Provenance investigations of Mesozoic basin infill histories in the Irish and Celtic Seas and developments in Raman spectroscopy applications for earth science research

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McCarthy, Odhrán
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University College Cork
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Part 1: Sedimentary provenance analysis is a powerful tool for interrogating the history of sedimentary basins. In this study, Quantitative provenance analysis (QPA) is applied to interpret the sedimentary infill of North Celtic Sea Basin, Saint George’s Channel Basin, Fastnet Basin and Goban Spur Basin offshore of Irelands southeast coast. This research was conducted to further develop understanding of the sediment routing and infill in these basins and therefor provide insights to basin connectivity. Basin structure are important for further economic developments in carbon storage, hydrocarbon exploration and mapping of reservoir fairways in the Irish and Celtic Sea. Prior to this study, all published hypothesis addressing the provenance of Mesozoic sediments in the Irish and Celtic Sea basins have considered sediment sourcing and routing from the post Caledonian cover sequences and basement rocks of the Irish and Welsh Massifs. Multiple environmental and tectonic events took place during the Mesozoic in the Irish and Celtic sea region. However the impact of these events has not been accounted for. To test these hypotheses as well as the impact of environmental and tectonic change on the provenance of basin infill, two studies were conducted on; i) Middle Jurassic to Upper Cretaceous successions and, ii) Triassic to Lower Jurassic successions in these basins. A multi-proxy investigation of detrital zircon, white mica and apatite geochronology along with heavy mineral analysis and petrographic methods were chosen. Results from these find evidence that marine transgression-regression cycles and tectonism exhibited a first-order control on sediment routing and provenance throughout the Mesozoic. Significantly, these findings show that sediment routing and sourcing was not principally derived from the Irish and Welsh Massifs. Four distinct provenance switches are detected throughout the 185 million years of basin evolution. Contrary to previous hypothesis, the Irish and Welsh Massifs are only identified as the primary source during the Late Jurassic and Early Cretaceous. Findings of these two bodies of research have fundamentally changed our understanding of basin infill and sedimentary provenance in the Irish and Celtic Sea basins during the Mesozoic Era. More broadly, this study can be used as a case study for the impacts of environmental or tectonic activity on sedimentary provenance. Part 2: Raman spectroscopy is a developing tool in sedimentary provenance analysis as well as the geosciences more broadly. Developing the accessibility and interoperability of this tool and derived data is of benefit to the broader geo-science community, particularly within petrographic studies. Its appeal as a multi-faceted analytical tool is sometimes overlooked due to financial, computational or access barriers. Data processing and visualisation of large Raman data sets or mapped data sets can be an additional challenge as standard freeware has a limited capacity to processes these files or lacks a rasterization capability (e.g., R, spectralgryph and crystal sleuth). To overcome this challenge and to capitalise on recent developments in Raman spectroscopy, the fourth chapter in this thesis presents an in-house, automated Raman peak analysis and rasterization freeware called “Ramaster”. To demonstrate the potential applications for this program, two case studies were chosen including; i) Raman maps of detrital zircon grains and, ii) characterisation of phosphatised dermal tissues from 40 Ma anuran (frog) skin. Ramaster significantly saved processing time and produced detailed maps of zircon growth structures and phosphatised anuran fossil tissue structures. This work has excellent potential for future development and offers a simple but effective solution for the rasterisation of mapped Raman data sets. Part 3: Constraining the chronology of tectonic events is a ubiquitous challenge for geoscience researchers. Investigatory tools available for tectonic research are typically qualitative and lack workable data sets (e.g., Cathodoluminescence imaging) or are destructive to the sample material (e.g., LA-ICP-MS). Today there exists a broad range mineral characterization and discrimination techniques for which Raman spectroscopy is a developing tool. This study aims to demonstrate the application of Raman spectroscopy in differentiating a ubiquitous mineral throughout the earths lithosphere (quartz), which has applications in provenance research as well as other economic, social and scientific fields. In the fifth chapter of this thesis, Raman and Fluorescence spectroscopy are applied to differentiate multiple generations of vein-hosted quartz. We find that Raman spectroscopy analysis can be used to differentiate different multiple generations of quartz as well as providing insights to the origin of hydrothermal fluids, tectonic deformation histories. The differentiation of alpha quartz has not been demonstrated in an in-situ sample to date and represents a significant development in the field of mineral discrimination techniques.
Provenance , Geochronology , Celtic Sea Basin , Irish Sea Basin , Raman , Zircon , Heavy minerals
McCarthy, O. 2021. Provenance investigations of Mesozoic basin infill histories in the Irish and Celtic Seas and developments in Raman spectroscopy applications for earth science research. PhD Thesis, University College Cork.