The use of microscopic analysis revealed the detailed texture and structure of these deposits, and was particularly important in interpreting fine‐grained sediments produced by low‐energy overland flow. This technique served as the basis for the differentiation of solifluction deposits and high‐density flow deposits. The active‐layer detachment deposit (adjacent to the slip plane) was characterised by a heterogenous texture and breccia‐type structure with domains and clasts oriented parallel to the slope. The deposit included erosional surfaces and individual slip planes. The solifluction deposit was a clayey diamicton with a banded structure oriented parallel to the slope. The low‐energy overland flow deposit was laminated and sorted with laminae oriented parallel to the slope. The high‐energy overland flow deposit was a homogeneous and massive diamicton with a silty/sandy matrix and randomly oriented clasts and grains. The following characteristics helped identify the sediment type: the degree of homogenisation, texture, sedimentary structure and fabric. Features including plasmic fabric, deformation structures and microporosity played an additional role in identifying the studied deposits. In relict slope deposits, these features may be formed as a result of depositional or postdepositional processes. Copyright © 2015 John Wiley & Sons, Ltd.

Formation and transformation of Pleistocene periglacial slope deposits in the Spessart Mountains (Hesse, Germany)

The bedrock of the Spessart Mountains is covered by Pleistocene periglacial slope deposits (PPS- Ds). These slope deposits are supposed to have formed in a periglacial environment by a variety of processes. For this study soil profiles in the Spessart Mountains were analyzed with respect to features elucidating processes forming and transforming PPSDs. Field and laboratory analyses were complemented by micro- morphological investigations to gain more detailed information. The results verify aeolian sedimentation, solifluction and cryoturbation as most important formation processes. Furthermore, several findings sug- gest the influence of additional genetically active processes. PPSDs provide the parent material for Holocene soil formation. In addition, they experience alteration by bioturbation and anthropogenic influence on relief and soil. Pedogenic transformation is dependent on the PPSDs material composition. Particularly the content of silt-sized allochthonous material controls the efficacy of silicate weathering and depth of soil development. The coincidence of pedogenic boundaries and layers often reported in the literature is partly falsified: Eluviation and illuviation of clay is not separated at the boundary between upper and intermediate layer. PPSDs experience strong alteration by bioturbation: This process may transform characteristics that could point to formation processes. Furthermore, thin sec- tion analyses support the distinction of Holocene colluvium and PPSDs.

Impact of sedimentary processes and paleopedogenesis on Holocene Luvisol formation

stacking of periglacial layers: A differentiation of eluvial (E-) and illuvial (Bt-) horizon is already developed within the upper layer. The intermediate layer carries the main argillic horizon of those profi les whereas the within the upper layer. The intermediate layer carries the main argillic horizon of those profi les whereas the basal layer is only marginally affected by soil formation. By the help of soil micromorphology it was possible basal layer is only marginally affected by soil formation. By the help of soil micromorphology it was possible to identify numerous fragments of paleosol material within the intermediate layer (2Bt-horizon) accountto identify numerous fragments of paleosol material within the intermediate layer (2Bt-horizon) accounting for large proportions of the total clay content of this horizon. While the formation of the upper layer, ing for large proportions of the total clay content of this horizon. While the formation of the upper layer, parts of the intermediate layer were reworked and incorporated into the newly formed slope deposit. As a parts of the intermediate layer were reworked and incorporated into the newly formed slope deposit. As a result, the lower part of the upper and the whole intermediate layer contained large amounts of clay before result, the lower part of the upper and the whole intermediate layer contained large amounts of clay before the onset of Holocene pedogenesis. Recent lessivation, evidenced by undisturbed clay illuviations, affected the onset of Holocene pedogenesis. Recent lessivation, evidenced by undisturbed clay illuviations, affected the profi le. Consequently this soil formation masks prior differences in clay content due to included paleosol the profi le. Consequently this soil formation masks prior differences in clay content due to included paleosol material. Soil formation is dominated by the paleosol remnants and therefore elucidates the impact of late material. Soil formation is dominated by the paleosol remnants and therefore elucidates the impact of late glacial conditions on Holocene soils. glacial conditions on Holocene soils. Besides, a Luvisol was identifi ed which was not formed in periglacial slope deposits but in Holocene colBesides, a Luvisol was identifi ed which was not formed in periglacial slope deposits but in Holocene colluvium. In this case paleosol remnants were totally absent. Hence, a precise reconstruction of Luvisol-genesis luvium. In this case paleosol remnants were totally absent. Hence, a precise reconstruction of Luvisol-genesis is enormously improved by micromorphological analyses. is enormously improved by micromorphological analyses.

