| 1. |
- Frisk, Henrik, et al.
(författare)
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Acts of Creation : Introduction
- 2015
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Ingår i: Acts of Creation : Thoughts on artistic research supervision - Thoughts on artistic research supervision. - 9789187483165 ; , s. 7-18
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Lindberg-Sand, Åsa, et al.
(författare)
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Contextual and conceptual ambiguities in supervision of artistic research : experiences from Konstnärliga forskarskolan
- 2015
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Ingår i: Acts of Creation : thoughts on artistic research supervision. - 9789187483165 ; , s. 189-220
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Bokkapitel (refereegranskat)abstract
- To accept the nomination to become the supervisor of a PhD candidate is not only to step into a specific, challenging and potentially rewarding relationship, but also to enter a new zone of uncertainty: what kind of contribution to this relationship is expected from me? In what ways is this new professional task framed and supported by the institutional context to which I belong? What do I gain from becoming a supervisor? In this chapter we draw together our experiences of spending many hundreds of hours listening to and discussing with supervisors of PhD candidates from a wide variety of research domains. We use our experiences from ten years of arranging pedagogical support for supervisors in the form of courses and seminars, and use what we have learned in these meeting places as material to describe how we perceive the cultural and contextual conditions for supervising PhD candidates both in general and in the emerging field of artistic research. The aim is therefore not to describe or evaluate our pedagogical efforts, but to use what we have encountered and reflected on in seminars with supervisors over the years. Another aim is to shed some light on the cultural and contextual conditions for supervising artistic research by comparing and contrasting the situation of the supervisors in this relatively new field with the situation in other fields of research. A more personal aim is to try to disentangle some of the persistent puzzlement that followed us through the years with Konstnärliga forskarskolan (KFS). Why was it that over and over again we were troubled by a feeling that the supervisors, compared to our expectations, were not regarded as being crucially important for the development of artistic research?In this chapter we will first discuss the importance of supervisors for doctoral education and for the regeneration and development of research, both in general and for new fields, with continuous references to artistic research, as it was mirrored to us through KFS. We will then continue along a road where we look at a number of contextual conditions (such as the learning trajectories of artists) and practiced concepts (such as interdisciplinarity and practice-based research), where we have experienced intriguing differences in artistic research when compared to other research environments. Finally, we offer two scenarios staging the institutional and cultural conditions for supervising artistic research in two quite different ways. They are constructed as ideal types and as a tool to disentangle some of the ambiguities supervisors have to face in the real settings where they meet their PhD candidates, and where everything is mixed up, as in life itself. Finally, we end our chapter by pointing out a ghost scenario, which we hope will disappear with the continued development of artistic research.
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| 3. |
- Anrup, Roland, et al.
(författare)
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Centrala universitetsvärden hotas av bolagiseringsidén
- 2013
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Ingår i: Dagens nyheter. - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Högskolestiftelser. Förslaget att driva svenska universitet i stiftelseform öppnar för bolagisering. Men det är ingen riktig utredning, utan en politisk pamflett utan eftertanke. Privatisering av universitet hotar både oberoendet, forskningskvaliteten och samhällsnyttan, skriver 36 forskare vid svenska högskolor och universitet.
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| 4. |
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| 5. |
- Brosse, Morgane, et al.
(författare)
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Conodonts from the Early Triassic Microbialite of Guangxi (South China) : Implications for the Definition of the Base of the Triassic System
- 2015
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 58:3, s. 563-584
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Tidskriftsartikel (refereegranskat)abstract
- We describe a new Early Triassic (Griesbachian) succession of conodont faunas from a high-resolution sampling of the basal Early Triassic microbial limestone and the base of the overlying unit at the Wuzhuan section (Nanpanjiang Basin, Guangxi, South China). The microbial limestone records the earliest phase of the Early Triassic biotic recovery after the end-Permian mass extinction. For the first time, rich conodont faunas are reported from within the microbialite. The faunas from Wuzhuan are largely dominated by anchignathodontids, including several Isarcicella species, which were previously documented only from strata above the microbialite. A total of 14 conodont species assigned to three genera is recorded from the Wuzhuan section. Starting from the base of the microbialite upwards, several species are sequentially added to the conodont assemblage. The alpha diversity peaks at the top of the microbialite. The conodont record in the considered microbialite interval at Wuzhuan is presumably unaffected by local ecological changes. It therefore more likely represents an evolutionary rather than an ecological pattern. We compare the Wuzhuan's conodont record with a well-supported phylogenetic model and suggest that the sequence of first occurrences at Wuzhuan is the closest to the true' sequence of evolutionary events that took place during this Griesbachian radiation of anchignathodontids. Based on comparisons with the GSSP section at Meishan, we suggest further that the first occurrence of Hindeodus parvus in Meishan does not correspond to its first appearance datum.
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| 6. |
- Brosse, Morgane, et al.
(författare)
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New data from Oman indicate benthic high biomass productivity coupled with low taxonomic diversity in the aftermath of the Permian-Triassic Boundary mass extinction
- 2019
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Ingår i: Lethaia. - : WILEY. - 0024-1164 .- 1502-3931. ; 52:2, s. 165-187
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Tidskriftsartikel (refereegranskat)abstract
- A new Early Triassic marine fauna is described from an exotic block (olistolith) from the Ad Daffah conglomerate in eastern Oman (Batain), which provides new insights into the ecology and diversity during the early aftermath of the Permian-Triassic Boundary mass extinction. Based on conodont quantitative biochronology, we assign a middle Griesbachian age to the upper part of this boulder. It was derived from an offshore seamount and yielded both nektonic and benthic faunas, including conodonts, ammonoids, gastropods and crinoid ossicles in mass abundance. This demonstrates that despite the stratigraphically near extinction at the Permian-Triassic Boundary, Crinoidea produced enough biomass to form crinoidal limestone as early as middle Griesbachian time. Baudicrinus, previously placed in Dadocrinidae, is now placed in Holocrinidae; therefore, Dadocrinidae are absent in the Early Triassic, and Holocrinidae remains the most basal crown-group articulates, originating during the middle Griesbachian in the Tethyan Realm. Abundant gastropods assigned to Naticopsis reached a shell size larger than 20 mm and provide another example against any generalized Lilliput effect during the Griesbachian. Whereas the benthic biomass was as high as to allow the resumption of small carbonate factories, the taxonomic diversity of the benthos remained low compared to post-Early Triassic times. This slow benthic taxonomic recovery is here attributed to low competition within impoverished post-extinction faunas.
