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Geodynamic models of orogenic wedges usually involve significant weakening occurring along basal detachments to allow large-scale horizontal displacement. The mechanical weakening that allows these structures to accommodate major horizontal shortening is commonly attributed to the presence of mineralogically weak fault rocks, the development of overpressured pore fluids or other various strain-induced softening mechanisms related to grain-size reduction. Here, we explore the role of lithological control over weakening mechanisms - and the potential role played by dynamic weakening during co-seismic slip - that lead to the localization of slip along specific units in the tectonic context of large-scale thrust faults, employing an approach that combines field observations, petrography and microstructural documentation and frictional experiments to investigate the sedimentary rocks of the Cambro-Ordovician sequence of the Moine Thrust Zone foreland. The Cambro-Ordovician shallow-marine sedimentary succession was involved in an intricate system of imbricates and duplexes within the structurally lower thrust sheets of the Moine Thrust Zone, during the late stages of emplacement of this Caledonian thrust belt. The fine-grained clastic units and carbonate-dominated formations of this sedimentary succession have been appointed as the lithologies in which slip tends to localise within the imbricates and the detachments. The slip localization is, generally, attributed to frictional weakness of these sedimentary units. Field work corroborated the observations previously made by other authors, and expanded on that, appointing other stratigraphic unis potentially localizing slip. At a grain-scale, the rocks involved in the lower structural sheets of the Moine Thrust Zone deform primarily in a brittle manner, with a significant additional contribution from fluid-assisted diffusion mechanisms. Pressure solution, evidenced by changes in the shape of minerals along cleavage surfaces and the presence of dissolution seams and caps, is widespread throughout the studied rock sequences. The profuse occurrence of this grain-scale mechanism makes it very likely a syn-deformational fluid-influx occurred. This is substantiated by the anomalously high content of authigenic K-feldspar found particularly to affect the fault rocks derived from the fine-grained clastic units of the Cambro-Ordovician sequence. The compositional heterogeneities within the sedimentary succession are enhanced by the K-enriched fluid alteration affecting the lithologies differently, and have markedly influenced the way that these rocks accommodate deformation. ii Cambro-Ordovician powdered rocks were tested in a rotary shear apparatus, to investigate the frictional strength and stability of the gouges. The mechanical data derived from these experiments show that, different from what was previously proposed, the rheological contrast produced by the frictional weakness of the Cambro-Ordovician protoliths is not enough plausibly to explain the deformation localization observed in the field. Our experiments demonstrated that the fine-grained clastic and carbonate-dominated lithologies - previously appointed as weak layers - exhibit a substantial shift from original frictional and stability behaviours, following an imposed episode of co-seismic slip, particularly in the presence of a hydrous fluid. Initially, all the investigated lithologies exhibit similar frictional strength and velocity-strengthening behaviour (prone to stable sliding). After a simulated earthquake is imposed, the fine-grained clastic units change drastically their behaviour to a consistent velocity-weakening response - this is a shift to an unstable behaviour, that allows the material to host and, furthermore, nucleate other earthquakes. The carbonate-dominated gouges retain their stable behaviour but show a significant drop in frictional strength. The units that show a significant change in frictional response are those largely observed to concentrate slip within the MTZ lower sheets. Based on these results, we propose an alternative model to account for those observations and to help explain the observed strain partitioning in the field. Our work on the Cambro-Ordovician synthetic gouges suggest that beyond lubricating faults during co-seismic slip, the occurrence of a seismic slip episode can trigger lasting changes in frictional strength and stability of fault gouges. These findings have important repercussions for earthquake propagation at shallower crustal depths and provide fresh perspective on the role played by the frictional properties controlling deformation localization within the foreland sedimentary rocks of Moine Thrust Zone and potentially other foreland fold and thrust belts.

In this thesis I have illustrated the value of our geological heritage and geodiversity by focussing on a particular detailed aspect of the geological and palaeontological record, i.e. the trace fossil record associated with the end Ordovician (Hirnantian) global glaciation and extinction episode. The major elements of this work that are new are: • a significantly improved understanding of the nature of the soft sediment deformation, and in particular the role of "debrites" as basal landslide decollements in the Lower Palaozic Llangrannog rock succession of West Wales, • a much more detailed description of the trace fossil ichnocoenose present in the Llangrannog succession than has previously been published • an improved understanding of the nature of the ecological perturbation associated with the Hirnantian (Late Ordovician) Glacial "ice-house", and the apparent role of an opportunistic soft body fauna in filling ecological niches vacated as a consequence of the associated extinction. • Considerable thought has been given to the question of how to value abiotic nature, and it is argued that the methods of conservation valuation associated with "Geosystem services" and in particular "Natural Capital" hold considerable potential for the Geoconservation community to engage with the public and with policy makers. • As a direct result of this research, two formal proposals have been put forward for new RIGS sites, together with a new geological SSSI.

Ostracods form a significant component of the Late Ordovician fossil fauna of the Ellis Bay Formation, Anticosti Island, Canada. Sixty-two ostracod species are identified, belonging to 36 genera. These include 14 species described as new, and 13 species described in open nomenclature. The ostracod fauna reveals new and important data bearing on the biostratigraphical, palaeogeographical and palaeoecological significance of the Ellis Bay Formation. The stratigraphic distribution of the ostracods permits the recognition of four successive intervals: (A) the Longiscula subcylindrica Biozone, (B) the Eurychilina erugoface Biozone, (C) the Tetradella anticostiensis Biozone and (D) an Interregnum. Stratigraphical intervals A, B and D can be related to Copeland’s (1973) ostracod biozonation for the Ellis Bay Formation. Biozone C is equivalent to three of Copeland’s (1973) ostracod sub-zones. Presence/absence analysis of the ostracod distribution patterns in the Ellis Bay Formation identifies two palaeoecologically discrete assemblages: an open marine assemblage characterises most of the formation (lithostratigraphical members 1 to 6); whilst a lower diversity assemblage typifies the uppermost Member 7. Biogeographically, the Ellis Bay Formation ostracod fauna is typically North American (Laurentian), but also shares affinities with the Late Ordovician ostracod assemblages of palaeocontinental Baltica and Avalonia.

Ostracods form a numerically important component of certain Late Ordovician faunas of the Girvan district, southwest Scotland. Fifty-two ostracod taxa are identified, including twenty-three discussed in open nomenclature, and seventeen species that are considered as nomen dubia. The fauna reveals new and important data bearing on the biostratigraphic, palaeogeographic and palaeoecologic significance of the Girvan Lower Palaeozoic succession. Much of the Ordovician ostracod fauna of the Girvan district preserved in clastic deposits represents transported material. However, those ostracods from the early Katian Craighead Limestone Formation define shallow marine and open marine faunas respectively. The Girvan ostracods include many short-ranging species which are useful for inter-regional correlation of the Late Ordovician succession of Scotland and North America; these include Hippula ventrospinosa, Balticella deckeri, Eurychilina sunbloodensis and Baltonotella parsispinosa which characterize Sandbian age strata, and Kinnekullea comma which is typical for the Katian (anceps graptolite Biozone). Biogeographically most of the Girvan fauna is typically of North American aspect at the species level but from the early Katian onwards shows generic links with Baltica and Avalonia. The spatial and temporal distribution patterns of the Girvan Late Ordovician ostracod fauna are assessed in the context of the entire Late Ordovician Laurentian ostracod assemblage particularly for the Sandbian interval, where ostracod diversity was highest at species and genus level. Multivariate analysis demonstrates that geography had the strongest control on the global distribution of Ordovician benthic ostracods. Within Laurentia Sandbian ostracods show striking inter-basinal endemism at species level, ranging from 25% endemic in the Foxe Basin of the Franklin district, Canada to 75% in the Michigan basin. This pattern of endemism is common in other benthic groups such as brachiopods, and may indicate rapid speciation in microhabitats. Despite the strong overprint of local endemism, pan-continental faunal differences are noticed between the midcontinent and marginal Laurentian ostracod assemblages that are confirmed by multivariate analysis, and these allow the demarcation of a ‘Midcontinent’ and a southern ‘Marginal’ province for the Sandbian. Ostracod assemblages of the two provinces appear to have been controlled by physical parameters such as temperature and salinity which are related to water depth and latitude.

