No description available.

No description available.

Northeastern England and the North Sea Basin is a critical location to examine the influence of glaciation in the northern Hemisphere during the Quaternary. This region was a zone of confluence between the British and Fennoscandian Ice Sheets, and harboured several dynamic ice lobes sourced from northern Scotland, the Cheviots, the Lake District and the Southern Uplands. The region thus has some of the most complex exposures of Middle to Late Pleistocene sediments in Britain, with both interglacial and glacial sediments deposited in terrestrial and marine settings, and being sourced from both the British Isles and northern continental Europe. The research undertaken involved a thorough reinvestigation of the Quaternary sediments of northeast England, making use of enhanced exposures in coastal sections following the cessation of colliery waste dumping, and in boreholes from the North Sea. It used detailed sedimentological, stratigraphical, chronostratigraphical, lithological, petrological, and geochemical techniques to investigate their depositional processes, age, provenance signatures, and regional correlatives to construct an independent model of the eastern margin of the British-Irish Ice Sheet (BUS) throughout the Quaternary, and its interaction in the North Sea Basin with the Fennoscandian Ice Sheet (PIS). This region was a zone of confluence between ice lobes sourced from northern Scotland, the Cheviots, the Lake District and the Southern Uplands, and is ideally placed for investigating the geological record of the North Sea Lobe during the Late Devensian. In addition. County Durham has one of the most northerly exposures of Middle Pleistocene sediments in Britain, including a raised beach and a Scandinavian till. This project focussed on a variety of localities in northeastern England and in the North Sea Basin, including Whitburn Bay, Shippersea Bay, Hawthorn Hive, and Warren House Gill. At Whitburn Bay, the Blackhall and Horden glacigenic members are exposed in superposition and are Late Devensian in age. The lower Blackhall Member here is interpreted as a subglacial traction till with a high percentage of locally derived erratics. A boulder pavement at the top of the till points to a switch in ice-bed conditions and the production of a melt-out lag prior to the deposition of the upper, Horden Member. This second traction till contains erratics and heavy minerals derived from crystalline bedrock sources in the Cheviot Hills and northeast Scotland, including tremolite, andalusite, kyanite and rutile. Within the Horden Member are numerous sand, clay and gravel-filled channels incised into the diamicton, which are attributed to a low energy, distributed, subglacial canal drainage system. Coupled with the hydrofractures and the boulder pavement, this suggests that a partly decoupled, fast flowing ice stream deposited the Horden Member. The eastward, on-shore direction of ice movement indicates that the ice stream was confined in the North Sea Basin, possibly by the presence of Scandinavian ice. From Hawthorn Hive to Warren House Gill, the Blackhall and Horden members are separated by the Peterlee Sands and Gravels, ice-proximal outwash sediments. Beneath the glacial sequence, some 500 m to the south is the Easington Raised Bench. The partly calcreted interglacial beach lies directly on Magnesian Limestone bedrock at 33 m O.D., and consists of beds of unconsolidated, well-bedded, imbricated, well- rounded sands and gravels. It has been dated to MIS 7 by amino acid geochronology and OSL dating. The beach contains exotic gravel, including flint, and previous workers have reported Norwegian erratics. The only currently extant source for these is the Scandinavian Drift at Warren House Gill. Warren House Gill is a classic Middle Pleistocene site, and has a complex stratigraphy, consisting of a lower "Scandinavian Drift" with overlying estuarine sediments, and an upper "Main Cheviot Drift", which comprises two tills and glaciotectonised, interstratified sands and silts, traditionally interpreted as Devensian in age. The lowest grey Scandinavian Drift is a grey, laminated clay with dropstones. It contains marine bivalve fragments, foraminifera, and clasts of northeastern Scotland and Norwegian provenance, as well as Magnesian Limestone, chalk, flint, and Triassic red marl from the North Sea. Reworked palynomorphs include Eocene dinoflagellate cysts. This is interpreted as a Middle Pleistocene glaciomarine deposit, and is renamed the 'Ash Gill Member' of the Warren House Formation, with inputs from both Scottish and Scandinavian sources. It is dated to the Middle Pleistocene by AAR dates on the shell fauna, and by the relationship to the MIS 7 age raised beach. The overlying well sorted pink and red interbedded sands and silts contain carbonate nodules and rare clasls. These shallow subaqueous sediments were deposited through suspension settling and bottom current activity, and they may be reworked loess. They are named the 'Whitesides Member' and are the highest member in the Warren House Formation. The overlying "Cheviot Drift" consists of two ice-marginal traction tills (the Blackhall and Horden members), separated by interbedded glaciofluvial red silts and sands. The till lithologies are indicative of a northern British provenance, and are rich in limestone, coal, sandstone, greywacke and dolerile. The Blackhall Member was deposited by ice during MIS 4, during a period of maximum extent of the British and Fennoscandian ice sheets and contact in the central North Sea. The Horden Member was deposited in an ice- marginal landsystem by the Late Devensian North Sea Lobe, and is correlative with the Skipsea Member in Yorkshire and the Bolders Bank Formation offshore. The Swarte Bank, Coal Pit, Fisher and Bolders Bank formations from the North Sea Basin were also examined. These subglacial and glaciomarine sediments, ranging from MIS 12 to MIS 2 in age, were all found to show a similar provenance from the Grampians, Aberdeenshire and the Scottish Highlands, indicating repeat ice-flow pathways during the Quaternary. This research has significant implications for British Quaternary stratigraphy, as it indicates that Fennoscandian ice was a significant influence on the BIIS throughout the Quaternary, and that on multiple occasions, Fennoscandian ice directly impacted the coast of eastern England. During MIS 12, a marine embayment opened in northeast England between the British and Fennoscandian ice sheets. Ice rafted material derived from both Scottish and Norwegian sources was deposited in this marine embayment. The Ash Gill Member of the Warren House Formation is an isolated remnant of this ancient glaciomarine environment, and it is separated from the overlying Devensian sediments by a substantial unconformity. During the Early Devensian, ice sourced in Scotland flowed eastwards through the Tyne Gap, where it was joined by a minor component of Lake District ice. This was a stage of maximum configuration of the BIIS, with contact with the FIS offshore. During the Last Glacial Maximum, the North Sea Lobe was constrained by the FIS offshore, forcing the North Sea Lobe onshore. This project found no evidence of Lake District erratics in County Durham, but found detrital material in the subglacial tills from the coast of northeastern Scotland.

