In this article, we present new glacial geomorphological data from the eastern part of the Kuusamo Ice Lobe (KIL) in eastern Finland. The focus is on glacial lineations (about 9000 individual features) and interpretation of ice lobe evolution based on streamlined erosional and depositional formations, hummocky and ribbed moraines and glaciofluvial formations. Glacial geomorphological mapping was performed based on interpretation and classification of LiDAR data according to the Geological Survey of Finland’s new Glacier Dynamic database. The results revealed that modern surficial deposits were formed during three different ice flow phases. The oldest remains are seen as occasional NW-SE megalineations and unclassified glacially lineated terrains and erosional valleys representing the Middle Weichselian glaciation. The younger morphologies were formed from the two overlapping drumlin fields of the Tuoppajärvi and Kuusamo ice flow phases, with origins in the Late Weichselian deglaciation. Analysis of different erosional and depositional formation patterns was used to separate ice flow phases and estimate the evolution, subglacial conditions and mass balance of KIL during the last deglaciation. The morphological interpretation revealed that the Tuoppajärvi ice flow stage was large and homogeneous, while the later Kuusamo ice flow stage was more concentrated, narrower and heterogeneous, following a fan-type pattern that is also emphasised by the meltwater channel systems, including both erosional and depositional features. Furthermore, on both margins (northern and southern), part of the ice masses formed stagnant areas. The length of the lineations also indicates both glacier flow velocity and transport distances, which in the case of megalineations and drumlins are longer than in the fluted terrain. Ribbed moraines in the western (core part) of KIL indicate a very different depositional environment relating to strong quarrying and short transport distances under cold-based subglacial conditions, near the core area and the late ice divide zone of the Scandinavian Ice Sheet.
{"title":"Evolution of the eastern part of the Kuusamo Ice Lobe, based on geomorphological interpretation of high-resolution LiDAR data","authors":"P. Sarala, J. Räisänen","doi":"10.17741/BGSF/89.2.002","DOIUrl":"https://doi.org/10.17741/BGSF/89.2.002","url":null,"abstract":"In this article, we present new glacial geomorphological data from the eastern part of the Kuusamo Ice Lobe (KIL) in eastern Finland. The focus is on glacial lineations (about 9000 individual features) and interpretation of ice lobe evolution based on streamlined erosional and depositional formations, hummocky and ribbed moraines and glaciofluvial formations. Glacial geomorphological mapping was performed based on interpretation and classification of LiDAR data according to the Geological Survey of Finland’s new Glacier Dynamic database. The results revealed that modern surficial deposits were formed during three different ice flow phases. The oldest remains are seen as occasional NW-SE megalineations and unclassified glacially lineated terrains and erosional valleys representing the Middle Weichselian glaciation. The younger morphologies were formed from the two overlapping drumlin fields of the Tuoppajärvi and Kuusamo ice flow phases, with origins in the Late Weichselian deglaciation. Analysis of different erosional and depositional formation patterns was used to separate ice flow phases and estimate the evolution, subglacial conditions and mass balance of KIL during the last deglaciation. The morphological interpretation revealed that the Tuoppajärvi ice flow stage was large and homogeneous, while the later Kuusamo ice flow stage was more concentrated, narrower and heterogeneous, following a fan-type pattern that is also emphasised by the meltwater channel systems, including both erosional and depositional features. Furthermore, on both margins (northern and southern), part of the ice masses formed stagnant areas. The length of the lineations also indicates both glacier flow velocity and transport distances, which in the case of megalineations and drumlins are longer than in the fluted terrain. Ribbed moraines in the western (core part) of KIL indicate a very different depositional environment relating to strong quarrying and short transport distances under cold-based subglacial conditions, near the core area and the late ice divide zone of the Scandinavian Ice Sheet.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2017-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43809019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Putkinen, N. Eyles, S. Putkinen, A. Ojala, J. Palmu, P. Sarala, T. Väänänen, J. Räisänen, J. Saarelainen, N. Ahtonen, Hannu Rönty, A. Kiiskinen, Tom Rauhaniemi, T. Tervo
Newly available high resolution airborne LiDAR (Light Detection And Ranging) technology is generating unprecedented next-generation imagery of Earth surface features. LiDAR datasets are being employed by the Geological Survey of Finland (GTK) as part of a new national geological initiative (Glacier Dynamic database: GDdatabase) to rapidly and cost-effectively map glacial landforms and sediments left by the last (Late Weichselian) Fennoscandian Ice Sheet (FIS). There is a high demand for such data in hydrogeological, geoengineering and mineral exploration projects and also for the identification of glacial landforms that provide key information regarding ice sheet rheology, growth and decay. An important step forward with this new technique is the recognition of paleoice stream corridors with fast flowing ice (> 3 km yr-1 based on modern ice sheets), surrounded by stagnant or sluggish-flowing ice. Precise geomorphic criteria are now available for recognition of paleo-ice streams, based on the elongation of subglacial streamlined bedforms and the presence of megascale glacial lineations. Flow sets of drumlins and megascale glacial lineations can now be mapped in high resolution using LiDAR and are now seen as genetically related forms in a continuum that records increasing ice flow velocity and the creation of a low friction bed. This paper briefly outlines the nature of the GDdatabase and the methodology behind its construction and provides examples of principal bedform types that record the dynamic interplay of paleo-ice stream lobes in the Finnish sector of the last FIS.
