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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The application of automated mineralogy to the provenance study of red-bed successions : a case study from the Permo-Triassic of SW England

McVicar Wright, Sarita Eleanor January 2014 (has links)
This thesis reviews heavy mineral separation techniques for red-bed heavy mineral provenance studies. It demonstrates the effectiveness of automated mineralogy for mineral comparisons and targeted mineral analysis, resulting in new provenance history conclusions for the Permo-Triassic of SW England. The methodology was developed to remove iron-oxide coatings from grains and provide optimal separation of heavy mineral concentrates in comparison to hydroseparation and panning. Step-wise methodology iterations were validated at each stage using the QEMSCAN (Quantitative Evaluation of Minerals by SCANing electron microscopy). The QEMSCAN works in a similar way to the SEM (scanning electron microscope) and electron-microprobe. Four EDS (energy dispersive spectroscopy) detectors measured X-rays, secondary electrons and back-scattered electrons from the sample. The software allocated these to defined geochemical SIP (species identification protocol) categories. The SIP was back-validated using the electron-microprobe, XRD (X-ray diffraction), microscopy and SEM. QEMSCAN was the primary analysis technique. The results included false colour mineral maps and semi-quantitative statistics for the SIP categories. This enabled targeted mineral analysis with supporting techniques. The methodology was applied to the Permo-Triassic of SW England. The QEMSCAN was able to pick up small scale and large scale heavy mineral provenance trends. Case study 1 showed regional heavy mineral trends and allowed lithological correlation of outliers. Case study 2 used heavy minerals to confirm contemporaneous structural evolution and the base of the Upper Permian in South Devon. Case study 3 allowed a re-evaluation of the base Triassic. Case study 4 targeted biotite minerals at Corbyn's Head. Case study 5 reviewed local vertical and horizontal trends in comparison to regional trends. This has significant oil and gas exploration implications as it gives confidence in correlating deposits over 10s km and can be applied to North Sea barren red-beds. Finally, some mineral firsts, including rammelsbergite and a topaz rhyolite were identified.
2

Post-IR IRSL dating of K-feldspar from Loess at Lowland Point, SW England : Developing a Chronology for Past Climate Records / Post-IR IRSL datering av kalifältspat från löss vid Lowland Point, sydvästra England : utveckling av kronologi för tidigare klimatregister

Törnqvist, Elin January 2022 (has links)
Loess deposits are terrestrial clastic sediments derived from aeolian deposition. Loess is transported in periglacial conditions and was mainly deposited in cold environments around glaciers during the Quaternary period. To be able to understand and interpret past climate and how it was changing, loess deposits can be used as an indicator for example wind circulation and dustiness in the atmosphere. However, good independent chronological control is essential for using loess as a past climate archive. This study has examined loess from Lowland Point in the southwest of England. The loess at Lowland Point is relatively thin at 180 cm compared with more studied loess deposits further east on continental Europe. To be able to date the k-feldspar mineral grains from the loess deposit at Lowland Point, two values should be constrained for each sample: the equivalent dose (DE), a quantitative factor of the amount of energy accumulated by the mineral grain during burial from ionising radiation, and the dose rate (DR), a rate of ionising radiation absorbed from the surrounding environment per year. By using the post infrared-infrared stimulated luminescence (post-IR IRSL) method, the DE values were obtained, and by examine radioactive isotopes in the samples, the DR values were attained. The results of each average age per sample depth was then identified and the loess deposit could be determined to the age about 10.8-22.4 ka, which is suggested to have been deposited by meltwater from the British Irish Ice Sheet and permafrost. / Lössjordar är avlagringar av markbundna klastiska sediment härledda från eolisk deposition och transporteras under periglaciala förhållanden för att huvudsakligen deponeras i kalla miljöer runt glaciärer under kvartärperioden. För att kunna förstå och tolka tidigare klimat och hur det förändrades kan lössavlagringar användas som en indikation över till exempel vindcirkulation och dammighet i atmosfären. Denna studie har undersökt löss från Lowland Point i sydvästra England. Lössen vid Lowland Point är relativt tunn, med en tjocklek på 180 cm, jämfört med mer studerade lössjordar. För att kunna datera kalifältspat från lössjorden vid Lowland Point var förhållandet mellan två komponenter av betydelse; ekvivalentdosen (DE), en kvantitativ faktor för den mängd energi som mineralkornet ackumulerar vid sedimentering, och doshastigheten (DR), en hastighet av den mängd energi som absorberas i den omgivande miljön per år. Genom att använda metoden post infraröd-infraröd stimulerad luminescens (post-IR IRSL) erhölls DE-värden och genom att undersöka radioaktiva isotoper i proverna hittades DR-värden. Resultaten av varje medelålder per provdjup identifierades sedan och lössavlagringen kunde bestämmas till en ålder av cirka 10,8–22,4 ka, vilket indikerar en möjlig avsättning av smältvatten från det brittiska irländska istäcket och permafrost.

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