The three projects described herein focus on two instances of exceptional preservation and on potential source of bias in the fossil record. The occurrence of exceptionally preserved fossil assemblages and the existence of systematic bias in the fossil record from a variety of sources represent opposing forces acting on the information quality of the fossil record. Exceptionally preserved assemblages capture features of anatomy and components of assemblages not normally recorded in the fossil record. Systematic biases affecting the fossil record do the opposite, skewing our perception of patterns of diversity, the relative dominance of clades and changes in ecosystems through time. Chapter one presents the results of an analog modeling analysis to assess whether and how a newly proposed potential mechanism, the preferential sampling of larger specimens during fossil sampling due to the greater likelihood of larger specimens being intersected by a fracture surface, contributes to the lithification bias. Chapters two and three focus on the exceptionally preserved vermiform fossils from the Winneshiek Lagerstätte in northeastern Iowa and microfossils from the Doushantuo Formation of South China, respectively. Chapter two aims at resolving the identity of the Winneshiek vermiform fossils and presents evidence that these structures represent phosphatized bromalites, an ichnologic category that includes coprolites and cololites. Chapter three presents a biostratigraphy study of exceptionally preserved microfossils at three sections of the Doushantuo Formation in South China. Acanthomorphic acritarchs represent a promising tool for subdivision and correlation of the Doushantuo Formation of South China and Ediacaran strata around the world. However, the occurrence of acanthomorphic acritarchs within the Doushantuo Formation is controlled by the availability of early diagenetic chert nodules that host microfossils such as acanthomorphic acritarchs. One of these sections contains the rare occurrence of early diagenetic cherts in an upper slope section. This new biostratigraphic data adds to the growing body of integrated chemostratigraphic and biostratigraphic data from the Doushantuo Formation. By understanding both exceptional preservation and sources of bias in the fossil record it is possible to separate artifact and noise from the true signal of the history of life. / PHD

The Swedish mining company LKAB is using limestone as additives for the production of its iron ore pellets. The company is considering five new proposals of limestones since the Nordkalk Company is soon no longer able to provide limestone from the Storugns quarry which is the one that is used today. The first purpose in this study was to characterize and compare these five new limestones in respect to their texture and their disintegration during the transport from the quarry to the final destination in Malmberget, considering the Storugns limestone as a reference material. The second aim was to focus on finding any link between texture and disintegration properties of the limestones. Another intention is that the methodology which is used in this study will help the company to consider new proposals of limestones in the future. Six limestones from the Orsa, Storugns, Stucks, Vasalemma, Verdal and Võhmuta quarries were analyzed by an optical microscopy analysis of the textures. Two types of physical tests were also included in the study: a tumbler test and a breakage test. Six different textures were identified by a qualitative thin section analysis which shows similarities between the limestones from different origins but also a high variability of texture within a same quarry. A more quantitative optical microscopy analysis led to the assumption of both the degree of lithification and the amount of initial micro-cracks for each sample. According to the physical test results, the limestones disintegrate as follows, from the less to the more disintegrated: Stucks (7,6%), Storugns (9,4%), Verdal (10,3%), Võhmuta (11,1%), Vasalemma (11,8%) and Orsa (17,6%). There is no evident textural parameter which is controlling directly the disintegration of limestone. However the samples with a rather high lithification and a rather low fracturing disintegrate less than samples with a rather low lithification and a rather high fracturing. It is assumed that the combination of degree of lithification together with the amount of initial micro-cracks is somehow controlling the disintegration of limestone. / Validerat; 20101217 (root)

<p> A microscopic study of two samples of the Gowganda Formation, both having undergone pure shear deformation at greenschist f acies metamorphism has shown: Sample A -Reduction in quartz grain size, and pressure solution shadows were evidence for strong pressure solution activity. Pre-lithification fractures provided channelways for the removal of quartz and water out of the system. Matrix quartz was not recrystallized. Sample B -Extensive local recrystallization of quartz due to pressure solution activity caused metamorphic segregation and the formation of a cleavage. Cleavage behaviour differs in the matrix from that observed in an area of contact strain, as produced by a buckled quartz vein. There is no evidence for removal of quartz from the system. </p> <p> A comparison between the two samples suggests that (a) water, in this case at least, is necessary to produce metamorphic segregation, (b) the system has to be closed to reach metamorphic segregation and (c) original features may be preserved through limited metamorphism if the rock is dried out early in its history. </p> / Thesis / Bachelor of Science (BSc)

No description available.

Les structures de déformation pré-lithification s’enregistrent dans les sédiments meubles. Ces structures sont abondantes dans les domaines sous-glaciaires et marins profonds en raison du développement de surpressions de fluide. A partir de cas d’études choisis dans ces deux environnements, leurs implications sur les (1)reconstructions paléoenvironnementales, leurs impacts sur la (2) morphologie glaciaire, et sur les (3) propriétés pétrophysiques ont pu être définis.(1) L’analyse de ces structures de déformation a permis de mieux contraindre les paléoenvironnements sédimentaires. Ces structures de déformation ont été utilisées comme des «proxy » permettant d’estimer les variations de la vitesse d’écoulement, de l’épaisseur de glace, de la production d’eaux de fonte et de la position de la marge glaciaire.(2) Les séries sédimentaires des vallées tunnels ordoviciennes enregistrent la mise en place de nombreuses structures de déformation liées aux surpressions de fluides. L’analyse de ces structures a permis de proposer un nouveau modèle de creusement des vallées tunnels induits par des pressions de fluides élevées. Ce modèle de creusement, lié aux surpressions de fluide, est favorisé dans les zones d’inter ice-stream. A l’inverse, sous les ice-stream, l’écoulement des eaux de fonte se produit à l’interface glace-substrat et favorise d’autres modèles de formation des vallées tunnels.(3) Les processus de remobilisation sédimentaire ont un impact sur les propriétés pétrophysiques des réservoirs sableux. Les études pétrophysiques menées sur des grès déposés en environnements marins profonds et glaciaires ont permis de mettre en évidence l’impact des surpressions de fluides sur les propriétés réservoirs des sables. Les processus de fluidisation sont capable de créer de bons réservoirs, tandisque les processus d’élutriations ont tendance a réduire la porosité/perméabilité. / Soft-sediment deformation structures (SSDs) occur in unconsolidated sediments, during or shortly after deposition. SSDs are abundant in subglacial and deep-marine environments because of the development of fluid overpressure. Case studies of these two sedimentary environments were used (1) to reconstruct palaeoenvironments from SSDS, and (2) to define the impacts of SSDS on glacial morphologies and (3) petrophysical properties.(1) Analyses of strain regimes, deformation mechanisms, and chronologies in SSDs served to improve palaeoenvironmental reconstructions. These structures were used as proxys to estimate variations of ice flow velocities, ice thickness, meltwater production, and position of the ice margin.(2) The sedimentary series of ordovician tunnel valleys record numerous SSDs induced by fluid overpressure. A new model of tunnel valley formation controlled by the increase of porewater pressure in the bed is proposed. This model of formation occurs in inter-ice stream zones, where meltwater is transferred to the substratum. In ice-stream corridors, meltwater circulates at the ice-bed interface and promotes the formation of tunnel valleys controlled by meltwater processes.(3) Remobilisation processes triggered by the increase of fluid pressure have an impact on the granular framework and on the geometry of reservoirs. Petrophysical studies of subglacial and deep-marine sandstones demonstrated the impact of fluid overpressure on reservoir properties. Processes of fluidisation are responsible for the increase in porosity/permeability, while elutriation processes lead to a decrease in these petrophysical properties.