The Ylitornio area in northern Finland is a typical example of a poorly outcropping, multiply deformed, complex Precambrian terrain. U–Pb, Sm-Nd and geochemical data from metavolcanic, metasedimentary and plutonic rocks combined with structural data define the lithodemic units and tectonostratigraphy of the area. The Mellajoki, Martimo, Hosiojoki, Kierovaara and Uusivirka suites form the Ylitornio nappe complex. Although main thrust stacking had occurred between 1.92– 1.89 Ga, later reverse faulting probably continued until 1.78 Ga. The Väystäjä bimodal volcanic rocks (2.09–2.05 Ga) from the Martimo suite are plume-related EMORB-OIB rocks formed during a continent breakup. The Kaskimaa greywacke of the Martimo suite is inferred to represent sedimentation in a deepening rift basin in the continental margin. The coeval Hosiojoki felsic rocks with A-type affinity and the Kierovaara suite granites (2.00–1.98 Ga) represent dry melting of a dominantly 2.1–2.05 Ga contaminated mafic underplate, and hydrous melting of both the mafic underplate and a refractory lower crust of Archean age, respectively. The older rocks of the Uusivirka suite are early-collisional (1.92–1.91 Ga) and derived from poorly mixed local sources, whereas younger psammite-pelite associations (Ristivuoma) are syn-collisional (1.91– 1.89 Ga) and derive from multiply recycled and thoroughly mixed sources. These rocks were deformed during continued collision with the development of foreland foldand
{"title":"Geochemical and U-Pb and Sm-Nd isotopic constraints on the evolution of the Paleoproterozoic Ylitornio nappe complex, northern Fennoscandia","authors":"R. Lahtinen, H. Huhma, L. Lauri, M. Sayab","doi":"10.17741/BGSF/91.1.003","DOIUrl":"https://doi.org/10.17741/BGSF/91.1.003","url":null,"abstract":"The Ylitornio area in northern Finland is a typical example of a poorly outcropping, multiply deformed, complex Precambrian terrain. U–Pb, Sm-Nd and geochemical data from metavolcanic, metasedimentary and plutonic rocks combined with structural data define the lithodemic units and tectonostratigraphy of the area. The Mellajoki, Martimo, Hosiojoki, Kierovaara and Uusivirka suites form the Ylitornio nappe complex. Although main thrust stacking had occurred between 1.92– 1.89 Ga, later reverse faulting probably continued until 1.78 Ga. The Väystäjä bimodal volcanic rocks (2.09–2.05 Ga) from the Martimo suite are plume-related EMORB-OIB rocks formed during a continent breakup. The Kaskimaa greywacke of the Martimo suite is inferred to represent sedimentation in a deepening rift basin in the continental margin. The coeval Hosiojoki felsic rocks with A-type affinity and the Kierovaara suite granites (2.00–1.98 Ga) represent dry melting of a dominantly 2.1–2.05 Ga contaminated mafic underplate, and hydrous melting of both the mafic underplate and a refractory lower crust of Archean age, respectively. The older rocks of the Uusivirka suite are early-collisional (1.92–1.91 Ga) and derived from poorly mixed local sources, whereas younger psammite-pelite associations (Ristivuoma) are syn-collisional (1.91– 1.89 Ga) and derive from multiply recycled and thoroughly mixed sources. These rocks were deformed during continued collision with the development of foreland foldand","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2019-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49001368","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}
Joanna Rychel, B. Woronko, M. Błaszkiewicz, T. Karasiewicz
Formation of dunes in the Płock Basin of the Vistula River valley in Central Poland is connected with the aeolian processes that occurred within the European Sand Belt during the Late Pleistocene. Changes in sedimentation conditions, from fluvial (unit G1), to fluvio–aeolian (unit G2) then to aeolian (unit G3), were respectively recorded in the fluvioglacial terrace sand dune profiles in the village of Goreń Duży (the Płock Basin, Central Poland). Both fluvial and aeolian processes occurred in the periglacial zone of the last glaciation, the northern limit of which is defined by the Last Glacial Maximum (LGM), being 18.4 ka in the Płock Basin. River and ice-marginal valley terrace sand sediments, in association with glacial deposits, could be the source material for the studied aeolian bedforms. The results of morphoscopic analysis of dunal sand quartz grains indicate that rapid deposition occurred more often than did long-term longrange grain transport. Grain transport genesis begins during the Older Dryas, which is confirmed by optically stimulated luminescence (OSL) dating performed for unit G2: 13.06±0.76 ka and 13.54±0.84 ka. During dune formation, dead-ice blocks remained intact in a subglacial channel until the Allerød, which suggests that aeolian processes continued after block melting, throughout the Younger Dryas. Successional aeolian processes have resulted in the extensive dune fields of the Płock Basin.
