| 1. |
- 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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| 2. |
- Egenhoff, Sven O., et al.
(författare)
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The complexity of mudstone diagenesis–some insight from the Tøyen Shale, Lower to Middle Ordovician, southern Sweden
- 2019
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 141:1, s. 54-67
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Tidskriftsartikel (refereegranskat)abstract
- The Lower to Middle Ordovician Tøyen Shale in southern Sweden, a biostratigraphically well-dated siliciclastic mudstone unit, shows 18 distinct authigenic cements that include sulfides, carbonates, silicates, clays, and phosphates. Marcasite, sphalerite, galena, and six texturally distinct types of pyrite characterize the sulfides whereas only one type of dolomite and three different generations of calcite are observed in this unit. Quartz, phosphate, and organic matter occur as only one generation each. Authigenic clay minerals are represented by chlorite and kaolinite. The paragenetic sequence of cements is subdivided into the two pre-burial carbonates, succeeded by ten relatively early burial cements, and six late burial cements, the kaolinite being the latest of them all and potentially being of Cretaceous age. Based on textural relationships, the paragenetic sequence of alterations started with dolomite precipitation followed by calcite, and then five different generations of pyrite. All eleven other phases post-date these initial seven cements in the Tøyen Shale.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Fishman, Neil S., et al.
(författare)
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Pyritization history in the late Cambrian Alum Shale, Scania, Sweden: Evidence for ongoing diagenetic processes
- 2020
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Ingår i: Mudstone diagenesis: Research perspectives for shale hydrocarbon reservoirs, seals, and source rocks. - 9780891814252 ; 120, s. 83-102
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Bokkapitel (refereegranskat)abstract
- Detailed diagenetic studies of the late Cambrian Alum Shale in southern Sweden were undertaken across an interval that includes the peak Steptoean Positive Carbon Isotope Excursion (SPICE) event to evaluate the pyrite mineralization history in the formation. Samples were collected from the Andrarum-3 core (Scania, Sweden); here the Alum was deposited in the distal, siliciclastic mudstone-rich end of a shelf system. Abundant cryptobioturbation is observed in the Alum, which points to oxic–dysoxic conditions prevailing during deposition. Petrographic examination of polished thin sections (n = 65) reveals the presence of numerous texturally distinct types of pyrite, including matrix framboids, two different types of framboid concretions (those with rims of iron-dolomite and those lacking rims), disseminated euhedral pyrite crystals, concretions of euhedral pyrite crystals, overgrowths of pyrite on these different pyrite generations, anhedral pyrite intergrown with bedding parallel mineralized fractures (i.e., “beef”), and massive vertical/subvertical accumulations of pyrite.Paragenetic relationships outline the relative timing of formation of the texturally distinct pyrite. Framboids and framboid concretions formed prior to precipitation of any euhedral pyrite crystals, and these pyrite generations precipitated prior to the pyrite overgrowths on them. As Alum Shale sediments are all distorted by these texturally different pyrite generations, they are likely to have formed early in the postdepositional history of the formation. In contrast, pyrite associated with “beef” is likely temporally related to the onset of hydrocarbon generation, which in this part of Sweden is thought to have been many tens of millions of years after deposition. Because vertical/subvertical massive pyrite features distort “beef,” they clearly postdate it. Of all these pyrite textures, only framboid concretions appear to be restricted to the SPICE interval.The texturally distinct nature of the pyrite generations, along with evidence of their formation at different times in the postdepositional history of the Alum Shale, is the key outcome of this petrographic study. Because the petrographic data presented herein point to a postdeposition origin for all generations of pyrite, diagenetic processes—not those processes associated with deposition—were responsible for the complex pyritization history observed in the Alum, in the Andrarum-3 core.
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| 7. |
- 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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| 8. |
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