The lower Whitby Mudstone Formation of the Cleveland Basin in North Yorkshire (UK) is a world renowned location for the Early Toarcian (T-OAE). Detailed climate records of the event have been reported from this location that shed new light on the forcing and timing of climate perturbations and associated development of ocean anoxia. Despite this extensive previous work, few studies have explored the well-preserved sediments below the event that document different phases finally leading to large-scale (global) anoxia, which is the focus of this project. We resampled the underlying Grey Shale Member at cm-scale resolution and conducted a detailed multi-proxy geochemical approach to reconstruct the redox history prior to the Toarcian OAE. The lower Whitby Mudstone Formation, subdivided into the Grey Shale Member overlain by the Jet Rock (T-OAE), is a cyclic transgressive succession that evolved from the relatively shallow water sediments of the Cleveland Ironstone Formation. The Grey Shale Member is characterised by three distinct layers of organic rich shales (~10-60 cm thick), locally named as the ‘sulphur bands’. Directly above and below these conspicuous beds, the sediments represent more normal marine mudstones. Further upwards the sequence sediments become increasingly laminated and organic carbon rich (up to 14 wt %) representing a period of maximum flooding that culminated in the deposition of the Jet Rock (T-OAE). Detailed analyses of the Grey Shale Member, with a focus on the sulphur bands, for TOC and total sulfur concentrations, microscopy, iron speciation (FeHR/FeT, FePyrite/FeHR), trace element concentrations, molecular biomarkers, and bulk carbon and sulphur isotopes confirm highly variable redox conditions prior to the Toarcian OAE, with repeated anoxia/euxinia during periods of sulphur band deposition. Cm-scale geochemical records from the lower sulphur band actually suggest significant, short term variations in redox within the bed, with one full cycle from anoxia/euxinia to oxic conditions and back. We speculate that these cyclic variations in redox during and possibly also between sulphur band formation were driven by orbital forcing, however, better chronological information is necessary to validate this interpretation. The bioturbated mudstones between and below the sulphur bands show less enrichment of TOC, reactive iron and trace elements, but still suggest conditions close to the Fe-proxy threshold characteristic of anoxia (FeHR/FeT = 0.38). Further up the section in the bioturbated mudstones, highly reactive iron and trace elements are significantly depleted, indicating a return to more oxic conditions, which persisted up the top laminated unit of the Grey Shale. This observation challenges the general concept that anoxia/euxinia was limited to the Toarcian OAE, at least in the Cleveland Basin of North Yorkshire. This thesis discusses the detailed dynamics of redox variations and biogeochemical elemental cycling in the run-up to this major event in Earth history. The mechanisms behind the short redox events documented in the sulphur bands may have had some similarities to those proposed for the small hyperthermals post-dating the Paleocene-Eocene thermal maximum (PETM) and other OAE’s. Enhancement of run off from land via enhanced hydrological cycling could have temporarily created conditions in the Jurassic Cleveland III Basin that favoured stratification, high productivity, and development of extreme (euxinic) redox condition with high sulphur and carbon burial. The increasing amplitude of perturbations from the first sulphur band to the T-OAE, and their progressive spatial expansion from proximal to global, may argue for a unifying causal connection, orbital forcing. Further work will have to validate these conclusions and assumption.

