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Around once every millenium, a large magnitude explosive eruption occurs on Earth dispersing volcanic ash across millions of square kilometers. Volcanic ash uniquely poses a wide-range of hazards to human health, infrastructure and the environment, the impacts of which are felt close to source to >1000's of km from the volcano. Importantly for large eruptions, the removal of the ash is almost impossible, which means the material remains and is remobilised in the environment, posing secondary hazards for 100's of years after the initial eruption. Here I present a study of the processes the produce, transport and deposit ash from large eruptions. I use the ~7.7 ka climactic eruption of Mount Mazama as a case study because the tephra was predominantly deposited on-land facilitating widespread data collection. I collate locations where the Mazama tephra has been recorded to produce a new isopach map and estimate of the total erupted volume (176 km³ bulk or 61 km³ Dense-Rock-Equivalent). The compilation of tephra thickness data also showed how the Mazama tephra deposit has been remobilised through time, exemplifying the uncertainties associated with field data. Remobilised deposits also provide insight into the types of secondary ash hazards that persist following large magnitude eruptions. I also investigate the physical and chemical properties of Mazama ash to provide insight into eruptive processes such as co-PDC plumes and distal ash transport. I determine from the composition of Fe-Ti oxides, that the distal ash can be attributed to the later stages of the climactic Mazama eruption. I also observe that the Grain Size Distribution (GSD) of the distal Mazama tephra is remarkably stable, a trend that is observed for other large distal deposits. This study also investigates the methods we use to analyse grain size in volcanology and outlines a new protocol for measuring the size and shape of volcanic ash using Dynamic Image Analysis (DIA). The benefits of DIA include the capacity for simultaneous particle size and shape characterisation, and the insight into particle density if used in parallel with sieve analysis. The new estimate of the total erupted volume and distal GSD of the Mazama were integrated with Ash3D, a numerical model of volcanic ash transport and deposition, to simulate the eruption and test the sensitivity of Ash3D to uncertainty in the eruption source parameters. The results stress the need to integrate radial spreading in the umbrella cloud region with advection-diffusion models when simulating the ash transport during large magnitude eruptions. Furthermore, it highlights significant knowledge gaps regarding the deposition of very fine-ash during any scale of eruption. This underscores the benefits of studying fine-ash deposition using the deposits from large eruptions where significant depositional areas and ash volumes facilitate extensive data collection and model testing.

Palaeoenvironmental sequences from the Mediterranean have, for many years, been a cornerstone of our understanding of ecological responses to Quaternary climate change. Lake Ioannina (NW Greece) is one such archive, with a vegetation record which spans multiple glacial-interglacial cycles. This PhD builds upon earlier work at Ioannina, seeking to characterise last glacial millennial-scale palaeoenvironmental change at the site through study of core I-08. Detailed visible and 'crypto-' tephra analysis identifies deposits associated with explosive volcanism at Italian volcanic sources, including Campi Flegrei, Pantelleria, and the Aeolian islands for the first time at Ioannina. Two visible tephra layers, the Campanian Ignimbrite (CI/Y-5; ca. 39.8 ka BP) and Pantelleria Green Tuff (PGT/Y-6; ca. 45.7 ka BP) are identified, as well as the Holocene Vallone del Gabellotto cryptotephra marker (E-1; ca. 8.3 ka BP). Evidence for repeated remobilisation and redeposition of CI/Y-5 tephra material is outlined, and the potential mechanisms and impacts of sediment reworking in lake environments are examined. Bayesian modelling, which incorporates the new tephra ages with earlier radiocarbon ages, extends the I-08 core chronology back to ca. 46 ka BP. New, centennial-scale palaeoenvironmental analysis of the I-08 core is presented, spanning the section of core ca. 46 to 38 ka BP, chronologically well-constrained by the two visible tephra deposits. The data comprise pollen, loss-on-ignition, XRF, and particle size analyses. Pollen data suggest multiple expansions and contractions of temperate woodland during this window, however these changes are not always in phase with changes in sedimentology, suggesting a complex local response to millennial-scale climatic variability associated with North Atlantic D-O cyclicity. In contrast, ca. 40 ka BP both sediment and vegetation changes occur synchronously and can be attributed to abrupt cooling and drying at the Ioannina site associated with Heinrich stadial 4. Tephra isochrons, particularly the ca. 39.8 ka BP Campanian Ignimbrite eruption, facilitate direct correlation of the I-08 palaeoenvironmental record to other high resolution last glacial pollen sequences in the Mediterranean such as Lago Grande di Monticchio (Italy) and Tenaghi Philippon (Greece) with less ambiguity than work reliant on traditional geochronological approaches.

