| 1. |
- Ahlberg, Per, et al.
(författare)
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Miaolingian (Cambrian) trilobite biostratigraphy and carbon isotope chemostratigraphy in the Tingskullen drill core, Öland, Sweden
- 2021
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Ingår i: Estonian Journal of Earth Sciences. - : Estonian Academy Publishers. - 1736-7557 .- 1736-4728. ; 70:1, s. 18-35
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Tidskriftsartikel (refereegranskat)abstract
- The Cambrian succession of the Tingskullen drill core from northern Öland comprises Cambrian Series 2 and Miaolingian (Wuliuan Stage) siliciclastic strata. The major portion of the succession is represented by the Miaolingian Borgholm Formation, which, in ascending order, is subdivided into the Mossberga, Bårstad and Äleklinta members. The Äleklinta Member is barren of body fossils, whereas the Mossberga and Bårstad members are moderately to highly fossiliferous and biostratigraphically reasonably well constrained. Trilobites and agnostoids from the Bårstad Member are indicative of the Acadoparadoxides pinus Zone.The Mossberga Member has not yielded any zonal guide fossils but is tentatively assigned to the Eccaparadoxides insularis Zone. A δ13Corg curve throughout the Borgholm Formation shows a general positive trend upsection without any distinctive excursion, suggesting that the Wuliuan Acadoparadoxides (Baltoparadoxides) oelandicus Superzone (the ‘Oelandicus beds’) of Öland is younger than the negative Redlichiid–Olenellid Extinction Carbon isotope Excursion (ROECE), which is known from near the top of Stage 4 and close to the traditional ‘Lower–Middle Cambrian boundary’ in several parts of the world.
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| 2. |
- Ahlberg, Per, et al.
(författare)
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Minnesord Sven Stridsberg
- 2020
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Ingår i: Geologiskt forum. - 1104-4721 .- 1104-4721. ; :105
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Annan publikation (populärvet., debatt m.m.)
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| 3. |
- 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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| 4. |
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| 5. |
- Bergström, Stig M., et al.
(författare)
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The δ13C chemostratigraphy of Ordovician global stage stratotypes : geochemical data from the Floian and Sandbian GSSPs in Sweden
- 2020
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 142:1, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- The δ13C chemostratigraphy of five of the seven Ordovician global stages has been published previously but no such data have been available from the Floian GSSP and most of the Sandbian GSSP in Sweden. This lack of information has now been remedied by isotope data obtained from series of closely spaced shale samples collected from the Floian stratotype at Diabasbrottet in Västergötland and the Sandbian stratotype at Fågelsång in Scania. Although the bases of these stages cannot be precisely tied to levels of conspicuous δ13C excursions, that of the Floian Stage, which is marked by the appearance of the graptolite Tetragraptus approximatus, is between the closely spaced excursions named LTNICE and BFICE. The base of the Sandbian Stage, which is defined as the appearance level of the graptolite Nemagraptus gracilis, is just below a negative excursion previously known as the “Upper Kukruse Low”, which is nowadays known as the LSNICE. The relations between chemostratigraphy and graptolite and conodont biostratigraphy in the Swedish GSSPs and some coeval key sections in Baltoscandia, China, and America are briefly discussed. It is concluded that the data at hand indicate that there is good regional agreement in these relations.
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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. |
- Harper, David A.T., et al.
(författare)
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Early Cambrian brachiopod-dominated shell concentrations from North-East Greenland: Environmental and taphonomic implications
- 2021
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 204, s. 103560-103560
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of a series of thin but persistent early Cambrian (Cambrian Age 4) brachiopod shell concentrations extending along a transect of some 150 km in NE Greenland, indicates the ability of the group to form widespread, skeletal pavements very early in the history of the phylum, its gregarious behaviour and ability to harness available nutrients. These extensive shell pavements within the Bastion Formation mark biological events within the basin, the abundance of shells perhaps associated with oscillating redox conditions prompting the dissolution of phosphate and its spread across the shelf. The shells were subsequently reworked and deposited by episodic distal storm surges with some winnowing.
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| 8. |
- Kirscher, Uwe, et al.
