The development of U-Pb dating techniques for speleothem deposits has enabled the scientific community to exceed the upper limit of the U-Th chronometer (-600 ka), creating new opportunities for innovative research into palaeoenvironmental change over 106-107 year timescales. However, despite the great potential of the technique, its application in research has been limited, with just 21 papers published over the last 17 years. This paucity of research can be attributed to the technical challenges associated with measuring small quantities of radiogenic Pb and limited UlPb ratio spread measurable by low-spatial resolution techniques such as 10-TIMS and MC-ICPMS. In this thesis I investigate the use of in-situ U/Pb ratio analysis by LA MC-ICPMS, to take advantage of the increased spatial resolution compared to conventional low-spatial resolution techniques in order to better resolve UlPb ratio heterogeneity in speleothem calcite. To test the feasibility, accuracy and precision of U-Pb speleothem dating by LA MC-ICPMS, four speleothem samples, previously dated by low-spatial resolution U-Pb methods, were reanalysed using a 193 nm ArF excimer laser ablation system, coupled to a Nu Plasma HR MCICPMS. Following the initial feasibility study, rates of Quatemary landscape evolution were investigated at two field sites: the Ogof Draenen cave system, Brecon Beacons National Park, South Wales, UK; and the Mulu caves of the Gunung Mulu National Park, Malaysian Borneo. In the feasibility study (Chapter 3), U-Pb dating by LA MC-ICPMS of samples of known age, ranging from -0.25-2.50 Ma, were shown to be concordant with conventional low-spatial resolution U-Pb dating results, yielding typical age uncertainties of 5-6% per isochron. Using age-depth modelling techniques, age uncertainties of as little as 2-3% were achieved. Under normal conditions, U/Pb ratio data for a 40-point isochron could obtained in -1 hour by LA MC-ICPMS, with sample consumption rates of as little as -0.026 mg of calcite per isochron. U-Pb dating of speleothem samples from Ogof Draenen (Chapter 4) was used to quantify past rates of fluvial incision in the Usk Valley during the Quaternary, yielding maximum incision rates of between 0.194-0.231 m ka-1 over the last -1250 ka. Scarp retreat rates along western flank of the Usk Valley for the same period were highly variable and localised, with rates of as little as 0.06 m ka-1 at Cwm y Nant up to 0.542 m ka-1 at Cwm Llanwenarth. U-Pb dating of speleothems from the Mulu caves (Chapter 5) presented a greater challenge, with many samples displaying anomalous UlPb ratios, indicating the presence of unsupported common Pb. Despite this, U-Pb dating of flowstone WR-09-18-03 by LA MC-ICPMS yielded a basal age of 1181.3 +278.0/-256.1 ka, equating to a mean incision rate of 0.216 +0.060/-0.41 m ka-1. This result shows a good level of agreement with the mean rate of 0.190 +0.030/-0.040g m ka-1 obtained by Farrant et al. (1995) for palaeomagnetic sediment dating. In summary, U-Pb dating of speleothems by LA MC-ICPMS offers several key advantages over conventional low-spatial techniques, including a significant increase in measurable U/Pb ratio spread for individual isochrons and a major reduction in sample preparation and analysis time, as well as sample consumption rates. Ultimately, this technique represents a new and valuable alternative to conventional low-spatial resolution U-Pb dating methods.

This thesis examines the artificial islets of the Inner Hebrides with emphasis given to a detailed case study of the islands of Mull, Coll, Tiree, and Islay. Initially, a literature survey is undertaken to establish the number of sites observed in the past and the features that were noted on them. Field and underwater inspection of the lochs on the islands included a detailed, measured survey of each of the artificial islets, including those not recorded in the early references. The visible, structural features of the artificial islets of the central Inner Hebrides are then analysed and their recurrent characteristics examined. This exercise shows that progress in the study of artificial islets can be made by applying simple analytical techniques to a sizeable number of artificial islets confined to a specific geographic region. In this case the characteristics of the data examined provide evidence which runs counter to current, widely-held theories concerning the nature, form and utility of artificial islets. Therefore alternative conclusions are proffered. Another aim of the thesis is to analyze the location and spatial positioning of these artificial islet sites. Techniques are developed to propose how site positioning was employed by the early inhabitants in relation to potential farming and maritime resources. The final part of this study compares these artificial islets with other crannog/artificial islet sites elsewhere in Scotland. Particular effort is made to see whether there is any discernible difference between Inner Hebridean sites and those on the mainland and in the Outer Hebrides respectively, but conclusions are limited because of the restricted data available.

