| 1. |
- Bergström, Stig M., et al.
(författare)
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Darriwili (Keskordoviitsiumi) δ13Corg kemostratigraafia koos graptoliitide biostratigraafiaga klassikalisel röstånga alal skåne maakonna loodeosas lõunarootsis
- 2020
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Ingår i: Estonian Journal of Earth Sciences. - : Estonian Academy Publishers. - 1736-4728. ; 69:3, s. 121-133
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Tidskriftsartikel (refereegranskat)abstract
- The largely covered Middle Ordovician succession in the classic geological Röstånga area in northwestern Scania has not been studied for some 80 years. A new drill core through a succession ranging from the lower–middle Darriwilian to the lower Sandbian has provided a unique opportunity to investigate the graptolite biostratigraphy and the δ13Corg chemostratigraphy, and clarify their stratigraphic relations, through this ~90 m thick interval, which is developed within a black shale facies. The lithology, biostratigraphy and chemostratigraphy are closely similar to those of the coeval strata in the Fågelsång area, southcentral Scania, including the presence of the Fågelsång Phosphorite, which was previously unrecorded in the Röstånga area. The new data are particularly important in providing evidence of the relations between graptolite biostratigraphy and δ13Corg chemostratigraphy. The Fågelsång3 and Röstånga2 drill core successions are currently the only Darriwilian sequences in the world where these relations have been well established.
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| 2. |
- Bergström, Stig M., et al.
(författare)
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Darriwilian (Middle Ordovician) chemostratigraphy linked to graptolite, conodont and trilobite biostratigraphy in the Fågelsång-3 drill core, Scania, Sweden
- 2018
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Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 140:3, s. 229-240
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Tidskriftsartikel (refereegranskat)abstract
- A recent core drilling in the geologically classical Fågelsång area resulted in a 58.70-m-long drill core through the lowermost Sandbian Sularp Shale, the Darriwilian Almelund Shale and Komstad Limestone, and part of the late Tremadocian to earliest Darriwilian Tøyen Shale. The shales contain zone index graptolites that are used for an update of the standard Darriwilian graptolite zone succession in Baltoscandia in which six zones are now recognized. The Komstad Limestone interval and lowermost part of the Almelund Shale have beensubdivided into four conodont zones. The δ13Corg chemostratigraphy, which has been established through the entire drill core based on 120 closely spaced samples, shows a somewhat subdued development of the middle Darriwilian Isotope Carbon Excursion (MDICE), which is dated in terms of graptolite biostratigraphy. The Fågelsång isotope curve is correlated with a closely similar δ13Ccarb curve from a coeval, apparently stratigraphically essentially continuous, succession at Kårgärde in south-central Sweden, which previously has been subdivided into 13 conodont zones and subzones. For the first time, these conodont zonal units can be calibrated with Fågelsång graptolite zones using δ13Corg chemostratigraphy. The several new results of this study are expected to be useful for assessing biostratigraphic relations between units in shale and carbonate facies in Baltoscandia and elsewhere in the world.
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| 3. |
- Egenhoff, Sven O., et al.
(författare)
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Sedimentology of SPICE (Steptoean positive carbon isotope excursion): A high-resolution trace fossil and microfabric analysis of the middle to late Cambrian Alum Shale Formation, southern Sweden
- 2015
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Ingår i: Geological Society of America. Special Papers. - : Geological Society of America. - 0072-1077. ; 515, s. 87-102
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Tidskriftsartikel (refereegranskat)abstract
- The Cambrian Alum Shale Formation in the Andrarum-3 core from Scania,southern Sweden, consists of black siliciclastic mudstone with minor carbonate intercalations. Four facies comprise three siliciclastic mudstones and one fine-grained carbonate. The facies reflect deposition along a transect from deep ramp to basin on a Cambrian shelf. The three mudstone facies contain abundant clay clasts and laterally variable siltstone laminae. Bed-load transport processes seem to have dominated deposition on this deep shelf. These sedimentary rocks record mainly event deposition, and only relatively few, thin laminae probably resulted from suspension settling. The Alum Shale Formation deep shelf did not show a bioturbation gradient, but fecal strings are common and Planolites burrows are rare in all mudstone facies. Evidence for biotic colonization indicates that this mudstone environment was not persistently anoxic, but rather was most likely intermittently dysoxic. The Alum Shale Formation in the Andrarum-3 core shows an overall decrease of grain size, preserved energy indicators, and carbonate content upsection interpreted to reflect a deepeningupward. The succession can also be divided into four small-scale fining-upwardcycles that represent deepening, and four overlying coarsening-upward cycles that represent upward shallowing.
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| 4. |
- Egenhoff, Sven, et al.
