| 1. |
- Alwmark, Carl
(författare)
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Traces in Earth's geological record of the break-up of the L-chondrite parent body 470 Ma
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with signatures in sediments on Earth related to the L-chondrite parent body break-up event at 470 Ma. The aim of this thesis is twofold: (1) investigate if the increased flux of extraterrestrial material to Earth, following the disruption of the L-chondrite parent body included larger, asteroid-sized bodies (2) try to develop new methods and tools for finding and classifying relict cosmic material in sediments. The material studied originates from Middle and Late Ordovician sedimentary rocks from different localities within Sweden and in one case from Estonia. Traces of the L-chondrite break-up found and studied include extraterrestrial chromite grains, relict silicate inclusions in extraterrestrial chromite grains, pseudomorphosed chondrules in fossil meteorites and shock metamorphic features in quartz. Studies of extraterrestrial chromite grains in the resurge deposit of the early Late Ordovician (458 Ma) Lockne impact crater in central Sweden, show that the structure was formed by an L-chondritic impactor. This together with the fact that vast amounts of chromite with an L-chondritic composition is found in the 466 Ma Osmussaar Breccia in Estonia, suggesting yet another L-chondritic impact event, imply that the increased flux of extraterrestrial material to Earth, following the disruption of the L-chondrite parent body included larger bodies. This is further corroborated by the verification of the Granby structure as being impact derived, based on the findings of PDFs in quartz in the infill breccias. Although the projectile type is unknown, the timing of the impact (467 Ma) raises the suspicion that it too originates from the L-chondrite parent body. The finding of abundant sediment-dispersed extraterrestrial chromite grains (0.45 grain kg−1) with an L-chondritic composition in limestone in the mid-Ordovician Gärde quarry in central Sweden, suggests that the enhanced flux of L-chondrites prevailed at the time the Brunflo meteorite fell ca. 5 Ma after the meteorites from the Thors¬berg quarry settled on the seafloor. New chondrule-size measurements for the Brunflo mete¬orite indicate that it too is an L-chondrite, and thus most likely a part of this increased flux of L-chondritic matter. Furthermore, the low TiO2 (1.8 wt%), the Dmax of relict chromite and the relatively sharp chondrule definition imply that Brunflo is of petrographic type 4. The discov¬ery of extraterrestrial chromite grains in impact related material shows that physical pieces of larger projectiles can survive the impact process. Chemical analyses of chromite show that the majority of the recovered grains have retained their primary composition and that they thus can be used to classify the impacting projectile. Primary inclusions of olivine, pyroxene, merrillite and plagioclase have been identified in chromite of extraterrestrial origin, both in recent and fossil meteorites, as well as in sediment-dispersed extraterrestrial chromite grains. The systematic compositional difference in Fa in the chromite-hosted olivine and the more or less analogous Fs-content in Ca-poor pyroxene, compared to matrix phases, makes it pos¬sible to establish ranges for inclusions analogous to the well established classification system based on Fa in olivine and Fs in Ca-poor pyroxene, for ordinary equilibrated chondrites. Thus, making this a good tool in classification of fossil meteorites, as well as the origin of sediment-dispersed chromite grains from decomposed meteorites and larger impacts, where no other matrix minerals have survived, or are present.
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| 2. |
- Axheimer, Niklas
(författare)
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The lower and middle Cambrian of Sweden: trilobites, biostratigraphy and intercontinental correlation
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on studies of Cambrian successions in Sweden, with particular focus on the middle Cambrian biostratigraphy and its correlative relationship to the proposed global agnostoid zonation. The investigated material, mainly trilobites, was collected from both outcrops and drill cores from five provinces in Sweden: Skåne (Scania), Öland, Västergötland, Jämtland and Lapland. The Almbacken drill core penetrated c. 30 m of Cambrian strata, constituting one of the stratigraphically most complete successions of this age in Scania. Thirty-two trilobites were identified to species level and used to subdivide the core into seven biozones; from the Ptychagnostus gibbus Zone of the lower middle Cambrian to the Lejopyge laevigata Zone of the upper middle Cambrian. Another drill core (Andrarum-3) was taken at Andrarum, south-eastern Scania. It covers c. 29 m of middle Cambrian to Furongian (upper Cambrian) strata. Based on the fossil content, the core was subdivided into eight biozones; from the middle Cambrian P. atavus Zone to the Furongian Parabolina spinulosa Zone. A series of alum shale samples yielded a positive ?13C excursion corresponding to the globally recognisable Steptoean Positive Carbon Isotope Excursion (SPICE). This is the first time SPICE is documented in Baltica, and based on organic matter from an alum shale setting. New material collected from Västergötland showed that the P. punctuosus and Goniagnostus nathorsti zones are considerably more extensively developed in this area than previously thought. Trilobites collected from eight localities show that the two zones are represented in a 15 cm thick and impersistent conglomeratic limestone at both Mount Kinnekulle and in the larger area of Falbygden-Billingen. Moreover, the classical locality of Gudhem yielded a trilobite fauna including several widespread key agnostoid species. In particular, L. laevigata (Dalman, 1828) was studied as its first appearance datum (FAD) currently is proposed to define the base of the uppermost stage in the Cambrian Series 3. We suggested that the base of the L. laevigata Zone of Scandinavia should be defined by the FAD of the eponymous species. Of similar global stratigraphical importance is P. atavus (Tullberg, 1880). Its FAD is proposed to define the base of the middle stage of the Cambrian Series 3. A syntype series collected from the Forsemölla-Andrarum area of Scania of both this species and the closely similar P. intermedius (Tullberg, 1880) were studied. It was concluded that they are conspecific, and that P. intermedius is the junior synonym of P. atavus. A revision of the conspicuous eodiscoid Dawsonia oelandica (Westergård, 1936) was made, based on well preserved material from Mon, Jämtland. Reconstructions of this species were presented, and its functional morphology and relationship to closely related taxa were discussed. Associated trilobites placed the material stratigraphically within the lower middle Cambrian P. praecurrens Zone. Another eodiscoid fauna, including the first reported occurrence from Scandinavia of Neocobboldia aff. dentata (Lermontova, 1940) and Chelediscus acifer Rushton, 1966, was also studied. These eodiscoids, recovered from the Luobákti section, Lapland, offered a tentative correlation between the uppermost lower Cambrian strata of Baltica and eastern and western Avalonia. From the studies included in this thesis it has been shown that the proposed global zonation can be applied to Swedish middle Cambrian successions, substituting the traditional zonation in our overall strive for a common global zonation. Accordingly, eight biozones can be recognised (in ascending order): the Eccaparadoxides insularis, P. praecurrens, P. gibbus, P. atavus, P. punctuosus, G. nathorsti, L. laevigata and Agnostus pisiformis zones.
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| 3. |
- Cronholm, Anders
(författare)
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The flux of extraterrestrial matter to Earth as recorded in Paleogene and Middle Ordovician marine sediments
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims at reconstructing events in the solar system, mainly collisional events in the asteroid belt, by searches for extraterrestrial minerals in Paleogene and Middle Ordovician marine sediments on Earth. Recent empirical evidence show that Earth has experienced a few brief periods during the Phanerozoic when the flux of extraterrestrial matter significantly increased. The most prominent of these occurred at approximately 470 Ma, as a consequence of the massive break-up of the L-chondrite parent body in the asteroid belt. The finds of more than 87 fossil L chondritic meteorites (Ø = 1-21 cm) in mid-Ordovician strata at Thorsberg, Kinnekulle, give testimony to the spectacular flux of meteorites that followed the break-up event. The fossil meteorites are almost completely pseudomorphed, with the exception of chromite, an exceptionally resistant accessory mineral (~0.25 wt%) in ordinary chondrites. Extraterrestrial chromite (EC) is distributed in the immediate surrounding limestones beds of the fossil L chondrites, indicating that most meteorites that reached the sea floor were dissolved, dispersing the EC grains in the contiguous sediments. The distribution of EC has previously been studied at mid- Ordovician sections in Sweden. The goals of this thesis are threefold: (1) establish the normal background distribution of EC to corroborate the extraordinary circumstances recorded during the mid-Ordovician; (2) investigate the global pattern of the EC distribution during the mid-Ordovician, by studying a remote site; (3) study variations in the marine osmium isotope (187Os/188Os) record across the EC-rich interval at Hällekis, Kinnekulle. The Paleogene marine sediments at Gubbio and Massignano, Italy, were analysed for EC content, yielding 7 EC in a total of 377 kg whole-rock (0.019 EC kg-1). This result is very similar to previously studied mid-Ordovician strata, forming prior to the L-chondritic breaking event, in Sweden and China (0.009-0.013 EC kg-1). In addition, the low EC content at Massignano contradicts a proposed ordinary (L) chondritic meteorite shower in the late Eocene. The general trend in the distribution of sediment-dispersed EC in Swedish strata during the mid-Ordovician has been reproduced in the coeval stratigraphic interval at Puxi River, central China. At this time, the Chinese section was positioned at mid-latitudes on the southern hemisphere, a few 1000 km east of the Swedish sites. The EC-rich interval at Puxi typically has 1-4 EC grains per kg rock, equivalent to previous results for coeval Swedish limestone. Consequently, a global correlation has been established for the EC distribution across the Arenig-Llanvirn transition. A close temporal correlation has also been suggested for the main phase of the Great Ordovician Biodiversification Event and the disruption of the L-chondrite parent body at ~470 Ma, based on bed-by-bed records of EC, 187Os/188Os and invertebrate fossils in Middle Ordovician sediments in Baltoscandia and China. The intense species radiation and level of change in biodiversity of this event changed the biological composition of the Earth’s oceans forever. The causes of the event remain elusive, although influences of extraterrestrial origin cannot be excluded, and further studies are warranted. At Hällekis, the first appearance of common EC grains is marked by a negative 187Os/188Os excursion in the strata, verifying an increased influence of unradiogenic osmium. This source is most likely extraterrestrial in origin, as corroborated by stable strontium isotope ratios from late Arenig to early Llanvirn. In all, 665 kg of Paleogene and Middle Ordovician sediments from Italy and China has been searched for EC grains in this thesis work. The composite background material from the Italian and Chinese sections represents 487 kg of rock, and yielded only 8 EC altogether. The EC-rich Ordovician interval, representing the sequential L. variabilis, Y. crassus and M. hagetiana conodont zones, yielded a total of 290 EC grains in 178 kg of limestone, signifying an average 1.63 EC per kg rock. This clearly shows a two orders-of-magnitude increase in the flux of L-chondritic matter during the mid-Ordovician. In conclusion, the largest documented break-up event in the asteroid belt has left a prominent signature in the coeval sediments on Earth, and this thesis corroborates the significance and global consequences of this event.
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| 4. |
- Dahlqvist, Peter
(författare)
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Late Ordovician-Early Silurian facies development and stratigraphy of Jämtland, central Sweden
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on studies of Lower Palaeozoic sedimentary successions within the central Scandinavian Caledonides. These deposits have been transported by considerable nappe displacement (several kilometres), and are today relatively isolated from the nearest coeval outcrops (Dalarna 250 km, Oslo Region 350 km). As a consequence, and due to the previously limited biostratigraphical control the investigated area have received little attention the last decades. Therefore, a detailed investigation, using several untried geological tools was performed. During the study it became clear that the strata reflected substantial changes in depositional environment and complexity in lateral facies relationship during the Late Ordovician?Early Silurian. This was a time characterised by global environmental changes such as glacio-eustasy and climate change, in particular during the end-Ordovician (Hirnantian) glaciation. Facies and sequence stratigraphical analysis of two key units (the Ede Quartzite and the Kyrkås Quartzite) and their preceding and succeeding units resulted in reinterpretations and refinement of the stratigraphy. The new data implied that the successions could be linked to known Hirnantian sea-level fluctuations. This correlation was subsequently supported, and our understanding of the timing of changes was improved, by biostratigraphical evidence (conodonts, graptolites, and brachiopods). This revealed a ca 5 myr stratigraphical gap, within the Ede Quartzite, spanning the Ordovician?Silurian boundary. It is concluded that the interaction of allocyclic changes (sea level and climate) were the overriding controls on deposition during the Late Ordovician?Early Silurian in the Jämtland basin. The contrasting sedimentary architecture of the Ede Quartzite to the west and the partly coeval Kyrkås Quartzite to the east remained enigmatic. Provenance studies (radiometric dating of zircons) tentatively indicate different dominating source areas, but further studies are needed to solve their relationship.