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Fracture permeability in some reservoirs may be stress sensitive; which can affect fluid flow during production and should be taken into account in reservoir management. However, the petroleum industry rarely incorporates the impact of stress sensitive fracture permeability into production simulation models. This study investigates the potential impact of stress sensitive fracture permeability in the Clair Field using a unique approach that integrates data and workflows from geology, petrophysics, geophysics, geomechanics and numerical simulation. This is first tested on a synthetic block model and is later implemented on the Clair Field reservoir model to confirm the impact of changes in fracture permeability during production on productivity index (PI). This is one of the first studies where the stress path parameters are mechanically justified to determine the appropriate simulation method to be used. Despite offering extensive reservoir and production data for this study, the Clair Field is an incredibly complex and heterogeneous reservoir. The 27 year appraisal period alone demonstrates the high level of complexity, particularly in terms of its fracture system, much of which remains to be understood. In this respect, this study is particularly ambitious. Analogue outcrops have been studied, increasing the understanding of the controls on fracture distribution in the Clair Field. Fracture spacing Is shown to have no impact on the stress sensitive permeability, whereas fracture apertures, which are difficult to obtain, may have a significant impact. Evaluation of fracture representation in synthetic block models reveal explicit and implicit models may produce very different simulated results, particularly when describing large scale stress sensitive fracture zones that connect wells. This demonstrates the danger of poor representation of the fracture system in the simulation model. Despite increased computational expense, more accurate fracture descriptions are likely to generate more precise simulation outcomes. A significant impact on PI was observed in the synthetic block models, while little variation was observed in the Clair full field model because during production the reservoir experiences very little pressure drawdown. Non-unique and highly heterogeneous full field simulation outputs, however, are difficult to interpret. Furthermore, owing to the poor understanding of relative permeability and insufficient knowledge regarding the fracture distribution render the results of this study largely inconclusive. While PI may be used to demonstrate stress sensitivity, time-dependent or pressure-dependent changes in PI may also be accredited to other factors. These should be ruled out or confirmed to obtain a more realistic expectation of what drives the PI changes during production. Therefore, an appropriate decision of whether to incorporate stress sensitive permeability to the simulation can be made. Although much attention has been given to the case study in this work, the same methodology and recommendations are applicable to other fractured reservoirs. It is both difficult and impractical to design a general study whereby findings can be used to make generalizations for all reservoirs due to the natural variability of oil and gas reservoirs worldwide. Synthetic block models demonstrate that homogeneous and small scale simulations cannot necessarily be used to make inferences to the behaviour of full field heterogeneous reservoir models. However, with appropriate fracture parameter input, both these simulation and pre-simulation studies of how stress changes are likely to impact the permeability can provide good approximations of the likely reservoir stress sensitivity. This highlights the importance of real data in this study.