{"title":"Aeolian processes records within last glacial limit are as based on the Płock Basin case (Central Poland)","authors":"Joanna Rychel, B. Woronko, M. Błaszkiewicz, T. Karasiewicz","doi":"10.17741/BGSF/90.2.007","DOIUrl":"https://doi.org/10.17741/BGSF/90.2.007","url":null,"abstract":"Formation of dunes in the Płock Basin of the Vistula River valley in Central Poland is connected with the aeolian processes that occurred within the European Sand Belt during the Late Pleistocene. Changes in sedimentation conditions, from fluvial (unit G1), to fluvio–aeolian (unit G2) then to aeolian (unit G3), were respectively recorded in the fluvioglacial terrace sand dune profiles in the village of Goreń Duży (the Płock Basin, Central Poland). Both fluvial and aeolian processes occurred in the periglacial zone of the last glaciation, the northern limit of which is defined by the Last Glacial Maximum (LGM), being 18.4 ka in the Płock Basin. River and ice-marginal valley terrace sand sediments, in association with glacial deposits, could be the source material for the studied aeolian bedforms. The results of morphoscopic analysis of dunal sand quartz grains indicate that rapid deposition occurred more often than did long-term longrange grain transport. Grain transport genesis begins during the Older Dryas, which is confirmed by optically stimulated luminescence (OSL) dating performed for unit G2: 13.06±0.76 ka and 13.54±0.84 ka. During dune formation, dead-ice blocks remained intact in a subglacial channel until the Allerød, which suggests that aeolian processes continued after block melting, throughout the Younger Dryas. Successional aeolian processes have resulted in the extensive dune fields of the Płock Basin.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42922240","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 diversity of origins of peatland basins in Central Poland allowed the peatlands to be distinguished by location (in valleys or upland mires) and by the processes forming their basins (e.g. glacigenic, aeolian, fluvial or thermokarst processes). Peats prevail in the structure of the sediments in the analysed basins of peatlands; among them the most predominant are fens, whereas the amount of raised bogs is low. In parts of the analysed objects there are lake sediments, which usually form the bottom sections of the profiles of the biogenic sediments, and were usually deposited in the Late Vistulian. In the Holocene, peat series were accumulated. In the examined peatlands located on morainic uplands, lacustrine sediments of the Late Vistulian and Early Holocene covered by Late Holocene peats are documented. Peatlands located near aeolian forms do not show evidence of continuous accumulation of biogenic deposits. They are particularly sensitive to changes in humidity and they underwent frequent modifications during phases of aeolian activity. The sediments of valley peatlands are not suitable objects for stratigraphic analyses, but they are appropriate for reconstructions of short events that occurred in the river valleys.
