1. |
- Artigas Soler, María, et al.
(author)
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Genome-wide association and large-scale follow up identifies 16 new loci influencing lung function.
- 2011
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In: Nature genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 43:11, s. 1082-90
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Journal article (peer-reviewed)abstract
- Pulmonary function measures reflect respiratory health and are used in the diagnosis of chronic obstructive pulmonary disease. We tested genome-wide association with forced expiratory volume in 1 second and the ratio of forced expiratory volume in 1 second to forced vital capacity in 48,201 individuals of European ancestry with follow up of the top associations in up to an additional 46,411 individuals. We identified new regions showing association (combined P < 5 × 10(-8)) with pulmonary function in or near MFAP2, TGFB2, HDAC4, RARB, MECOM (also known as EVI1), SPATA9, ARMC2, NCR3, ZKSCAN3, CDC123, C10orf11, LRP1, CCDC38, MMP15, CFDP1 and KCNE2. Identification of these 16 new loci may provide insight into the molecular mechanisms regulating pulmonary function and into molecular targets for future therapy to alleviate reduced lung function.
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2. |
- Dalton, A. S., et al.
(author)
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An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex
- 2020
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 234
-
Journal article (peer-reviewed)abstract
- The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 [Dyke et al., 2003]; 'Quaternary Glaciations - Extent and Chronology, Part II' [Dyke, 2004]). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km(2), which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world's largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval. (C) 2020 Elsevier Ltd. All rights reserved.
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3. |
- Berndt, Sonja I., et al.
(author)
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Genome-wide meta-analysis identifies 11 new loci for anthropometric traits and provides insights into genetic architecture
- 2013
-
In: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 45:5, s. 501-U69
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Journal article (peer-reviewed)abstract
- Approaches exploiting trait distribution extremes may be used to identify loci associated with common traits, but it is unknown whether these loci are generalizable to the broader population. In a genome-wide search for loci associated with the upper versus the lower 5th percentiles of body mass index, height and waist-to-hip ratio, as well as clinical classes of obesity, including up to 263,407 individuals of European ancestry, we identified 4 new loci (IGFBP4, H6PD, RSRC1 and PPP2R2A) influencing height detected in the distribution tails and 7 new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3 and ZZZ3) for clinical classes of obesity. Further, we find a large overlap in genetic structure and the distribution of variants between traits based on extremes and the general population and little etiological heterogeneity between obesity subgroups.
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4. |
- Heid, Iris M, et al.
(author)
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Meta-analysis identifies 13 new loci associated with waist-hip ratio and reveals sexual dimorphism in the genetic basis of fat distribution
- 2010
-
In: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 42:11, s. 949-960
-
Journal article (peer-reviewed)abstract
- Waist-hip ratio (WHR) is a measure of body fat distribution and a predictor of metabolic consequences independent of overall adiposity. WHR is heritable, but few genetic variants influencing this trait have been identified. We conducted a meta-analysis of 32 genome-wide association studies for WHR adjusted for body mass index (comprising up to 77,167 participants), following up 16 loci in an additional 29 studies (comprising up to 113,636 subjects). We identified 13 new loci in or near RSPO3, VEGFA, TBX15-WARS2, NFE2L3, GRB14, DNM3-PIGC, ITPR2-SSPN, LY86, HOXC13, ADAMTS9, ZNRF3-KREMEN1, NISCH-STAB1 and CPEB4 (P = 1.9 × 10⁻⁹ to P = 1.8 × 10⁻⁴⁰) and the known signal at LYPLAL1. Seven of these loci exhibited marked sexual dimorphism, all with a stronger effect on WHR in women than men (P for sex difference = 1.9 × 10⁻³ to P = 1.2 × 10⁻¹³). These findings provide evidence for multiple loci that modulate body fat distribution independent of overall adiposity and reveal strong gene-by-sex interactions.
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5. |
- Coviello, Andrea D, et al.
(author)
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A genome-wide association meta-analysis of circulating sex hormone-binding globulin reveals multiple Loci implicated in sex steroid hormone regulation.
- 2012
-
In: PLoS genetics. - : Public Library of Science (PLoS). - 1553-7404 .- 1553-7390. ; 8:7
-
Journal article (peer-reviewed)abstract
- Sex hormone-binding globulin (SHBG) is a glycoprotein responsible for the transport and biologic availability of sex steroid hormones, primarily testosterone and estradiol. SHBG has been associated with chronic diseases including type 2 diabetes (T2D) and with hormone-sensitive cancers such as breast and prostate cancer. We performed a genome-wide association study (GWAS) meta-analysis of 21,791 individuals from 10 epidemiologic studies and validated these findings in 7,046 individuals in an additional six studies. We identified twelve genomic regions (SNPs) associated with circulating SHBG concentrations. Loci near the identified SNPs included SHBG (rs12150660, 17p13.1, p=1.8×10(-106)), PRMT6 (rs17496332, 1p13.3, p=1.4×10(-11)), GCKR (rs780093, 2p23.3, p=2.2×10(-16)), ZBTB10 (rs440837, 8q21.13, p=3.4×10(-09)), JMJD1C (rs7910927, 10q21.3, p=6.1×10(-35)), SLCO1B1 (rs4149056, 12p12.1, p=1.9×10(-08)), NR2F2 (rs8023580, 15q26.2, p=8.3×10(-12)), ZNF652 (rs2411984, 17q21.32, p=3.5×10(-14)), TDGF3 (rs1573036, Xq22.3, p=4.1×10(-14)), LHCGR (rs10454142, 2p16.3, p=1.3×10(-07)), BAIAP2L1 (rs3779195, 7q21.3, p=2.7×10(-08)), and UGT2B15 (rs293428, 4q13.2, p=5.5×10(-06)). These genes encompass multiple biologic pathways, including hepatic function, lipid metabolism, carbohydrate metabolism and T2D, androgen and estrogen receptor function, epigenetic effects, and the biology of sex steroid hormone-responsive cancers including breast and prostate cancer. We found evidence of sex-differentiated genetic influences on SHBG. In a sex-specific GWAS, the loci 4q13.2-UGT2B15 was significant in men only (men p=2.5×10(-08), women p=0.66, heterogeneity p=0.003). Additionally, three loci showed strong sex-differentiated effects: 17p13.1-SHBG and Xq22.3-TDGF3 were stronger in men, whereas 8q21.12-ZBTB10 was stronger in women. Conditional analyses identified additional signals at the SHBG gene that together almost double the proportion of variance explained at the locus. Using an independent study of 1,129 individuals, all SNPs identified in the overall or sex-differentiated or conditional analyses explained ∼15.6% and ∼8.4% of the genetic variation of SHBG concentrations in men and women, respectively. The evidence for sex-differentiated effects and allelic heterogeneity highlight the importance of considering these features when estimating complex trait variance.
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6. |
- Jansen, Willemijn J, et al.
(author)
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Prevalence Estimates of Amyloid Abnormality Across the Alzheimer Disease Clinical Spectrum.
- 2022
-
In: JAMA neurology. - : American Medical Association (AMA). - 2168-6157 .- 2168-6149. ; 79:3, s. 228-243
-
Journal article (peer-reviewed)abstract
- One characteristic histopathological event in Alzheimer disease (AD) is cerebral amyloid aggregation, which can be detected by biomarkers in cerebrospinal fluid (CSF) and on positron emission tomography (PET) scans. Prevalence estimates of amyloid pathology are important for health care planning and clinical trial design.To estimate the prevalence of amyloid abnormality in persons with normal cognition, subjective cognitive decline, mild cognitive impairment, or clinical AD dementia and to examine the potential implications of cutoff methods, biomarker modality (CSF or PET), age, sex, APOE genotype, educational level, geographical region, and dementia severity for these estimates.This cross-sectional, individual-participant pooled study included participants from 85 Amyloid Biomarker Study cohorts. Data collection was performed from January 1, 2013, to December 31, 2020. Participants had normal cognition, subjective cognitive decline, mild cognitive impairment, or clinical AD dementia. Normal cognition and subjective cognitive decline were defined by normal scores on cognitive tests, with the presence of cognitive complaints defining subjective cognitive decline. Mild cognitive impairment and clinical AD dementia were diagnosed according to published criteria.Alzheimer disease biomarkers detected on PET or in CSF.Amyloid measurements were dichotomized as normal or abnormal using cohort-provided cutoffs for CSF or PET or by visual reading for PET. Adjusted data-driven cutoffs for abnormal amyloid were calculated using gaussian mixture modeling. Prevalence of amyloid abnormality was estimated according to age, sex, cognitive status, biomarker modality, APOE carrier status, educational level, geographical location, and dementia severity using generalized estimating equations.Among the 19097 participants (mean [SD] age, 69.1 [9.8] years; 10148 women [53.1%]) included, 10139 (53.1%) underwent an amyloid PET scan and 8958 (46.9%) had an amyloid CSF measurement. Using cohort-provided cutoffs, amyloid abnormality prevalences were similar to 2015 estimates for individuals without dementia and were similar across PET- and CSF-based estimates (24%; 95% CI, 21%-28%) in participants with normal cognition, 27% (95% CI, 21%-33%) in participants with subjective cognitive decline, and 51% (95% CI, 46%-56%) in participants with mild cognitive impairment, whereas for clinical AD dementia the estimates were higher for PET than CSF (87% vs 79%; mean difference, 8%; 95% CI, 0%-16%; P=.04). Gaussian mixture modeling-based cutoffs for amyloid measures on PET scans were similar to cohort-provided cutoffs and were not adjusted. Adjusted CSF cutoffs resulted in a 10% higher amyloid abnormality prevalence than PET-based estimates in persons with normal cognition (mean difference, 9%; 95% CI, 3%-15%; P=.004), subjective cognitive decline (9%; 95% CI, 3%-15%; P=.005), and mild cognitive impairment (10%; 95% CI, 3%-17%; P=.004), whereas the estimates were comparable in persons with clinical AD dementia (mean difference, 4%; 95% CI, -2% to 9%; P=.18).This study found that CSF-based estimates using adjusted data-driven cutoffs were up to 10% higher than PET-based estimates in people without dementia, whereas the results were similar among people with dementia. This finding suggests that preclinical and prodromal AD may be more prevalent than previously estimated, which has important implications for clinical trial recruitment strategies and health care planning policies.