{"title":"High-resolution LiDAR mapping of glacial landforms and ice stream lobes in Finland","authors":"N. Putkinen, N. Eyles, S. Putkinen, A. Ojala, J. Palmu, P. Sarala, T. Väänänen, J. Räisänen, J. Saarelainen, N. Ahtonen, Hannu Rönty, A. Kiiskinen, Tom Rauhaniemi, T. Tervo","doi":"10.17741/BGSF/89.2.001","DOIUrl":"https://doi.org/10.17741/BGSF/89.2.001","url":null,"abstract":"Newly available high resolution airborne LiDAR (Light Detection And Ranging) technology is generating unprecedented next-generation imagery of Earth surface features. LiDAR datasets are being employed by the Geological Survey of Finland (GTK) as part of a new national geological initiative (Glacier Dynamic database: GDdatabase) to rapidly and cost-effectively map glacial landforms and sediments left by the last (Late Weichselian) Fennoscandian Ice Sheet (FIS). There is a high demand for such data in hydrogeological, geoengineering and mineral exploration projects and also for the identification of glacial landforms that provide key information regarding ice sheet rheology, growth and decay. An important step forward with this new technique is the recognition of paleoice stream corridors with fast flowing ice (> 3 km yr-1 based on modern ice sheets), surrounded by stagnant or sluggish-flowing ice. Precise geomorphic criteria are now available for recognition of paleo-ice streams, based on the elongation of subglacial streamlined bedforms and the presence of megascale glacial lineations. Flow sets of drumlins and megascale glacial lineations can now be mapped in high resolution using LiDAR and are now seen as genetically related forms in a continuum that records increasing ice flow velocity and the creation of a low friction bed. This paper briefly outlines the nature of the GDdatabase and the methodology behind its construction and provides examples of principal bedform types that record the dynamic interplay of paleo-ice stream lobes in the Finnish sector of the last FIS.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2017-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47972316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
U–Pb zircon single grain dating using the LA-MC-ICP-MS technique was utilized to determine the age of the host rocks of the Juomasuo Au–Co–Cu deposit located in the late Archean Kuusamo supracrustal belt. Even though the dated samples have diverse geochemical signatures that imply felsic volcanic and sedimentary precursors, the U–Pb data revealed heterogeneous detrital zircon populations for all samples. The host rocks are thus considered to belong to reworked sedimentary/volcano-sedimentary sequences. The maximun depositional ages of the samples fall in the 2.75–2.65 Ga age window, and no Paleoproterozoic ages were recovered in the examined zircon grains (151 analytical spots in total). In addition, a younger population (2.65–2.60 Ga) of internally featureless, BSE-pale/CL-dark zircon and zircon domains, was found in the mineralized sequences. These homogenized zircon grains resemble zircon formed in postmagmatic solid–state processes, in which zircon is recrystallized in metamorphic– hydrothermal conditions. This metamorphic-hydrothermal event most probably occurred in the original provenance area of the metasedimentary rocks.
