Deeply rooted glaciotectonism in western Denmark: geological composition, structural characteristics and the origin of Varde hill‐island

Høyer, Anne‐Sophie; Jørgensen, Flemming; Piotrowski, Jan A.; Jakobsen, Peter Roll

doi:10.1002/jqs.2667

Cited by 21 publications

(13 citation statements)

References 44 publications

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“…We found that the RF residuals exhibit a spatial correlation explicitly in the hill island landscape in western Denmark, indicating that one or more essential covariates may be missing in the current model setup. As outlined by Høyer et al (), the geomorphological setting of the hill islands in western Denmark is very complex due to several sequences of glaciotectonic deformation and erosion. A high‐resolution groundwater model or a detailed geomorphological map may resolve some of these issues, but further investigations are needed to identify the crucial covariates needed to improve the RF in the hill island landscape.…”

Section: Discussionmentioning

confidence: 99%

Modeling Depth of the Redox Interface at High Resolution at National Scale Using Random Forest and Residual Gaussian Simulation

Koch

Stisen

Refsgaard

et al. 2019

Water Resources Research

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The management of water resources needs robust methods to efficiently reduce nitrate loads.Knowledge on where natural denitrification takes place in the subsurface is thereby essential. Nitrate is naturally reduced in anoxic environments and high-resolution information of the redox interface, that is, the depth of the uppermost reduced zone is crucial to understand the variability of the denitrification potential. In this study we explore the opportunity to use random forest (RF) regression to model redox depth across Denmark at 100-m resolution based on~13,000 boreholes as training data. We highlight the importance of expert knowledge to guide the RF model in areas where our conceptual understanding is not represented correctly in the training data set by addition of artificial observations. We apply random forest regression kriging in which sequential Gaussian simulation models the RF residuals. The RF model reaches a R 2 score of 0.48 for an independent validation test. Including sequential Gaussian simulation honors observations through local conditioning, and the spread of 800 realizations can be utilized to map uncertainty. Emphasis is put on adequate handling of nonstationarities in variance and spatial correlation of the RF residuals. The RF residuals show no spatial correlation for large parts of the modeling domain, and a local variance scaling method is applied to account for the nonstationary variance. Moreover, we present and exemplify a framework where newly acquired field data can easily be integrated into random forest regression kriging to quickly update local models.Plain Language Summary Nutrients, such as nitrogen in form of nitrate are essential for plant growth. Despite their benefits, nutrient surplus can cause adverse health and ecological effects. In fact, nitrate leaching from agricultural fields is one of the major water resources management challenges in today's agricultural landscapes. During the transport through the subsurface, nitrate can potentially be degraded in anoxic layers below the redox interface. This is referred to as denitrification and its potential varies spatially depending on the local landscape. The location of the redox interface is thus essential knowledge toward a spatially differentiated water resources management. We applied a machine learning method to model the redox depth at 100m spatial resolution across Denmark, based on redox data obtained from~13,000 boreholes and environmental variables that explain redox variability. We highlight the importance of expert knowledge in guiding the machine learning model by adding artificial observations in underrepresented landscapes. As an add-on, a geostatistical model is used to honor local data at grid scale and quantify the spatial uncertainty elsewhere. Lastly, we outline and exemplify a framework that allows an easy integration of newly acquired field data for updating local models of the depth to the redox interface.

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Section: Discussionmentioning

confidence: 99%

Modeling Depth of the Redox Interface at High Resolution at National Scale Using Random Forest and Residual Gaussian Simulation

Koch

Stisen

Refsgaard

et al. 2019

Water Resources Research

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“…Høyer et al . () have noted evidence of deep‐seated glaciotectonism in Denmark, indicative of loading by thick ice, and thus inferred that past ice margins were steep, the ice exceeding 1000 m thickness within 6 km of its margin. It is thus plausible that this region was covered on at least one occasion by thick enough ice to replicate ∼1000 m of sediment loading, thus explaining Japsen's (1998) results.…”

Section: Discussionmentioning

confidence: 99%

“…Although Denmark was only partly ice-covered during MIS 6 and MIS 2, the ice was more extensive during the Elster glaciation (MIS 12) and apparently again in MIS 8, the Treldenaes Glaciation (Houmark-Nielsen, 2011). Høyer et al (2013) have noted evidence of deepseated glaciotectonism in Denmark, indicative of loading by thick ice, and thus inferred that past ice margins were steep, the ice exceeding 1000 m thickness within 6 km of its margin. It is thus plausible that this region was covered on at least one occasion by thick enough ice to replicate $1000 m of sediment loading, thus explaining Japsen's (1998) results.…”