The Cambrian to Ordovician Durness Group was deposited on the Scottish sector of the passively-subsiding, continental margin of the Laurentian craton, and now forms part of the Hebridean terrane, lying to the west of the Moine Thrust zone. It represents c. 920 m of shallow marine, peritidal carbonates with minor siliciclastic and evaporitic strata. Facies analysis shows that the carbonates represent deposition within coastal sabkha, intertidal and shallow subtidal to shelfal environments and sedimentary logging of all available sections has revised the thicknesses of the lithostratigraphic formations within the Durness Group. A diverse array of microbialites is documented, and their application for interpreting the sea-level and palaeoenvironmental history is discussed. The enigmatic ‘leopard rock’ texture is here concluded to represent a thrombolite, thus significantly increasing the abundance of microbial facies within the section. A revised conodont biostratigraphy for the Ordovician upper five formations of the Durness Group allows more precise correlation with the once contiguous sections in western Newfoundland and Greenland and dating of the lithostratigraphical and sequence stratigraphical subdivisions for the first time. Based upon the new conodont biostratigraphy, a sequence stratigraphical model for the Cambro-Ordovician strata in Scotland is proposed, comprising four depositional megasequences, which correlate well with the Sauk sea level sequence recognised across Laurentia. This study allows for further correlation with Laurentian margin sections and the global sea-level record.

This project reports an investigation to determine controls on the distribution of quartz over growth cement and other pore filling authigenic minerals in the Ordovician Mamuniyat Formation reservoir, NC174 concession, Murzuq Basin, Libya. A case study was undertaken using samples of Mamuniyat sandstone collected from 7 wells to characterise subsurface relationships between authigenic minerals and porosity. Diagenetic features were characterised using electron microscopy, fluid inclusion analysis, cathodoluminesence, stable isotope analysis, and x-ray diffraction. The sandstone samples were mainly very fine to coarse-grained quartz arenites with minor subarkose and sublithic arenite. Detrital mineralogy is dominated by monocrystalline and minor amounts of polycrystalline quartz grains, feldspar grains, lithic fragments, and mica (muscovite). The texture is grain or grain cement supported and both packing and compaction are generally low to medium. Authigenic minerals m the sandstone include quartz and siderite, ferroan dolomite/dolomite, kaolinite, illite and pyrite. The dominant authigenic cement phase is quartz overgrowths cement (up to 13% by volume) and is the major mechanism for porosity reduction. Authigenic quartz was mainly sourced internally from the pressure solution and possible dissolution of detrital grain and where externally sourced was from the overlying Tanezzuft shale (with the silica released from clay mineral during diagenetic processes). Kaolinite and illite were present as gram coating clay minerals and resulted from mechanical infiltration. Authigenic kaolinites and authigenic illite were sourced mainly from dissolution of K-feldspar. Kaolinite is related to sedimentary facies with water saturation the main control on the volume of kaolinite precipitation. IIlite formation was related to sedimentary facies.

Gastropods are a major component of modern marine ecosystems and can be found in nearly every type of marine ecosystem. They experienced their first notable radiation during the Great Ordovician Biodiversification Event (~470 Ma), during which their diversity tripled. This study examines the gastropod assemblage preserved in the Basin and Range Province of the Western United States to establish the environmental context for the Ordovician gastropod radiation. Gastropods are present within every facies examined, but their relative abundance and distribution varies. Gastropods are rare in normal marine settings and abundant in harsh (i.e., dysoxic, hypersaline) environments. Their environmental context is shown to impact survivorship through the end-Ordovician extinction event and throughout the Paleozoic and Mesozoic. Collecting accurate density data for fossil deposits can prove challenging, especially when beds are not exposed in plane view. In these cases, paleontologists are tasked with reconstructing shellbed density from cross section exposure. This study presents a mathematical model to calculate the density of fossil material within a bed from bedding cross section counts. The model is calibrated against an Ordovician biofacies comprised of oncoids, macluritid gastropods and receptaculitids exposed in the Arrow Canyon Range of Southern Nevada, where unique preservation provides both cross section exposures and plan view of fossil concentrations. University Earth Science Departments seeking to establish impactful geoscience outreach programs often pursue large-scale, grant funded programs. While this type of outreach is highly successful, it is also extremely costly, and grant funding can be difficult to secure. Here, we present the Geoscience Education Outreach Program (GEOP), a small-scale, very affordable model tested over five years in the Department of Earth Sciences at UCR. GEOP provides a variety of outreach events and allows UCR Earth Sciences to participate in a wide range of community events. The GEOP model prioritizes simplicity, flexibility and affordability in order to best meet the educational needs of Riverside County, CA. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

The late Ordovician was a period of major climatic and biological change, much of which is poorly understood. Global cooling began in the Caradoc (early Katian) with the build-up of ice in southern polar regions of the palaeocontinent of Gondwana. Cooling continued into the Ashgill (late Katian) but may have been interrupted by a brief period of global warming, the Boda Event, in the Cautleyan-Rawtheyan immediately prior to the Hirnantian glacial maximum. The proceeding Hirnantian Stage of the Upper Ordovician was a period of abrupt global change in the biosphere, climate and ocean geochemistry. These events are marked by: (1) an abrupt positive Hirnantian isotopie carbon excursion (HICE); (2) one of the three global Phanerozoic mass extinctions and (3) an extensive drop in sealevel associated with the maximum extent of the Gondwanan ice sheet. Biostratigraphic correlation for the Late Ordovician between basin and shelf sections in the Welsh Basin is limited. The current study describes three new chitinozoan taxa, Spinachitina penbryniensis, Belonechitina reticulatus and Belonechitina ceredigionensis and developed a chitinozan biostratigraphic scheme for the Welsh Basin. Four of the six Avalonian Ashgill chitinozoan biozones are recognized: the bergstroemi fossensis, umbilicata and taugourdeaui Biozones. The Baltoscandian and Laurentian index taxon Hercochitina gamachiana is recorded for the first time in Avalonia and a new lower Hirnantian regional biozone, the new Belonechitina reticulatus n. sp. Biozone is erected. The Cautleyan-Rawtheyan (late Katian) rugata Biozone was not recorded. Four depth-facies biotopes for chitinozoa from the upper Katian-Hirnantian (Upper Ordovician) of Avalonia have been identified herein. These are: 1) an open ocean shallow-water epipelagic biotope which includes Cyathochitina campanulaeformis; 2) an open ocean middle-depth mesopelagic biotope comprising Hercochitina and Spinachitina; 3) an open ocean deep-water meso-bathypelagic biotope characterized by Bursachitina umbilicata and 4) a shelf biotope containing predominantly Desmochitina. The taxonomic composition of the open ocean middle- depth mesopelagic biotope changes from one dominated by Hercochitina and Spinachitina in the Upper Katian to one comprising Ancyrochitina in the Hirnantian post-glacial transgression. The distribution of the deep-water meso- bathypelagic biotope and the shelf biotope is affected by basin hydrography and sea level respectively. Changing hydrography induced by climate belt reconfiguration along the southern margin of lapetus in the Rawthean (late Katian), displaced deep-water taxa into the semi-restricted Welsh Basin. With sea level fall in the early Hirnantian, taxa from the shelf biotope expanded into the shallower basin. Origination of biostratigraphically useful taxa in such segregated environments, e.g. Bursachitina umbilicata, restricts their distribution to periods of climatic and environmental change. Gradual change in climate and, hence, distribution of important biozone taxa, leads to diachroneity of chitinozoan bio-zones. During the Katian and Hirnantian, the Welsh Basin, UK, lay on the northern margin of the palaeocontinent of Avalonia at mid-latitudes (estimated between 32-45 s), within the boundaries of the present-day position of the STHP. It therefore provides a suitable environment to test for sensitivity of palaeo-climate belt movement in a mid-palaeolatitude setting (Armstrong et al, in revision).When the Inter-Tropical Convergence Zone (ITCZ) and Sub-Tropical high pressure belt (STHP) were in a southerly position, mid-palaeolatitudes, which includes the Welsh Basin, were positioned beneath south-easterly trade winds. This climate belt configuration is recorded in the Welsh Basin by the deposition of organic-rich laminated hemipelagites deposited during wind-driven coastal up-welling. Coastal upwelling, increased productivity and organic carbon burial are recorded by increased Ba/Th, increased TOC wt% and negative δ(^13)C. Negative δ (^13)C excursions are interpreted to represent remobilization of (^12)C֊enriched waters during upwelling from the deep-ocean. The onset of the expression of climate belt movement during Boda Event times is later in the Welsh Basin than at low-palaeolatitudes. At low-palaeolatitudes the δ(^18)Ο response to shifting ITCZ occurred in the Cautleyan whilst in the Welsh Basin the isotopic and lithological response to moving STHP began in the Rawtheyan. This delay in expression of events is accounted for by ice-sheet- moderated rectification of insolation in the run-up to the glacial maximum. The onset of the Hirnantian glacial maximum is orbitally-moderated and is interpreted to represent an orbital configuration when eccentricity wag high, obliquity low and aphelion occurred during Austral summer. It represents a threshold at which the Gondwanan ice-sheet was able to survive precession and obliquity-induced ablation. Once this threshold had been reached, global climate belt position stabilized in a position where the ITCZ lay north of the equator and the STHP lay north of Avalonia. Four positive δ (^13)Corp excursions in Hirnantian-age rocks from the Welsh Basin have been recognized in this study and are considered to represent the HICE. They correlate well between basin and shelf environments and also with a proposed sequence stratigraphic model for the Hirnantian in the Welsh Basin. Two excursions of up to 3 %(_00) occur in the lower Hirnantian reticulatus chitinozoan Bio- zone and two excursions of 1 %(_00) are present in the late Hirnantian taugourdeaui Biozone. Higher carbon storage in the basin, coincident with positive δ (^13)Corp excursions during glacial periods, indicate a shift in the locus of carbon burial from the shelf to the basin during low sealevel. The topology of the regional Hirnantian isotope curve for the Welsh Basin compares with only a few curves from other parts of the world indicating strong regional carbon cycling. Comparison of the relative timing of the onset of HICE and peak HICE values from other palaeocontinents demonstrate little, if any, consistency with palaeolatitude or basin setting. It is demonstrated that this chemostratigraphic diachroneity of HICE can be attributed to the process of signal rectification of δ (^13)Corp records most likely due to numerous local carbon cycling processes.

