No description available.

No description available.

No description available.

No description available.

Studying the thermal history of Earth's mantle can provide a better understanding of Earth's evolution on a planetary scale. In this work, several mechanisms affecting the thermal evolution of Earth's mantle are investigated. The Nusselt-Rayleigh power law relationship (Nu(Ra)) was calculated from the results of a series of models with three dimensional spherical geometry and free slip boundary conditions. Basally and internally heated convection was examined. For Nu(Ra) = aRaP, (5 was found to be 0.294 0.004 for basally heated systems and 0.337 0.009 for internally heated systems. Model cases were extended to Rayleigh numbers higher than any previous study (109). 0 was not observed to reduce at high Rayleigh number, therefore, as this mechanism cannot be invoked to moderate thermal flux in the past, the influence of time dependent layering on thermal evolution was considered. A parameter space exploration of Rayleigh number and 660 km phase change Clapeyron slope demonstrates that present day Earth could have a partially layered mantle and that full two layer convection is possible in the past at higher Rayleigh numbers. Evolution of mantle temperature was modelled, with the models cooling from an initially layered state. As layering breaks down at high Rayleigh numbers, the mantle passes through a wide domain of partial layering before achieving whole mantle convection. The partially layered regime is characterised by a series of avalanches from the upper into the lower mantle. When an avalanche reaches the core mantle boundary it triggers a pulse of plume-like instabilities in the opposing hemisphere, producing a pulse in global surface heat flux. As the mantle cools, the avalanche-pulse events evolve towards higher frequency and lower magnitude. If this mechanism occurs within Earth, the gradualist view of Earth's thermal evolution may need to yield to a more event-driven model. The mechanics of avalanche-pulse events could also provide an explanation for geochemical observations of periodic maxima in melt extraction from the mantle. The modelling of Earth's mantle produces large data volumes. A distributed computing solution to the data storage problem was investigated. The system, MantleStor, is based on Peer-to-Peer technology and intended to operate over hundreds of standard workstations. A trial implementation demonstrates that MantleStor is able to safely store data in a challenging network environment. Data integrity was maintained with over 30% loss of storage machines. MantleStor is an example of an e-Science project, a discussion of e-Science and its implications is presented.

No description available.

The Hampden Section of South Island, New Zealand, is used to generate a multiproxy record of middle Eocene palaeoclimate. The Hampden Formation is a calcareous clay-rich siltstone deposited in a shelf edge environment, containing exceptionally well-preserved micro- and nannofossils. A range of sedimentary, geochemical and fossil assemblage records from this formation are combined to provide new insights into middle Eocene climate in the southern Pacific Ocean. A palaeoclimate record generated through the formation spans the period from -42.1 to -39.3 Ma and shows clear cooling in ocean mixed-layer temperatures from -18 C to -14 C, with long period cyclicity (likely -405 k.y.) superimposed. This cooling trend is punctuated by a transient warm excursion of - 2.5 C lasting -450 k.y. that may represent the Middle Eocene Climatic Optimum. There is a brief influx of the tropical planktonic foraminifer Hantkenina australis during this time and the excursion is also marked by a substantial drop in the sand fraction of the sediment, indicating that the warm interval had a significant impact on the terrestrial realm. The water temperatures produced from this record are warmer than those previously estimated for similar latitudes, likely due to the excellent preservation of the microfossils reducing the effect of diagenesis on their geochemistry. These temperatures suggest that during the middle Eocene, the site lay in the path of a warm southward flowing current rather than a cold Antarctic gyre. They also support the hypothesis that the global latitudinal temperature gradient was reduced during the middle Eocene. A shorter high-resolution record of climate was also obtained. This shows -18 k.y. cyclicity in a range of palaeoclimatic and palaeonvironmental proxies that is considered to have been orbitally forced. The Mg/Ca derived bottom water temperatures range from -11 to 13 C and the TEXg6 derived surface water temperatures from -22.5 to 24 C through these cycles. The combination of 8 O and Mg/Ca in foraminiferal carbonates indicates that there was little or no ice present globally. Despite the lack of ice available to amplify the cycles they had a major and complex effect on both the marine and terrestrial environments.