The Swedish Timescale (STS) is a composite varve chronology that spans the last ca 14,000 years and comprises over 1,000 individual varve thickness records. It has primarily been used to reconstruct the deglaciation of the Fennoscandian Ice Sheet but has also been used to derive age estimates for Baltic Ice Lake drainage events. Several researchers have suggested that there may be up to 900 varve years missing during the Lateglacial and Holocene periods. This research presents the results of microfacies analysis and tephrochronology from three sites in Östergötland to test the existing regional varve chronology and timing of deglaciation. Comparison between macro and microscale analyses of varves indicate that the analytical precision of µXRF, X-radiograph and macroscale sedimentology do not allow for accurate characterisation of sediments. Up to 40% more varves were identified under thin section than from macroscale counts which is the traditional means of varve analysis within the STS. Microfacies analysis enabled reconstruction of local sediment processes that are fundamental for the construction of accurate varve chronologies. These results suggest that there may be fundamental flaws within the STS that stem from a lack of detailed sediment descriptions and sediment process information. The identification of tephra at all three sites demonstrates the potential to independently correlate and date varve records within the STS. Bayesian age modelling integrates the varve count data and tephra ages and has: 1) enabled more precise age estimates of the tephras; 2) anchored the varve chronologies to a calendar-year timescale; and 3) provided calendar year estimates for deglaciation. The identification of the Askja-S tephra within glacial varves at Asplången indicates that the site became ice-free around 11,044±43 cal. yrs BP which is in disagreement with the published Younger Dryas age for site deglaciation. Critically, this suggests that the Baltic Ice Lake existed during the early Holocene. The presence of proximal varves in Östergötland during the early Holocene suggests that the ice margin was in the Middle Swedish End Moraine Zone at its pre-drainage position at Mt Billingen during this time. Therefore, it is proposed that the final drainage of the Baltic Ice Lake occurred sometime after 11,044±43 cal. yrs BP. These results do not support the current timing for the final Baltic Ice Lake drainage which at present is dated to the Younger Dryas-Preboreal transition ca 11,500 cal. yrs BP. If this inference is correct, the final Baltic Ice Lake drainage may have impacted early Holocene climatic cooling events.

Across Europe, palaeoclimatic records dated to the Last Glacial-Interglacial Transition (LGIT; 16-8 cal. ka BP) provide evidence for several abrupt climatic oscillations on millennial and centennial-timescales. Understanding the spatial and temporal environmental response to these climatic events on a continental scale is important for providing insight into future climate scenarios. This relies on providing precise chronologies for palaeoenvironmental records, but issues with large dating uncertainties, and the practice of tuning/wiggle-matching different records together, has limited our ability to test for (a)synchroneity for abrupt climate transitions. In this study, the temporal and spatial complexity of LGIT climatic events, specifically, the Younger Dryas (YD) and earliest Holocene (EH) were investigated. Several of the most precisely dated pollen records were selected, spanning from northern to southern Europe. These sites were chosen using selection criteria that required independent chronologies based on radiocarbon dating and tephrochronology. To broaden the geographic range, a cryptotephra investigation was also undertaken on two palaeoenvironmental records from Romania (Lake Lia and Lake Brazi). Using Bayesian chronological modelling, each site's ages and the widespread tephra layers were remodelled. Pollen records were also re-investigated using the statistical methods of Principal Curve analysis to assist in identifying abrupt climatic transitions. The INTIMATE Integration tool was utilised to enable quantified comparisons between these terrestrial sites and the high-resolution Greenland ice core records. The results from the Romanian cryptotephra investigation highlight the importance of this region to expand tephrostratigraphic frameworks across Europe, the Mediterranean and Anatolia. The identification of ultra-distal tephra layers allowed for a broader investigation into the timing of LGIT events. This study showed that even with the most precisely dated sites and, despite the methodological approaches employed here, identifying a clear time-transgression for the YD and centennial-scale events within the EH remains difficult due to chronological uncertainties. Issues with proxy and dating resolutions currently limit the chronological approach undertaken. Nonetheless, using widespread tephra layers and statistical methods on proxy records can help to evaluate the potential asynchrony of abrupt climate transitions and the possible climatic drivers. Overall, this study highlights the need to provide robust chronologies by undertaking high-resolution radiocarbon dating and proxy reconstruction, supplemented by tephrochronology. By employing these approaches with Bayesian age modelling, the temporal and spatial response to abrupt climatic shifts can be further explored.

