John A. Matthews, Henriette Linge, Atle Nesje, Peter Wilson, Richard W. Mourne, Stefan Winkler, Geraint Owen, Jennifer L. Hill, Stefan Haselberger, Jesper Olsen
Surface exposure–age dating was applied to rock surfaces associated with ice-marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here 10Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio-isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar 10Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt-hammer R-values and independent Schmidt-hammer exposure-age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine-ridge morphology and estimates of equilibrium-line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short-lived re-advances of active glaciers, at least the lower reaches of which were warm-based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway.
{"title":"Deglaciation of the highest mountains in Scandinavia at the Younger Dryas–Holocene transition: evidence from surface exposure-age dating of ice-marginal moraines","authors":"John A. Matthews, Henriette Linge, Atle Nesje, Peter Wilson, Richard W. Mourne, Stefan Winkler, Geraint Owen, Jennifer L. Hill, Stefan Haselberger, Jesper Olsen","doi":"10.1111/bor.12644","DOIUrl":"10.1111/bor.12644","url":null,"abstract":"<p>Surface exposure–age dating was applied to rock surfaces associated with ice-marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here <sup>10</sup>Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio-isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar <sup>10</sup>Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt-hammer <i>R</i>-values and independent Schmidt-hammer exposure-age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine-ridge morphology and estimates of equilibrium-line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short-lived re-advances of active glaciers, at least the lower reaches of which were warm-based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12644","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139153699","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marie Holst Riis, Lasse Sander, Lars Nielsen, Jan-Pieter Buylaert, Amélie Juliette Marie Challier, Nicolaj Krog Larsen
Denmark has been subject to complex interactions of isostatic uplift and eustatic sea level changes since the last deglaciation. Prominent coastal beach ridges as well as lagoonal and lake deposits from this period have been investigated at a number of sites in the region to constrain the relative sea level (RSL) changes. However, despite the common occurrence of former coastal lagoons and lakes in proximity to raised beach ridges, they have rarely been studied in combination. In this study, we use a multiproxy approach including geospatial data, lake sediment coring, ground penetrating radar and optically stimulated luminescence dating to investigate the Holocene coastal evolution and RSL history at Rugård in Mols Bjerge National Park, on the east coast of the Jutland Peninsula. Our results show that the coastal area at Rugård was transgressed between c. 7.6 and 7.0 cal. ka BP and that RSL was ~4.5 m higher than present between c. 6.6 and 5.9 ka ago, when the highest section of the beach ridge plain was deposited. The elevation and timing of this relative highstand are in good agreement with previous estimates of the Littorina transgression and contribute to our combined knowledge about RSL history and coastal evolution in the southern Kattegat. Subsequently, isostatic adjustment has caused uplift and erosion of the beach ridge plain, but renewed progradation and deposition of a lower beach plain have taken place since c. 1740 CE. Our results demonstrate the value of using a multiproxy approach to study RSL changes and coastal evolution.
{"title":"Middle and Late Holocene relative sea level changes and coastal development at Rugård, Denmark","authors":"Marie Holst Riis, Lasse Sander, Lars Nielsen, Jan-Pieter Buylaert, Amélie Juliette Marie Challier, Nicolaj Krog Larsen","doi":"10.1111/bor.12642","DOIUrl":"https://doi.org/10.1111/bor.12642","url":null,"abstract":"<p>Denmark has been subject to complex interactions of isostatic uplift and eustatic sea level changes since the last deglaciation. Prominent coastal beach ridges as well as lagoonal and lake deposits from this period have been investigated at a number of sites in the region to constrain the relative sea level (RSL) changes. However, despite the common occurrence of former coastal lagoons and lakes in proximity to raised beach ridges, they have rarely been studied in combination. In this study, we use a multiproxy approach including geospatial data, lake sediment coring, ground penetrating radar and optically stimulated luminescence dating to investigate the Holocene coastal evolution and RSL history at Rugård in Mols Bjerge National Park, on the east coast of the Jutland Peninsula. Our results show that the coastal area at Rugård was transgressed between <i>c.</i> 7.6 and 7.0 cal. ka BP and that RSL was ~4.5 m higher than present between <i>c.</i> 6.6 and 5.9 ka ago, when the highest section of the beach ridge plain was deposited. The elevation and timing of this relative highstand are in good agreement with previous estimates of the Littorina transgression and contribute to our combined knowledge about RSL history and coastal evolution in the southern Kattegat. Subsequently, isostatic adjustment has caused uplift and erosion of the beach ridge plain, but renewed progradation and deposition of a lower beach plain have taken place since <i>c.</i> 1740 CE. Our results demonstrate the value of using a multiproxy approach to study RSL changes and coastal evolution.