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Collection of conference abstracts presented at the vDEUQUA2021 (2021-09-30 to 2021-09-01), the virtual meeting of the German Quaternary Association (DEUQUA).

Geoscientific concepts and hypotheses are usually formulated based on empirical data from the field or the laboratory (induction). After translation into models they can be applied to case study scenarios (deduction). However, the other way around – expressing hypotheses explicitly by models and test these by empiric data – is a rarely touched trail. There are several models tailored to investigate the boundary conditions and processes that generate, mobilise, route and eventually deposit sediment in a landscape. Thereby, the last part, sediment deposition, is usually omitted. Essentially, there is no model that explicitly focuses on mapping out the characteristics of sedimentary deposits – the material that is used by many disciplines to reconstruct landscape evolution. The R package sandbox is a model framework that allows creating and analysing virtual sediment sections for exploratory, explanatory, forecasting and inverse research questions. sandbox is a probabilistic and rule-based model framework for a wide range of possible applications. It has been advanced and linked to another model to allow the full work flow of modelling luminescence measurements. This contribution introduces news about recent developments and shows a set of applications.

Polygon tundra with tundra-steppe vegetation cover and growing syngenetic ice-wedge nets evolved during stadial and interstadial periods of the late Quaternary in non-glaciated Beringia. The depositional relict of such environments is called Ice Complex (IC; ледовый комплекс [ledovyi kompleks] in Russian) permafrost. The IC archives preserve information of past periglacial and climate landscape conditions of mid- and late Pleistocene Beringian environments. In certain locations of the East Siberian Arctic, IC remnants of different age and extent are known. While using IC deposits as archives of palaeo-landscape and palaeo-environmental dynamics, summer and winter conditions over large time-scales are detectable. Commonly applied summer proxy include palaeontological proxy such as pollen, plant macrofossils, insect fossils and, most prominent, mammal fossils of the Mammoth fauna, while geochemical and stable isotope properties of ground ice allow for insights into freezing and winter conditions. IC chronologies are challenging because the deposition and post-sedimentary preservation of ice-rich permafrost are triggered by palaeo-relief settings and related processes as well as by the intensity of thermokarst. This complicates geochronological interpretations, as representatives of consecutive late Quaternary periods may be found at laterally different positions and altitudes in coastal and riverine exposures. Shifts between permafrost aggradation and degradation over time frequently cause gaps in sequences. Furthermore, numerical dating of IC mainly includes different approaches such as radiocarbon (14C) dating of organic material, infrared and optically-stimulated luminescence (IRSL, OSL) dating on feldspar and quartz grains, radioisotope disequilibria of thorium-230 to uranium-234 (230Th/U) dating of peat, and chlorine-36 to chloride ratios (36Cl/Cl) of ground ice. The application of various geochronologic methods to cover the age intervals of certain IC deposits implies that different permafrost components (organic, mineralic, ice) as well as different geochemical and physical properties have to be employed. At the southern coast of Bol'shoy Lyakhovsky Island at least four distinct IC strata were previously described and dated, which cover among the longest time interval of late Quaternary terrestrial permafrost deposition in East Siberia; starting about 200 kyr ago. With this contribution we seek to present and discuss our current understanding of IC chronologies preserved on the New Siberian Archipelago including MIS2 Yedoma (Sartan) IC, MIS3 Yedoma (Molotkov) IC, MIS5 Buchchagy IC, and MIS7a Yukagir IC. Geocryological and palaeo-environmental proxy data highlight past periglacial landscape and deposition processes to deduce past climate conditions and Beringian palaeo-ecological settings and dynamics.

