http://hdl.handle.net/2262/15 Geology 2013-05-24T22:07:48Z http://hdl.handle.net/2262/64063 Title: Chemical abrasion applied to SHRIMP zircon geochronology: An example from the Variscan Karkonosze Granite (Sudetes, SW Poland) Author: CROWLEY, QUENTIN G Abstract: Thermal annealing followed by acid etching of zircon (chemical abrasion or CA) can be successfully utilised to minimize or eliminate the effects of major and cryptic Pb-loss for SIMS U–Pb zircon dating. The procedure is demonstrated by applying the U–Pb SIMS technique to both untreated and chemically abraded zircons from the Karkonosze Granite, Sudetes, SW Poland. Conventional U–Pb SIMS dating of untreated zircons yields an apparently coherent age population (n = 9) with a weighted mean 206Pb/238U age of 306 ± 4 Ma. Some untreated zircons display anomalously young 206Pb/238U ages (c. 225 and 238 Ma) and are likely to have suffered substantial Pb-loss. A sub-set of zircons from the same sample was chemically abraded. Physically, zircons treated in this manner display a range in the degree of etching and partial dissolution. Extreme examples developed a 3D network of sub-μm channels which follow high-U (dark CL) zones or linear defects, such as micro fractures or indistinct cleavage planes. U–Pb SIMS dating of treated zircons (n = 11) yields a mean 206Pb/238U age of 322 ± 3 Ma. Two analyses of treated zircons still display younger 206Pb/238U ages (c. 297 and 301 Ma) ascribed to the effects of Pb-loss. For the analysed sample, U–Pb ages determined from chemically abraded zircons are c. 5 % older than those from untreated zircons. This is attributed to effective removal of metamict domains susceptible to Pb-loss. The CA technique also removes micro-inclusions thus lowering common Pb and reducing matrix effects. A cryptic Pb-loss in untreated zircons is only recognised when compared with chemically abraded counterparts or ages determined using other isotope techniques. This clearly demonstrates the utility of CA to high-spatial resolution methods and stresses that Pb-loss is detectable at a range of scales, regardless of the analytical technique used. Description: PUBLISHED 2012-01-01T00:00:00Z http://hdl.handle.net/2262/63827 Title: Changes in the hydrological cycle in tropical East Africa during the Paleocene- Eocene Thermal Maximum Author: NICHOLAS, CHRISTOPHER JOHN Abstract: The Paleocene-Eocene Thermal Maximum (PETM), at ca. 55.8 Ma, is one of the most studied instances of past greenhouse gas-induced global warming. As such, it provides a rich opportunity to examine the impact of such global change on local climates. The effect of increased continental and sea surface temperatures on local precipitation and humidity during the PETM remain poorly constrained and studies reveal complex, regional differences; whilst some localities appear to experience a net increase in humidity, others exhibit the opposite. Crucially, there are few records of hydrological change from tropical regions. Recent onshore drilling expeditions in Tanzania have yielded expanded sedimentary sections, deposited in a marine environment, that span much of the Late Cretaceous and Paleogene and show exceptionally good preservation of both calcareous microfossils and organic matter. The PETM interval has previously been constrained by both biostratigraphy and carbon isotopic records and spans ca. 7 m of section. Lipid distributions, including various terrestrial, marine and bacterial biomarkers and their hydrogen isotopic compositions, as well as mineralogy, were used to examine East African vegetation and hydrological responses to the global change occurring at the PETM. Although total organic carbon contents decrease, the concentrations of both higher plant (n-alkanes, n-alkanoic acids) and soil bacterial (glycerol dialkyl glycerol tetraethers) biomarkers increase dramatically at the onset of the PETM negative carbon isotope excursion (CIE), suggesting an increased discharge of fluvial sedimentary organic matter. Similarly, mineralogical indicators of terrestrial input – including Ti/Al and Si/Al ratios, quartz contents and, notably, the proportion of kaolinite – also increase at the onset of the CIE. However, higher plant leaf