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| 5. |
- Eneroth, Erik
(författare)
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Nanomagnetic and Micromagnetic Properties of Rocks Minerals and Sulphide Oxidation Products
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic and related properties of rocks and products from oxidation of sulphide minerals have been investigated with magnetisation measurements (rocks and oxidation products), magnetic force microscopy (rocks), scanning electron microscopy (rocks and oxidation products), transmission electron microscopy (oxidation products), Mössbauer spectroscopy (oxidation products) and powder X-ray diffraction (oxidation products). The investigations have shown the following: During thermal oxidation of pyrite (cubic FeS2) and marcasite (orthorombic FeS2) in air, nano-crystals of a-Fe2O3 and g-Fe2O3 were formed. If smaller grains of FeS2 were used, then smaller crystals of both a-Fe2O3 and g-Fe2O3 were formed, and the relative amounts of g-Fe2O3 increased. The g-Fe2O3 was investigated with magnetisation measurements, showing decreasing crystal sizes when the temperature was increased above 500°C. The increased amount of g-Fe2O3 during oxidation of small FeS2 grains was due to the lower surface energy compared to a-Fe2O3. Due to the small crystal sizes, a large surface area will be accessible for adsorption of heavy metals and sulphate ions in oxidised FeS2. Therefore, the nano-crystalline nature must affect the geochemical behaviour of similarly formed industrial waste products. During oxidation of a FeSO4 solution with a bacterial suspension, the resultant phases were a function of starting pH of the solution, and they were investigated in the magnetically ordered state (below 80 K) with Mössbauer spectroscopy. It was argued that the amount of bound sulphate in schwertmannite increased with decreasing pH of the solution. During investigation of the rock samples, a new method to report demagnetisation properties was applied. It was based on calculation of the total sum of the lengths of the demagnetisation steps, and the determination of linearity parameters, unblocking data and calculation of the fraction of characteristic remanent magnetisations. Magnetic properties of two rock formations were determined, and results related all other methods of observation. They were the following rocks: (1) granulites from SW Sweden; and (2) sheeted dykes from the Seve Nappe Complex, N Sweden. In the granulites, it was possible two discern two magnetisation components and to quantitatively determine their relative contributions to the natural remanent magnetisation (NRM). There was a 930 Ma old high blocking component in exsolved hematite-ilmenite, and a Cretacceous - recent component in multidomain (MD) magnetite. The relative importance of the MD-component increased with increased metamorphic retrogression (due to changed rock composition), but the hematite-ilmenite component still gives rise to a negative aeromagnetic anomaly in the area. In the sheeted dyke samples, the properties were due to a mixture of SD and MD grains. The latter occurred as silicate-oxide intergrowths. These were better resolved with thermal than alternating field demagnetisation. The magnetic mineralogy of the dykes was directly related to different degrees of contact metamorphism, thereby allowing detailed characterisation of processes affecting magnetic properties of rocks in the continent - ocean transition. It is argued that reports of NRM unblocking data should be important in paleomagnetism and rock-magnetism.
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| 6. |
- Eriksson, Mårten
(författare)
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Silurian Carbonate Platforms of Gotland, Sweden - Archives of Local, Regional and Global Environmental Changes
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats the Silurian carbonate platforms of Gotland, Sweden, which formed close to the equator within the East Baltic Basin. Three different time intervals, all involving changes in facies composition and structure of the platforms, have been studied; Late Homerian, latest Homerian ? earliest Gorstian, and late Ludfordian, respectively. Two of the intervals, the Late Homerian and the late Ludfordian, are known globally as periods of substantial environmental change, including sea-level changes, faunal extinctions (the Mulde and Lau events, respectively) and perturbations in the global carbon cycle, whereas the latest Homerian-earliest Gorstian is not associated with such global environmental changes. The aim of the project has been to study and interpret causes and effects of the environmental changes as reflected by sedimentary facies from low latitude shallow shelf environments. Facies analysis of outcrops and drillcores has formed the basis of the study, but for the late Ludfordian time interval, geochemical data (d13C and d18O) have been used in addition. The results of this study can be categorized into five main groups; 1) Stratigraphical improvements ? local refinement of the stratigraphy has been made in several different areas (e.g. the Ytterholmen islet and the Burgen and Lau outliers), and the knowledge about subsurface facies and geometries of stratigraphical units has been improved by recovery and study of several drillcores, 2) Increased understanding of depositional and erosional processes ? strata have been put into a context of depositional environments, and related to depositional and erosional processes. For example, the Burgsvik Sandstone has been re-interpreted as comprising reworked delta deposits, 3) Documentation of sea-level changes ? the studied strata have been put into a sequence stratigraphical context, revealing that sequence boundaries may not correspond with the traditional topostratigraphical boundaries. Evidence for forced regressions have been identified within all the three time intervals, of which the Late Homerian and the late Ludfordian are interpreted as glacio-eustatic, whereas the latest Homerian ? earliest Gorstian is interpreted as a relative sea-level fall affecting at least parts of the East Baltic Basin, 4) Relationships between sedimentary changes and faunal reorganisations ? This thesis has clarified relationships between faunal changes and environmental changes. The Mulde and Lau events are associated with the most rapid and substantial changes in facies composition and platform evolution within the entire Gotland succession. The significant decrease in biodiversity within the (post-event) Burgsvik Sandstone indicates that major faunal reorganisations also occurred on local scales due to autocyclic processes, 5) Silurian global climate ? based on the combined use of sedimentary facies and stable oxygen isotope (d18O) data, a glaciation is inferred to have occurred during the late Ludfordian. This hence challenges the common view of a prolonged Silurian greenhouse climate following the Late Ordovician-Early Silurian icehouse-period. The globally recognized, positive, carbon isotope excursion within the late Ludfordian has been closely linked to the glacio-eustatic sea-level fall.
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| 7. |
- Hermansson, Tobias
(författare)
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The tectonic evolution of the western part of the Svecofennian orogen, central Sweden : Insight from U/Pb and 40Ar/39Ar geochronology at Forsmark
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Forsmark area, in the western part of the Svecofennian orogen, central Sweden, is situated between two major Palaeoproterozoic tectonic domains that show contrasting histories with respect to timing of igneous activity, ductile deformation and metamorphism. At Forsmark, WNW to NW trending, ductile deformation belts anastomose around tectonic lenses with an inferred lower degree of ductile strain. Geological features common to both of the adjacent tectonic domains are found in the area, which, consequently, is of key importance for the understanding of the tectonic evolution of the Svecofennian orogen in this region. U/Pb zircon dating (6 ages), in combination with detailed field work, have revealed the existence of two calc-alkaline igneous suites at Forsmark. The older and most voluminous plutonic suite intruded at 1.89-1.87 Ga. It is affected by penetrative ductile deformation under amphibolite-facies metamorphic conditions. The younger, less voluminous and hypabyssal suite intruded at 1.86-1.85 Ga, during the waning stages of penetrative deformation and, thus, constrains the main phase of penetrative ductile amphibolite-facies deformation to between 1.87 and 1.86 Ga. Cross-cutting granite dykes, belonging to the younger suite, place an absolute minimum age for this deformational event to c. 1.85 Ga. U/Pb titanite data (4 ages) support the constraints on the penetrative deformation. However, the data also suggest that the Forsmark area has been affected by one or more tectonothermal events after the intrusion of the 1.85 Ga granite dykes. This is confirmed by 40Ar/39Ar hornblende data (16 ages), which demonstrate the existence of two age generations, 1.83-1.82 Ga and 1.81-1.80 Ga, that are suggested to represent resetting of the argon isotope system in response to retrogressive, lower amphibolite- to upper greenschist-facies deformation restricted to discrete high-strain zones within the broader deformation belts. Furthermore, the data suggest that cooling to c. 500 °C took place at around 1.85 Ga and that the area then remained at similar temperatures until the 1.81-1.80 Ga tectonothermal event, during which it was uplifted to higher crustal levels. In addition, 40Ar/39Ar muscovite (5 ages) and biotite (29 ages) data suggest that cooling to 350 °C occurred around 1.75-1.70 Ga, whereas cooling to 300 °C took place at 1.73-1.66 Ga. The estimated uplift rate was at this time c. 22 m/m.y. The Forsmark data, in combination with a compilation of available geochronological data for the time interval 1.91-1.84 Ga in central Sweden, point to the existence of at least two major tectonic cycles. Each cycle is characterised by igneous activity associated with extension, a short interval of compression (c. 10 m.y.), and migration of the tectonic activity. In this thesis, two contrasting conceptual tectonic models, which may explain the cyclic tectonic evolution of the western Svecofennian orogen in central Sweden, are discussed. The favoured model involves continuous subduction beneath a single active continental margin, combined with alternating subduction hinge retreat and advance. This model includes migration of what has been described as tectonic switching in some younger orogenic belts.
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| 8. |
- Mehlqvist, Kristina
(författare)
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Early land plant spores from the Paleozoic of Sweden – taxonomy, stratigraphy and paleoenvironments
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Silurian through earliest Devonian, between ca 444 and 412 million years ago, was characterized by significant changes in global climate and environment. At that time, plants and animals had begun to expand the colonization of previous relatively desolate terrestrial landscape. Macrofossils of land plants are very rare from this period because these early land plants lacked large and robust tissues that could be easily fossilized. The spores produced by these early land plants are, therefore, an important tool for resolving the establishment of the early vegetation on Earth. Spore walls are composed of sporopollenin, a complex mix of biopolymers incorporating long chains of fatty acids, phenolics, phenylpropanoids and traces of carotenoids that are, collectively, very resistant to desiccation, pressure and high temperatures. These properties make spores easily preserved as fossils in the sedimentary deposits. Fossil spores can be used as a tool to: study diversity of the terrestrial vegetation, date and correlate sedimentary successions (biostratigraphy), make paleoenvironmental and paleoclimatic interpretations and, finally, assess the potential for hydrocarbon (gas, oil and coal) generation in the sediments. During the Silurian, the paleocontinent Baltica, of which Sweden was a part, was covered by shallow seas. However, the study area in central and southern Skåne was not too distant from the coast. The sediments here were deposited in foreshore to shoreface environments with water depths no more than a few tens of meters, and in some areas, represented by Lower Devonian successions, possibly even in non-marine environments such as rivers and lakes. Spores from the early land plants were transported by river water into the shallow sea and sank to the bottom as they lost buoyancy. Today these spores from early land plants are preserved in the mid-Paleozoic sedimentary rocks exposed in present day Skåne and on Gotland. In this project, sedimentary rock samples obtained from drill cores and outcrop at several localities in Skåne and Gotland, were processed by acid dissolution techniques to recover assemblages of organic-walled palynomorphs – mainly plant spores, detrital organic material, and marine palynomorphs. These palynological assemblages were studied by light microscopy to determine the diversity of spore taxa through several short stratigraphic intervals at various sites. Many of the bore cores were drilled by the Swedish Geological Survey during the 1960s and have never been investigated for their fossil spore content. Overall, there have been very few studies of spores from the Silurian of the Baltic region and the knowledge about the composition of the early land floras from this part of the world is sparse. In this thesis, rich and well-preserved assemblages of early land plant spores are described from both drill core and outcrop samples from Skåne. Both cryptospores (produced by the earliest land plants) and trilete spores (produced by vascular plants) have been recovered. In total, 66 species of both cryptospores and trilete spores were identified in the upper Silurian and Lower Devonian successions of Skåne. These results reveal a rather diverse early terrestrial flora previously unrecognized in the region. Further, a revised stratigraphy for the Öved Sandstone Formation is presented as the c. upper 100 metres of the succession is based on palynostratigraphy of this study shown to represent Devonian strata. From the Burgsvik Formation, on Gotland, sediments coeval to the studied sections in Skåne, also yielded spores from early land plants. In these beds, the earliest land plant fossil with in situ cryptospores from Baltica was discovered. These remains consist of spore masses with part of the sporangium still preserved, a possible land plant axis, and also more poorly preserved spore masses interpreted to be coprolites (fossil feaces) from arthropods. This last category represents one of the earliest examples of plant-animal interactions globally. Further, this study reports the oldest evidence of land plants in Sweden. This is in the form of spores identified in Upper Ordovician sedimentary successions in drill core material from Röstånga, Skåne.