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12642","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139090867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We conducted a detailed field vegetation investigation combined with the collection of surface soil samples for pollen analysis in the alpine meadow and steppe vegetation zones (30 sites in each zone) in the hinterland of the Tibetan Plateau. Our objectives were to determine the source area of exotic pollen, the relationship between pollen percentages and the cover of the major plant taxa, and the characteristics of the pollen assemblages from surface soils and lake sediments and their vegetation significance. Our principal findings are: (i) the two vegetation zones are herbaceous although arboreal pollen types are present in the related pollen assemblages (2 and 16.8% in the alpine meadow and steppe zones, respectively); (ii) arboreal pollen is assumed to be transported mainly by the Indian monsoon from the forests of the southern Himalayan foothills or river valleys – the spatial distribution of the percentages and concentrations of arboreal pollen in the study sites shows that pollen concentrations have the strongest correlation with the Indian monsoon's variations; (iii) there are regional differences in (a) the relationship between pollen percentages and the cover of the main plant taxa and (b) the indicator plant taxa representative of pollen assemblages and vegetation types zones – the regional vegetation of the study region and pollen productivity variations between plant taxa are likely to be the main causes behind these differences; and (iv) the pollen assemblages from surface soils and lake sediments have similar characteristics and correspond well to the regional vegetation of the alpine meadow zone. In the alpine steppe zone, the pollen assemblages from surface soils and lake sediments are quite different, caused mainly by the over-representation of Artemisia. Our study supplies a detailed description of pollen–vegetation relationships on the hinterland of the Tibetan Plateau and provides scientific references for interpreting stratigraphic pollen assemblages and reconstructing regional vegetation.
{"title":"Modern pollen assemblages from the hinterland of the Tibetan Plateau and their significance for reconstructions of past vegetation","authors":"Linyuan Ma, Zhiguang Li, Qinghai Xu, Hongmei Li, Kailong Zhang, Yuecong Li, Ruchun Zhang, Xianyong Cao, Shengrui Zhang","doi":"10.1111/bor.12641","DOIUrl":"https://doi.org/10.1111/bor.12641","url":null,"abstract":"<p>We conducted a detailed field vegetation investigation combined with the collection of surface soil samples for pollen analysis in the alpine meadow and steppe vegetation zones (30 sites in each zone) in the hinterland of the Tibetan Plateau. Our objectives were to determine the source area of exotic pollen, the relationship between pollen percentages and the cover of the major plant taxa, and the characteristics of the pollen assemblages from surface soils and lake sediments and their vegetation significance. Our principal findings are: (i) the two vegetation zones are herbaceous although arboreal pollen types are present in the related pollen assemblages (2 and 16.8% in the alpine meadow and steppe zones, respectively); (ii) arboreal pollen is assumed to be transported mainly by the Indian monsoon from the forests of the southern Himalayan foothills or river valleys – the spatial distribution of the percentages and concentrations of arboreal pollen in the study sites shows that pollen concentrations have the strongest correlation with the Indian monsoon's variations; (iii) there are regional differences in (a) the relationship between pollen percentages and the cover of the main plant taxa and (b) the indicator plant taxa representative of pollen assemblages and vegetation types zones – the regional vegetation of the study region and pollen productivity variations between plant taxa are likely to be the main causes behind these differences; and (iv) the pollen assemblages from surface soils and lake sediments have similar characteristics and correspond well to the regional vegetation of the alpine meadow zone. In the alpine steppe zone, the pollen assemblages from surface soils and lake sediments are quite different, caused mainly by the over-representation of <i>Artemisia</i>. Our study supplies a detailed description of pollen–vegetation relationships on the hinterland of the Tibetan Plateau and provides scientific references for interpreting stratigraphic pollen assemblages and reconstructing regional vegetation.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12641","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139090782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Coralie André, Dante de Ruijsscher, Wim De Clercq, Frieda Bogemans, Bart Van de Vijver, Annelies Storme, Stephen Louwye
The region of Bruges (Flanders, Belgium) was an economic and cultural centre during the Late Middle Ages because it was connected to the North Sea via a large tidal inlet called the Zwin, along which smaller towns developed. One of these towns was Aardenburg (Zeeland, The Netherlands), which developed from a Roman castellum to become one of the important medieval towns in the hinterland of Bruges. Unfortunately, archaeological, historical and (palaeo)environmental data about the Roman to medieval evolution of the Zwin area are scarce. However, the continuous occupation of Aardenburg during the first millennium AD and its location on a Pleistocene sand ridge bordering the coastal plain provide a unique opportunity to investigate the natural dynamics of the coastal evolution and the interplay with the human impact that shaped the Zwin region before its heyday. The variable character of the depositional environments on the dynamic coastal plain makes local environmental studies essential for understanding larger patterns, which were previously reduced to a simplistic outdated model over the entire region. Palynological and diatom assemblages of two sequences in Aardenburg allow the reconstruction of the terrestrial and aquatic palaeoenvironments from the Middle Holocene to the high Middle Ages. The results reveal landscape evolution in relation to woodlands, peat bogs, coastal environments and human presence, consistent with previous regional landscape evolution. A distinct increase in marine influence during the Roman and early medieval periods, when human activities played a significant role, was followed by an increase in inland indicators from the high medieval period onwards. This evolution is in accordance with the expansion of the town and the reclamation of the coastal landscape as it evolved to become a cultural centre in the Late Middle Ages.