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7. |
- Speliotes, Elizabeth K., et al.
(author)
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Association analyses of 249,796 individuals reveal 18 new loci associated with body mass index
- 2010
-
In: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 42:11, s. 937-948
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Journal article (peer-reviewed)abstract
- Obesity is globally prevalent and highly heritable, but its underlying genetic factors remain largely elusive. To identify genetic loci for obesity susceptibility, we examined associations between body mass index and ~2.8 million SNPs in up to 123,865 individuals with targeted follow up of 42 SNPs in up to 125,931 additional individuals. We confirmed 14 known obesity susceptibility loci and identified 18 new loci associated with body mass index (P < 5 × 10−8), one of which includes a copy number variant near GPRC5B. Some loci (at MC4R, POMC, SH2B1 and BDNF) map near key hypothalamic regulators of energy balance, and one of these loci is near GIPR, an incretin receptor. Furthermore, genes in other newly associated loci may provide new insights into human body weight regulation.
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8. |
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9. |
- Clayton, L, et al.
(author)
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Glaciation of Wisconsin
- 2006
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In: Wisconsin Geological and Natural History Survey Educational Series. ; :36
-
Journal article (peer-reviewed)
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10. |
- Remmert, Izabella, et al.
(author)
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Seasonal subglacial ponding deposits in a thick till sequence, Dösebacka drumlin, southwest Sweden
- 2022
-
In: Sedimentary Geology. - : Elsevier BV. - 0037-0738. ; 440
-
Journal article (peer-reviewed)abstract
- Current melting of glaciers has increased interest in understanding glacier hydrology and the interplay between subglacial meltwater, the glacier bed, and ice behavior. However, little is known about the sedimentology of subglacial meltwater deposits, and no sediment type or sequence has been identified as being unique to subglacial settings. Here, we analyze a repetitive, coarsening-upward, sorted-sediment sequence in a thick, diamicton section that we interpret to be seasonal, subglacial meltwater deposits. Over 20m of diamicton that we interpret to be subglacial traction till is exposed in a rock-cored drumlin at Dösebacka, Sweden, and the till contains multiple interbeds, 25–75cm thick, of sorted sediment, each consisting of a coarsening-upward sequence of laminated clay, graded laminae of silt, and sand with pebbles. Based on sediment logs, grain-size, thin-section analysis, structural analysis, and field sedimentology, we investigate the genesis of these interbeds and conclude the interbeds to represent subglacial pond deposits. The coarsening-upward sequence represents cessation of till deposition due to hydrostatic bed separation followed by (1) suspension settling of clay in a subglacial blister/pond with drop-grains from an ice roof, (2) suspension settling of pulses of silt and very fine sand in still water coupled with occasional turbidites, (3) traction sedimentation (and loading) of sand and gravel from flowing water, and (4) renewed till deposition following reattachment. The interbeds also reveal deformation that is oriented parallel to the ice-flow direction and which we attribute to deformation during ice-bed reattachment. This sediment sequence parallels in character the seasonal behavior of supraglacial meltwater development on Greenland and moulin drainage, and we argue that the interbeds represent pond deposits during seasonal meltwater drainage. Drainage formed a subglacial blister/pond when the ice reached floatation point, and clay and, later, silt were deposited. With time, drainage became better integrated, and sand and pebbles were deposited by flowing water until reattachment when till deposition resumed. Additionally, based on our interpretation and the attitude of the beds in the drumlin, which parallel the drumlin slope, we argue the drumlin to have been formed by accretion rather than erosion. The anomalous thickness of the till and the numerous interbeds also imply a relatively rapid sedimentation rate, indicating the drumlin formed quickly (10's of years). This stoss-side environment allowed for preservation of the unique interbeds.
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11. |
- Becher, G. P., et al.
(author)
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Sedimentology and internal structure of murtoos-V-shaped landforms indicative of a dynamic subglacial hydrological system
- 2021
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In: Geomorphology. - : Elsevier BV. - 0169-555X. ; 380:May
-
Journal article (peer-reviewed)abstract
- Knowledge about processes beneath ice sheets, and in particular the processes connected to subglacial hydrology, is crucial for an understanding of ice sheets and how they react in a warming climate. Recently, v-shaped subglacial landforms (murtoos) have been found in those parts of the former Fennoscandian Ice Sheet where rapid ice-margin retreat occurred. Based on their geomorphology and distribution, murtoos have been suggested to form where the bed experienced high influxes of meltwater. Here, we investigate the sedimentology and internal structure of murtoos at four localities in southern Sweden to better understand murtoo genesis. The excavated murtoos consist of heterogenous diamict showing reasonably strong fabrics interbedded with sorted sediments. Sediments show signs of ductile deformation and lquefaction. We interpret these landforms as sub glacial landforms created by till deposition and sedimentation from meltwater with subsequent deformation. Cross-cutting relationships and inter-bedding of sorted sediments suggest a stepwise formation including periodic deformation events. We propose a model that is based on a dynamic subglacial meltwater system. We suggest that the subglacial environment is within the distributed system where the bed receives meltwater from repeated influxes of supraglacially derived meltwater. The processes suggested in this model of formation are strikingly similar to the character of glaciological and hydrological dynamics observed on the Greenland ice sheet today. ? 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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12. |
- Benediktsson, Ivar Örn, et al.
(author)
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Architecture and structural evolution of an early Little Ice Age terminal moraine at the surge-type glacier Mulajokull, Iceland
- 2015
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In: Journal of Geophysical Research - Earth Surface. - 2169-9011 .- 0148-0227 .- 2156-2202. ; 120:9, s. 1895-1910
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Journal article (peer-reviewed)abstract
- The internal architecture and structural evolution of the Arnarfellsmular terminal moraine at Mulajokull, a surge-type glacier in central Iceland, is described in order to demonstrate submarginal and proglacial glaciotectonic processes during glacier surging, as well as constraining the age of the maximum extent of the glacier. The moraine is 4-7m high, 50-100m wide, and composed of a highly deformed sequence of loess, peat, and tephra that is draped by till up to the crest. The internal architecture is dominated by steep, high-amplitude overturned folds and thrusts in the crest zone but open, low-amplitude folds on the distal slope. Section balancing suggests a basal detachment (decollement) depth of 1.4m and a total horizontal shortening of around 59%. This implies that the glacier coupled to the foreland about 70m up glacier from its terminal position to initiate the formation of the moraine. The structural evolution is polyphase in that the formation commenced with low-amplitude open folding of the foreland, followed by overfolding and piggyback thrusting. Radiocarbon dating and analysis of tephra layers, along with historical references, indicate that the most likely time of moraine formation was between A.D. 1717 and 1760, which suggests that Mulajokull had its Little Ice Age maximum and most extensive surge earlier than many other surge-type glaciers in Iceland.
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13. |
- Benediktsson, Ívar Örn, et al.
