The high-energy open shelf along the southern Australian continental margin is blanketed by heterozoan cool-water carbonates of late Pleistocene and Holocene age. Three distinct assemblages have been identified and radiocarbon dated. These include: i) Holocene grains, unaltered biofragments deposited during Marine Isotope Stage 1; ii) stranded grains, grey and buff-colored abraded biofragments and intraclasts marooned during the sea level rise associated with the latter stages of Marine Isotope Stage 2; and iii) relict grains, highly abraded, iron-stained intraclasts originally deposited during the intermediate sea-level stands of Marine Isotope Stages 3 and 4. Whereas the skeletal makeup of Holocene grains has been previously detailed, attributes of the older grains have not been elucidated. Relict-grain skeletal composition indicates that during Marine Isotope Stages 3 and 4 shallow, warm, oligotrophic, marine grassbed environments developed across the western portion of the region, whereas more heterozoan assemblages to the east imply cooler marine waters and that an overall upwelling regime was in effect. Stranded grains (Marine Isotope Stage 2) are mostly heterozoan across the whole region, reflecting deposition on narrower shelves (restricted euphotic zone) and in generally cool waters. Stable isotopic compositions of relict and stranded foraminifera indicate that the western portion of the region (the Great Australian Bight) had water of elevated salinity. Environments analogous to outer Shark Bay are interpreted to have formed across the Great Australian Bight during portions of Marine Isotope Stages 2, 3 and 4. Comparison between relatively unaltered Holocene grains and altered late Pleistocene stranded and relict grains reveals pathways of early diagenesis in this cool-water marine realm. Both calcitic and aragonitic biogenic grains display dissolution features. Dissolution of calcitic components over the past ~20,000 years is incomplete (stranded and relict sediments are predominantly Mg-calcite). Aragonitic skeletons, however, are mostly dissolved over this same time period. Contemporaneously, micritic cement also precipitates in this environment, wherein Mg-calcite (~12 mol%) infills skeletal pores of many stranded and most relict skeletons. Similar cement locally precipitates between grains, forming cemented grain aggregates. Mobilization of metals in the slightly reducing pore waters of the southern Australian margin has resulted in the formation of Fe- and Mn-oxides that discolor the stranded and relict grains. Such oxides precipitated on the surface of shells, in empty microbial borings, and in skeletal micropores, scavenge other trace metals, altering the original elemental makeup of these cool-water carbonates. Trace element analysis of Holocene carbonate grains and of living gastropod skeletons indicates that these coatings begin to precipitate during or soon after shell formation. Marine dissolution/precipitation dynamics in addition to mobilization of metals in pore water, fundamentally changes the sedimentological and chemical attributes of these cool-water carbonates on the seafloor soon after deposition. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2008-01-14 09:41:25.35

The Nullarbor Plain in southern Australia is an uplifted succession of Cenozoic marine carbonates whose surface has been exposed for ~14 m.y. This succession of limestones, particularly in the surfical middle Miocene Nullarbor Limestone, hosts a complex and prolonged record of meteoric diagenesis. Alteration took place through 3 broad phases of diagenesis encompassing 8 stages that are interpreted to have taken place over a dramatic regional climate change. Phase 1 diagenesis occurred under a humid middle Miocene climate and involved mineralogical equilibration with meteoric fluids, calcite cementation, widespread microkarst, and regional lacustrine and palustrine sedimentation producing copious amounts of ooids. These ooids are interpreted to have formed via microbial secretions and sediment aggradation over multiple seasons of changing rainfall and soil hydration states. Cortical laminations are proposed to represent microbial mucus envelopes during wet seasons alternating with dehydration during dry seasons and precipitation of fibrous clay minerals and CaCO3 that preserve the pre-existing microbial fabrics. Phase 2 alterations took place under a more temperate climate from the late Miocene to Pliocene with a later pronounced humid interlude. This phase encompassed ~8 m.y. and was dominated by karst process where deep cave dissolution occurred at depressed water tables related to globally low sea levels and later shallow caves developed during a Pliocene sea level highstand. Phase 3 has occurred since the late Pliocene and is indicative of the onset of modern semi-arid climatic conditions. This final phase involved the creation of subsoil hollows filled with blackened limestone lithoclasts, deep and shallow dolines, and indurated pedogenic calcrete that now forms much of the surface of the Nullarbor Plain. Blackened limestone clasts have been shown to form at the B-C boundary in soil profiles where roots have their cellular structures calcified and during this process incorporate trapped organics that ultimately produce the distinctive black colouration. The importance of this comprehensive diagenetic record is its direct applicability to the understanding of ancient subaerial exposure surfaces. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-07-16 12:09:35.842

No description available.