{"title":"The Roman to medieval landscape transformation at Aardenburg (southern The Netherlands) based on palynology and diatom analysis","authors":"Coralie André, Dante de Ruijsscher, Wim De Clercq, Frieda Bogemans, Bart Van de Vijver, Annelies Storme, Stephen Louwye","doi":"10.1111/bor.12640","DOIUrl":"10.1111/bor.12640","url":null,"abstract":"<p>The region of Bruges (Flanders, Belgium) was an economic and cultural centre during the Late Middle Ages because it was connected to the North Sea via a large tidal inlet called the Zwin, along which smaller towns developed. One of these towns was Aardenburg (Zeeland, The Netherlands), which developed from a Roman <i>castellum</i> to become one of the important medieval towns in the hinterland of Bruges. Unfortunately, archaeological, historical and (palaeo)environmental data about the Roman to medieval evolution of the Zwin area are scarce. However, the continuous occupation of Aardenburg during the first millennium AD and its location on a Pleistocene sand ridge bordering the coastal plain provide a unique opportunity to investigate the natural dynamics of the coastal evolution and the interplay with the human impact that shaped the Zwin region before its heyday. The variable character of the depositional environments on the dynamic coastal plain makes local environmental studies essential for understanding larger patterns, which were previously reduced to a simplistic outdated model over the entire region. Palynological and diatom assemblages of two sequences in Aardenburg allow the reconstruction of the terrestrial and aquatic palaeoenvironments from the Middle Holocene to the high Middle Ages. The results reveal landscape evolution in relation to woodlands, peat bogs, coastal environments and human presence, consistent with previous regional landscape evolution. A distinct increase in marine influence during the Roman and early medieval periods, when human activities played a significant role, was followed by an increase in inland indicators from the high medieval period onwards. This evolution is in accordance with the expansion of the town and the reclamation of the coastal landscape as it evolved to become a cultural centre in the Late Middle Ages.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12640","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134902516","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We, the editors, are grateful to all reviewers for their help in processing volume 52 of Boreas.
Jan A. Piotrowski
Nicolaj Krog Larsen
我们,编辑们,感谢所有审稿人在处理Boreas第52卷时给予的帮助。Jan A.PiotrowskiNicolaj Krog Larsen
{"title":"Boreas Reviewers, volume 52","authors":"","doi":"10.1111/bor.12638","DOIUrl":"https://doi.org/10.1111/bor.12638","url":null,"abstract":"<p>We, the editors, are grateful to all reviewers for their help in processing volume 52 of Boreas.</p><p>Jan A. Piotrowski</p><p>Nicolaj Krog Larsen</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12638","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50152194","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Niklas Leicher, Lorenzo Monaco, Biagio Giaccio, Sebastien Nomade, Alison Pereira, Giorgio Mannella, Sabine Wulf, Gianluca Sottili, Danilo M. Palladino, Giovanni Zanchetta, Bernd Wagner
In the lacustrine succession F4-F5 of the Fucino Basin, central Italy, 20 visible tephra layers were identified in the time interval 250–315 ka (Marine Isotope Stages 8–9). Fifteen of them contained suitable material to explore their volcanic sources. Among these tephra some well-known eruptions and eruptive sequences of the Roman and Roccamonfina volcanoes were identified, such as the Tufo Giallo di Sacrofano and the Lower White Trachytic Tuff, respectively. Furthermore, the sediment succession documents a more complex eruptive history of the Sabatini, Vulsini, Colli Albani and Roccamonfina volcanic complexes during the investigated period, as inferred from previously undescribed tephra deposits. Single-crystal-fusion 40Ar/39Ar dating of two of the inspected tephra layers combined with two already published tephra ages provided the basis for a Bayesian age-depth model. The modelled tephra ages allow chronological constraining of so-far undefined eruptions of the Sabatini (272.5±4.7, 281.8±4.7, 308.5±2.8, 312.8±2.1 ka), the Vulsini (311.7±2.3, 311.9±2.3 ka) and the Colli Albani (301.0±3.6 ka) volcanic districts. Two tephra layers of an undefined volcanic source from the Roman volcanoes have modelled ages of 309.5±2.7 and 310.5±2.6 ka. The new 40Ar/39Ar and modelled ages were further used for a reassessment of the timing of already known and dated eruptive units, such as the Tufo Giallo di Sacrofano (40Ar/39Ar: 289.3±4.8 ka). Tephra tentatively correlated with the Valle Santa Maria, Case Pisello and the White Trachytic Tuff Unit E3 or Unit F offer modelled ages for these eruptions of 296.6±3.9, 301.8±3.5 and 303.6±3.4 ka, respectively. The results complete the tephrostratigraphical investigations of the c. 425 ka old F4-F5 record, extend the Mediterranean tephrostratigraphical framework and provide a significant contribution for improving knowledge on Italian volcanic explosive activity.