(författare)
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Age constraints for the Trachilos footprints from Crete
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an updated time frame for the 30 m thick late Miocene sedimentary Trachilos section from the island of Crete that contains the potentially oldest hominin footprints. The section is characterized by normal magnetic polarity. New and published foraminifera biostratigraphy results suggest an age of the section within the Mediterranean biozone MMi13d, younger than similar to 6.4 Ma. Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma. By integrating the magneto- and biostratigraphic data we correlate the Trachilos section with normal polarity Chron C3An.1n, between 6.272 and 6.023 Ma. Using cyclostratigraphic data based on magnetic susceptibility, we constrain the Trachilos footprints age at similar to 6.05 Ma, roughly 0.35 Ma older than previously thought. Some uncertainty remains related to an inaccessible interval of similar to 8 m section and the possibility that the normal polarity might represent the slightly older Chron C3An.2n. Sediment accumulation rate and biostratigraphic arguments, however, stand against these points and favor a deposition during Chron C3An.1n.
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| 9. |
- Kozik, Nevin P., et al.
(författare)
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Progressive marine oxygenation and climatic cooling at the height of the Great Ordovician Biodiversification Event
- 2023
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Ingår i: Global and Planetary Change. - 0921-8181. ; 227
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Tidskriftsartikel (refereegranskat)abstract
- The oxygen content of ancient seawater has been hypothesized to be a major controlling factor for biodiversity throughout Earth's history. The Great Ordovician Biodiversification Event (GOBE) represents one of the largest increases in biodiversity during the Phanerozoic, with peak rates of diversity occurring in the Middle–Late Ordovician. Multiple causal factors have resulted in this long-term adaptive radiation, but direct links to marine oxygen levels remain poorly characterized. Here we utilize a multiproxy dataset from the Röstånga-2 drillcore, Skåne (Scania), southernmost Sweden, to constrain local and global marine paleoredox dynamics using a multi-proxy approach throughout the Middle–Late Ordovician (Darriwilian–early Sandbian stages). Pyrite sulfur isotopes (δ34Spyr), iron speciation and trace metal concentrations (V, U, and Mo) all indicate pervasive locally reducing conditions, and thallium (ε205Tl) isotopic compositions indicate significant changes in global Mn-oxide burial. This is one of the first studies to utilize direct local and global paleoredox proxies to identify changes in marine oxygen associated with peak rates of biodiversification in the Ordovician. Our new thallium isotope and pyrite sulfur isotope trends from black shale are combined with previously published carbonate-based redox proxy data (δ238U and δ34SCAS–carbonate-associated sulfate) from time equivalent successions in Baltica, Laurentia and Argentine Precordillera, indicating a global shift towards enhanced Mn-oxide burial, decreased anoxic seafloor area, and decreased pyrite burial, respectively. Thus, oceanic conditions during the Middle–Late Ordovician are interpreted to have transitioned from pervasive, highly reducing conditions towards more oxygenated marine settings. These changes in global paleoredox coincide with paleotemperature proxy data that indicated an overall climatic cooling trend during this time. Significant cooling of Ordovician oceans and climate would have permitted enhanced ventilation of marine environments, that in turn likely facilitated new ecospace development/utilization and ultimately drove marine biodiversification. Our results show a protracted, yet progressive oxygenation of marine environments over an interval of ∼11 Myr coinciding with peak rates of biodiversification during the GOBE.
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| 10. |
- Kozik, Nevin P., et al.
(författare)
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Protracted oxygenation across the Cambrian–Ordovician transition : A key initiator of the Great Ordovician Biodiversification Event?
- 2023
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 21:3, s. 323-340
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Tidskriftsartikel (refereegranskat)abstract
- Fluctuations in marine oxygen concentrations have been invoked as a primary driver for changes in biodiversity throughout Earth history. Expansions in reducing marine conditions are commonly invoked as key causal mechanisms for mass extinctions, while increases in marine oxygenation are becoming an increasingly common causal mechanism invoked for biodiversification events. Here we utilize a multiproxy approach to constrain local and global marine paleoredox conditions throughout the late Cambrian–Early Ordovician from two drill core successions in Baltoscandia. Local paleoredox proxies such as manganese concentrations and iron speciation reveal that both sites in the Baltic paleobasin had persistently anoxic and predominantly euxinic (anoxic and sulfidic) bottom water conditions throughout the study interval. Corresponding trace metal datasets indicate nuanced contraction and expansion of global anoxic and euxinic conditions along continental margins during the late Cambrian–Early Ordovician. Lastly, thallium isotope data from these locally reducing sections suggest a global expansion of oxygenated shelf and deeper marine environments from the late Cambrian into the Early Ordovician. This evidence for increasingly oxic marine environments coincides with increases in burrowing depth and tiering in marine animals, as well as diversification of body fossils throughout this ~8-million-year interval. The collective geochemical datasets provide some of the first direct paleoredox evidence for an increase in marine oxygen concentrations as a key mechanism for the Ordovician radiation of marine life.
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