This thesis has studied aspects of biomineralisation, covering the inorganic mineral, the organic matrix, the possible use of phospholipid bilayer vesicles to control mineralisation, calcium and other metal binding to an antibiotic ionophore, Lasalocid-A and a study of a known inhibitor of biomineralisation, the glycopeptide antifreeze found in the plasma of fish which live under polar conditions. The mineral systems studied have been calcium carbonate formations in otoconia and otoliths, crystals which form part of the balance organs of the inner ear, and coccoliths, the earliest eukariotic formation of calcium carbonate, from an alga. Both these systems have been studied by ultra-high resolution electron microscopy with the observation that both types of structures grow in a unique manner, quite distinct from their geological counterparts; indeed the coccolith system involves two distinct mechanisms of growth for different parts of its structure, which is only 2 μm in diameter. Mechanisms of growth of both biominerals are proposed. The study of the organic matrix was less successful in that it was not possible to fully characterise an acidic matrix protein, but it has been shown that the soluble matrix consists of many polypeptide chains cross-linked together, which undergo a conformational change on dissolution from the insoluble matrix on which they lie in vivo and consequently give in vitro results which do not mimic the in vivo condition. Equally, the use of vesicles to control the formation of calcium carbonate was shown to be possible on occasion, but lipids are very unstable in the presence of calcium and no means of stabilising the system to produce consistent results was determined. Two studies were made by ¹H-nmr, the metal-ion complexes of the ionophore Lasalocid-A and the antifreeze glycopeptide of polar fish, in order to demonstrate principles of the handing of isolated ions and of crystallisation inhibition. In both cases, the biological action of the system was mimicked and followed by nmr and a mechanism for their function proposed.

Recent studies have demonstrated the potentially robust nature of U-Pb and Pb/Pb systematics within certain sedimentary and metamorphic carbonates (e.g. Moorbath et al., 1987; Jahn, 1988; Jahn et al., 1990; DeWolf and Halliday, 1991). During the course of this work, the Pb/Pb dating technique has been applied successfully to the direct dating of Proterozoic stromatolitic carbonates from Western Australia and India, Silurian stromatoporoidal carbonates from Sweden and Archaean marbles from India, permitting the direct age determination of depositional/early diagenetic, late diagenetic and metamorphic events. Results indicate that large variations in μ value (²³⁸U/²⁰⁴Pb) and virtually homogeneous initial Pb isotopic compositions are a recurrent feature of sedimentary and metamorphic carbonates. Authigenic marine carbonates may incorporate U and Pb through a variety of geochemical mechanisms; <ul> <li>organic complexing;</li> <li>crystal lattice substitution;</li> <li>adsorption onto particulate oxyhydroxides and</li> <li>early diagenetic reduction.</li> </ul> Since modern and ancient carbonates have U and Pb concentrations of the order of ppm, whereas dissolved U and Pb in the oceans occur at 3.2 ppb and 0.003 ppb, preconcentration within the water column must be an important factor in the establishment of appropriate geochemical conditions. The rapid scavenging of Pb, compared to rates of U fixation under suboxic conditions, means that depositional μ values seldom approach the sea water figure of c.80,000. Owing to the largely independent geochemical behaviour of U and Pb, early diagenetic, late diagenetic and metamorphic recrystallisation may either partially disturb Pb/Pb and U-Pb systematics or effect complete resetting of radiometric ages. Consequently, results from geochronological studies should be interpreted only after due consideration of all available geological information. The extensive distribution of metamorphic and sedimentary carbonates throughout the geological record, coupled with the apparent robustness of Pb/Pb systematics, means that this technique can offer an effective means of event dating, stratigraphic correlation and time scale calibration, particularly in the Precambrian where independent age constraints are limited. In addition, the identification of late diagenetic recrystallisation ages offers exciting potential for constraining the diagenetic histories of sedimentary basins.