在意大利中部富奇诺盆地的湖沼演替 F4-F5 中,在 250-315 ka(海洋同位素阶段 8-9)的时间间隔内发现了 20 个可见的凝灰岩层。其中 15 层含有合适的材料来探索其火山来源。在这些火山碎屑中,发现了罗马火山和罗卡蒙菲纳火山的一些著名喷发和喷发序列,如 Tufo Giallo di Sacrofano 火山和下白曲凝灰岩。此外,沉积物演替记录了萨巴蒂尼、武尔西尼、科利阿尔巴尼和罗卡蒙菲娜火山群在调查期间更为复杂的喷发历史,这是从以前未曾描述过的沉积物中推断出来的。对其中两个检查过的沉积层进行的单晶融合 40Ar/39Ar 测定与两个已经公布的沉积层年龄相结合,为贝叶斯年龄深度模型提供了依据。根据建模的表土年龄,可以对迄今尚未确定的萨巴蒂尼(272.5±4.7、281.8±4.7、308.5±2.8、312.8±2.1 ka)、武尔西尼(311.7±2.3、311.9±2.3 ka)和科利阿尔巴尼(301.0±3.6 ka)火山区的喷发进行年代测定。来自罗马火山的两个未确定火山源的火山灰层的模拟年龄分别为 309.5±2.7 ka 和 310.5±2.6 ka。新的 40Ar/39Ar 和模拟年龄被进一步用于重新评估已知的和已确定年代的喷发单元的时间,如 Tufo Giallo di Sacrofano(40Ar/39Ar:289.3±4.8 ka)。与 Valle Santa Maria、Case Pisello 和 White Trachytic Tuff Unit E3 或 Unit F 初步相关的沉积物为这些喷发提供了模拟年龄,分别为 296.6±3.9、301.8±3.5 和 303.6±3.4 ka。这些结果完成了对距今约 425 ka 的 F4-F5 记录的表层岩层学研究,扩展了地中海表层岩层学框架,为增进对意大利火山爆发活动的了解做出了重要贡献。
{"title":"Central Mediterranean tephrochronology for the time interval 250–315 ka derived from the Fucino sediment succession","authors":"Niklas Leicher, Lorenzo Monaco, Biagio Giaccio, Sebastien Nomade, Alison Pereira, Giorgio Mannella, Sabine Wulf, Gianluca Sottili, Danilo M. Palladino, Giovanni Zanchetta, Bernd Wagner","doi":"10.1111/bor.12637","DOIUrl":"10.1111/bor.12637","url":null,"abstract":"<p>In the lacustrine succession F4-F5 of the Fucino Basin, central Italy, 20 visible tephra layers were identified in the time interval 250–315 ka (Marine Isotope Stages 8–9). Fifteen of them contained suitable material to explore their volcanic sources. Among these tephra some well-known eruptions and eruptive sequences of the Roman and Roccamonfina volcanoes were identified, such as the Tufo Giallo di Sacrofano and the Lower White Trachytic Tuff, respectively. Furthermore, the sediment succession documents a more complex eruptive history of the Sabatini, Vulsini, Colli Albani and Roccamonfina volcanic complexes during the investigated period, as inferred from previously undescribed tephra deposits. Single-crystal-fusion <sup>40</sup>Ar/<sup>39</sup>Ar dating of two of the inspected tephra layers combined with two already published tephra ages provided the basis for a Bayesian age-depth model. The modelled tephra ages allow chronological constraining of so-far undefined eruptions of the Sabatini (272.5±4.7, 281.8±4.7, 308.5±2.8, 312.8±2.1 ka), the Vulsini (311.7±2.3, 311.9±2.3 ka) and the Colli Albani (301.0±3.6 ka) volcanic districts. Two tephra layers of an undefined volcanic source from the Roman volcanoes have modelled ages of 309.5±2.7 and 310.5±2.6 ka. The new <sup>40</sup>Ar/<sup>39</sup>Ar and modelled ages were further used for a reassessment of the timing of already known and dated eruptive units, such as the Tufo Giallo di Sacrofano (<sup>40</sup>Ar/<sup>39</sup>Ar: 289.3±4.8 ka). Tephra tentatively correlated with the Valle Santa Maria, Case Pisello and the White Trachytic Tuff Unit E3 or Unit F offer modelled ages for these eruptions of 296.6±3.9, 301.8±3.5 and 303.6±3.4 ka, respectively. The results complete the tephrostratigraphical investigations of the <i>c.</i> 425 ka old F4-F5 record, extend the Mediterranean tephrostratigraphical framework and provide a significant contribution for improving knowledge on Italian volcanic explosive activity.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12637","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136034781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sarah L. Greenwood, Rachael S. Avery, Richard Gyllencreutz, Carl Regnéll, Karol Tylmann
The Baltic Ice Stream, a large fast-flowing sector of the last Fennoscandian Ice Sheet that occupied the present-day Baltic Sea basin, was first conceptualized in the earliest days of glacial geological research in Scandinavia. Landform and sedimentological evidence from the terrestrial margins support the concept and numerical ice-sheet models demonstrate its existence and possible evolution. However, with evidence for the Baltic Ice Stream thus far limited to the terrestrial periphery, its true form, scale, function, and role in deglaciation have proven enigmatic. Here we present geomorphological evidence directly from the Baltic seabed that confirms the existence of and sheds light on the behaviour of the Baltic Ice Stream. Based on an extensive collection of high-, moderate- and low-resolution bathymetric terrain models covering a large proportion of the Baltic Sea floor, and complemented by LiDAR-data for the Baltic islands, we have identified and mapped >20 000 individual subglacial bedforms, meltwater landforms and grounding line landforms. We reconstruct