No description available.

Using core lithology and palaeoecological analyses, the vegetational and landscape development and local hydrological conditions since c. 6000 BP in two areas of the Somerset Levels has been studied. Focusing on the former characteristics of the river Brue, the floodplain upstream from Glastonbury and the area near Panborough Gap in Wedmore Ridge were investigated. In the latter area a distinct palaeochannel thought to be the prehistoric course of the Brue is present. Both areas show a similar development with saltmarsh and lagoonal environments until 6000 BP, followed by a prolonged period of Alnus - Salix carr and sedge fens. In the Panborough area freshwater deposition was interrupted by distal saltmarsh and lagoon sedimentation between 2900 BP and 2200 BP. This marine incursion caused stagnation of river discharge upstream which led to the growth of Cladium-rich "tloodinq layers" in the central raised bog area. After embankment of the rivers in the Middle Ages the changed hydrological conditions caused deposition of the upper floodplain clays. Until medieval embankment and canalisation determined its present day course, the river Brue did not have a fixed course but consisted of several small short-lived channels. The palaeochannel in the Panborough area is filled with sediment from the Sheppey while its course is inherited from a tidal channel that was incised between 2900 BP and 2200 BP. Blocked by the raised bog in the west the Brue water took a northerly drainage route, and it seems likely that it contributed to this palaeochannel system. The Brue sediment however was deposited as floodplain and backswamp clays in the Glastonbury area, and the long-held opinion that the palaeochannel is the 'Old river Brue' therefore cannot be maintained. Processes in the coastal region have been inferred from the local hydrological changes and these inferences have partly been verified with a simplified, two-dimensional hydrogeological model.

No description available.

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.

No description available.

No description available.

Carbon and oxygen stable isotope analyses have been performed on well preserved calcareous fossils from Callovian, Oxfordian and Kimmeridgian (Jurassic) mudrock facies of Britain. Assemblages of ammonites, bivalves and belemnites have been sampled from the Lower Oxford Clay of the English Midlands, the Kimmeridge Clay of Wiltshire and the Dorset coast, and the Staffin Shale Formation of Skye. In this way it was hoped to cover a wide stratigraphic and geographic range. Carbon isotope stratigraphy reveals a positive excursion in the Callovian, which is interpreted as an oceanic anoxic event. On the basis of palaeontological and sedimentological evidence, the Callovian has long been viewed as a time of oxygen deficiency. These views are supported by this, the first detailed isotopic study of the stage. A comparison of the 613 C values of the ammonites and infaunal bivalves reveals a major anomaly, in that the latter show very positive values. Tentative suggestions are put forward to account for this. Oxygen isotope (and hence palaeotemperature) stratigraphy reveals a cooling through the Upper Callovian and Oxfordian, consistant with the "Boreal spread" of Arkell (1956), with a warming into the Lower Kimmeridgian. Palaeotemperature variations within individual assemblages raise important questions about palaeoecology. On the basis of this data, it appears that bivalves previously considered to be nekto - or pseudoplanktonic did not occupy the upper reaches of the water column. Suggestions have been made that ammonites were benthic rather than nektonic, but the evidence presented here implies that this was not the case. Relative to the rest of the assemblage, belemnite temperatures tend to be low, highlighting their migratory nature. Boreal ammonites are found to precipitate their shells in cooler waters than those from the Tethyan Realm. The significance of this, and other factors, in terms of controls on provinciality are discussed.

No description available.

No description available.

Bibliography: p. 155-175. / Palynological analysis of organic sediments from a freshwater lake near Port Elizabeth (34°S,25°30'E) has provided a high- resolution vegetation history of the area for the last 2200 years. Detailed identification and counting of the fossil pollen resulted in the generation of a pollen diagram. Changing frequencies in fossil pollen over time are represented, and inferences are made regarding environmental conditions which influenced the vegetation. A detailed narrative of vegetation history in response to environmental change is presented, and this is compared to results from related studies. The significance of the Lake Farm study site has been noted in terms of its location as a 'zone of convergence' for a variety of vegetation types. Results of fossil pollen analysis indicate that environmental conditions prior to 1 500BP were drier than at present. Forest and fynbos vegetation were not well-represented in the pollen spectrum at this time, and it is suggested that they were not favoured by these conditions. Environmental conditions ameliorated after 1500BP, becoming more mesic, which favoured the proliferation of both forest and fynbos vegetation types. At present xeric and grassland elements are declining, while shrubs increase, indicating an enhanced human-induced disturbance regime. It is suggested that the partial decline in forest elements at present 1s most likely attributable to human-induced disturbance of the environment. The introduction of exotic trees has been noted (approx. 280BP) and is seen to have coincided with the influx of european settlers to the region. Principal Components Analysis has revealed that the vegetation distribution in the area has been most heavily influenced by human activity and moisture availability. The necessarily subjective interpretation of the statistical results, however, casts some doubt on the validity of the conclusions drawn. The validity of the conclusions drawn from this study becomes apparent not only in terms of what is learned about the history of forests, but also the form any future management should take.