(author)
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Progressive formation of modern drumlins at Múlajökull, Iceland: stratigraphical and morphological evidence
- 2016
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In: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45, s. 567-583
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Journal article (peer-reviewed)abstract
- © 2016 Collegium Boreas. Published by John Wiley & Sons Ltd The drumlin field at Múlajökull, Iceland, is considered to be an active field in that partly and fully ice-covered drumlins are being shaped by the current glacier regime. We test the hypothesis that the drumlins form by a combination of erosion and deposition during successive surge cycles. We mapped and measured 143 drumlins and studied their stratigraphy in four exposures. All exposures reveal several till units where the youngest till commonly truncates older tills on the drumlin flanks and proximal slope. Drumlins inside a 1992 moraine are relatively long and narrow whereas drumlins outside the moraine are wider and shorter. A conceptual model suggests that radial crevasses create spatial heterogeneity in normal stress on the bed so that deposition is favoured beneath crevasses and erosion in adjacent areas. Consequently, the crevasse pattern of the glacier controls the location of proto-drumlins. A feedback mechanism leads to continued crevassing and increased sedimentation at the location of the proto-drumlins. The drumlin relief and elongation ratio increases as the glacier erodes the sides and drapes a new till over the landform through successive surges. Our observations of this only known active drumlin field may have implications for the formation and morphological evolution of Pleistocene drumlin fields with similar composition, and our model may be tested on modern drumlins that may become exposed upon future ice retreat.
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14. |
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15. |
- Bouvier, Vera, et al.
(author)
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Distribution, genesis and annual-origin of De Geer moraines in Sweden: insights revealed by LiDAR
- 2015
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In: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 137:4, s. 319-333
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Journal article (peer-reviewed)abstract
- Abstract: De Geer moraines (DGMs) were first identified in Sweden by Gerard De Geer in 1889 and have been mapped since then in many parts of Sweden. Using airborne Light Detection and Ranging (LiDAR) data, we have mapped DGMs over the entire country, and we show that they occur predominantly in two distinct areas: in south-central Sweden north of the Middle Swedish end-moraine zone and in northeast Sweden. DGM formation occurs predominantly where the local relief is low, the ice-margin retreat rate was high and the sedimentation rate low. Formation of DGMs occurred over short time spans of a few hundred years – between 11 500 and 11 000 cal years BP for the southern group and from 10 700 and 9900 cal years BP for the DGMs in the north. DGMs have been suggested to be made by a number of processes at subaquatic ice margins, including pushing during winter readvance, squeezing into subglacial crevasses, deformation during calving events and deposition as subaquatic fans. Therefore, we recognize DGMs to be equifinal landforms, made by several related mechanisms. However, we observe that the most common occurrence of DGMs in Sweden are as regularly spaced even ridges below the highest shoreline whose spacing closely corresponds to independently determined ice-margin retreat rates. We therefore suggest that where regular evenly spaced DGMs occur, their spacing likely represents the local ice-margin retreat rate, and that the majority of these ridges were made annually by winter advances.
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16. |
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17. |
- Francus, Pierre, et al.
(author)
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The rise of varves
- 2013
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In: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:3-4, s. 229-230
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Research review (peer-reviewed)abstract
- Varves are exceptional in many aspects: they are rare, can be used to constrain and build chronologies, and contain highresolution records of past environment and climate. Moreover, their occurrence and reproducibility in different settings allows for an internal validation of their continuity and integrity. Gerard De Geer of Sweden understood the value of varved sediments over a century ago. Although other geologists during his time had described rhythmic, glacial lake sediments that they interpreted as annual layers (e.g. Smith 1832; Hitchcock 1841; Upham 1884), it was De Geer who saw the potential of varves (from the Swedish word varv, meaning cycle), for dating the retreat of the Scandinavian ice sheet, and by extension, the late Quaternary. And it was De Geer and his students who built the socalled Swedish Time Scale, which extends from the present to over 13,000 years before present. Much of De Geer’s early work was in fact published in GFF (e.g. De Geer 1908, 1921, 1935). However, De Geer’s considerations of teleconnections (today, a hot topic in climate research), along with strong reservations from North American geologists about the implications of the varve chronology in the Connecticut River valley by Ernst Antevs (one of De Geer’s ler-jungar; Antevs 1922, 1928), led many to doubt the annual nature of varves. Ages for the New England varves, based on the, at that time, new 14C technique, as well as varves’ similarities to the turbidites that Philip Kuenen was describing, convinced many that varves were not annual (for details, see Ridge and Larsen 1990; Ridge et al. 2012). Today, the varves that De Geer (as well as Antevs) looke
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18. |
- Hedeving, Anna, et al.
(author)
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Thin loess in Southwestern Sweden
- 2024
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In: GFF. - 1103-5897 .- 2000-0863.
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Journal article (peer-reviewed)abstract
- A thin (20-80 cm), patchy layer of silt-rich sediment occurs at the surface throughout Svartedalen, a nature reserve 30 km north of Gothenburg, Sweden. This surface silt mantles a bedrock-dominated, fracture-valley landscape. Using data from grain-size analysis, OSL dating and detrital-zircon U-Pb dating, we argue that the silt is loess sourced from glacial sediment that was eroded from local bedrock. The sediment has a grain-size distribution typical of wind-blown silt and is especially similar to thin deposits of loess overlying coarser material. OSL ages on five samples range from 1 to 8 ka, although analysis of equivalent dose distributions of one may suggest an age as old as 11 ka. The dates may represent true depositional ages and represent several Holocene eolian events. However, we consider as more likely that the loess was deposited during deglaciation, and quartz-grain signals have been partially reset during bioturbation. U-Pb ages on 273 zircon grains from the loess show prominent peaks at 1.6 and 1.8 Ga, as well as smaller numbers of grains from 1.0 to 1.6 Ga. These ages match dates from the Idefjord Terrane which comprises the bedrock of the study area. We argue that during ice-margin retreat, debris in the glacier was dominated by locally derived debris. This glacial sediment was left in thin patches uplands and particularly in large ice-marginal deltas. These deposits served as the proximal source for the loess. The presence of thin loess in Svartedalen suggests loess to be common in soils of southwest Sweden.
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19. |
- Ingolfsson, Olafur, et al.
(author)
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Glacial geological studies of surge-type glaciers in Iceland — Research
- 2016
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In: Earth-Science Reviews. - : Elsevier BV. - 0012-8252. ; 152, s. 37-69
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Journal article (peer-reviewed)abstract
- Surging glaciers are potential analogues for land-terminating palaeo-ice streams and surging ice sheet lobes, and research on surge-type glaciers is important for understanding the causal mechanisms of modern and past ice sheet instabilities. The geomorphic signatures left by the Icelandic surge-type glaciers vary and range from glaciotectonic end moraines formed by folding and thrusting, crevasse-squeeze ridges, concertina eskers, drumlins and fluted forefields, to extensive dead-ice fields and even drift sheets where fast ice-flow indicators are largely missing. We outline some outstanding research questions and review case studies from the surge-type outlets of Brúarjökull, Eyjabakkajökull and Tungnaárjökull (Vatnajökull ice cap), Múlajökull and Sátujökull (Hofsjökull ice cap), Hagafellsjökull and Suðurjökull (Langjökull ice cap), Kaldalónsjökull, Leirufjarðarjökull and Reykjarfjarðarjökull (Drangajökull ice cap), as well as the surge-type cirque glaciers in northern Iceland. We review the current understanding of how rapid ice flow is sustained throughout the surge, the processes that control the development of the surge-type glacier landsystem and the geological evidence of surges found in sediments and landforms. We also examine if it is possible to reconstruct past surge flow rates from glacial landforms and sediments and scale-up present-day surge processes, landforms and landsystems as modern analogues to past ice streams. Finally,we also examine if there is a climate/mass-balance control on surge initiation, duration and frequency.
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20. |
- Iverson, N. R., et al.
(author)
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A Theoretical Model of Drumlin Formation Based on Observations at Múlajökull, Iceland
- 2017
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In: Journal of Geophysical Research - Earth Surface. - 0148-0227 .- 2156-2202. ; 122:12, s. 2302-2323
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Journal article (peer-reviewed)abstract
- Abstract The drumlin field at the surge-type glacier, Múlajökull, provides an unusual opportunity to build a model of drumlin formation based on field observations in a modern drumlin-forming environment. These observations indicate that surges deposit till layers that drape the glacier forefield, conform to drumlin surfaces, and are deposited in shear. Observations also indicate that erosion helps create drumlin relief, effective stresses in subglacial till are highest between drumlins, and during quiescent flow, crevasses on the glacier surface overlie drumlins while subglacial channels occupy intervening swales. In the model, we consider gentle undulations on the bed bounded by subglacial channels at low water pressure. During quiescent flow, slip of temperate ice across these undulations and basal water flow toward bounding channels create an effective stress distribution that maximizes till entrainment in ice on the heads and flanks of drumlins. Crevasses amplify this effect but are not necessary for it. During surges, effective stresses are uniformly low, and the bed shears pervasively. Vigorous basal melting during surges releases debris from ice and deposits it on the bed, with deposition augmented by transport in the deforming bed. As surge cycles progress, drumlins migrate downglacier and grow at increasing rates, due to positive feedbacks that depend on drumlin height. Drumlin growth can be accompanied by either net aggradation or erosion of the bed, and drumlin heights and stratigraphy generally correspond with observations. This model highlights that drumlin growth can reflect instabilities other than those of bed shear instability models, which require heuristic till transport assumptions.