This study interprets the stratigraphic evolution of the mid-Cretaceous Urgonian Carbonate Platform sensu lato exposed in the northwestern Subalpine Chains of southeast France within a framework of dynamic environmental and climatic changes including relative sea-level fluctuations. Macroscopic observations of stratal geometries, especially stratal packaging within the succession revealed by differential weathering patterns have been integrated with the petrographic examination of limestone samples to assist in the interpretation of the carbonate succession. Seven hundred and twenty-eight rock samples were examined under the microscope as either thin sections or acetate peels and twenty five component parameters were used to define sediment composition within the data set. New and emerging analytical techniques have been used to interpret these data rather than the more traditional static fixed facies belts. Sequence stratigraphic concepts have been used to interpret platform evolution within the context of relative sea-level changes. In order to define microfacies and identify underlying environmental gradients computer optimized Jaccard's similarity coefficients matrices have been calculated between samples and component parameters using two computer programs SedUtil and JaccMat run on an IBM compatible Pentium personal computer. Computer optimized Jaccard's similarity coefficients similarity matrices are able to model both gradational and abrupt changes in facies composition in response to palaeogeographic and stratigraphic controls. Computer optimized similarity matrices between limestone compositional parameters from a series of logs show differences in the spatial and temporal nature of variations in sediment composition in response to environmental changes across the platform. The contrasts between the configurations of optimized similarity matrices are interpreted as indicating a palaeogeography at the beginning of the Urgonian characterised by a more strongly subsident basin to the southeast of the field area connected to the topographically-higher, tectonically more stable parts of the platform by low-angle slopes; the basin was eliminated by the end of the Urgonian. In addition optimized similarity matrices calculated between samples have been used to assist in defining eight-eight conventional microfacies assemblages which are described and illustrated using photomicrographs and pie-diagrams of modal composition. Despite the apparently conformable nature of the succession as observed in individual exposures, changes in the stratigraphy of the Urgonian platform sensu lata as traced along two southwest-northeast transects constructed through the Aravis and Bargy Chains indicate the existence of a low-angle distally steepened ramp topography at the top of the Hauterivian basement that sloped into a more strongly subsident basin. The Urgonian succession is divided into two third-order depositional sequences termed Depositional Sequence 1 and 2. In Depositional Sequence 1 all three systems tract are developed whereas Depositional Sequence 2 only contains transgressive and highstand systems tracts. The lowstand systems tract of Depositional Sequence 1 preserved in the southwest of the Aravis and Bargy Subalpine Chains is volumetrically significant, being dominated by hemipelagic deposits that shallow laterally to intertidal deposits to the northeast and also contain calciturbidites and two spectacular megabrecciahorizons. The two megabreccia horizons are interpreted as thin surficial collapse horizons formed by net extension on a very-low angle, previously kinematically stable slope, during fourth-fifth order relative sea-level falls. The lower sequence boundary of Depositional Sequence 1 passes laterally from being conformable in the southwest (deep-water basin) to being a major unconformity in the northeast ('inner' platform). However, this sequence boundary appears planar and concordantly bedded in the main and it is only in the northeastern Bargy Chain that it is observed as a erosional angular unconformity. The top of Depositional Sequence 1 is marked by the end of rudist lagoonal sediments and the deposition of beach facies which contain evidence of grain dissolution, overlain by Orbitolinidae foraminiferal rich horizons. By the top of Depositional Sequence 1 the low angle slope to the southwest had been totally subdued by sediment infilling and/or a decrease in the rate of differential subsidence. Depositional Sequence 1 was terminated by a comparatively minor relative sea-level fall followed by an immediate return to a major third-order relative sea-level rise and the basal transgressive deposits of Depositional 2. Depositional Sequence 2 re-establishes rudist sediment lagoonal deposition on the platform. It is often difficult to differentiate the transgressive and highstand systems tracts from one another in Depositional Sequence 2 and the boundary may be transitional. The upper sequence boundary of Depositional Sequence 2 is marked by a subaerial karst overlain by phosphatic greensands interpreted as reflecting a major relative sea-level fall and subsequent reflooding. Factors unique to carbonate depositional systems and their implications for the use of 'traditional' sequence stratigraphic models for carbonates are also discussed.

No description available.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Robert H. Pelton. Includes bibliographical references. Also available online.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Robert H. Pelton. Includes bibliographical references. Also available online.

Thesis (Ph.D.) in Chemical Engineering--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 192-196).