a six-stage sequence of ice flow and retreat, finding that streaming was persistent in the Baltic but that pathways were variable in extent, timing and duration: different sectors of the Baltic exhibit asynchronous streaming and out-of-phase grounding line changes. During deglaciation, grounding line re-advances occurred in both the southwestern and the northern Baltic Proper, and, while abundant iceberg ploughmarks attest to calving as a significant ice loss mechanism, lobate margins suggest supply to the Baltic catchment was consistently high. Our reconstruction is limited by a fragmentary geomorphic record. Here we put forward a first hypothesis for how the Baltic Ice Stream evolved, and hope it stimulates new geomorphic, stratigraphical and core data collection to extend the landform record, provide insights into subglacial and grounding line processes, and constrain the chronology for Baltic Ice Stream flow and retreat.
{"title":"Footprint of the Baltic Ice Stream: geomorphic evidence for shifting ice stream pathways","authors":"Sarah L. Greenwood, Rachael S. Avery, Richard Gyllencreutz, Carl Regnéll, Karol Tylmann","doi":"10.1111/bor.12634","DOIUrl":"10.1111/bor.12634","url":null,"abstract":"<p>The Baltic Ice Stream, a large fast-flowing sector of the last Fennoscandian Ice Sheet that occupied the present-day Baltic Sea basin, was first conceptualized in the earliest days of glacial geological research in Scandinavia. Landform and sedimentological evidence from the terrestrial margins support the concept and numerical ice-sheet models demonstrate its existence and possible evolution. However, with evidence for the Baltic Ice Stream thus far limited to the terrestrial periphery, its true form, scale, function, and role in deglaciation have proven enigmatic. Here we present geomorphological evidence directly from the Baltic seabed that confirms the existence of and sheds light on the behaviour of the Baltic Ice Stream. Based on an extensive collection of high-, moderate- and low-resolution bathymetric terrain models covering a large proportion of the Baltic Sea floor, and complemented by LiDAR-data for the Baltic islands, we have identified and mapped >20 000 individual subglacial bedforms, meltwater landforms and grounding line landforms. We reconstruct a six-stage sequence of ice flow and retreat, finding that streaming was persistent in the Baltic but that pathways were variable in extent, timing and duration: different sectors of the Baltic exhibit asynchronous streaming and out-of-phase grounding line changes. During deglaciation, grounding line re-advances occurred in both the southwestern and the northern Baltic Proper, and, while abundant iceberg ploughmarks attest to calving as a significant ice loss mechanism, lobate margins suggest supply to the Baltic catchment was consistently high. Our reconstruction is limited by a fragmentary geomorphic record. Here we put forward a first hypothesis for how the Baltic Ice Stream evolved, and hope it stimulates new geomorphic, stratigraphical and core data collection to extend the landform record, provide insights into subglacial and grounding line processes, and constrain the chronology for Baltic Ice Stream flow and retreat.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12634","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135858311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michael J. C. Walker, Andrew M. Bauer, Matthew Edgeworth, Erle C. Ellis, Stanley C. Finney, Philip L. Gibbard, Mark Maslin
Current debate on the status and character of the Anthropocene is focussed on whether this interval of geological time should be designated as a formal unit of epoch/series rank in the International Chronostratigraphic Chart/Geological Time Scale, or whether it is more appropriate for it to be considered as an informal ‘event’ comparable in significance with other major transformative events in deeper geological time. The case for formalizing the Anthropocene as a chronostratigraphical unit with a base at approximately 1950 CE is being developed by the Anthropocene Working Group of the Subcommission on Quaternary Stratigraphy. Here we outline the alternative position and explain why the time-transgressive nature of human impact on global environmental systems that is reflected in the recent stratigraphical record means that the Anthropocene is better seen not as a series/epoch with a fixed lower boundary, but rather as an unfolding, transforming and intensifying geological event.