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21. |
- Jan, Mangerud, et al.
(author)
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The Fennoscandian Ice Sheet during the Younger Dryas Stadial
- 2022
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In: European Glacial Landscapes: The Last Deglaciation. - 9780323918992 ; , s. 437-452
-
Book chapter (other academic/artistic)abstract
- The Younger Dryas (YD) moraines have been mapped almost continuously around the Fennoscandian ice sheet. Segments of the moraine have individual names, best known are the Salpausselkä in Finland, the Middle Swedish moraines in Sweden and the Ra and the Herdla-Halsnøy moraines in Norway. The outline of the ice margin was very different around the ice sheet, with narrow fjord glaciers in western Norway and smoother margins and wide lobes in the lowlands of Sweden and Finland. The form and composition of the ice-marginal deposits also vary from narrow till ridges to large deltas and sandurs. Along many stretches there are two or more parallel ice-marginal deposits, notably in Finland and Sweden, whereas there is often only one ridge in western Norway. Most of the moraines are confidently dated to the YD, but with some variation in precise timing; the Herdla-Halsnøy moraines were formed at the very end of the YD, the outermost Salpausselkä and Middle Swedish moraines were formed earlier during the YD. In a few places it is unclear if all parallel ridges are of YD age.
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22. |
- Jennings, Carrie, et al.
(author)
-
The Quaternary of Minnesota
- 2011
-
In: In J. Ehlers, P.L. Gibbard and P.D. Hughes, editors: Developments in Quaternary Science, Vol. 15, Amsterdam, The Netherlands, 2011, © Copyright 2011 Elsevier B.V.. - Amsterdam : Elsevier. - 9780444534477 ; , s. 499-511
-
Book chapter (other academic/artistic)abstract
- The rich and complex sedimentary record of glaciation in Minnesota includes deposits of glaciers, associated rivers and lakes, as well as windblown and other periglacial deposits that span the Quaternary Period and are at the surface in nearly every part of the state. The thickness of these deposits is commonly more than 100 m. One of the thickest, and perhaps most stratigraphically complete, records of the Quaternary in Minnesota lies beneath the Coteau des Prairies, an inter-ice stream sediment highland that spans the Minnesota–South Dakota border where over 300-m of fine-grained diamictons are preserved (Fig. 38.1). Though the glacial deposits of the state are dominated by a complex Late Wisconsinan history (marine isotope stage (MIS) 2), Minnesota has many lithostratigraphical units from the Middle and likely Early Pleistocene. For example, Minnesota has units older than the Sangamon Geosol (>125 ka), units older than volcanic ashes derived from Yellowstone (>610 ka) (Boellstorff, 1978), as well as magnetically reversed units from prior to the Brunhes– Matayuma boundary (>788 ka). Recent cosmogenic burial dating of glacigenic sediment (Balco et al., 2005) indicates that numerous glacial stratigraphical units were deposited prior to MIS 14. A rare bedrock exposure in the southern part of the Coteau des Prairie highland was striated as early as 640–740 ka (MIS 16 or 14) based on cosmogenic exposure dating of the quartzite using a paired-isotope system (Bierman et al., 1999). A stack of 12 tills surrounding this isolated bedrock high is therefore most likely a record of glaciation prior to and including MIS 14–16. Ice streams that were active primarily during MIS 2 focused erosion on either side of the Coteau des Prairie leaving it as a remnant between broad erosional unconformities (Fig. 38.1). The southeastern corner of Minnesota was also glaciated many times early in the Quaternary Period but remained ice-free duringMIS2–4, during which time it was affected by strong, northwesterly, periglacial winds and permafrost (Zanner, 1999). Thus, the earlier record of glaciation of this part of Minnesota is obscured and in places, confined to sinkholes and caves (e.g. Milske et al., 1983). The southern margin of the Late Wisconsinan (MIS 2) Laurentide ice sheet produced many dynamic ice protuberances or lobes that emanated from discrete ice-source areas (Fig. 38.2). Some of the tributary ice sheds had distinctive bedrock geology allowing the provenance of the ice as well as the evolution of ice sheds to be discerned. This condition has produced distinct lithologic compositions for the tills derived from different ice centres and has provided a basis for differentiating and formalising lithostratigraphical units (Johnson et al., in preparation). Four broad source regions have been identified and their characteristics are shown in Table 38.1 and Fig. 38.3. Minnesota’s pre-MIS 2 till units share the same broadly defined provenance regions indicating that older glaciations had similar sources areas. However, the shape of the former ice margins is much more difficult to determine from the scattered subsurface information and therefore ice dynamics more difficult to infer. Where the pre-MIS 2 ice limits are at the surface, their breadth and more southerly extent suggest that at the very least, the ice lobes were broader. It remains possible that the ice dynamics were substantially different at times in the past and did not lead to the creation of ice streams and lobes, for example, during the ice-sheet-build-up phase of each glaciation and prior to the Middle Pleistocene transition (when the frequency of glaciation and volume of changed from 41,000-year periodicity to
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23. |
- Johnson, Mark D., 1954, et al.
(author)
-
A FORMAL LITHOSTRATIGRAPHY FOR THE QUATERNARY OF MINNESOTA
- 2011
-
In: Geological Society of America abstracts with programs Minneapolis 2011.
-
Conference paper (peer-reviewed)abstract
- The Minnesota Geological Survey has created a formal lithostratigraphy for the Quaternary deposits of Minnesota that will be published on-line and in-print, fall 2011. We followed guidelines of the North American Commission on Stratigraphic Nomenclature (2005) to create a framework for establishing formal lithostratigraphic units in Minnesota, and we evaluated the approximately 120 lithostratigraphic names and units that have been identified and used in Minnesota since the time when geologic mapping of glacial deposits began. Of these, eighty-one (81) units are considered to be useful lithostratigraphic units of formation and member rank, and these are formally accepted in this open-file report or will be in future volumes. These 81 units include previously named formal lithostratigraphic units that are recognized and accepted as originally defined, but also formally defined units that we have revised or redefined to better fit into our stratigraphic framework. The remaining lithostratigraphic units have been used informally in earlier reports or are newly named. Twenty-three units are no longer considered valid as lithostratigraphic units are abandoned even though some of these are well-known among state geologists. These units include previously used units of both formal and informal status. Many units, especially in the subsurface, are undefined at the present time because their character and extent are poorly known.
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24. |
- Johnson, Mark D., 1954, et al.
(author)
-
Active drumlin field revealed at the margin of Múlajökull, Iceland: A surge-type glacier
- 2010
-
In: Geology. ; 38:10, s. 943-946
-
Journal article (peer-reviewed)abstract
- ABSTRACT Recent marginal retreat of Múlajökull, a surge-type outlet glacier of Hofsjökull, Iceland, has revealed a drumlin fi eld consisting of more than 50 drumlins. The drumlins are 90–320 m long, 30–105 m wide, 5–10 m in relief, and composed of multiple beds of till deposited by lodgment and bed deformation. The youngest till layer truncates the older units with an erosion surface that parallels the drumlin form. Thus, the drumlins are built up and formed by a combination of subglacial depositional and erosional processes. Field evidence suggests each till bed to be associated with individual recent surges. We consider the fi eld to be active in the sense that the drumlins are shaped by the current glacial regime. The Múlajökull fi eld is the only known active drumlin fi eld, and is therefore a unique analogue to Pleistocene drumlin fi elds.
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25. |
- Johnson, Mark D., 1954, et al.
(author)
-
Geomorphology and sedimentology of features formed at the outlet during the final drainage of the Baltic Ice Lake
- 2022
-
In: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 51:1, s. 20-40
-
Journal article (peer-reviewed)abstract
- We present a conceptual model for the character of the 11.6 cal. ka BP drainage of the Baltic Ice Lake in the outlet area based on a new geomorphological map as well as new sedimentological information. We combine this new information with a review of the previous work on this well-studied area. The model includes the premise of remnant ice in the Langen valley as suggested by previous workers and indicates the drainage began subglacially. Cobbly sediment on northeast Billingen formerly interpreted as beach sediment is interpreted to be a subglacial lag deposit. The ridge at Timmersdala is composed of drainage sediment from the initial phases of the drainage, deposited in a subglacial tunnel that emptied out on to central Klyftamon. Continued drainage widened the tunnel by frictional melting, eventually lifting and fracturing the ice. Pendant bars, expansion bars and boulder sheets on central and southern Klyftamon formed during the drainage event. Cobbly and bouldery drainage sediment in the bars, which is massive and poorly sorted, was deposited as bedload from sediment-charged water. Imbrication, bar orientation, and changes in grain size and Cambrian-clast content indicate flow to the west-northwest. Most sediment in the bars was derived from erosion on Klyftamon, but Cambrian rock from Billingen is present, delivered directly by the flood waters and/or from debris-rich icebergs from the broken-up remnant ice. This flood event is distinguished from other Quaternary megafloods by being sediment-supply limited and having a short, subaerial floodway (20 km).