At about 2900km deep beneath our planet surface, there is a sharp boundary where solid rock from the Earth's mantle gives way to the molten iron-nickel alloy comprising the Earth's outer core, with temperatures over 2000ºC. Further 2200km deeper into the Earth, very high pressure turns the core into solid iron, with temperatures exceeding 5000ºC. The interaction and heat transfer between the solid and liquid cores combined with the Earth's rotation movements generates the Earth's magnetic or geomagnetic field, in a process known as the geodynamo. Direct observations through navigation records, geomagnetic observatories and satellites have taught us that the geomagnetic field constantly changes at the Earth's surface and sometimes deviates considerably from the theoretical models, in non-cyclical fluctuations called secular variations. To study the geomagnetic field in the geological past, we rely on magnetic minerals such as magnetite and haematite present in rocks at the Earth's cold crust, which have the ability to preserve the orientation (described as declination and inclination) and sometimes the strength (called palaeointensity) of the ancient geomagnetic field at the time the rock was formed. In this sense, lake and marine sediments are valuable stratified archives since they can provide high-resolution and continuous records of the Earth's magnetic field fluctuations that have occurred through time, known as palaeosecular variations (PSV). Recent numerical and computational models of the geodynamo indicate that secular variations respond to localized changes at the 2900km depth core-mantle boundary, which means that PSV records can potentially give us insight into the evolution and dynamics of the Earth's core and lower mantle through geological time and for specific regions. The present PhD project produced the first PSV record for Scotland and the UK covering the last 19,000 years from the Late Pleistocene and throughout The Holocene (Late Quaternary), using lake sediment cores from Bardowie Loch in the Central Belt of Scotland. This is also one of the few studies that describes the variations of the geomagnetic field in direction and intensity during The Holocene in the UK, making the hereby results a valuable piece in the puzzle of the geodynamo behaviour in the northern North Atlantic region, which has been particularly distinctive during the Late Holocene. PSV records of North America, Greenland, Iceland, Fennoscandia (Norway, Sweden, Finland and Russia), most recently Lake Windermere (England) and now Bardowie Loch (Scotland) are consistent with direct observations and computational models of two regions of concentrated geomagnetic flux (called flux lobes) at the core-mantle boundary beneath Canada and Siberia. The declination and palaeointensity patterns of the mentioned PSV records agree with significant oscillations in strength between both flux lobes for the last 5000 years. These are especially evident in the records from Bardowie Loch, Lake Windermere and the northern North Atlantic (Greenland and Iceland marine-cores), which suggest that the Canadian flux lobe has been weakening while the Siberian flux lobe has considerably increased in strength for the last 2000 years. The Late Pleistocene section of the Bardowie Loch PSV record shows two intervals of exceptional deviation in direction at ca 18.3ka to ca 16.2ka and ca 15ka to ca 12.8ka. The deepest interval displays rare shallow inclinations (~20º) for Scotland's latitude joined by large oscillations in the declination (a maximum of 70-degree deviation). Such substantial variations in the geomagnetic field orientation agree with the poorly known Hilina Palli Excursion, dated between 22ka and 17ka and observed globally in volcanic rocks, marine and lake cores from Hawaii and California to Lake Baikal and China. The upper interval of anomalous geomagnetic field behaviour, close to the end of The Pleistocene, exhibits the largest drop of inclination from present-day values (about 70º) to negative inclinations (-12º), while the declination presents oscillations over 50-degrees. These dramatic variations in orientation are consistent with the controversial Gothenburg Excursion (ca 12.3 to ca 13.8ka), which were originally reported in sediments from the Scandinavian Glacial Interstadial and also observed in North American glacial lakes, with poorly constrained ages from 7.6ka to 14ka. Arguments against this event are based on the large climatic changes taking place at the end of The Pleistocene, which could have affected the preservation process of the geomagnetic field in such sediments. Numerical models have indicated that excursions are caused by magnetic field reversals taking place only in the Earth's outer liquid core, unlike complete reversals where the geomagnetic field changes polarity throughout the outer and inner core. This could explain why geomagnetic reversals usually last hundreds of thousands to millions of years, while geomagnetic excursions only have from few thousand years of duration, like the events observed in the Bardowie Loch PSV record, to a maximum of ten thousand years. Bardowie Loch was selected as the study site based on its small-size basin, which is part of a glacial landscape, and limited catchment area without any sizeable river system. This ensures a low energy environment, which is necessary for the magnetic minerals to align with the Earth's magnetic field at the sediment/water interface during deposition. Our geological analyses suggest that Bardowie Loch originally formed as consequence of the movement of large glaciers, possibly at the time of the last