The present account is based on the geological survey, of 110 oquare miles of dissected, upland country developed in the, p2, E, H, and RI faunal divisions of the Carboniferous system and located in the S. E. of the Aekrigg Block in the Pennine Chain of Yorkshire (refer to Plate 2). The succession embraces approximately 1750' of strata both of Yoredale (limestone, shale, sandstone) -and 'of Millstone Grit facies (sandstones and shales). The sediments of Yoredale facies comprise eight rhythmic units, or cyclothems, five of which are of lower Carboniferous age. All remaining beds are of upper Carboniferous age. They ý include the three highest Yoredale cyclothems and rocks of Millstone Grit faciese The S,im onstone cyclothem varies greatly. in thickness'from north to south, this beine due to n, thinning of the shäles and sandstones. The-- Middle, cyclothem. is characterised by great local thickening of the Middle Limestone. This latter-horizon shows a tripartite division throughout the -area, with a central part carrying abundant Gia ntorroductus. A'less persistent band with, 0rionastraea, occurs at several localities near the base of the limestone. The-measures above the. Middle Limestone are everywhere thin and in the south of the area yield an extensive normal shale fauna, but are replaced by sandstones in the north which may however belong to -the Five-Yard or possibly the Three Yard cyclothem. Owing to the absence of the Five Yard Limestone in the north of the area no full proof, of the age of, these latter beds is forthcoming.The Five' Yard L1mest"one is restricted to the döü. th° of the area. Its lower Leaf is characteri'sed' by a Lithostrot ion- Gipontopi ductus fauna in upper Coverdole and upper ialdendale. The 3h231es above the 1imestorie are 'cönfined to the söütli of the area and carry a large fauna which includes several new species and s 'new genus of ostracod. ' Sudýeticerns ordinetüm, Moore, a P2 goniatite, is also recorded. The Three Yard Limestone consists of two leaves, an upper persistent leaf and a lower impersistent one. The measures above the Three Yard Limestone are chiefly : andstönes in they north of the area, but shales dominate in the extreme south. Revised correlations of the beds at thekThree Yard-Five Yard Limestone level are put forward for the - outcrops of these beds in upper Coverdale 'and Nidderdale on the bäs'is of the- present work, 'using -the findings of Moore (1955) as essential evidence. The Underset Lim°stoneý-varies considerably ' in' thickness and carries within it a coral bed in' the extreme P1. W. of the area. Local 1d1e velopments of chert above`nnd below the limestone and of calcareous shales bel6%v the main leaf of the limestone are detailed. The sediments above the limestone are everywhere thick, except in the N. E. "of the area, where they thin abruptly. ' ? Cravenoceras sp. has been recorded about 25' above the top of the Ünderset Limestone, providing confirmatory evidence for placing the baue of the Pendleicn eboüt 10` Above the top of `this limestone. The Main Limestone varies jqr`eatly in`thickness, possibly owing to overstep at the base of the Little Limestone which is overlain by the Richmond Chert Series. These latter beds are extremely, thick in the'N. of the area. Axtreassossment of the chert problem is presented in the light of the field evidence from the present-ground. A cane is put for local chertification below the plane-of the intra--Eli unconformity in upper Nidderdale. The -Crow cyclothem- is, recognised in the north of the present area. ' It is overlapped by-the sub-Grassington Grit (intra-E1) unconformity, which transgresses southwards across the sediments of 'the upper four cyclothems , in the ý area. A synopsis of present knowledge relating to the. antra-Ei unconformity, is given and the natureiof the overstep in the present area is elucidated by means of-a map and sections. The, Grassington Grit Group is shown to°alter laterally into a serien- of shales with impersistent sandstones ` in,,, the north of the: area. Cravenoceras cowlinaense is first recorded"inloitu from the area and is described from several localities together with a-large supporting-fauna. A widespread distribution of the Cockhill Marine Band is demonstrated and C. cowlin aense is recorded from--the extreme north of the area. By means of these occurrences a'nörthwards thinning of the Grassington Grits and shales is "shown to occur, a process of thinning which is-shown to be continued farther to the N. W. in the 'work of Scanlon-}(1955). 