wax n-alkanes (C27, C29 and C31) become more deuterium-enriched throughout the same interval, suggesting a more arid and/or hotter, rather than a more humid, environment. This evidence collectively suggests an East African early PETM climate characterised by overall hot and arid conditions punctuated by intense, perhaps seasonal, precipitation events. These data match observations from other locations at mid-latitudes, suggesting that the humid climate often suggested for the PETM was not globally widespread. Description: IN_PRESS 2012-01-01T00:00:00Z http://hdl.handle.net/2262/63813 Title: Evaluating the utility of 15N and 18O isotope abundance analyses to identify nitrate sources: A soil zone study Author: GOODHUE, ROBBIE; COXON, CATHERINE ELIZABETH Abstract: 15N and 18O isotope abundance analyses in nitrate (NO3−) (expressed as δ15N-NO3− and δ18O-NO3− values respectively) have often been used in research to help identify NO3− sources in rural groundwater. However, questions have been raised over the limitations as overlaps in δ values may occur between N source types early in the leaching process. The aim of this study was to evaluate the utility of using stable isotopes for nitrate source tracking through the determination of δ15N-NO3− and δ18O-NO3− in the unsaturated zone from varying N source types (artificial fertiliser, dairy wastewater and cow slurry) and rates with contrasting isotopic compositions. Despite NO3− concentrations being often elevated, soil-water nitrate poorly mirrored the 15N content of applied N and therefore, δ15N-NO3− values were of limited assistance in clearly associating nitrate leaching with N inputs. Results suggest that the mineralisation and the nitrification of soil organic N, stimulated by previous and current intensive management, masked the cause of leaching from the isotopic prospective. δ18O-NO3− was of little use, as most values were close to or within the range expected for nitrification regardless of the treatment, which was attributed to the remineralisation of nitrate assimilated by bacteria (mineralisation-immobilisation turnover or MIT) or plants. Only in limited circumstances (low fertiliser application rate in tillage) could direct leaching of synthetic nitrate fertiliser be identified (δ15N-NO3− < 0 ‰ and δ18O-NO3− > 15 ‰). Nevertheless, some useful differences emerged between treatments. δ15N-NO3− values were lower where artificial fertiliser was applied compared with the unfertilised controls and organic waste treatments. Importantly, δ15N-NO3− and δ18O-NO3− variables were negatively correlated in the artificial fertiliser treatment (0.001 ≤ p ≤ 0.05, attributed to the varying proportion of fertiliser-derived and synthetic nitrate being leached) while positively correlated in the dairy wastewater plots (p ≤ 0.01, attributed to limited denitrification). These results suggest that it may be possible to distinguish some nitrate sources if analysing correlations between δ variables from the unsaturated zone. In grassland, the above correlations were related to N input rates, which partly controlled nitrate concentrations in the artificial fertiliser plots (high inputs translated into higher NO3− concentrations with an increasing proportion of fertiliser-derived and synthetic nitrate) and denitrification in the dairy wastewater plots (high inputs corresponded to more denitrification). As a consequence, nitrate source identification in grassland was more efficient at higher input rates due to differences in δ values widening between treatments. Description: PUBLISHED 2012-01-01T00:00:00Z http://hdl.handle.net/2262/63769 Title: Arctic Bay Formation, Borden Basin, Nunavut (Canada): basin evolution, black shale, and dissolved metal systematics in the Mesoproterozoic ocean Author: KAMBER, BALZ SAMUEL Abstract: The Arctic Bay Formation (Nunavut, Canada) represents a late Mesoproterozoic muddy terrigenous ramp and contains >200 m of black shale. The formation was studied in order to decipher the tectonostratigraphic and geochemical evolution of the basin, address the origin of metal enrichment, and determine whether this frontier basin has the potential to host sedimentary-exhalative or polymetallic black shale