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26. |
- Johnson, Mark D., 1954
(author)
-
, Ice-walled-lake plains in North America and Europe--description, genesis, and paleoglaciological implications
- 2004
-
In: GFF. ; 126
-
Journal article (peer-reviewed)abstract
- Ice-walled-lake plains (IWLPs) are conspicuous but little-known landforms associated with the broad bands of hummocks that mark the southern margins of the former ice sheets in Europe and North America. They are circular to irregular, flat-topped hills up to 50 m in relief and up to a few kilometers wide surrounded by glacial hummocks. Laminated lake sediment up to tens of meters thick underlies the centers of many IWLPs, and coarser wave-washed, deltaic, and debris-flow sediment is typically present around their edges, often forming a rim ridge. These lake plains provide evidence for the final disintegration of the ice and the distribution of debris from the melting ice. IWLPs and hummocks formed where supraglacial debris slumped down ice slopes into open thaw lakes in a zone of stagnant ice. Some debris was reworked by supraglacial streams or in the ice-walled lakes. Some IWLPs, especially those in Alberta, Minnesota, and southern Sweden seem to contain more till-like material than lake sediment, indicating a continuum from IWLPs with little to abundant lake sediment. Paleoclimatic, as well as geologic, evidence shows that sediment in IWLPs was derived from supraglacial sources. At the end of the last glaciation, permafrost allowed ice-walled-lakes to persist in stagnant ice long after the active ice margin receded. Paleoclimatic evidence from North Dakota shows that ice-walled lakes persisted into the early Holocene, indicating that stagnant ice could only have survived with a thick cover of supraglacial debris. Although this supraglacial theory has been challenged in recent years, we are unaware of any evidence that indicates a substantial amount of subglacial material being squeezed up into the ice-walled lakes, nor does a subglacial squeezing hypothesis explain the existence of these lakes long after the climate warmed. IWLPs occur in areas where the marginal zone of the glacier contained abundant supraglacial debris. Compressive flow and freezing-on near the ice margin, enhanced by permafrost or readvances of ice into areas of stagnant ice, likely contributed to the accumulation of thick masses of debris-rich ice that yielded thick supraglacial debris as the ice melted. Paleoclimatic, topographic, and glacial-geologic evidence indicates that the southern margins of the great ice sheets advanced up adverse slopes, into areas of permafrost, and often at relatively high ice velocities, all of which enhanced thrusting and freezing-on of subglacial debris and its transport to englacial and supraglacial positions. The hummocky moraine surrounding the ice-walled-lake plains formed when the supraglacial debris was let down as the last ice melted.
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27. |
- Johnson, Mark D., 1954, et al.
(author)
-
Lithostratigraphy for Quaternary glacial deposits: “If it ain’t broke, don’t fix it!”
- 2009
-
In: GSA Today. ; 19:9, s. 15-15
-
Journal article (peer-reviewed)abstract
- (A response to an article by Räsänen) Räsänen and others (2009) claim that lithostratigraphic classification of Quaternary glacial deposits is so problematic that it is time to use allostratigraphy instead. Our immediate response from a Midwest perspective is—what problems? Formal lithostratigraphic classification of glacial deposits works. Since its initial use to define Pleistocene units in the Midwest (Willman and Frye, 1970), there has never been a serious reason to question this practice. Indeed, formal lithostratigraphies have been progressively established in most Midwestern states.
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28. |
- Johnson, Mark D., 1954, et al.
(author)
-
New exposures of Baltic Ice Lake drainage sediments, Götene, Sweden
- 2010
-
In: GFF. - 1103-5897. ; 132:1, s. 1-12
-
Journal article (peer-reviewed)abstract
- New exposures created during the construction of highway E20 near Götene, Sweden, reveal poorly sorted gravelly sand overlain and underlain by varved clay. The stratigraphy at Pellagården consists of, from the bottom up, striated gneiss, till, varved marine clay, the gravelly sand unit, and varved marine clay. The varves represent deglacial marine sediment deposited in 40–50 m deep water. The gravelly sand unit contains graded bedding, indistinct horizontal bedding, mud clasts and interstitial mud. It is poorly sorted and poorly organised. The unit has a pebble fabric indicating flow to the northwest. These characteristics and the great water depth suggest that the gravelly sand was deposited from a hyperconcentrated traction current or from concentrated to hyperconcentrated density flows. We interpret the gravelly sand bed to be sediment deposited during the Baltic Ice Lake drainage at around 10,000 14C years BP. The unit likely represents rapidly deposited sediment at the very start of the drainage and does not indicate the duration of the drainage event. The bed was deposited during a single drainage event rather than as a series of events over a few weeks or months. Based on the number of varves and regional ice retreat rates, the ice-margin was 0.2 to 5 km north of Götene at the time of the drainage. These sites represent the first reported occurrences of the drainage sediment in a stratigraphic sequence since the work of Simon Johansson (1926, 1937, and 1941).
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29. |
- Johnson, Mark D., 1954, et al.
(author)
-
SOUTHERN LAURENTIDE ICE SHEET DEAD-ICE TOPOGRAPHY: THE ‘WISCONSIN VIEW' AND NEW OPPORTUNITIES
- 2011
-
In: Geological Society of America abstracts with programs Minneapolis 2011.
-
Conference paper (peer-reviewed)abstract
- Much of the Late Glacial Maximum margin of the Laurentide Ice Sheet in Wisconsin is marked by extensive tracts of dead-ice topography. These areas are characterized by numerous irregular hummocks and swales occurring together in a band parallel to the former ice-margin position and extending several kilometers up ice. Ice-walled-lake plains are a common feature in these landscapes. We have analyzed the geomorphology and internal composition of these hummocks while making county maps throughout the state. This dead-ice topography is produced by gradual melting of stagnant ice that had thick supraglacial debris. The supraglacial debris was derived from the ice bed by freezing-on, thrusting, and stacking near the margin. There is abundant evidence that the ice lobes that left behind hummocks topography advanced into permafrosted terrain and, in many cases, likely at fast-flow rates (surging or streaming). These two factors, along with up-gradient bed slopes in places, accentuated the marginal thrusting processes and increased the amount of supraglacial debris. In places, preferred orientation of hummocks likely reflects structures in the parent ice. The presence of tunnel channels cutting through hummocky terrains is also an expression of ice with a frozen toe and rapid ice flow. Following stagnation, the presence of permafrost controlled the rate and timing of dead-ice melting.
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30. |
- Johnson, Mark D., 1954
(author)
-
Stratigraphy and age of Quaternary sediment in the Middle Swedish End Moraine zone
- 2006
-
In: , Bulletin of the Geological Society of Finland. ; :Special Issue 1
-
Journal article (peer-reviewed)abstract
- Recent drilling and geophysical studies in the moraine ridges of the Middle Swedish End Moraine Zone (MSEMZ) show them to be made primarily of clay, but also to contain coarser sediment (sand and some till) particularly on their proximal slopes. Resistivity measurements reveal structures in the clay that are interpreted as thrusts. The moraines are interpreted to be thrust moraines, formed subaqueously at the margin of the Scandinavian Ice Sheet. In addition to the thrust ridges, numerous sites along the former ice-margin positions reveal proximal meltwater sediment deposited in ice-contact deltas that were fed by subglacial meltwater channels. Recent drilling in the intermorainic flats reveal 20 to 30 m of stratified fine sediment (gray to brown silt and clay) overlying till or bedrock. The fine sediment is capped by sand and gravel that contains abundant shale and sandstone clasts eroded from Mt. Billingen. The fine sediment is similar in color, grain size, and sedimentary structure to the clay in the moraine ridges; however their stratigraphical relationship is unclear. That is, it is not clear if the clay in the intermorainic positions is a younger, an older, or the same stratigraphic unit as the clay in the thrust ridges. Two OSL dates on sand grains from the clay in the thrust-moraine ridges yield preliminary dates of 45±5 ka and 67±8 ka, similar to previously reported luminescence ages on the same clay. These dates suggest the clay in the ridges to have been deposited before the Late Weichselian.
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31. |
- Johnson, Mark D., 1954, et al.
