The Cenozoic represents the transition from the greenhouse world of the Cretaceous to the ice house world of today. Nonetheless, it was not a steady linear trend from an ice free world to an ice house, and there were several reversals along the way. One such reversal was the Mid Miocene Climatic Optimum (MMCO, 14-17 Ma). Material from the Ocean Drilling Program Site 926 on Ceara Rise in the Equatorial Atlantic Ocean is used to examine two intervals within the MMCO from 16.4-15.9 Ma and 15.7-15.3 Ma. Stable isotopes and trace element ratios in two species of benthic foraminifera, Cibicidoides wuellerstorfi, and Oridorsalis umbonatus, and one planktonic foraminifer, Globigerinoides trilobus are used to reconstruct multiple climatological parameters at 2-4 kyr resolution. Paired Mg/Ca and δ18O measurements from the benthic species examined suggest that sea level varied by as much as 40m during the MMCO. Sea level variability was accompanied by changes in sea surface salinity, as measured using δ18O and Mg/Ca from G. trilobus, which suggests that the Intertropical Convergence Zone (ITCZ) was responding to high-latitude forcing centred upon the Northern Hemisphere. The implication is that significant Northern Hemisphere ice sheets were present during the Middle Miocene, some 13 Ma before their currently held date of inception during the Pliocene. These changes in sea level were accompanied by large changes in benthic and planktonic carbonate saturation states (Δ[CO32-]), which are inferred to be representative of changes to global alkalinity and dissolved inorganic carbon. Changes in global export productivity, as evidenced by benthic foraminiferal accumulation rates and the planktonic-benthic gradient of δ13C, are inferred to be controlling the carbon cycle and atmospheric pCO2ATM during the MMCO. The ITCZ is also inferred to be controlling primary productivity at Ceara Rise. Additionally, the relationship between multiple trace element/Ca ratios and Δ[CO32-] are examined using core-tops taken from the Norwegian Sea. The relationship between Mg/Ca and Δ[CO32-] in C. wuellerstorfi is confirmed by expanding the available holothermal data. Mg/Ca in the benthic species Pyrgo murrhina appears to respond exclusively to changes in Δ[CO32-], and the relationship of U/Ca in P. murrhina to Δ[CO32-] is the opposite of that seen in C. wuellerstorfi and O. umbonatus.

An initial review of the various theories of frost heave indicated that Miller's theory of secondary heave was the most convincing. The crucial area in this is the representation of the behaviour in the partially frozen region, known as the frozen fringe, which exists below the lowest ice lens. However, the computational difficulties of the associated mathematical model were likely to limit its application. A simpler quasi-static approach for a semi-infinite region had therefore been initiated, for a restricted range of conditions, by Holden. The work described in this thesis traces the development of the quasi-static approach and its application to the unidirectional freezing of a finite soil column. The resulting generalised model successfully predicts the freezing behaviour under a wide range of conditions. In particular, it is applicable to all overburden pressures, including zero. At low overburdens the frozen fringe disappears, but the final phase is nevertheless modelled to its ultimate equilibrium state. The predictions of the model agree with published experimental data from a number of investigators, and thus support the validity of Miller's theory. Parametric studies with the model have highlighted the importance of the hydraulic conductivity and the relationship between suction, temperature and ice content in the frozen fringe. Simulations are relatively insensitive to variations in thermal conductivity. The model has proved to be robust and stable and should form a sound basis for further studies. However, its full application will depend on the development of experimental techniques to determine the hydraulic conductivity in the frozen fringe.