deposits. Samples were analysed in the laboratory for major and trace elements, total organic carbon (TOC), 4-step loss-on-ignition (LOI), and Pb isotopes. Non-calcareous black shale exhibits neither Ce nor Y anomalies, reflecting euxinia in the lower water column, whereas slightly dolomitic black shale has both Ce and Y anomalies, reflecting the dolomite's probable origin as a precipitate in the upper water column. The stratigraphic distribution of the rare earth elements (REEs) indicates an evolving sediment provenance, and Pb isotopic data indicate that the source of clay in the black shale was dominated by weathered, juvenile, mantle-derived material. Base metals and redox-sensitive metals, expressed as enrichment ratios relative to conservative lithophile elements, are elevated and exhibit coherent covariations in the black shale. Enrichment in the redox-sensitive elements, such as Mo and U, correlates with dolomite content of the shale, rather than with organic C or Fepy. From a deep-time ocean evolution perspective, this important observation suggests that enrichment in these metals cannot necessarily be attributed to metal incorporation at an interface between sediment and euxinic water. Instead, in Arctic Bay Formation black shale, the metals were either scavenged onto dolomite as it precipitated in the water column, or secondarily re-distributed within the sediment according to its dolomite content. The base metals that are concentrated in the black shale (e.g., Zn) were probably sourced from diffuse hydrothermal venting, and although there is no evidence at the studied location for a nearby point source of metals (vent), persistent bottom- water euxinia would have ensured the effective scavenging of any dissolved metals supplied, and so the basin has at the very minimum a hypothetical potential for SEDEX and polymetallic mineralisation. Whole-rock U-Th-Pb isotope analysis of black shale yielded a date of 1092 ± 59 Ma, which is considered to be the Arctic Bay Formation's depositional age. Description: PUBLISHED 2012-01-01T00:00:00Z http://hdl.handle.net/2262/62534 Title: Acid Treatment effects on the stable isotopic signature of fossils Author: NICHOLAS, CHRISTOPHER JOHN Abstract: Prior to geochemical analyses, fossil bones and teeth are often extracted from any surrounding lithified sediments using chemical techniques such as immersion in acid. As stable isotope analysis becomes more commonplace in palaeoecological investigations, it is important to consider what effects these chemical preparation techniques may have on any subsequent isotopic data and to constrain these effects as quantitatively as possible. This study aims to elucidate these effects, as it is vital that variability in a data set should not be introduced as a result of protocols used during sample preparation; in addition, it defines the most effective and viable method of carbonate removal for processing bulk fossil samples without causing alteration of their stable isotopic signatures. Various strengths of two weak acids commonly used during palaeontological preparation were tested to evaluate their effects on the δ15N and δ13Corg isotopic signatures of the vertebrae of a large Eocene fossil fish. Changes in the isotopic values occurred over time regardless of which acid was used, each causing a variable response in both δ15N and δ13Corg isotopic values. Without careful monitoring of the acidification process in a controlled environment, any resulting data could therefore confound interpretation. Based on these experiments, it is recommended that 2 m acetic acid be used for the pretreatment of fossils prior to the acquisition of N and C isotope data where carbonate removal is necessary. Description: PUBLISHED 2012-01-01T00:00:00Z http://hdl.handle.net/2262/59848 Title: A Toba-scale eruption in the Early Miocene: the Semilir eruption, East Java, Indonesia Author: CROWLEY, QUENTIN G Abstract: The Indonesian archipelago is well known for volcanic activity and has been the location of three catastrophic eruptions in the last million years: Krakatau, Tambora and Toba. However, there are no reports of large magnitude eruptions during the earlier Cenozoic despite a long volcanic