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| 7. |
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| 8. |
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| 9. |
- Ebbestad, Jan Ove R., et al.
(författare)
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Gastropods and tergomyans from the Upper Ordovician (Viru–Harju) of the Fågelsång area, Scania, southern Sweden
- 2013
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Ingår i: Journal of Systematic Palaeontology. - : Informa UK Limited. - 1477-2019 .- 1478-0941. ; 11:3, s. 295-336
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Tidskriftsartikel (refereegranskat)abstract
- A diverse tergomyan and gastropod assemblage is described from the Global Boundary Stratotype Section and Point (GSSP)section of the Sandbian Stage, Upper Ordovician, in the Fågelsång area, Scania, southern Sweden. Deep water graptolitic mudstone and shale comprise the succession, and previously only one gastropod species was known. The new material spans the Sularp Formation through the Lindegård Mudstone (Nemagraptus gracilis–Dicellograptus complanatus biozones). Fourteen species are described: two tergomyan, five bellerophontoid gastropods, and seven anisostrophically coiled gastropods.Three species are new: Peelerophon hodites, Tetranota scanica and Lophospira sandbiana. Three taxa (Tritonophon subtrilobatus,Tetranota scanica and Holopea mobergi) are found high in the Lindegård Mudstone (Vormsi–Pirgu stages). Cyrtodiscus, Peelerophon and Tritonophon are recorded for the first time in Baltoscandia. Some taxa may have been transportedfrom shallower water settings, whereas species of Peelerophon, Joleaudella, Mestoronema and Sinuites may have been partof the local benthos. Except for Bucania erratica, no species are shared with the fauna of the coeval Dalby Limestone in Sweden. Deaechospira elliptica, common in the Dalby Limestone, is not recorded at Fågelsång, although two closely relatedspecies are found (Deaechospira rotunda and Deaechospira? sp.). The Fågelsång assemblage has more in common with the older to coeval fauna of the Elnes and Arnestad formations in the Oslo Region, Norway (e.g. sharing Joleaudella, Sinuites, Mestoronema and Pararaphistoma). The Sandbian fauna of Fågelsång includes peri-Gondwanan taxa, e.g. Cyrtodiscus,Peelerophon and Deaechospira. Nevertheless, cluster analysis reveals that the faunas of Baltica and Laurentia were most similar, whereas faunas from Perunica and Baltica remained distinct and separated during the Darriwilian–Sandbian. The few similarities may result from spread of a temperate fauna supplementing rather than replacing taxa in deep water assemblages.The main Fåagelsång assemblage coincides both with the Baltoscandian Middle Caradoc Faunal Turnover and the Gutenberg Carbon Isotope Excursion.
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
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Tergomyans, gastropods, and biogeography in the Upper Ordovician of the Fågelsång district, southern Sweden
- 2009
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Ingår i: Absolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 4. - Copenhagen : Geological Museum, Natural History Museums. ; , s. 24-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During the Ordovician, deep-water graptolitic mudstone and shale formed in what is now the classical succession at Fågelsång, southern Sweden. Previously, only one gastropod species was described from the succession, but during this study diverse tergomyan and gastropod assemblages have been recognized both from outcrop and drill-core collections. The material spans the Sularp Shale through the Lindegård Mudstone (Nemagraptus gracilis − Dicellograptus complanatus Zones; Sandbian − Katian, Viru − Harju regional stages). Altogether 14 species are described; two tergomyan, five bellerophontoid gastropods, and six anisostrophically coiled gastropods. Three taxa (Tritonophon, Tetranota and Holopea) are found in the Lindegård mudstone. The first record of Tritonophon in the Ordovician of Baltoscandia occurs in the Fågelsång and nearby Röstånga area. The remaining taxa are from the Sularp, Skagen, and Mossen formations. Specimens may have been transported into the area from shallower settings, while species of Peelerophon, Cyrtodiscus, Joleaudella, and Sinuites, are interpreted as having been part of the local benthos. With the exception of Bucania and Deaechospira, no other taxa are common to the hitherto described gastropod fauna of the coeval Dalby Limestone in other parts of Sweden. The Fågelsång assemblages have more in common with the slightly older or coeval fauna of the Elnes to Arnestad formations in the Oslo Region (e.g. Joleaudella, Sinuites, Mestoronema, Pararaphistoma). The Sandbian taxa show similarities with peri-Gondwanan faunas (e.g. Peelerophon, Cyrtodiscus). Both Peelerophon and Cyrtodiscus are for the first time recorded from Baltoscandia. The hitherto endemic Baltoscandian taxon Deaechospira may also be recognized in Bohemia and Morocco.
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| 14. |
- Ebbestad, Jan Ove R., et al.
(författare)
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Terminal Ordovician stratigraphy of the Siljan district, Sweden
- 2015
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 137:1, s. 36-56
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Forskningsöversikt (refereegranskat)abstract
- Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive delta C-13 excursions are identified (from bottom) - the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The delta C-13 values through the Boda Limestone are 1-2 parts per thousand higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5 parts per thousand in the bottom of the core of the Boda Limestone up to 3 parts per thousand in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the Metabolograptus persculptus Biozone, at or close to the Hindella beds in the Upper Boda Member. The late Katian (Pirgu) age of Holorhynchus in the Siljan district is clear and its co-occurrence with the chitinozoan Belonechitina gamachiana in Estonia supports a Katian age for this zone. The base of the Ozarkodina hassi Biozone may occur within units B-C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the M. persculptus Biozone. The Hirnantia-Dalmanitina faunas reported from the lowermost part of the Loka Formation and units B-D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older (=extraordinarius) and a younger (=persculptus) fauna.