Four selected piston cores (i.e. CD1715, CD1730, CD1739 and CD1738) in a north-south transect from Charles Darwin Cruise CD18/86 are investigated in this study. The northern Arabian sea is under the influence of both variable northwesterly dust winds and seasonal upwelling. Their characteristic effects on the mineralogy and chemistry of the sediments are analysed both areally and temporally. From the accumulation rates of lithogenic and biogenic elements an attempt has been made to understand the climatic conditions of cold and warm periods of late Pleistocene time. For this purpose, an age model developed based on oxygen isotope and carbonate stratigraphy of a core RC-2761. Carbonate content variations of four cores show that southern cores CD1715 and CD1730 record a sedimentation history of last 250,000 years. Cores CD1738 and CD1739 have been dated to the base of stage 5 (i.e. 120 Kys). These cores were sampled at 10cm intervals and sediments were subjected to mineralogical and geochemical analysis (Si, Al, Fe, Ca, Mg, K, Ti, P, Sr, Cr, Ni, Zn, Cu, Br, I, Zr, Ba, La, Ce, Nd, organic carbon, biogenic silica δ13C, δ15N). Optical examination reveals that sediments contain various proportions of terrigenous and biogenous components. SEM examination of detrital grains shows rounded and pitted quartz grains and subhedral dolomite, indicative of aeolian transport. Biogenic components largely include, planktonic foraminiferids and diatoms. Semi-quantitative mineralogical studies by XRD has shown that quartz, feldspar, chlorite and illite are the major minerals in the sediments. Peak intensity ratios of Qtz/Fld, Qtz/Chl and Qtz/Ill indicate that cores in the north relatively contain more chlorite, and feldspar is low compared to quartz. Cores CD1715 and CD1730 are relatively impoverished in quartz and chlorite but contain more feldspar. The relative change of peak intensity ratios in different climatic stages is not very clear. The geochemistry of major elements Si, Fe and K and their ratios to Al covary with peak ratios of specific minerals and these indicate both a textural control as well as areal and temporal variations in mineralogy of the sediments. Northern cores (i.e. CD1738 and CD1739) are relatively coarser grained as shown by higher Si/Al ratios and higher Fe/Al ratios implying more chlorite. The ratios of Si/Al, K/Al generally show contrasting trends in glacial and interglacial stages. The minor element geochemistry of the sediments shows more complex relationships. The patterns of Ti, Cr and Zr ratios to Al are different. Ti/Al and Zr/Al profiles tend to follow each other, while Cr/Al profiles show inconsistent trends. The Zr/Al ratio is invariable in cores and shows a persistent aeolian input. Cr and Cr/Al ratios are very high and suggest derivation from local ophiolites and transport to the deep sea by pluming or by turbidity currents. The geochemistry of the biogenic constituents include calcite, organic carbon, biogenic silica, Ex Ba (aluminosilicate free). Their causal relationship with metals (i.e. Cu, Ni, Zu) possibly suggests a genetic or diagenetic association. Biomarkers contents are higher in cores CD1715 and CD1730 than in cores CD1738 and CD1739. The changing patterns of biomarkers between cold and warm stages show increased biological production in the Holocene (stage 1), interglacial stages 3, 5 and 7. Isotopic analysis of δ13C and δ15N shows that organic matter is of marine origin throughout the cores. Halogens geochemistry (iodine and bromine) and their ratios to organic carbon indicates an oxic depositional environment. Iodine relative to bromine shows preferential loss as a result of burial diagenesis. Halogens and their ratios to organic carbon in glacial/interglacial stages follow organic carbon contents and this suggests a possible association with biological productivity. However, the higher ratios in cores CD1738 and CD1739 may be a result of high sediment accumulation rates. Sedimentation rates increase from cores CD1715 and CD1730 to cores CD1739 and CD1738. Lithogenic fluxes of quartz, aluminium, dolomite, zirconium and titanium show a marked gradient from north to south. This implies provenance from the north and northwest and aeolian transport by northwesterly winds. This source has been persistent throughout the last 250,000 years. Lithogenic flux values are higher in glacial stages and indicate change in climate. The highest lithogenic fluxes are seen in glacial stage 2, and indicates the greatest aridity during the last 250,000 years climatic history. Biogenic fluxes (calcite, organic carbon, excess Ba and biogenic silica) decrease towards the north. Variations of biogenic fluxes between climatic stages show antipathetic trends to that observed for the lithogenic fluxes. This confirms the idea that distribution of biogenic and lithogenic components in NW Arabian Sea sediments is more controlled by the climatic patterns and the peculiar features associated with them. The Halocene and interglacial periods (3, 5 and 7) are characterised by strong SW monsoon winds and upwelling and higher biogenic fluxes occur during these times. The lower biogenic values during the earliest interglacial stages suggest erosion of the sediment. This is evident from the comparison of productivity record of excess Ba flux from ODP core 722 (2000m water depth) and deep sea cores of this study. At stage boundaries 3/4, 5/6 and 6/7 the ridge core (ODP 722) shows high values of excess Ba flux; low values in basin cores at these boundaries are explained by the physical removal due to bottom currents.