Graptolite fossils provide a means for separating Late Ordovician autochthonous Martinsburg foreland basin strata (Appalachians, Pennsylvania, USA) from tectonically emplaced allochthonous Hamburg succession rocks. The youngest allochthonous rocks (Dauphin Formation) are Middle Ordovician, late Darriwilian 3 to 4a age, approximately two graptolite zones older than the foreland strata. Nineteen taxa described from the Dauphin Formation include Archiclimacograptus cf. A. riddellenis (Harris), Cryptographs schaeferi Lapworth, Normalograptus antiquus (Ge), Pterograptus elegans Holm, Hustedograptus teretiusculus (Hisinger)?, Pseudophyllograptus augustifolius s.l. (J. Hall), Haddingograptus oliveri (Boucek), Bergstroemograptus crawfordi (Harris), Tetragraptus cf. T. erectus Mu, Geh & Yin, and Kalpinograptus spp. (nov?). Newly described taxa are Pseudotrigonograptus ? ricardo sp. nov., and two (possibly more) reteograptids. The initial allochthonous incursion (Unit H-1; = Cocalico Formation ?) into the foreland carried a synorogenic piggyback basin of mid-to-late Nemagraptus gracilis Zone turbidites (Unit M-1). Emplacement was upon the Hershey/Myerstown Formation deposited during earliest regional foreland subsidence. Emplacement of allochthonous Unit H-2 followed which was covered by foreland Unit M-2 (late Climacograptus bicornis Zone), containing allochthonous fragments. The foreland basin then spread laterally over the Jacksonburg Formation and equivalent "basal limestones" as Unit M-3 (Martinsburg Formation. s.s.) during Dicranograptus clingani time. The Hamburg succession (= Dauphin Formation) contains basin sediments deposited within the Octoraro Sea adjacent to the northern fringe of the microcontinent "Baltimoria". Late Cambrian through Early Ordovician age rocks are composed of quartzfeldspathic, micaceous strata overlain by phosphorites, and covered by a black shale and quartzose-ribbon limestone package; lower to middle Arenig rocks are mostly starved clastic hemipelagites. After a biostratigraphic gap of 3-4 graptolite zones those rocks were incorporated into a Middle Ordovician, trench-origin olistostrome, formed as the Octoraro Sea closed, and co-occur with turbidites, distal pelagites and extrusive/intrusive volcanics.

The diversity of the Late Ordovician Soom Shale Lagerstatte ecosystem is increased by the identification of three new species. The phyllocarid arthropod Caryocaris cedarbergensis n. sp. is described, extending the geographical, ecological and temporal range of the family Caryoarididae and providing the first evidence of a zooplanktonic constituent in the Soom Shale biota. The scolecodont species Xanioprion? n. sp. is distinguished, based on poor material and the species Syntaptogenys rietvleiensis n. gen., n. sp. is described, providing the first documented scolecodont fauna from South Africa and the first apparatus based taxonomic study of specimens from Gondwana.;Two new soft-bodied organisms, which would both have had an extremely low preservation potential, are added to the Soom Shale ecosystem. A scyphozoan medusoid exhibits features that can be related to those observed in modern scyphozoans and is the second zooplanktonic organism identified in the Soom Shale ecosystem. A xenusiid lobopodian, showing features homologous to those of other Palaeozoic marine lobopodians, is the first definite marine lobopodian to be described outside of the Cambrian and adds a rare benthic component to the Soom Shale ecosystem.;The recognition of three new types of arthropod, comprising large carapaces of unknown affinities, a possible nektonic crustacean and a nektonic predatory stem-group chelicerate, increase the diversity of arthropods in the Soom Shale ecosystem, and confirms the arthropods as the most diverse fauna from the Soom Shale community.;The identification of fibrous clay mineral coatings, which could be a result of diagenetic or metamorphic growth, complicates the current models for the taphonomy of the Soom Shale. An additional preservation mechanism, pyrite mineralization, occurs along with clay and alunite replacement, organic films and the late stage fibrous clay growth.

The extent to which the Murzuq Basin, southwest Libya was glacierised during the late Ordovician is investigated by field studies, which are complemented by LANDSAT TM and seismic data analyses. A clear four-fold glaciation during the late Ordovician is supported by sediment architectural analysis of upper Ordovician rocks and the interpretation of syn-sedimentary deformation structures contained within them. Each phase of ice sheet advance is characterised by the development of a subglacial erosion surface or a correlative glacioisostatic-Ioading surface in front of it. Evidence for subglacial erosion includes streamlined subglacial bedforms ranging in scale from striations to palaeo-ice streams. At the ice sheet termini, glaciotectonic deformation structures formed with sustained ice sheet advance. Multigenerational, cross cutting tunnel valleys were incised under enhanced hydrostatic pressure and filled during ice sheet recession. The architectural development of both tunnel valleys and their intervalley areas was dependant upon whether ice sheets were grounded in terrestrial or marine settings. During ice sheet recession, sandstone deposition occurred on ice-proximal sandar, intertidal to shallow marine ice contact fans, and laterally extensive, storm and tide dominated open shelf areas. Turbidites were deposited in the lee of continental slope aprons and within tunnel valleys. Mudrock deposition was restricted to low energy ice distal locations and topographic lows. During the final deglaciation of the basin, glacioisostatic rebound occurred and reactivated long lived basement structures, promoting regional uplift and the development of both Gilbert-type delta systems and a "structured basin", consisting of half-graben depocentres and associated forced folds.

