Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to this interpretation. The structure has a submarine central mound, which is elevated some 40 m above the adjacent sea floor. It has a very distinct tangential and radial on-shore fracture pattern as seen in the topographic map. Along the southwestern shore of the Bay, an enigmatic quartzite breccia of unknown age occurs as part of a larger outcrop of polymict breccia with clasts of crystalline rocks and quartzite of unknown age. In thin section, planar fractures can be observed in quartz and feldspar grains. A detailed investigation showed that in a few cases the quartz grains contained microdeformation features closely resembling PDFs.
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to
ABSTRACT The Oxisolic Baltic paleosol is a well preserved Neoproterozoic weathering sequence loca... more ABSTRACT The Oxisolic Baltic paleosol is a well preserved Neoproterozoic weathering sequence located in the Russian Platform of the East-European Craton, former Baltica continent. The Baltic paleosol is developed on different host rock types ranging from amphibolites and metagabbros to gneissic rocks and is characterized by up to several metres of thick weathered uppermost residuum composed of kaolinite (>60%), Fe-oxyhydroxides and residual quartz. The mineral index of alteration (MIA) and molecular weathering indices (CIA, CIA − K, PIA) all indicate strong and deep weathering most likely under warm and humid climate. Geochemical climofunctions, although not directly applicable to the Precambrian Baltic paleosol, agree with this interpretation suggesting high mean annual temperatures (>17 °C) and precipitation (1300–1800 mm yr−1) similar to modern day tropical conditions. The age of the weathering is between 560 and 600 Ma. During that time interval the Baltica continent was not drifting at tropical latitudes, but it is plausible that the Baltic paleosol was formed as a consequence of increased weathering rates during greenhouse event(s) possibly related to the termination of the Ediacaran Gaskiers and/or Fauquier glaciations, or in the relation to the Shuram–Wonoka isotope excursion. The Baltic paleosol is most likely one of the few well preserved examples of paleosol formation in the latest Neoproterozoic because it developed in a tectonically stable interior of the Baltica paleocontinent while physical denudation prevailed on other continental blocks due to the build-up of Gondwana that erased weathering profiles from the geological record.
The Neoproterozoic was a time when repeated global cooling events, interrupted by supergreenhouse... more The Neoproterozoic was a time when repeated global cooling events, interrupted by supergreenhouse phases, preceded environmental change toward a modern oxygen-rich atmosphere and the eventual emergence of animal life. Cyclically increased atmospheric CO2 levels intensified weathering of continental silicates, but little is known about the influence of Neoproterozoic climates on soil morphogenesis, which acts as a direct proxy of conditions at the time of formation. However, being typically fragmented in time and space, these mineralic soils (paleosols) had a low preservation potential. An exceptionally well preserved Neoproterozoic deeply weathered paleosol on the Baltica paleocontinent provides new information on weathering during the Precambrian. The kaolinite-Fe-oxyhydroxide composition of this paleosol is indicative of intense weathering in a stable landscape at a time when Baltica was positioned between intermediate to high southern latitudes. It is plausible that this paleosol...
Proc. Estonian Acad. Sci. Geol.. 2004, 53, 3, 149-164 Outlines of the Precambrian basement of Est... more Proc. Estonian Acad. Sci. Geol.. 2004, 53, 3, 149-164 Outlines of the Precambrian basement of Estonia Alvar Soesoo3, Vaino Puurab, Juho Kirsb, Valter Petersellc, Mati Niinc, and Tarmo AllblC ''Institute of Geology at Tallinn University of Technology. Estonia pst. 7, 10143 ...
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to this interpretation. The structure has a submarine central mound, which is elevated some 40 m above the adjacent sea floor. It has a very distinct tangential and radial on-shore fracture pattern as seen in the topographic map. Along the southwestern shore of the Bay, an enigmatic quartzite breccia of unknown age occurs as part of a larger outcrop of polymict breccia with clasts of crystalline rocks and quartzite of unknown age. In thin section, planar fractures can be observed in quartz and feldspar grains. A detailed investigation showed that in a few cases the quartz grains contained microdeformation features closely resembling PDFs.
Abstract— The well-preserved Kärdla impact crater, on Hiiumaa Island, Estonia, is a 4 km diameter... more Abstract— The well-preserved Kärdla impact crater, on Hiiumaa Island, Estonia, is a 4 km diameter structure formed in a shallow Ordovician sea ˜455 Ma ago into a target composed of thin (˜150 m) unconsolidated sedimentary layer above a crystalline basement composed of migmatite granites, amphibolites and gneisses. The fractured and crushed amphibolites in the crater area are strongly altered and replaced with secondary chloritic minerals. The most intensive chloritization is found in permeable breccias and heavily shattered basement around and above the central uplift. Alteration is believed to have resulted from convective flow of hydrothermal fluids through the central areas of the crater. Chloritic mineral associations suggest formation temperatures of 100–300 °C, in agreement with the most frequent quartz fluid inclusion homogenization temperatures of 150–300 °C in allochthonous breccia. The rather low salinity of fluids in Kärdla crater (<13 wt% NaCleq) suggests that the hydrothermal system was recharged either by infiltration of meteoric waters from the crater rim walls raised above sea level after the impact, or by invasion of sea water through the disturbed sedimentary cover and fractured crystalline basement. The well-developed hydrothermal system in Kärdla crater shows that the thermal history of the shock-heated and uplifted rocks in the central crater area, rather than cooling of impact melt or suevite sheets, controlled the distribution and intensity of the impact-induced hydrothermal processes.