Sensitivity of frost weathering and aeolian deposition during genesis of Late Quaternary periglacial slope covers on calcareous rocks of a Muschelkalk landscape, eastern Thuringian Basin, Germany

Pleistocene, periglacial loose rock covers on calcareous rocks of Mesozoic Muschelkalk contain sediments, which are derived from loess deposition, frost weathering as well as limestone dissolution processes. Distinct sediments form periglacial slope deposits (PSD) with a layered vertical structure, consisting of Basal Layers (BL), Intermediate Layers (IL) and Upper Layer (UL). The Basal Layer has in part a notably more complex structure than on siliceous or quartz bedrock. The lithological and petrological properties of calcareous rock types are reflected by remarkably different structure, thickness and clast properties of frost shattered debris within the investigated Muschelkalk landscape as well as in chemical weathering rates within the debris. Furthermore, we could detect a high variability in the thickness and distribution of aeolian matter, too. We assume that the deposition of loess sediments might be sensitive to both properties and patterns of debris cover and to the amount of pre-existing “Braunlehm” that resulted from limestone dissolution processes. Soil moisture conditions and vegetation cover might have been as crucial factors for loess distribution as luff-/lee-effects of the regional wind system or karst surface morphology. Considering the ecological consequences implied by the structure and heterogeneity of periglacial loose rock cover, limestone landscapes in general seem to be vulnerable to degradation processes. Particularly sites of shallow sediment depth or rich in rock debris might be rapidly degraded by soil erosion, have low protection potential against groundwater pollution and might have a high sensitivity towards climatic impacts like water shortage and drought stress.

Environmental changes in Northern Iceland since the Younger Dryas inferred from periglacial slope deposits

The slopes in Northern Iceland show the widespread occurrence of solifluction features, indicative of an active periglacial environment due to annual mean temperatures around 3°C at sea level and seasonal soil frost. In order to reconstruct periods with active and inactive solifluction in the past we excavated 18 solifluction lobes for analysing the sediment sequences. Dating of the sediments was realised mainly by tephrochronology and 14C. The oldest solifluction layer could be dated to the Younger Dryas (YD), just after the deglaciation of Northern Iceland. The early to mid Holocene up to the deposition of Hekla 3 Tephra (~3 ka BP) is characterized by the accumulation of loess and tephra layers, which show no signs of secondary remobilisation or erosion, indicating stable slopes during the mid-Holocene climatic optimum (MCO). After the deposition of Hekla 3 Tephra and especially during the ‘Little Ice Age’ (LIA), solifluction reappeared in the profiles as a probable consequence of Neoglacial cooling. The results fit well with other proxies from Iceland (glacier variations, pollen), from North Atlantic marine cores and from Greenland ice records.

ＯＳＬ年代およびＡＭＳ｀１４´Ｃ年代に基づく北海道北部における化石周氷河現象の形成年代の推定

In northern Hokkaido, only a few absolute ages have been obtained from periglacial phenomena, which characterize the landscape of the area. The present lack of age constraints has prevented studies on precise geomorphic development and terrestrial palaeoenvironmental reconstruction in this area during the last glacial period. The aim of this study is to apply optically stimulated luminescence (OSL) dating and AMS14C dating methods to establish the chronology of fossil frost cracks, periglacial slope deposits, and involutions from a region in northern Hokkaido including Rishiri Island. The samples for OSL dating were taken from five localities. To compare OSL and AMS14C aging, a loess sample for OSL dating and a charcoal sample for AMS14C were collected at Loc. 3 from the same homogeneous silt layer. Besides, at Loc. 4, an OSL and a charcoal sample were collected from a channel deposit. These charcoal samples were subjected to AMS14C dating as independent age controls. OSL ages and calibrated 14C ages from the charcoal were in close agreement in each locality. These results suggest that OSL ages of loess and channel deposit in this study are reliable. From Horonobe (Loc. 1) in the southern Soya hills and from Rishiri Island (Loc. 2), two OSL ages from periglacial slope deposits indicate 21 and 22 ka. Their OSL ages, showing involution from east of Wakkanai (Loc. 3), suggest that the sand was deposited between 54 and 42 ka and that the involution was formed afterwards before 13 ka. At Loc. 4, the fossil frost crack southeast of Cape Soya was formed between 120 and 13 ka, and at Loc. 5, the fossil frost crack was formed between 24 and 15 ka. These results indicate that many periglacial phenomena were possibly formed at about 20 ka in northern Hokkaido.