0 Sediments of lovier Arnsbergian age are the Nidderdsle shales with local impersistent sandstones and the, -Red Scar Grit with an imperaistent coal, the variations of which are treated in detail. The Red Scar Grit develops ,a fossilif erous phase in the upper leaf in the north of-the ground tind a fauna is also recorded from the shales with the, Woogill Coal. The Colaterdale Marine Series consist of shales with a thin limestone characterised by Cravenoceratoides nitidus (Phillips), overlain and underlain by shales with Anthracoceras au cilobum (Phillips) and Dimor-phoceras sp. together with a large additional fauna. A local thickening of the beds beneath the Colsterdale Limestone accompanied by the development of a nuculid-gastropod phase occurs in the north, in Colsterdale. Diagrams and text with full details of the faunal divisions and changes at this level are given. The Nar Hill Beds and the Lower Follifoot Grit, also of Arnsbergian age, consist of variable sandstones with shales prominently developed in the former unit. Beds at these levels have been re-named-following the discovery of Homoceras bevrichianum (Haug) and Homoceras aff. subplobosun (Bisat) in the Ganister Beds. The Ganister Beds are the only sediments of Sabdenian age and include the above mentioned fossils which constitute the first record of H zone goniatites on the Askrigg Block. The Cayton Gill Shell Bed yields an extensive suite of fossils and is overlain by the Agill Sandstone which has yielded the only extant Upper Carboniferous ophiuroid. The Libishaw Sandstone and Capelshaw Shales are locally fossiliferous. New correlations of sediments at the level of these R1 shell beds are put forward. The massive Brimham Grits are separated by shales which yield a band with Lim sp. The beds dip in an easterly direction at about ,2 degrees and though no continuous mesh of faults occurs, they are locally abundant. Aa-analysis "ofstructural trends is given together with a structure contour map. The margins of the drift and periglacial phenomena associated with the Main Dales Glaciation are described and include new records of overflow channels. A synthesis of work on fossils js iprovided, Nvith , comments , on the zonal, use of several forms, palaeo-ecology and techniques of separation of specimens. The chief rock types are examined from. the genetic and descriptive standpoints. Comparison , is made with the . conclusions of other authors relating to ,. the genesis of . sediments of the Yoredale and Millstone Grit facies. _ Accounts of previous workings for coal, lead, etc.., are given together with a statement-of the problems which have beset dam builders in the past when constructing reservoirs, in the area.

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Dating ductile shear zones is daunting because we have to demonstrate either that the chronometer of choice grew during shear zone operation or that crystal-plastic deformation induced age resetting. By adopting a petrochronological approach in this project combining petrographic, geochemical, U-Pb isotopic, and quantitative microstructural data U-Pb isotopic dates are linked with certain shear zone processes. The study area is the South Range of the world-class Sudbury Impact Structure. Specifically, mylonitic shear zones at the Creighton Mine (South Range, Sudbury) operated during three distinct tectonothermal events at ca. 1.75 Ga, 1.65 Ga, and 1.45 Ga. The age dating of texturally and geochemically characterised titanite grains from a shear zone exposed at the 5400 level of the Creighton Mine, indicates operation of the shear during the Mazatzalian – Labradorian orogeny (1.7 – 1.6 Ga). Meso-scale sulphide structures of mechanical remobilization, within the main body of the examined shear zone, show that this event facilitated the local-scale transfer of sulphides to satellite positions. Three age populations of ca. 1.75 Ga, 1.65 Ga, and 1.45 Ga are also prevalent in shear zones from deeper levels of the Creighton Mine. These age populations yield new insights into the orogenic history of the South Range and the Southern Province, and provide further constraints on the comparison of accretionary provinces of the North American Mid-continent and the Southwest United States. Taking into consideration the fluid-mediated and crystal-plasticity textural features in the examined titanite populations it is suggested that these dates record events of syndeformational fluid percolation. Within the 1.75 Ga textural population of titanite grains survived inclusions of inherited titanite grains with shock-metamorphic features. Microstructural and micro to nano-scale crosscutting relationships suggest that the shock wave during the 1.85 Ga impact event induced in these grains the growth of 75°/<010> and 108°/<010> shock microtwins. The nucleation of twins induced a work hardening effect that allowed their survival during the later polyorogenic reworking of the basin (1.75 to 1.45 Ga). U-Pb age dating of these grains yield accurately the age of impact (i.e. 1851 ± 12 Ma). In comparison, titanite grains located within Archaean target rocks ofthe Vredefort structure show identical crystallographic features and partial age resetting. The differential response is attributed to the different distance of the samples from the base of the impact melt sheet that was the dominant heat source. The ore-controlling character of the examined shear zones in the Sudbury mining camp can provide critical information about the exploration potential of these structures in metallogenetic settings. Preliminary mineral-chemical analysis, from major to trace element level, of fabric-forming silicates show distinct trends in the abundance of pathfinder elements (e.g. transition metals). Further, work that will collate the different datasets using multivariable statistical methods will be pursued in order to untangle the vectoring potential of different elements.

No description available.