Search

OCTOPUS v.2 is an Open Geospatial Consortium (OGC) compliant web-enabled database that allows users to visualise, query, and download cosmogenic radionuclide, luminescence, and radiocarbon ages and denudation rates associated with erosional landscapes, Quaternary depositional landforms, and archaeological records, along with ancillary geospatial (vector and raster) data layers. The database follows the FAIR (Findability, Accessibility, Interoperability, and Reuse) data principles and is based on open-source software deployed on the Google Cloud Platform. Data stored in the database can be accessed via a custom-built web interface and via desktop geographic information system (GIS) applications that support OGC data access protocols. OCTOPUS v.2 hosts five major data collections. CRN Denudation and ExpAge consist of published cosmogenic 10Be and 26Al measurements in modern fluvial sediment and glacial samples respectively. Both collections have a global extent; however, in addition to geospatial vector layers, CRN Denudation also incorporates raster layers, including a digital elevation model, gradient raster, flow direction and flow accumulation rasters, atmospheric pressure raster, and CRN production scaling and topographic shielding factor rasters. SahulSed consists of published optically stimulated luminescence (OSL) and thermoluminescence (TL) ages for fluvial, aeolian, and lacustrine sedimentary records across the Australian mainland and Tasmania. SahulArch consists of published OSL, TL, and radiocarbon ages for archaeological records, and FosSahul consists of published late-Quaternary records of direct and indirect non-human vertebrate (mega)fauna fossil ages that have been systematically quality rated. Supporting data are comprehensive and include bibliographic, contextual, and sample-preparation- and measurement-related information. In the case of cosmogenic radionuclide data, OCTOPUS also includes all necessary information and input files for the recalculat

Fracturing of bedrock promotes water-rock interactions and influences the formation of the life-sustaining layer of soil at Earth's surface. Models predict that present-day stress fields should influence bedrock fracture openness, but testing this prediction has proven difficult because comprehensive fracture data sets are rarely available. We model the three-dimensional present-day stress field beneath the deglaciated, low-relief landscape of Forsmark, Sweden. We account for ambient regional stresses, pore pressure, topography, sediment weight, and seawater loading. We then compare the modeled stresses to a data set of similar to 50,000 fractures reaching depths of 600 m at Forsmark. We show that modeled failure proxies correlate strongly with the fraction of observed open fractures to depths of similar to 500 m. This result implies that the present-day regional stress field, affected by surface conditions and pore pressure, influences fracture openness in bedrock hundreds of meters beneath the surface, thereby preparing the rock for further weathering. Plain Language Summary The "critical zone"-the life-sustaining part of the Earth that extends from the top of the tree canopy to the bottom of permeable bedrock-is essential for ecosystems and agriculture. The opening of bedrock fractures and onset of water-rock interaction are crucial to the formation of the critical zone. Within the bedrock, the intensities of horizontal regional forces and vertical gravitational forces typically increase with depth. These force intensities, or stresses, are modified by surface effects associated with topography, the weight of overlying seawater and sediment, and by groundwater pressure. However, the influence of these surface effects on fractures has been difficult to observe because comprehensive fracture data sets are rare. In this study, we examine whether, and to what depths, bedrock may fracture under the influence of stress associated with surficial conditions. We compare b, QC 20210120

In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultantboulder spreadsare covers of large, angular boulders, many with glacial transport distances of 1-100 m. Boulder spreads occur alongside partly disintegrated roches moutonnees and associated fracture caves, and are associated withdisrupted bedrock, which shows extensive fracture dilation in the near surface. These features are distributed in ice-flow parallel belts up to 10 km wide and extend over distances of >500 km. Our hypothesis is that the assemblage results from (1) hydraulic jacking and bedrock disruption, (2) subglacial ripping and (3) displacement, transport and final deposition of boulders. Soft sediment fills indicate jacking and dilation of pre-existing bedrock fractures by groundwater overpressure below the ice sheet. Overpressure reduces frictional resistance along fractures. Where ice traction overcomes this resistance, the rock mass strength is exceeded, resulting in disintegration of rock surfaces and ripping apart into separate blocks. Further movement and deposition create boulder spreads and moraines. Short boulder transport distances and high angularity indicate that glacial ripping operated late in the last deglaciation. The depths of rock mobilized in boulder spreads are estimated as 1-4 m. This compares with 0.6-1.6 m depths of erosion during the last glaciation derived from cosmogenic nuclide inventories of samples from bedrock surfaces without evidence of disruption. Glacially disrupted and ripped bedrock is also made ready for removal by future ice sheets. Henceglacial rippingis a highly effective process of glacial erosion.

Quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas. Combining in situ Be-10 and Al-26 analysis of bedrock, boulder, and river sand samples, geomorphological mapping, and field investigations, we examine glacial erosion patterns of former ice caps in the Shaluli Shan of the southeastern Tibetan Plateau. The general landform pattern shows a zonal pattern of landscape modification produced by ice caps of up to 4000 km(2) during pre-LGM (Last Glacial Maximum) glaciations, while the dating results and landforms on the plateau surface imply that the LGM ice cap further modified the scoured terrain into different zones. Modeled glacial erosion depth of 0-0.38 m per 100 ka bedrock sample located close to the western margin of the LGM ice cap, indicates limited erosion prior to LGM and Late Glacial moraine deposition. A strong erosion zone exists proximal to the LGM ice cap marginal zone, indicated by modeled glacial erosion depth >2.23 m per 100 ka from bedrock samples. Modeled glacial erosion depths of 0-1.77 m per 100 ka from samples collected along the edge of a central upland, confirm the presence of a zone of intermediate erosion in-between the central upland and the strong erosion zone. Significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate restricted glacial erosion during the last glaciation. Our study, for the first time, shows clear evidence for preservation of glacial landforms formed during previous glaciations under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the Haizishan ice cap during the LGM.

The following report constitutes a final report of a comprehensive study on denudation and glacial erosion conducted at Forsmark and in the surrounding Uppland province, Sweden, between 2015 and 2019. The aim was to quantify the amount of past denudation at the Forsmark site and the broader Uppland region, with special focus on glacial erosion, by employing a range of methodologies. The methods included geomorphological mapping and analysis of the bedrock surface and Quaternary deposits, cosmogenic exposure dating, bedrock fracture mapping, and shallow bedrock stress modelling. The results were also used together with results from a long-term climate modelling study to quantify the potential amount of glacial erosion at Forsmark over the coming one million years. The study was initiated by Jens-Ove Näslund (SKB) and it was jointly designed by Jens-Ove Näslund, Adrian Hall (Stockholm University), Karin Ebert (Södertörn University), Bradley Goodfellow (Stockholm University, SGU), Clas Hättestrand (Stockholm University), Jakob Heyman (University of Gothenburg) and Arjen Stroeven (Stockholm University). Adrian Hall coordinated the scientific work within the study, and also conducted the studies on long-term burial and erosion history (Chapter 2) and glacial erosion (Chapter 4). Karin Ebert developed the digital elevation models of the unconformity and derived the glacial erosion estimates derived from summit erosion surfaces. Bradley Goodfellow contributed across the project and conducted the study of topographic stress perturbation, with mathematical modelling by Seulgi Moon (University of California, Los Angeles) (Chapter 3). Clas Hättestrand developed geomorphological maps of the unconformity and of glacial bedforms. Maarten Krabbendam (British Geological Survey) contributed to Chapter 2 on the longterm burial and erosion history and to Chapter 4 on glacial erosion and mapped landforms associated with glacial ripping in Uppland. Sample site selection and cosmogenic n

The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bolling-Allerod warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bolling-Allerod and Younger Dryas.