The end-Ordovician mass extinction dramatically altered the course of conodont evolution. This extinction event is probably unique in that it can be strongly correlated with a glacial climatic control. This study has identified, through the application of high-resolution stratigraphy, events within the extinction and recovery intervals. Elements of the uppermost Ordovician Shelf-edge Biofacies were severely affected by the oceanic cooling and introduction of cold-water currents associated with the initiation of the glacial maximum. In contrast, elements of the Shelf Biofacies were more severely affected by the intense cooling, shallowing and overcrowding during the glacial maximum. A number of the Shelf-edge taxa that had survived the glacial maximum suffered extinction at the hands of increasing water temperatures, rising anoxia and/or the cessation of oceanic circulation during the post-glacial transgression. Recovery was initiated by the appearance of Crisis Progenitor Taxa within the glacial maximum in the Shelf Biofacies and during the post-glacial transgression in the Shelf- edge- Slope biofacies. The Shelf-edge Biofacies identified within the uppermost Ordovician is not recognised in the Lower Silurian. Two main biofacies occurred on the Shelf and Slope, which had directly evolved from their Upper Ordovician equivalents. The long-term recovery involved the evolution of Crisis Progenitor Taxa and Ecological Generalists within the Shelf and Slope Biofacies (autochthonous taxa). Punctuated equilibrium likely predominated in the Shelf Biofacies as a consequence of widely fluctuating physical conditions. In contrast, the more stable environments of the slope encouraged gradualistic evolution within the Slope Biofacies (Plus ça change Model). Transgressive episodes within the Llandovery, possibly linked to eccentricity cycles, caused the iterative appearance of Long-term Refugia Taxa (allochthonous taxa), sourced from a Pterospathodontid Biofacies. The transgressive episodes also drove elements of the Slope Biofacies onto the shelf. It has been observed that the mechanisms driving extinction, namely environmental disruption and temperature changes, were also responsible for fuelling the subsequent recovery.

This thesis presents new graptoloid biostratigraphic range charts for the Ordovician and Silurian of Britain. The Ordovician graptoloid succession is represented by two separate biostratigraphic frameworks; one for England and Wales, another for Scotland, due to significant stratigraphic disparity between the graptoloid faunal assemblages of the two regions. The British Silurian sequence is represented by a single graptoloid biostratigraphic scheme reflecting more uniform graptoloid assemblages. The reliability of the taxonomic foundation upon which the range charts are based is tested using the dominant Ludlow Series (Silurian) graptoloid subfamily Saetograptinae Urbanek. The results suggest that intraspecific variation has led to over-elaborate taxonomic subdivision of this group at the species and subspecies level. The poor preservation of some of the type material has resulted in problems of misidentification and reinforces the need for a full taxonomic review of the saetograptids. Despite this, three basic theca/spine relationships can be recognised which may serve as a basis for future species identification: a chimaera-type morphology whereby thecal spines project form the middle of the apertural margin; a leintwardinensis-type structure, in which the spine extends from the free ventral wall of the proceeding theca; and a colonus-type relationship whereby the lower part of the apertural margin is prolonged into a hook-like lip. Graptoloid biodiversity data extracted from the new range charts highlights several periods of biotic crisis during the Ordovician and Silurian of the UK. These 'events' correlate with globally recognised intervals of major graptoloid extinctions, which in turn correspond with large-scale palaeoenvironmental fluctuations, such as eustatic sea-level and climate change. Patterns of morphological change within UK graptoloids are also linked to these biodiversity trends and consequently, to environmental controls.

The effects of explosive volcanism on local ecosystems are investigated in Middle Ordovician siliciclastics from the Welsh Basin. Bulk sampling analysis has provided quantitative data, regarding population proportions and abundance, following ash deposition in nearshore, shallow dysaerobic basin, and deeper basinal facies. Consistent ecological effects include the destruction of small sessile benthos by rapid burial, followed by re-establishment of mobile and opportunistic taxa, and a bimodal, planktic-benthic bloom in dysaerobic facies. The results are explained through vertical circulation initiated by turbid surface waters following ash deposition. Upwelling of subsurface, nutrient-rich waters of stratified basins is accompanied by downwelling of oxygenated surface waters, entrained into broadly spaced columns. The duration and nature of the events are investigated by ecological, sedimentological, and mechanical approaches, and high sedimentation rate invoked, resulting from seismicity associated with local volcanism. Systematic studies are included on Porifera, Echinodermata and Palaeoscolecida, the unusual preservation of each resulting from volcanism-related processes. The poriferan fauna provides significant information on non-lithistid demosponges and hexactinellids, including the earliest representatives of several groups. Rapid silicification of the proteinaceous skeleton of two species indicates a new source of soft-tissue preservation. Echinoderms comprise the most diverse pre-Caradoc fauna known from Britain, including six crinoids, three asteroids, and a cystoid.

The Late Cambrian to earliest Ordovician coniform-dominated conodont faunas recovered from the platform carbonate sequences of western North Greenland, central East Greenland, and northwest Scotland comprise a total of22 multi-element genera. Four genera and seven species are new to this study. Although the faunas exhibit a strong North American Midcontinent Province affinity, a FranklinianlArctic fauna (typified by Pagetopetalon gen. nov. and Loxognathodus Ji and Barnes) has also been identified - a fauna which was restricted to the margins ofthe Laurentian craton (Greenland, northwest Scotland, western Newfoundland, and the Canadian Arctic Islands). Furthermore, conodonts recovered from the upper Eilean Dubh Formation of northwest Scotland, traditionally considered to be faunally barren, have unequivocally established an Ordovician (c. lindstromi Biozone) age; thus placing the Cambrian-Ordovician boundary at an interval within the formation. Revised apparatus reconstructions have been proposed for three genera: A septimembrate apparatus is proposed for Variabiloconus bassleri (Pander), and its homology with that of the Fauna 0 taxa Aloxoconus stauffiri (Furnish), Colaptoconus quadraplicatus (Branson and Mehl), Eucharodus parallelus (Branson and Mehl) and Ulrichodina deflexus Furnish, has significant implications regarding the actual diversity of samples over this interval. In contrast, Rossodus Repetski and Ethington is reconstructed with a quinquemembrate apparatus ofprioniodontid affinity (based on P element morphology). A trimembrate, crushing apparatus has also been proposed for Clavohamulus Furnish as a consequence of its comparative morphology with certain species of the Raja.

The phylogeny of the Family Pliomeridae and the Ordovician representatives of the Encrinuridae was investigated using cladistics. This resulted in the diagnosis of seven subfamilies; five of pliomerids (including one erected herein) and two subfamilies of encrinurid: the Cybelinae and Encrinurinae. Some 75 genera and 12 subgenera are also diagnosed on the basis of cladistic analysis of over 180 relatively complete species. This facilitated the placement of numerous incomplete or anomalous species such that the overall analysis allowed the systematic placement of over 300 species including 159 species of pliomerid and 149 species of encrinurid. The phylogenies produced by this analysis are robust, being resistant to disruption by the addition of incomplete taxa and in showing a close match between branching order and stratigraphy. A recurring evolutionary pattern is demonstrated. Very short initial periods of rapid diversification of clades, accompanied by reduced levels of character burden, were followed by steady ramification of the newly developed subclades. This pattern of development is observed to be independent of scale, occurring at all levels of systematic hierarchy. As a result many taxa are expressly paraphyletic which may be the norm in cladistic analyses. The taxa studied provided an excellent geographical and temporal spread for the investigation of Ordovician palaeobiogeography; the Pliomeridae being particularly useful of the early Ordovician, the Encrinuridae for the middle and late Ordovician. The palaeobiogeography was investigated by first elucidating the phylogeny of the clades and subclades through time and then assessing the palaeogeographical distribution of the taxa in the light of their evolutionary relationships. This palaeobiogeographical assessment was made both qualitatively and by means of geographical character optimisation and calculated gain/loss ratios. The two approaches supported each other. In addition to the detailed terrane-by-terrane results for each subclade, the following recurring patterns were observed: During the early Ordovician, Laurentia was juxtaposed to the eastern margin of Gondwana and close to areas of South America. Towards the end of the early Ordovician, Laurentia and Gondwana diverged, and did not subsequently re-approach each other during the Period although the Argentine Precordillera was situated in a position between Laurentia and Gondwana in the Llanvirn. This supports a modified version of the model of Dalziel for the early Ordovician in which Laurentia and Gondwana are close, but not in contact, but that of Scotese & McKerrow and others for the mid- and late Ordovician. Throughout the Ordovician oceanic islands provided stepping stones for faunal migration between the main continental plates.