{"title":"The diversity of geomorphological features of peatland basins in Central Poland and its paleoecological significance – a review","authors":"J. Forysiak","doi":"10.17741/BGSF/90.2.003","DOIUrl":"https://doi.org/10.17741/BGSF/90.2.003","url":null,"abstract":"The diversity of origins of peatland basins in Central Poland allowed the peatlands to be distinguished by location (in valleys or upland mires) and by the processes forming their basins (e.g. glacigenic, aeolian, fluvial or thermokarst processes). Peats prevail in the structure of the sediments in the analysed basins of peatlands; among them the most predominant are fens, whereas the amount of raised bogs is low. In parts of the analysed objects there are lake sediments, which usually form the bottom sections of the profiles of the biogenic sediments, and were usually deposited in the Late Vistulian. In the Holocene, peat series were accumulated. In the examined peatlands located on morainic uplands, lacustrine sediments of the Late Vistulian and Early Holocene covered by Late Holocene peats are documented. Peatlands located near aeolian forms do not show evidence of continuous accumulation of biogenic deposits. They are particularly sensitive to changes in humidity and they underwent frequent modifications during phases of aeolian activity. The sediments of valley peatlands are not suitable objects for stratigraphic analyses, but they are appropriate for reconstructions of short events that occurred in the river valleys.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44389017","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}
{"title":"Editorial: INQUA Peribaltic Working Group Excursion and Meeting – active cooperation between Quaternary researchers in the Baltic Sea region","authors":"P. Sarala","doi":"10.17741/BGSF/90.2.ED","DOIUrl":"https://doi.org/10.17741/BGSF/90.2.ED","url":null,"abstract":"","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49188745","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}
J. Nitychoruk, Łukasz Zbucki, J. Rychek, B. Woronko, L. Marks
The Neple site is located on a marginal moraine between the valleys of Bug and Krzna rivers in the southern part of the Polish–Belarusian border area. A glacial diamicton is overlain there by glaciofluvial sand and gravel. The glacial diamicton is laminated and, based on petrographic examination, it was ascribed both to the Sanian 2 Glaciation (Elsterian) and the Warta Stadial ice-sheet of the Odranian Glaciation (Saalian). The sediments were glaciotectonically deformed during readvance of the Warta Stadial icesheet. A local stress field was from the northwest and north but it partly encountered resistance from the glacial lobe located in the present-day river-mouth of the Krzna River. Similar glaciotectonic deformations are common also along the southwestern slope of the present Bug River valley, demarcating the maximum extent of the Warta Stadial (Saalian) ice-sheet in this area.
{"title":"Extent and dynamics of the Saalian ice-sheet margin in Neple, eastern Poland","authors":"J. Nitychoruk, Łukasz Zbucki, J. Rychek, B. Woronko, L. Marks","doi":"10.17741/bgsf/90.2.004","DOIUrl":"https://doi.org/10.17741/bgsf/90.2.004","url":null,"abstract":"The Neple site is located on a marginal moraine between the valleys of Bug and Krzna rivers in the southern part of the Polish–Belarusian border area. A glacial diamicton is overlain there by glaciofluvial sand and gravel. The glacial diamicton is laminated and, based on petrographic examination, it was ascribed both to the Sanian 2 Glaciation (Elsterian) and the Warta Stadial ice-sheet of the Odranian Glaciation (Saalian). The sediments were glaciotectonically deformed during readvance of the Warta Stadial icesheet. A local stress field was from the northwest and north but it partly encountered resistance from the glacial lobe located in the present-day river-mouth of the Krzna River. Similar glaciotectonic deformations are common also along the southwestern slope of the present Bug River valley, demarcating the maximum extent of the Warta Stadial (Saalian) ice-sheet in this area.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46003649","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. Rusakov, P. Sorokin, A. Golyeva, L. Savelieva, E. Rusakova, S. Safronov
Investigations of the composition of the buried soils formed on the surface of the kame hill (the northwestern part of the East European Plain, Leningrad region) to which the medieval Izhora burial mound was tied showed that the original soil cover was represented by combinations of automorphic Entic (and/or Albic) Podzols (Lamellic, Arenic). These soils are also characteristic of modern biogeocenoses, which indicates a practically changeless trend of pedogenesis in the average time interval. It was determined that during the construction of the mound and leveling of its surface the soil cover was scalped to a significant degree. The diagenetic changes in soils during the time of their burial (~800 years) were determined. Based on the data of phytolith and spore-pollen analyses it was shown that the original coniferous forest was cut down, partly burnt. Then the site with ash was plowed for cereal crops. After a short time, when the fertility of the soil had decreased, the site was abandoned and began to overgrow with forest (from small-leaved species to coniferous). At this stage, the forest was rebuilt for burial mounds.