{"title":"U-Pb zircon ages of the host rocks of the Juomasuo Au-Co-Cu deposit, northeastern Finland","authors":"P. Nikkola, I. Mänttäri, O. T. Rämö","doi":"10.17741/BGSF/89.1.002","DOIUrl":"https://doi.org/10.17741/BGSF/89.1.002","url":null,"abstract":"U–Pb zircon single grain dating using the LA-MC-ICP-MS technique was utilized to determine the age of the host rocks of the Juomasuo Au–Co–Cu deposit located in the late Archean Kuusamo supracrustal belt. Even though the dated samples have diverse geochemical signatures that imply felsic volcanic and sedimentary precursors, the U–Pb data revealed heterogeneous detrital zircon populations for all samples. The host rocks are thus considered to belong to reworked sedimentary/volcano-sedimentary sequences. The maximun depositional ages of the samples fall in the 2.75–2.65 Ga age window, and no Paleoproterozoic ages were recovered in the examined zircon grains (151 analytical spots in total). In addition, a younger population (2.65–2.60 Ga) of internally featureless, BSE-pale/CL-dark zircon and zircon domains, was found in the mineralized sequences. These homogenized zircon grains resemble zircon formed in postmagmatic solid–state processes, in which zircon is recrystallized in metamorphic– hydrothermal conditions. This metamorphic-hydrothermal event most probably occurred in the original provenance area of the metasedimentary rocks.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43321692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Salittu Formation is one of the few metavolcanic successions in the Svecofennian orogen that contain ultramafic rocks. New samples were collected from the picritic and basaltic rocks as well as spatially associated gabbroic rocks, and their major and trace element compositions are presented and discussed here. Although the metavolcanic rocks have experienced primary alteration and two metamorphic events, elements that are insensitive to alteration (rare earth elements, Zr, Nb, Ni) have been used to infer their source and evolution. Based on the similar shapes of the rare earth element patterns in the metabasalt and metapicrite, basaltic melt derived from picritic one by fractional crystallization. The high Ni and Mg contents, Ni/MgO and Zr/Nb ratios, and multielement patterns make a slightly enriched garnet lherzolite a likely source for the metapicrite. With the exception of synvolcanic gabbros within the metavolcanic rocks, the gabbroic intrusions at Salittu have no genetic link to the metavolcanic rocks. Geochemical comparison with modern basalts suggests that the picritic and basaltic melts were generated in a mature arc environment during a rifting event. Picritic melt rose from convective mantle to the crust and formed a magma chamber. Basaltic melt fractionated in the chamber and extruded upon an earlier formed volcanic pile as basalt and synvolcanic gabbro. Soon after extrusion of the basalt, picritic melts, similar in composition to the earlier picrite, rose through the crust and extruded on top of the basalt. Comparison with three other metapicrite occurrences in southern Finland suggests that although the occurrences may be considered broadly comagmatic, each had their specific sources and probably also tectonic environments during emplacement.
{"title":"The Salittu Formation in southwestern Finland, part II: Picritic-basaltic volcanism in mature arc environment","authors":"M. Nironen","doi":"10.17741/BGSF/89.1.001","DOIUrl":"https://doi.org/10.17741/BGSF/89.1.001","url":null,"abstract":"The Salittu Formation is one of the few metavolcanic successions in the Svecofennian orogen that contain ultramafic rocks. New samples were collected from the picritic and basaltic rocks as well as spatially associated gabbroic rocks, and their major and trace element compositions are presented and discussed here. Although the metavolcanic rocks have experienced primary alteration and two metamorphic events, elements that are insensitive to alteration (rare earth elements, Zr, Nb, Ni) have been used to infer their source and evolution. Based on the similar shapes of the rare earth element patterns in the metabasalt and metapicrite, basaltic melt derived from picritic one by fractional crystallization. The high Ni and Mg contents, Ni/MgO and Zr/Nb ratios, and multielement patterns make a slightly enriched garnet lherzolite a likely source for the metapicrite. With