Understanding the impacts of the transition from the warmth of the middle Pliocene to the large amplitude, 100 ka glacial-interglacial cycles of the late Pleistocene helps us to better interpret both the local forcings and global impacts of possible future climate changes. In this thesis, changes in ocean circulation over the last 3.5 million years (Ma) are investigated using a marine sediment core recovered from the SE Atlantic Ocean, a region often described as an ocean gateway because it includes the transfer of heat and salt from the Indian to the Atlantic Ocean between Antarctica and South Africa (the “Agulhas Leakage”). However, the response of this region to Pliocene-Pleistocene climate evolution remains unclear. This thesis analyses the climate information recorded at Ocean Drilling Program (ODP) Site 1087 (31º28’S, 15º19’E, 1374m water depth) to investigate the history of Agulhas Leakage and associated ocean circulation changes including the Antarctic Circumpolar Current to the south, and the productive Benguela upwelling system to the north. This thesis presents the results generated using several organic geochemistry proxies and foraminiferal analyses to reconstruct the climate history at ODP 1087. These include the UK37’ index (for sea surface temperatures, SSTs), the TEX86 index (for ocean temperatures and an upwelling indicator), pigment analysis (for productivity changes), foraminifera assemblages (as water mass indicators), and dinoflagellate assemblages (for SSTs and water mass indicators). During the Pliocene and early Pleistocene, ODP 1087 was dominated by the Benguela Upwelling system, which had shifted south relative to today, and three prominent cold periods punctuate the overall warmth (during the M2 and KM2 stages, and at 2.8 Ma). From 2.2 Ma a longer term cooling trend begins, and further cooling occurs at 1.6 Ma, both of which are interpreted to represent periods of intensification of the Benguela Upwelling. The start of modern Agulhas Leakage occurs at ~0.9 Ma, marked by the start of early warming at the site ahead of the terminations. Finally, from 0.6 Ma there is an intensification of Agulhas Leakage which has led to an overall warming of SSTs which span both glacial and interglacial stages. Overall, the ODP 1087 record shows that this region is more reactive to southern hemisphere and local forcings such as changes in the southern wind field and ice expansion around Antarctica, rather than to northern hemisphere forcing.

This thesis describes the stratigraphy, sedimentology and diagenesis of the Pendleside Limestone (Asbian age), a sequence of limestones, shales and dolostones in the Clitheroe area of N. W. England. Field study of 19 measured sections indicates that it was deposited in a rhythmically subsiding basin (Craven Basin) because of movements on the Mid-Craven Fault which was active in Dinantian times. The sequence is up to 190m thick and consists mostly of distal turbidite deposits which have been reworked at horizons when sediment accumulation built up to the wave base. The original depositional fabric and mineralogy of the Pendleside Limestone Group has been extensively modified by diagenetic processes including cementation, authi­genesis, dolomitization and silicification. These processes have been studied using a wide variety of laboratory techniques. The carbonate cements of the PendIeside Limestone consist predominantly of ferroan calcite and non-ferroan calcite with microdolomite incIusions. The former is probably a stable replacement of original-high-magnesian calcite. Cementation was accompanied by the formation of authigenic albite and quartz. Much of the upper part of the Pendleside Limestone has been extensively dolomitized and chertified. Several distinct zones of dolomitization are found which increase in thickness and intensity towards the top of the Pendleside Limestone Group. The dolostone horizons correspond to coarser-grained lithologies deposited during periods of shallow water sedimentation. The composition of the dolomites changes from ferroan dolomite in the lower part of the Group to non-ferroan dolomite in the upper part. The low strontium and sodium content of the dolostones in association with the other evidence suggests that the dolomitization was brought about in an open system by the mixing of marine and fresh water in phreatic lens which were established at periodic intervals. The dolomitization was closely associated with chertification although this was initiated by the dissolution of siliceous spicules which provided the necessary source of silica.

No description available.

No description available.