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| 9. |
- Mellgren, Johanna
(författare)
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Conodont biostratigraphy, taxonomy and palaeoecology in the Darriwilian (Middle Ordovician) of Baltoscandia - with focus on meteorite and extraterrestrial chromite-rich strata
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with conodont biostratigraphy and palaeoecology in the Darriwilian (Middle Ordovician) of Baltoscandia, with focus on limestone strata showing traces of the ~ 470 Ma L-chondrite parent body break-up. The evidence for this cosmic event includes abundant centimeter to decimeter-sized fossil meteorites and elevated levels of sediment-dispersed extraterrestrial L-type chromite found in a stratigraphical interval corresponding to the uppermost Lenodus antivariabilis, the L. variabilis, and the Yangtzeplacognathus crassus conodont biozones, and the lower Microzarkodina hagetiana Subzone of the Lenodus (Eoplacognathus?) pseudoplanus Zone. Whereas these fossil meteorites are found only on freshly-sawed limestone-slabs at the active Thorsberg quarry on Mount Kinnekulle, southern Sweden, the occurrence of chromite has been recorded from various localities in Sweden, as well as in Russia and south-central China. A high-resolution conodont biostratigraphy over the c. 2.5 m thick, chromite-rich interval at the abandoned Hällekis quarry, Kinnekulle, was established in order to improve correlation between chromite-yielding sequences. Since the meteorite/chromite-rich interval here directly associates with a conspicuous rock sequence known as the ‘Täljsten’ interval, these strata were also investigated for palaeoecological and environmental changes. This anomalous interval has previously been suggested to represent a relative sea-level fall, but it has also been speculated that its formation could have been linked to the L-chondrite parent body break-up. Hence, the nature of the ‘Täljsten’ needed to be further explored in terms of faunal dynamics and depositional setting. The conodont fauna demonstrated continuous faunal reorganizations throughout the sampled sequence, as did additional microfaunal components. Along with observed changes in microfacies, it could be verified that the chromite-rich interval coincides with a gradually progressing regression-transgression cycle. An interesting find of tiny Panderodus conodont elements, including a serrate arcuatiform element, was made in a bed deposited just prior to the inferred maximum lowstand of the ‘Täljsten’ interval. Such serrate elements have previously been referred to as ecophenotypes of non-serrate forms, but sometimes also as distinctive species or subspecies. The Hällekis specimens, described as Panderodus serratus hallekisensis, represent one of the earliest records of the genus and hence provided clues to the primitive morphology and suprageneric relationship of Panderodus. Due to an observed tendency for overlapping morphologies and inconsistencies in identifications, the shapes of dextral Pa-elements from the zonal indices L. variabilis, Y. crassus and L. (E?) pseudoplanus were quantitatively compared using landmark-based geometric morphometrics. Linear shape of the posterior and posterio-lateral denticle rows combined was considered to best reflect the overall shape of the element-type in question, and 23 landmarks were used for the analysis; 4 fixed and 19 sliders (semi-landmarks). The analyses highlighted large-scale shape and symmetry related differences between the three species, but also revealed some overlaps. It also became clear that the three taxa display notable shape-variation of the dextral Pa element, a matter only looked into closer for L. variabilis. The Y. crassus elements included in the analysis suggest that the Baltoscandian and Chinese forms cannot be regarded as equivalents. The contingencies regarding the zonal indices naturally influence, e.g., the potential for a high-resolution correlation of chromite distribution between Kinnekulle and coeval sedimentary sequences at other localities. It was recently shown that the >1000km2 Osmussaar Breccia in north-western Estonia contains non-reworked L-type chromite, suggesting a connection to an L-chondritic impactor. An assessment of the conodont fauna of the limestones above the brecciate layers indicates that the formation of the breccia concurred with the deposition of the meteorite/chromite-yielding strata in Sweden. The limestone bed immediately superposing the breccia could be brought to the Microzakodina ozarkodella Subzone of the L. (E?) pseudoplanus Zone, i.e. only slightly higher stratigraphically than the recognized upper limit for high abundances of extraterrestrial material. This stratigraphical divergence as compared to the Swedish interval can be explained by a period of non-deposition and a resulting hiatus, a conceivable scenario considering the numerous sedimentation-gaps characterizing the early Darriwilian of north-western Estonia.
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| 10. |
- Olsson, Ingela
(författare)
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Thermal history of the Phanerozoic sedimentary succession of Skåne, southern Sweden, and implications for applied geology
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Post-depositional thermal conditions have been investigated throughout the Phanerozoic sedimentary succession in Skåne. Clay mineralogy and illite crystallinity have been the main tools for the Lower Palaeozoic strata. Within the Mesozoic sequence thermal influence was examined using RockEval pyrolysis and vitrinite reflectance analysis. Clay mineralogy of the Lower Palaeozoic shales and mudstones is generally very uniform with illite and chlorite present. Illite crystallinity values (Kübler index) for these rocks range between 0.41–1.2 (delta degrees two theta) (air-dried), indicating diagenetic to high-diagenetic/anchimetamorphic conditions. In SW Skåne a trend with improved illite crystallinity in the more deeply buried and older strata is observed. This is to be expected in a sedimentary basin subjected to burial controlled diagenetic/thermal impact only. However, in the Sorgenfrei-Tornquist Zone (STZ), where illite crystallinity data show no obvious relationship with stratigraphical position, a more complex thermal history is implied. Most striking in the illite crystallinity data from the STZ is perhaps the improved illite crystallinity recorded for the Upper Silurian Colonus Shale and Öved-Ramsåsa Group, i.e., the youngest Palaeozoic strata in Skåne. High-grade illites there indicate a Post-Silurian thermal event, probably caused by the intrusion of numerous dolerite dykes during the Permian and Carboniferous. Besides thermal effects close to intersecting dykes, the subsequent superficial effusives have constituted more extensive thermal impact on the uppermost part of the sedimentary column. In the proximity of intruding dykes anomalous clay mineralogy has been observed, in contact-metamorphosed shale. For example kaolinite has been found at Åkarpsmölla, where a 40 m wide dolerite dyke intrudes Upper Cambrian Alum Shale. Swelling clay minerals, exotic to the Colonus Shale in Skåne, has been identified in the dolerite quarry at Rönnarp. Here a mixed-layer chlorite/smectite mineral was present in the innermost contact-zone, whereas illite was lacking. Mesozoic thermal conditions generally indicate low to moderate palaeotemperatures in the range of c. 40–90 degrees (C). These data are in agreement with burial estimates and suggest that burial imposed the main diagenetic impact. A deviation from this picture of limited thermal influence has been observed from the Höör Sandstone in Central Skåne and is also indicated in SW Skåne close to the Svedala Fault. Hot fluids derived from tectonic and volcanic activity are believed to have affected these strata causing their anomalous thermal maturity.
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| 11. |
- Petersson, Andreas
(författare)
-
Evolution of continental crust in the Proterozoic : growth and reworking in orogenic systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To understand the growth of continental crust, the balance between juvenile mantle derived extraction, infracrustal reworking and crustal recycling, needs to be estimated. Since the beginning of the century, the use of coupled in situ zircon U–Pb, Lu–Hf and O isotope analyses as a tool to address these questions have increased exponentially. Numerous compilations of ever growing datasets have been presented, leading to new, and sometimes contrasting models of continental growth. Many of theses models, however, suffer from a number of assumptions, including a mantle reservoir that has been homogeneously and linearly depleted since the Hadean. Further, the use of (mainly) detrital zircon, taken out of their geological context, and the application of their depleted model-ages clearly hamper the validity of these models. To accurately address the question regarding continental crustal growth using combined zircon U–Pb-Lu–Hf(-O) isotope data, one needs to have contextual control and minimise the uncertainties of the applied models. In papers included in this thesis such an approach has been used on three different Palaeo- to Meso-Proterozoic orogenic belts; in Fennoscandia, in North American Grenville and in the Birimian terrane of the West African craton. The eastern part of the Sveconorwegian Province, located in the southwestern part of the Fennoscandian Shield, is made up of granitiod rocks that were emplaced through sequential tapping of a reservoir that formed through mixing between a 2.1–1.9 Ga juvenile component and Archaean crust. Between 1.7 and 1.4 Ga the continental crust of the Eastern Segment was reworked with little or no generation of new crust. Further to the west, in the Idefjorden terrane of the Sveconorwegian Province, 1.65 to 1.33 Ga rocks have isotopic signatures that indicate reworking of older continental crust, including sediments. However, overall the isotopic signatures in the Idefjorden terrane indicate an increase in juvenile material with time, consistent with development of an extensional back-arc rift geotectonic setting, accommodating deposition of the local metasedimentary basin, Stora Le-Marstrand. Isotope data from rocks within the Grenville orogen in subsurface Ohio suggest a common c. 1.65 Ga juvenile source to a majority of the sampled bedrock. Emplacement of this juvenile crustal contribution was followed by sequential reworking of that reservoir with little or no additional contribution to the source. The c. 2.31–2.06 Ga Birimian terrane in Ghana, West African craton, is a commonly cited example of plume initiated crustal growth, that is known to have largely juvenile signatures. However, we can show that reworked Archaean crust contribute in a much larger extent than previously known, once again highlighting the importance of infracrustal reworking during emplacement of continental crust. Further, the emplacement of felsic rocks during the Eoeburnean pre-dates suggested plume related rocks, contradicting a suggested plume initiated crustal growth. Collectively, these studies highlight the importance of infracrustal reworking in Palaeo- to Meso-Proterozoic accretionary orogens. These studies also provide good examples of combined zircon U–Pb-Lu–Hf-(O) isotope analyses on rocks and rock suites with known affinity where the validity of chosen models can be justified.
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| 12. |
- Rehnström, Emma
(författare)
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Geography and geometry of pre-Caledonian western Baltica: U-Pb geochronology and Palaeomagnetism
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In an attempt to reconstruct the pre-Caledonian cratonic margin of Fennoscandia, U-Pb geochronological and geochemical investigations have been performed on allochthonous orthogneisses in the northern Swedish Caledonides. The crystalline basement of the nappes have also been examined to further constrain the continuation of various chronologically defined orogenic belts. To constrain the global palaeogeographic setting for Baltica prior to the Silurian Caledonian collision, palaeomagnetic data from Cambrian and Ordovician sedimentary rocks were recorded. The basement in the Torneträsk region in northern Sweden consists of 1785-1800 Ma granites, whereas the 1871 Ma Ritsem Granite in the Akkajaure area further south is much older. The Torneträsk rocks can be correlated with rocks of similar age both to the west, north and east. The Ritsem Granite provides an important link between the Perthite Monzonite Suite, of Caledonide foreland in the east and the Hopen and Lødingen intrusions in the Lofoten area, in the west. Ages of the allochthonous orthogneisses from the Akkajaure-Sarek-Kvikkjokk areas fall into two groups. The older group (1779-1800 Ma) consists of granites from the Akkajaure area and these are correlated with similarly aged felsic magmatism in the Lofoten region. The younger group consists of the Tielma Magmatic Complex (TMC), which is a disrupted and telescoped AMCG-suite. The age of the TMC is bracketed between 1776 and 1761 Ma, however, with felsic dyke magmatism as late as 1731 Ma. The TMC is closely correlated with the Lofoten AMCG-complex on petrological grounds, but the bulk magmatism is younger. The complex could however, represent a younger phase of magmatism not represented onshore present-day Lofoten. No Archaean or older Palaeoproterozoic (e.g. 1860-70 Ma) ages were indicated in the nappes and it is concluded that these domains probably did not extend very much further than today, in pre-Caledonian times. The only metamorphic overprint that was recorded comes from 637 Ma old titanites from a granitic gneiss tectonostratigraphically overlying the TMC. The Cambrian palaeomagnetic data, obtained in this study, place Baltica in intermediate southerly latitudes, in an up-side-down position. Data from the early and late Cambrian show small differences, which has implications for the current discussions on a true polar wander event in the Cambrian. The results also suggest a likely palaeogeographic setting, with subduction under the Kara Block in the Ægir Sea realm for the formation of the Cambrian- Early Ordovician eclogites now present in the Caledonian nappes. Palaeomagnetic data from Early Ordovician limestones in southern Sweden give temporal constraints on the Baltica- Avalonia docking. A partial remagnetisation in the Late Ordovician is attributed to thermochemical resetting by orogenic fluids.
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| 13. |
- Söderlund, Pia
(författare)
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40Ar/39Ar, AFT and (U-Th)/He thermochronologic implications for the low-temperature geological evolution in SE Sweden
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Oskarshamn and Forsmark areas in the Fennoscandian Shield, SE Sweden, have been chosen as potential sites for hosting highly radioactive nuclear waste. To evaluate their respective suitability, the geological history of the bedrock in these two areas has been investigated. This study has focused on the thermal evolution, from c. 500 °C to c. 50 °C. 40Ar-39Ar geochronology on hornblende, muscovite and biotite, was applied to determine cooling from c. 500 °C to c. 300 °C, whereas apatite fission-track (AFT) and (U-Th)/He thermochronology were used to determine the thermal evolution between c. 120 °C and c. 50 °C. The crystalline bedrock in the Forsmark area consists of c. 1.89-1.85 Ga meta-igneous rocks that form part of the Svecofennian orogen. 40Ar-39Ar muscovite ages indicate cooling through c. 350 °C between 1.76 and 1.71 Ga. Biotite ages from surface samples suggest that the present erosion surface cooled below c. 300 °C at 1.73-1.66 Ga. The results show that the area has remained at temperatures below 300 °C since c. 1.7 Ga. The cooling of the Forsmark area reflects either slow cooling after the tectonothermal activity during the Svecofennian orogeny, or uplift in response to far-field effects of 1.7 Ga orogenic activity further to the west (or a combination of these processes). The 1.80 Ga rocks at Oskarshamn belong to the Transscandinavian Igneous Belt (TIB). Younger, 1.45 Ga granites and c. 0.95 Ga dolerite dykes are also present in the area. 40Ar-39Ar hornblende ages indicate initial rapid cooling down to c. 500 °C after the emplacement of TIB rocks. Subsequent cooling through c. 300 °C initially occurred at 1.6 Ga (40Ar-39Ar biotite ages). A 1.51-1-47 Ga 40Ar-39Ar biotite age group reflects either incomplete resetting by younger granitic intrusions in the area or thermal activity related to either the youngest manifestations of rapakivi intrusions or to the initiation of the Danopolonian event in the south. A 1.43-1.42 Ga biotite age group represents cooling after intrusion of the c. 1.45 Ga granites. The (U-Th)/He and AFT data were obtained from borehole and surface samples. Although the uncorrected (U-Th)/He and the AFT borehole ages at Oskarshamn are identical, and similar age/depth trends from the two thermochronometers are present at Forsmark, the (U-Th)/He ages are older (or AFT ages younger) than expected with respect to the closure temperatures of the two systems. The systematic age shift may be controlled by α-recoil damage of the (U-Th)/He system in U-rich apatite, possibly in combination with radiation-enhanced track annealing in the AFT system, and by invalid FT-correction of the (U-Th)/He system due to a heterogeneous distribution of U in apatite. Thermal modelling of the AFT ages reveals similar thermal histories in the two areas. Complete track annealing indicates that the present ground surface was situated at a depth of >4 km prior to c. 200 Ma. Subsequent uplift started between Late Palaeozoic and Early Mesozoic time and waned c. 100 Ma ago. Uplift may have been related to transtensional tectonics in southernmost Sweden and/or extensive volcanic activity to the south and west. After the modification in the uplift rate, continued exhumation was considerably slower.