Applicability of ground‐penetrating radar as a tool for nondestructive soil‐depth mapping on Pleistocene periglacial slope deposits

AbstractSoil depth plays a decisive role in determining soil properties in mountainous regions for ecological site assessment. To evaluate the use of ground‐penetrating radar (GPR) for fast and high‐resolution mapping within mountainous regions, we examined the possibilities and limitations of GPR to determine soil depth over bedrock and to delineate individual substrate layers formed during the Pleistocene in a periglacial environment (Pleistocene periglacial slope deposits, PPSD). Selected catenae in representative subregions of the study area (Dill catchment, SE Rhenish Massif, Germany) have been successfully mapped using GPR. A practicable method was developed using a 400 MHz antenna to reach a mean penetration depth of 1.5 m and to map different substrates and layers of PPSD based on calibrations of the GPR at soil pits along 12 catenae. Colluvium, the three types of PPSD layers, as well as the in situ bedrock could be distinguished in most sections of the GPR surveys. Characteristic GPR facies caused by intrinsic material properties of the different substrates, such as stone content and soil moisture content, could be distinguished in different geomorphologic and lithological settings. A layer‐based velocity distribution was determined for characteristic substrate layers at soil pits enabling us to considerably enhance the accuracy of soil‐depth prediction. Compared to traditionally surveyed soil profiles, our results demonstrate an accuracy of layer thickness surveying within a standard deviation of approx. 0.1 m. It is demonstrated that the combination of GPR with conventional soil‐pit mapping is an efficient and valid method to produce high‐resolution data of substrate distribution.

Characterisation and prediction of thickness and material properties of periglacial cover beds, Tharandter Wald, Germany

Soils of Central European subdued mountain ranges are structured by various layers of relic periglacial slope deposits (Pleistocene cover beds). These have great impact on subsurface substrate properties. Therefore, gaining extensive spatial information on material composition and thickness of slope deposits is essential. Here we present a GIS-supported approach to predict layer properties which goes beyond existing, deterministic procedures. In a section of the Tharandter Wald, Saxony, Germany, we deduced subsurface structures from soil pits and auger cores. Substrates were analysed to clarify stratigraphical setting and relation to parent rock types. We assume cryoturbation, solifluction, slope wash and aeolian sediment admixture to be important processes of periglacial cover bed formation. These processes are mainly controlled by geological and geomorphological factors. Combining assumptions and field data, we determine properties of periglacial cover beds. Based on relief parameters, an integrated data set is generated, which provides information for a geostatistical interpolation of measured layer thicknesses. The composition of solifluidally dislocated substrate is approximated by a modified flow model. Modelling returned thicknesses of loess-bearing layers, i.e. upper layer and intermediate layer. Prediction of the upper layer involved an inverse distance weighted approach and yielded an inaccuracy of < 10 cm for 75% of the validation data (< 15 cm for 90%, i.e. RMSE of 10 cm and standard deviation of 10 cm). The lower unit (intermediate layer) was approximated using topographic parameters, which returned an inaccuracy of < 5 cm for 75% of the validation data (< 6 cm for 90%, i.e. RMSE of 8 cm, standard deviation of 8 cm). Due to data limitations, thicknesses of underlying, loess-free slope deposits (basal layers) were not calculated. The modified flow model is able to predict the distribution of rock types dislocated from their original outcrops very accurately, except for basalt clasts, which were transported farther than predicted.

Doline Fills - Case Study of the Faverghera Plateau (Venetian Pre-Alps, Italy)

The sedimentary fills of two dolines in the Faverghera plateau in the Venetian Pre-Alps, south of Belluno, have been investigated. This small plateau is a sub-horizontal surface about 0.5 km2 wide, located on the northeastern slope of Mt. Faverghera (1640 m a.s.l.) hosting nearly 40 karst dolines partially filled by periglacial slope deposits. Topographic survey, electric resistivity tomography (ERT), soil and pollen analyses have been carried on. The structure of the dolines and the characters of the filling deposits indicate that the evolution of these forms has been controlled by the alternation of different climatic and environmental conditions during the Pleistocene. The results indicate that the dolines are “filters” for the sediments, more than good traps, archiving only some of the climatic and environmental changes.