(författare)
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Sedimentology and sequence stratigraphy of a pronounced Early Ordovician sea-level fall on Baltica - The Bjorkasholmen Formation in Norway and Sweden
- 2010
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 224:1-4, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The Bjorkasholmen Formation consists of interbedded carbonates, shales, and glauconitic beds and is characterized by heavy bioturbation and few preserved sedimentary structures. The unit shows five facies shale, glauconitic packstone, and three predominantly mud-dominated carbonate facies. Carbonates and shales are arranged in small-scale deepening-upward cycles. A minimum of fourteen of these small-scale cycles are recognized in the Bjorkasholmen Formation. They are arranged in stacks of 3 to 5, forming a total of four medium-scale cycles separated by decimeter-thick shale units. Based on the predominance of mud-rich facies the succession is interpreted to have been deposited in an overall tranquil setting during one mayor sea-level fall and subsequent initial rise of third order. Time-estimates suggest that the 14 small-scale cycles fall into the Milankovitch band of precessional forcing, and the overriding medium-scale cycles likely represent short eccentricity. The sequence stratigraphic interpretation shows that the Bjorkasholmen Formation is characterized by failing stage, lowstand and initial transgressive systems tracts. Consequently, the contact between the Bjorkasholmen and the underlying Alum Shale Formation represents the basal surface of forced regression. The maximum regressive surface is defined by a hiatus in the Oland sections and by shallow-marine packstones within mud-rich distal ramp carbonates in Norway. The top of the Bjorkasholmen Formation represents a flooding surface at the base of the transgressive systems tract. A comparison of time-equivalent successions worldwide suggests that the Bjorkasholmen Formation represents a tectonically-enhanced lowstand with two overriding short-term Milankovitch eustatic signals. Although deposition of the Bjorkasholmen Formation coincides with the initiation of a foreland basin in the Caledonides of Norway it remains unclear how these tectonic movements may have lead to the widespread Bjorkasholmen lowstand during the Early Ordovician. It is Suggested in this Study that a combination of compressional forces from Avalonia and the Caledonian margin may have acted in concert to produce an uplift of larger parts of the Baltica plate for a time-span of approximately 0.5 Myr.
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| 5. |
- Egenhoff, Sven, et al.
(författare)
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Sedimentology of the Lower Ordovician (upper Tremadocian) Bjørkasholmen Formation at Flagabro, southern Sweden
- 2018
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Ingår i: GFF. - : TAYLOR & FRANCIS LTD. - 1103-5897 .- 2000-0863. ; 140:1, s. 55-65
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Tidskriftsartikel (refereegranskat)abstract
- The Lower Ordovician Bjørkasholmen Formation at Flagabro, Scania, southern Sweden, consists of a 0.8m thick succession of carbonates with three siliciclastic mudstones, 5, 1 and 100mm thick, intercalated in the central part of the unit. Carbonate and siliciclastic mudstone beds show both normal and inverse grading. The carbonates are mud-rich and subdivided into a mudstone, a wackestone and a packstone facies. Grain types in the carbonates are mostly shells and shell fragments of brachiopods and trilobites. The carbonate rocks are strongly bioturbated seen as in roundish burrows filled with mud and a clear cement; additionally, bioturbation is reflected in the random orientation of shells. The siliciclastic mudstones are subdivided into two facies; one contains large amounts of shells and is in part grain-supported, the other is matrix-dominated and laminated to massive. The succession reflects sedimentation on a low-inclined shelf equivalent to a mid-ramp to basinal setting. Most mud- and wackestones (facies 3 and 4) represent fair-weather sedimentation, and the intercalated wacke- and packstones (facies 4 and 5) represent concentration of shell debris during high-energy storm. The siliciclastic mudstones in the central part of the succession reflect deposition in a basinal setting. The entire BjOrkasholmen Formation at Flagabro is equivalent to a lowstand of third (?) order without a well-developed internal cyclicity and is in that respect similar to the Bjørkasholmen Formation of oland, but different from the age-equivalent Norwegian sections.
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| 6. |
- Egenhoff, Sven, et al.