glacial maximum about twenty thousand years ago. Then from ~19ka to ca 11.5ka, the Bardowie Loch basin was part of a Proglacial Environment, a lake fed with sediments transported by glacial melt-water. We carried out rock magnetic characterisation studies based on the magnetic properties of the glacial lake-sediments, which were supported by microscopic and geochemical analyses. The results show that there are pulses of substantial deposition into the lake basin of sediments eroded from nearby Palaeozoic volcanic rocks, rich in magnetic mineral grains. Additionally, there are layers made of very fine sediments (clay and fine silt) that present large concentrations of chemical elements associated to biological productivity in the lake-water ecosystem, joined by abundant quantities of microscopic-algae fossils (diatoms). These layers also give indications of anoxic conditions at the lake-bottom and strong evidence of magnetite produced by a remarkable type of bacteria, called magnetotactic bacteria (MTB). The results from these glacial lake-sediments analyses were correlated with published data from Greenland ice-cores. We found that the largest deposition pulses occurred when temperatures abruptly increased at the end of two distinctive periods of colder glacial conditions called Stadials, at ca 14.8Ka for Stadial 2 and ca 11.6Ka for Stadial 1 (in Bardowie Loch chronology), which implies that these high detrital input events might be the result of significant melting of glaciers close to the Bardowie Loch basin. We also found that two different warming climate events produced the fine-sediments layers containing diatoms and possible MTBs. The first was a period of mild environmental conditions in the North Atlantic region known as the Last Glacial Interstadial, between ca 14.8ka and ca 13.2ka (Bardowie chronology), and the second event was the global warming that marked the onset of The Holocene, dated between 11.7ka and 11.3ka for these layers in the Bardowie Loch sequence. A thousand percent surge in organic matter content combined with a substantial decrease of sediment input from the Palaeozoic volcanic rocks and significantly lower concentration of magnetic minerals characterised the Holocene sediments of the Bardowie Loch sequence. Results from geological, geochemical and rock magnetic studies of these layers indicate that Bardowie Loch has been through three very different stages. Between ca 11.5ka and ca 8ka Bardowie was a thermally stratified lake, denoted by laminated muds and alternation of oxic and anoxic phases, with strong indications of MTBs at the lake bottom. These observations imply first that the Bardowie basin was larger and considerable deeper at that stage than today and second, large temperature contrasts from winters to summers during this time., From ca 8ka to ca 4ka we found the largest concentrations of organic matter joined by rapid increments of elements related to biological productivity and abundant accumulation of insects remains, all of which imply significant climate warming at this time. We also found compelling evidence for basin shallowing at this stage combined with strong indications of soil formation at ~4.5ka. This shallowing could be the result of the Earth's crust rising to adjust for the deformation caused by the large ice sheet loads during the Pleistocene.

Volcanic ash (tephra) deposits from large, explosive events travel great distances and can form visible or invisible (cryptotephra) layers in sedimentary archives. These layers have unique chemical (glass) compositions which are useful for stratigraphic correlations; correlating tephra over wide regions can provide temporal constraints on varying magma chemistry, eruption style, frequency and magnitude. Eruptive behavior has been proposed as partially controlled by ice-unloading at the end of the Last Glacial Maximum, ~18 ka. This thesis aims to compile detailed eruption records from southern South America over the last 80 ka to improve event frequency datasets, facilitate stratigraphic correlations, and enable the evaluation of climatic influences, particularly ice-unloading, on explosive volcanism. The visible tephra layers of two sedimentary archives, Lago Puyehue (Chile) and Laguna Potrok Aike (Argentina) were examined. Tephra componentry (via microscopy), and geochemical characterisation of glass-shards (via WDS-EPMA major elemental analysis) were used to investigate temporal changes in the frequency and composition of tephra deposits. A reference chemistry database was developed by analysing glass-shards from proximal deposits to produce robust tephrocorrelations. These records provide evidence for numerous eruptions in southern South America over the past 80 ka. The records do not show any systematic changes in eruption composition or frequency over time, suggesting the effect of changing ice loads is limited in this context. These records often have tephra layers that appear to be primary but are actually reworked, with low glass concentrations, rounded minerals, and/or heterogenous glass compositions. This reworking is likely caused by wind, basin morphology, and tephra loading. Cryptotephra records from three Falkland Islands peat archives were also examined to better understand the dispersal of Andean volcanic deposits. Moreover, extensive age-modelling was undertaken in this thesis to refine the ages of 49 explosive Quaternary eruptions from southern South America. The eruption stratigraphies of particular volcanoes were also modelled using novel Kernel Density Estimates to better constrain temporal variation in frequency and the age-uncertainties.