record in Indonesia during subduction of Indian Ocean lithosphere since the Eocene. Here we report an Early Miocene major eruption, the Semilir eruption, in south Java, the main phase of which occurred at 20.7 ± 0.02 Ma. This major volcanic eruption appears similar in scale, but not in type, to the 74 ka Toba event. Its products can be identified elsewhere in Java and are likely to have been distributed widely in SE Asia and adjacent oceans. The Semilir eruption could have triggered a climate response, but cannot yet be linked with certainty to Early Miocene climatic events such as glaciations. Description: PUBLISHED 2011-01-01T00:00:00Z http://hdl.handle.net/2262/57422 Title: Geochronology of the Tardree Rhyolite Complex, Northern Ireland: Implications for zircon fission track studies, the North Atlantic Igneous Province and the age of the Fish Canyon sanidine standard Author: CHEW, DAVID Abstract: The British-Irish Palaeogene Igneous Province (BIPIP) is part of the larger North Atlantic Igneous Province and includes the lava fields of Antrim, Mull, and Skye. The Tardree Rhyolite Complex (TRC) in Northern Ireland forms an important stratigraphic unit between the Lower and Upper Basalt Formations of the Antrim Lava Group (ALG). Previous zircon age determinations obtained from the TRC have been used as a standard in zircon fission track studies, but contradict several 40Ar/39Ar sanidine and U-Pb zircon results. We provide new 40Ar/39Ar sanidine and U-Pb CA-TIMS zircon ages which resolve this discrepancy. Two sanidine samples from the Sandy Braes vent and the columnar-jointed dome-forming rhyolites of Tardree Forest yield a weighted mean 40Ar/39Ar age of 61.13 ± 0.42 Ma (2σ, internal error). Ten U-Pb CA-TIMS zircon analyses were undertaken, eight of which employed the CA-TIMS approach on both multi-grain fractions and single grains. Six of the CA-TIMS data yield a disequilibrium-corrected weighted mean 206Pb-238U age of 61.32 ± 0.09 Ma (2σ). The consistency of the 40Ar/39Ar ages with the CA-TIMS U-Pb zircon age, points to a closed system of both K and Ar since eruption. We propose that the crystallization age of the TRC be taken as 61.32 ± 0.09 Ma and that the currently used age of the zircon fission track standard (58.4 ± 0.7 Ma) be changed accordingly. This also places the eruption of the TRC in magnetochron C26r, which is consistent with the reversed polarity magnetic remanence observed in the ALG, and supports the conclusion of Ganerød et al. (2010) that the Lower Basalt Formation is older than the Vaigat Formation in Western Greenland. No resolvable zircon inheritance has been detected by the TIMS analyses, consistent with the fact that the temporal and geographic extent of rhyolitic magmatism within this sector of the BIPIP was very limited, and hence was unlikely to provide inherited magmatic zircons from slightly older magmas (antecrysts). Potentially older zircon xenocrysts would be derived from the underlying Caledonian basement (> 400 Ma) or yet older rocks. These should be easily detectable if the Tardree zircon was to be employed as a U-Pb zircon standard. The paired 40Ar/39Ar and 206Pb-238U results from this study indicate an age of 28.393 ± 0.194 Ma for the widely used Fish Canyon sanidine standard and gives further support to the recent calibrations of Kuiper et al. (2008) and Renne et al. (2010). Description: PUBLISHED 2011-01-01T00:00:00Z http://hdl.handle.net/2262/57312 Title: Monitoring Deposited Dust in The Old Library, Trinity College Dublin Author: SMITH, ALLYSON; BIOLETTI, SUSAN; GOODHUE, ROBBIE Abstract: A study is currently being undertaken to characterise the accumulation rate, distribution, particle size, type and source of dust in the Old Library, Trinity College Dublin, in order to investigate its impact on the collection of more than 300,000 books and manuscripts held there. The majority (approximately 200,000 books, dating from 15th – 19th century) are held on open shelves in the Long Room and Gallery. As well as being a research facility, the Old Library is an exhibition space, and a major tourist attraction as home to a renowned medieval manuscript (the Book of Kells, c.800). It is open to the public seven days a week, almost year-round. Description: PUBLISHED; The International Centre [ IFLA ] publishes three times a year the newsletter, "International Preservation News" [ http://www.ifla.org/en/publications/international-preservation-news ], that reports on the preservation activities and events that support efforts to preserve materials in the world's libraries and archives. This publication is distributed free of charge by the Regional Centres to any library, institution, association or person interested in preservation and wishing to receive it. The PAC Regional Centres regularly contribute with articles. 