Acritarchs have been recovered from late Ordovician-early Silurian strata in Anticosti Island, the type Ashgill and Llandovery areas, and from subsurface material in Estonia. Samples have yielded 54 genera (3 new: Acutesphaera, Asperasphaera and Magnasphaera), 229 species (36 new) and 100 species described in open nomenclature. The acritarchs from Anticosti Island and Estonia are diverse and well preserved, allowing for the establishment of a detailed biostratigraphy. The type Ashgill and Llandovery areas have low to moderate diversity and less well preserved assemblages due to a greater degree of thermal maturation. The International Stratotype for the Ordovician-Silurian boundary at Dob's Linn, Scotland, yields poorly preserved acritarchs and was excluded from further study. Large numbers of acritarch taxa were casualties of the end-Ordovician extinction event, especially thick/double walled acritarchs. Morphologically complex forms also temporarily disappeared from the carbonate environments of Anticosti Island and Estonia, as did species of Veryhachium. The composition of floras from the carbonate rocks of Anticosti Island and Estonia show a greater similarity than with the clastic rocks of the Llandovery area, thus suggesting facies control on acritarch distribution. Lowermost Llandovery assemblages are dominated by geographically widespread and long ranging taxa. Recovery of morphologically complex forms, the reappearance of Veryhachium and the introduction of new thick/double walled genera occurred by the middle Aeronian. Recovery appears to have occurred earlier in the clastic environments of the type Llandovery area than the carbonate environments of Anticosti Island and Estonia. Current models for the end-Ordovician extinction do not adequately explain the selective extinction and temporary disappearance of certain groups of acritarchs. The main phase of extinction, during the mid Hirnantian, coincided with the glacial maximum, and it is likely that associated changes in oceanic circulation and stratification, and nutrient supply combined to affect acritarch productivity.

Approximately 300 field and well samples from the Ordovician to Devonian interval of the Anti Atlas, Morocco have been prepared for palynological investigation. Of these, 118 were selected for detailed analysis based on the quality of the palynological recovery, an attempt to achieve the best stratigraphic coverage as possible from the material available and also based on the presence of macrofossil data. A rapid palynological preparation technique for observation by light microscopy has been developed to analyse thermally mature, brittle assemblages, such as those encountered. Reviews of the Acritarcha, the fossil Prasinophyta and the Chitinozoa are presented with discussion of their morphology, biological affinity and classification. Taxa from these groups are treated systematically with 389 described species recorded, assignable to 115 genera. A total of 71 unpublished forms are described in open nomenclature. Miospores; have also been recorded to enhance biostratigraphic resolution and environmental interpretation of the assemblages studied. The miospore taxa recorded are illustrated with their authors cited in the plate captions. Semi-quantitative analyses of the assemblages has enabled the recognition of 33 Palynological Associations from the Ordovician through Devonian based on the presence, absence and abundance of the tax & recorded. Cluster analysis of the samples has been undertaken to assist in the recognition and to quantify the similarity of the assemblages. The Ordovician field samples yielded poorly preserved assemblages from which 12 Associations are recognised. The Silurian to Lower Devonian field samples yielded moderate to well preserved assemblages despite the high thermal grade of the material. Twelve Associations are defined from this interval, the ages of which are all highly constrained by the generally rich graptolite assemblages. Nine Associations are recognised from the Devonian assemblages recovered from Well Oum Doul-I core samples. These assemblages are well preserved with abundant and often diverse marine and terrestrial elements present. 'Me age interpretations of the 33 Associations are based on both macrofaunal evidence, when present, and on comparison with previous palynological studies, primarily those from Northern Gondwana. A general palaeoenvironmental, interpretation of the formations studied is attempted from the semi quantitative analysis of the relative proportions of environmentally sensitive palynomorph groups and the relative proportions of morphotypes within palynomorph groups. The major bathymetric fluctuations in the environment of deposition which are evident from the palynological, assemblages (e.g. the deep water event in the early Silurian) are believed to be eustatically controlled during the Ordovician to Devonian in the Anti Atlas. The broad nature of the study, geographically and stratigraphically, has revealed much potential for future work, of both academic and commercial interest, in the North African and Middle East region.

The Soom Shale lagerstatte is unusual in three respects: it is Ordovician in age, a time when there is a dearth of other conservation deposits; it was deposited at a high latitude under glacial influences; and, the mode of preservation of hard and soft tissues is unique. The Soom Shale is a finely-laminated black shale and contains a highly restricted marine biota. Several taxa preserve soft tissues, notably the giant conodont Promissum pulchrum Kovacs which preserves muscle tissues through replacement by clay minerals to the subcellular level, a level of detail which has only previously been reported in phosphatized soft tissues. Replacement of soft tissues by clays occurred either directly, or indirectly through a phosphate precursor. Bottom and pore water conditions were dominantly anoxic-euxinic and without carbonate to buffer the pH, the biominerals aragonite, calcite and apatite were rapidly dissolved. The extremely low pH environment may have also militated against the authigenesis of phosphate indicating that direct replacement of soft tissues by colloidal clays was the most likely taphonomic route. Recalcitrant biomolecules such as chitin and scleratin show either complete replacement or coatings of clay minerals, suggesting the reactivity of the substrate was important in controlling mineralization. Longicone orthocones in the shale are associated with Ungulate brachiopods, ostracodes and cornulitids. Orthocone-epibiont relationships demonstrate that the size distribution of epibionts on the host may determine the timing of epibiont attachment. The orbiculoid epibionts on one orthocone attached whilst the host was alive as did cornulitids, which have grown aligned to a forward head-on orthocone swimming direction. Three orthocones preserve radulae which represent the oldest in the fossil record and have a tooth configuration more comparable with coleoids and ammonoids than with nautiloids.