Robust reconstructions of glacial retreat are required to elucidate controls on ice-sheet deglaciation and (a)synchronicity in the climate system. Such reconstructions can be derived through detailed geological investigations of glacial landforms and sediments. Patagonia, in southern South America, contains a well-preserved glacial record and occupies an important location regarding major Southern Hemisphere climate systems. However, resolving the history of ice-sheet deglaciation has proven problematic, owing to generally low-resolution geomorphological mapping, and a paucity of high-precision dating control. This thesis explores the deglacial history of the Lago General Carrera-Buenos Aires (LGC-BA) and Lago Cochrane-Pueyrredón (LC-P) ice lobes (46-48°S) of the former Patagonian Ice Sheet (PIS). The region is chosen because there are uncertainties associated with: (i) the deglacial configuration and evolution of retreating ice lobes and proglacial lake systems; and (ii) the sub-millennial timing of deglacial events. A new glacial geomorphological map is produced to reconstruct the spatio-temporal evolution of ice lobes and proglacial lakes. The elevation(s) of relict lake shorelines are examined to quantify glacio-isostatic adjustment and accurately assign former lake levels, lake outflows, and ice-margin positions, through the last deglaciation. These new reconstructions are used to target sites for high-resolution dating. A ~1000-year varve chronology is developed at LGC-BA after examining the sedimentary properties of laminated glaciolacustrine sequences. Tephrochronology anchors this record to the calendar-year timescale. The chronology indicates that PIS retreat commenced at 18,086 ± 214 cal a BP, and accelerated from 5 to 18 m yr-1 over the next ~1000 years. The new timing for deglaciation at LGC-BA allows an exploration of climate forcing mechanisms. Comparisons with palaeoclimatic records reveal a hemisphere-wide warming influence on LGC-BA deglaciation. Moreover, spectral analyses of varve thickness time-series demonstrate a likely teleconnection with tropical Pacific climate oscillations, and PIS sensitivity to short-term variations in melt-season temperature.

Understanding the abrupt climatic oscillations that characterised the Last Glacial to Interglacial Transition (LGIT, ca. 16-8 ka) requires an ability to precisely correlate the archives within which such transitions are recorded. One way in which to scrutinise the timing of abrupt events in the LGIT is tephrochronology, a technique which exploits the isochronous potential of tephra horizons derived from the geologically 'instantaneous' settlement of volcanic ash. In NW Europe, macro- and crypto-tephra layers of varying age and provenance have become increasing utilised as a means to correlate palaeoclimate records, and to test the spatial and temporal synchronicity of key climatic transitions. At present, however, tephrostratigraphies in NW Europe are limited by: 1) the number of horizons that have robust chronological constraint, and 2) our abilities to trace these tephras across multiple sites. As a result, the potential of generating continental-scale tephra lattices is greatly restricted, and a spatial disparity in the number and type of tephras has emerged. It is hypothesised that part of this disparity may relate to the resolution at which sequences are studied and the inconsistent manner in which methodologies are applied. In order to test this hypothesis, five terrestrial basins from western Scotland were examined in detail for tephra content. Four of the sites were examined contiguously at high resolutions, whilst the fifth was examined using traditional 'scan and resample' strategies. Three new tephras for the LGIT are identified, and several existing tephras previously unknown in the British Isles were also detected. The results from this tephrostratigraphic study suggest that the series of eruptive episodes impacting Northern Britain through the LGIT is richer than appreciated hitherto. Results also indicate that tephras may have been missed in previous tephrostratigraphic investigations due to: 1) incomplete stratigraphic refinement, 2) a propensity to focus on tephras of greatest concentration, and 3) a conflation of horizons. Using the high-resolution site-tephrostratigraphies, a composite tephrochronological age model was developed. The purpose of this exercise was to establish whether age models constructed exclusively from tephra horizons could provide a viable means to constrain abrupt climatic oscillations in sites which traditionally are difficult to date e.g. carbonate basins. The resulting age model achieves centennial-decadal scale precision through the early Holocene, and is used to accurately constrain the first record incidence of the 10.3 ka event in the British Isles. This study emphasises the importance of contiguous high resolution refinement, and demonstrates that this approach is essential if the true tephrostratigraphic complexity of NW Europe is to be fully understood, and if tephras are to be used successfully in constraining abrupt climatic events.

Three continuous terrestrial high-resolution palaeoenvironmental records for the Late-glacial and the Holocene have been reconstructed for different ecosystems in Fuego-Patagonia on a longitudinal transect at latitude 53°S. The records describe the nature and extent of environmental and climatic changes inferred from palynological evidence supported by lithostratigraphy, tephrochronology and radiocarbon dating. The environmental changes recorded at the three sites displays a significant degree of synchrony in response to similar large-scale climatic changes. Clear stratigraphical evidence alongside the pollen record indicates a shift to warmer interstadial conditions between c. 14,800 Cal yr BP and 14,400 Cal yrs BP. During the period coeval with ACR the vegetation was dominated by cold resistant dry land herbs such as Poaceae, Asteraceae (Suf. Asteroideae) and Acaena, by c. 13,200 Cal yr BP the vegetation changed from the dominance of cold resistant dry land herbs towards more mesic conditions and the expansion of steppe dominated by Poaceae with patches of Nothofagus forest. The establishment of the forest and an eastward shift of the forest-steppe ecotone by c. 12,500 Cal yr BP from which a gradual shift from colder to warmer conditions and the relatively stronger influences of the SSWs is inferred. The sequence of Late-glacial environmental changes places Fuego-Patagonia within the new palaeoecological data provided by this study includes “the earliest” evidence for the establishment of subantarctic Nothofagus forest during the LGIT in Fuego-Patagonia. During the Early-Holocene two major phases of Nothofagus forest expansion were registered between c. 11,700 - 10,500 Cal yr BP and c. 9,500 - 8,200 Cal yr BP. These intervals of expansion of Nothofagus forest are separated by an interval of forest contraction in response to lower effective moisture between c. 10,500 - 9,500 Cal yr BP. An intense arid phase is inferred between c. 8,250 Cal yr BP and 6,800 Cal yr BP and probably leading to an increase in the amount of dry fuel available during the mid-Holocene in Fuego-Patagonia leading to the highest fire activity promoted by very weak SSWs at this time. The later Holocene was characterised by an increase in humidity and an inferred intensification of the SSWs.