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| 15. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
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Upper Ordovician carbon isotope records in the Siljan district, Sweden
- 2009
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Ingår i: <em>Absolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 4</em>. - Copenhagen : Geological Museum, Natural History Museums. ; , s. 23-24
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Upper Ordovician Boda Limestone and the unconformably overlying Glisstjärn Formation in the Siljan district, Sweden, were sampled for carbon isotope analysis. The aim is to combine chemo- andAbsolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 424biostratigraphy for detailed regional correlation. This may help further studies of the time interval spanning the two-phased end Ordovician extinction. Expanding upon the study by Schmitz & Bergström (2007), five quarries, eight sections (669 samples) were studied; two sections each in Kallholn, Osmundsberget, and Solberga, and one section each in Östbjörka and Jutjärn. The Glisstjärn Formation is exposed only in one section at Kallholn, both sections at Osmundsberget, and possibly at one section in Solberga. A cephalopod event bed is recognized in one section in Kallholn and the two sections in Osmundsberget. Additionally, a thick coquina consisting of the brachiopod Hindella is found in all quarries except Solberga. The Hirnantian Isotope Carbon Excursion (HICE) was positively identified in seven of the eight sections. The peak occurs at the Hindella bed in all sections. The beginning of the excursion in Osmundsberget is placed slightly higher than in the previous study, at about 14 m from the top of the Boda Limestone, which means it is above the level with the brachiopod Holorhynchus (identified both in Osmundsberget and Solberga). In Osmundsberget, Östbjörka and Jutjärn, sampling of the deeper parts of the Boda Limestone yielded δ13C values between + 1 and + 3 ‰, with two or three peaks higher than + 3 ‰, that may be correlated between the sections
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| 16. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
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Upper Ordovician gastropods of the Fågelsang area, Southern Sweden
- 2009
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Ingår i: <em>Lundadagarna i Historisk Geologi och paleontology XI, 11-12 March, 2009, Abstracts with programme</em>. ; , s. 12-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Ordovician succession of the Fågelsång area in southern Sweden is classical geology embodied. A deeper water setting and graptolitic mudstones and shales has allowed an almost unprecedented level of stratigraphical detail. Moreover, with the establishment of the international stratotype (GSSP) for the Sandbian Stage, marking the base of the Upper Ordovician, the sections here now serve as global references. The present project documents for the first time the diverse tergomyan and gastropod fauna in the Upper Ordovician of the Fågelsång area. Altogether 13 species are described, including two tergomyan species, five bellerophontoid gastropods and sixanisostrophic ally coiled gastropods. The specimens come from both outcrop and drill core collections, spanning the Sularp Shale through the Lindegård Mudstone (Nemagraptus gracilis to the Dicellograptus complanatus graptolite zones; Sandbian-Katian stages, Viru-Harju regional stages). Three taxa (e.g. Tritonophon, Tetranota and Haplospira?) are found in the youngest strata - the Lindegård mudstone, while the remaining forms are from the deeper facies of the Sularp, Skagen, and Mossen formations. Many of the taxa may have been transported into the area from shallower settings, and only Sinuites may have been part of the local benthic community. Besides the taphonomy, the fauna recorded is interesting from both a taxonomic and palaeobiogeographic point of view. However, the emphasis in this presentation is on the latter aspect. With the exception of Bucania, Haplospira, and Deaechospira, no other taxa are common to the hitherto described gastropod fauna of the coeval Dalby Limestone in other parts of Sweden. The Fågelsång fauna have more in common with the slightly older and coeval fauna of the Elnes to Arnestad formations in the Oslo Region (e.g. Joleaudella, Sinuites, Mesteronema, Pararaphistoma), but significant similarities with peri-Gondwanan faunas are also evident (e.g. Peelerophon, Cyrtodiscus, Tritonophon). Both Peelerophon and Cyrtodiscus are for the first time recorded in Baltoscandia while the Fågelsång Tritonophon is stratigraphically the oldest in Baltoscandia.
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| 17. |
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| 18. |
- 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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| 19. |
- 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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| 20. |
- 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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| 23. |
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| 24. |
- Eriksson, Mats, et al.
(författare)
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Polychaete palaeoecology in an early Late Ordovician marine astrobleme of Sweden
- 2011
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Ingår i: Geological Magazine. - 0016-7568 .- 1469-5081. ; 148:2, s. 269-287
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Tidskriftsartikel (refereegranskat)abstract
- The post-impact Dalby Limestone (Kulcruse; Upper Ordovician) of the Tvaren crater, southeastern Sweden, has been analysed with regards to polychaetes, as represented by scolecodonts. A palaeoecological succession is observed in the Tvaren-2 drill core sequence, as the vacant ecospace was successively filled by a range of benthonic, nektonic and planktonic organisms. Scolecodonts belong to the first non-planktonic groups to appear and constitute one of the most abundant fossil elements. The polychacte assemblage recorded has an overall composition characteristic of that of the Upper Ordovician of Baltoscandia. Oenonites, Vistulella, Mochtyella and the enigmatic 'Xanioprion' represent the most common genera, whereas Pteropelta, Protarabellites?, Atraktoprion and Xanioprion are considerably more rare. The assemblage differs from coeval ones particularly in its poorly represented ramphoprionid fauna and the relatively high frequency of 'Xanioprion'. A taxonomic succession and changes in abundance and relative frequency of different taxa is observed from the deepest part of the crater and upwards towards more shallow water environments. The initial post-impact assemblage does not, however, necessarily represent a benthonic colonization of the crater floor. Instead it seems to be a taphocoenosis, as indicated by its taxonomic correspondence to the rim facies fauna recovered from Dalby Limestone erratics of the Ringson island. The Tvaren succession has yielded considerably richer scolecodont assemblages than hitherto recorded from the approximately coeval Lockne crater, possibly as a consequence of shallower water settings in the former area.
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| 25. |
- Frisk, Åsa, et al.
(författare)
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A marine impact crater as an Ordovician ecosystem; the Tvären crater
- 2005
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Ingår i: SEPM Research Conference; The sedimentary Record of Meteorite Impacts.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A marine impact crater as an Ordovician ecosystem; the Tvären craterFrisk, Å.1, Lindström, M.2 & Holmer, L.E11Department of Earth Sciences, Palaeobiology, Uppsala University, Norbyvägen 22, SE-752 36 Uppsala, Sweden, asa.frisk@geo.uu.se, lars.holmer@pal.uu.se2Department of Geology and Geochemistry, Stockholm University, Sweden, maurits.lindström@geo.su.seThe Tvären crater was formed as a result of an impact in the Ordovician Baltoscandian epicontinental sea, now situated in the Stockholm Archipelago, Sweden. The bolide impact resulted in an approximately 2 km wide crater and the pre-impact sedimentary sequence consists of Ordovician carbonates resting on non-lithified sands of Early to earliest Middle Cambrian age. After the impact event and the settling of the impact ejecta and resurge material, deposition of carbonates continued (Dalby Limestone). The lithology and thickness of the post-impact Dalby Limestone vary depending on the depositional environment relative to the cratered seascape. The crater itself acted like a sheltering rim for the deposition of sediments, also causing a fairly rapid sedimentation rate compared to the normal sedimentation of the Dalby limestone. The area consequently displayed pure new settings for the marine fauna still living in the surrounding sea, though not affected by the impact, and thus creating a new ecosystem. This particular condition makes it possible to get a good precision of the sedimentation and faunal succession occurring in the crater. Drillings in the Tvären crater were conducted in 1991 resulting in an almost complete drill core through the sedimentary succession in the crater. The base of the core consists of crystalline breccia followed by resurge deposits and then the sedimentation of the Dalby Limestone. The post-impact fossil fauna mostly consists of chitinozoans, graptolites, trilobites, bryozoans, ostracodes, echinoderms, cephalopods and brachiopods. Certain groups are restricted to deeper or lower water levels, varying during the sedimentation, while some occur throughout the succession. A detailed biostratigraphy through the post-impact succession of the drill core is being conducted to understand how the abundance of species changed in relation to the varied environments and how the pre-impact faunal groups recovered gradually as life returned onto a sterile seafloor.