(author)
-
Stratigraphy, sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end-moraine zone
- 2010
-
In: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 39:2, s. 199-214
-
Journal article (peer-reviewed)abstract
- Deglaciation of the Middle Swedish end-moraine zone and age of the sediment in and between the moraines have been discussed for about a hundred years. The goal of this project was to determine the stratigraphy and age of the sediment in and between the moraines. Inter-moraine flats are underlain by clay, 10–25 m thick, overlying thin sand and gravel or till on bedrock. The clay is overlain by a few metres of sand and gravel. Much of the clay beneath the flats consists of rhythmites that grade from grey to red and are 2–74 cm thick. Our interpretation of these rhythmites as being varves is supported by grain size and mineralogical and elemental variations. Foraminifera and ostracods show that the clay was deposited in an arctic marine environment, while radiocarbon dating of the microfossils indicates that the clay was deposited 12 150 cal. 14C years ago, during the Younger Dryas chronozone (YD). Most of the optical stimulated luminescence dates on the clay are much older, containing quartz sand that was insufficiently bleached. The stratigraphy indicates that the moraines are composed of YD clay pushed into ridge forms during ice-front oscillations. It is not possible to determine how far north the Scandinavian Ice Sheet retreated prior to the YD advance. We neither support nor reject the suggestion that the ice margin retreated to the northern edge of Mt. Billingen during the Allerød, causing the Baltic Ice Lake to drain.
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32. |
- Johnson, Mark D., 1954, et al.
(author)
-
SUBMARINE PUSH MORAINES OF THE MIDDLE SWEDISH END MORAINE ZONE
- 2011
-
In: Geological Society of America abstracts with programs Minneapolis 2011.
-
Conference paper (peer-reviewed)abstract
- During the Younger Dryas cold event (YD), the Scandinavian Ice Sheet formed the Middle Swedish end-moraine zone (MSEMZ) in south-central Sweden. The area around Skara was below sea level during the YD, and thick marine, varved clay was deposited proglacially on scoured bedrock in the ocean prior to, during, and after the YD. Recent highway exposures in four of the seven ridges in the MSEMZ reveal that, during overall retreat, the ice margin oscillated and, during each oscillation, deformed the marine clay into moraine ridges. The push moraines have little to no till, and then only on the proximal sides. A range of deformation structures are present including folded-and-thrusted to remobilized varved clay. At Ledsjö, a double oscillation is apparent with a grounding-line fan of sand formed between the two oscillations, which was then deformed. The grounding-line-fan sands are faulted and boudinized within 100 m of the former ice margin. Sand in boudins in places retains primary sedimentary structures, but elsewhere show fluidized flow. Farther up-ice, the clay and sands are complexly sheared along down-glacier-dipping reverse faults of several scales (cm to 10´s of m) indicating a subglacial tensional environment. At Ledsjö and Gullhammar, an upper, structureless clay likely represents proglacial, submarine, mudflow sediment deposited on the distal slope of the moraine. These exposures provide models for recent submarine push moraines imaged in fjords in Norway and Svalbard.
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33. |
- Johnson, Mark D., 1954, et al.
(author)
-
The Ledsjo end moraine-a subaquatic push moraine composed of glaciomarine clay in central Sweden
- 2013
-
In: Proceedings of the Geologists' Association. - : Elsevier BV. - 0016-7878. ; 124:5, s. 738-752
-
Journal article (peer-reviewed)abstract
- During the Younger Dryas cold event, the Scandinavian ice sheet readvanced in southwest Sweden and formed the Middle Swedish end-moraine zone (MSEMZ). Recent highway construction near Skara has created an exposure through the prominent ridge at Ledsjo. Through sketching and measurement of structural information, we have documented the internal character of the Ledsjo moraine. The moraine consists predominantly of clay with numerous sand pods and lenses, which show undeformed, brittle deformed, or fluidized structures. Based on geomorphology and structural geology, it is clear the moraine was made during two advances. As ice advanced, proglacial marine clay was subglacially mobilized by the ice and extruded at the ice margin forming a ramp of debris-flow sediment. Contemporaneously, subglacial meltwater transported sand to the margin, where the meltwater became a buoyant plume, and sand was deposited near the ice margin by currents moving away from as well as toward the ice margin. These processes resulted in interbedded sand and clay. Continued advance of the ice margin deformed this package and further pushed the assemblage into a ridge form with gravity sliding of portions of the ridge. Prior to the second advance, sand was deposited on the proximal side of the initial ridge. During readvance, this sand was thrust faulted and intruded by mobilized clay. Up ice of the intruded sands, subglacial, extensional deformation created a complex shear zone of faulted sand and clay. The Ledsjo moraine represents a subaerial example of submarine push moraines like the submerged moraines recently documented in Svalbard. (c) 2012 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.
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34. |
- Johnson, Mark D., 1954
(author)
-
The status of glacial mapping in Minnesota
- 2004
-
In: Quaternary Glaciations- Extent and Chronology: Part II: North America. - : Elseveir. ; , s. 119-123
-
Book chapter (other academic/artistic)abstract
- A summary of the current status of lithostratigraphy in Minnesota and the development of ice lobes and glacial lakes over the Quaternary.
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35. |
- Johnson, Mark D., 1954, et al.
(author)
-
Unraveling Scandinavian geomorphology: the LiDAR revolution
- 2015
-
In: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 137:4, s. 245-251
-
Journal article (peer-reviewed)abstract
- In the observational sciences, technical advances are often followed by dramatic increases in scientific discoveries and improved theory. Leuwenhoek’s microscope and Galileo’s telescope gave us a “better look” at the microworld and the cosmos, which led to revolutions of past paradigms. In geomorphology and landscape analysis, similar advances have accompanied new maps and new mapping techniques. The first accurate globes, where the puzzle-piece fit of the southern continents was quickly noticed, were soon followed by the first mention of what would be continental drift. The first topographic maps were accompanied by similar shifts in thinking. For example, accurate topographic maps of the western US brought about the realization that even in arid regions, fluvial erosion can be the dominant landscaping force. Aerial photography provided a similar advance in observation, mapping and understanding. Satellite imagery of the Earth and other planets has dramatically revealed the geomorphic processes operating in inaccessible places, for example meteor impacts, volcanism and the importance of eolian and fluvial processes. Recent observations of Pluto and Mars attest to this fact. Satellite imagery also led to a revolution in glacial geomorphology by providing continent-wide images of features heretofore unnoticed, for example the palimpsest flow indicators of the Laurentide Ice Sheet (Boulton & Clark 1990). In the 90s, the production of digital elevation models (DEMs) and the development of geographic information system (GIS) tools allowed for new highly quantitative analysis of landscapes. The advent of LiDAR (Light Detection and Ranging) technology is poised to provide a similar rapid advance in observations and the potential for significant advances in geomorphic theory. We see that the ever increasing use of LiDAR technology is creating a similar leap forward in geomorphology, and this issuie celebrates that.
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36. |
- Johnson, Mark D., 1954, et al.
(author)
-
Varved glaciomarine clay in central Sweden before and the Baltic Ice Lake drainage: a further clue to the drainage event at Mt. Bilingen
- 2013
-
In: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:3-4, s. 293-307
-
Journal article (peer-reviewed)abstract
- Glaciomarine clay found west of Mt Billingen, central Sweden, contains two distinct varve units separated by a sand layer that we interpret to be sediment deposited in the North Sea during the catastrophic drainage of the Baltic Ice Lake (BIL). The lower varve series was deposited proximal to the retreating ice margin and consists of varves that grade upward from gray to red. The upper varve series was deposited after the drainage event when fresh water within the Baltic basin flowed westward north of Billingen; the upper varves grade from red to gray. Grain size, elemental composition (determined by X-ray fluorescence (XRF)), iron and organic-carbon content vary within each varve, with values that grade upward through each varve, but with a sharp contact with the overlying varve. The two varve units differ from each other, with the lower sequence being coarser and the upper containing a higher iron and organic-carbon content. We attribute the differences between pre- and post-drainage varves to reflect changes in distance to the ice margin and provenance. The stratigraphy at the site suggests that the BIL drainage lasted ,1 year. Lithostratigraphic correlations to the Lake La°ngen basin west of Mt Billingen support the idea of glacier ice in the La°ngen basin during the drainage and a retreat and advance of the ice sheet during Allero¨d and Younger Dryas, including the possibility of an earlier, Allero¨d drainage.
