An integrated biostratigraphical scheme consisting of 6 biozones, based on the distribution of microfossil groups (acritarch, algal, conodont and ostracod), is proposed for the Leintwardine Group of the type area and coeval sections in the Welsh Basin. 20 species of prasinophycean algae (2 new species and 12 in open nomenclature), 114 acritarch species (2 new genera, 8 new species, 52 in open nomenclature and 1 new combination), 12 ostracod species (6 in open nomenclature), 10 conodont species (3 in open nomenclature), 6 spore species (5 in open nomenclature) and 8 chitinozoan species (4 in open nomenclature) are described from the Welsh Basin. New genera are: Maceriasphaera and Flammulasphaera. New named species are: Cymatiosphaera intricata, Cymatiosphaera pumila, Cymbosphaeridium molyneuxii, Eisenackidium parvum, Flammulasphaera bella, Lophosphaeridium hillii, Maceriasphaera pustula, Percultisphaera iticompta, Salopidium aldridgei and Umbellasphaeridium richardsii. Graphic correlation reveals that an hiatus at Sunnyhill Quarry corresponds to the major lithological change at the base of the Leintvvardine Group at Aymestrey. A stratigraphic break has also been recognised within the Leintwardine Group on the Whitcliffe. Palaeoenvironmental and palaeoecological investigation of acritarchs and algae show, that different morphological groups occupied separate habitats. Palynomorphs were also recovered from the Sauvere, Himmiste and Uduvere beds (Paadla Stage, Ludlow Series) and the Tahula Beds (Pridoli Series) of Saaremaa Island, Estonia. 14 species of prasinophycean algae (2 new and 6 in open nomenclature), 79 acritarch species (4 new, 40 in open nomenclature and 2 new combinations), 6 spore species (5 in open nomenclature) and 12 chitinozoan species (6 in open nomenclature and 3 new described in open nomenclature) have been recognised. New named species are: Cymatiosphaera caperata, Dictyotidium contortwn, Helosphaeridium siveterii, Lophosphaeridium peatii, Salopidium balticum and Vermiculatisphaera hispida. Acritarchs suggest that the Tahula Beds correlate with the Ludfordian Stage in Great Britain and are older than previously described.

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.

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.

The main taxonomical part is devoted to a study of the Family Cytherettidae, with the description of 49 species and subspecies belonging to the genus Cytheretta and 8 to the genus Flexus. Of these, 26 and 4 respectively are new. The type species, C. rubra Muller, is redescribed, together with l8 species and subspecies from the highest Middle Eocene and Upper Eocene of N.W. Europe, l6 from the Oligocene, and 13 from the Oligocene of Aquitaine. 38 species and subspecies are described from the Sannoisian of the Anglo-Paris Basin, including two new genera Vecticypris and Hammatocythere, one new subgenus Limnocythere (Cladarocythere), and 12 new species. The base of the Upper Eocene is defined as the base of the Bartonian, which coincides with the N. prestwichianus Band of the Hampshire Basin. The Barton Clay is correlated with the Marnes a P. ludensis in the Paris Basin, so that the underlying Sables moyens are referred to the Middle Eocene. The base of the Oligocene is taken as the base of the Rupelian; the lower part of this is the Sannoisian sub-stage. The Lattorfian is older and is placed in the Upper Eocene, while the Tongrian is in part equivalent to the Lattorfian and in part to the Sannoisian; this leads to the rejection of its use as a stage name. The term Lattorfian as used in the Tethyan province is considered to be equivalent to the Sannoisian and not the type Lattorfian, and is therefore Lower Oligocene.