Perennially-frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine, deep marine, and glacier records because of the long-term and good preservation of fossil records under stable permafrost conditions. A permafrost tunnel in the Vault Creek Valley (Chatanika River Valley, near Fairbanks) exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late Quaternary environmental history of Interior Alaska. The multi-proxy approach includes different dating techniques (radiocarbon-accelerator mass spectrometry [AMS 14C], optically stimulated luminescence [OSL], thorium/uranium radioisotope disequilibria [230Th/U]), as well as methods of sedimentology, paleoecology, hydrochemistry, and stable isotope geochemistry of ground ice. The studied sequence consists of 36-m-thick late Quaternary deposits above schistose bedrock. Main portions of the sequence accumulated during the early and middle Wisconsin periods. The lowermost unit A consists of about 9-m-thick ice-bonded fluvial gravels with sand and peat lenses. A late Sangamon (MIS 5a) age of unit A is assumed. Spruce forest with birch, larch, and some shrubby alder dominated the vegetation. High presence of Sphagnum spores and Cyperaceae pollen points to mires in the Vault Creek Valley. The overlying unit B consists of 10-m-thick alternating fluvial gravels, loess-like silt, and sand layers, penetrated by small ice wedges. OSL dates support a stadial early Wisconsin (MIS 4) age of unit B. Pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site. The following unit C is composed of 15-m-thick ice-rich loess-like and organic-rich silt with fossil bones and large ice wedges. Unit C formed during the interstadial mid-Wisconsin (MIS 3) and stadial late Wisconsin (MIS 2) as indicated by radiocarbon ages. Post-depositional slope processes significantly deformed both, ground ice and sediments of unit C. Pollen data show that spruce forests and wetlands dominated the area. The macrofossil remains of Picea, Larix, and Alnus incana ssp. tenuifolia also prove the existence of boreal coniferous forests during the mid-Wisconsin interstadial, which were replaced by treeless tundra-steppe vegetation during the late Wisconsin stadial. Unit C is discordantly overlain by the 2-m-thick late Holocene deposits of unit D. The pollen record of unit D indicates boreal forest vegetation similar to the modern one. The permafrost record from the Vault Creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation, and formation of ice-wedge polygons and post-depositional deformation by slope processes. The record represents a typical Wisconsin valley-bottom facies in Central Alaska.

The region of perennially frozen ground constitutes one quarter of the northern hemisphere landmass. Negative annual mean air temperatures and ground freezing periods exceeding ground thaw periods are the prerequisites for downward freezing of loose deposits and bedrock in non-glaciated regions. Hence, permafrost distribution and thickness on Earth are closely related to late Quaternary climate variations and ecosystem modifications. Generally, glacial stages are expected to promote permafrost accretion and ground ice formation in accumulating sediments,whereas interglacial stages lead to intense permafrost thaw and ground-ice melt. Deep freezing synchronous with ongoing sedimentation is termed as syngenetic while epigenetic freezing occurs in pre-existing deposits. Typical landforms of syngenetic permafrost are ice-wedge polygons of past tundra environments. Ice-rich silty and/or peaty deposits intersected by large ice wedges (up to several decameters in height and meters in with) build-up unique Ice Complex (IC) strata, which are aligned to mid- and late Pleistocene stadial and interstadial stages. The most prominent example for such formations is the Yedoma IC of MIS 3 interstadial age. Increasing air and ground temperatures during warm stages disturbed the thermal equilibrium at the upper permafrost boundary and subsequently led to permafrost thaw, ground-ice melt and surface subsidence. Typical permafrost degradation processes are thermokarst and thermo-erosion that result in large lake-filled basins (up to kilometers in diameter) and valley structures, respectively. The modern periglacial surface in Alaskan and East Siberian lowlands preserves Yedoma IC remnants in uplands and hills next to widely-distributed thermokarst basins since lateglacial and Holocene warming affected up to 70% of the original IC distribution on an area of more than 1,000,000 km2. The overarching climate-driven pattern of cold-stage IC permafrost accretion and warm-stage IC permafrost degradation provides, however, only a first-order approximation in understanding past permafrost dynamics. Beside long-term freezing conditions also thin snow cover and winter precipitation were required to create ice-rich permafrost such as Yedoma IC. Its dynamics are furthermore altered by on-site conditions in water supply, relief and vegetation, which promote either aggradation or degradation processes. For example, current climate warming certainly enables large-scale permafrost thaw and widespread thermokarst. But, ice-wedge growth and permafrost accretion occurs in places after local disturbance such as thermokarst lake drainage causing a change from lacustrine to palustrine environments. Repeated occupation of thermokarst basins by lakes is commonly described as thaw-lake cycle although hereditary structures, i.e. pre-existing basins promote the lacustrine refill and highlight the path-dependence of thermokarst processes and the importance of the paleo-relief. Traces of periglacial landforms preserved in permafrost deposits are indicative of the interplay between past climate and landscape settings. Besides climate control on-site periglacial morphology, hydrology and vegetation alter permafrost regimes, and are to be taken into account when interpreting late Quaternary permafrost chronologies. In summary, the completeness of certain vertical permafrost sequences depends (1) on paleo-relief that defined past accumulation and (thermo-)erosion areas, and (2) on overprints of degradation periods that erased older formations.

