http://theses.ncl.ac.uk/jspui/handle/10443/3625 2026-02-04T10:18:27Z http://theses.ncl.ac.uk/jspui/handle/10443/3631 Title: The sedimentology and diagenesis of the Raisby Formation (Z1 carbonate), Northern England Authors: Lee, Martin Robert Abstract: The Raisby Formation is the basal Zechstein (Upper Permian) carbonate, that crops out in northeast England. It was deposited in environments ranging from shallow water, above wave base, into a deeper water carbonate slope. The shallow water sediments are skeletal wackestones and packs tones which contain some sandstone horizons, whereas those deposited in deeper waters are mudstones, incorporating resedimented carbonates of variable thickness and extent. Many slope sediments were lithified early, forming nodular horizons. These cements, dominantly high magnesian calcite and aragonite, also occluded intra-skeletal pores, and were followed by the precipitation of framboidal pyrite. Early lithification of slope sediments had a significant influence on their stability, and response to resedimentation. Much of the Raisby Formation which was deposited on lower parts of the slope, was removed during an episode of catastrophic slope failure close to the end of first cycle carbonate deposition. During early burial, some sediments which were lithified early, neomorphosed to low-magnesian calcite microspar, which at a few localities was accompanied by the formation of coarsely crystalline calcite concretions. At the same time, or slightly earlier, sediments which did not lithify early, and some of those which did, were dolomitized and replaced by gypsum and anhydrite. Replacement by both dolomite and calcium sulphates was directly related to the deposition of the Hartlepool Anhydrite Formation. During burial, following calcium sulphate precipitation, the formation was relatively diagenetically inactive. Patchy Cu-Pb-Zn mineralization may have resulted from thermochemical reduction of anhydrite, in association with methane, and base metal-rich fluids derived from the Palaeozoic basement. During Tertiary uplift of the formation, a meteoric aquifer was established, which led to dissolution and calcitization of dolomite, anhydrite, and gypsum, and the precipitation of calcite cements. The calcite cements are associated with different types of iron and clay minerals and internal sediments. Luminescence petrography and stable isotope geochemistry demonstrate that most calcitization and calcite cementation was concentrated in two areas of the aquifer; a distal zone where fluids of elevated temperatures calcitized dolomite, gypsum and anhydrite, and precipitated pyrite, marcasite, barite and fluorite, and a proximal zone in which calcite cementation and dolomite calcitization was driven by CO₂degassing of calcite saturated, oxic groundwaters. Description: PhD Thesis 1990-01-01T00:00:00Z http://theses.ncl.ac.uk/jspui/handle/10443/3626 Title: A review of British Upper Jurassic ichthyosaurs Authors: Kirton, Angela M. Abstract: The introduction to the thesis presents a synopsis of British Jurassic stratigraphy, and a brief account of the occurrence of British Upper Jurassic ichthyosaur remains which highlights the importance of the Leeds Collection of ichthyosaurs. A historical review of the publications concerning British Upper Jurassic ichthyosaurs (members of the order Ichthyopterygia) is presented. The British Upper Jurassic ichthyosaur taxa are reviewed. Of the five genera and fourteen species erected, only four generic and four specific names are found to be valid. The rejected names are listed with reasons for their rejection. After a listing and discussion of the synonymy of each valid species, a diagnosis and list of referable material is presented, then each species is described in detail. New reconstructions of the skull in dorsal and lateral views, the palate, the lower jaw and the complete skeleton of Ophthalmosaurus icenicus are presented. A reinterpretation of the forepaddle of O. icenicus proposes that previous interpretations have presented the forepaddle laterally inverted. The discovery that a bone of uncertain homology, designated element B, is present in the temporal region of the skull of O. icenicus, has important implications in the problem of the phylogeny and affinities of the Ichthyopterygia, and this is discussed. The presence of element B in the skull, which has been denied by previous authors, leads to the proposal of two alternative hypotheses concerning the relationships of the Ichthyopterygia to other reptiles. The preferred hypothesis is one that states that element B is a neomorph, and that the Ichthyopterygia are diapsid derivatives. A critique of previous schemes of classification of the Ichthyopterygia is presented, and a new classification is proposed. The validity of the division of the Ichthyopterygia into two groups, the latipinnates and longipinnates, is questioned. Finally, a discussion of functional aspects of the anatomy of O. icenicus is presented. Description: PhD Thesis 1983-01-01T00:00:00Z