The development of fluid inclusion geothermometry is described from its nineteenth century beginnings down to the present time. A method for the preparation of samples for fluid inclusion work and the experimental technique using the Leitz 1350 heating stage are described. The problems involved in obtaining representative geothermometric data are outlined. When a sample consists of well-formed crystals it is relatively easy to determine the thermal history of the sample but not so with massive material. A preliminary investigation was undertaken to assess the variation of data obtained from different sections cut from the one sample and on arbitrary grounds a minimum number of sections and of temperature measurements is suggested so that approximately representative data may be obtained. An investigation of the relationship between filling temperatures of fluid inclusions and the thickness of the enclosing section is described. It was found that on reducing the thickness of a section, the filling temperatures of inclusions decreased. Statistical tests showed the decrease in filling temperatures to be significant and it is suggested that the rate of heating adopted by the writer is too fast to allow equilibrium between the inclusion and the heating stage to be achieved and that the observed filling temperatures are somewhat higher than the actual filling temperatures. A preliminary investigation into the problems of leakage in fluid inclusions is described. Experiments showed that moderate overheating above the filling temperature of an inclusion did not cause leakage but that heating to 100°C. above the filling temperature usually induced leakage. A theory that over-heating may cause fluid to migrate into inter-atomic spaces and that, on cooling, this fluid may move back into the inclusion cavity was not proved. All the recent published works on British geothermometry are reviewed and the published data are compiled as an appendix.

Quantitative analysis of modern submarine channels has permitted a more rigorous classification than has hitherto existed. Channel sinuosity varies with slope gradient, reaching a maximum sinuosity at an optimum gradient. Modern submarine channels may be classified by maximum sinuosity and slope gradient giving high-sinuosity, low-gradient, to low-sinuosity, high-gradient channels. This study highlights similarities between the geometry of submarine meanders and those of large terrestrial rivers. An architectural element analysis scheme is presented in this thesis to enable qualitative comparisons between modern and ancient channels. For submarine channels, using this architectural element scheme, two end-member models are proposed for modern and ancient systems. This thesis examines the classic channel-complex deposits of the Eocene Hecho Group, south-central Pyrenees, Spain, to emphasise the range of channel architectural styles found in a foreland basin. Seven distinct channel types are recognised in this basin, generally representing different levels of erosional and depositional architecture and facies. A variety of modern and ancient submarine channel elements have been studied to show that channel architecture is strongly controlled by the type of channelised flow process. Synthesising data from modern and ancient channels provides some predictions about preferential sites of sand accumulation within channel-levee complexes, e.g., at channel bends associated with flow stripping; channel confluences; point bar deposits; channel benches and terraces; channel thalwegs; and other hitrachannel hydraulic jump sites, such as cross channel growth faults.

The characterisation of formation heterogeneities requires a multidisciplinary study of data acquired using a large number of numerical geophysical and geological measurements and a rigorous evaluation of the precision and accuracy of the data. Another essential aspect of the appraisal of any measurement is the quality assessment and quality control of the data. In this work multivariate statistical techniques and an Artificial Neural Network (ANN) are used provide lithofacies characterisation and to identify heterogeneities in complex formations as well as to evaluate the boundaries they generate. The precision and accuracy of the data from different sources are very important and are considered here by using sample support in the integration of measurements at different scales. We use examples from two holes of the Ocean Drilling Program and two oilfield holes to show the differences in characterisation obtained with each technique. Multivariate Statistical Analysis are initially used to group the petrophysical, geophysical and geological parameters extracted from the downhole measurements into distinct geologically definable zones. This technique has the advantage of being quasi-independent of any pre-determined ideas we have about the whole dataset, and has proved very reliable in formation characterisation. Thus the result obtained here is used as a basis for comparison with that obtained from the Neural Network. Artificial Neural Network is used to characterise the different lithology sequences present in each well. Neural Networks are relatively new tools and have proved very useful in applications where conventional computing methods are inadequate. Another application is the possibility of determining quantitative petrophysical parameters from well logs and core data in uncored intervals. The results are presented as a comparison between the two techniques. We show that both methods are very encouraging. When comparing the ANN derived petrophysical parameter logs with actual core measurements and other petrophysical parameters prediction techniques we see a good match. Low quality petrophysical measurements can be determined by a mismatch between the responses.