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| 27. |
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| 28. |
- Frisk, Åsa, et al.
(författare)
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Faunal recovery in the Ordovician Lockne and Tvären craters
- 2005
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Ingår i: Lundadagarna i Historisk Geologi och Paleontologi IX.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- FAUNAL RECOVERY IN THE ORDOVICIAN LOCKNE AND TVÄREN CRATERÅsa Frisk1, Maurits Lindström2 & Lars Holmer11Uppsala University, Department of Earth Sciences, Palaeobiology, Norbyvägen 22, SE-752 36 Uppsala, Sweden.2Stockholm University, Department of Geology and Geochemistry, SE-106 91 Stockholm, SwedenLimited amount of work has been carried out looking at the aftermath of marine impacts; in particular the patterns of faunal recovery in and around marine craters have never been studied in detail. In Baltoscandia several marine impacts occurred during the Ordovician, and this project focuses on the Lockne and Tvären craters. The Lockne crater in Jämtland, Sweden, is well exposed on land while the Tvären crater, located under water in the Stockholm archipelago, Sweden, is available as drill cores and erratic boulders. The impacted sedimentary sequence at Tvären consisted of Ordovician carbonates resting on non-lithified sands of Early to earliest Middle Cambrian age whereas at Lockne the same kind of limestone rests on Middle to Upper Cambrian bituminous mud. After the impact events and the settling of the impact ejectas and resurge materials, deposition of carbonates continued (Dalby Limestone).After impact the substrate became devoid of life. Large areas were affected by the local extinction of the fauna and thus provided virgin ground for the settling of marine fauna still living in the surrounding sea, though not affected by the impact. A dramatic alteration of the seafloor topography, caused by the impact, offered new habitats characterized by the crater morphology and sheltering rims. The immigrating biota, mostly consisting of chitinozoans, graptolites, trilobites, bryozoans, ostracodes, echinoderms, cephalopods and brachiopods, developed new ecosystems. Certain groups are restricted to deeper or lower water levels, varying during the sedimentation in the crater, while some occur throughout the succession. A detailed biostratigraphic study of the post-impact succession in the craters is being carried out in order to understand how the abundance of species changed in relation to the varied environments and how the pre-impact faunal groups recovered gradually as life returned onto a sterile seafloor.
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| 29. |
- Frisk, Åsa, et al.
(författare)
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Linguliform and Craniiform Brachiopods from the Ordovician Tvären Crater, Sweden
- 2005
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Ingår i: The 5th International Brachiopod Conference, Copenhagen, Denmark.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Linguliform and Craniiform Brachiopods from the Ordovician Tvären Crater, SwedenÅsa M. Frisk1 and Lars E. Holmer11Department of Earth Sciences, Palaeobiology, Uppsala University, Norbyvägen 22, SE-752 36 Uppsala, SwedenDuring the Ordovician several bolides hit the Baltoscandian Epicontinental Sea. One of the impacts occurred at a water depth of 300 m and resulted in the 2 km wide Tvären crater, now situated in the Stockholm Archipelago, Sweden. The pre-impact sedimentary sequence at Tvären consisted of Ordovician carbonates resting on non-lithified sands of Early to earliest Middle Cambrian age. Following the impact event, deposition of carbonates continued (Dalby Limestone). The crater acted like a sheltering rim for the deposition of sediments, also displaying pure new settings for the fauna still living in the surrounding sea.The studied material from Tvären consists of glacial erratics from the area immediately southeast of the bay of Tvären on the coast of Södermanland. The limestone boulders are all fairly fossiliferous and have yielded numerous ostracods and brachiopods, the brachiopods being the next most common group; however the brachiopod fauna has never been previously studied in detail. The linguliform brachiopod fauna recorded from the erratic boulders include a large new lingulid genus and species, as well as new species of Schizotreta and Paterula. Eoconulus robustus Holmer is the only linguliform species previously recorded from the Dalby Limestone in Sweden.
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| 30. |
- Frisk, Åsa M., et al.
(författare)
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Biostratigraphy of an Early Ordovician (Tremadoc) epicontinental carbonate facies : the Baltoscandian Bjørkåsholmen Formation
- 2006
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Ingår i: Geological Society of America Abstracts with Programs. ; , s. 551-551
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The Lower Ordovician in Baltoscandia was initiated by extensive carbonate deposition forming the Tremadoc Bjørkåsholmen Formation (formerly the Ceratopyge Limestone), a distinctive unit corresponding to the Apatokephalus serratus trilobite Zone. The unit is remarkable in its near homogenous facies, lithologic and faunal composition throughout the Baltoscandian platform, representing a shallow water epicontinental environment. Similar facies are recognized in the autochthonic Caledonides believed to have been deposited 400 km to the west of the present Norwegian shoreline, while the easternmost outcrops are found on the island Öland off the east coast of Sweden. This gives an east-west extension of nearly 2000 kilometres, while the north-south extension is less well known owing to lack of exposures. However, glauconitic sandstones replace the carbonates both in the Siljan District of Dalarna, Sweden, and in the easternmost baltoscandian platform in Estonia and the St. Petersburg area of Russia. Trilobites are the dominant fossil group, with 36 species belonging to 26 genera. For the ongoing study of trilobite biostratigraphy of the unit, the trilobite abundance distribution has been investigated for two localities on southern Öland, Sweden. In both investigated sections the resulting abundance distributions are consistent, with diversity declining upward. The abundancy distribution compares in detail with several sections studied earlier from the Oslo Region of Norway. A section in Västergötland, halfway between the Oslo Region and Öland, is currently also under study. However, preliminary comparison across the Baltoscandian platform between the Oslo Region and Öland, suggests an extensive stable environment and fauna during deposition of the Bjørkåsholmen Formation.
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| 31. |
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| 32. |
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| 33. |
- Frisk, Åsa M., et al.