The Caucasus is a land corridor between the Black and Caspian seas, linking Africa to Northern Eurasia, and is considered a migratory route for Neanderthals and Anatomically Modern Humans (AMH). Numerous cave sites in Armenia, Azerbaijan, Georgia and southwestern Russia indicate that Neanderthals and AMH occupied the region, but poor chronological control meant that the precise timing of the occupations was unknown. This work involved identifying and geochemically characterising volcanic ash layers (tephra) in archaeological cave and open air sites spanning approximately 125 ka to 30 ka to generate a tephrostratigraphic framework. This framework was used to correlate the sites and assess the synchronicity of Neanderthal and AMH occupation across the region. Tephra investigations were also carried out on a core (M72/5-25-GC1) from the southeast Black Sea (that spans the last ~ 60 ka), with the aim of linking the archaeological sites to this palaeoenvironmental archive, to investigate the impact changes in climate had on the archaeology in the region. Eleven of the archaeological sites investigated (Gubs rock shelter and Weasel Cave in Russia; Ortvale Klde, Ortvale Cave, Sakajia and Undo Cave in Georgia; Aghitue 3, Lusakert 1, Fantan and Kagasi in Armenia; and Azokh Cave in Azerbaijan) had tephra, 30 cryptotephras and 8 visible layers, preserved. Twenty-two tephra layers were identified in the Black Sea core, with distinct periods of frequent volcanic activity separated by long periods, up to 9 ka, of seemingly volcanic quiescence in the region. The glass chemistry of the tephra found in the archaeological sites and the core, determined using a wavelength-dispersive electron microprobe, was used to characterise and correlate the units between the sedimentary sequences. Although some widespread tephra from the major Mediterranean sources (3.6 ka Minoan eruption from Santorini, Greece and the ~39 ka Campanian Ignimbrite super eruption from Campi Flegrei, Italy) were identified in the Black Sea core, none of the archaeological sites contained Mediterranean tephra. Most of the tephra layers in the archaeological sites investigated and the Black Sea core are from sources in the Caucasus and Turkey. The limited information on the volcanic history and compositional data of these sources in the region does not allow most of the units to be correlated to particular eruptions or volcanoes. However, some of the cryptotephra units have been correlated to eruptions from Nemrut, Acigöl and Erciyes Dagi volcanoes in Turkey. Unfortunately, there are no tephra layers that are common to the Black Sea core and any of the archaeological sites, prohibiting direct correlation of the sites to this detailed palaeoenvironmental record. However, the ~30 ka Nemrut Formation (NF) eruption from Nemrut volcano, Turkey, is found in the Lake Van palaeoenvironmental record and in two of the archaeological sites. This allows the archaeological sites to be correlated to each other and palaeoclimate information can also be imported into these sites. More detailed characterisation of the proximal deposits may allow more units to be correlated to eruptions and will enable these distal records to be used to further constrain the tempo of explosive volcanic activity in the region. A few compositionally distinct tephra layers were found and a suite of new radiocarbon dates were obtained at various sites, allowing archaeological occupations to be dated and the synchronicity between sites to be assessed. A distinct rhyolitic tephra correlates a layer with an Upper Palaeolithic stone technology, associated with AMH, in Azokh Cave (Azerbaijan) to a layer in Sakajia cave (Georgia) that contains Neanderthal remains. This is clear evidence that AMH and Neanderthals were in the region (within 600 km) at the same time. Other sites have also been correlated with tephra. A dacitic tephra correlates a unit with an Upper Palaeolithic lithic and bone tool techno-complex in Ortvale Klde (Georgia) to a unit with a Middle Palaeolithic lithic assemblage in Lusakert 1 (Armenia). The Middle Paleolithic tool assemblage in Lusakert 1 is clearly different from the Upper Paleolithic assemblage that is clearly associated with AMH in Ortvale Klde, but it is not clear whether the other assemblage is associated with Neanderthals, archaic modern humans or AMH. This correlation between different lithic assemblages clearly indicates that there were different groups, with different technologies, occupying the region at the same time. The NF tephra is also found shallower in the sequences at both Lusakert 1 and Ortvale Klde. This time marker shows that the Middle Paleolithic assemblage is still being used in Lusakert 1 at ~30 ka, indicating that a less diverse stone techno-complex was used for a prolonged period of time in central Armenia. There does not appear to be any direct relationship between occupation in the region and the climate at the time, implying that this had little effect on the archaeological story in the region. A new radiocarbon based age model that combines new dates with published data for the sites within the Caucasus shows temporal overlap between AMH and Neanderthals in the region. This confirms the tephra correlations and clearly indicates both species co-existed in the Caucasus. The new radiocarbon data also suggest that AMH arrived in the region earlier than previously thought, at ~50-44 ka cal BP. The arrival of AMH in the Caucasus is now temporally similar to other early AMH sites in northern Eurasia.