{"title":"Soils of a medieval burial mound as a paleoenvironmental archive (Leningrad region, Northwest Russia)","authors":"A. Rusakov, P. Sorokin, A. Golyeva, L. Savelieva, E. Rusakova, S. Safronov","doi":"10.17741/BGSF/90.2.013","DOIUrl":"https://doi.org/10.17741/BGSF/90.2.013","url":null,"abstract":"Investigations of the composition of the buried soils formed on the surface of the kame hill (the northwestern part of the East European Plain, Leningrad region) to which the medieval Izhora burial mound was tied showed that the original soil cover was represented by combinations of automorphic Entic (and/or Albic) Podzols (Lamellic, Arenic). These soils are also characteristic of modern biogeocenoses, which indicates a practically changeless trend of pedogenesis in the average time interval. It was determined that during the construction of the mound and leveling of its surface the soil cover was scalped to a significant degree. The diagenetic changes in soils during the time of their burial (~800 years) were determined. Based on the data of phytolith and spore-pollen analyses it was shown that the original coniferous forest was cut down, partly burnt. Then the site with ash was plowed for cereal crops. After a short time, when the fertility of the soil had decreased, the site was abandoned and began to overgrow with forest (from small-leaved species to coniferous). At this stage, the forest was rebuilt for burial mounds.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43937361","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}
J. Forysiak, Aleksandra Majecka, L. Marks, D. Okupny
In the examined part of central Poland, there are numerous kettle-hole basins filled with mineral and biogenic sediments of the Eemian Interglacial and Early Weichselian. These basins are located in varied geological and geomorphological locations with variable thicknesses of the sediments and deposits. The infillings were investigated by lithological and palaeobotanic methods. Lithology of the biogenic sediments is diverse, primarily gyttja and peat, but also organic silt. A number of the documented sites contain a record of environmental changes throughout the glacial-interglacial cycle from the end of the Warta Stadial (Saalian) to Early Weichselian. Local geological, geomorphological and hydrological conditions influenced the possibility of continuous peat-lake accumulation and the timing of the completion of this accumulation. Biogenic sediments are covered with the Middle and Late Weichselian mineral sediments which indicate climatic changes and are the main reason for rapid and synchronic degradation of kettle-hole infillings.
{"title":"Eemian to Early Weichselian organic deposits in the watershed kettle-hole basins in central Poland","authors":"J. Forysiak, Aleksandra Majecka, L. Marks, D. Okupny","doi":"10.17741/bgsf/90.2.005","DOIUrl":"https://doi.org/10.17741/bgsf/90.2.005","url":null,"abstract":"In the examined part of central Poland, there are numerous kettle-hole basins filled with mineral and biogenic sediments of the Eemian Interglacial and Early Weichselian. These basins are located in varied geological and geomorphological locations with variable thicknesses of the sediments and deposits. The infillings were investigated by lithological and palaeobotanic methods. Lithology of the biogenic sediments is diverse, primarily gyttja and peat, but also organic silt. A number of the documented sites contain a record of environmental changes throughout the glacial-interglacial cycle from the end of the Warta Stadial (Saalian) to Early Weichselian. Local geological, geomorphological and hydrological conditions influenced the possibility of continuous peat-lake accumulation and the timing of the completion of this accumulation. Biogenic sediments are covered with the Middle and Late Weichselian mineral sediments which indicate climatic changes and are the main reason for rapid and synchronic degradation of kettle-hole infillings.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48126591","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}
This study concerns small-scale features in the form of denivation structures, periglacial involutions, sharp-edged blocks, fragipan layers and frost fissures observed in various depositional environments of Central Poland. These are terrestrial evidence for the Vistulian (Weichselian) decline cool-climate intervals (Older Dryas and Younger Dryas). The structures developed in the presence of either permafrost or deep seasonal frost. In this study, the authors analyse their distinctive properties and origins, and their relations to the sedimentary successions and morphogenetic processes. The study demonstrates that the discussed features can be useful supplementary diagnostic markers for the comprehensive reconstruction of cold environmental conditions.
