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Sökning: WFRF:(Dahlqvist Peter)

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34.
  • Dahlqvist, Peter (författare)
  • Late Ordovician-Early Silurian facies development and stratigraphy of Jämtland, central Sweden
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis is based on studies of Lower Palaeozoic sedimentary successions within the central Scandinavian Caledonides. These deposits have been transported by considerable nappe displacement (several kilometres), and are today relatively isolated from the nearest coeval outcrops (Dalarna 250 km, Oslo Region 350 km). As a consequence, and due to the previously limited biostratigraphical control the investigated area have received little attention the last decades. Therefore, a detailed investigation, using several untried geological tools was performed. During the study it became clear that the strata reflected substantial changes in depositional environment and complexity in lateral facies relationship during the Late Ordovician?Early Silurian. This was a time characterised by global environmental changes such as glacio-eustasy and climate change, in particular during the end-Ordovician (Hirnantian) glaciation. Facies and sequence stratigraphical analysis of two key units (the Ede Quartzite and the Kyrkås Quartzite) and their preceding and succeeding units resulted in reinterpretations and refinement of the stratigraphy. The new data implied that the successions could be linked to known Hirnantian sea-level fluctuations. This correlation was subsequently supported, and our understanding of the timing of changes was improved, by biostratigraphical evidence (conodonts, graptolites, and brachiopods). This revealed a ca 5 myr stratigraphical gap, within the Ede Quartzite, spanning the Ordovician?Silurian boundary. It is concluded that the interaction of allocyclic changes (sea level and climate) were the overriding controls on deposition during the Late Ordovician?Early Silurian in the Jämtland basin. The contrasting sedimentary architecture of the Ede Quartzite to the west and the partly coeval Kyrkås Quartzite to the east remained enigmatic. Provenance studies (radiometric dating of zircons) tentatively indicate different dominating source areas, but further studies are needed to solve their relationship.
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35.
  • Dahlqvist, Peter (författare)
  • Late Ordovician (Hirnantian) depositional pattern and sea-level change in shallow marine to shoreface cycles in central Sweden
  • 2004
  • Ingår i: Geological Magazine. - 0016-7568. ; 141:5, s. 605-616
  • Tidskriftsartikel (refereegranskat)abstract
    • The Upper Ordovician Kyrkas Quartzite Formation at the Nifsasen Quarry (Jamtland, Sweden) exhibits c. 90 m of siliciclastic sedimentary rocks deposited on a shallow shelf at the cratonattached part of tile Caledonian foreland basin. Five lithologies are distinguished, including claystone, mudstone, siltstone, subarkose and sublitharenite. Based on these five lithologies, sedimentary structures and biota, three marine facies associations are defined: the Mudstone association (FA1) deposited close to storm wave base, the Sandstone/mudstone association (FA2) formed between storm and fair-weather wave bases, and the Sandstone association (FA3) accumulated above fair-weather wave base. The facies associations are arranged in two sequences, c. 50 and 40 in thick, separated by a transgressive surface, indicating repeated shoreline progradation. Both sequences commence with marine heterolithic shales and siltstones, with upwardly increasing frequency of tempestites. Continued shoaling is indicated by a dominance of hummocky and trough (locally tabular) crossstratified sandstone beds in the upper part of each sequence. Sand beds are increasingly amalgamated up-sequence, reflecting progressively diminishing accommodation space. The depositional style and sedimentary structures indicate that the study area was storm-dominated with an abundant supply of siliciclastic material. Biostratigraphic data tie the depositional changes to the globally recognized Late Ordovician (Himantian) glacial interval. These data suggest that the first sequence was formed during the initial phase of regression in the earliest Hirnantian. The lowermost part of the overlying sequence contains elements of atypical Hirnantia fauna followed by beds yielding Normalograptus persculptus, suggesting a second regressive cycle in the Jamtland basin during the early N. persculptats Biozone.
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36.