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37. |
- Johnson, Mark D., 1954
(author)
-
Världsunikt fynd
- 2010
-
In: Geologiskt Forum. - 1104-4721. ; 17:68, s. 24-25
-
Journal article (other academic/artistic)abstract
- Drumliner har kaptiverat intresse av många geologer och geomorfologer under åren. Över 1500 vetenskapliga artiklar har skrivits just om drumliner, och intresse för deras genes har ökat in senare år eftersom de tros kan vara bevis för snabbrörande (surging eller streaming) glaciärer, som i sin tur, kan berätter hur glaciärer kan påverka och påverkas av klimat under en istid. Trots stor intresse har knapast få drumliner hittats vid nuvarande glaciärar—enstaka drumliner har hittats i Schweiz, Alaska och Island. Men drumliner som lämnats av den stora inlandsisen oftast frankommer i fält med 100-tals till 1000-tals drumliner. Några forskare har påpekats saknandet av nuvarnade drumlinfält och har tyckt att det är konstigt att de inte finns. (En kreationist har påståt att saknandet av nutids drumliner vid glaciärer stödjer hypotesen att de skapats igentiligen inte av isen men av Noachs flod!). Så det var med stor överaskning att vi stötade på det som visade sig vara världens ända aktivdrumlin fält i Island under fältarbete, sommaren 2009. Vi helikopterade in till Muöajökull, en utlopps glaciär från Hofsjökull. Vi var fem geologer från Sverige, Island, Danmark, Scotland, och England, och var plan var att beskriva den utmärkta push-moranen som bildats under lilla istiden, men också för att etablera GPS punkter för fotogrammetric analys av en rad historisk flygbilder, och därför kunna kvantifiera mängder av till som flyttats av Mulajökull när den surging glaciären rycker fram med 20-40 år mellan rum. Dvs, ingen tänkte på drumliner! Vi var beväpnad med senaste flygbilder, men de var från 1995. Därför var det en underbar överaskning under förste dagarnas recognizering att isen, som hade smältat tillbacka en kilometer, hade dagat en äkta drumlinfält bestående av 50+ av dem sked-formade former. Det fanns till och med en eller två drumliner som skurits öppen av erosion för att blotta till och andra sediment som drumlin består av. Under kvällarnas samtalen under de förste dagarna växte realizationen att vi hade hittat någonting viktigt och jätte spännande—världens ända aktiv drumlin fält. En artikel om fältet har nyligen publicerats i tidskriften Geology. Genom analys av den exponerade tillen, kunde vi visa att drumliner troligtvis har skapats progressivt genom deposition och erosion under några glaciär ’surges.’ Vi kan också påstå att fler drumliner finns under isen och att ’surges’ som kommer vill fortsätta att forma drumlinerna, till och med dem som är blottade idag. På detta sättet kan vi säga att drumlin fält är aktiv.
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38. |
- Johnson, Mark D., 1954, et al.
(author)
-
Younger Dryas glaciomarine sedimentation, push-moraine formation and ice-margin behavior in the Middle Swedish end-moraine zone west of Billingen, central Sweden
- 2019
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 224
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Journal article (peer-reviewed)abstract
- New highway exposures and drilling reveal the stratigraphy and structure of the Middle Swedish end-moraine zone west of Billingen, Sweden. The material in the end moraines is primarily glaciomarine clay of Younger Dryas age that was deposited as varved clay in front of the retreating glacier and then pushed glaciotectonically to form push moraines during minor ice-margin oscillations during overall retreat during the Younger Dryas cold event. The moraines are composed of deformed and remobilized clay with some clayey diamicton and penecontemporaneously deposited and deformed sand. Between the moraines lie 'intermoraine flats,' composed of undeformed varved clay of Younger Dryas age and surface sands of Younger Dryas to early Holocene age. Based on estimations of moraine volume, sedimentation rate and ice-margin retreat rates, we calculate the overall ice-margin retreat and end-moraine construction to span 350-800 years within the Younger Dryas. Because the number of moraines in the Middle Swedish end-moraine zone varies across Sweden, we regard the individual oscillations west of Billingen to be driven by local physical and glaciologic factors rather than ice-sheet wide climate drivers. The study area is also the location of the early and final drainages of the Baltic Ice Lake. The final drainage of the Baltic Ice Lake took place several decades after the youngest moraine was formed. We consider it likely that the earlier, Allerod drainage of the Baltic Ice Lake (BIL) also took place at Billingen, despite the lack of clear local stratigraphic evidence. However, based on our model, a retreat driven solely by climate would not have exposed the outlet at Billingen, and we propose a dynamic break-up of the ice-margin likely centered on Valle Harad that was driven by the head difference between the BIL and the sea. (C) 2019 The Authors. Published by Elsevier Ltd.
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39. |
- Johnsson, Andreas, 1977, et al.
(author)
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GEOLOGICALLY RECENT DEBRIS FLOWS IN A WELL-PRESERVED IMPACT CRATER, MARS: INSIGHTS FROM TERRESTRIAL ANALOGS IN SPITSBERGEN, SVALBARD.
- 2011
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In: 42nd Lunar and Planetary Science Conference. ; 42:2541
-
Conference paper (peer-reviewed)abstract
- Gullies on Mars are known to display a range of different morphologies but typically include an alcove, channel and apron. Several processes have been invoked to explain their genesis ranging from grain flow, debris flow to fluvial erosion with alluvial deposition. Albeit there is a general consensus that the medium involved is water, more attention is now drawn towards the dominant depositional processes of the gully fan formation. The observed range of fan morphologies asks for several depositional mechanisms and likely vary at different sites due to regional and local differences in climate and colluvial source material. Studies indicate that the common mechanism is fluvial deposition in contrast to debris flow dominated fans which have only been documented at three sites. These sites formed debris deposits of apparently fine grained dusty mantle material. Here we report on unusual Martian debris flows in an unnamed southern hemisphere crater which is rich in coarse grained colluvial material that forms well preserved debris flows, debris plugs and levees. It also displays numerous fresh looking rock falls. This raises the following questions: Why does so well-developed debris flows occur here and not in other nearby craters? What role does the coarse colluvial material play in debris flow initiation and development? Here we describe the debris flow morphology and we compare the morphology of debris flow deposits in Svalbard as potential terrestrial analogs. Furthermore, we investigate the sieve-deposition model as an explanation for the unusual morphology of these debris deposits.
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40. |
- Johnsson, Andreas, 1977, et al.
(author)
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PRISTINE DEBRIS FLOWS IN A WELL-PRESERVED IMPACT CRATER IN THE AONIA REGION, MARS.
- 2010
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In: EPSC Abstracts 2010. ; 5:EPSC2010-641
-
Conference paper (peer-reviewed)abstract
- Gullies on Mars are known to display a range of different morphologies but typically include an alcove, channel and apron. Several processes have been invoked to explain their genesis ranging from dry granular flows, debris flows to fluvial erosion with alluvial deposition. Albeit there is a general consensus that the medium involved is water, more attention is now drawn towards the dominant depositional processes of the gully fan formation. The observed range of fan morphologies asks for several depositional mechanisms and likely vary at different sites due to regional and local differences in climate and colluvial source material. Studies indicate that the common mechanism is fluvial deposition in contrast to debris flow dominated fans which have only been documented at three sites. These sites formed debris deposits of apparently fine grained dusty mantle material. Here we report on unusual Martian debris flows in an unnamed southern hemisphere crater which is rich in coarse grained colluvial material that forms well preserved debris flows, debris plugs and levees. It also displays numerous fresh looking rock falls. This raises the following questions: Why do so well-developed debris flows occur here and not in other nearby craters? What role does the coarse colluvial material play in debris flow initiation and development? Here we describe the debris flow morphology and we investigate the sieve-deposition model as an explanation for the unusual morphology of these debris deposits.
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41. |
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42. |
- Jónsson, Sverrir Aðalsteinn, et al.
(author)
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The drumlin field and the geomorphology of the Múlajökull surge-type glacier, central Iceland
- 2014
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In: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 207, s. 213-220
-
Journal article (peer-reviewed)abstract
- Here we present a new geomorphological map of the active drumlin field and the forefield of Múlajökull, a surge-type outlet glacier, Iceland. The map is based on aerial photographs taken in 1995 and LiDAR data recorded in 2008. Mapping was done using ArcGIS 10 software on orthorectified imagery, LiDAR data and digital elevation models. The mapped landforms were initially identified on the aerial imagery and LiDAR and then ground-checked in the field. We mapped subglacial, supraglacial, ice-marginal, periglacial, and glaciofluvial landforms. The geomorphology of the Múlajökull forefield is similar to that of the forefields of other surge-type glaciers in Iceland: with a highly streamlined forefield, crevasse-fill ridges, and series of glaciotectonic end moraines. However, the large number (i.e., 110) of drumlins forming the drumlin field is unique for modern Icelandic surge-type glaciers and, as yet, unique for contemporary glaciers in general. Also apparent is that the drumlins are wider and shorter in the distal part of the drumlin field and narrower and longer in the proximal part. Hence, the mapping reveals a development of the drumlins toward a more streamlined shape of the proximal landforms that have experienced more surges. The drumlins in the drumlin field are active, i.e., they form during the modern surges of Múlajökull.
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43. |
- Jonsson, Sverrir, et al.
(author)
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THE MÚLAJÖKULL DRUMLIN FIELD - SEDIMENTOLOGY AND GEOMORPHOLOGY
- 2011
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In: Geological Society of America abstracts with programs Minneapolis 2011.