Tephrochronologies for three marine core sequences from the Adriatic Sea have been constructed. Two of the sequences, PRAD 1-2 and RF93-77, are located in the central Adriatic and the third, SA03-03, lies in the southern Adriatic. Isotopic and biostratigraphic records are available for all three sequences, features of which have been used as isochronous markers in the region. This project aimed to establish whether tephra layers provide (a) secure, independent isochronous tie-lines and (b) a robust methodology for testing correlations based on other methods. A total of 54 tephra layers have been identified within these sequences, of which only 8 are visible layers, the remainder being classified as cryptotephras. Geochemical characterisation of the ash layers has been undertaken using electron microprobe analysis and laser-ablation trace element methods. Geochemical correlation to the detailed tephra record from Lago Grande di Monticchio was performed using chemical element biplots and discriminant function analysis. Bayesian-based age models were generated for the three Adriatic records using available chronological information that are independent of assumptions of synchroneity between proxy marker events. These models allowed comparisons with tephra and palaeoenvironmental data from Lago Grande di Monticchio and other Mediterranean sites. The results support some assumptions of synchronous regional changes, but not others. The key outcomes are (a) the recognition of additional (non-visible) distal ash layers that enhance the potential for correlating marine and terrestrial records in the central Mediterranean; (b) volcanic ash records preserved in Lago Grande di Monticchio and in some localities proximal to volcanic sources appear to be incomplete; and (c) isotopic records in Adriatic sediment sequences reflect regional forcing factors more than local conditions.

This thesis examines the extent to which geomorphological change in sub-arctic landscapes may be driven by rapid declines in population over timescales of decades to centuries. Demographic decline driven by disease in pastoral agricultural systems is expected to alter patterns of land use. Using a chronology with 20 visible dated tephra layers from AD 870 to present, 2625 tephra layers were identified in 200 sediment profiles. Rates of sediment accumulation dated by tephra provide a record of erosion in Skaftártunga, South Iceland. The scale of enquiry is that of individual landholdings (5–10 km2) over decades to centuries; in order to tackle questions of resilience and change within coupled socio-ecological systems larger and smaller spatial scales (regions of 400 km2 and individual sediment profiles) and longer and shorter temporal scales (2.6 ka and years to decades) are also considered. The novel application of photogrammetric techniques to recording stratigraphic sections increases the frequency of measurement from tens to hundreds per stratigraphic unit and the resolution from ±2.5 mm to ±1 mm. This technique improves the accuracy of representative measures of sediment accumulation and their use in measuring landscape change. Two little known 15th century AD Grímsvötn tephras are mapped and dated to AD 1432±5 and AD 1457± 5 using sediment accumulation rates. A period of landscape stability from AD 1389–1597 is consistent with reduced grazing pressure due to population declines of more than 30% after plague in AD 1402–1404 and AD 1494. Climatic deterioration from AD 1450-1500 does not increase erosion as much as expected; this may be due to decreased grazing pressure after population decline in the 15th century. Increased erosion from AD 935–1262 is related to woodland clearance and increases in sediment accumulation post AD 1625 are related to climatic cooling during the Little Ice age and the migration of erosion fronts into deep lowland sediments.