Section: Discussionmentioning

confidence: 99%

Isostatic compensation of Quaternary vertical crustal motions: coupling between uplift of Britain and subsidence beneath the North Sea

Westaway

2016

J Quaternary Science

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New data from offshore and onshore regions confirm the view that the Quaternary uplift of Britain and subsidence beneath the North Sea are coupled, mediated by lower‐crustal flow induced by the lateral pressure gradient caused by climate‐driven surface processes. Most measured onshore uplift rates, in both upland and lowland localities, are only applicable since the Mid‐Pleistocene Revolution; beforehand, generally lower rates prevailed. Earlier (?Oligocene–Pliocene) phases of uplift and subsidence had typically even lower rates; furthermore, the western margin of the North Sea depocentre was ∼200 km farther from the modern coastline of north‐east England. In the earliest Cenozoic, complex isostatic adjustments occurred in response to the magmatism associated with the Iceland mantle plume; the contemporaneous land surface (relative to the present‐day rock column) in northern England was typically ∼1500 m OD. However, this activity died out during the Palaeogene; the main effect of these events on the modern isostatic configuration was via the emplacement of thick mafic underplating, which now constricts the mobile lower‐crustal layer, explaining the Late Cenozoic ultra‐stability of Ireland. The evidence enables interpretations of the present‐day topography of Britain as static, caused by the Iceland mantle plume, or actively developing in response to plate motions or plate boundary forces, to be excluded.

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“…We present a field case from the area of Ølgod, Denmark, which has been the object of dense geophysical mapping with electrical, electromagnetic and seismic methods in connection with the KOMPLEKS project 2008–2012 aimed at mapping large‐scale geological structures to improve hydraulic modelling (Høyer et al ., 2011, 2013a, 2013b, 2014; He et al ., 2013). In this paper, we focus on the airborne transient electromagnetic survey carried out with the SkyTEM system in 2006 and 2009 (Sørensen and Auken, 2004; Auken et al ., 2006, 2009, 2017) and inverted with the WorkBench program (Auken et al ., 2014).…”

Section: Field Example: Using Airborne Em Data To Estimate Clay Thicknessmentioning

confidence: 99%

Using geophysical survey results in the inference of aquifer vulnerability measures

Christensen

Christiansen

2021

Near Surface Geophysics

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The physical parameter derived from the inversion of electromagnetic surveys, the distribution of subsurface conductivity, is interesting in itself only in very few instances. In most cases, the conductivity distribution will have to be interpreted in terms of the target properties of the survey, for example: a geological interpretation of lithology; a hydrogeological interpretation of hydraulic conductivity; a biohazard/geotechnical interpretation of polluted/not‐polluted ground; and/or an archaeological interpretation of manmade/natural finds. The parameters of interest in these categories are often called derived products, indicating that the parameter of interest is not the same as the parameter whose distribution is found in the inversion process of the geophysical data. The interpretation process can be done in a wide variety of ways; from a predominantly cognitive approach based on professional experience, to an application of rigorous quantitative relations found from scientific endeavours. In most practical situations, the number of locations with independently measured information on the derived product is considerably smaller than the number of geophysics locations. It is precisely this sparsity of primary information on the derived product that encourages the use of geophysical inversion results as a sort of qualified interpolator through a formulation of a correlation between a geophysical parameter and the parameter characterising the derived product. In this paper, a general, quantitative approach to deriving the parameter of interest is presented using statistical analytic measures and an advanced use of an interpolation method that takes uncertainties into account. The approach is demonstrated in a field example from Ølgod, Denmark, where the cumulated clay thickness in the upper 30 m is estimated using a combination of borehole drilling records and an airborne transient survey.

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Deeply rooted glaciotectonism in western Denmark: geological composition, structural characteristics and the origin of Varde hill‐island

Cited by 21 publications

References 44 publications

Modeling Depth of the Redox Interface at High Resolution at National Scale Using Random Forest and Residual Gaussian Simulation

Modeling Depth of the Redox Interface at High Resolution at National Scale Using Random Forest and Residual Gaussian Simulation

Isostatic compensation of Quaternary vertical crustal motions: coupling between uplift of Britain and subsidence beneath the North Sea

Using geophysical survey results in the inference of aquifer vulnerability measures

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