During the Early Palaeozoic, the southern British Isles were part of a microcontinent Eastern Avalonia. In the early Ordovician Eastern Avalonia was close to the continent of Gondwana. in high southern latitudes. Northward drift of Eastern Avalonia during the Ordovician brought it towards Baltica and Laurentia, resulting in continental collision in the Silurian. Three major tectonic events have been postulated in the earlier history of the microcontinent rifting from Gondwana, onset of subduction and subduction of the mid-ocean ridge. Evidence for such events may be sought in the contemporaneous sedimentary basins: their type and geometry and the depositional environment and composition of their sediment fill. The Skiddaw Group (Tremadoc to Llanvirn) of Cumbria. comprises turbidites. debrites and a major olistostrome. Sediment was sourced from an orogenic terrain with noncoeval continental volcanic arcs, unroofed plutons, metamorphic basement and sedimentary cover. An additional source of quartzose sediment (e.g. a sandy shelf or delta) was present Two periods of submarine fan development display the following facies associations: depositional lobe, lobe fringe and interlobe, distributary channel, and proximal channel-levee. The first spans the Tremadoc-Arenig boundary and channels distributed sediment to both east and west Axial flow along a trough orientated approximately east-west is inferred. Contemporaneous depositional lobe fades association in the Isle of Man could represent a more distal portion of this system. The Manx Group displays sediment of similar facies and compositions to the Skiddaw Group. Turbidity current flow on a submarine fan of Arenig age was strongly influenced by sea floor topography. A palaeocurrent interpretation is presented which uses the theory of oblique reflection of turbidity currents (Kneller, Edwards, McCaffrey and Moore, 1991). The angular relationship between sole mark current directions and ripple current directions is used to infer the orientation of intra-basinal topographical features. With additional evidence from thickness variations of sandstone bodies and the orientation of pre-mid Ordovician faults, a tectonic model of syn-depositional extensional faults trending northnorthwest, with fault blocks tilted to the northeast is proposed. The controls of fan development are discussed. Gravitational deformation in the Llanvirn is expressed as slump folds in partially lithified sediment, debrites and an olistostrome with sandstone rafts. Slump fold orientations are used to demonstrate the development of a regional westerly palaeoslope which preceded uplift of the depositional basin prior to subaerial volcanism of the Eycott and Borrowdale volcanic groups. The undated Ingleton Group is described and contrasted with the Skiddaw and Manx Groups. A lithological correlation with Arenig sediments recovered from the Beckermonds Scar borehole is supported, but a continental margin volcanic arc provenance and deposition as a coarse grained lobe of a submarine fan suggests the dispersal system was separate from that of the Skiddaw Group. Lithological comparison is made with contemporaneous strata of southeast Ireland. With consideration of early Ordovician geology across the Southern British Isles, a tectonic model is proposed which incorporates transtensional and transpressional phases of oblique sinistral slip in the overriding plate above a subduction zone of general southerly dip. The present day active margin of Chile is used as an analogue. The long and complex history of Eastern Avalonia's northern margin is analysed to identify the three tectonic events mentioned above.

The Saq Sandstone is 600m thick and of Cambro-Ordovician age (?). It is vertically and laterally uniform succession, >90% of which cross-stratified. It is a texturally and mineralogically mature, fine to coarse-grained quartz arenite, with subordinate shale, siltstone, breccia and conglomerate. The Saq Sandstone comprises an upward maturing and fining sequence. It was -largely derived from a craton interior made up of pre-existing and multi-cycle sedimentary rocks. A new formation (The Idwah Formation) overlying the Precambrian-Cambrian basement and older than the Saq Sandstone has been defined. This is a remnant of an earlier extensive cover over the peneplained Precambrian-Cambrian surface. The sandstone was partly or totally deposited in a tide-dominated shallow-shelf marine environment. Six Facies Associations have been recognized: (1) Facies Association A (Bar areas); (2) Facies Association B (Inter-Bar); (3) Facies Association C (Inner-shelf); (4) Facies Association D (Shoreline) and (5) Facies Association E (Scree). The Saq Sandstone was deposited intially during a transgression (Lower and Middle) and then during a regression (Upper) cycle. The regression producing a laterally extensive sheet of beach sandstone. The palaeocurrent pattern throughout Saq Sandstone is unidirectional (NE). This together with the orientation of the beach lamination, suggest that the source lay S to SW of the Saq Basin, although it is difficult to reconstruct a palaeoslope from tidally induced flows. The dominance of a single palaeoflow suggest a strongly asymmetrical tidal system.

The Llandeilo-Llandovery stratigraphic succession of west Wales comprises fourteen formations and consists of two dominant lithologies, namely sandstone and mudstone, the distribution of which is largely determined by eustatic sea-level changes. The sediments are interpreted as representing distal shelf, sandstone lobes, lobe fringes and slope environments. The turbidite systems developed within the Welsh depositional basin as a Type 1 (unchannelled sandstone lobes) system. The tectonic setting of the basin for the entire period of deposition was that of an active margin. Petrographic and geochemical data, however, indicate a passive margin tectonic setting for the basin. Critical examination of the models suggests that the sedimentary provenance indicators are incorrect and that the signature is a relict one, presumably derived from the Precambrian basement. Laminated hemipelagites are recorded from a number of formations. These formed under anaerobic conditions within the basin. They all contain layered pyrite framboids which are interpreted as having formed diagenetically within the sediment. It is also possible that some of the framboids may have formed syngenetically in the water column. The strata contain a diverse and relatively abundant ichnofaunal assemblage consisting of sixteen ichnogenera: Chondrites, Circulichnis, Cochlichnus, Cosmorhaphe, Desmograpton, Gordia, Helminthoida, Helminthopsi s, Nereites, Neonereites, Palaeophycus, Paleodictyon (Glenodictyon), Paleodictyon (Squamodictyon) , Planolites , Protopaleodictyon and Spirophycus. The ichnogenera are unevenly distributed throughout the succession, the main controlling factors being toponomy, anoxia and a global extinction event.

The Ordovician rocks of the Bail Hill area, Sanquhar, South Scotland : volcanism and sedimentation in the lapetus Ocean. by M. J .McMurtry. The Bail Hill area lies in the "Northern Belt" of the Southern Uplands and contains sedimentary and volcanic rocks of Llandeilo/Caradoc age. The sedimentary succession has been divided into four formations - the Glenflosh, Kiln, Spothfore and Guffock Formations. The Glenflosh and Guffock Formations are mainly arenaceous and were largely deposited by turbidity currents flowing to the southwest. They typically consist of Tae units. The fine-grained sandstones and siltstones of the Kiln Formation were also deposited by turbidity currents. Parallel-laminated units in the lower part of the formation represent "overbank" deposits, whilst lenticular- bedded units in the upper part are interpreted as channel- mouth deposits. Bouma sequences are not common in these lithologies. The Spothfore Formation consists of rudites deposited by a variety of sediment and fluid gravity flows close to a feeder system. The petrography of greywackes within the formations shows no significant variation across strike, in contrast to successions studied to the southwest. The provenance of detritus in the sediments is believed to be the north-westerly Laurentian continent with a significant but variable intrabasinal contribution of sedimentary and volcanic debris. A stratigraphic succession for the area is proposed, although graptolite evidence for the relative ages of the formations is equivocal. A new stratigraphic unit, the Bail Hill Volcanic Group, is proposed and the petrography and field relations of the subdivisions within this group are discussed. Field relations suggest that the Bail Hill volcano was a composite, central-type structure. Early basaltic lavas were succeeded by more differentiated lithologies and pyroclastic activity increased with time. The mineral and whole-rock chemistry indicates the Bail Hill Volcanic Group has differentiated along the sodic alkaline series (alkali basalt - hawaiite - mugearite - trachyte). Gabbroic and dioritic xenoliths in the extrusive rocks are believed to be fragments of a large sub-volcanic intrusive mass that underlay the Bail Hill volcano in Ordovician times. The volcanic pile as a whole has undergone metamorphism to zeolite facies grade. Higher grade assemblages in the xenoliths suggest that they were hydrothermally altered prior to incorporation in the extrusive rocks. It is concluded that the Bail Hill Volcanic Group represents the remnants of a seamount within the Iapetus Ocean, whilst the sedimentary rocks record the transition from the abyssal plain into a Lower Palaeozoic trench. Northwesterly subduction of the lapetus Ocean crust resulted in the accretion of the Bail Hill area on to the facing edge of the northwesterly Laurentian continent.