Magnetic and geochemical properties of five late Holocene peat and loessial soil sections in SE Iceland have been studied. The aims were (i ) to establish a reliable tephrochronology for the sections, using geochemical analysis of tephra shards; (ii) to establish high resolution bulk sample records of mineral magnetic and geochemical properties; (iii) to test the ability of magnetic properties to correlate distal tephra layers; (iv) to assess the possible environmental significance of mineral magnetic time series and (v) to use records of loessial accumulation rates to assess human impact on the environment in SE Iceland. The work has been successful in establishing a reliable tephrostratigraphy for the studied sections. This was achieved using electron microprobe analyses (EMPA) of the geochemistry of tephra shards concentrated using a density separation technique. The results of detailed mineral magnetic measurements suggest that the main magnetic minerals in the tephras are probably ferrimagnetic minerals (e.g. magnetite) and canted anti ferromagnetic minerals (e.g. haematite), with abundant paramagnetic material also present. Cross plots of MrJMs vs. (Bo)c.l(Bo)c and Xfd% vs. XARM/SIRM indicate the main magnetic grain size in the tephras are pseudo-single domain (PSD) and multi domain (MD). The results indicate that the 'fingerprint' of both hysteresis and Curie temperature properties are insufficiently consistent within the tephra layers to provide an obviously sound basis for correlating tephra layers from one profile to the next. However, initial correlation of tephra layers was achieved, using all the measured magnetic parameters, by the use of the multivariate statistical measures of Similarity Coefficient (SC) and Euclidean Distance (ED). Tephra layer correlation was performed first time here using magnetic measurements. This demonstrates that magnetic techniques can potentially assist in the identification and correlation of distal tephra. Iceland offers a unique opportunity to study the role of humans in land degradation processes because of the late and well documented literature of settlements 1100 years ago. In this context, higher sedimentation rates in the upper part of two soils and one peat profile are interpreted as reflecting the effect of Landnam on deforestation and soil degradation.

This thesis investigates tephrostratigraphy associated with key paleoanthropological sites in the Middle Awash region, Afar Rift, Ethiopia. East Africa contains a rich hominid evolutionary record spanning six million years. Tephra layers and associated stratigraphic horizons of interest to this study are estimated between 3.5-1.5 Ma, with particular emphasis placed on deposits in the ~2-2.5 Ma range. Using combined field evidence, grain-specific (EMP) and bulk purified (DCP-OES and ICP-MS) tephra glass geochemistry, and statistical methodologies (similarity coefficients and cluster analysis) numerous tephra horizons have been correlated between separate localities thereby establishing relative timelines between them. Furthermore, at least three of these tephra horizons have probable correlatives in southern Ethiopia and northern Kenya. These long-distance geochemical links provide additional absolute age constraints for the tephra and associated fossil localities in the Middle Awash, and provide new evidence of widely dispersed silicic eruptions in East Africa during the ~2-2.5 Ma time period.

Despite being recognized for many years, bentonites in the Middle Permian (Guadalupian Series) type area of west Texas and southeastern New Mexico, have received little research attention. As these important deposits act as geologic timelines, they can be used as tools for long distance stratigraphic correlation and high-precision radioisotopic age dating. An important problem that these bentonites can address is the lack of temporal control for the Guadalupian. This is an important time interval for significant changes in Earth’s climate and biodiversity that include events leading up to, and potentially including, the first pulse of a double-phase mass extinction at the end of the Paleozoic. Also needed is better temporal constraint for key Guadalupian global chemostratigraphic and geomagnetic markers. In light of this, the duration of the Guadalupian stages and boundary age estimations need to be updated in order to assess cause and effect of these significant events. Refinement of the regional stratigraphic framework of units that comprise the Guadalupian type area is also necessary. Ambiguities are present regarding the shelf-to-basin relationships of units within the Capitan depositional system. Additionally, correlation of key sections of biostratigraphic and chronostratigraphic significance is needed. To address these problems, a tephrochronologic framework was established using apatite-based geochemical bentonite correlations in conjunction with high-precision zircon U-Pb radioisotopic dating.Electron microprobe analyses of apatite phenocrysts indicate that a geochemical fingerprint may be established for Guadalupian type area bentonties, allowing correlation of samples between localities. These correlations have linked several sections to the location of the GSSP for the base of the Capitanian at Nipple Hill in Guadalupe Mountains National Park. This fingerprinting has also led to a new shelf-to-basin timeline based on the interpreted correlation of a sample from the shelfal Yates Formation to the basinal Rader Limestone Member of the Bell Canyon Formation, providing biostratigraphic control for the bentonite within the Rader by extension.The calculation of new U-Pb ID-TIMS dates in the Guadalupian type area indicate the need for changes to the geologic time scale and the temporal relationships of global events. These new data suggest that current estimates of the Wordian-Capitanian boundary and probably the Roadian-Wordian boundary are too old. This extends the duration of the Wordian to c. 3 myr and decreases the duration of the Capitanian to c. 4 myr. Results here also provide age estimates for the Illawarra geomagnetic reversal (c. 266.5 Ma) and the onset of the Kamura cooling event (c. 262.5 Ma). The latter provides constraint on the proposed within Guadalupian (Capitanian) mass extinction, placing it temporally closer to the main extinction pulse at the Permo-Triassic boundary than previously understood.