Eolian chronology reveals causal links between tectonics, climate, and erg generation

The onset and intensification of eolian activity mark climatic transitions that promote wide-scale aridification, recorded by the generation and preservation of massive sand deposits. Evaluating the impact and implications of such repositories on Earth systems requires knowledge about the timing of their emplacement and the mechanisms responsible for their generation, which remain highly uncertain. Here we provide time constraints for the establishment of the Kalahari Erg, which is the largest continuous body of sand on Earth. We apply cosmogenic nuclide dating of sand from the Kalahari Desert combined with numerical modeling to determine when sand was introduced into the interior of southern Africa. Through the consideration of several scenarios, we show that major events of eolian sand transport and accumulation occurred between ~2.5 and 1 Myr ago. This substantial activity, which significantly altered environmental settings, corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for hominin evolution and migration throughout the African continent during the Pleistocene.

Slope Failure in a Period of Increased Landslide Activity: Sennwald Rock Avalanche, Switzerland

The Säntis nappe is a complex fold-and-thrust structure in eastern Switzerland, consisting of numerous tectonic discontinuities and a range of hillslopes prone to landsliding and large slope failures that modify the topography irreversibly. A slope failure, namely the Sennwald rock avalanche, occurred in the southeast wall of this fold-and-thrust structure due to the rock failure of Lower Cretaceous Helvetic limestones along the Rhine River valley. In this research, this palaeolandslide is examined in a multidisciplinary approach for the first time with detection and mapping of avalanche deposits, dynamic run-out modelling and cosmogenic nuclide dating. During the rock failure, the avalanche deposits were transported down the hillslope in a spreading-deck fashion, roughly preserving the original stratigraphic sequence. The distribution of landslide deposits and surface exposure age of the rock failure support the hypothesis that the landslide was a single catastrophic event. The 36Cl surface exposure age of avalanche deposits indicates an age of 4.3 ± 0.5 ka. This time coincides with a notably wet climate period, noted as a conditioning factor for landslides across the Alps in the mid-Holocene. The contemporaneity of our event at its location in the Eastern Alps provide additional support for the contention of increased regional seismic activity in mid-Holocene.

The origin of elevated low-relief surfaces in the Eastern Alps from geomorphic criteria and cosmogenic nuclide dating

<p>Elevated low-relief surfaces are peculiar landforms found in many areas across the Eastern Alps, most notably on the plateaus of the Northern Calcareous Alps and the southern metamorphic ranges from Nock Mountains to Koralpe. Found in domains both glaciated and unglaciated during the Pleistocene, (peri-)glacial erosion as well as fluvial prematurity have been cited as two opposing models for their formation. In order to contribute to this debate, we present a map of the existing low-relief surfaces in the Eastern Alps, bridging both glaciated and unglaciated regions, using a combined effort of field mapping and GIS-based mapping. Hypsometric statistics and analysis of longitudinal channel profiles show clear differences between formerly glaciated, partly-glaciated and unglaciated regions and their relations to the mapped surfaces. Furthermore, the pace of late- to post-Miocene incision is quantified via cosmogenic nuclide dating (<sup>26</sup>Al, <sup>10</sup>Be, <sup>21</sup>Ne) of allogenic siliceous sediments from discrete elevations correlating with the low-relief surfaces, in particular from cave sediments in the Northern Calcareous Alps. This information can be used to demonstrate that low-relief surfaces in many unglaciated regions, but also in some glaciated regions can be interpreted in terms of pre-Pleistocene relict landscapes.</p>

Implementing the Sparrow laboratory data system in multiple subdomains of geochronology and geochemistry

<p>Data sharing between laboratories is critical for building repeatable, comparable, and robust geochronology and geochemistry workflows. Meanwhile, in the broader geosciences, there is an increasing need for standardized access to aggregated geochemical data tied to basic geological context. Such data can be used to enrich sample and geochemical data repositories (e.g., EarthChem, Geochron.org, publisher archives), align geochemical context with other datasets that capture global change (e.g., Neotoma, the Paleobiology Database), and calibrate digital Earth models (e.g., Macrostrat) against geochronology-driven assessments of geologic time.</p><p>A typical geochemical lab manages a large archive of interpreted data; standardizing and contributing data products to community-level archives entails significant manual work that is not usually undertaken. Furthermore, without widely accepted  interchange formats, this effort must be repeated for each intended destination.</p><p>Sparrow (https://sparrow-data.org), in development by a consortium of geochronology labs, is a standardized system designed to support labs’ efforts to manage, contextualize, and share their geochemical data. The system augments existing analytical workflows with tools to manage metadata (e.g., projects, sample context, embargo status) and software interfaces for automated data exchange with community facilities. It is extensible for a wide variety of geochemical methods and analytical processes.</p><p>In this update, we will report on the implementation of Sparrow in the Arizona Laserchron Center detrital zircon facility, and how that lab is using the system to capture geological context across its data archive. We will review similar integrations underway with U-Pb, <sup>40</sup>Ar/<sup>39</sup>Ar, SIMS, optically stimulated luminescence, thermochronology, and cosmogenic nuclide dating. We will also discuss preliminary efforts to aggregate the output of multiple chronometers to refine age calibrations for the Macrostrat stratigraphic model.</p>