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Ice streams are the dominant drainage pathways of contemporary ice sheets and their location and behaviour are viewed as key controls on ice sheet stability. Identifying palaeo-ice streams is of paramount importance if we are to produce accurate reconstructions of former ice sheets and examine their critical role in the oceanclimate system. Many workers have invoked palaeo-ice streams from a variety of former ice sheets, despite a limited understanding of their glacial geomorphology. This thesis addresses the problem by predicting several diagnostic geomorphological criteria indicative of ice stream activity. These are developed objectively from the known characteristics of contemporary ice streams and can be summarised as: large flow-set dimensions (>20 km wide and >150 km long), highly convergent flow patterns, highly attenuated subglacial bedforms (length:width >10: 1), Boothia-type dispersal plumes, abrupt lateral margins «2 km), ice stream marginal moraines, evidence of pervasively deformed till, and submarine sediment accumulations (marine-terminating ice streams only). Collectively, the criteria are used to construct conceptual landsystems of palaeo-ice stream tracks. Using satellite imagery and aerial photography to map glacial geomorphology, identification of the criteria is used to validate the location of a previously hypothesised ice stream and identify a hitherto undetected palaeo-ice stream from the former Laurentide Ice Sheet. Implications for ice stream basal processes are explored and their ice sheet-wide significance is assessed. On Victoria Island (Arctic Canada) five of the geomorphological criteria are identified and the extent of the marine-based M'Clintock Channel Ice Stream is reconstructed at 720 km in length and 140 km in width. The ice stream (operating between 10,400 and 10,000 yr BP) was located within a broad topographic trough, but internal glaciological processes, rather than properties of the bed controlled the margin locations. It eroded into pre-existing unconsolidated sediments and left a spectacular pattern of subglacially-produced landforms, recording a snapshot view of the bed prior to ice stream shut-down. Sediment availability appears critical to its functioning (deformable bed?) and the debris flux of the ice stream is inferred to have been high. Frictional shut-down occurred once down-cutting through sediments reached hard bedrock close to the terminus. The presence of four of the geomorphological criteria are used to identify a terrestrial ice stream which drained the Keewatin Sector of the Laurentide Ice Sheet between ca. 10,000 and 8,500 yr BP. Its size is reconstructed at over 450 km in length and 140 km in width, and it left behind a subglacial bedform pattern consisting of highly attenuated drumlins (length:width ratios up to 48: 1) displaying exceptional parallel conformity. This represents an isochronous bedform pattern and variations in lineament elongation ratio are thought to be a useful proxy for ice velocity. Highest elongation ratios occur immediately downstream of a topographic step where the ice stream entered a sedimentary basin. It is inferred that the ice stream was triggered by climatic warming which altered the ice sheet configuration and the thermal state of the bed. A switch from cold to warm-based conditions probably triggered rapid basal sliding. The ice stream (and a tributary) shut down when it ran out of ice, causing widespread thinning of the ice sheet and subsequent deglaciation. These ice streams denote considerable ice sheet instability over both hard and soft (deformable) beds and emphasise the enormous effects that ice streams had in controlling the deglaciation of the Laurentide Ice Sheet.

No description available.

Palaeoglacier margins from the Zanskar Range of the north-western Indian Himalaya are reconstructed through geomorphological mapping and sedimentology. These are dated ilsing Optically Stimulated Luminescence (OSL) techniques on quartz extracted from related fluvioglacial and lacustrine deposits. A glaciated palaeosurface with broad, gentle slopes >280m above river level and high grade metamorphic erratics represents the oldest and most extensive glaciation, the Chandra Stage. This formed an ice-cap with its ice-shed to the south over the High Himalaya. A change from broad glacial troughs to narrow V -shaped gorges along with large subdued moraine ridges and drift/erratic limits defines an extensive valley glaciation, the Batal Stage, with its maximum close to -78.0±12.3ka BP (Oxygen Isotope Stage (OIS) 4). Distinct sets of moraine ridges represent a less extensive glaciation, the Kulti Stage, which is dated to shortly after the global Last Glacial Maximum (OIS 2) and a minor advance, the Sonapani, is represented by sharp crested moraine ridges < 2km from current ice bodies. The change in glacier extent and style from the Chandra Stage to the later glaciations may be related to uplift of more southerly ranges blocking monsoon precipitation and incision of the landscape such that ice reached lower altitudes over shorter horizontal distances. Batal and Kulti Stage Glacier Elevation Indexes (GEls) calculated for this and adjacent areas increase from south-west to the north-east, but decrease again towards the Indus valley, reflecting attenuation of the south-westerly monsoon and possible channelling of westerly depressions along the broad upper Indus valley. GEl values were depressed by ~500m during the Batal Stage and -300m during the Kulti Stage. Six new OSL age estimates from the Zanskar Range greatly improve the glacial chronology of the north-west Himalaya and reinforce the emerging asynchrony between this region and the Central and Eastern Himalaya, which experienced its maximum glaciation during OIS 2 rather than OIS 4. Improved glacier mass balance data, palaeoclimatic proxy data for the summer monsoon and particularly the winter westerlies, and numerical age estimates from Himalayan glaciers are required to explain this asynchronous maximum.

"Since the publication of the work of Jehu and Charlesworth the distribution and significance of the glacial deposits of the Irish Sea have remained in a somewhat confused condition." So said Professor W.D. Evans in 1964. This thesis represents an attempt to remove the confusion from one small corner of the Irish Sea basin; it is concentrated largely in North Pembrokeshire, and aims to resolve some of the stratigraphic and chronological problems concerned with the Pleistocene deposits of the region. There is a long history of research into the glaciation of North Pembrokeshire. Most of the early work was undertaken in Dewisland (the St. David's Peninsula), but in the major contributions of Jehu (1904) ond Charlesworth (1929) something was revealed of the Pleistocene history of North Pembrokeshire as a whole. Subsequent work has been greatly influenced by these two authors, and there has been no detailed field study of the area since Charlesworth. As a result, many controversies have arisen in recent years; these range from the purely stratigraphic problems of the classic tripartite drift succession and the nature of the Upper Boulder-clay to the absolute age of the Pembrokeshire drifts. Again, there is doubt concerning the number of glaciations represented in North Pembrokeshire; about the existence of the South Wales End-moraine, the pro-glacial lakes, and the so-called overflow channels of Charlesworth; and about the age and origins of the coastal features of the county. These are among the problems that this thesis attempts to answer.