The Eurasian ice sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea-level lowering. Whilst recent terrestrial and marine empirical insights have improved understanding of the chronology, pattern and rates of retreat of this vast ice sheet, a concerted attempt to model the deglaciation of the EISC honouring these new constraints is conspicuously lacking. Here, we apply a first-order, thermo-mechanical ice sheet model, validated against a diverse suite of empirical data, to investigate the retreat of the EISC after 23 ka BP, directly extending the work of Patton et al. (2016) who modelled the build-up to its maximum extent. Retreat of the ice sheet complex was highly asynchronous, reflecting contrasting regional sensitivities to climate forcing, oceanic influence, and internal dynamics. Most rapid retreat was experienced across the Barents Sea sector after 17.8 ka BP when this marine-based ice sheet disintegrated at a rate of similar to 670 gigatonnes per year (Gt a(-1)) through enhanced calving and interior dynamic thinning, driven by oceanic/atmospheric warming and exacerbated by eustatic sea-level rise. From 14.9 to 12.9 ka BP the EISC lost on average 750 Gt a(-1), peaking at rates >3000 Gt a(-1), roughly equally partitioned between surface melt and dynamic losses, and potentially contributing up to 2.5 m to global sea-level rise during Meltwater Pulse 1A. Independent glacio-isostatic modelling constrained by an extensive inventory of relative sea-level change corroborates our ice sheet loading history of the Barents Sea sector. Subglacial conditions were predominately temperate during deglaciation, with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network. Moreover, the maximum EISC and its isostatic footprint had a profound impact on the proglacial hydrological network, forming the Fleuve Manche mega-catchment which h

In this article, we present a map of the glacial geomorphology of the Altai andWestern Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 mresolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region., Central Asia Paleoglaciology Project (CAPP)

Cosmogenic exposure dating of glacial boulders is commonly used to estimate the timing of past glaciations because the method enables direct dating of the duration a boulder has been exposed to cosmic rays. For successful dating, the boulders must have been fully shielded from cosmic rays prior to deposition and continuously exposed to cosmic rays ever since. A common assumption is that boulder height (the distance between the top of the boulder and the surrounding surface) is important, and that tall boulders are more likely to have been continuously exposed to cosmic rays than short boulders and therefore yield more accurate exposure ages. Here we test this assumption 'based on exposure age clustering for groups of glacial boulders (and single cobbles) Be-10 exposure ages that have recorded boulder heights (3741 boulders; 579 boulder groups with >= 3 boulders). Of the full set of boulder groups with >= 3 boulders, 21% fulfill a reduced chi square criterion (chi(2)(R) < 2) for well-clustered exposure ages. For boulder groups containing only tall boulders, the fraction of well-clustered exposure age groups is consistently larger. Moreover, this fraction of well-clustered exposure age groups increases with the minimum boulder height in each group. This result confirms the common assumption that tall boulders are generally better targets for cosmogenic exposure dating compared to short boulders. Whereas the tall boulder groups have a significantly larger fraction of well-clustered exposure age groups, there is nonetheless a dominant fraction (>50%) of the boulder groups with scattered exposure ages, highlighting the problem with prior and incomplete exposure for cosmogenic dating of glacial boulders.

We present a glacial geomorphological map at a scale of 1: 200,000 of the Maidika region in the southeastern part of the central Tibetan Plateau covering 13,600 km(2). Based on the 90 m resolution SRTM elevation model, the 30 m resolution ASTER GDEM elevation model, and the Landsat ETM+ satellite imagery of 30/15 m resolution, we have mapped glacial valleys, marginal moraines, glacial lineations, and hummocky terrain. Glacial landforms occur frequently and indicate extensive past glaciation with alpine style valley glaciers as well as more extensive ice fields. Of particular interest is the presence of glacial lineation swarms, which is unusual for the Tibetan Plateau glacial landform record. Based on the distribution of glacial landforms, we present a generalized maximum glacial extent reconstruction covering 6045 km(2) or 44% of the map.

An important constraint on the reliability of cosmogenic nuclide exposure dating is the rigorous determination of production rates. We present a new dataset for Be-10 production rate calibration from Mount Billingen, southern Sweden, the site of the final drainage of the Baltic Ice Lake, an event dated to 11,620 +/- 100 cal yr BP. Five samples of flood-scoured bedrock surfaces (58.5 degrees N, 13.7 degrees E, 105-120 m a.s.I.) unambiguously connected to the drainage event yield a reference Be-10 production rate of 4.19 +/- 0.20 atoms g(-1) yr(-1) for the CRONUS-Earth online calculator Lm scaling and 4.02 +/- 0.18 atoms g(-1) yr(-1) for the nuclide specific LSDn scaling. We also recalibrate the reference Be-10 production rates for four sites in Norway and combine three of these with the Billingen results to derive a tightly clustered Scandinavian reference Be-10 production rate of 4.13 +/- 0.11 atoms g(-1) yr(-1) for the CRONUS Lm scaling and 3.95 +/- 0.10 atoms g(-1) yr(-1) for the LSDn scaling scheme.