(författare)
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Facies distribution of post- impact sediments in the Ordovician Lockne and Tvären impact craters : Indications for unique impact-generated environments
- 2007
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Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379 .- 1945-5100. ; 42:11, s. 1971-1984
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Tidskriftsartikel (refereegranskat)abstract
- The Lockne and Tvaren craters formed in the Late Ordovician Baltoscandian epicontinental sea. Both craters demonstrate similarities concerning near-synchronous age, target seabed, and succeeding resurge deposits; however, the water depths at the impact sites and the sizes of the craters were not alike. The post-impact sedimentary succession of carbonates, i.e., the Dalby Limestone, deposited on top of the resurge sediments in the two craters, is nevertheless similar. At least three main facies of the Dalby Limestone were established in the Lockne crater, depending on sea-floor topography, location with respect to the crater, and local water currents. The dominating nodular argillaceous facies, showing low values of inorganic carbon (IC), was distributed foremost in the deeper and quiet areas of the crater floor and depressions. At the crater rim, consisting of crushed crystalline basement ejecta, a rim facies with a reef-like fauna was established, most certainly due to topographical highs and substrate-derived nutrients. Between these facies are occurrences of a relatively thick-bedded calcilutite rich in cephalopods (cephalopod facies). In Tvaren, the lower part of the succession consists of an analogous argillaceous facies, also showing similar low IC values as in Lockne, followed by calcareous mudstones with an increase of IC. Occasionally biocalcarenites with a distinctive fauna occur in the Tvaren succession, probably originating as detritus from a facies developed on the rim. They are evident as peaks in IC and lows in organic carbon (Corg). The fauna in these biocalcarenites corresponds very well with those of erratic boulders derived from Tvaren; moreover, they correspond to the rim facies of Lockne except for the inclusion of photosynthesizing algae, indicating shallower water at Tvaren than Lockne. Consequently, we suggest equivalent distribution patterns for the carbonates of the Dalby Limestone in Lockne and Tvaren.
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| 34. |
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| 35. |
- Frisk, Åsa M., 1974-, et al.
(författare)
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Late Ordovician brachiopod distribution and ecospace partitioning in the Tvären crater system, Sweden
- 2013
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 369, s. 114-124
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Tidskriftsartikel (refereegranskat)abstract
- Patterns of distribution and ecospace utilization of Late Ordovician brachiopods in a recently formed, contemporary meteorite crater are described and analyzed. Rhynchonelliformean brachiopod communities, dominated by a wide range of orthides and strophomenides, colonized the newly formed crater. At the crater rim communities were established early on, although the crater depression was not inhabited until deposition of the upper third of the remaining crater fill. The crater formed a protected but restricted microenvironment where sediments four times the thickness of the nearby basinal succession accumulated. Within this narrow space environments varied from shallow-water to deeper-waters, about 200 m in depth, and from well oxygenated to hypoxic. Such varied environments generated a rough ecological landscape, facilitating niche partitioning across a relatively small geographic area. Analysis of the guild structure of the fauna permits explanation of a local biodiversity hotspot in otherwise low-diversity strata elsewhere in the Scandinavian region. The Tvären impact event had an important palaeobiologic effect upon the fossil record as it served as a local pump and reservoir for biodiversity. Moreover the development of new community types and narrowly-defined niches helped further drive both α and β biodiversity during a critical phase of the Great Ordovician Biodiversification Event.
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| 36. |
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| 37. |
- Frisk, Åsa M
(författare)
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Late Ordovician Faunal Distribution and Ecospace Partitioning in Marine Impact Craters : The Aftermath of the Lockne and Tvären Events
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the Middle to Late Ordovician a boost of marine biodiversity occurred which is regarded as the most rapid diversity in Earth’s history, and termed the Great Ordovician Biodiversification Event. This time is also unique in that at least four marine meteorite craters with a good record of post-impact sediments are preserved in Baltoscandia. Catastrophic impacts can serve as constructive events and produce wide-ranging environments providing new ecological niches for a diverse biota to occupy. Additionally, they generate distinctive patterns of biological destruction and recovery. This, and the study of distribution and ecospace utilisation of Late Ordovician faunas, has been analysed in two almost contemporary (around 455 million years ago) meteorite craters (Lockne and Tvären, Sweden). Within the confined space of the impact craters environments varied from shallow and reef-like to over 200 m in depth and from well oxygenated to hypoxic. These types of environments favored colonization of different individual groups. In Tvären rhynchonelliformean brachiopod assemblages from the shallow crater rim include a range of morphotypes, not established elsewhere in the crater. Within the crater depression rhynchonelliformean brachiopods were not established until the upper third of the remaining crater fill. Colonization of post-impact faunas varies dependent on topography, depth and susbstrate within the impact craters. This is recognised for scolecodonts in Tvären and for gastropod-like mollusks, linguliform and craniiform brachiopods in both of the craters, as they inhabit a wide range of ecospace. A succession of different taxa is observed from the deepest part of each crater and upwards towards inferably more shallow, higher energy, water settings. The development of new community types and narrowly-defined niches in the craters helped further drive both α and β biodiversity during a critical phase of the Great Ordovician Biodiversification Event.
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| 38. |
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| 39. |
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| 40. |
- Frisk, Åsa M., et al.
(författare)
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Palaeoenvironmental aspects of Late Ordovician Sericoidea shell concentrations in an impact crater, Tvären, Sweden
- 2011
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 44:4, s. 383-396
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Tidskriftsartikel (refereegranskat)abstract
- Numerous studies have reported the presence of the small, thin-shelled cosmopolitan rhynchonelliformean Sericoidea as being environmentally controlled and, together with its close relatives, characteristic of deep-water, distal, clastic Ordovician and Silurian settings. Assemblages of Sericoidea have been analysed from post-impact strata in a newly formed Late Ordovician impact crater. In the crater succession, colonization of benthic faunas can be monitored through the post-impact limestone, demonstrating a number of environmental preferences. Consequently, the crater, as a result of its restricted area, provides an experimental arena for faunal distributions to be correlated with specific environments. The continuous infilling of the crater following its formation reveals a transition from argillaceous mudstones to carbonates deposited in deeper-water environments to shallower regimes. Rhynchonelliformean brachiopods inhabited the crater depression very late after the impact and are entirely represented by the genus Sericoidea, occurring abundantly in the upper third of the existing crater infill. The deep-water regime that existed in the depression during the initial interval of crater formation had been substantially reduced. Clearly Sericoidea-bearing associations associated with shaly substrates did not merely favour and occupy deep-water environments as previously suggested. The unfavourable conditions triggered by the impact and the inhospitable aftermath allowed Sericoidea to exploit a less-crowded ecospace. This reorganization, following the catastrophe, from a deep-water related ecological niche to considerable shallower settings suggests that Sericoidea was a pioneer colonist displaying an opportunist r-strategy. The shell beds analysed are related to shallower water and this may, moreover, help unravel the dilemma of the general absence of Sericoidea in the deeper-water Foliomena fauna.
