DSpace Collection:
http://theses.ncl.ac.uk/jspui/handle/10443/3625
2024-02-07T22:00:26ZThe sedimentology and diagenesis of the Raisby Formation (Z1 carbonate), Northern England
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 COâ‚‚degassing
of calcite saturated, oxic groundwaters.
Description: PhD Thesis1990-01-01T00:00:00ZA review of British Upper Jurassic ichthyosaurs
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 Thesis1983-01-01T00:00:00Z