International audience; _____________________________________________________________________________________________ Abstract For routine luminescence dating applications the commonly used Risø readers are bundled with analysis software, such as Viewer or Analyst. These software solutions are appropriate for most of the regular dating and publication jobs, and enable assessment of luminescence characteristics and provide basic statistical data treatment. However, for further statistical analysis and data treatments, this software may reach its limits. In such cases, open programming languages are a more appropriate approach. Here, we present the R package 'Luminescence' for a more flexible handling of luminescence data and related plotting purposes, using the statistical programming language R. The R language as well as the package and the source code are provided under the General Public License (GPL) conditions and are available for free. The basic functionality of the package is described along with three application examples. This package is not an alternative to the existing software (Analyst, Viewer) but may provide a collection of additional tools to analyse luminescence data and serve as a platform for further contributions.

International audience; A practical guide for the R package 'Luminescence' is provided. An introduction on data types in R is given first, followed by a guideline on how to import, analyse and visualise typical SAR-OSL measurement data. Introduction Since the R package 'Luminescence' has been introduced by Kreutzer et al. (2012) the developer team is continuously asked for advice from the luminescence dating community. Such requests considerably help us to further improve the package and make the tools more efficient and user friendly. However, most of these queries are not directed to specific problems of the provided functions but rather on the usage of R and the package in general. Motivated by an e-mail conversation with Geoff Duller this contribution aims to provide an example-based, short practical guide to R and the package 'Luminescence'. First, we focus on properties and ways to index different sorts of data structures, which are essential for an efficient use of the R package 'Luminescence'. A second section describes processing steps for luminescence data, from importing a BIN-file to plotting a D e distribution. A third section comprises the examples in a comprehensive code section. Throughout the manuscript R calls or R related code snippets are typed in monospaced letters. In some cases, numerical and graphical output was truncated for illustrative reasons.

Rock glaciers contain valuable information about the spatial and temporal distribution of permafrost. The wide distribution of these landforms in high mountains promotes them as useful archives for the deciphering of the environmental conditions during their formation and evolution. However, age constraints are needed to unravel the palaeoclimatic context of rock glaciers, but numerical dating is difficult. Here, we present a case study assessing the potential of luminescence techniques (OSL, IRSL) to date the inner sand-rich layer of active rock glaciers. We focus on the signal properties and the resetting of the signal prior to deposition by investigating single grains. While most quartz shows low signal intensities and problematic luminescence characteristics, K-feldspar exhibits much brighter and well-performing signals. Most signals from plagioclases do not show suitable properties. Luminescence signals far below saturation indicate distinct but differential bleaching. The finite mixture model was used to determine the prominent populations in the equivalent dose distributions. The luminescence ages represent travel times of grains since incorporation into the rock glacier and hence, minimum ages of rock glacier formation. Luminescence ages between 3 ka and 8 ka for three rock glaciers from the Upper Engadine and Albula region (Swiss Alps) agree well with independent age estimates from relative and semi-quantitative approaches. Therefore, luminescence seems to have the potential of revealing age constraints about processes related to the formation of rock glaciers, but further investigations are required for solving some of the problems remaining and reducing the dating uncertainties.