(författare)
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Tectonically-Induced Lowstand on an Ordovician Ramp – the Björkåsholmen Formation of Scandinavia
- 2008
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Ingår i: 2008 Houston Annual Meeting (5–9 October 2008).. - : Geological Society of America. ; , s. 393-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Tremadoc Björkåsholmen Formation is an approximately one meter thick unit consisting of several carbonate beds with intercalated shales and some glauconite content in its upper part. It is underlain by the Cambrian-Ordovician Alum Shale Formation throughout Scandinavia, and in Norway and westernmost Sweden overlain by the Lower- to Middle Ordovician Tøyen Formation. The Björkåsholmen Formation is remarkably widespread in Scandinavia with relatively little variation in thickness or faunal composition. Internally, the unit consists of thin beds at the base with thicker ones in the center and again thinner beds towards the top. Thin beds are generally mud-rich while thicker ones display packstones. In the Norwegian sections the grain-rich facies have been mostly diagenetically overprinted, whereas eastern Swedish localities are characterized by much better facies preservation regardless of lithology. The overall mud-rich facies of the Björkåsholmen Formation reflects deposition on a low-inclined ramp environment. Coarse-grained sediments represent the proximal facies while increasing mud content shows deeper water middle to outer ramp deposition. Facies trends indicate that the Björkåsholmen Formation consists of at least five regressions and successive transgressions with a maximum lowstand represented by its coarse-grained central portion. As the Björkåsholmen Formation is sandwiched between two prominent outer shelf shales in the Norwegian and westernmost Swedish localities it also represents the most pronounced sea-level lowstand in the Early Ordovician of Scandinavia.This lowstand is within the upper part of the Aorograptus victoriae Biozone and the basal Kiaerograptus supremus Biozone. Deposition of the Björkåsholmen Formation therefore likely represents a fairly short time-span. However, this remarkably strong lowstand in Scandinavia is not paralleled by base-level falls in Bolivia, China or Newfoundland. It is therefore suggested that the Björkåsholmen Formation reflects a tectonic rather than a eustatic event which is restricted exclusively to Baltoscandia.
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| 7. |
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| 8. |
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| 9. |
- Lehnert, Oliver, et al.
(författare)
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The Siljan Meteorite Crater in central Sweden – an integral of the Swedish Deep Drilling Program (SDDP)
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- New drill cores from the largest known impactstructure in Europe, the Siljan crater, provide superbpossibilities to reconstruct Early Palaeozoic marineenvironments and ecosystems, and to document changes insedimentary facies, sea-level and palaeoclimate. Themeteorite crater is a major target of the project ConcentricImpact Structures in the Palaeozoic (CISP) in theframework of the Swedish Deep Drilling Program.Studies of Ordovician and Silurian strata in the SiljanDistrict have a long tradition and many scientific papersdeal with the geology of the area. The Palaeozoicsuccession starts with the Tremadocian Obolusconglomerate, the youngest pre-Caledonian strata areMiddle Silurian shales of the Nederberga Formation.However, exposures are limited, there are few continoussections, and the Early Palaeozoic sedimentary rocksresting on the Precambrian basement are incompletelyinvestigated.Detailed sedimentological and biostratigraphicalstudies of the cores and the Nittsjö trench together withanalysis of the carbon isotope chemostratigraphy will allowintra- and intercontinental correlations and the dating ofCaledonian movements. Our preliminary studies show thatdifferent and yet undefined facies belts are preserved in theSiljan District. The recent findings of palaeokarst in thearea together with similar new findings in other parts ofBaltoscandia reflect times of subaerial exposure of thebasin regionally and challange the idea that theBaltoscandian basin was a deep and tranquil depositionalenvironment.Our preliminary data provide a first base forreinterpretations of this part of Sweden, previouslyregarded as representing a stable cratonic area unaffectedby the Caledonian collision between Baltica and Laurentia.The erosional unconformity and the substantial hiatusbetween Middle Ordovician limestones and late EarlySilurian shales in the western part of the crater suggests anextended period of uplift and erosion presumably related toflexural forebulge migration toward the east due to tectonicloading by the Caledonian nappes to the west. The Lowerto Middle Ordovician carbonate succession is only about21 m thick, with a sharp flooding surface on top of theMid-Ordovician Holen Formation. The overlyingsiliciclastic succession (Upper Llandovery, based ongraptolite data) comprises a minimum thickness of about224 m. The sudden deepening after the eastward migrationof the forebulge is indicated by rapid deposition of shalesand shale/mudstones displaying unstable conditionsexpressed by megaslumps, debris flows, turbidites andseveral synsedimentary tectonic features. The intercalationof a sandstone unit reflects a strong regression in this shalebasin followed by rapid transgression and deposition ofdark, organic-rich shale and mudstone.In contrast to this development, a classicalOrdovician/Silurian carbonate/shale succession, well103 IODP/ICDP Kolloquium Kiel, 07. – 09.03.2012Figure 6: Bathymetry map of Lake Ohrid. Proposed sites aremarked by the red dots.Figure 5: Multichannel seismic line crossing the DEEP-Site inthe central basin of Lake Ohrid.known from other parts of Sweden, formed in the northern(Skattungbyn-Kallholn), northeastern (Furudal), andsoutheastern part (Boda) of the Siljan District. Detailedsampling of the cores for stable isotopes, thermal maturity,geochemistry, sediment provenance, facies and microfaciesstudies in the autumn of 2011 now helps in solvingregional problems as well as stratigraphical andpalaeogeographical questions.
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| 10. |
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