{"title":"Small-scale geologic evidence for Vistulian decline cooling periods: case studies from the Łódź Region (Central Poland)","authors":"D. Dzieduszyńska, J. Petera-Zganiacz","doi":"10.17741/bgsf/90.2.006","DOIUrl":"https://doi.org/10.17741/bgsf/90.2.006","url":null,"abstract":"This study concerns small-scale features in the form of denivation structures, periglacial involutions, sharp-edged blocks, fragipan layers and frost fissures observed in various depositional environments of Central Poland. These are terrestrial evidence for the Vistulian (Weichselian) decline cool-climate intervals (Older Dryas and Younger Dryas). The structures developed in the presence of either permafrost or deep seasonal frost. In this study, the authors analyse their distinctive properties and origins, and their relations to the sedimentary successions and morphogenetic processes. The study demonstrates that the discussed features can be useful supplementary diagnostic markers for the comprehensive reconstruction of cold environmental conditions.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42288861","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}
D. Subetto, S. Shvarev, A. Nikonov, N. Zaretskaya, A. Poleshchuk, M. Potakhin
The territory of investigations is located in the SE periphery of the Fennoscandian Shield. It served as an arena of periodic significant restructuring of the hydrographic network associated with the filling and discharge of large late-glacial and Holocene basins during the degradation of the Scandinavian ice sheet and in postglacial time. One such restructuring is a sudden change of the Saimaa Lake direction of flow in the middle Holocene from the west to south to the Lake Ladoga basin via the drainage hollow, inherited by modern Vuoksi River valley. Origin of the Vuoksi River is associated with the catastrophic water breakthrough of the Saimaa Lake across the marginal ridge Salpausselkä I of about 5.7 cal. kyr BP. This event usually connects with water accumulation and overflow due to non-uniform post-glacial uplift according to modern concepts. The authors propose a great earthquake as the immediate cause of the break waters of Saimaa Lake. This suggestion is based on the study of specific deformations of the rocky riverbed in the area of breakthrough and of the loose deposits in the banks of the Vuoksi River valley downstream. Open cracks and horizontally displaced rock blocks were discovered in the area of the former rapids near town Imatra. Their systematic displacements on the both sides of the rocky gorge indicate the shear kinematics of fault zone. Different types of deformations had occurred in loose sediments of the low terraces (3–4 m) in the Vuoksi River valley and 20–30 km below the headwaters. In three studied stratigraphic sections the three cardinal different types of deformations 276 D. A. Subetto, S. V. Shvarev, A. A. Nikonov, N. E. Zaretskaya, A. V. Poleshchuk and M. S. Potakhin were discovered: 1) normal fault with vertical displacements, 2) tectonic inclination, and 3) traces of catastrophic mudflow. The time diapason of the terrace forming (and of the corresponding deformations) is determined of 8.3 to 1.8 cal. kyr BP (by the ages of adjacent terrace levels), which corresponds to the origination time of the Vuoksi River. The earthquake, which presumably was a trigger for the formation of the Vuoksi River, was generated by the activation of ancient fault zone, manifested in the crystalline foundation. Periodic post-glacial tectonic activity of this zone is revealed in traces of strong seismic events both in the bedrock (initial emergence of the gorge, its renewal during the breakthrough), and in loose deposits (deformations in different levels of
{"title":"New evidence of the Vuoksi River origin by geodynamic cataclysm","authors":"D. Subetto, S. Shvarev, A. Nikonov, N. Zaretskaya, A. Poleshchuk, M. Potakhin","doi":"10.17741/BGSF/90.2.010","DOIUrl":"https://doi.org/10.17741/BGSF/90.2.010","url":null,"abstract":"The territory of investigations is located in the SE periphery of the Fennoscandian Shield. It served as an arena of periodic significant restructuring of the hydrographic network associated with the filling and discharge of large late-glacial and Holocene basins during the degradation of the Scandinavian ice sheet and in postglacial time. One such restructuring is a sudden change of the Saimaa Lake direction of flow in the middle Holocene from the west to south to the Lake Ladoga basin via the drainage hollow, inherited by modern Vuoksi River valley. Origin of the Vuoksi River is associated with the catastrophic water breakthrough of