  • Dahlqvist, Peter, et al. (författare)
  • Late Ordovician palaeoceanographic changes as reflected in the Hirnantian-early Llandovery succession of Jamtland, Sweden
  • 2004
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 1872-616X .- 0031-0182. ; 210:2-4, s. 149-164
  • Tidskriftsartikel (refereegranskat)abstract
    • A study of the Upper Ordovician-Lower Silurian strata in Jamtland, central Sweden, shows that large-scale changes in shelf deposition took place close to the systems boundary. These changes include unconformity development and the replacement of a siliciclastic shelf with a carbonate-dominated shelf, suggesting the interaction of allocyclic controls such as changing eustatic sea-level and climate. The 6-m-thick Ede Formation is a key lithosome for interpretation of this transition. Its sediments were deposited in the Caledonian foreland basin, situated east of the closing Iapetus Ocean on the western margin of the Baltic craton. A major part of the late. Caradoc to late Ashgill (into the Hirnantian) was characterised by continuous and uniform deposition over wide areas (Kogsta Formation), whereas erosional surfaces and complex lateral facies relationships characterise the Ordovician-Silurian boundary strata (Ede Formation and lateral equivalents). The Ede Formation represents the end of terrigenous deposition, which in the middle Aeronian was followed by regional expansion of carbonate deposition (Berge Formation). A syn-sedimentary erosional surface, with at least I in of relief locally, forms the lower boundary of the Ede Formation. This surface is overlain by two types of conglomerate. Lower parts of the Ede Formation consist of medium to thick-bedded quartzites. A second erosional surface with only minor (few centimetres) relief occurs on top of these quartzites. The upper parts of the Ede Formation consist of a thin, basal favositid biostrome overlain by thin bedded, calcareous sandstones, limestones and intensely bioturbated shales. Analysis of stratigraphic boundaries and the facies succession suggests that the lower Ede Formation represents a major downward shift in coastal onlap and by-pass sedimentation that created the lower erosional surface. The erosional surface in the middle of the Ede Formation is inferred to have formed during the subsequent maximum lowstand or as a ravinement surface, and is interpreted as an unconformity. The succession is subdivided into four facies associations, each corresponding to a specific systems tract: (a) a Shale-Siltstone Association (uppermost Kogsta Formation), deposited during a highstand situation in mid-outer shelf areas; (b) a Quartzite Association (the lower Ede Formation), deposited during forced regression in a shoreface environment; (c) a Mixed Carbonate-Siliciclastic Association (the upper Ede Formation), deposited during transgression in a wave-dominated, proximal shelf environment when elastic supply was reduced; and (d) a Micritic Limestone Association (lowermost Berge Formation), deposited during a second highstand situation in a low-energy, offshore environment. Conodont data, together with a previously reported Hirnantia fauna, constrain the position of the Ordovician-Silurian boundary to the lower 1.65 m of the Ede Formation, or less likely, to the uppermost metre of the underlying Kogsta Formation, i.e., within a 2.65-m-thick uncertainty interval. The base of the Berge Formation is about 4 m above the top of the uncertainty interval, and is dated as being mid-Aeronian in age, suggesting condensation and/or a hiatus close to, or at, the Ordovician-Silurian boundary. These data tie the unconformity and the regional facies change from a siliciclastic to a carbonate-dominated shelf to Late Ordovician-Early Silurian eustatic and climatic changes. (C) 2004 Elsevier B.V. All rights reserved.
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37.
  • Dahlqvist, Peter, et al. (författare)
  • Late Ordovician shelly faunas from Jamtland: palaeocommunity development along the margin of the Swedish Caledonides
  • 2010
  • Ingår i: Bulletin of Geosciences. - : Czech Geological Survey. - 1214-1119 .- 1802-8225. ; 85:3, s. 505-512
  • Tidskriftsartikel (refereegranskat)abstract
    • Late Ordovician shelly faunas occur at several localities in the Ostersund area of Jamtland (Sweden) and developed against a background of intense and rapid global climate change. In the eastern part, approximately in the middle parts of the Krykas Quartzite, and in the western part in the uppermost Kogsta Siltstone changes in faunas and sedimentary patterns provide regional evidence of these global events. In both areas the faunas occur in shale and siltstone facies and are used to effect correlations between the eastern and western parts of the region, which show major differences in facies development. These sub-basins, situated on the margins of a developing mountain belt, reacted differently to global signals providing further evidence of the heterogeneous responses to climate change at the end of the Ordovician Period.
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39.
  • Dahlqvist, Peter, et al. (författare)
  • Potential benefits of managed aquifer recharge MAR on the Island of Gotland, Sweden
  • 2019
  • Ingår i: Water. - : MDPI AG. - 2073-4441. ; 11:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The Island of Gotland (3000 km2), east of mainland Sweden, suffers from insufficient water availability each summer. Thin soils and lack of coherent reservoirs in the sedimentary bedrock lead to limited reservoir capacity. The feasibility of Managed Aquifer Recharge (MAR) is explored by identifying suitable areas and estimating their possible contribution to an increased water availability. MARis compared to alternative water management measures, e.g., increased groundwater abstraction, in terms of costs and water availability potential. Results from GIS analyses of infiltration areas and groundwater storage, respectively proximity to surface water sources and surface water storage were classified into three categories of MAR suitability. An area of ca 7700 ha (2.5% of Gotland) was found to have good local conditions for MAR and an area of ca 22,700 ha (7.5% of Gotland) was found to have moderate local conditions for MAR. These results reveal the MAR potential on Gotland. The water supply potential of MAR in existing well fields was estimated to be about 35% of the forecasted drinking water supply and 7% of the total water demand gap in year 2045. It is similar in costs and water supply potential to increased surface water extraction. © 2019 by the authors.
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