the exception of synvolcanic gabbros within the metavolcanic rocks, the gabbroic intrusions at Salittu have no genetic link to the metavolcanic rocks. Geochemical comparison with modern basalts suggests that the picritic and basaltic melts were generated in a mature arc environment during a rifting event. Picritic melt rose from convective mantle to the crust and formed a magma chamber. Basaltic melt fractionated in the chamber and extruded upon an earlier formed volcanic pile as basalt and synvolcanic gabbro. Soon after extrusion of the basalt, picritic melts, similar in composition to the earlier picrite, rose through the crust and extruded on top of the basalt. Comparison with three other metapicrite occurrences in southern Finland suggests that although the occurrences may be considered broadly comagmatic, each had their specific sources and probably also tectonic environments during emplacement.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48278523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Paleoproterozoic Pados-Tundra ultramafic complex, ~6 x 1.5–2.1 km in size and ~2.1 Ga in age, located in the Kola Peninsula of Russia, is the main representative of the Serpentinite belt in the northern Fennoscandian Shield. It is composed of fragmented or foliated bodies of dunite–harzburgite –orthopyroxenite; these have an elevated potential for Cr and the platinum-group elements (PGE). In general, the complex consists of the Dunite Zone (olivine cumulates) and Orthopyroxenite Zone (orthopyroxene + olivine cumulates, interlayered); its upper zones of more evolved rocks of mafic compositions appear to have been removed by erosion. The complex shows well-recognized patterns of cryptic layering, documented along cross-sections in grains of olivine and Ca-poor pyroxene. Narrow ranges of high-Mg compositions are observed in olivine [Fo85.5–90.6] and orthopyroxene [Wo<0.1–3.0En85.1–91.2Fs8.1–12.5]. Their trends of crystallization indicate that cumulate olivine, orthopyroxene, and olivine–orthopyroxene rocks (dunite and orthopyroxenite, with subordinate harzburgite and olivine-bearing orthopyroxenite) become, in general, more evolved toward the internal portions of the complex; stratigraphically lower and early-crystallizing cumulates are exposed closer to its outer contact. The compositions of early phases of cumulus origin, Fo91 olivine and En91, orthopyroxene are notably magnesian, implying an elevated Mg# in the parental magma. The anomalously Cr–Al-rich grains of serpentine (up to ~2.5 wt.% Cr2O3 and ~4.0wt.% Al2O3), hitherto unreported, are present in specimens of dunite near the northeastern margin of the complex. Supercooling and metastable crystallization likely affected the melt in the eastern portion of the complex near the Dunite block (i.e., host for segregations and stratiform-like layers of chromitite) and relatively close to the outer contact. An uncommon mineralization of the PGE is associated with the chromitite deposits at Pados-Tundra.
{"title":"The structure and cryptic layering of the Pados-Tundra ultramafic complex, Serpentinite belt, Kola Peninsula, Russia","authors":"A. Barkov, A. A. Nikiforov, R. Martin","doi":"10.17741/BGSF/89.1.003","DOIUrl":"https://doi.org/10.17741/BGSF/89.1.003","url":null,"abstract":"The Paleoproterozoic Pados-Tundra ultramafic complex, ~6 x 1.5–2.1 km in size and ~2.1 Ga in age, located in the Kola Peninsula of Russia, is the main representative of the Serpentinite belt in the northern Fennoscandian Shield. It is composed of fragmented or foliated bodies of dunite–harzburgite –orthopyroxenite; these have an elevated potential for Cr and the platinum-group elements (PGE). In general, the complex consists of the Dunite Zone (olivine cumulates) and Orthopyroxenite Zone (orthopyroxene + olivine cumulates, interlayered); its upper zones of more evolved rocks of mafic compositions appear to have been removed by erosion. The complex shows well-recognized patterns of cryptic layering, documented along cross-sections in grains of olivine and Ca-poor pyroxene. Narrow ranges of high-Mg compositions are observed in olivine [Fo85.5–90.6] and orthopyroxene [Wo<0.1–3.0En85.1–91.2Fs8.1–12.5]. Their trends of crystallization indicate that cumulate olivine, orthopyroxene, and olivine–orthopyroxene rocks (dunite and orthopyroxenite, with subordinate harzburgite and olivine-bearing orthopyroxenite) become, in general, more evolved toward the internal portions of the complex; stratigraphically lower and early-crystallizing cumulates are exposed closer to its outer contact. The compositions of early phases of cumulus origin, Fo91 olivine and En91, orthopyroxene are notably magnesian, implying an elevated Mg# in the parental magma. The anomalously Cr–Al-rich grains of serpentine (up to ~2.5 wt.