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| 41. |
- Frisk, Åsa M., et al.
(författare)
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Paragastropoda, Tergomya and Gastropoda (Mollusca) from the Upper Ordovician Dalby Limestone, Sweden
- 2007
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Ingår i: WOGOGOB 2007. 9th meeting of the Working Group on Ordovician Geology of Baltoscandia.. ; , s. 89-
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Exceptional carbonate deposits of the Dalby Limestone developed during the Upper Ordovician (KukruseStage to Idavare substage) in the area of Tvären and Lockne (Sweden) as a result of two nearly coeval bolide impacts into the marine environment. The deposits are characterized by thicknesses numerous times greaterthan common for the unit and with a wider range of facies. The type area for the Dalby Limestone in the Siljan District, Dalarna, (Sweden) is used together with the Kårgärde section in Siljan for comparison of gastropod diversity and distribution together with the Lockne and Tvären successions. A fauna of 12 species, comprising about 200 specimens, of paragastropods, tergomyans and gastropods is described presenting a higher diversity than previously documented from the limestone. Species recognized from Tvären include Bucania erratica Frisk & Ebbestad, 2007, Holopea? sp., Eotomaria cf. E. notabilis (Eichwald, 1840), Lophospira cf. L. subulata (Koken in Koken & Perner 1925), and Pleurorima? sp. These have been found in erratics originated from the shallower rim facies in the Tvären crater. The fauna from Lockne includes Sinuites cf. S. corpulentus Koken in Koken & Perner, 1925, Deaechospira cf. D. elliptica (Hisinger, 1831), and Ectomaria sp. In Dalarna (Fjäcka and Kårgärde) Mimospira tenuistriata Wängberg-Eriksson, 1979 has previously been recorded (Wängberg-Eriksson, 1979). Besides this species, an in situ specimen of Eccyliopterus regularis Remelé, 1888 and museumcollections of Laeogyra reinwaldti (Öpik, 1930), Sarkanella epelys Frisk & Ebbestad, 2007 and Deaechospira elliptica (Hisinger, 1831) are recognised from the type locality, Kårgärde, and Furudal. Significant biostratigraphical and biogeographical results from this study are 1) the presence of Mimospira, Laeogyra, Sarkanella epelys indicates a strong faunal connection with Bohemia, Czech Republic. 2) Sarkanella is reported from outside Bohemia for the first time. 3) Bucania erratica n. sp. represents one of the earliest records of the genus in Baltoscandia. A single case of shell repair from failed predation is recorded in this species. 4) Synonyms for Eccyliopterus princeps Remelé and E. regularis Remelé are proposed. 5) The significance of Laeogyra, Eccyliopterus, and Deaechospira for regional correlation within the Upper Ordovician of Baltoscandia is confirmed.
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| 42. |
- Frisk, Åsa M., et al.
(författare)
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Paragastropoda, Tergomya and Gastropoda (Mollusca) from the Upper Ordovician Dalby Limestone, Sweden
- 2007
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 129:2, s. 83-99
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Tidskriftsartikel (refereegranskat)abstract
- A fauna of 12 species of paragastropods, tergomyans and gastropods is described from the Upper Ordovician (Kukruse Stage to Idavare substage) Dalby Limestone of Tvären, Lockne, and Fjäcka (Sweden), presenting a higher diversity than previously recognized. The presence of Mimospira, Laeogyra, Sarkanella epelys n. sp. indicates a strong faunal connection with Bohemia, Czech Republic. Sarkanella is reported from outside Bohemia for the first time. Bucania erratica n. sp. represents one of the earliest records of the genus in Baltoscandia. A single case of shell repair from failed predation is recorded in this species. Synonyms for Eccyliopterus princeps Remelé and E. regularis Remelé are proposed. The significance of Laeogyra, Eccyliopterus, and Deaechospira for regional correlation within the Upper Ordovician of Baltoscandia is confirmed.
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| 43. |
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| 44. |
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| 45. |
- Frisk, Åsa M, et al.
(författare)
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Trilobite bio and ecostratigraphy of the Tremadocian Djupvik and Köpingsklint formations (A. serratus trilobite Zone) on southern Öland, Sweden
- 2008
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Ingår i: GFF. - 1103-5897 .- 2000-0863. ; 130:3, s. 153-160
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Tidskriftsartikel (refereegranskat)abstract
- Trilobites of the late Tremadocian Apatokephalus serratus trilobite Zone, the Ceratopyge fauna, are abundant and widely distributed across Baltoscandia. During the Tremadocian they occur in the initial stable carbonate deposits on the platform (the Bjørkåsholmen Formation in the west; Djupvik and Köpingsklint formations in the east). Two sections at Ottenby and Degerhamn, southern Öland, Sweden, were investigated for trilobite abundance distribution. At Degerhamn and Ottenby the fauna is restricted to 70 and 78 cm respectively. In the Degerhamn quarry the fauna appears in the Djupvik Formation. At both localities the abundance distributions are similar, with an initial dominance of Ceratopyge acicularis and Shumardia pusilla, followed by a marked shift to a dominance of nileid species (Symphysurus angustatus, Varvia longicauda, Nileus limbatus). Comparisons with the Oslo Region showed a remarkably similar distribution pattern, and three biofacies are recognized. In the Oslo Region the Ceratopyge-Shumardia biofacies, the Bienvillia biofacies, and the nileid biofacies are developed. Only two of these are present on Öland, where the short lived drowning represented by the Bienvillia biofacies in the Oslo Region is not recorded. Within the nileid biofacies, Nileus and Varvia are more frequent on Öland than in the Oslo Region. The three biofacies may be applied to other areas of the Baltoscandian platform where this facies is present and potentially be used to discriminate depth gradients.
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| 46. |
- Frisk, Åsa, et al.
(författare)
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Palaeoecology of a marine impact crater in the Ordovician sea
- 2005
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Ingår i: Palaeontological Association 49th Annual Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Palaeoecology of a marine impact crater in the Ordovician seaÅsa Frisk1, Maurits Lindström2 and Lars Holmer11Department of Earth Sciences, Palaeobiology, Uppsala University, Sweden2Department of Geology and Geochemistry, Stockholm University, SwedenThe aftermath of marine impacts, in particular the patterns of faunal recovery in and around marine craters, are poorly understood. In the Ordovician Baltoscandian epicontinental sea a bolide impact resulted in the Tvären crater. At present it is located in the Stockholm archipelago, Sweden, where drillings in 1991 resulted in two drill cores.