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| 14. |
- Terfelt, Fredrik
(författare)
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Upper middle Cambrian through Furongian of Scandinavia with focus on trilobites, paleoenvironments and correlations
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on studies of upper middle Cambrian through Furongian strata in Scandinavia with focus on trilobite biostratigraphy, taxonomy, paleoecology, and intercontinental correlation. The material studied derives mainly from Västergötland and Scania, southern Sweden. Three new trilobite species are described: Macropyge (Promacropyge) scandinavica, Elkanaspis kinnekullensis, and Parabolinella sandtorpensis. The former two proved important for correlations with China and North America, respectively, whereas the latter is important for our understanding of the systematic position of the genus Parabolinella. All these species were recovered from Mount Kinnekulle, Västergötland, Sweden. The strata studied at Kinnekulle show features here interpreted as indicative of an intrabasinal paleohigh, including current-oriented fossils, the presence of thin sand wedges, the large proportion of limestone, different limestone lithologies, and gaps in the succession. This is in contrast to the biostratigraphically complete, upper middle Cambrian through Furongian successions in Scania, where the strata are unaffected by water movements and reflect a deeper water setting on the outer shelf. The succession in Scania is, however, punctuated by five major fossil-barren intervals. The upper part of such an interval, in the uppermost middle Cambrian Agnostus pisiformis Zone, yielded phosphatocopines, protoconodont elements, and enigmatic trace fossils. Thus, these intervals, or at least parts of them, are, not necessarily barren of fossils, but of the normal, trilobite-dominated faunas. Moreover, the phosphatocopine-dominated and trilobite-dominated intervals represent two interdigitating biofacies of which the former, anomalous facies, correlates with a trilobite extinction event in North America and the onset of the globally recognizable Steptoean Positive Carbon Isotope Excursion (SPICE). The lowermost Furongian biozone in Scandinavia, the Olenus & A. (Homagnostus) obesus Zone, has here been replaced by two new zones; the globally recognized Glyptagnostus reticulatus Zone and the Olenus Zone. A drill core comprising middle Cambrian (Ptychagnostus atavus Zone) to Furongian (Parabolina spinulosa Zone) strata from Andrarum, Scania, southernmost Sweden, was sampled for ?13Corg-analysis. The resulting curve has a distinct positive ?13Corg excursion corresponding to the SPICE. This is the first time that the SPICE has been recorded in Baltica and from organic matter in an alum shale setting. A study from another drill core comprising upper Furongian strata recovered from c. 2500 m depth at Håslöv, in the southwesternmost tip of Scania, revealed a succession comparable to other sections and cores in Scania regarding biostratigraphy, lithology and the presence of major barren intervals. Moreover, from this drilling the conodont Cordylodus proavus Müller? was recovered from non-reworked sediments for the first time in Sweden. A review of 10 species and subspecies of upper Furongian trilobites originally described by Moberg and Möller (1898) and Moberg (1898), revealed that they, in fact, represent 12 species and subspecies. One species name was regarded as a junior subjective synonym, and lectotypes for three species were selected.
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| 15. |
- Wigforss-Lange, Jane
(författare)
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Geochemical and sedimentary signatures of Phanerozoic events.
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Geological and biological catastrophic events have occurred repeatedly in the Earth's history, leaving traces in the global stratigraphical record in the form of sedimentary features, geochemical anomalies and biotic turnovers. This thesis focuses on the sedimentological and geochemical signatures of several key events in the Phanerozoic stratigraphical record, and aims to interpret the different signals and the causal mechanisms behind each of these events. Three intervals are investigated; the Upper Silurian (late Ludfordian), Jurassic-Cretaceous and the Cretaceous-Paleogene (K-T) boundaries. Sedimentological investigations coupled with analyses of major and trace element concentrations and of carbon and oxygen isotopic compositions were undertaken on drillcore and outcrop samples of Late Silurian age from central Scania, Sweden. Sedimentological and trace element analyses were performed on samples from the Jurassic-Cretaceous transition from Scania, Sweden and on ejecta sediments from the K-T transition along the Mexico-Belize border, close to the Chicxulub impact site. The common characteristic of these successions is that they represent special depositional environments related to exceptional short-lived events. The geochemical event in the Upper Silurian sedimentary rocks is marked by carbon and oxygen isotope anomalies in marine carbonates. The ?13C values increase from ca +1 ? to +10 ?, which represent the heaviest values recorded in this interval from Baltica. The ?18O values rise from ca -10 ? to -5 ? and show a somewhat unstable pattern. None of the conventional mechanisms for 13C enrichment can independently cause a ?13C shift in the oceanic dissolved inorganic carbon (DIC) that would answer to the observed magnitude of change. Thus, multiple causes are suggested herein. The isotopic excursions coincide with a mass occurrence of cyanobacteria, and the most extreme ?13C values may be explained by 13C enrichment in DIC through regional increases in photosynthetic activity, probably superimposed on an already 13C enriched (ca +3 ? to +5 ?) ocean. This initial anomaly still lacks a reasonable explanation. In the Scanian deposits an evaporitic environment is confirmed by the presence of e.g. cerebroid ooids, which form in highly saline waters and it is suggested that evaporation is responsible for the 18O enrichments. Degassing of CO2 may also explain the 13C enrichment in deposits that are not closely associated with cyanobacteria. It is, however, arguable whether evaporation, although prolonged and widespread, could modify the carbon isotope composition in deep marine settings. Still, it is possible that the pCO2atmos and cyanobacteria-stromatolites may be linked in some way that in turn links to the ?13C anomaly. However, the causes of the event remain enigmatic and further analyses of ?13C and ?18O from various environments (e.g. paleosols and lake sediments) and from different parts of the world are required. Sedimentary beds reflecting an atypical event were identified in the Jurassic-Cretaceous transition (within the Vitabäck Clays) at Eriksdal, Sweden. Samples were selected from an excavated ditch for geochemical, mineralogical and palynological analyses. Additional sedimentological studies where performed in field. Well-preserved assemblages of miospores and for the first time, dinoflagellates were identified in the Vitabäck Clays. The palynological assemblage corroborates an Early Cretaceous (Berriasian) age. The Vitabäck Clays consist predominantly of greenish to dark grey clays, but a coarse-grained unit is enclosed within the homogenous fine-grained sediments and these beds are also recognized by anomalous sedimentary structures and fossil content. The relatively short succession (ca 1.5 m) documents a change in energy of the transport media by the sharp erosive base, coarse-grained lithology, the incorporation of plant fragments and a fauna of mixed terrestrial and marine origin. This anomalous succession is herein interpreted to represent a tsunami deposit, possibly generated by tectonic activity or by an asteroid impact, the Mjølnir impact in the Barents Sea being a possible candidate. The Cretaceous-Paleogene boundary event relates to the Chicxulub impact in Mexico. The Upper Cretaceous Barton Creek Dolomite and the overlying two-layered ejecta deposit, collectively spanning the K-T boundary, were sampled at several sites along the Mexico-Belize border. The employed sedimentological and geochemical investigations document the chaotic circumstances following the impact. The geochemical analyses provided a genetic link between the proximal ejecta, the target rocks and K-T boundary deposits at other sites. There has been considerable debate as to whether this particular impact in fact took place at the K-T boundary. The results of this study envisage that the Chicxulub impact produced the global K-T boundary layer.
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| 16. |
- Alwmark, Sanna
(författare)
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Terrestrial consequences of hypervelocity impact – shock metamorphism, shock barometry, and newly discovered impact structures
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Impact cratering was once considered a rare geological process of no, or little, importance to the evolution of the Solar System and planet Earth. After more than 50 years of space exploration and the discovery of numerous (~190 as of October 2016) impact structures on Earth, this view has changed, and it is now clear that impact craters are in fact one of the most common morphological features on solid bodies in the Solar System. The formation of a (hypervelocity) impact crater involves extreme conditions that cannot be compared with any other natural geological process, with extreme pressures and temperatures causing melting and/or vaporization of both projectile and portions of the target rocks. Upon impact, shock waves are generated at the projectile-target interface, which pass through the target rocks at supersonic velocity. The passage of the shock waves induce irreversible changes, so called shock metamorphic effects in the target rocks, including the formation of high pressure mineral polymorphs, diaplectic glasses, and microdeformation features in minerals. The most investigated of these microstructures are planar deformation features (PDFs) in quartz. These are straight, parallel, closely spaced (2-10 µm apart), sets of (when fresh) glass lamellae only naturally formed by impact cratering. PDFs are oriented parallel to specific crystallographic planes, with the most frequently reported orientations being parallel to low Miller-Bravais index planes (e.g., {10‾13}, {10‾12}). The orientation pattern of a PDF population differ depending on the pressure that the host quartz grain was subjected to, meaning that the orientations of PDFs can be used as a shock barometer, allowing e.g., production of shock barometry profiles that illustrate shock attenuation at impact structures. The research presented in this thesis focuses on impact craters, and the process by which they form, impact cratering, with special emphasis on shock metamorphic features in target rocks at the Siljan impact structure (Sweden). The results and discussion highlight the importance of the way datasets of PDF statistics are obtained and processed, using manual and/or automated methods of indexing. The interpretation of the dataset can influence the shock barometry models, and the need for a unified method is discussed. With regards to the Siljan impact structure, the pre-erosional rim-to-rim diameter of the crater was estimated to be on the order of 60 km, based on a combination of shock barometry and numerical simulation, produced by a collision between a ~5 km diameter projectile and Earth. Results of the numerical modeling are consistent with a sedimentary thickness overlying the crystalline basement at the time of impact of ~2.5 km, and post-impact erosion of the crater on the order of 3 to 3.5 km.The thesis also encompasses studies of two other, newly confirmed, Swedish impact structures, Målingen and Hummeln. The possible means of formation for both Målingen and Hummeln had been discussed for many years before the first bona fide evidence for the impact origin of the two structures was presented in papers included in this thesis.Furthermore, terrestrial impact structures with reliable ages (i.e., errors on age of less than 2 %) are discussed in the context of possible variations in the impactor flux to Earth over time. According to the results, there is presently no evidence for the existence of a periodic contribution to the terrestrial impact population.
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| 17. |
- Beckman, Victoria
(författare)
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Metamorphic zircon formation in gabbroic rocks – the tale of microtextures
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dating of metamorphic events is crucial for the understanding and reconstruction of large-scale geological processes such as orogenesis. Zircon is one of the most commonly used minerals for dating of igneous and metamorphic events. Zircon incorporates uranium and excludes lead during crystallization, and with time the uranium decays to lead. The diffusion rates of both elements are slow, making zircon resilient to isotopic resetting. However, in order to date geological events, it is imperative to know exactly by which process the dated zircon formed. For example, regional metamorphism is a dynamic process taking place over millions of years. During tectonic burial and heating the rock gradually responds to the increasing temperature and pressure, giving rise to prograde mineral assemblages, whereas retrograde metamorphism takes place during cooling and exhumation. So, in a regionally metamorphosed rock, does the zircon age date the tectonic burial or the exhumation? The interpretation of how zircon formed has direct influence on the tectonic interpretation. Zircon can form or recrystallize within a wide range of metamorphic pressures and temperatures and by several different processes. This means that, for meaningful interpretation of a metamorphic zircon age, the zircon growth needs to be linked to the mineral reactions in the rock. Due to the high closure temperature of zircon (the temperature below which zircon will not undergo isotope diffusion), zircon ages have traditionally been assigned to date the peak of metamorphism (the highest temperature). On the other hand, mass balance models suggest that, in mafic rocks, zircon dissolves during prograde and grows during retrograde mineral reactions and therefore generally dates cooling and exhumation.If hydrous fluids are not present, mafic igneous rocks may remain largely unaffected during a metamorphic event. Coarse-grained mafic rocks such as gabbro are the least permeable, and may record the gradual transition from pristine gabbro to its completely metamorphic recrystallized equivalent. Such metamorphic transitions zones provide information about how metamorphic zircon formed. Two different metamorphic transition zones have been investigated in detail in this thesis: a) a gabbro to eclogite transition at Vinddøldalen in south-central Norway and, b) a gabbro to garnet amphibolite transition at Herrestad in South-central Sweden. The aim has been to link reaction textures to zircon growth and to obtain a direct U-Pb age of the metamorphic process. A third study investigates and reviews the zircon-forming textures in a number of metagabbro and metadolerite bodies metamorphosed at different pressures and temperatures. The results in this thesis show that zircon formation is remarkably similar in all of the investigated metagabbroic rocks, and that zircon is mainly produced by the breakdown of igneous baddeleyite during prograde mineral reactions. The metamorphic mineral reactions and the associated zircon formation in gabbroic rocks are tightly linked to deformation and infiltration of hydrous fluids, and to a lesser extent dependent of variations in pressure and temperature. Therefore, in most gabbroic rocks, zircon formation will take place at the earliest stage of metamorphic recrystallization.