This thesis examines the potential of NEXTMap imagery for the study of glacigenic landforms in parts of the Scottish Highlands. NEXTMap Digital Elevation Mapping (DEM) was developed in 1998 and a comprehensive set of DEMs for the British Isles generated in 2004. However, very few maps based on NEXTMap technology had been published for the British Isles before the start of this PhD, and so its full potential had not been realised. The objectives of the PhD were therefore to establish the degree to which NEXTMap imagery could improve the mapping of Quaternary landforms. To test its capabilities, NEXTMap images were obtained for the Loch Lomond area, which had previously been mapped in some detail using both field observation and aerial photography. Appropriate protocols were therefore developed for an area where NEXTMap images could be 'ground-truthed' by independent ground mapping. Methods were developed for optimizing the appearance of landforms on NEXTMap images and mapping their distributions; the results show close correspondence with the results of detailed ground mapping, suggesting that confidence can be attached to landform maps derived using NEXTMap, while the latter can also provide subtle but important new geomorpho logical information. The second part of the thesis applied the methodology developed in the Loch Lomond study to the study of landforms in and around Glen Roy, in the western Scottish Highlands. This area was chosen as it also had already been mapped in detail and proved to be critical for establishing the extent and timing of the last major glaciers in Scotland. The area also contains a unique set of well preserved ancient lake shorelines - the Parallel Roads of Glen Roy. These features extend for miles across the study area, providing an outstanding opportunity to test the spatial and vertical resolution of ii NEXTMap images, and hence to establish the limits of maps and models based upon them. This part of the project included direct tests of the vertical resolution achievable using NEXTMap, which gives surprisingly accurate data for flat and gently-inclined surfaces. The results of trend surface analysis of nearly 32,000 altitude measurements obtained from the shoreline surfaces shows that despite the fact that they are significantly deformed and dislocated, they nevertheless retain consistent along-shore surface gradients. Both the overall gradients and the localized deformation features associated with the shorelines (Ire attributed to a combination of regional and local isostatic stresses. The thesis finishes with a synthesis of the new evidence and perspectives that NEXTMap has provided for the Glen Roy area, and with a synopsis of where interpretations differ from those previously based on ground mapping.

Isochronous tephra layers provide the potential for the precise correlation of environmental records and, in the case of tephra layers of known age, for the importation of age estimates into sequences that lack independent ages, or for which the chronology is equivocal. This PhD project explored this potential for three important late Quaternary core sequences from the Mediterranean Sea: ODP975, which lies close to the Balearics in the western Mediterranean; LC21 in the Aegean Sea, close to Crete; and OPD967 in the far eastern Mediterranean, close to Cyprus. Each sequence was investigated for the presence of visible volcanic ash and cryptotephra layers. Very low amounts of volcanic glass shards were found in the ODP975 sequence, while 15 discrete tephra layers were found in core LC21 and 5 in the ODP967 sequence. These were geochemically analysed for constituent major and trace element ratios using EPMA-WDS, LA-ICP-MS and SIMS micro-analytical methods. Correlations of tephra layers were based on graphical comparison of the resulting geochemical data-sets to a developing data-base of the representative glass chemical compositions of European proximal and distal tephra deposits. The results reveal evidence for 19 separate volcanic eruptions spanning the last 166 ka, originating from Campania, Pantelleria, Santorini, Yali/Nisyros and Kos, and possibly also from Central Anatolia and Iceland. 12 of these eruptions were previously unknown and thus are here characterised for the first time. The results add to the tephrostratigraphical record ofthe eastern Mediterranean, but also demonstrate that further progress requires some crucial procedural problems to be -addressed first. Several chronologically distinct tephra layers have identical elemental abundances, which complicates their applicability as robust stratigraphic and chronological markers. In addition, proximal and distal deposits derived from the same eruption phase may have different geochemical attributes, and some evidence suggests a degree of chemical heterogeneity between different distal components of the same eruption. If confirmed, these findings have serious implications for assigning distal tephra layers to a contemporaneous proximal deposit, and hence impede the reliable transfer of age estimates obtained from proximal layers to distal tephra and environmental records. These problems notwithstanding, the discovery of 12 previously unknown tephra layers demonstrates that the tephrostratigraphical record of the eastern Mediterranean is far from complete, and highlights the need for further research of this type. In particular, rhvolitic eruptions from Santorini are here shown to be more common than were previously thought. These findings therefore have importance for augmenting the history of volcanic activity in the region, especially as a contribution to understanding magma recharge rates and eruption frequencies and their relevance for developing more robust hazard assessments. 3

