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In situ 14C in quartz provides a recently developed tool to date exposure of bedrock surfaces up to ~25 000 years. From outcrops located in east-central Sweden, we test the accuracy of in situ 14C dating against (i) a relative sea level (RSL) curve constructed from radiocarbon dating of organic material in isolation basins, and (ii) the timing of local deglaciation constructed from a clay varve chronology complemented with radiocarbon dating. Five samples of granitoid bedrock were taken along an elevation transect extending southwestwards from the Baltic Sea coast near Forsmark. Because these samples derive from bedrock outcrops positioned below the highest postglacial shoreline, they target the timing of progressive landscape emergence above sea level. In contrast, in situ 14C concentrations in an additional five samples taken from granitoid outcrops above the highest postglacial shoreline, located 100 km west of Forsmark, should reflect local deglaciation ages. The ten in situ 14C measurements provide robust age constraints that, within uncertainties, compare favorably with the RSL curve and with the local deglaciation chronology. These data demonstrate the utility of in situ 14C to accurately date ice sheet deglaciation, and durations of postglacial exposure, in regions where cosmogenic 10Be and 26Al routinely return complex exposure results. [ABSTRACT FROM AUTHOR]

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 ~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 ~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 bedrock stress calculations with ~50,000 fractures from 18 cores reaching depths of 600 m at Forsmark, Sweden. We find that the present‐day stress field influences the opening of fractures to depths of 500 m, contributing to the formation of the critical zone and the preparation of rock for weathering hundreds of meters beneath the surface, much deeper than previously thought. Key Points: We calculate three‐dimensional present‐day subsurface stress fields in a low‐relief landscape at Forsmark, SwedenPresent‐day stress fields correlate strongly with the fraction of observed open fractures in cores down to ~500 m depthSubsurface bedrock stress influenced by surface conditions and pore pressure contributes to the formation of the deep critical zone [ABSTRACT FROM AUTHOR]

In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultant boulder spreads are covers of large, angular boulders, many with glacial transport distances of 1–100 m. Boulder spreads occur alongside partly disintegrated roches moutonnées and associated fracture caves, and are associated with disrupted 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. Hence glacial ripping is a highly effective process of glacial erosion. [ABSTRACT FROM AUTHOR]

Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque-and-valley moraines, valley-side moraines, complex moraines and cross-valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice-sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice-sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation. [ABSTRACT FROM AUTHOR]