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| 18. |
- Bjärnborg, Karolina
(författare)
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Origin of the Kleva Ni-Cu sulphide mineralisation in Småland, southeast Sweden
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Kleva Ni-Cu sulphide deposit is situated within a gabbro-diorite intrusive complex in southeast Sweden. The basement north of the intrusive complex is dominated by 1.81–1.77 Ga granites of the Palaeoproterozoic Transscandinavian Igneous Belt (TIB). Slightly older (1.83–1.82 Ga) rocks of the Oskarshamn Jönköping Belt, which hosts numerous syngenetic and epigenetic base metal mineralisations, occur just south of the Kleva intrusive complex. The aim of this PhD-thesis is to deduce the origin of the Kleva deposit, the mineralisation itself as well as its host rocks through geochemical, geochronological and petrological studies. U-Pb age determination of zircon dates igneous crystallisation to 1.79 Ga, which is the age of the Kleva intrusive complex and confirms its temporal association with the voluminous TIB magmatism. Major- and trace element systematics are in accordance with a basaltic magma that formed through partial melting of a metasomatically refertilised mantle wedge underneath an Andean-type continental magmatic arc. Lu-Hf signatures of zircon, together with other rocks of Palaeoproterozoic Fennoscandia indicate alternating stages of extension and compression across the subduction zone, facilitating ascent of the mafic magma. Evidence for contamination of the magma through crustal assimilation during its ascent are inconclusive. Low IPGE/Ni together with high S/Se, indicate sulphide melt saturation prior to final emplacement, possibly induced by crustal contamination. Nb/La vs La/Sm indicate contamination with mid-crustal rocks, and radiogenic Os of magmatic pyrite suggests <10% contamination with Archean crust. OJB aged rocks are thus unlikely contaminants, despite the numerous rock inclusions of similar geochemical composition within the intrusive complex. δ34S of Kleva mineralised rocks and the country rocks corresponds with the mantle range, and local or mantle origin of S can neither be proven nor rejected. Sulphide melt segregated from an evolved magma and partially accumulated into massive lenses, which is in accordance with a magmatic conduit setting. The mineralisation contains massive, net-textured and disseminated sulphides of typical magmatic association and is interpreted to be contemporaneous with silicate melt crystallisation, consistent with a Re-Os 1.71 ±0.2 Ga isochron for massive pyrite with magmatic texture. Re-Os isochrons of secondary pyrite indicate metamorphic disturbance of the mineralisation at least twice; at c. 1.61 Ga and 1.39 Ga, which can be linked to orogenic events further to the south and west. The mineralisation was heterogeneously affected by tectonic disturbance, resulting in remobilisation of chalcopyrite into veins, plastic deformation of sulphides and host rock, micro-faulting and brittle deformation of oxides and sulphides and recrystallisation of pyrite in fractures. To summarise, the deposit is an example of a subduction related magmatic Ni-Cu mineralisation affected by multi-stage deformation and alteration.
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| 19. |
- Cecys, Audrius
(författare)
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Tectonic implications of ca. 1.45 Ga granitoid magmatism at the southwestern margin of the East European Craton
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Between ca 1.53 and 1.40 Ga, the southwestern margin of the East European Craton was subjected to extensive magmatism and deformation. While various suites of anorthositic, mangeritic and charnockitic-granitic rocks were emplaced between ca. 1.53 and 1.50 Ga, a major event of A-type granitic magmatism took place around 1.45 Ga. During that event, numerous voluminous plutons were intruded in a wide region around the southern Baltic Sea (“the SBS region”). Petrologically, the various SBS granitoids are rather similar to each other. Like many A-type granites worldwide, they are enriched in silica, high field strength elements (HFSE) and rare earth elements (REE), and have high Fe/Mg and K/Na ratios. The most common ferromagnesian silicate minerals are biotite and amphibole, clinopyroxene occurring occasionally. Another feature characteristic of the SBS plutons is their formation by the emplacement of multiple pulses of melt. Such pulses were occasionally responsible for separate suites of rocks and appear to have originated from slightly different sources. In general, however, the melt sources of the SBS granitoids were relatively juvenile and rich in aluminum and potassium as well as in HFSE:s and REE:s. The isotopic characteristics of the rocks may also suggest some interaction between crustal and mantle materials. During the ca.1.45-Ga event, the Blekinge-Bornholm region experienced notable regional compression and ENE-WSW shortening. That compression caused syn- and post-magmatic deformation of the involved granitoids as well as deformation and metamorphism of the host rocks. Due to its activity, also EW-striking shear zones were either developed or reactivated and apparently controlled the emplacement of the SBS granitoids. As different from the traditional concept of a liaison between A-type granitic magmatism and anorogenic extension of the crust, the present study thus strongly evidences that the SBS granitoids were intruded during compressional tectonic processes. Causally, they are interpreted to have been related to the Mesoproterozoic Danopolonian orogeny which may have led to the collision of the East European Craton with another proto-continent, possibly Proto-Amazonia (Bogdanova, 2001).
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| 20. |
- Einarsson, Elisabeth
(författare)
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Palaeoenvironments, palaeoecology and palaeobiogeography of Late Cretaceous (Campanian) faunas from the Kristianstad Basin, southern Sweden, with applications for science education
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is thematically divided into two sections: Part1 presents studies related to the palaeoenvironments,palaeoecology and palaeobiogeography of the LateCretaceous (Campanian) faunas from the KristianstadBasin of southern Sweden; Part 2 reports on applicationsof palaeontological research for science education inschools.Part 1 was based on personally conducted fieldworkand biostratigraphical analysis at various Santonian-Campanian localities throughout Skåne. However, themost complete section at Åsen provided the primary datasource and was systematically excavated with a team ofvolunteers, who employed wet-sieving methods to extractbulk fossil material from each bed within the sequence. Aseries of globally correlated temperature-induced changeswas detected in the stepwise declining abundanceand disappearance of rudists, sclerorhynchids and therajiforms Rhinobatos and Squatirhina, as well as marinecrocodilians, various mosasaurid lizard taxa. A rangeof local palaeoenvironments were also reconstructed,including estuaries, rocky coastlines, sandy beaches,drowned river valleys, shallow neritic settings, anddeeper offshore conditions. An archipelago bordering theFennoscandian landmasses also supported continentalecosystems comprising ferns, conifers and early floweringplants, with dinosaurs, pterosaurs and non-marine turtles.Trophic levels within the marine system incorporatedred algae and dinoflagellates as primary producers, withcorals, brachiopods, bivalves, echinoids, barnacles anddecapod crustaceans as benthos, and belemnites withinthe water column. Actinopterygian fish, sharks, rays andchimaeroids, chelonioid sea turtles, marine crocodilians,polycotylid and elasmosaurid plesiosaurians, variousmosasaurids and aquatic hesperornithiform birdscollectively represented middle level and apex predators.Herbivorous and carnivorous dinosaurs, lizards and softshelledtryonichid turtles evidence elements of terrestrialisland communities. The palaeobiogeographicalrelationships and dispersal of these local assemblageswas probably influenced by marine transgressions andregressions. These would have affected habitat availabilityand connectivity via changing water depths.Part 2 presents three school education projects aimed atincreasing awareness of geoscience and natural history inschools. The better integration of geological time conceptsand geosciences into the Swedish school curriculum isalso discussed. The first study described a project wherebyfossils were found in the sandboxes in preschools, andtheir use as a tool for learning about dinosaurs, fossilsand natural history. A survey of teachers and childrenfound that both increased their knowledge base throughthis approach, and that the local context of the fossilsin particular generated interest about the subject. Theconcepts of geological time was similarly addressed in thesecond study, which utilized timescale projects and otherhands-on activities to create memory triggers for childrenand students, and to demonstrate how the perspective of‘deep time’ is relevant for understanding large-scale Earthprocesses, such as evolution and environmental change.The integration of geosciences into the Swedish schoolcurriculum is currently inadequate. Therefore, the finalpaper in this sequence discusses how geosciences forman interdisciplinary bridge between school subjects andcan be used to teach geography and biology at all schoollevels.
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| 21. |
- Gren, Johan
(författare)
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Molecular, micro- and ultrastructural investigations of labile tissues in deep time
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis comprises investigations of microstructures and molecular remains, preserved in a variety of fossil specimens. The results are presented in six papers, collectively aiming to thoroughly examine fossil traces of such remains by employing a combination of both established and relatively new analytical methods. The main questions asked are: What can we learn about the biology, ecology and behaviour of ancient organisms by studying these fossilised remnants, and what methods are best suited to accomplish this?The work presented herein has been conducted through a series of case studies performed on fossils representing an array of taxa, collected from different geological ages and settings. Methods applied include light and electron microscopy, computed tomography, and molecular analyses, such as time-of-flight secondary ion mass spectrometry, IR microspectroscopy and X-ray absorption spectroscopy. Microscopic analysis and histology of teeth from Mesozoic marine reptiles allowed calculations of dentine formation and tooth replacement rates. My findings include evidence that while teeth of larger mosasaur taxa took longer time to develop, their dentine formation rates were more rapid, relative to that of smaller species.In other fossils, microscopic investigations of eye, skin and feather remnants revealed aggregations of micrometre-sized, sub-rounded to elongate structures. Because similar microbodies have previously been described alternatively as relict melanosomes (i.e. pigment-containing, eukaryotic cellular organelles) and lithified bacteria, my co-authors and I performed chemical and molecular analyses in order to explore the affinity of these structures. To ascertain the chemical identity of our fossil samples, corresponding analyses were carried out also on molecularly similar compounds, including modern eumelanin, as controls. My studies show chemical evidence of animal eumelanin in close association with the microbodies, advocating the melanosome interpretation for the analysed specimens.Beyond the results reported in the included papers, this thesis provides a short review of melanin formation in vertebrate eyes and integument, as well as in fungi and bacteria which also produce this type of pigment. An overview of the various methods applied is presented and followed by a discussion about possible outcomes and pitfalls when studying fossil microstructures and molecular palaeontology. Whereas remnant melanosomes could potentially provide new insight into a multitude of biological and ecological aspects of ancient life, there is still no straight-forward approach to determine the affinity of ‘melanosome-like’ microstructures found in fossils. Therefore, a thorough investigation of such remains, including chemical analyses, should be applied in each study – at least until a consensus has been reached regarding the minimum amount of criteria to be used for a confident recognition.
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| 22. |
- Gumsley, Ashley
(författare)
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Validating the existence of the supercraton Vaalbara in the Mesoarchaean to Palaeoproterozoic
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the longevity and continuity of the Vaalbara supercraton is addressed in six papers aimed at placing new temporal and spatial constraints onthe supercraton in the Mesoarchean to Paleoproterozoic. It has been speculated since the 1960’s that the Kaapvaal Craton in southern Africa, together withthe Pilbara Craton in Western Australia existed as a single landmass during the Precambrian – the Vaalbara supercraton. Many studies have demonstrated thegeological similarities between the cratons, particularly in terms of their Mesoarchean to Paleoproterozoic unconformity-bounded sequences. These unconformity-bounded sequences have continuously been refined and developed, especially since the 1990’s. The first main stratigraphic similarities lie in the volcanic and sedimentary successions found in the Neoarchean Fortescue Group and Ventersdorp Supergroup basins on the Pilbara and Kaapvaal cratons, respectively, along with other associated basins. The unconformably overlying Hammersley (and Turee Creek) Group and Transvaal Supergroup on the Pilbara and Kaapvaal cratons, respectively, also show many stratigraphic similarities, and both host world-class deposits of hydrothermally-upgraded iron formations. However, no marker beds or precise age matches have yet been made, especially in the extensive Mesoarchean to Paleoproterozoic mafic dyke swarms and sill provinces present in each craton from the time interval discussed in this thesis. Regardless, the geological discussions has been aided by geochronological and paleomagnetic studies, which have both credited and discredited the existence of the Pilbara and Kaapvaal cratons as nearest neighbours for the time interval between ca. 2.87 Ga and ca. 2.65 Ga.In this thesis, the so-called magmatic barcode record of large igneous provinces (LIPs), which are extensive and short-lived volcanic events, of the KaapvaalCraton is presented together with that of the Pilbara Craton in conjunction with previous geochronological and paleomagnetic studies. This magmatic barcoderecord refines temporal, and through paleomagnetism, spatial constraints, and invalidates the existence of Vaalbara as a distinct continuous supercraton. Magmatic and paleomagnetic linkages between the 2.99-2.98 Ga Usushwana Complex on the Kaapvaal Craton and the ca. 2.87 Ga Millindinna Complex on thePilbara Craton are shown to be incorrect with new ages for the Usushwana Complex and Badplaas dyke swarm presented in Gumsley et al. (2015). Extensivemafic dyke swarms associated with Neoarchean Fortescue volcanism on the Pilbara Craton and Ventersdorp volcanism on the Kaapvaal Craton also show lesssimilarities from new paleomagnetic and geochronological constraints. These constraints are presented in Gumsley et al. (2016) and Evans et al. (2017) for thenewly identified White Mfolozi and Black Range mafic dyke swarms, respectively, on the Kaapvaal and Pilbara cratons. Gumsley et al. (2017) and Kampmannet al. (2015) also present a new LIP, the Ongeluk, on the Kaapvaal Craton which has not been identified on the Pilbara Craton. This new LIP is composed ofthe Ongeluk Formation in the Transvaal Supergroup on the western margin of the Kaapvaal Craton, as well as the Westerberg Sill Province and a north-trendingmafic dyke swarm. The Ongeluk LIP appears to break some of the stratigraphic comparison between the upper Transvaal Supergroup on the Kaapvaal Cratonand the Turee Creek Group on the Pilbara Craton. In addition, a new late Paleoproterozoic mafic dyke swarm, the Tsineng swarm, is presented for the western Kaapvaal Craton in Alebouyeh Semami et al. (2016), which is correlated with Hartley Formation volcanism in the Olifantshoek Supergroup. This magmaticevent may also define a new LIP on the western Kaapvaal Craton. This mafic dyke swarm and its associated volcanism has also not been documented on thePilbara Craton.Instead, it is proposed that the Pilbara and Kaapvaal cratons were part of a much larger continent or supercontinent in the Neoarchean to Paleoproterozoic.This large crustal block likely included the Wyoming, Superior and Hearne cratons of North America, together with the Kola-Karelia Craton located between Russia and Finland, as well as possibly the Singhbhum Craton of India and the Samartia terrane of Russia and Ukraine. This continent or supercontinent, termed ‘Supervaalbara’ here, allows for the Kaapvaal and Pilbara cratons to share many geological similarities without being nearest neighbours, along possiblythe same passive margin. The geological evolution of all these cratons is very similar, particularly in the Paleoproterozoic, and which may have been driven byglobal processes. These global processes may include true polar wander, the submergence and subsequent remergence of continents with sea-level rise and fall, as well as atmospheric oxygenation and global glaciation. Paleomagnetic studies provide further continuity supporting the existence of Supervaalbara, which appears geologically distinct from the Rae family of cratons, suggesting perhaps two different continents in the early Paleoproterozoic before the assembly of the supercontinent Columbia (Nuna) in the late Paleoproterozoic.