% Cr2O3 and ~4.0wt.% Al2O3), hitherto unreported, are present in specimens of dunite near the northeastern margin of the complex. Supercooling and metastable crystallization likely affected the melt in the eastern portion of the complex near the Dunite block (i.e., host for segregations and stratiform-like layers of chromitite) and relatively close to the outer contact. An uncommon mineralization of the PGE is associated with the chromitite deposits at Pados-Tundra.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48762695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A multiple till succession at Koivusaarenneva in Central Ostrobothnia, adjacent to the Gulf of Bothnia, was studied using conventional sedimentological techniques. In addition, a sand-rich unit between two till beds was dated by the Optical Stimulated Luminescence (OSL) method and organic-bearing silt was subjected to pollen analysis. The methods were applied to determine the Pleistocene sedimentation history of the area. The results obtained indicate that the lowest till above the crystalline bedrock at Koivusaarenneva was deposited from the NNW during the Saalian glaciation, whereas the organic-bearing sediments and deformed sand and silt above, were laid down during the Eemian and the Early Weichselian stages. Two till beds above the Early Weichselian sediments indicate that at least two separate Scandinavian Ice Sheet advances took place in the area, most likely in the early Middle Weichselian and the Late Weichselian
{"title":"Stratigraphy of the Koivusaarenneva exposure and its correlation across central Ostrobothnia, Finland","authors":"J. Lunkka, P. Lintinen, K. Nenonen, P. Huhta","doi":"10.17741/BGSF/88.2.001","DOIUrl":"https://doi.org/10.17741/BGSF/88.2.001","url":null,"abstract":"A multiple till succession at Koivusaarenneva in Central Ostrobothnia, adjacent to the Gulf of Bothnia, was studied using conventional sedimentological techniques. In addition, a sand-rich unit between two till beds was dated by the Optical Stimulated Luminescence (OSL) method and organic-bearing silt was subjected to pollen analysis. The methods were applied to determine the Pleistocene sedimentation history of the area. The results obtained indicate that the lowest till above the crystalline bedrock at Koivusaarenneva was deposited from the NNW during the Saalian glaciation, whereas the organic-bearing sediments and deformed sand and silt above, were laid down during the Eemian and the Early Weichselian stages. Two till beds above the Early Weichselian sediments indicate that at least two separate Scandinavian Ice Sheet advances took place in the area, most likely in the early Middle Weichselian and the Late Weichselian","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2016-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67631311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Amon, L. Saarse, J. Vassiljev, A. Heinsalu, S. Veski
In this study, the deglaciation chronology of the Pandivere Upland is defined, and the late-glacial vegetation trends of north-eastern Estonia are summarised. The multi-proxy study includes accelerated mass spectrometry 14C dating, plant macrofossil, magnetic susceptibility, loss-on-ignition and grain-size distribution data of the lacustrine sediment record from one previously unpublished study site (Kursi), and the study discusses the results in combination with five previously published study locations from the area. The results indicate that the deglaciation of the Pandivere Upland started at approximately 14 200 cal. yr BP and was completed by 13 800 cal. yr BP. The ice recession rate was approximately 180 m yr-1. Based on these new radiocarbon dates, the Baltic Ice Lake stage A1 submerged the northern and western ice-free areas of Estonia by ca. 13 800 cal. yr BP. The prevalent vegetation type in north-eastern Estonia during the late-glacial period was tundra with local variations in the dominant shrub species. The region remained treeless until the Holocene.