No description available.

Le climat du Quaternaire est défini par une succession de périodes glaciaires et interglaciaires enregistrées dans les archives climatiques à différentes latitudes. La carotte de glace d’EPICA Dome C fournit un enregistrement haute résolution sur les derniers 800 ka du δ18Oatm (i.e. δ18O de la molécule d’oxygène de l’air) qui combine les variations passées du cycle hydrologique des basses latitudes et de la productivité de la biosphère. En l’absence du comptage des couches annuelles, ce proxy peut être utilisé comme méthode de datation orbitale des carottes de glace, en lien avec l’insolation au 21 juin à 65°N. Cependant, un décalage de 6 ka entre le δ18Oatm et l’insolation, généralement observé lors des terminaisons glaciaires-interglaciaires, est appliqué sur l’ensemble de l’enregistrement lors de la construction de l’échelle d’âge. Ce décalage et la complexité du signal du δ18Oatm expliquent l’incertitude élevée de 6 ka des carottes de glace, ce qui limite leur interprétation en termes de variations climatiques et environnementales conjointement à d’autres archives. J’ai donc développé une nouvelle chronologie pour les carottes de glace, basée sur le lien entre le δ18Oatm et le δ18Ocalcite des spéléothèmes est-asiatiques, à partir de nouvelles mesures isotopiques permettant d’avoir pour la première fois un enregistrement complet sur les derniers 800 ka à Dome C. Cette nouvelle chronologie permet de réduire les incertitudes par rapport à la chronologie actuelle et d’avoir une meilleure séquence des évènements entre les hautes et basses latitudes. J’ai ensuite développé un modèle simulant la composition isotopique de l’oxygène atmosphérique afin de répondre au manque d’interprétations quantitatives de ce proxy ainsi que pour vérifier son lien avec le δ18Ocalcite sur plusieurs cycles climatiques. Pour modéliser le δ18Oatm nous avons dû coupler le modèle climatique de complexité intermédiaire iLOVECLIM avec le modèle de végétation CARAIB. Le δ18Oatm simulé par le modèle couplé sur plusieurs dizaines de milliers d’années confirme que ses variations sont en phase avec celles de l’insolation de l’hémisphère Nord (hormis lors d’évènements de Heinrich) et avec celles du δ18Ocalcite via des modifications du cycle hydrologique des basses latitudes, impactant la composition isotopique de l’eau de pluie utilisée par la biosphère terrestre lors de la photosynthèse. / Quaternary glacial-interglacial cycles are recorded in various climatic archives from high to low latitudes. The EPICA Dome C ice core provides a high-resolution record over the last 800 ka of δ18Oatm (i.e. δ18O of atmospheric O2) which combines past variations of the low latitude water cycle and of the biosphere productivity. In absence of annual layer counting, this proxy can be used for orbital dating in association with the June 21st insolation at 65°N to build an ice core chronology. However a lag of 6 ka between the δ18Oatm and the insolation, classically observed during glacial-interglacial terminations, is applied to the entire record during the chronology construction. This lag and the complexity of the δ18Oatm signal are the main reasons why the ice core chronology presents a high 6 ka uncertainty which limits their interpretation, jointly with other paleoclimate archives, in terms of past climate and environmental variations. To solve this issue I have developed a new ice core chronology based on the relation between the δ18Oatm and the δ18Ocalcite of east-asian speleothems, using new isotope measurements allowing for the first time a complete record over the last 800 ka at Dome C. This new chronology reduces the uncertainties compared to the actual ice core chronology strongly based on δ18Oatm and shows a better sequence of events between the high and low latitudes records. Then, I have developed a model to reproduce the isotopic composition of atmospheric O2 to address the lack of quantitative interpretations of this proxy and to check our assumption of synchronicity with the δ18Ocalcite over several climatic cycles. To reproduce the variations of the δ18Oatm, it was necessary to couple the intermediate complexity climate model iLOVECLIM and the vegetation model CARAIB. Finally, the δ18Oatm variations simulated with the new coupled model over several thousand years are in phase with the insolation of the Northern hemisphere (except during Heinrich events) and with low latitudes δ18Ocalcite variations. This can be explained by changes in the low latitude water cycle related to changes in the isotopic composition of meteoric water used by the terrestrial biosphere during photosynthesis.