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| 23. |
- Heingård, Miriam
(författare)
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Exceptional fossil preservation: implications for palaeobiology and taphonomy
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although fossils are relatively common in some sedimentary deposits, the majority consists of fragmented or distorted skeletal hard parts (such as shell and bones). However, in rare cases, special burial and diagenetic conditions have allowed a greater portion of the original anatomy to be incorporated into the fossil record. This exceptional type of preservation is characterised by the retention of labile soft to sclerotized tissues and/or delicate, three-dimensional, articulated skeletal units. Exceptionally preserved fossils contribute with important data that greatly enhance our understanding of the evolution of life on Earth. In particular, when analysed using sophisticated and sensitive techniques, these unique fossils have the potential to reveal new insights into both biological and ecological aspects of ancient life.In this thesis, a selection of fossils representing different types of exceptional preservation is analysed using a multi-proxy approach that includes microscopic, tomographic and molecular techniques. The material encompasses: (1) pigmented internal and integumentary soft tissues, (2) a virtually intact bird skull, and (3) arthropod cuticle (occurring in both sclerotized and naturally biomineralised form). The greater part of the material has been collected from the earliest Eocene Ølst and Fur formations of north-western Jutland, Denmark, although complementary fossils from the stratigraphically older (Cretaceous) Weno and Pawpaw formations are also included. This work is presented as a series of cases studies, and aims at inferring novel aspects of palaeobiology and taphonomy from these rare fossils.Detailed microscopic and molecular analyses of remnant internal and integumentary soft tissues in fossil fish larvae revealed that these organic remains are dominated by residues of the biochrome eumelanin. Similarly, sclerotized cuticle in Eocene insects consists chiefly of eumelanic pigments, whereas most other organic components (such as chitin and proteins) have been lost during the course of time. In addition to eumelanic pigments, the investigated insect exocuticle also exhibited a finely laminated organisation comparable to those biophotonic nanostructures that produce metallic colours in modern insects.Analyses of Cretaceous crab cuticle showed that all originally chitinous components were replaced by secondary minerals. This finding has implications for interpretations of the original composition and function of fossilised cuticle also in other extinct arthropods.Finally, computed tomography was employed on a pristine, three-dimensionally preserved Eocene bird skull. The excellent preservation of the fossil bird allowed the production of a detailed digital 3D version of its skull, from which the brain and inner ear could be faithfully reconstructed. This imaging analysis revealed that virtual renderings are useful not only for phylogenetic studies but also for providing clues about potential sensory and behavioural capabilities.Collectively, the findings from these studies highlight the diversity of information that can be gained from exceptionally preserved fossils, including novel aspects of phylogeny, colour-mechanisms and their functions, as well as insights into the taphonomy of animal fossils.
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| 24. |
- Herrmann, Maria
(författare)
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Geochronology of impact structures - constraining syn- and post-impact processes using the 40Ar/39Ar and U-Pb techniques
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The discovery, at the beginning of the 20th century, that elements can transform into other elements, due to the spontaneous decay of an instable to a stable atomic nuclei, gave rise to a powerful source for age information in many fields of earth science. For impact structures, it is crucial to establish well-defined and precise ages in order to understand how impact events affect the Earth’s geo and biosphere and also with regard to possible future events that can have devastating effects on our civilization.During the impact cratering process immense amount of energy is released in relatively short time, resulting in extreme temperature and pressure conditions that can even melt and vaporize rocks. The thermal impact is so high that in consequence, the composition between instable and stable nuclei in a melted rock or mineral is changed due to the loss of stable nuclei through diffusion. Thus, the atomic or isotopic clock of a rock or mineral is reset and the accumulation of new stable nuclei starts again, preserving the imprint of the impact event. Traditionally, impact structures are dated by 40Ar/39Ar on impact melts. Such melts quench soon after their formation and thus, inhibit the diffusional loss of newly-formed stable nuclei. Therefore, these melts can be used to date an impact event. Further, individual minerals can yield impact-related ages, too, such as zircon. The U-Pb decay in zircon is the most widely used dating method. Due to the recrystallisation or new growth of zircon within impact melts, Pb is lost, indicating an impact relation. However, even though impact events have a devastating effect, in some cases minerals preserved in the target rock show no sign of shock, but instead, be affected by post-impact processes, such as by hydrothermal activity. Thus, impact crater ages are not always straight forward and should be interpreted with great care.The U-Pb analyses of zircon grains from the target rock of the Siljan impact structure in Sweden can be explained by different residency time of zircon at shallow, cool crustal levels rather than by the impact event. Prior to the uplift by the impact event about 380 Ma ago, zircon grains near the crater centre resided at greater depth, where radiation-damaged lattice is able to anneal due to higher temperatures, leading to much less Pb loss. Whilst zircon grains distal to the crater centre was preserved near the erosional surface at temperatures that inhibit any annealing of radiation damage since >1260 Ma and thus, prone to lose more Pb.The 40Ar/39Ar age data of biotite and amphibole from the Siljan target rock exclude an impact age, as well, and instead, indicate an imprint by hydrothermal fluids driven by the impact. Whilst the 40Ar/39Ar dating of whole rock impactites from the Hummeln and Mien impact structures in Sweden and the Puchezh-Katunki impact structure in Russia suggests a correlation with an impact event, even though Hummeln shows only a partial reset of the 40Ar/39Ar system and Puchezh-Katunki yield an age range between 192 and 196 Ma.Further challenges combine dating with element mapping and microtextural analyses. Highly shocked zircon, extracted from impact melts of the Mien crater, with certain textural features can yield U-Pb ages that are impact-related. It shows that the formation of shock textures in zircon is promoted when the lattice is metamict, i.e., damaged by radiation due to the U-Pb decay.
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| 25. |
- Larsson, Linda
(författare)
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Climate and vegetation during the Miocene - evidence from Danish palynological assemblages
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several Danish exposures and one drill core spanning the upper Oligocene-upper Miocene interval of the Cenozoic (i.e., 24–5 Myr ago) were palynologically investigated. The sediments were deposited in alternating deltaic, marginal marine and fully marine settings, and reveal a rich and diverse miospore flora, associated with abundant dinoflagellate cysts. The results consistently demonstrate that coastal areas in what is now Denmark were inhabited by Taxodium swamp forests that also hosted a range of terrestrial angiosperms, such as Nyssa, Betula, Alnus and Myricaceae. Further inland, mixed deciduous-evergreen forests prevailed and in drained soils, or in elevated areas, conifer-forests dominated by Pinus, Sequoia and Sciadopitys thrived. By employing the Coexistence Approach, the mean annual temperatures were calculated to 15.5–21.1º C for the late Oligocene-late Miocene. The warmest periods occurred during the earliest Miocene and the middle Miocene, respectively. The latter period represents a prolonged climatic warming event approximately 17–14 Myr ago. This warming is globally recognized and referred to as the middle Miocene Climate Optimum. Following this event, a marked climatic cooling occurred at about 11 Ma, which coincides with the beginning of the globally identified late Miocene Cooling phase.
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| 26. |
- Lindgren, Johan
(författare)
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Early Campanian mosasaurs (Reptilia; Mosasauridae) from the Kristianstad Basin, southern Sweden
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Marine strata of latest early Campanian age (sensu germanico) in the Kristianstad Basin, Skåne (Scania), southern Sweden, have yielded a diverse mosasaur fauna comprising six to eight taxa, including Tylosaurus ivoensis, Clidastes propython, Hainosaurus minor n. sp., Halisaurus sternbergii, Platecarpus cf. somenensis, Platecarpus? sp., Dollosaurus sp., and possibly yet another mosasaurine or halisaurine. The material consists mainly of isolated shed tooth-crowns, although a number of vertebrae and other, fragmentary bones have been recorded as well. The assemblage is similar in composition to approximately coeval mosasaur faunas from the Western Interior and the Gulf Coast of North America. The giant T. ivoensis was formerly believed to be a species of Mosasaurus (i.e. M. hoffmanni ivoensis and M. ivoensis of earlier authors). Nevertheless, its dental and vertebral morphology correspond perfectly to those of tylosaurine mosasaurs. Tylosaurus pembinensis (a nominal species originally assigned to Hainosaurus) from the late early Campanian of southern Manitoba, Canada, may be a junior synonym of T. ivoensis, as its teeth (both marginal and pterygoid) and vertebrae are very similar to those of the latter taxon. The occurrence of C. propython in the early Campanian of southern Sweden represents the first record of both the genus and species outside of North America. In the Kristianstad Basin area remains of Clidastes are found in deposits representing a shallow water archipelago environment. This is in stark contrast to the deeper water, outer shelf environment advocated by one author as the preferred habitat for this species. Another intercontinental mosasaur; H. sternbergii, was originally described from an unspecified horizon in the late Coniacian-earliest Campanian Smoky Hill Chalk in western Kansas, USA. The Kristianstad Basin population of H. sternbergii was probably derived from individuals that migrated from the Mississippi Embayment sometime during the early Campanian. A new species of Hainosaurus; H. minor n. sp., has been identified from very well preserved marginal tooth-crowns. The nominal species can be distinguished from the early Maastrichtian H. bernardi (the only other valid nominal species of Hainosaurus) by its relatively small-sized and heavily faceted teeth. At, or near, the early/late Campanian boundary, the mosasaur faunas in North America and northern Europe were severely decimated. New low-diversity faunas with Mosasaurus, Plioplatecarpus and Prognathodon replaced species-rich assemblages dominated by Clidastes, Platecarpus and Tylosaurus. The great distance and markedly different palaeoenvironments between different areas affected by the reorganization (e.g. sub-tropical outer shelf in Alabama vs. warm temperate shallow water archipelago in the Kristianstad Basin area) indicate that the faunal turnover was caused by a (undetermined) global catastrophic event, or a series of events, rather than by local, independent deteriorations of the environment.