This thesis presents a multi-proxy reconstruction of Holocene sea-level change at the Steart Peninsula in Bridgwater Bay, Somerset. Single- and multi-proxy transfer functions were developed from diatom and foraminifera training data from two sites on the Severn Estuary coast. Constrained and partial constrained ordination estimated that 5.5% of the intertidal diatom variation and 11.4% of the intertidal foraminifera variation in the training sets was explained independently by elevation within the tidal frame. Foraminifera provided more favourable transfer function prediction statistics but were low in abundance in parts of the intertidal zone, resulting in a smaller than optimal training set. The preferred transfer function combined diatom and foraminifera data to optimise prediction statistics and intertidal coverage. An 11.22m fossil core was retrieved from the Steart Peninsula for stratigraphic and micropalaeontological analyses. Analogue matching revealed that combining the two proxies increased the number of fossil samples with good or fair modern analogues in relation to the single proxies separately. The preferred multi-proxy transfer function was applied to the fossil micropalaeontological data. The sediment stratigraphy, biostratigraphy and transfer function-based estimates indicated an overall rise in relative sea-level of about 13m between 7,582-7,345 and 1,804-1,690 cal. years before present (cal. yr BP), beginning with an initial rapid phase of sea-level rise and silty clay deposition in a minerogenic saltmarsh environment. Between 6,188-6,007 and 3,942-3,759 cal. years BP three main fluctuations in marine influence occurred, allowing organic upper saltmarsh conditions to develop periodically, but the data scatter and large vertical error bars prevent a detailed interpretation of absolute sea-level change. Diatoms and foraminifera were sparse or absent between 4,053-3,869 and 1,927-1,806 cal. years BP. Finally, foraminifera assemblages indicated a possible tidal flat environment and increase in marine influence between 1,927-1,806 and 1,682-1,619 cal. years BP. This research concludes that multi-proxy methods have the potential to improve the accuracy and precision of relative sea-level reconstruction in an extremely macrotidal setting such as that of the Severn Estuary, but that a number of issues such as sediment autocompaction and possible Holocene tidal range changes need to be quantified in order for the broad sea-level history presented to be constrained further.

Orbital forcing is a dominant climate driver on multi-millennial time scales, as it modulates the seasonal distribution of incoming solar radiation on the Earth's surface. Geological evidence of orbitally-forced cyclicity is found globally in numerous sedimentary sequences, especially in marginal basins such as the Mediterranean Sea. In the late Miocene (11.61-5.33 Ma), a large portion of the North African catchment is thought to have drained in the Mediterranean Sea, as the main fresh water input into the basin, regulated by precessional changes the North Arican summer monsoon. The distinctive sedimentary cyclicity observed in the Mediterranean Sea is thought to result from the basins biogeochemical response to oscillations in its hydrologic budget, which represents the balance between inflowing (precipitation and river input) and outflowing (evaporation) water, and exchange with other basins. Yet until now, most of the hypotheses about the phasing between orbital forcing and Mediterranean cyclic sedimentary sequences, through changes in the hydrology, are largely untested. The global late Miocene proxy record is sparse and patchy, but the majority of the data are concentrated in the Mediterranean region, which contains palaeoarchives with an exceptionally high temporal resolution. This thesis combines a unique ensemble of numerical simulations through a full precession cycle with the interpretation of geological data; with this experimental design, model results can be compared directly to the Mediterranean sedimentary record. This enables the testing and quantification of a variety of processes relative to past extreme environmental changes in this region, such as the Messinian Salinity Crisis. Seasonal changes in the North Arican monsoon and in the Mediterraneans hydrologic fluxes are explored on precessional timescales, but additional orbitally-driven moisture sources affecting the basin are also investigated. Implications for the sedimentary record are drawn globally and regionally for both the Mediterranean Sea and the Paratethys (the precursor of the Black and Caspian seas). In addition, this work emphasises the reduction in the global model-data mismatch for the late Miocene when orbital variability is included in the climate simulations.