the Saimaa Lake across the marginal ridge Salpausselkä I of about 5.7 cal. kyr BP. This event usually connects with water accumulation and overflow due to non-uniform post-glacial uplift according to modern concepts. The authors propose a great earthquake as the immediate cause of the break waters of Saimaa Lake. This suggestion is based on the study of specific deformations of the rocky riverbed in the area of breakthrough and of the loose deposits in the banks of the Vuoksi River valley downstream. Open cracks and horizontally displaced rock blocks were discovered in the area of the former rapids near town Imatra. Their systematic displacements on the both sides of the rocky gorge indicate the shear kinematics of fault zone. Different types of deformations had occurred in loose sediments of the low terraces (3–4 m) in the Vuoksi River valley and 20–30 km below the headwaters. In three studied stratigraphic sections the three cardinal different types of deformations 276 D. A. Subetto, S. V. Shvarev, A. A. Nikonov, N. E. Zaretskaya, A. V. Poleshchuk and M. S. Potakhin were discovered: 1) normal fault with vertical displacements, 2) tectonic inclination, and 3) traces of catastrophic mudflow. The time diapason of the terrace forming (and of the corresponding deformations) is determined of 8.3 to 1.8 cal. kyr BP (by the ages of adjacent terrace levels), which corresponds to the origination time of the Vuoksi River. The earthquake, which presumably was a trigger for the formation of the Vuoksi River, was generated by the activation of ancient fault zone, manifested in the crystalline foundation. Periodic post-glacial tectonic activity of this zone is revealed in traces of strong seismic events both in the bedrock (initial emergence of the gorge, its renewal during the breakthrough), and in loose deposits (deformations in different levels of","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44857432","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 area under study is located in the south-eastern periphery of the Fennoscandian crystalline shield. At present this is a tectonically quiet region without large seismic events. But it is well known that in post-glacial time the Fennoscandian shield was an arena of active postglacial tectonics and large earthquakes. The evidence for such events was found in various parts of Fennoscandia. The traces left by some paleoearthquakes show an undisputed character of large post-glacial faults some tens of kilometres long and of a few meters in displacement. However, some other features left by earthquakes are under discussion. Numerous deformations in bedrock and in soft sediments which can be considered as being due to earthquakes were found in the Russian Karelia. Interpretation of some of these deformation structures can lead to different conclusions about their origin, for example, weathering, cryogenic, glacial, and gravitational factors. One possible way to overcome these difficulties is an integrated study of different types of deformations at key sites, comparison of these with each other and with the tectonic features of the region, and the search for common structural and kinematic features. Another problem is the estimation of parameters of paleoearthquakes. This problem includes the determinations of their location, intensities, magnitudes, and age. Bulletin of the Geological Society of Finland, Vol. 90, 2018, pp 257–273, https://doi.org/10.17741/bgsf/90.2.009 258 S. V. Shvarev, A. A. Nikonov, M. V. Rodkin, A. V. Poleshchuk The key site under study is located in the northern part of the Karelian Isthmus in the re-activated (during post-glacial time) tectonic zone (the Vuoksi Fault Zone), whose signature in the relief is seen in the form of the straight-line valley of the Vuoksi River. We studied different types of post-glacial seismogenic deformations at this locality. There are seismically induced gravitational and vibrational deformations in solid rock, as well as folds and ruptures in loose sediments. The key site of large deformation examined here includes three zones: 1) the main zone of deformations or the Central Fractured Massif (CFM); 2) the seismically induced colluvial zone; 3) the outer zone of deformations in loose sediments. We have established that all types of deformations are kinematically similar in the CFM and around it (at distances of a few kilometres). A detailed examination of deformations and their spatial and temporal relationships allows us to distinguish three generations of earthquake-induced deformations: 1) Late Glacial, 2) Early Holocene, and 3) Middle to Late Holocene. We estimate the intensities of the respective earthquakes as I=IX, IX, and VII-VIII. Clearly, the intensities decrease from post-glacial to present time, but the recent level of seismicity is unclear and may be much higher than hypothesized. In addition, the evidence for shear kinematics of the fault shows that earthquakes were not only caused