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| 47. |
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| 48. |
- Frisk, Åsa
(författare)
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The Bjorkåsholmen Formation (Tremadoc): a homogenous distribution of Trilobites throughout the Baltoscandian platform
- 2005
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Ingår i: Lundadagarna i Historisk geologi och paleontologi IX.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- THE BJØRKÅSHOLMEN FORMATION (TREMADOC): A HOMOGENOUS DISTRIBUTION OF TRILOBITES THROUGHOUT THE BALTOSCANDIAN PLATFORMÅsa FriskUppsala University, Department of Earth Sciences, Palaeobiology, Norbyvägen 22, SE-752 36 Uppsala, Sweden.Extensive carbonate depositions initiate the Lower Ordovician succession of Baltoscandia forming the Tremadoc Bjørkåsholmen Formation, formerly the Ceratopyge Limestone, a distinctive unit corresponding to the trilobite zone of Apatokephalus serratus. In older studies a combined bio-litho stratigraphical concept of the unit has mostly been used, however a modern lithostratigraphical definition was given by Owen et al. (1990). The definition of the formation is based on the hypostratotype at Bjørkåsholmen in Slemmestad, Norway, and should be referred to instead of the historical synonym. The limestone succession has a broad regional distribution and its associated sediments were deposited across the Baltoscandian platform in a shallow water epicontinental sea. Similar depositional conditions are not known today. The unit is remarkable in its near homogenous facies, lithologic and faunal composition throughout the platform. The most recent revision of trilobites from the Ceratopyge fauna recognized 36 species assigned to 28 genera (Ebbestad 1999).In the present study sequences at Ottenby and Degerhamn on southern Öland, Sweden, were logged and compared for trilobite biostratigraphy. In both investigated localities the resulting trilobite abundance distributions are very consistent. The trilobite fauna from the Bjørkåsholmen Formation in the Oslo Region, Norway, and Öland are composed of the same typical Ceratopyge assemblage. Trilobite abundance data from both areas are nearly identical and demonstrate an upward declination of trilobite specimens. Comparison across the Baltoscandian platform between the westernmost occurrences in the Oslo Region and the easternmost outcrops on Öland therefore suggests widespread stable conditions of the Ceratopyge fauna during the sedimentation of the Bjørkåsholmen Formation.Ebbestad, J.O.R. 1999: Trilobites of the Tremadoc Bjørkåsholmen Formation in the Oslo Region, Norway. Fossils and Strata 47. 118 pp.Owen, A.W., Bruton, D.L., Bockelie, J.F. Bockelie, T.G. 1990: The Ordovician successions of the Oslo Region, Norway. Norges geologiske undersøkelse Special Publication 4. 54 pp.
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| 49. |
- Frisk, Åsa
(författare)
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The Bjørkåsholmen Formation (Tremadoc): a homogenous distribution of trilobites throughout the Baltoscandian platform
- 2004
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Ingår i: 48th Palaeontological Association Annual Meeting. ; , s. 199-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Bjørkåsholmen Formation (Tremadoc): a homogenous distribution of trilobites throughout the Baltoscandian platformÅsa FriskDepartment of Earth Sciences, Palaeobiology, Uppsala University, Norbyvägen 22, SE-752 36 Uppsala, Sweden The Lower Ordovician succession of Baltoscandia is initiated by extensive carbonate deposition forming the Tremadoc Bjørkåsholmen Formation, formerly the Ceratopyge Limestone, a distinctive unit corresponding to the trilobite zone of Apatokephalus serratus. The limestone succession has a broad regional distribution and its associated sediments were deposited across the Baltoscandian platform in a shallow water epicontinental sea. Similar depositional conditions are not known today. The unit is remarkable in its near homogenous facies, lithologic and faunal composition throughout the platform. This is clearly demonstrated in the present study, where sequences at Ottenby and Degerhamn on southern Öland, Sweden, were logged and compared for trilobite biostratigraphy. In both investigated localities the resulting trilobite abundance distributions are very consistent. The trilobite fauna from the Bjørkåsholmen Formation in the Oslo Region, Norway, and Öland are composed of the same typical Ceratopyge assemblage. Trilobite abundance data from both areas are nearly identical and demonstrate an upward declination of trilobite specimens. Comparison across the Baltoscandian platform between the westernmost occurrences in the Oslo Region and the easternmost outcrops on Öland therefore suggests widespread stable conditions of the Ceratopyge fauna during the sedimentation of the Bjørkåsholmen Formation.