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| 27. |
- Lindskog, Anders
(författare)
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Early–Middle Ordovician biotic and sedimentary dynamics in the Baltoscandian paleobasin
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Baltoscandian region forms part of the paleocontinent Baltica, which was largely covered by a shallow epeiric sea throughout much of the Ordovician (c. 485.5–444 Ma). This ancient sea is today recorded by a thin succession of sedimentary rocks. During the Early–Middle Ordovician (c. 485.5–457.5 Ma), Baltica was situated in mid-latitudes on the southern hemisphere and cool-water carbonates formed across large areas of the Baltoscandian paleobasin. The so-called orthoceratite limestone is the most widely distributed rock type from the Early–Middle Ordovician in Sweden. It developed in a time-transgressive manner geographically, but much of the Lower–Middle Ordovician succession in the mainland of Sweden is typically characterized by this lithology. The depositional environment of the ‘orthoceratite limestone’ has long remained poorly understood in many respects. This is in large part due to a lack of analogous depositional environments in modern seas, but also due to remaining gaps in our knowledge about the rock type in general. It has generally been agreed upon that the ‘orthoceratite limestone’ is a cool-water deposit formed in a sediment-starved epeiric sea, but interpretations have differed widely with regards to prevailing water depth.The eight papers appended to this doctoral dissertation are based on various investigations of the ‘orthoceratite limestone’ in Sweden and coeval rocks in surrounding countries. Detailed macroscopic and microscopic studies of the biotic and sedimentary characteristics have added information about the Baltoscandian paleobasin and the biotic and paleoenvironmental development during the Early–Middle Ordovician. It is concluded that the depositional environment of the ‘orthoceratite limestone’ varied considerably through both space and time; it spanned from intertidal areas to settings many tens of meters deep. Variations inthe overall characteristics and fossil content of the ‘orthoceratite limestone’ and coeval regional rocks appear to mainly record variations in (relative) sea level.The collective results indicate that sea level varied significantly throughout the Early–Middle Ordovician, likely in large part as a response to variations in climate and related changes in global marine water volume. The inferred variations are consistent across multiple different proxies – abiotic and biotic alike – and cyclic patterns occur in the datasets. Geochemical data suggest that the global climate changed considerably during the Early–Middle Ordovician, and that the climate ultimately entered an ‘Icehouse’-like state. The onset of the latter phase is recorded as a distinct drop in sea level during the Middle Ordovician. The aforementioned changes reverberated through the marine realm and likely contributed to the rapid diversification that is seen among fossils during the so-called Great Ordovician Biodiversification Event (GOBE). Based on a refined absolute and relative time scale for the Middle Ordovician, the GOBE can be confidently shown to be unrelated to a prolonged meteorite bombardment that occurred during this time interval.The papers in the dissertation collectively show that a combination of approaches and analytic techniques leads to maximal information output and confidence in interpretations. The use of state-of-the-art analytic and imaging techniques further allows for the discovery of previously undocumented rock characteristics and fossils, and better description and understanding of such documented before.
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| 28. |
- Martell, Josefin
(författare)
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Leave no trace: A non-destructive correlative approach providing new insights into impactites and meteorites
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Impact cratering is today recognized as a fundamental geological process on all rocky bodies in the solar system. On Earth, however, processes such as plate tectonics and erosion have eradicated most craters from the geological record, or they may be buried under sediments, oceans, and vegetation. The formation of a hypervelocity impact crater involves extreme pressures and temperatures that induce permanent changes in the target rocks, so-called shock-metamorphic effects, which can be used to identify and confirm impact structures. The research in this thesis focuses on the impact cratering process, both during the formation, and post-impact. A number of terrestrial impactites and meteorites were analyzed using a multi-modal approach, including correlative non-destructive neutron and X-ray imaging, and detailed 2D analysis using scanning electron microscopy and electron backscatter diffraction. The material encompasses (1) impactites from the Mien impact structure, (2) a sample of the Martian Miller Range (MIL) 03346 meteorite, (3) a Chicxulub drill core sample, (4) a sample of Libyan Desert Glass, and (5) a sample of impact melt rock from the Luizi impact structure. The first study investigated shock deformation in zircon grains from the Mien impact structure in Sweden, using electron backscatter diffraction (EBSD). The results show that several of these grains contain evidence of the former presence of a high-pressure phase that is only known from impact structures. These grains would be suitable candidates for refining the age of the impact event. In paper II, combined NCT and XCT were employed to investigate the three-dimensional distribution of hydrogen-rich material in MIL 03346, by utilizing the neutrons’ sensitivity to hydrogen. The results revealed that the hydrogen-rich material occurs in localized clusters, with limited interconnectivity between clusters. This suggests that the fluid source could be small patches of sub-surface ice and that the alteration event likely was short-lived, meaning that the source terrain of this sample was likely not habitable. In Paper III we combined XCT and NCT to test if these methods can be used to locate projectile material in impactites. After careful investigations of the 3D images, an iron-nickel silicide spherule could be pin-pointed in the Libyan Desert glass. The sample was then polished for detailed analysis using scanning electron microscopy. Overall, the non-destructive nature of XCT and NCT makes these methods highly relevant for studying rare samples, such as meteorites and returned samples.
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| 29. |
- Nilsson, Mimmi
(författare)
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New constraints on paleoreconstructions through geochronology of mafic dyke swarms in North Atlantic Craton
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Earth history is punctuated by a series of events of supercontinent amalgamation and break-up. Fragments of old continents display rifted margins and orogenic sutures that testify their involvement in supercontinent cycles. Periods of break-up are associated with widespread magmatism due to extensional thinning and rifting of the lithosphere and in some instances the arrival of mantle plumes. Mantle plumes are thought to, at least in part, be responsible for Large Igneous Provinces (LIPs for short), voluminous short-lived outburst of mafic magmatism, whose products are continental flood basalts and oceanic plateaus, layered intrusions, sills and dykes. While continental flood basalts and oceanic plateaus are sensitive to subsequent erosion and subduction, the plumbing system of LIPs comprising deep-seated intrusions, sills and dykes have a high preservation potential. Thus, these events should be possible to trace back in time through multiple supercontinent cycles. LIPs typically have temporal scales of a few million years, but spatial scales of several hundred to thousand kilometers. After break-up and subsequent ocean basin opening, the products of LIPs may end up on different continents. Ancient crustal fragments, or cratons, have experienced a number of magmatic events, and thus have their individual record. Cratons that were once adjacent in a single landmass should share a part of their magmatic record during the interval of time they were connected. Because mafic rocks contains trace amounts of baddeleyite (ZrO2), and because baddeleyite incorporate abundant uranium but only neglible amounts of lead in its crystal structure, we can age determine mafic intrusions using U-Pb geochronology. H Date: 2016-05-16 ence, we can elucidate these events, craton by craton, and compare them to each other. Multiple individual age matches between different cratons suggest a common ancestry in a supercontinent or supercraton. In addition, dyke swarms provide geometric information as they often display radiating or parallel patterns. Fragments of ancient supercontinents or larger landmasses can thus theoretically be reconstructed by comparing geometry of dyke swarm matches in the magmatic record. My PhD-project has been focused on Paleoproterozoic mafic dykes from the present-day southern Greenland part of the Archean North Atlantic Craton (NAC). Precise U-Pb baddeleyite age determinations of multiple events of dyke emplacement are presented in this thesis at ca. 2500, 2375−2365, 2215−2210, 2165−2160, 2125 and 2050−2020 Ma. This magmatic record show temporal correlations with a number of Archaean cratons worldwide, and notably share multiple matches with Superior and Dharwar cratons in present day Canada and India, respectively. A tentative paleoreconstruction of possible cratonic configurations of North Atlantic, Superior and Dharwar cratons during the time interval 2.37−2.17 Ga is presented in the context of supercraton Superia.
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| 30. |
- Olsson, Johan
(författare)
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U-Pb baddeleyite geochronology of Precambrian mafic dyke swarms and complexes in southern Africa - regional scale extensional events and the origin of the Bushveld Complex
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dolerite dykes are formed when iron- and magnesium-rich (mafic) mantle-derived magmas ascend through the lithosphere (upper part of the mantle) and crystallize as ‘hydro-fractures’ within the crust. Dykes may exist in great numbers to form dyke swarms (linear or radiating), which can be linked to time periods of continental break-up, or attempted break-up events, associated with voluminous volcanism. Continental mafic dyke swarms are produced when the lithosphere is subjected to fracturing and therefore make up important markers of regional extensional events. Large dyke swarms have been hypothesized to represent the plumbing system to Large Igneous Provinces (LIPs), which are anomalously large magmatic settings (exceeding 100 000 km2) that apart from the dyke swarms also consist of thick flood basaltic lava flows and large mafic-ultramafic complexes. The origin of LIPs is debated, with the classical explanation involving melting triggered by a rising mantle plume (a column of very hot material from the deep mantle). Particularly dyke swarms with radiating patterns are believed to form during mantle plume generated melting events. Most of the continental landmasses on Earth contain very old (Archean; 3.8–2.5 billion years old) and geologically stable interiors, called cratons, which also preserve the oldest dyke swarms. Southern Africa encompasses the Kaapvaal and the Zimbabwe cratons, which were glued together (amalgamated) along the Limpopo Mobile Belt. Together, these two ancient cratons record some of the most spectacular geological formations on Earth, and preserve numerous mafic magmatic units including the largest mafic-ultramafic layered intrusion in the world, the Bushveld Complex, as well as abundant undated dolerite dyke swarms of a range of trends. The goal of this work was to provide initial dating on these swarms and investigate their links with known major magmatic events. In particular, a key goal was to investigate whether any Bushveld-aged radiating dykes exist in the Kaapvaal Craton; in order to test for its mantle plume origin. Rocks can be directly dated by isotopic systems on different types of minerals. Datings performed in the framework of this thesis comprises exclusively the uranium- (U) lead (Pb) isotope system on the mineral baddeleyite (ZrO2) to determine the crystallization age of dolerite dykes and their plutonic equivalents in the deeper parts of the crust. In short, U-Pb dating of mafic rocks in the oldest parts of the Kaapvaal Craton has revealed three separate, long-lived magmatic events, which represent important stages during the evolution of the craton, as well as a new model for the origin of the Bushveld Complex of which no mafic dykes have been found. There is evidence of a 2990–2965 million years old (Ma) mafic dyke swarm and associated mafic complex that was intimately related to the rifting of the Pongola Basin – the world’s oldest continental rift and associated Nsuze lavas. There is also a radiating swarm of mafic dykes that can be connected to a mantle plume that impacted the Kaapvaal lithosphere at 2700–2660 Ma and injected massive amounts of mafic magma into the more than 200 km thick lithosphere, as well as erupting as a thick sequence of flood basalts. At depth, these mafic rocks were transformed (metamorphosed) into denser compositions (eclogite rocks) and exerted an enhanced weight to the lithosphere, which controlled the Transvaal Basin development at the surface. Two billion years ago, Zimbabwe and Kaapvaal collided to form a single landmass. This tectonic event may have triggered the delamination of the dense plume-derived mafic root and thereby allowed for a rapid upwelling and massive decompressional partial melting of hot mantle, which produced the voluminous melts that had to be fed into the Bushveld Complex. Lastly, a northeast-trending dyke swarm was formed at 1875–1835 Ma along the northern border of the Kaapvaal Craton, and partially cutting across the Bushveld Complex. Together with the 1885–1870 Ma Mashonaland sill province in the Zimbabwe Craton, these intrusions represent the earliest coeval mafic magmatism across both cratons and hence support the hypothesis of a ca. 2.0 Ga collision between these two ancient cratons. However, this interpretation still remains to be tested by paleomagnetic constraints.
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| 31. |
- Paulsson, Oskar
(författare)
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U-Pb geochronology of tectonothermal events related to the Rodinia and Gondwana supercontinents -observations from Antarctica and Baltica
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents data from two areas, Dronning Maud Land, Antarctica, and the Scandinavian Caledonides, Baltica. In addition, a comparative geochronological study is presented. The bedrock of Dronning Maud Land (DML) is dominated by migmatitic gneisses and post-tectonic intrusions. A migmatitic gneiss at Jutulsessen nunataks, Gjelsvikfjella, has a protolith age of 1163 ± 6 Ma and a migmatisation age of 504 ± 6 Ma. The ages of post-tectonic rocks range from 486 ± 6 Ma to 521 ± 4 Ma. The youngest age represents intrusion of granitic/pegmatitic dykes and fluids. Sm-Nd model ages for the Mesoproterozoic migmatitic gneiss in Jutulsessen vary between 1390 and 1770 Ma while the post-tectonic rocks have model ages between 970 and 2200 Ma. The age of the protolith and the model ages are in accordance with a Mesoproterozoic correlation between Dronning Maud Land and the Natal Province in South Africa made by earlier authors. Consequently, it is suggested that the investigated area in DML was a part of the Kalahari (Kaapvaal) Carton since Mesoproterozoic time. The regional migmatisation and the post-tectonic intrusions are all in accordance with a post-collision collapse. It is suggested that the post-collision event is caused by the collision between the Kalahari craton and the combined block of East Antarctica and Australia, and that it completed the assembly of Gondwana. By investigating the Seve-Kalak Nappe Complex in the Scandinavian Caledonides, Baltica, it is possible to reconstruct the pre-Caledonian margin of Baltoscandia. The intrusion age of a granite–gabbro complex, hosted by mainly sedimentary migmatites and augen gneisses, has been determined to 845 ± 14 Ma. Analyses from zircon cores indicate Paleoproterozoic (1778 ± 11 Ma) and Archaean protolith ages. Bimodal magmatism of this age is not found within the Baltic shield but the age pattern allows correlations within the Seve-Kalak Nappe Complex 300km to the north. It is suggested that the bimodal magmatic complex intruded into a sedimentary basin in a continental rift setting, but that rifting was not successful. When analysing U-rich zircons from DML with the SIMS technique, reversed discordant analyses are often obtained. In order to reveal the character of these zircons the very same zircon crystals were analysed by ID-TIMS. The results show that the reverse discordance is an artefact of the SIMS analytical procedure, probably caused by a difference in the sputtering and ionizing behaviour of U-rich zircons versus that of the U-poor zircon standard. In such cases it is thus important to put more emphasis of the 207Pb/206Pb ages, which are not dependent on these differences.