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to this interpretation. The structure has a submarine central mound, which is elevated some 40 m above the adjacent sea floor. It has a very distinct tangential and radial on-shore fracture pattern as seen in the topographic map. Along the southwestern shore of the Bay, an enigmatic quartzite breccia of unknown age occurs as part of a larger outcrop of polymict breccia with clasts of crystalline rocks and quartzite of unknown age. In thin section, planar fractures can be observed in quartz and feldspar grains. A detailed investigation showed that in a few cases the quartz grains contained microdeformation features closely resembling PDFs.
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to
ABSTRACT The Oxisolic Baltic paleosol is a well preserved Neoproterozoic weathering sequence loca... more ABSTRACT The Oxisolic Baltic paleosol is a well preserved Neoproterozoic weathering sequence located in the Russian Platform of the East-European Craton, former Baltica continent. The Baltic paleosol is developed on different host rock types ranging from amphibolites and metagabbros to gneissic rocks and is characterized by up to several metres of thick weathered uppermost residuum composed of kaolinite (&gt;60%), Fe-oxyhydroxides and residual quartz. The mineral index of alteration (MIA) and molecular weathering indices (CIA, CIA − K, PIA) all indicate strong and deep weathering most likely under warm and humid climate. Geochemical climofunctions, although not directly applicable to the Precambrian Baltic paleosol, agree with this interpretation suggesting high mean annual temperatures (&gt;17 °C) and precipitation (1300–1800 mm yr−1) similar to modern day tropical conditions. The age of the weathering is between 560 and 600 Ma. During that time interval the Baltica continent was not drifting at tropical latitudes, but it is plausible that the Baltic paleosol was formed as a consequence of increased weathering rates during greenhouse event(s) possibly related to the termination of the Ediacaran Gaskiers and/or Fauquier glaciations, or in the relation to the Shuram–Wonoka isotope excursion. The Baltic paleosol is most likely one of the few well preserved examples of paleosol formation in the latest Neoproterozoic because it developed in a tectonically stable interior of the Baltica paleocontinent while physical denudation prevailed on other continental blocks due to the build-up of Gondwana that erased weathering profiles from the geological record.
The Neoproterozoic was a time when repeated global cooling events, interrupted by supergreenhouse... more The Neoproterozoic was a time when repeated global cooling events, interrupted by supergreenhouse phases, preceded environmental change toward a modern oxygen-rich atmosphere and the eventual emergence of animal life. Cyclically increased atmospheric CO2 levels intensified weathering of continental silicates, but little is known about the influence of Neoproterozoic climates on soil morphogenesis, which acts as a direct proxy of conditions at the time of formation. However, being typically fragmented in time and space, these mineralic soils (paleosols) had a low preservation potential. An exceptionally well preserved Neoproterozoic deeply weathered paleosol on the Baltica paleocontinent provides new information on weathering during the Precambrian. The kaolinite-Fe-oxyhydroxide composition of this paleosol is indicative of intense weathering in a stable landscape at a time when Baltica was positioned between intermediate to high southern latitudes. It is plausible that this paleosol...
Proc. Estonian Acad. Sci. Geol.. 2004, 53, 3, 149-164 Outlines of the Precambrian basement of Est... more Proc. Estonian Acad. Sci. Geol.. 2004, 53, 3, 149-164 Outlines of the Precambrian basement of Estonia Alvar Soesoo3, Vaino Puurab, Juho Kirsb, Valter Petersellc, Mati Niinc, and Tarmo AllblC ''Institute of Geology at Tallinn University of Technology. Estonia pst. 7, 10143 ...
Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnia... more Åvike Bay is a 270° degree wide near-circular, 114 m deep bay on the Swedish coast of the Bothnian Sea, northeast of Sundsvall. The structure has a diameter of about 10 km. It was classified as a probable impact structure because of its extraordinary circular topography in the overwiew of impact structures in Fennoscandia. Recent studies lend further support to this interpretation. The structure has a submarine central mound, which is elevated some 40 m above the adjacent sea floor. It has a very distinct tangential and radial on-shore fracture pattern as seen in the topographic map. Along the southwestern shore of the Bay, an enigmatic quartzite breccia of unknown age occurs as part of a larger outcrop of polymict breccia with clasts of crystalline rocks and quartzite of unknown age. In thin section, planar fractures can be observed in quartz and feldspar grains. A detailed investigation showed that in a few cases the quartz grains contained microdeformation features closely resembling PDFs.
Abstract— The well-preserved Kärdla impact crater, on Hiiumaa Island, Estonia, is a 4 km diameter... more Abstract— The well-preserved Kärdla impact crater, on Hiiumaa Island, Estonia, is a 4 km diameter structure formed in a shallow Ordovician sea ˜455 Ma ago into a target composed of thin (˜150 m) unconsolidated sedimentary layer above a crystalline basement composed of migmatite granites, amphibolites and gneisses. The fractured and crushed amphibolites in the crater area are strongly altered and replaced with secondary chloritic minerals. The most intensive chloritization is found in permeable breccias and heavily shattered basement around and above the central uplift. Alteration is believed to have resulted from convective flow of hydrothermal fluids through the central areas of the crater. Chloritic mineral associations suggest formation temperatures of 100–300 °C, in agreement with the most frequent quartz fluid inclusion homogenization temperatures of 150–300 °C in allochthonous breccia. The rather low salinity of fluids in Kärdla crater (<13 wt% NaCleq) suggests that the hydrothermal system was recharged either by infiltration of meteoric waters from the crater rim walls raised above sea level after the impact, or by invasion of sea water through the disturbed sedimentary cover and fractured crystalline basement. The well-developed hydrothermal system in Kärdla crater shows that the thermal history of the shock-heated and uplifted rocks in the central crater area, rather than cooling of impact melt or suevite sheets, controlled the distribution and intensity of the impact-induced hydrothermal processes.
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