The stratigraphy of three ostracod-mussel bands occurring respectively in the Lower Modiolaris, Upper Communis and Upper Similis-Pulchra Zones of the Northumberland and Durham Coal Measures is described. The Hopkins' Band in the Dower Modiolaris Zone is compared with similar bands at an equivalent stratigraphical horizon in the Midgeholme and Cumberland coalfields. The dominant non-marine lamellibranchs in this band resemble, or are related to, Anthracosia regularis and Garbonicola oslancis. The Three Quarter ostracod-mussel band from the Communis Zone contains Ourvirimula and Garbonicola declevis, while the Claxheugh Shell Bed from the Upper Similis-Pulchra Zone contains Naiadites and forms resembling Anthraconauta phillipsi. The ostracod, annelid, plant and fish remains in these bands are also described. The validity and distinction of the ostracod genera Jonesina and Geisina are established and the species J. fastigiata, G. arcuata and G. subarcuata are described in detail. The ostracod species Carbonita cf. evelinae, C. of. rankiniana, C. humilis, G. pungens. G. inflata, C. secans and C. concava sp. nov. are described from the Hopkins' Band and the presence of moults and dimorphic forms of these species is shown in the ostracod populations of the bands. The synonomay, morphology and stratigraphical ranges of the above species of ostracods from the British Coal Measures are reviewed and discussed. The true generic assignment and growth forms of the worm Microconchus (Spirorbis) pusillus are discussed. Vertical sequences of six "faunal phases" for the Hopkins' Band and three for the Three Quarter Band are deduced from a study of the respective faunas at several localities. These faunal phases are subsequently related to changing ecological conditions. The conditions under which the sediments of the Hopkins' Band were laid down are deduced from a study of the petrology of the sediments and their chemical composition. The orientation and associations of fossils in the sediments are recorded and the published information on palaeoecology and comparative ecology of living mussels and ostracods is reviewed. It is concluded that the Hopkins' Band was deposited in a brackish lagoonal environment at the beginning of a typical Coal Measures cyclothem. At first the richly carbonaceous bottom sediment of this lagoon prohibited the establishment of a benthonic fauna, but a change in the source and type of sediment and increase in turbulence enabled a mussel fauna to thrive with a reduction of the previously abundant pseudo-planktonic ostracod fauna. Increased sedimentation eliminated this fauna and the conditions became more deltaic. Similar environmental conditions are deduced for the Three Quarter Band, but the Claxheugh Shell Bed is believed to have formed in a small isolated brackish or fresh water lake within the main delta or swamp.

ln the present state of knowledge, thirty-one trace-fossil 'species' are known from the English Jurassic: seventeen (55%) are feeding burrows; eleven (36%) are dwelling burrows; two (6%) are crawling trails; one (3%) is a resting impression. No meandering grazing trails occur. Six new 'species' are described;- Arenicolites skeltonensim - basal Upper Lias, Yorkshire. Diplocraterion arkelli - widespread. Diplocraterion statheri - Bajocian, Yorkshire. Glossifungites lymensis - Ellerbeck Bed, Yorkshire. Asterosoma osteri _ Dogger, Yorkshire. Asterosoma multilobatum - Scarborough beds, Yorkshire. Bathymetric zones for the Jurassic sea may be defined in terms of commonly occuring assemblages of trace fossils. Littoral zones consist of monotypic banks of Thalassinoides; arenicolites spp. or Corophioides spp.; or Ophiomoreha. Gyrochorte from the littoral zone show strong orientation and U-turns are common. In sublittoral zones monotypic banks of Rhizocoralliua occur inshore; more varied assemblages, with Teichichnus. Asterosoma and Chondrites, offshore. Zoophycos, diagnostic of still-water neritic zones, is absent. Different trace-fossil ‘species’ are recognised from ironstone, calcareous and well-sorted sandstone “regimes” of sedimentation, though ‘genera’ may be identical. Rhizocorallium jenense and Rhizocorallium cicatricosus occur in ferruginous environments ; Rhizocorallium commune in impure calcareous environments. The stomatopoda are considered likely producers of Rhizocorallium commune. On basis of comparative ecological categories of trace fossils, the system which most strongly resembles the English Jurassic is the bohemian Ordovician. The middle Jurassic of Yorkshire does not compare closely with either the German middle Jurassic or the Northumbrian mamurian. The Jurassic trace-fossil fauna of England is the richest in dwelling and feeding burrows of any system so far described. In the total number of trace-fossil ‘species’ it is exceeded only by the Swiss Flysch.

Ostracods are a diverse group of arthropod crustaceans with a geological record from the Ordovician. Their radiation from marine to non-marine environments is a key step in the evolution of the group. The nature and chronology of this transition is examined, and proxies for non-marine environments determined. The Mississippian of the Midland Valley of Scotland contains a wide range of marine to non-marine ostracods, macrofauna and sediments that make it an ideal study area. This study documents the evidence for early Mississippian freshwater ostracods, 20 million years older than previously recorded. Twentyfive ostracod species from the orders Myodocopida, Palaeocopida and Podocopida are described, four of which are new species. Macrofossils are used to interpret the environmental tolerance of the ostracods. Important brackish to freshwater macrofauna are the bivalves Carbonicola, Curvirimula and Naiadites, the vermiform microconchid “Spirorbis”, conchostracans and fish. Eurytopic ostracods are species of Cavellina, palaeocopes and Shemonaella siveteri n. sp. Key brackish to freshwater ostracods are species of Geisina arcuata, and Paraparchites circularis n. sp. Freshwater ostracods are species of Carbonita. Non-marine sediments contain three new types of algal palynomorph, Botryococcus sp., and arthropod fragments. The algal palynomorphs are interpreted as freshwater. Brackish to freshwater habitats identified include estuaries, lakes, temporary pools and swamps. A protocol for the examination of diagenetic alteration of ostracods and macrofossils is proposed, which is essential prior to any isotope analysis. Diagenetically altered ostracods may be mistaken as pristine specimens, without a study of the carapace ultrastructure. This is assessed by comparing Carboniferous and Recent specimens. The Carboniferous ostracods have undergone seven diagenetic stages: 1. neomorphic calcite; 2. dissolution and pitting; 3. euhedral pyrite; 4. ferroan calcite; 5. ferroan dolomite; 6. iron oxide; 7. sphalerite and barite. The carbon and oxygen stable isotope data from the ostracods reflect these stages of diagenesis.