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| 32. |
- Rimsa, Andrius
(författare)
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Understanding Zircon Geochronology - Constraints from Imaging and Trace Elements
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Formation of incipient charnockite in Söndrum, SW Sweden and the Kerala Khondalite Belt (KKB), S. India is accompanied by zircon growth. The age of the dehydration event is constrained by dating newly formed zircon to 1397±4 Ma (2?, MSWD=1.7) in Söndrum and ca. 520-510 Ma in S. India by secondary ionization mass spectrometry (SIMS). The formation of incipient charnockites correlates with regional magmatic or metamorphic events. In Söndrum, SW Sweden, charnockitisation is simultaneous with the formation of the Varberg Charnockite- Granite Association (CGA). Identical ages for incipient charnockite formation in studied localities in the KKB, S. India imply that charnockitisation is a major regional event related to the latest stage of Pan-African orogeny. Commonly observed bulk rock HREE depletion in incipient charnockites is not caused by zircon dissolution but by involvement of garnet as a reactant in the dehydration reactions. The Kerala Khondalite Belt, S. India, previously believed to be an entirely supracrustal belt, in fact contains magmatic rocks as a major lithological component. Ages (SIMS U-Pb on zircon) of magmatic garnet-biotite gneiss (1877±24; 2?, MSWD=0.6), augen gneiss (1891±36; 2?, MSWD=1.04) and massive charnockite (1865±16; 2?, MSWD=0.41) identify a previously unknown, Paleoproterozoic magmatic major crust forming event in the Kerala Khondalite Belt, S.India. Two distinct metamorphic events at 580-550 Ma and 520-510 Ma, identical in age in three studied localities of garnet biotite ortho- and paragneiss and augen gneiss, have been identified. The pervasive 580-550 Ma regional metamorphic event dates deformation and migmatisation of the magmatic and sedimentary rocks in the Kerala Khondalite Belt during Pan-African orogeny. The second metamorphic event is related to formation of the incipient charnockites. The entire population of magmatic oscillatory zoned zircons in a migmatised granitic sample from the Tjärnesjö intrusion, SW Sweden, experienced brittle hydraulic fracturing and rapid healing. The oscillatory zoned zircon fragments are rotated but not dispersed. Fractures between individual fragments are sealed by newly formed CL-bright zircon. Both the internal structure of fractured zircons and the LREE-enriched, low-Th character of CL-bright zircon suggest that cracks between oscillatory zoned zircon fragments were rapidly sealed after fracturing by hydrothermal CL-bright zircon. Zircon fracturing and crack-sealing has been dated by SIMS U-Pb on zircon to 920 ± 51 Ma with a limit for the youngest possible age of 960 ± 16 Ma provided by sector zoned rims that form overgrowths on the fractured cores.
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| 33. |
- Störling, Tjördis
(författare)
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Changes in ocean geochemistry across the K-Pg boundary interval
- 2024. - LITHOLUND THESES
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Cretaceous - Paleogene boundary (K-Pg, 66 Ma) was a time interval with dramatic changes in the Earth’s climate and the ocean environment. It was characterized by severe disruptions of marine biogeochemical cycles due to a meteorite impact during a time of active volcanism. The extinction of calcifiers, among others, influenced biogeochemical cycles and changed the conditions for carbonate deposition in the global ocean. Our understanding of how these cycles and the ocean geochemistry have changed through this time is still limited. Questions remain about the extent of these changes and their relationship to the biotic recovery in the surface and deep ocean. This thesis aims to provide more insights into the changes in the ocean geochemistry across the K-Pg boundary and the Paleocene (66 – 56 Ma) to improve our knowledge. A goal is to investigate how the marine silicon (Si) cycle has been changed and recovered during this time. This is important due to its link to carbon drawdown and climatic changes via silicate weathering and the biological pump. Additionally, a goal is to gain a better understanding of how ecosystems reacted and recovered in the aftermath of the crisis.The Cerithium Limestone Member (Mb) was deposited in the earliest Paleocene in the aftermath of the crisis and provides an excellent opportunity to investigate the development of non-tropical carbonate depositional systems throughout this time interval. Paper I aims, therefore, to better constrain the genesis and paleoenvironmental conditions of the deposition of Cerithium Limestone Mb. For this study, a detailed analysis of the microfacies and microfossil content of the Cerithium Limestone in the Rødvig section of Stevns Klint succession in Denmark was made. Analysis of thin sections and SEM has revealed four different microfacies with varying amounts of bioclasts in two distinct stratigraphic parts. The lowermost part consists of a thin layer of a bryozoan-rich packstone, which is interpreted as reworked material from the crests of the underlying Maastrichtian mounds. In the upper part, the microfacies appear randomly distributed due to significant bioturbation. The Cerithium Limestone is interpreted as formed in a mainly low-energy, open-marine, outer ramp-like sedimentary environment. Cyanobacteria are likely producers of the micrite of the Cerithium Limestone, as indicated by the dominance of very fine crystals (1– 4 μm).Silicon plays a crucial role in global biogeochemical cycles as an essential nutrient for many marine organisms due to its link to the biological pump. Since the onset of the Phanerozoic, Si cycling has been strongly impacted by the biosilicification of sponges and radiolaria. The stable silicon isotope composition (δ30Si) of siliceous marine diatoms, radiolaria and sponges can be used as a proxy for past changes in dissolved Si (dSi) concentrations and Si cycling processes. Paper II discusses the changes in the marine Si cycle across the K-Pg boundary with the main focus on the early-mid Paleocene. The study presents the results of δ30Si analyses of sponge spicules and radiolaria from sediment samples from DSDP Site 208 (Leg 21) in the Southwest Pacific and suggests that the deep Southwest Pacific was already dSi depleted at the base of the Paleogene (66 Ma).In recent years, the Si isotope fractionation during radiolaria biomineralization has been a topic of interest in the scientific community. In this context, the determination of order-specific and taxa-specific fractionation factors of radiolaria is crucial for the accurate interpretation of the δ30Si record. Paper III investigates the δ30Si signatures of radiolaria from the orders Nassellaria and Spumellaria. Our results show that it is crucial to consider changes in d30Si of individual taxa (especially from the same order) by the interpretation of the d30Si record in the past. We advise caution when interpreting d30Si signatures from the taxa Spongodiscoidea due to the potential influence by deeper dwelling species on their d30Si record.This thesis fills some of the existing knowledge gaps regarding the development of the Si cycle across the K-Pg boundary and in the early-mid Paleocene and provides new insight into the genesis and paleoenvironmental conditions of the deposition of Cerithium Limestone.
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| 34. |
- Tual, Lorraine
(författare)
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P-T evolotion and High-temperature deformation of Precambrian eclogite, Sveconorwegian orogen
- 2016. - Litholund Thesis
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The 1.1-0.9 Ga Sveconorwegian orogen is one of several Grenvillian-aged orogenic belts that mark the amalgamation of supercontinent Rodinia. The highest-pressure rocks in the Sveconorwegian orogen are eclogites in the Eastern Segment (SW Sweden). The eclogites occur in a nappe in the high-grade metamorphic level of the Eastern Segment that represents a window into the deepest part of this Precambrian mountain belt. The aim of this thesis is to reconstruct the metamorphic history of the eclogite-bearing nappe by characterizating the deformation associated with exhumation (Paper I) and by reconstructing the P–T evolution (pressure and temperature; papers II and III).Paper I focuses on the deformation structures in the basal shear zone of the eclogite-bearing nappe. These structures developed during exhumation at high-temperature conditions. Top-to-the-east shear and east-directed flow produced intense folding, interpreted as formed by a combination of simple and pure shear. The interplay of shearing, folding, and melt localization lead to localized shear, high-temperature brittle fracturing, and the formation of high-temperature chevron folds in high-strain zones.Paper II retraces the metamorphic evolution of the eclogite-bearing nappe by thermodynamic modelling (THERMOCALC©) and construction of P–T pseudosections for two different types of eclogite. One of the samples gave information on both the prograde and the retrograde paths, and an estimate of peak metamorphic conditions of 850–900 °C and ~18 kbar. The first stage of the prograde path, representing a medium P/T gradient, is recorded in the core of garnet grains. The second part of the prograde path and the retrograde path are both steep. The chemical growth zoning of garnet is preserved which, together with the shape of the P–T path, reflects short residence time at high temperatures.Paper III reports the results of two independent trace element thermometers, which are based on the Zr-contents in rutile and Ti-contents in quartz. The combination of these two methods confirmed the P–T evolution calculated in Paper II. In particular, Ti-in-quartz thermometry are in agreement with the pseudosection estimates at high temperatures, and the minerals appear unaffected by diffusional resetting. A pseudosection model, showing the changes in modal abundance of different phases along the P–T path, demonstrates that rutile grains in the matrix recrystallized from smaller-sized rutile grains, and that this process was simultaneous with the main dehydration reaction in the rock (continuous breakdown of hornblende and formation of clinopyroxene). This study illustrates that Zr-in-rutile and Ti-in-quartz thermometry cannot only robustly constrain a prograde evolution, but when combined with a pseudosection model can also yield information on recrystallization processes. In fact, the combination of these methods provides an unrivalled tool for petrologic interpretation.The data presented in this thesis testifies to westward tectonic burial of continental crust at ~65 km depth and 890 °C at a late stage of the Sveconorwegian orogenesis. The following foreland-directed tectonic exhumation of the eclogite-bearing nappe was associated with partial melting, ductile flow folding and shearing. The character of both prograde and retrograde P–T paths suggests rapid tectonic burial and exhumation consistent with collision at the end of the Sveconorwegian orogeny.
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| 35. |
- Mousavi Takami, Kourosh, 1971-
(författare)
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Process Control and Simulation of Ferromagnetic Strip in the Power Transformers and Electrical Machines Applications : Electric power systems
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates optimization of the control of electrical and thermal equipment by using FEM and CFD modeling in combination with dynamic simulation models. The thesis focuses on the production of electrical strips and the control system with the aim of reducing losses and improving magnetic properties. Several parameters and factors contribute to core losses. Thickness deviations in strip production, high levels of impurities in the core, orientation, ageing, surface oxidation, overloading, and hot spot temperature are among the reasons for losses in the core. Some of the losses occur during strip cutting and core assembly. This dissertation focuses on the reduction of losses in the cold rolling, annealing and manufacturing stages. The cold rolling process has a direct influence on the accuracy of the strip thickness and magnetic ageing of sheets. Some disturbances such as eccentricity, working rolls gap deviation, shape and edge deflections have to be removed in order to achieve accurate thickness. Thickness measurement makes up an important portion of loss evaluation in electrical equipment. Impurities and dirty strip surfaces in the cold rolling step can increase the carbon content of strips that pass through the annealing furnaces after cold rolling. The slab should be cleaned before reeling and rewinding. As the strip passes through the annealing furnaces, the temperature should be homogenous over the entire strip. According to simulations of furnace and strip temperature computed in the COMSOL environment, homogenous temperatures may be achieved using high electrical power reflectors which are equipped with molybdenum disilicide (MoSi2) electrical heating elements to replace the gas fired burners that are currently used. Modelling of the cold rolling process is conducted in order to find the correlation between control system parameters. A multivariable mathematical model for the rolling process is derived here, which reveals the interactions of the influencing variables. This approach provides numerically efficient algorithms, which are necessary for running in a real-time environment. A control model is applied in the MATLAB environment in order to determine the strip thickness at online-offline state using a robust algorithm. The critical problem in the thickness control loop is analysed, and an adaptive control algorithm is proposed. A number of control methods are investigated to improve the final strip properties. Cold rolled strip thickness deviations, eccentricities and shape defects are compensated for. The simulation results are verified with measurement data and the most significant sources of disturbances are detected. Finally, to solve the hottest spot problem in large scale electric power transformer, a new apparatus, oil spraying, is proposed and analysed.
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| 36. |
- Löf, Henrik, 1974-
(författare)
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Iterative and Adaptive PDE Solvers for Shared Memory Architectures
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Scientific computing is used frequently in an increasing number of disciplines to accelerate scientific discovery. Many such computing problems involve the numerical solution of partial differential equations (PDE). In this thesis we explore and develop methodology for high-performance implementations of PDE solvers for shared-memory multiprocessor architectures. We consider three realistic PDE settings: solution of the Maxwell equations in 3D using an unstructured grid and the method of conjugate gradients, solution of the Poisson equation in 3D using a geometric multigrid method, and solution of an advection equation in 2D using structured adaptive mesh refinement. We apply software optimization techniques to increase both parallel efficiency and the degree of data locality. In our evaluation we use several different shared-memory architectures ranging from symmetric multiprocessors and distributed shared-memory architectures to chip-multiprocessors. For distributed shared-memory systems we explore methods of data distribution to increase the amount of geographical locality. We evaluate automatic and transparent page migration based on runtime sampling, user-initiated page migration using a directive with an affinity-on-next-touch semantic, and algorithmic optimizations for page-placement policies. Our results show that page migration increases the amount of geographical locality and that the parallel overhead related to page migration can be amortized over the iterations needed to reach convergence. This is especially true for the affinity-on-next-touch methodology whereby page migration can be initiated at an early stage in the algorithms. We also develop and explore methodology for other forms of data locality and conclude that the effect on performance is significant and that this effect will increase for future shared-memory architectures. Our overall conclusion is that, if the involved locality issues are addressed, the shared-memory programming model provides an efficient and productive environment for solving many important PDE problems.
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