所研究的区域位于芬诺斯坎迪亚水晶盾的东南边缘。目前，这是一个构造平静的地区，没有大的地震事件。但众所周知，在后冰期，芬诺斯坎地盾是活跃的后冰期构造和大地震的舞台。在芬诺斯坎迪亚的各个地方都发现了这些事件的证据。一些古地震留下的痕迹显示出一个无可争议的特征，即大的冰期后断层，长几十公里，位移几米。然而，地震留下的其他一些特征正在讨论中。在俄罗斯卡累利阿发现了基岩和软沉积物中的许多变形，这些变形可以认为是由于地震引起的。对其中一些变形结构的解释可以得出关于其起源的不同结论，例如，风化、低温、冰川和重力因素。克服这些困难的一种可能的方法是对关键地点的不同类型的变形进行综合研究，将这些变形相互比较并与该地区的构造特征进行比较，并寻找共同的结构和运动特征。另一个问题是古地震参数的估计。这个问题包括确定它们的位置、强度、震级和年龄。S. V. Shvarev, A. A. Nikonov, M. V. Rodkin, A. V. Poleshchuk研究的重点地点位于卡累利阿地峡北部(冰川后)重新活跃的构造带(Vuoksi断裂带)，其特征在地形中以Vuoksi河的直线山谷形式出现。研究了该地区不同类型的冰后发震变形。在固体岩石中存在地震引起的重力和振动变形，在松散的沉积物中也存在褶皱和破裂。这里考察的大变形关键部位包括三个区:1)主要变形区或中央断裂地块(CFM);2)地震诱发崩塌带;3)松散沉积物的外变形带。我们已经确定，CFM及其周围(距离几公里)的所有类型的变形在运动学上是相似的。通过对地震变形及其时空关系的详细研究，我们可以区分出3代地震变形:1)晚冰期，2)全新世早期，3)中至晚全新世。我们估计各自地震的烈度为I=IX, IX和VII-VIII。显然，从冰期后到现在，地震强度有所下降，但最近的地震活动水平尚不清楚，可能比假设的要高得多。此外，断层的剪切运动证据表明，地震不仅是由冰后反弹引起的，而且可能是由不同的构造机制引起的，可能与板块构造有关。
{"title":"The active tectonics of the Vuoksi Fault Zone in the Karelian Isthmus: parameters of paleoearthquakes estimated from bedrock and softsediment deformation features","authors":"S. Shvarev, A. Nikonov, M. Rodkin, A. Poleshchuk","doi":"10.17741/BGSF/90.2.009","DOIUrl":"https://doi.org/10.17741/BGSF/90.2.009","url":null,"abstract":"The area under study is located in the south-eastern periphery of the Fennoscandian crystalline shield. At present this is a tectonically quiet region without large seismic events. But it is well known that in post-glacial time the Fennoscandian shield was an arena of active postglacial tectonics and large earthquakes. The evidence for such events was found in various parts of Fennoscandia. The traces left by some paleoearthquakes show an undisputed character of large post-glacial faults some tens of kilometres long and of a few meters in displacement. However, some other features left by earthquakes are under discussion. Numerous deformations in bedrock and in soft sediments which can be considered as being due to earthquakes were found in the Russian Karelia. Interpretation of some of these deformation structures can lead to different conclusions about their origin, for example, weathering, cryogenic, glacial, and gravitational factors. One possible way to overcome these difficulties is an integrated study of different types of deformations at key sites, comparison of these with each other and with the tectonic features of the region, and the search for common structural and kinematic features. Another problem is the estimation of parameters of paleoearthquakes. This problem includes the determinations of their location, intensities, magnitudes, and age. Bulletin of the Geological Society of Finland, Vol. 90, 2018, pp 257–273, https://doi.org/10.17741/bgsf/90.2.009 258 S. V. Shvarev, A. A. Nikonov, M. V. Rodkin, A. V. Poleshchuk The key site under study is located in the northern part of the Karelian Isthmus in the re-activated (during post-glacial time) tectonic zone (the Vuoksi Fault Zone), whose signature in the relief is seen in the form of the straight-line valley of the Vuoksi River. We studied different types of post-glacial seismogenic deformations at this locality. There are seismically induced gravitational and vibrational deformations in solid rock, as well as folds and ruptures in loose sediments. The key site of large deformation examined here includes three zones: 1) the main zone of deformations or the Central Fractured Massif (CFM); 2) the seismically induced colluvial zone; 3) the outer zone of deformations in loose sediments. We have established that all types of deformations are kinematically similar in the CFM and around it (at distances of a few kilometres). A detailed examination of deformations and their spatial and temporal relationships allows us to distinguish three generations of earthquake-induced deformations: 1) Late Glacial, 2) Early Holocene, and 3) Middle to Late Holocene. We estimate the intensities of the respective earthquakes as I=IX, IX, and VII-VIII. Clearly, the intensities decrease from post-glacial to present time, but the recent level of seismicity is unclear and may be much higher than hypothesized. In addition, the evidence for shear kinematics of the fault shows that earthquakes were not only caused","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45771883","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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