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| 50. |
- Frisk, Åsa
(författare)
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Trilobite biostratigraphy of the Tremadoc Bjørkåsholmen Formation on Öland, Sweden
- 2004
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Ingår i: WOGOGOB-2004 Conference materials. ; , s. 141-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Trilobite biostratigraphy of the Tremadoc Bjørkåsholmen Formation on Öland, SwedenThe Lower Ordovician of Baltoscandia is characterized by the initiation of extensive carbonate deposits of the Ceratopyge Limestone. The limestone succession has a broad regional distribution and its associated sediments were deposited in a shallow water epicontinental sea across the Baltic platform during the late Tremadoc (Jaanusson 1976, 1982; Dronov & Holmer 1999). Those particular depositional factors have no present day equivalents. The unit is definitely remarkable in its apparent homogenous facies, lithological and faunal composition. The significance of the Ceratopyge Limestone succession was early referred by numerous authors and recognized sedimentologically and stratigraphically. Tjernvik (1956) reinvestigated the Lower Ordovician beds in Sweden in detail and completed an account of the rich Ceratopyge fauna.In older studies a combined bio-litho stratigraphical concept of the unit has mostly been used, however a modern lithostratigraphical definition was given by Owen et al. (1990). The definition of the formation is based on the hypostratotype at Bjørkåsholmen in Slemmestad, Norway, and should be referred to instead of the historical synonym. The transition from the dark underlying Alum Shale Formation to the grey limestone beds marks the base of the Bjørkåsholmen Formation (BHF), this is evident in the change in not only lithology but also the typical associated fauna e.g. the Ceratopyge fauna (Tjernvik 1956; Ebbestad 1999). In Sweden the BHF is followed by the Hunneberg-Billingen Latorp Limestone and Volkhov Lanna Limestone. Shales of the Tøyen Formation follow the partially glauconitic limestone in Norway (Owen et al. 1990). The most recent revision of the trilobite fauna recognized 36 species assigned to 28 genera (Ebbestad 1999).The present study investigates trilobite distribution of the BHF in southern Öland, the easternmost outcrop of the formation. The underlying crystalline bedrock on Öland dips weakly to the east resulting in the exposition of the oldest overlying sedimentary rocks in the west and the youngest beds in the east (Jaanusson & Mutvei 1982). The upper Cambrian Alum Shale Formation is continued in the Lower Ordovician successions and is subsequently overlain by the upper Tremadoc limestone deposits represented by the BHF. Outcrops of this unit are fairly rare, confined to a few localities in the southern and south-central parts of the island.The material presented in this study was collected at the coastal section at Ottenby and at the Cementa quarry in Degerhamn. Sequences at Ottenby and Degerhamn were logged and material collected for a biostratigraphical study. To obtain trilobite abundances the sample frequency method (Jaanusson 1979; Nielsen 1995; Ebbestad 1999) was applied. The lower boundary of the BHF in Öland is marked by the occurrence of glauconiferous limestone nodules, represented in both localities. The main limestone beds in Öland, e.g. constituting continuous beds having the main trilobite abundance, are grey and micritic, and with some intercalations of glauconitic shale. In addition scattered grains of glauconite and small accumulations of pyrite are evident in the main limestone. The uppermost bed in the two successions, devoid in trilobites, marks the upper boundary of the formation, it is also exceptionally glauconitic suggesting slow deposition and starvation of sedimentation. The BHF at both Degerhamn and the Ottenby section has an approximately thickness of 0.6 meter and several discontinuity surfaces are evident.The trilobite abundance logs give a proposal for the distribution of the trilobite fauna during the upper Tremadoc in Öland. The material collected from the section in Degerhamn and Ottenby belongs to the Ceratopyge fauna and biostratigraphically the unit is connected to the Apatokephalus serratus Zone. The trilobite abundance distribution from each of the localities is very consistent. Additionally, the fossil assemblages in Öland and the Oslo Region (Ebbestad 1999) are built up by the same typical Ceratopyge fauna, indicating a correlation. Faunal signals show several similarities in the trilobite abundance data and both areas have an upwards declination of trilobite quantities in the sequences. Faunal distribution of trilobites of the Ceratopyge fauna is thus very coherent throughout the platform. This suggests widespread stable conditions of the fauna throughout the Baltic Platform during sedimentation of the BHF. The Central Baltoscandian Confacies Belt (Jaanusson 1976), to which Öland belongs, and the Oslo Region belonging to the Oslo Confacies Belt, demonstrate no facies differentiation of the platform until post-Tremadoc (Jaanusson & Mutvei 1982).The basal limestone nodules at the two investigated sections are devoid of trilobite remains. Periods of oxygenated lime mud sedimentation, reflected by the basal limestone nodules incorporated in the shale, may indicate times of fluctuations in the sea level. The main limestone units have little or no intercalations of shale, thus representing episodes of more stable sedimentary facies. The unstable settings may suggest non-favourable environments for the establishment of nileid communities (Fortey 1975), here represented by the Ceratopyge fauna, described by the absence of trilobites in the lowermost limestone nodules. Fluctuations of the sea level was probably confined to local settings and are suggested by extended periods with large inputs of oxygen during lime mud sedimentation. Constrained settings are most likely a result of diverse bottom topography and differences in current and wave distribution throughout the area (Ebbestad 1999). The faunal logs clearly demonstrate this idea. Ebbestad (1999) stated similar conditions for the depositions of the basal limestone beds in the BHF of the Oslo Region. The Ceratopyge fauna display coherent distribution in Öland and certainly across the platform, moreover, the distribution does not correlate with specific beds, presumably demonstrating dissimilar sedimentological developments of the two localities, suggesting that the deposition was diachronous.The upper Tremadoc and early Arenig represents a time of large global sea-level changes by the lowering of the seas (Fortey 1984), this event the Ceratopyge Regressive Event (CRE) (Erdtmann & Paalits 1995) could have resulted in the depletion of sediments. In Baltica this is clearly shown by the end of the Apatokephalus serratus zone, the top of the Bjørkåsholmen Formation, and in addition the disappearance of its associated Ceratopyge fauna.References:Dronov, A. & Holmer, L. 1999: Depositional sequences in the Ordovician of Baltoscandia. ActaUniversitatis Carolinae - Geologica 43, 133-136.Ebbestad, J.O.R. 1999: Trilobites of the Tremadoc Bjørkåsholmen Formation in the Oslo Region,Norway. Fossils and Strata 47. 118 pp.Erdtmann, B.D. & Paalits, I. 1995: The Early Ordovician ’Ceratopyge Regressive Event’ (CRE): itscorrelation and biotic dynamics across the East European Platform. Lithuanian Geological Society,Geologija, 1994, 17, 36-57.Fortey, R.A. 1984: Global earlier Ordovician transgressions and regressions and their biologicalimplications. In: Bruton, D.L. (ed.). Aspects of the Ordovician System. PalaeontologicalContributions from the University of Oslo, No. 295, Universitetsförlaget, 37-50.Jaanusson, V. 1976: Faunal dynamics in the Middle Ordovician (Viruan) of Baltoscandia. In: BasettM.G. (ed): The Ordovician System. University of Wales Press, Cardiff, 301-326.Jaanusson, V. 1979: Ecology and faunal dynamics. In: Jaanusson, V., Laufeld, S. & Skoglund, R.(eds:): Lower Wenlock faunal and floral dynamics – Vattenfallet Section, Gotland. SverigesGeologiska Undersäkning C 762, 253-294.Jaanusson, V. & Mutvei, 1982: Jaanusson, V. & Mutvei, H. 1982: Ordovician of Öland. Guide toexkursion 3. IV International Symposium on the Ordovician System, Oslo 1982, 23 pp.Nielsen, A.T. 1995: Trilobite systematics, Biostratigraphy and palaeoecology of the Lower OrdovicianKomstad and Huk Formations, southern Scandinavia. Fossils and Strata 38. 374 pp.Owen, A.W., Bruton, D.L., Bockelie, J.F. Bockelie, T.G. 1990: The Ordovician successions of theOslo Region, Norway. Norges geologiske undersøkelse Special Publication 4. 54 pp.Tjernvik. T.E. 1956: On the Early Ordovician of Sweden. Bulletin of the Geological Institutions ofUppsala 35, 108-284.
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