本研究确定了Pandivere高地的消冰年代学，总结了爱沙尼亚东北部晚冰期植被的变化趋势。多代理研究包括加速质谱14C测年、植物宏观化石、磁化率、着火损失和湖泊沉积物粒度分布数据，这些数据来自一个以前未发表的研究地点(Kursi)，该研究结合该地区五个以前发表的研究地点讨论了结果。结果表明，pandiwe高地的消冰作用开始于14 200 cal. yr BP，结束于13 800 cal. yr BP。冰退缩速率约为1.8 m年-1。根据这些新的放射性碳年代，波罗的海冰湖A1阶段在大约13800 calybp之前淹没了爱沙尼亚的北部和西部无冰区。爱沙尼亚东北部晚冰期植被类型以冻土带为主，灌木种类在不同地区存在差异。该地区直到全新世都没有树木。
{"title":"Timing of the deglaciation and the late-glacial vegetation development on the Pandivere Upland, North Estonia","authors":"L. Amon, L. Saarse, J. Vassiljev, A. Heinsalu, S. Veski","doi":"10.17741/BGSF/88.2.002","DOIUrl":"https://doi.org/10.17741/BGSF/88.2.002","url":null,"abstract":"In this study, the deglaciation chronology of the Pandivere Upland is defined, and the late-glacial vegetation trends of north-eastern Estonia are summarised. The multi-proxy study includes accelerated mass spectrometry 14C dating, plant macrofossil, magnetic susceptibility, loss-on-ignition and grain-size distribution data of the lacustrine sediment record from one previously unpublished study site (Kursi), and the study discusses the results in combination with five previously published study locations from the area. The results indicate that the deglaciation of the Pandivere Upland started at approximately 14 200 cal. yr BP and was completed by 13 800 cal. yr BP. The ice recession rate was approximately 180 m yr-1. Based on these new radiocarbon dates, the Baltic Ice Lake stage A1 submerged the northern and western ice-free areas of Estonia by ca. 13 800 cal. yr BP. The prevalent vegetation type in north-eastern Estonia during the late-glacial period was tundra with local variations in the dominant shrub species. The region remained treeless until the Holocene.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2016-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67631415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Because of the relatively low metamorphic grade, low strain and well-preserved early structures in volcanic and volcaniclastic rocks, the Orijärvi triangle (in the center of the larger Orijärvi area) is one of the few locations in the Svecofennian orogen of southern Finland where lithostratigraphy has been determined. The geochemistry of the picriticbasaltic metavolcanic rocks of the Salittu Formation, located in the northeastern part of the Orijärvi area, has been characterized but otherwise the bedrock and structures have been barely touched. After remapping we give an interpretation of structural evolution, provide new age data to constrain duration of volcanism at Salittu, and refine the stratigraphy in the Orijärvi area. The original stratigraphy is visible at Salittu: metabasalt overlies migmatitic gneisses, and metapicrite is on top. The rocks were folded during early Svecofennian D1–D2 deformations, and the large synformal structures developed as D2–D5 interference structures formed during late Svecofennian D5 deformation. The structural pattern at Salittu is much the same as in the Orijärvi triangle. The new age data, combined with earlier published data, constrains the Salittu volcanism at ca. 1875 Ma. The stratigraphy in the Orijärvi area consists of the early (1.90–1.89 Ga) volcanic Orijärvi Formation, overlain by the sedimentary Vetio Formation, the volcanic Kisko Formation, the volcanic-sedimentary Ahdisto Formation, the volcanic Toija Formation, and on top the Salittu Formation, all emplaced at 1.88–1.87 Ga. We propose a model in which the Orijärvi Formation represents magmatism at the margin of a microcontinent, and the overlying package represents sedimentation and magmatism above a subduction zone during an initial stage of microcontinental accretion. D1 deformation occurred in an advanced stage of accretion, after emplacement of the volcanic rocks of the Salittu Formation.