Ordovician samples have been collected from various places from within three separate terranes in Scotland; the Highland Border Complex, the Southern Uplands and the Midland Valley. The samples have been palynologically processed and their assemblages studied with the aim of understanding some of the palaeoecological, biostratigraphical and thermal relationships of the three areas.Seventy one samples have been processed from nine localities of the Highland Border Complex and these have yielded fifteen species of chitinozoans in four genera, as well as indeterminate species of those genera. There are also five species of acritarchs in four genera as well as other microfossils. Black shales from the Complex yield the most diverse palynomorph assemblages, and were probably deposited from Arenig through to Caradoc although not necessarily at the same time in different parts of the basin. The preservation of palynomorphs appears to be better in the west of Scotland than in the east.From the Southern Uplands samples have been processed from Coldingham Bay and proved barren, from Barrhill the assemblages are poor, but from the Ordovician-Silurian bondary beds (C. peltifer to P. acuminatus Zones) at Dob's Linn they are quite diverse although abundance is very low, with forty three samples yielding thirty three species of acritarchs in eighteen genera, thirty one species of chitinozoans in thirteen genera and various other microfossils. The boundary cannot be delineated using the palynological assemblages, and although Tylotopalla sp. A and Ancyrochitina ancyrea Eisenack 1931 are common in most of the samples from the boundary the palynomorphs do not appear to mirror the changes that occur in the graptolite assemblages.From the Midland Valley samples have been processed from eight miscellaneous localities in the region of Girvan, giving very little biostratigraphical data, although one sample from Doularg Hill is dated as upper Arenig to lower Llanvirn. A section of twelve samples processed from the Mill and Shalloch Formations (D. complanatus and D. anceps Zones) at Woodland Point, Girvan, has yielded thirty five species of chitinozoans in twelve genera including a new species Angochitina woodlandensis and five new combinations; Belonechitina comma (Eisenack 1959), Belonechitina hirsuta (Laufeld 1967). Belonechitina micracantha (Eisenack 1931), Belonechitina schopfi subsp. americana (Taugourdeau 1965), and Belonechitina seriespinosa (Jenkins 1969). There are also forty seven species of acritarchs in twentyone genera, including two new species; Actinotodissus woodlandense, and Goniosphaeridium girvanense, and many scolecodonts. Spores are common and three species are recognised at Woodland Point. The samples are dated as Upper Ordovician and Calpichitina lenticularis (Bouche 1965) and Acanthochitina barbata appear to be important Upper Ordovician indicators, possibly being near-shore species as they are not found in rocks of the same age at Dob's Linn. Calpichitina lenticularis is very important in one sample and less so in all the others and it is suggested that it may be reworked. The palaeoecological picture at Woodland point shows an offshore situation in the Mill Formation, becoming more near-shore at the base of the Shalloch Formation and then more off-shore again.The palaeoecology of both Dob's Linn and Woodland Point are discussed and chitinozoans found to be more common in black shales than grey mudstones, although the acritarchs do not appear to be preferentially found in grey mudstones or black shales. Netromorph acritarchs are less common at Dob's Linn than was expected, but are very common at Woodland Point which may suggest that the sediments at Woodland Point were deposited more offshore than those at Dob's Linn but were more greatly influenced by turbiditic material. Sphaeromorph acritarchs at Woodland Point are very common and due to the variable thickness of the walls it is suggested that there is a mixing of near-shore and off-shore species, possibly by the turbiditic action mentioned above. Belonechitina is markedlymore important at Woodland Point than at Dob's Linn the reverse of which is true with Cyathochitina . The suggested reason for this is that Belonechitina is a near-shore species whilst Cyathochitina is an off-shore species. Veryhachium appears to become more important towards the end of the Ordovician, as a sample each from Woodland Point and Dob's Linn contain three species of this relatively rare genus, although the significance of this is not yet known.The sample from Dob's Linn and Woodland Point are compared with published works using the jacquard Coefficient and the results presented. The samples at Dob's Linn are compared with the Ordovician-Silurian boundary sediments elsewhere, and although different species are present at Dob's Linn and on Anticosti Island, and the abundance and diversity is lower at Dob's Linn, the boundary in Scotland has a much better palynomorph assemblage than was expected. The boundary assemblage presented here is quite similar to the one in Skane, Sweden.Finally the thermal history of the samples is discussed, and a general trend appears, with the samples from Girvan being the least altered, those from the Southern Uplands being moderately altered and finally the Highland Border Complex samples which have been subjected to temperatures probably between 200 and 300oC, and thus strongly altered.

The project has involved the revision of the stratigraphy of the upper part of the Ordovician succession in central Portugal. Using evidence derived principally from the study of measured sections, with some limited geological mapping, this thesis first considers a new lithostratigraphy of the upper Ordovician deposits. The scheme presented includes four groups, twelve formations and eleven members. Most of the elements of the scheme are described here for the first time. The sedimentology of the deposits has been studied to allow an interpretation of the depositional environment. The history of sedimentation in the upper Ordovician is divided into three broad phases. In the first of these (phase A) storm-dominated deposition of detrital clastics took place on a wide, flat, shallow shelf. During the second phase (B) a localised area of igneous activity developed in the area of highest subsidence seen in the preceding phase. This igneous activity was accompanied by the deposition of some carbonate sediments. The third phase of deposition (C) is linked to the effects of the upper Ordovician glaciation. A review of most of the macrofauna recovered 1s given. The faunas of Portugal form a highly distinct and homogeneous "province" with those of Armorica, Spain, Sardinia. The palaeoecology of the faunas Montagne Noire and collected during this study are discussed. Thirteen broad associations (sensu Lockley 1983) are identified. Factors other than latitude-related influences play an important role in controlling the diversity, abundance and taxonomic constitution of the palaeocommunities. Twelve biozones are erected to cover the range of fossiliferous Ordovician strata examined in this project. The correlation between the biostratigraphie scheme erected herein and the international standard is discussed. An overview attempts to place the study area within the context of the peri-Gondwana shelf, and within the Variscan fold-belt.

The Ordovician, Silurian and lower Devonian rocks of the Domes area (near Figueiro dos Vinhos), in central Portugal, form a continuous sedimentary sequence approximately 1450m thick. Folded Pre-Ordovician "Complexo xisto-grauvaquico" (CXG) is unconformably overlain by a transgressive quartzite, mudstone and greywacke succession of four Ordovician formations which are locally shelly and graptolitic. These formations are: Serra do Brejo Formation, Brejo Fundeiro Formation, Monte da Sombadeira Formation and Monte do Carvalhal Formation. The Ordovician rocks are conformably overlain by a Silurian sequence of graptolitic mudstones passing upwards into sandstones; these beds include the Vale da Ursa Formation, Foz da Serta Formation, Vale do Serräo Formation, Serra da Mendeira Formation and part of the Serra do Luacäo Formation. The Devonian rocks are represented by part of the Serra do Luagao Formation and the Dornes formation, a sandstone-madstone sequence passing up into Shelly limestones. Most of the Ordovician faunas are described and discussed including sixteen species of trilobite, five species of brachiopod and eleven ichnospecies of trace fossil. Faunal lists of material identified by specialists in the fields of Ordovician and Silurian graptolites, Ordovician echinoderms, Devonian brachiopods and Silurian microfossils are also given. The Ordovician faunas belong to the Selenopeltis province and show close links with those of Spain, France, Morocco and Bohemia. The correlation and palaeogeography of the Dornes area is discussed with emphasis on the Ordovician Period in the Ibero-Armorican area.

Llandeilo and Caradoc beyrichiocope Ostracoda are described from England and Wales. They are referred to 3 suborders (Palaeocopa, Binodicopa, Eridostraca), 8 families (Eurychilinidae. Ctenonotellidae. Tetradellidae (with 1 new subfamily); Bolliidae, Aechminidae, Circulinidae and Spinigeritidae; Eridoconchidae). 38 genera (7 new and 2 new subgenera) and 52 named species (35 new). Thirteen other forms are referred mainly to the Palaeocopa under open nomenclature, or are simply recorded. Sampling was concentrated on the sandstone/limestone sequences of Llandeilo and Caradoc age of South Wales. Superbly preserved silicified faunas were extracted using acid techniques. Casting methods extended sampling into the predominantly sandy facies of Caradoc age of the Welsh Bc.;erland, North Wales and northern England. Largely neglected,these ostracode mould faunas have provided an excellent source of material. Scanning electron microscopy has been extensively employed to illustrate the ostracodes recovered. The biostratigraphy of Llandeilo and Caradoc beyrichiocopes from England and Wales is documented. They are useful in local stratigraphic correlation and may prove helpful in defining the base of the Caradoc Series in South Wales. Their potential for inter-regional correlation is limited. British Ordovician ostracodes support other biogeographic evidence that during Llandeilo to Ashgill times, southern Britain moved closer to the Baltic and North American plates, as indicated by a breakdown in the provinciality of the British faunas.