Reconstructing the Holocene glacial history of northern Norway

<p>Detailed investigations into Holocene glacier fluctuations are a fundamental tool in developing reliable reconstructions of past climate variability and the detection of global climate change. There are, however, many mountain areas that have escaped detailed scrutiny. Here we present a large-scale glacial geomorphological and geochronological study of the central Troms and Finnmark county region in Arctic Norway (covering an area of 6,810 km<sup>2</sup>) in order to reconstruct glacier change from the early Holocene to present. We undertake the first glacial chronological study in the Rotsund Valley, central Troms and Finnmark county, based on moraine dating using a combination of absolute, calibrated, and relative age dating techniques (terrestrial cosmogenic nuclide dating (TCND), Schmidt hammer dating, and soil chronosequencing). Together with our chronological data, our detailed mapping from a much wider area reveals a complex picture of early-Holocene deglaciation and late-Holocene glacier re-advance and we postulate that specific moraine formations are linked to key climatic events including: the Erdalen Event (between 10,100 and 9,700 cal. yrs. BP), the Finse / ‘8.2 ka' Event (between 8,500 and 8,000 cal. yrs. BP), and the Neoglacial (from ~4,500 cal. yrs. BP to the LIA maximum).</p>

Cosmogenic nuclide dating of cave sediments in the Eastern Alps and implications for erosion rates

Karstic caves are created by water eroding and corroding rocks that can be dissolved. Since both the spring areas of caves (normally at the valley bottom) as well as the recharge is controlled by superficial processes, the morphology of the cave bears strong links to these influences. Lowering of local base levels promotes the development of horizontal phreatic cave passages at progressively lower elevations, resulting in the formation of multi-level karst systems. Upon the next lowering of base level, these upper systems become fossilized, and sediment trapped within them may remain preserved for millions of years. Dating these sediments gives clues regarding the time when the passages were last active, and thus may yield age information for old valley floors. The present paper presents cosmogenic nuclide datings of twelve samples from eight caves in the central part of the Northern Calcareous Alps of Austria. Besides three samples that gave no results, most of the obtained ages are at the Mio-Pliocene boundary or within the Pliocene, as was expected before sampling. No multi-level caves could be sampled at different elevations, thus, the obtained valley deepening rates are averages between the age of sediment deposition and the present-day valley floor. However, the valley deepening rates of 0.12 to 0.21 km/Ma are in accordance to previous findings and corroborate a comparatively slow evolution of base level lowering in the Eastern Alps compared to the fast (Late Quaternary) evolution in the Central and Western Alps.

Fine laminated clastic deposits revealing the delay of the deglaciation timing in the High Tatras Mts. (Central Europe) to Early Holocene

<p>The Tatra moraine relief and cosmogenic nuclide dating show glacier stabilizationand the maximum glacier extent in two phases,at26 – 21 ka and at 18 ka followed by a gradual retreat and  a termination of the glaciation during the Bølling/Allerød warming at 14.64 –12.9 ka (Makos etal., 2014). A renewed glaciation within the Younger Dryas (12.9 – 11.5 ka) formed smaller rock glaciers. This retreat was connected with the formation of the morainic, trough and cirque lakes and the beginning of light-grey silt sedimentation dated from 10ka to 16ka cal BP on the northern slopes of the Tatra Mountains and before 10ka cal BP on its southern slopes (Klapyta et al., 2016).</p><p>A new paleolimnic research led to a discovery of a cyclic fine laminated deposit in the four Tatra Mts. lakes. The laminae of thickness from 1 to 3 mm are built of couplets of light-coloured coarse detrital and fine dark-coloured laminae. Thicker light coloured laminae occasionally show a gradation ending in dark-coloured laminae. Laminae consist occasionally of low spherical angular grains of sand and gravel fractions, rarely up to size 10 mm which deformed underlying laminae. Light-coloured laminae are predominantly composed of quartz, followed by K-feldspar, plagioclase, mica, and clay-like particles. Dark-coloured laminae consist of clay-size clastic particles. These laminae were formed in cold, oxygen-rich, ultra-oligotrophic, slightly acid conditions in which the chironomids Pseudodiamesa nivosa and Micropsectra radialis-type dominated. We interpret these lamination as varves related to annual glacial melting. Once the valleys were ice-free, varve production stopped and a short deposition period of homogenous silt was replaced by gyttja. The radiometric C<sup>14</sup> age dating shows the deglaciation in the Tatra Mts terminated at the beginning of the Early Holocene, around 10ka cal BP – 9ka cal BP.</p><p> </p><p>The research was funded by APVV-15-0292 and the project Centre of Excellence for Integrated Research of the Earth's Geosphere, ITMS 26220120064.</p><p> </p><p>Klapyta P., Zasadni J., Pociask-Karteczka J., Gajda A., Franczak P., 2016. Late Glacial and Holocene Paleoenvironmental records in the Tatra Mountains, East-Central Europe, based on lake, peat bog and colluvial sedimentary data: A summary review. Quaternary International 415: 126-144.</p><p> </p><p>Makos M., Dzierzek J., Nitychoruk J., Zreda M., 2014. Timing of glacier advances and climate in the Tatra Mountains (Western Carpathians) during the Last Glacial Maximum. Quaternary Research 82: 1-13.</p>

Antarctic Ice Cores Might Be Older Than Dirt

Using cosmogenic nuclide dating, scientists determined a 10-meter core just below the surface to be over a million years old.