{"title":"The Anthropocene is best understood as an ongoing, intensifying, diachronous event","authors":"Michael J. C. Walker, Andrew M. Bauer, Matthew Edgeworth, Erle C. Ellis, Stanley C. Finney, Philip L. Gibbard, Mark Maslin","doi":"10.1111/bor.12636","DOIUrl":"10.1111/bor.12636","url":null,"abstract":"<p>Current debate on the status and character of the Anthropocene is focussed on whether this interval of geological time should be designated as a formal unit of epoch/series rank in the International Chronostratigraphic Chart/Geological Time Scale, or whether it is more appropriate for it to be considered as an informal ‘event’ comparable in significance with other major transformative events in deeper geological time. The case for formalizing the Anthropocene as a chronostratigraphical unit with a base at approximately 1950 CE is being developed by the Anthropocene Working Group of the Subcommission on Quaternary Stratigraphy. Here we outline the alternative position and explain why the time-transgressive nature of human impact on global environmental systems that is reflected in the recent stratigraphical record means that the Anthropocene is better seen not as a series/epoch with a fixed lower boundary, but rather as an unfolding, transforming and intensifying geological event.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12636","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135197916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Max Engel, Katharina Hess, Sue Dawson, Tasnim Patel, Andreas Koutsodendris, Polina Vakhrameeva, Eckehard Klemt, Philipp Kempf, Isa Schön, Vanessa M. A. Heyvaert
Tsunami deposits around the North Sea basin are needed to assess the long-term hazard of tsunamis. Here, we present sedimentary evidence of the youngest tsunami on the Shetland Islands from Loch Flugarth, a coastal lake on northern Mainland. Three gravity cores show organic-rich background sedimentation with many sub-centimetre-scale sand layers, reflecting recurring storm overwash and a sediment source limited to the active beach and uppermost subtidal zone. A basal 13-cm-thick sand layer, dated to 426–787 cal. a CE based on 14C, 137Cs and Bayesian age–depth modelling, was found in all cores. High-resolution grain-size analysis identified four normally graded or massive sublayers with inversely graded traction carpets at the base of two sublayers. A thin organic-rich ‘mud’ drape and a ‘mud’ cap cover the two uppermost sublayers, which also contain small rip-up clasts. Grain-size distributions show a difference between the basal sand layer and the coarser and better sorted storm layers above. Multivariate statistical analysis of X-ray fluorescence core scanning data also distinguishes both sand units: Zr, Fe and Ti dominate the thick basal sand, while the thin storm layers are high in K and Si. Enriched Zr and Ti in the basal sand layer, in combination with increased magnetic susceptibility, may be related to higher heavy mineral content reflecting an additional marine sediment source below the storm-wave base that is activated by a tsunami. Based on reinterpretation of chronological data from two different published sites and the chronostratigraphy of the present study, the tsunami seems to date to c. 1400 cal. a BP. Although the source of the tsunami remains unclear, the lack of evidence for this event outside of the Shetland Islands suggests that it had a local source and was smaller than the older Storegga tsunami (8.15 cal. ka BP), which affected most of the North Sea basin.