The study reported here involved detailed mapping, logging, stratigraphical, structural, sedimentological and petrographical analyses of sequences exposed in two areas: the Rhinns of Galloway, between Killantrlngan Bay (NW 9820 5700) and Clanyard Bay (NX 1010 3800) and the strike-wise equivalent sector on the east side of Luce Bay. The upper Ordovician and lower Silurian sediments exposed within these areas represent an aggregate thickness in excess of lOkm of greywackes, conglomerates and shales displaying the typical Southern Uplands structural style of broad steeply inclined northwest-younging belts abruptly terminated by steep strike-faults. Ten of these tectonostratigraphical tracts have been recognized within the study areas. Sedimentological, petrographical and biostratigraphical data have enabled 16 stratigraphical units (formations and members) to be defined in the Rhinns tracts and 8 units in the Glenluce area. Recognition of the diachronous development of some of these units in the two areas (both along- and across-strike) provides important evidence bearing on palaeoenvironmental and geotectonic evolution of this part of the Southern Uplands. Sedimentoloqical data from these sequences confirm their exclusively deep-water nature, while lithofacies analysis permits the recognition of a variety of depositional systems, the evolutionary trends of which have been determined. Two phases of tectono-sedimentary development are recognized: (1) During the Caradoc-Ashgill interval north- and northwest-prograding clastic slope aprons and axially diverted. Immature sand-rich fans were formed on the northern flanks of a contemporaneously active volcanic terrain. Petrographical and stratigraphical data suggest that this may have been a sinistrally displaced, tectonically migrating continental margin arc, briefly juxtaposed within a fore-arc and trench region: (2) During the Llandovery the depositional systems evolved from an axial wedge, to axially diverted sand-rich fans and, eventually, to mud-rich fans. Small local debris cones were also formed. These systems were probably also deposited in a fore-arc and were derived from sources to the north and northeast which initially included remnants of the arc terrain. The evolutionary trends displayed by the early Silurian systems indicate a general increase in sediment supply and/or a decrease In convergence rate during the Llandovery.

Oolitic ironstones occur within the Lower Palaeozoic Welsh Basin as isolated deposits found over a wide geographical area. There are two phases of ironstone deposition, a minor Upper Arenig phase and a Mid-Ordovician (Upper Llanvirn to basal Caradoc) phase. Both correlate with eustatic falls of sea level which exposed the Irish Sea Landmass lying immediately to the northwest. This exposure resulted in deep chemical weathering and generation of lateritic soils. Erosion of this material formed the source for the oolitic' ironstones in the Welsh Basin. The ironstones formed above stratigraphic hiatuses on sediment starved shallow water shoals, formed by synsedimentary faulting. These shoals were the favourable sites for the formation of berthierine peloids, which formed the nuclei for ooids. Additionally, they were also the site for the accumulation of berthierine mud, which was closely linked with the development of ferruginous algal mats. Bacterial reduction of organic material associated with ironstones, supplied the necessary reducing conditions for the formation and preservation of berthierine from a kaolinite/iron oxide precursor. Ooids formed by rolling over the muddy surface and mechanically accreting berthierine. Subsequent tidal current reworking of this sediment resulted in the formation of the characteristic lithological features of the ironstones, representing a shallowing-up sequence. Progressive current winnowing led to the formation of a sequence with an upward increasing ooid content and decreasing mud content. The upper facies of the ironstones is an ooid bar deposit worked by tidal currents. Cessation of current reworking allowed faunal colonisation of the bar with significant bioturbation of the sediment, destroying primary sedimentary structures. The presence of some grain-ironstones indicate the original sedimentary state of the upper facies. Tectonic instability during deposition, by synsedimentary faulting, resulted in the formation of disturbed ironstones, and debris flows within the ironstone sequences. Many features of the ironstones are diagenetic in origin, especially the formation of phosphate nodules within the ironstone sequence. These formed just below the sediment/sea water interface, and some nodules were reworked into overlying beds. The source was phosphorus released from adsorption on clays and iron oxides, and also released from organic material. Later siderite development in the ironstones is indicated by the presence of primary cements in grain-ironstones and secondary alterations in pack-ironstones. The generation of diagenetic siderite was dependant upon the amount of organic material within the ironstones, bacterial reduction of which resulted in the formation of bicarbonate and ferrous ions. Sane ironstones were subsequently altered during the Caradoc phase of volcanic activity. The formation of magnetite and stilpnomelane within the ironstones were caused by metasanatic activity associated with dolerite sills and microgranite intrusions. Siderite alteration and base metal sulphides resulted fram late stage hydrothermal activity by some microgranites. Contact metarrorphism by granophyric intrusions led to the extensive replacement of the ironstones by pyrite. Regional metarrorphism resulted in the progressive change of berthierine to chamosite and increased lattice ordering of chamosite.

Samples collected from mid-Ibexian (mid-Tremadoc) to late Whiterockian (Llandeilo) of East and eastern North Greenland have yielded a total of 9,725 identifiable conodont clements. The conodonts are referred to 54 multi-element genera and 115 species, new taxa include three genera (Macheticodus, Wandelia and Wcbcrina) and nine species (Eucharodus apion, Macheticodus lekiskus, Multioistodus? celox, Pteracontiodus armillatus, Scalpellodus? narvhalensis, Sibiriodus? kalalekus, Wandelia fuscina, Weberina candidisphaera and Weberina guyi). The faunas are coniform-dominated and generally similar to shallow water, Midcontinent Province faunas found in North America. Some degree of endemicity is indicated by the presence of species found only in the eastern Canadian Arctic Islands and Greenland. The conodonts are referred to ten biozones, of which three zones in the Ibexian are newly named (the Loxodus bransoni, Glyptoconus quadraplicatus and Oepikodus communis Zones) as are three Ibexian sub-zones (the Acodus deltatus,?Reutterodus andinus and Protoprioniodus aranda). These are all based on the previous, informal faunal divisions established in North America. In East Greenland, the oldest faunas recovered, from the base of the Cape Weber Formation on Ella Ø, are referred to the L.bransoni Zone (mid-Ibexian). Both upper and lower boundaries are, however, diachronous and on Albert Heim Bjerge, 150km to the north, the base of the formation contains conodonts of the younger G.quadraplicatus Zone. On Ella Ø, the lbexian-Whiterockian boundary occurs within the lower part of the Narwhale Sound Formation and the youngest conodonts recovered are referable to the Histiodella altifrons Zone (early Whiterockian). The youngest Ordovician conodonts recovered from East Greenland are from the Heim Bjerge Formation, directly underlying Devonian conglomerates, on C.H.Ostenfeld Nunatak; these faunas contain taxa of the Polyplacognathus sweeti Zone (late Whiterockian). In eastern North Greenland, the Wandel Valley Formation unconformably overlies Cambrian carbonates, and conodonts recovered from the base probably belong to the O.communis Zone (late lbexian). The Ibexian-Whiterockian boundary lies at or just above the lower boundary of the Upper Member and the top of the formation contains taxa referable to the Polyplacognathus friendsvillensis Zone (late Whiterockian). Contouring of the colour alteration indices (CAl) in North Greenland indicates that the isotherms are parallel to the margin of the Hazen Trough; to the east, in Kronprins Christian Land, they swing around to become parallel to the Caledonian front. Fused clusters recovered from the Cape Weber and Heim Bjerge Formations are amongst the oldest euconodont assemblages recorded. They are principally of coniform species and suggest a grasping function analogous to that of chaetognath spines.