Partial melting has been proposed as a mechanism for producing the low <I>a</I>H<SUB>2</SUB>O conditions characteristic of granulites, but the extent to which melts produced by water-undersaturated partial melting can be removed from granulite-facies migmatite complexes is less well understood. Three leucogneiss suites produced by water-undersaturated partial melting under high temperature, moderate pressure (6Kbar, 860°C), granulite-facies conditions have been distinguished on the basis of geochemistry and petrography. Type 1 Leucogneisses from the Brattstrand Bluffs coastline, eastern Antarctica, have near minimum-melt major element compositions (high SiO<SUB>2</SUB>, low Fe<SUB>2</SUB>O<SUB>3</SUB>, MgO) low Zr, Th and LREE concentrations, positive Eu anomalies and limited entrained residual material, suggesting efficient segregation of small melt volumes before equilibration with the source. The limited dissolution of accessory phases in water-undersaturated melts has led to a concentration of monazite and zircon and high LREE concentrations in melanosomes. Melting depleted the plagioclase component of the metapelite source rocks almost completely, producing melts with high Eu concentrations. Granitic melts formed under vapour-present conditions are unlikely to show such extreme LREE and HREE depletion or positive Eu anomalies, even at high degrees of partial melting. Type 2 Leucogneisses have high Fe<SUB>2</SUB>O<SUB>3</SUB>, MgO and TiO<SUB>2</SUB> contents and were formed at higher degrees of melting than the Type 1 Leucogneisses. Consequently they were more viscous, less extractable and more likely to entrain restitic and peritectic phases as the metapelitic source rocks lost their coherence. Type 3 Leucogneisses have strongly enriched Zr, Th and LREE abundances, negative Eu anomalies, and Zr/Zr<SUP>*</SUP> and LREE<SUB>t</SUB>/LREE<SUB>t</SUB><SUP>*</SUP> >1 resulting from preferential accessory phase entrainment.

No description available.

The estuarine biogeochemistries of Cd, Cu, Mn, Ni, Pb and Zn have been examined. Two adjacent, contrasting estuaries were selected to assess the effects of riverine discharge, hydrodynamic régime and particulate phase composition. Sampling throughout an annual cycle enabled seasonal differences in primary productivity and meteorological conditions to be included. Simultaneous nutrient determinations and fresh water flow measurements were used to assist in the interpretation of metal data. Dissolved Mn profiles in both estuaries are dominated by benthic inputs, a consequence of the reduction of Mn in sub-oxic sediments. Highest benthic fluxes occur in summer, and coincide with dissolved oxygen minima in the upper Forth. High wintertime fluxes are caused by the injection of porewater following sediment resuspension. Dissolved Ni and Zn are remobilised with Mn during summer in the Forth. Dissolved Cd concentrations in both estuaries increase with salinity as a result of chloro-complexation. Both Cd and Cu are remobilised during the breakdown of particulate material. Only about 5% of the Pb is in the dissolved phase. Suspended particulate trace element contents do not vary much within each estuary. The Ca contents, however, increase with distance seaward, since the coastal zone acts as a source of CaCO<SUB>3</SUB> to the estuaries. Non-detrital Mn contents increase in the outer Forth during summer, a consequence of precipitative Mn oxidation. The behaviours of Ni and Zn mimic that of Mn, as they are scavenged from the dissolved phase by newly formed particulate Mn oxides. Particulate Mn contents are higher in summer than in winter, and higher in the well-oxygenated Tay than in the Forth. This is attributed to faster Mn oxidation rates at higher temperatures and dissolved oxygen concentrations. Suspended particulate Cd contents in both estuaries are highest in summer due to the binding of Cd to phytoplankton cells. Partition coefficients in the Forth and Tay follow the order Pb > Mn, Zn > Ni > Cu > Cd.