评估海啸的长期危害需要北海盆地周围的海啸沉积物。在这里,我们展示了设得兰群岛最年轻海啸的沉积证据,这些证据来自设得兰群岛北部的一个沿海湖泊--弗鲁加思湖泊(Loch Flugarth)。三个重力岩心显示了富含有机质的背景沉积,其中有许多亚厘米级的沙层,反映了经常性的风暴冲刷以及仅限于活动海滩和最上层潮下带的沉积物来源。根据 14C、137Cs 和贝叶斯年龄-深度模型,在所有岩芯中都发现了厚度为 13 厘米的基底沙层,其年代为公元 426-787 年。高分辨率粒度分析确定了四个正常分级或块状亚层,其中两个亚层底部有反向分级的牵引地毯。最上层的两个亚层上覆盖着一层薄薄的富含有机质的 "泥 "垂和 "泥 "盖,其中还含有小的撕裂碎屑。粒度分布显示,基底砂层与上面较粗且分选较好的风暴层之间存在差异。对 X 射线荧光岩芯扫描数据的多元统计分析也区分了这两个砂层单元:Zr、Fe 和 Ti 在较厚的基底砂层中占主导地位,而较薄的风暴层则含有较多的 K 和 Si。基底砂层中富集的 Zr 和 Ti 以及磁感应强度的增加,可能与重矿物含量较高有关,这反映了海啸激活的风暴潮基底下的额外海洋沉积物来源。根据对两个不同公布地点的年代学数据的重新解释,以及本研究的年代地层学,海啸的年代似乎是大约公元前 1400 年。尽管海啸的源头尚不清楚,但由于设得兰群岛以外地区缺乏有关这一事件的证据,这表明海啸的源头在当地,而且比影响北海盆地大部分地区的更早的斯托雷加海啸(公元前 8.15 千年)要小。
{"title":"Sedimentary evidence of the Late Holocene tsunami in the Shetland Islands (UK) at Loch Flugarth, northern Mainland","authors":"Max Engel, Katharina Hess, Sue Dawson, Tasnim Patel, Andreas Koutsodendris, Polina Vakhrameeva, Eckehard Klemt, Philipp Kempf, Isa Schön, Vanessa M. A. Heyvaert","doi":"10.1111/bor.12635","DOIUrl":"10.1111/bor.12635","url":null,"abstract":"<p>Tsunami deposits around the North Sea basin are needed to assess the long-term hazard of tsunamis. Here, we present sedimentary evidence of the youngest tsunami on the Shetland Islands from Loch Flugarth, a coastal lake on northern Mainland. Three gravity cores show organic-rich background sedimentation with many sub-centimetre-scale sand layers, reflecting recurring storm overwash and a sediment source limited to the active beach and uppermost subtidal zone. A basal 13-cm-thick sand layer, dated to 426–787 cal. a CE based on <sup>14</sup>C, <sup>137</sup>Cs and Bayesian age–depth modelling, was found in all cores. High-resolution grain-size analysis identified four normally graded or massive sublayers with inversely graded traction carpets at the base of two sublayers. A thin organic-rich ‘mud’ drape and a ‘mud’ cap cover the two uppermost sublayers, which also contain small rip-up clasts. Grain-size distributions show a difference between the basal sand layer and the coarser and better sorted storm layers above. Multivariate statistical analysis of X-ray fluorescence core scanning data also distinguishes both sand units: Zr, Fe and Ti dominate the thick basal sand, while the thin storm layers are high in K and Si. Enriched Zr and Ti in the basal sand layer, in combination with increased magnetic susceptibility, may be related to higher heavy mineral content reflecting an additional marine sediment source below the storm-wave base that is activated by a tsunami. Based on reinterpretation of chronological data from two different published sites and the chronostratigraphy of the present study, the tsunami seems to date to <i>c</i>. 1400 cal. a BP. Although the source of the tsunami remains unclear, the lack of evidence for this event outside of the Shetland Islands suggests that it had a local source and was smaller than the older Storegga tsunami (8.15 cal. ka BP), which affected most of the North Sea basin.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12635","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134944122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marcelo Fernandes, Marc Oliva, José María Fernández-Fernández, Gonçalo Vieira, David Palacios, Julia Garcia-Oteyza, Josep Ventura, Irene Schimmelpfennig, ASTER Team
In the highest tributaries of the Upper Garonne Basin, Central Pyrenees, cirques up to 2600 m a.s.l. were already deglaciated by 15–14 ka. The long-term deglaciation during Termination-1 (T-1) was interrupted by glacial advances within the cirques during the Bølling–Allerød (B-A) interstadial and the Younger Dryas stadial. The cirques preserve a variety of glacial and periglacial landforms whose chronologies are poorly known. This study is focused on the Lòcampo cirque (42°38′06″N and 0°59′10″E), Upper Garonne Basin, where a detailed geomorphological map and 10Be terrestrial cosmic ray exposure (CRE) dating allowed us to constrain the chrono-sequence between the glacial and periglacial domains. In the small Lòcampo cirque, a glacier formed a cirque moraine between 2200 and 2300 m a.s.l., which surrounds a relict rock glacier encompassing several transversal ridges. Additionally, longitudinal ridges typically observed in debris-covered glaciers are preserved between the moraine and the rock glacier. The eight-sample data set of CRE ages indicates the formation of the cirque moraine during the second half of the B-A, by 13.2±1.1 ka. Exposure ages from the rock glacier boulders show a range between 13.6±0.9 and 11.9±0.7 ka, which did not allow its formation to be chronologically constrained. Therefore, the environmental evolution following the moraine stabilization could follow the formation of a debris-covered glacier at the bottom of the Lòcampo cirque, with the subsequent formation of the rock glacier. After the rock glacier formation, its front rapidly ceased at 13.6±0.9 ka, while the upper ridges gradually stabilized until it became definitively relict at 11.9±0.7 ka or afterwards. These results show evidence of the complex glacial to periglacial transition that needs more robust chronological data sets to better understand the role of climate forcing and local topography during the deglaciation in mid-latitude mountain environments.