No description available.

Geophysical measurements were made, which map the 3-dimensional variation in seismic velocity and density of the sediments of the Barbados Ridge Complex, and indioate their state of compaction. Profiles of velocity with depth were obtained from ESP and sonobuoy data, by a number of methods, and lateral density changes within the complex were inferred from gravity modelling. Comparison of velocity results with reflection profiles provided evidence for north-south changes in arc crustal structure, and a well defined uppermost velocity layer in the complex was identified with recent slope sediment. The pattern of physical properties indicates a division between undercompacted sediment at the toe of the complex, and a more oompacted region arcward, and variations in the arcward gradient of compaction were suggested to reflect episodic growth of the complex. Comparison of velocity profiles with reference data was used to infer the compaction state of the forearc sediments, and undercompacted material in the deeper coaplex was identified with the underplating of subdue ted material. Compaction modelling was used to examine the development of pore pressures at the toe of the complex, and in the incoming sediments. Very high pore pressures in the underthrust sequence were shown to be likely, with contrastingly lower pressures in the accreted sediments. Published physical property data from other accretionary margins were also considered.

The Fold and Nappe Province of the Cantabrian Zone, NW Spain displays a prolonged and complex geological history, initiated in the late Neoproterzoic by the Cadomian compression and followed by Cambro-Ordovician, Silurio-Devonian and Carboniferous phases of extensional and strike-slip basin formation as well as Variscan compression in the Carboniferous and Alpine compression in the Palaeogene. Within this thesis, quantified structural, sedimentological and stratigraphic analyses were utilised to produce basin models for the Palaeozoic Era when this region was north of the West African sector of Gondwana in the peri-Gondwana realm. The tectonostratigraphic framework and basin fill lithofacies provide the context for a detailed megasequence interpretation, burial history and thermal maturity models, Correlation and structural panels suggest sedimentation took place on a continental rifted margin, Sedimentation is greater in the hanging-wall side of high-angle, dip-slip, normal faults indicating syn-sedimentalY evolution. Stratigraphic thickening occurs in the mid-late Cambrian to early Ordovician Period, in the north-east of the region to the north of the peri-Gondwana realm and is attributed to the initiation phases of the Rheic Ocean. Stratigraphic thickening is also observed in the Silurian (upper Llandovery) to early Devonian (Lochkovian), in the south-east of the region, parallel to the northern Gondwana margin and is attributed to rifting and the opening of the Palaeotethys Ocean. Furthermore, syn-sedimentary faults are observed within the upper Formigoso and Furada/San Pedro Formations that are late Silurian to early Devonian in age. Back-stripped fault analysis indicates that east-west and northeast-southwest trending extensional faults were active during this time. Maximum Palacozoic tectonic subsidence values range from 1,750 m to 3,485 m and indicate phases of rapid subsidence in the mid-late Cambrian to early Ordovician, late Silurian to early-middle Devonian and in the late Carboniferous Periods, Carboniferous subsidence relates to the formation of the foreland basin ahead of the Variscan thrust belt. Pseudo-wells across the Fold and Nappe province display a similar burial history signature albeit varying due to its proximity to the Cantabrian high where lower subsidence rates are observed in the lower-middle Palacozoic Era. Thermal maturity models, constrained by radiometrically dated diagenetic muscovite mica of the Tanes Member of the Barrios Formation, indicate El mean burial and diagenetic age for the Cantabrian region at 384.4 Ma (Givetian Age). Calculated vitrinite %Ro values for the Formigoso Formation source-rock, broadly equivalent to the Tannezuft Formation source-rock in North Africa, indicate maturity for oil and gas in the Fold and Nappe Province from ~389 - 299 Ma. The Southern Versant Nappes of the Montagne Noire, Southern France and the Foreland and External Nappe Zones, Southern Sardinia display a similar Palaeozoic tectonostratigraphic history to the Cantabrian Zone, due to the proximity of the these terranes in the peri-Gondwana realm.