The chemistry of six sediment cores (1-11m in length), recovered in the eastern equatorial Pacific, has been investigated in an attempt to determine spatial and temporal variations in the biogenic and terrigenous components, and to relate these to local and global changes in palaeoproductivity and palaeoclimate. Cores P5 and P12 were recovered in the Panama basin during the R.R.S. Shackleton cruise (May, 1976), whereas CD38 cores were recovered during the R.R.S. Charles Darwin cruise (Valparaiso-Balboa, May, 1989). The cores represent a range of sediment composition from a suite of oceanographic environments (eg. water depth). The eastern equatorial Pacific is an area of very high biological productivity, lying at the interaction of the equatorial divergence and the continental margin upwelling systems, making it an ideal setting in which to conduct such a study. Cores were sampled at 2cm (P5 and P12) and 10cm (CD38 cores) intervals and subjected to geochemical (Si, Al, Fe, Mg, Na, K, Mn, P, Ca, Ti, Zn, V, Ni, Cu, Y, Nd, Nb, Ce, Zr, Cr, Sc, Sr, Rb, Ba, I, Br, Mo, U, Pb, Th and La) analysis using XRF; wet chemical techniques (biogenic silica, organic carbon and Cl); preliminary mineralogical analysis using XRD, and stable isotope (δ18O and δ13C) analysis using mass spectrometry. The δ18O signals in the carbonate tests of <i>Neogloboquadrina dutertei</i> and <i>Globigerinoides ruber</i> from cores CD3822, CD3826 and CD3827 provided oxygen isotope chronostratigraphies which were refined by geochemical correlation with well dated nearby cores (AII54-25PC and P6). The sediments are of Pleistocene age and the base of the cores in this study range from 24ka in P5 to 472ka in CD3826. The sediments divide into two groups: an eastern, hemipelagic set (CD3826, CD3827 and AII54-25PC) which is carbonate poor but enriched in terrigenous material; and a western, pelagic set (CD3814, CD3822 and P5) which is carbonate rich but depleted in terrigenous material. Terrigenous input increases during low sea level stand glacial times (especially stage II), and with decreasing distance from land; consistent with increased input of source material from the shelf, and/or increased wind intensity. The Holocene is a time of rapidly decreasing terrigenous input. Hydrothermal deposits, which have unusually high Si<SUB>terrig</SUB>/Al, Fe/Al and K/Al ratios, are present at 13.93ka in core P5 and at the base of core CD3814. Volcanic ash layers 'D'(56ka), 'L'(234ka) and 'K'(328ka), identified by their low Ti/Al and Cr/Al ratios, are present in core CD3826, and were used in age model development. Very high Ti contents in core P5 (especially during stage II) result from increased continental aridity and wind intensity, which promotes increased input of basaltic material from the Galapagos archipelago. Ti in other cores is derived from central America and the Galapagos archipelago. Cores CD3826 and CD3827, in the eastern part of the Panama basin, contain greater contents of quartz, feldspar and chlorite compared to the other cores; whereas cores P5 and CD3822, recovered in the western part of the basin, have higher contents of opaline silica and barite. Montmorillonite is the most common clay mineral present in these sediments.

No description available.

This thesis presents a detailed chemical and isotopic study of picritic and basaltic lava flows and dykes from Baffin Island, the most westerly and least studied part of the North Atlantic Igneous Province (NAIP). Most of the Baffin Island olivine phenocrysts are not in equilibrium with their host-rock compositions (MgO = 8-28 wt. %), and lava flows with > 14 wt.% MgO contain accumulated olivines. The wide range of calculated liquid compositions (9-20 wt. % MgO) indicates a complex magmatic system, in which several batches of magmas have been mixed and of which only a small proportion has reached the surface. The Baffin Island rocks were generated over a wide range of depths with estimated liquidus temperatures of 1211-1430°C and segregation pressures of 1.7-3.1 Gpa. trace element and isotope ratios show that two distinct mantle sources were available: (1) a relatively depleted source with (La/Sm)_n <1, Nb/Zr<0.04, negative ΔNb, ⁸⁷Sr/⁸⁶sr: 0.7030-0.7034 and ¹⁴³Nd/¹⁴⁴Nd ~0.5130m, and (2) a relatively enriched source with (La/Sm)_n >1, positive ΔNb, ⁸⁷Sr/⁸⁶Sr: 0.7039-0.7042 and ¹⁴³Nd/¹⁴⁴Nd: 0.51280-0.51284. with the exception of Pb-isotope ratios, which show evidence for some interaction with Precambrian basement rocks, isotope and trace element ratios are not significantly affected by crustal material. Therefore, the high-⁸⁷Sr/⁸⁶Sr, low-⁴¹Nd/¹⁴⁴Nd samples represent the most enriched endmember of the ancestral Iceland plume which was present at ca. 61 Ma but not evident today. The highest ³He/⁴He (up to 50 <i>R</i>_a) yet recorded from any terrestrial rocks are found in the low-⁸⁷Sr/⁸⁶Sr, high-⁴³Nd/¹⁴⁴Nd rocks. Mixing, at the 670-km thermal boundary, of depleted mantle material with primordial helium form the lower mantle may account for the association of high ³He/⁴He with depleted Sr- and Nd-isotope ratios.

