Shock metamorphic features in quartz grains from the Saarijärvi and Söderfjärden impact structures, Finland

Öhman, T.; Preeden, Ulla

doi:10.1111/maps.12112

Cited by 9 publications

(7 citation statements)

References 56 publications

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“…10) indicates earlier cooling of crustal rocks below the PAZ, and, together with the limited erosion of the Sokli carbonatite pipe and the preservation of Early Cambrian sedimentary rocks in the Saarijärvi impact structure in Ostrobothnia ( Fig. 1; Öhman & Preeden, 2013), suggest removal of <2 km of shield rock from above the backslope of the Saariselkä-Karelia escarpment. Within the core area of KAP magmatism (Fig.…”

Section: Synthesismentioning

confidence: 95%

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Hall¹

2015

NJG

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Contrasting views exist on the stability of the Earth's shield regions over the last 1 Ga that have major implications for reconstructing erosion patterns on shields and the supply of sediment to intra-cratonic and marginal basins. This paper explores Phanerozoic denudation rates and patterns on the northern part of the Fennoscandian Shield in the Kola Peninsula, Northwest Russia. This shield region was intruded by magmatic rocks of the Kola Alkaline Province (KAP) in the Devonian and Early Carboniferous. The KAP comprises a varied suite of alkali-ultramafic plutonic and hypabyssal intrusions, diatremes and dykes that was emplaced at various depths in the crust and allows assessment of depths and rates of erosion during and since the KAP magmatic episode. Further evidence of long-term denudation is provided by Mesoproterozoic and Neoproterozoic cover rocks found around the margins of the Kola Peninsula and in the White Sea. The burial and exhumation history is compared to available Apatite Fission Track (AFT) data for the Kola Peninsula and adjacent areas. Post-Devonian denudation rates on the shield rocks of the Kola Peninsula have varied in space and time. Around the periphery of the Kola Peninsula, low long-term denudation of shield rocks is indicated by the survival of Riphean cover rocks and Late Devonian lavas, kimberlite crater facies and near-surface emplacement of dykes. In contrast, in the main belts of KAP intrusions, 4-6 km of rock was removed in response to doming between 460 and 360 Ma. Deep denudation is indicated by the emplacement depths of alkaline intrusions and Phoscorite-Carbonatite pipes (PCPs). Erosion on the Kola Peninsula since 360 Ma has been far more limited. Extensive, shallow, late-stage magmatism associated with PCPs, dykes and the large alkaline intrusions in the KAP indicates that erosion depths nowhere exceeded 2 km. PostDevonian denudation has removed <1 km of rock from the margins of the Kola Peninsula and from the backslope of the Saariselkä-Karelia scarp in northern Finland. AFT data point to an important phase of erosion in the early Mesozoic but depths of unroofing of 3-5 km based on AFT cooling ages for this later phase are in conflict with the evidence of lesser erosion provided by the late-stage KAP intrusions and also require unrealistic depths of former Devonian to Triassic cover rocks. Mean denudation rates were greatest (up to 40 m/Myr) during the KAP magmatic phase. Post-Devonian rates across the Kola Peninsula and adjacent shield areas were much lower (<3-6 m/Myr) and are compatible with low long-term denudation rates for other cratons. Further resolution of long-term denudation patterns and rates on the Kola Peninsula requires the application of low-temperature thermochronometry, detailed examination of the regional geomorphology and firmer dating of ancient weathering episodes.

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Section: Synthesismentioning

confidence: 95%

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Hall¹

2015

NJG

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“…Similar impact crater is also in Taivalkoski, northern Finland where Saarijärvi meteorite crater is filled with unusual occurrence of un-metamorphosed kaolin-bearing clay-, silt-, and sandstones, which were dated to Neoproterozoic of age. Microfossil studies has confirmed a Neoproterozoic (Ediacaran, or Vendian) age of approximately 600 Ma for the kaolin bearing sediments (Öhman & Preeden, 2013;Tynni & Uutela, 1985). So deep weathering in northern Finland may also be of Neoproterozoic age.…”

Section: Earlier Studiesmentioning

confidence: 98%

The inselberg landscape in Finnish Lapland: a morphological study based on the LiDAR data interpretation

Nenonen¹,

Johansson²,

Sallasmaa³

et al. 2018

Bull Geol Soc Finland

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An advanced method to study geomorphology of the well-known inselberg landscape in Finnish Lapland is introduced. Conventionally topographical maps and altitude reference produced from stereographic aerial photographs has been used. Now the LiDAR data has opened a new way to study geomorphology and terrain in detail. We applied the new methods in eastern Finnish Lapland from where seven inselbergs have been identified and analysed. With an accurate elevation data and images we could identify the detailed morphology in the inselbergs and examine the processes that actively alter the terrain. LiDAR data opened a view to the preglacial history and processes. Some preliminary estimations of the rate and amount of preglacial erosion could be made. It seems that erosion rate may have been in order of 2-10 m/Myr in Lapland based on existing datings and stratigraphic observations. Weathering and erosion history in Lapland is long as the kaolinite clays of Late Cenozoic, Mesozoic or even Mesoproterozoic in age are found in the weathered bedrock. Although all disconformities older than the Mesozoic era have probably been eroded to an unidentifiable extent, there is good reason to suppose that the main characteristics of the relief, including inselbergs, originated as early as the Late Cretaceous or at least in the Palaeocene.

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“…2). These samples were also selected from green-grey mudrocks, which at Saarijärvi are distributed chaotically even among closely spaced cores, due to the displacement of megablocks associated with crater formation (see Öhman & Preeden, 2013).…”

Section: Geological Settingmentioning

confidence: 99%

“…Up to 156 m thickness of sediments is preserved within the ~1.5 km diameter crater. These packages of sediment are difficult to correlate even between closely spaced cores, likely as a result of separate cores intersecting different coherent megablocks of sediment arranged in a chaotic way (Hyyppä & Pekkala, 1987;Öhman & Preeden, 2013). The signatures of impact-disruption are evident throughout the cores: Sediments display significant changes in dip direction and angle over relatively short intervals of core depth.…”

Section: Geological Settingmentioning

confidence: 99%

“…Further, fractured angular clasts of basement rock (granite) are found within the sediments at several depths in different cores. Another notable feature is that even among soft lithologies the core material tends to break along shiny, polished surfaces which cut across the bedding; such features may represent subsequent fracturing of the sediments related to tectonism (Öhman & Preeden, 2013). Precise dating of the impact event has been difficult, and there are competing scenarios between a Proterozoic and an early Cambrian age impact hypothesis (see Öhman & Preeden, 2013).…”

Section: Geological Settingmentioning

confidence: 99%

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Late Ediacaran organic microfossils from Finland

Willman

Slater

2021

Geol. Mag.

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Here we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs).

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Shock metamorphic features in quartz grains from the Saarijärvi and Söderfjärden impact structures, Finland

Cited by 9 publications

References 56 publications

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

The inselberg landscape in Finnish Lapland: a morphological study based on the LiDAR data interpretation

Late Ediacaran organic microfossils from Finland

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