Intertidal sediments of modern British and Irish estuaries and embayments have been analysed to investigate the degree to which such deposits are characterised by their palynomorph assemblages. Localities selected for study were: the Ythan Estuary, Aberdeenshire; the Montrose Basin, Angus; Chichester Water, Sussex; the Tresillian and Fal estuaries, Cornwall; the Shannon and Clarinbridge estuaries, Ireland; and numerous estuaries feeding into the Solway Firth. At the head of a typical estuary there is a sharp and conspicuous change in the palynomorph assemblages: brackish and marine palynomorphs are abundant throughout the tidally influenced reaches whereas, except for a few specimens probably brought in by birds or other animals, they are absent upstream of the tidal limit. In general, marine and brackish forms show few distinguishable trends in distribution between the head and mouth of the estuary, being evenly spread by tidal flushing. Dinoflagellate cysts, for example, are as abundant in the upper reaches as they are downstream. The marine/estuarine transition is poorly characterised by changes in palynomorph assemblages. Relative proportions of most of the terrestrially-derived palynomorphs increase upstream although woody fragments have a greater relative abundance in the lower reaches, possibly because they are more resistant and can remain in suspension longer than most other types of plant debris. Biogenic pyrite and invertebrate faecal material both occur more commonly in estuarine deposits than in fluvial deposits. The samples contain a mixture of marine and brackish organisms and terrestrial palynomorphs. An eider duck faecal pellet, collected from the Ythan Estuary, contained a diverse palynomorph assemblage similar to that of the intertidal mud samples. Freshwater species are rare in intertidal deposits and comprise mainly turbellarian egg cases. Almost all aquatic palynomorphs present in the samples have been recorded by other workers from marine sediments. Of those which appear to be restricted to environments of reduced salinity, most are eggs or egg cases and one of these is described for the first time (Palynomorph Y). Fluvial and lacustrine samples contain terrestrial palynomorphs, turbellarian cocoons and a small number of unidentified cyst-like structures. An incidental observation showed that, on gentle heating, dinoflagellate cysts that had undergone palynological processing dehisced and released their cell contents. This may be a physical response of the cyst to heat, by expanding and rupturing, or the cysts may be sensing a 'spring' temperature rise and attempting to hatch. The viability of the emergent protoplasm is unknown. The contents of the thesis will help to refine the use of palynomorph assemblages in the reconstruction and predictive modelling of Quarternary and perhaps older depositional environments, in particular, in distinguishing estuarine sediments from fully marine and freshwater sediments.

The Mediterranean region is important for understanding the processes of diachronous continental collision. The Hatay Graben, Turkey, is located near the Bitlis suture zone, the Misis-Andirm Lineament, the Dead Sea Fault Zone, the East Anatolian Fault Zone and the Cyprus Arc. Fieldwork focused on the Palaeogene to Quaternary geology of the Hatay Graben and lead to a new two-stage tectonic model of a foreland basin that was dissected into a transtensional graben, a result of the westward tectonic escape of Anatolia. The orientation of the graben was probably influenced by pre-existing zones of crustal weakness related to the Early Mesozoic rifting of Neotethys. Normal faults are common in all formations and areas, but strike-slip faults are mainly observed within the Plio-­Quaternary fill of the graben. Three main trends of fault strike are observed within the Hatay Graben (NW-SE, N-S, NE-SW); these appear to have been active synchronously, suggesting an overall transtensional setting. During the Miocene the basin developed in the distal (southerly) part of a foreland basin of the Tauride allochthon, represented by the Misis-Andinn Mountains to the N. Crustal loading initially triggered the development of a flexural bulge to the south and normal faulting within the foreland basin. During the Plio-Quaternary; however, a pronounced topographic, fault-controlled, graben developed. The formation of this Hatay Graben <i>senso stricto </i>is inferred to have been influenced by the westward tectonic escape of Anatolia along the East Anatolia Fault Zone and left-lateral offset along the northward extension of the Dead Sea Transform Fault. The Hatay Graben is located at the interface between a zone of continental collision in the east and a pre-collisional area to the west, a setting that played a key role in its Plio-Quaternary development.

No description available.

No description available.