2011-01-01T00:00:00Z http://hdl.handle.net/2262/57091 Title: Basic volcanism contemporaneous with the Sturtian glacial episode in NE Scotland Author: CHEW, DAVID Abstract: The Dalradian Supergroup contains three distinct glacigenic units, formerly termed ‘Boulder Beds’, which are correlated with widespread Neoproterozoic glaciations. The oldest and thickest unit, the Port Askaig Formation, marks the Appin–Argyll group boundary of the Dalradian Supergroup and has been correlated with the Middle Cryogenian (Sturtian) glaciation. The Auchnahyle Formation, a diamictite-bearing sequence near Tomintoul in NE Scotland, exhibits strong lithological similarities to the Port Askaig Formation. Both these glacigenic ‘Boulder Bed’ units contain abundant dolomite clasts in their lower parts and more granitic material at higher levels. Both metadiamictite units are overlain by thick shallow-marine quartzite units. C isotope data from Appin Group carbonate strata below the Auchnahyle Formation support this correlation. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) detrital zircon data from the Auchnahyle Formation metadiamictite differ slightly from the Port Askaig Formation, but are similar to detrital zircon spectra obtained from the Macduff Formation, a diamictite unit in the younger Southern Highland Group of the Dalradian Supergroup; both apparently reflect derivation from local basement rocks. No detritus younger than 0·9 Ga is observed, so the data do not constrain significantly the depositional age of the glacial strata. A thin tholeiitic pillow basalt unit in the lower part of the Auchnahyle Formation is geochemically distinct from pre-tectonic metadolerite sills and from basic metavolcanic rocks up-section. A Sturtian (c. 720–700 Ma) age for the Auchnahyle Formation metadiamictite would imply that this basaltic volcanism represents the oldest recorded volcanic activity in the Dalradian Supergroup and is inferred to represent an early, local phase of proto-Iapetan rifting within the Rodinian supercontinent. Description: PUBLISHED 2010-01-01T00:00:00Z http://hdl.handle.net/2262/56373 Title: Hidden Archaean and Palaeoproterozoic crust in NW Ireland? Evidence from zircon Hf isotopic data from granitoid intrusions Author: CHEW, DAVID Abstract: The presence of major crystalline basement provinces at depth in NW Ireland is inferred from in situ Hf isotope analysis of zircons from granitoid rocks that cut structurally overlying metasedimentary rocks. Granitoids in two of these units, the Slishwood Division and the Tyrone Central Inlier, contain complex zircons with core and rim structures. In both cases, cores have average Hf values that differ from the average Hf values of the rims at 470 Ma (the time of granitoid intrusion). The Hf data and similarity in U–Pb age between the inherited cores and detrital zircons from the host metasedimentary rocks suggests local contamination during intrusion rather than transport of the grains from the source region at depth. Rims from the Slishwood Division intrusions have average Hf470 values of −7.7, consistent with a derivation from juvenile Palaeoproterozoic crust, such as the Annagh Gneiss Complex or Rhinns Complex of NW Ireland, implying that the deep crust underlying the Slishwood Division is made of similar material. Rims from the Tyrone Central Inlier have extremely negative Hf470 values of approximately −39. This isotopic signature requires an Archaean source, suggesting rocks similar to the Lewisian Complex of Scotland, or sediment derived wholly from it, occurs at depth in NW Ireland. Description: PUBLISHED 2009-01-01T00:00:00Z