The variations in the trace elements Rb, F, Pb, Sr, Mn, Zr, Zn, Cu, Ni and Fe have been studied in limestone wallrocks next to lead - zinc - fluorite - barite mineralization in the Northern Pennine Orefield and Derbyshire Orefield; and next to haematite orebodies in the Cumberland Ironfieldo. Trace element aureoles have also been investigated in sandstones and shales. An analytical technique for the determination of fluorine in limestones was developed using the optical emission spectrograph, and found to give satisfactory results. Standard X-ray fluorescence techniques were employed for the determination of the other trace elements. The petrology, mineralogy and chemistry of certain aureoles have been examined in detail. The heavy metal content of the limestone wallrocks in the majority of cases, illustrates widespread and irregular dispersion patterns. It is suggested that migration of the metals has taken place through fractures developed prior to, or contemporaneously with, the mineralization. Diffusion of the heavy metals has occurred into massive country rocks at certain localities and results in a logarithmic decrease in concentration away from the ore and more restricted aureoles. The width of the dispersion patterns varies next to the veins, but in general a wider aureole is developed in Derbyshire than in the Alston Block. It is concluded that, at the time of emplacement, the Derbyshire veins were at a higher pressure than the veins in the Alston Block, but that variation in the temperature of the ore solutions was not an important parameter controlling the migration of the heavy metals. The alteration of the limestone wallrocks is discussed and suggestions are put forward to explain the possible origin of some of the replacement minerals. Adjacent to the veins, a depletion in strontium is recorded. This is related to the recrystallisation of the calcite which has liberated strontium from the crystal lattice. The strontium content of the Great Limestone and the D(_2) Limestone, the respective sampling horizons in the Alston Block and the Derbyshire area, are considerably different and it is concluded that this reflects either the original aragonite content of the limestones, or differing conditions of deposition in the two areas. Migration by diffusion into massive country rocks has occurred in the Cumberland Ironfield to far greater distances than in the Pennine Orefields; the depletion of strontium is also more extensive. It is suggested that the ore solutions were emplaced at higher temperatures than in the Pennine Orefields. The trace element aureoles in sandstone and shale wallrocks indicate that the heavy metals have been migrated through fractures, as irregular and widespread patterns are observed. A comparative study was conducted on the trace element variations which occur next to the veins which intersect the Whin Sill (quartz- dolerite) in the Alston Block. Contrary to previously reported widespread dispersion aureoles in igneous rocks, a narrow aureole is formed where diffusion has taken place into the wallrocks. A profound chemical change between the unaltered and altered quartz- dolerite has occurred where CO(_2), K(_2)O and H(_2)O are enriched, while Na(_2)O, MgO, total iron and CaO are depleted. The quartz-dolerite has been converted into a carbonate and clay-rich rock called the White Whin. The chemical and mineralogical variations are related to the variations in the trace elements where Rb, Ba, Pb and Zn are concentrated while Cu, Ni, Zr, Sr, V and Cr are depleted next to the veins. A geological and geophysical survey over altered and mineralised quartz-dolerite dykes at Closehouse mine, Lunedale near Middleton-in- Teesdale has produced results, which, it is hoped, will elucidate the complexities of the area.

No description available.