在中比利牛斯山脉上加龙盆地的最高支流中,卷云高达2600个 m a.s.l.在15-14岁时就已经脱了冰 ka。Termination‐1(T‐1)期间的长期冰川消融被Bølling–Allerød(B‐A)间和Younger Dryas体育场期间冰斗内的冰川推进所打断。冰斗保存着各种冰川和冰缘地貌,其年代不详。这项研究的重点是上加龙盆地的Låcampo冰斗(42°38′06〃N和0°59′10〃E),在那里,详细的地貌图和10Be陆地宇宙射线暴露(CRE)测年使我们能够限制冰川域和冰缘域之间的时间序列。在小的Lócampo冰斗中,一座冰川在2200年至2300年间形成了冰斗冰碛 m a.s.l.,它围绕着一个包含几个横向山脊的残留岩石冰川。此外,通常在碎片覆盖的冰川中观察到的纵向山脊保存在冰碛和岩石冰川之间。CRE年龄的八个样本数据集表明,冰碛在B‐A的后半期形成了13.2±1.1 ka。岩石冰川巨石的暴露年龄在13.6±0.9和11.9±0.7之间 ka,不允许其形成受到时间限制。因此,冰碛稳定后的环境演变可能是随着Låcampo冰斗底部碎片覆盖的冰川的形成,以及随后岩石冰川的形成。岩石冰川形成后,其锋面在13.6±0.9处迅速停止 ka,而上脊逐渐稳定,直到11.9±0.7完全恢复 ka或之后。这些结果显示了复杂的冰川-冰缘过渡的证据,需要更可靠的年代数据集来更好地了解中纬度山区环境中冰川消融期间气候强迫和当地地形的作用。
{"title":"Geomorphological record of the glacial to periglacial transition from the Bølling–Allerød to the Holocene in the Central Pyrenees: the Lòcampo cirque in the regional context","authors":"Marcelo Fernandes, Marc Oliva, José María Fernández-Fernández, Gonçalo Vieira, David Palacios, Julia Garcia-Oteyza, Josep Ventura, Irene Schimmelpfennig, ASTER Team","doi":"10.1111/bor.12633","DOIUrl":"10.1111/bor.12633","url":null,"abstract":"<p>In the highest tributaries of the Upper Garonne Basin, Central Pyrenees, cirques up to 2600 m a.s.l. were already deglaciated by 15–14 ka. The long-term deglaciation during Termination-1 (T-1) was interrupted by glacial advances within the cirques during the Bølling–Allerød (B-A) interstadial and the Younger Dryas stadial. The cirques preserve a variety of glacial and periglacial landforms whose chronologies are poorly known. This study is focused on the Lòcampo cirque (42°38′06″N and 0°59′10″E), Upper Garonne Basin, where a detailed geomorphological map and <sup>10</sup>Be terrestrial cosmic ray exposure (CRE) dating allowed us to constrain the chrono-sequence between the glacial and periglacial domains. In the small Lòcampo cirque, a glacier formed a cirque moraine between 2200 and 2300 m a.s.l., which surrounds a relict rock glacier encompassing several transversal ridges. Additionally, longitudinal ridges typically observed in debris-covered glaciers are preserved between the moraine and the rock glacier. The eight-sample data set of CRE ages indicates the formation of the cirque moraine during the second half of the B-A, by 13.2±1.1 ka. Exposure ages from the rock glacier boulders show a range between 13.6±0.9 and 11.9±0.7 ka, which did not allow its formation to be chronologically constrained. Therefore, the environmental evolution following the moraine stabilization could follow the formation of a debris-covered glacier at the bottom of the Lòcampo cirque, with the subsequent formation of the rock glacier. After the rock glacier formation, its front rapidly ceased at 13.6±0.9 ka, while the upper ridges gradually stabilized until it became definitively relict at 11.9±0.7 ka or afterwards. These results show evidence of the complex glacial to periglacial transition that needs more robust chronological data sets to better understand the role of climate forcing and local topography during the deglaciation in mid-latitude mountain environments.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12633","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49230852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}