-
Conference paper (peer-reviewed)abstract
- The drumlin field in front of Múlajökull, a surge-style, outlet glacier from Hofsjökull in Iceland, is the only known active drumlin field (Johnson et al., 2010). The aim of this study is to further explore the formation of drumlins in a modern glacial environment. We use data from geological sections, DEMs, aerial imagery and field mapping. Here we present preliminary results from section logging and geomorphological mapping in the summer of 2011. Geomorphological mapping of the drumlin field both with DEMs and ground proofing has revealed over 100 drumlins and a number of drumlinized ridges. The drumlins furthest from the present ice margin appear broader and have lower relief than those closer to the ice. We suggest that this reflects an evolution of the drumlin form during recurrent surging. The drumlins farther away from the ice have experienced fewer surges than those that have just been uncovered due to retreat of the ice margin. During successive surges, the drumlins become narrower and develop higher relief. In one section close to the present ice margin, we identified at least 9 till beds in the crest of a drumlin, each likely the product of a surge, representing approximately 1/3 of the drumlin relief. The top till bed parallels the drumlin form and truncates the older tills. The older units also dip parallel to the drumlin form, but at a slightly lower angle. We believe that this represents an earlier, broader shape of the drumlin prior to the more recent surges, implying an evolution of form similar to that seen in the evolution in form in the drumlin field. The Múlajökull drumlins have thus grown during surging by erosion on the proximal end and sides of the drumlin followed by accretion of till sheets concentrically on the resulting form.
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44. |
- Lusardi, Barbara A., et al.
(author)
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QUATERNARY STRATIGRAPHY OF MINNESOTA—CHARACTERIZATION AND CORRELATION OF UNITS
- 2011
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In: Geological Society of America abstracts with programs Minneapolis 2011.
-
Conference paper (peer-reviewed)abstract
- Much of Minnesota is covered by Quaternary sediment largely deposited by multiple ice lobes that emanated from different source areas within the Laurentide ice sheet. Subdivision of this sediment sequence as stratigraphic units is ongoing and provides a basis for interpreting the history of glaciation, as well as sedimentation in associated rivers and lakes. In addition, quantitative characterization of the properties of these strata increasingly is needed for applications such as groundwater management. To support characterization and correlation of these sediments, primarily consisting of diamicton interpreted as till, Minnesota Geological Survey staff have built a database of analyses for over 26,000 glacial sediment samples. The database includes location and descriptive information, along with matrix texture as percent sand, silt, and clay. For most samples, the very coarse sand fraction (1-2 mm) is further subdivided on the basis of the percentage of crystalline, carbonate, and shale grains, along with identification of indicator rock types within these groups. Lithologic data are used to assign tills to one of four source areas: shale-rich Riding Mountain provenance to the northwest, carbonate-rich Winnipeg provenance, carbonate-free and Lake-Superior erratic-free Rainy provenance, and finally red sandstone and rhyolite-bearing Superior provenance to the northeast. Recent progress on Minnesota Quaternary stratigraphy suggests that the sediments can be correlated across the state and can be subdivided as follows: old tills and associated sediment including magnetically reversed deposits, the bulk of which are derived from the Winnipeg provenance, but also includes Rainy and Superior provenance units; pre-Sangamonian, Winnipeg-source Browerville Formation which may be older or younger than the Superior-source tills such as the Hawk Creek, Henderson, and River Falls formations; Wisconsinan Traverse des Sioux and associated sediment that is a mix of both Winnipeg and Rainy sources; Rainy provenance sediments including the Independence formation; Superior provenance sediments including the Cromwell and Barnum formations; Riding Mountain provenance sediments mostly consisting of the New Ulm Formation; and sorted sediments such as the deposits of Lake Agassiz.
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45. |
- McCracken, R. G., et al.
(author)
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Origin of the active drumlin field at Mulajokull, Iceland: New insights from till shear and consolidation patterns
- 2016
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 148, s. 243-260
-
Journal article (peer-reviewed)abstract
- Stratigraphic and morphologic data previously collected from the forefleld of Millajokull, Iceland, suggest that its recent surge cycles are responsible for the formation of drumlins there and that their relief reflects both deposition on drumlins and erosion between them. We have tested these ideas and aspects of leading models of drumlin formation by studying past patterns of bed deformation and effective stress in basal tills of the glacier's forefield. Patterns of till strain indicated by the anisotropy of magnetic susceptibility (AMS) of similar to 2300 intact till samples indicate that till was deposited during shear deformation, with shearing azimuths and planes that conform to the drumlin morphology. Thus, till deposition occurred as drumlins grew, in agreement with LiDAR data indicating that the degree of aggradation of the glacier forefleld is largest in areas subjected to the most surges. Previously described unconformities on the drumlin flanks, however, indicate that drumlin relief at Mulajokull has resulted, in part, from erosion. Given that the last surge deposited a till layer both on and between drumlins, a reasonable hypothesis is that erosion between drumlins occurred during normal (quiescent) flow of the glacier between surges. Densities of till samples, analyzed in conjunction with laboratory consolidation tests, indicate that effective stresses on the bed during such periods were on the order of 100 kPa larger between drumlins than within them, an observation consistent with subglacial channels at low water pressure occupying interdrumlin areas. Transport of sediment by turbulent flow in these channels or high effective stress adjacent to them causing enhanced till entrainment in ice or increased depths of bed deformation would promote the sediment flux divergence necessary to erode areas between drumlins. The observation that effective stresses were higher between drumlins than within them is the opposite of that presumed in leading models of drumlin formation. Moreover, the lack of AMS-fabric evidence of longitudinal compression in drumlin tills does not support some models of drumlin formation that invoke negative till-flux gradients in a deforming bed.
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46. |
- Ojala, A. E. K., et al.
(author)
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Ice-sheet scale distribution and morphometry of triangular-shaped hummocks (murtoos): a subglacial landform produced during rapid retreat of the Scandinavian Ice Sheet
- 2019
-
In: Annals of Glaciology. - : Cambridge University Press (CUP). - 0260-3055 .- 1727-5644. ; 60:80, s. 115-126
-
Journal article (peer-reviewed)abstract
- High-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, `murtoo'). Murtoos are typically 30-200 m in length and 30-200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.
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47. |
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48. |
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49. |
- Peterson, Gustaf, 1982, et al.
(author)
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Genesis of hummocks found in tunnel valleys: an example from Horda, southern Sweden
- 2018
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In: Gff. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 140:2, s. 189-201
-
Journal article (peer-reviewed)abstract
- In the south-central sector of the former Fennoscandian Ice Sheet, imprints of the sub-glacial hydrological system are present as glaciofluvial corridors, formed by glacial meltwater at the ice-bed interface during the BOlling-AllerOd warm period. Many of these are interpreted as tunnel valleys and are commonly characterized by hummocks on their valley floors. Contemporary ice sheets produce increased amounts of meltwater as a consequence of global warming, and occasionally it is observed that meltwater is suddenly released from supra- and subglacial lakes, suggesting a highly dynamic subglacial hydraulic system. Studies of the imprints and deposits from such systems on formerly glaciated terrain can expand our knowledge of ice-sheet response to increased meltwater production. Here, we study sediments exposed in two hummocks within the tunnel valley at Horda, south Sweden. One of the investigated hummocks is superposed by a small esker. This hummock consists of a diamict interpreted as a subglacial traction till, observed to be overlain by esker sediment. A second hummock displays deformed sediment at its base, which is glaciotectonically intercalated with above-lying diamict, a sub-glacial traction till. The sub-till sediments, interpreted as proglacial outwash, were deformed by overriding ice. The sediment was dated using optically stimulated luminescence (OSL), inferring a late MIS 4 or early MIS 3 age, congruent with other observations of sub-till sediments in south Sweden. The investigated hummocks on the floor of the Horda tunnel valley are interpreted to have been formed by sub-glacial fluvial erosion simultaneous with tunnel valley formation, most probably during the latest deglaciation of the area.
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50. |
- Peterson, Gustaf, 1982, et al.
(author)
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Glacial geomorphology of the south Swedish uplands – focus on the spatial distribution of hummock tracts
- 2017
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In: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 13:2, s. 534-544
-
Journal article (peer-reviewed)abstract
- We present the first comprehensive glacial-landform map of the south Swedish uplands (SSU), deglaciated 15–13ka ago, using one consistent method and dataset; a Light Detection and Ranging-derived digital elevation model. In particular, this map focuses on the spatial distribution of hummock tracts. The distribution of hummock tracts reinforces previous thinking of a broad lobate east–west zone of hummocks across the southern part of the SSU. But this map also reveals a pattern of hummock tracts confined in what we call hummock corridors that have a radial pattern sub-parallel to the overall ice-flow direction. Hummocks occur in a wide variety of morphologies, but we also show the distribution of two distinct forms: V-shaped hummocks and ‘ribbed moraine’. Cross-cutting relationships between hummocks and glacial lineations indicate a more complex chronology than previously suggested. In places, lineations are overlain by hummocks and in other places hummocks are overlain by lineations. Additionally, directional variation of glacial lineations together with a complex end-moraine pattern suggests a dynamic ice sheet with multiple small lobes. Finally, mapped end moraines help to better correlate the deglacial timescales of western and eastern Sweden.
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