{"title":"The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy","authors":"M. Nironen, I. Mänttäri, M. Väisänen","doi":"10.17741/BGSF/88.2.003","DOIUrl":"https://doi.org/10.17741/BGSF/88.2.003","url":null,"abstract":"Because of the relatively low metamorphic grade, low strain and well-preserved early structures in volcanic and volcaniclastic rocks, the Orijärvi triangle (in the center of the larger Orijärvi area) is one of the few locations in the Svecofennian orogen of southern Finland where lithostratigraphy has been determined. The geochemistry of the picriticbasaltic metavolcanic rocks of the Salittu Formation, located in the northeastern part of the Orijärvi area, has been characterized but otherwise the bedrock and structures have been barely touched. After remapping we give an interpretation of structural evolution, provide new age data to constrain duration of volcanism at Salittu, and refine the stratigraphy in the Orijärvi area. The original stratigraphy is visible at Salittu: metabasalt overlies migmatitic gneisses, and metapicrite is on top. The rocks were folded during early Svecofennian D1–D2 deformations, and the large synformal structures developed as D2–D5 interference structures formed during late Svecofennian D5 deformation. The structural pattern at Salittu is much the same as in the Orijärvi triangle. The new age data, combined with earlier published data, constrains the Salittu volcanism at ca. 1875 Ma. The stratigraphy in the Orijärvi area consists of the early (1.90–1.89 Ga) volcanic Orijärvi Formation, overlain by the sedimentary Vetio Formation, the volcanic Kisko Formation, the volcanic-sedimentary Ahdisto Formation, the volcanic Toija Formation, and on top the Salittu Formation, all emplaced at 1.88–1.87 Ga. We propose a model in which the Orijärvi Formation represents magmatism at the margin of a microcontinent, and the overlying package represents sedimentation and magmatism above a subduction zone during an initial stage of microcontinental accretion. D1 deformation occurred in an advanced stage of accretion, after emplacement of the volcanic rocks of the Salittu Formation.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2016-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67631518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Barkov, A. A. Nikiforov, T. Halkoaho, J. Konnunaho
We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of “normal spheroidal weathering” sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo87.5), which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. %) are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96) formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts) during a deuteric (autometasomatic) alteration. In contrast, oikocrystic Opx (En86.0) is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr) are observed. We infer that (1) the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2) Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3) The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions.
{"title":"The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia","authors":"A. Barkov, A. A. Nikiforov, T. Halkoaho, J. Konnunaho","doi":"10.17741/BGSF/88.2.004","DOIUrl":"https://doi.org/10.17741/BGSF/88.2.004","url":null,"abstract":"We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of “normal spheroidal weathering” sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo87.5), which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. %) are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96) formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts) during a deuteric (autometasomatic) alteration. In contrast, oikocrystic Opx (En86.0) is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr) are observed. We infer that (1) the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2) Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3) The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2016-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67631616","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Kotilainen, I. Mänttäri, M. Kurhila, P. Hölttä, O. T. Rämö
The Vaasa batholith, western Finland, is a large, peraluminous granitoid pluton that crystallized at 1.88–1.87 Ga during the culmination of the Svecofennian orogeny. The batholith has gradual contacts, through metatexites and diatexites, with the enveloping metasedimentary rocks of the Bothnian Belt. We present ID-TIMS U-Pb age data on monazite from granitoids and xenoliths of the Vaasa batholith and combine these with published U–Pb zircon ages in order to shed further light on the evolution of the Vaasa batholith. The apparent monazite ages for seven of the examined samples are 1870–1863 Ma, and 1855±3 Ma for one further sample from the southern part of the batholith. Combined with pre-existing data, the monazite ages of the granitoids are 9 to 18 Ma (face values) or 3 to 9 Ma (external errors considered) younger than the U–Pb zircon crystallization ages from respective samples. Our new data suggest slow cooling for the Vaasa batholith – the closure/saturation temperature of the monazite U–Pb system was probably reached in ~10 m.y. after the crystallization of magmatic zircon in the examined rocks.
{"title":"New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland","authors":"A. Kotilainen, I. Mänttäri, M. Kurhila, P. Hölttä, O. T. Rämö","doi":"10.17741/BGSF/88.1.001","DOIUrl":"https://doi.org/10.17741/BGSF/88.1.001","url":null,"abstract":"The Vaasa batholith, western Finland, is a large, peraluminous granitoid pluton that crystallized at 1.88–1.87 Ga during the culmination of the Svecofennian orogeny. The batholith has gradual contacts, through metatexites and diatexites, with the enveloping metasedimentary rocks of the Bothnian Belt. We present ID-TIMS U-Pb age data on monazite from granitoids and xenoliths of the Vaasa batholith and combine these with published U–Pb zircon ages in order to shed further light on the evolution of the Vaasa batholith. The apparent monazite ages for seven of the examined samples are 1870–1863 Ma, and 1855±3 Ma for one further sample from the southern part of the batholith. Combined with pre-existing data, the monazite ages of the granitoids are 9 to 18 Ma (face values) or 3 to 9 Ma (external errors considered) younger than the U–Pb zircon crystallization ages from respective samples. Our new data suggest slow cooling for the Vaasa batholith – the closure/saturation temperature of the monazite U–Pb system was probably reached in ~10 m.y. after the crystallization of magmatic zircon in the examined rocks.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2016-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67631505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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