- Title
- Advancement in speleothems petrography and microstratig-raphy as proxies of climate and environmental changes
- Creator
- Vanghi, Valentina
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor Philosophy (PhD)
- Description
- Stalagmites are acclaimed accurate proxies of climate variability because they can be precisely dated with radiometric techniques and preserve in their chemical and physical properties records of changes at sub-annual to orbital scales. Over the past two decades, stalagmite records have been used to reconstruct global teleconnections and synchronicity of events. At the same time, traditional proxies applications have not advanced as much as the development of new proxies has. The main goal of this thesis has been to fill this gap, by advancing knowledge on the physical aspects of stalagmites and other cave secondary mineral deposits (speleothems) that can be then be directly linked to climate and environmental processes. This main goal has been accomplished by using both conventional optical petrography and innovative, non-conventional methods such as Synchrotron Radiation based micro-XRF (SR-μXRF) and Neutron scattering. SR-μXRF has been demonstrated to be the most apt technique to complement petrography in the investigation of speleothems, which have been here considered for their association with a unique paleontological finding. In this thesis, a petrographic, morphologic and microstratigraphic study of some coralloid formations both directly and indirectly associated with the complete skeleton of an early Neanderthal man preserved in in Lamalunga cave (Southern Italy) is presented to prove the reliability of this speleothem as archive of palaeo-hydroclimate. The hypothesis pre-sented in this Thesis is that coralloids formation is linked to hydroaerosol generated by the frag-mentation of cave drip combined to enhanced apical evaporation. Thus, their sub-micrometre scale layers preserve records of alternating dry and wet periods. Because of the small scale of the microstratigraphic elements, only SR-μXRF could be used to obtain elemental mapping with the desired high spatial resolution. SR-μXRF maps support the genetic hypothesis here formulated, and demonstrates that the incorporation and distribution of trace element and organic material are related to fabric changes. The overarching conclusion of this investigation is that coralloids, de-spite their small size are one of the best tools we have to reconstruct the climate and environmental context of early humans in Southern Italy. This will contribute to consolidate and improve the link between speleothem science and paleoanthropology and archaeology. The absence of stalagmites in Lamalunga cave, which may prevent obtaining a long, continuous and exhaustive palaeoclimate record, has led to the exploration of possible analogue in a highly decorated cave at the same longitude in Central Italy. Stalagmites from Frasassi cave have then been selected and studied because at both Frasassi and Lamalunga locations, modern precipita-tions have similar δ¹⁸O composition, a phenomenon that is here assumed to have been the same throughout the Quaternary. Modern rainfalls isotopic signal variations, in the Italian peninsula, do not show a longitudinal gradient along the Adriatic coast, where both Lamalunga and Frasassi are located. With the aim of producing a stable isotopic record for Frasassi cave that could be used to complement the palaeoclimate reconstruction from Lamalunga coralloids, the first and necessary foundation has been benchmarking on the petrography the geochemical record of Frasassi cave. This ultimately allowed to interpret the δ¹³C signal of Frasassi stalagmite as reflect-ing local/regional scale humid/arid cycles, which coincide well with changes in petrography. By contrast, the δ¹⁸O signal does not follow petrographic changes and it is here concluded that it does not reflect drip rate variability (infiltration). It is highly probable that the δ¹⁸O reflects a mixed signal that of water stored in the aquifer for a relatively long time, “homogenized” through the years, rather than the immediate response to recharge. The interpretation of Frasassi stalagmite record highlights that, as in Lamalunga coralloids, fabrics best identify an immediate response of the speleothem archive to hydrological changes. Because of their importance, the analysis of speleothem fabrics has been pushed beyond the con-ventional microscopy and spectroscopy methods by employing for the first time neutron scatter-ing techniques. This can only been regarded as a pilot study within this Thesis, however the pre-liminary results are promising. The aim was to help recognizing features that may indicate path-ways of crystallization. Neutron diffraction data produced a compilation of different preferred orientations for various types of speleothems characterized by diverse fabrics, which hints at an internal organization characterized by various degrees of rotation of the units composing crystals most likely around a common c-axis. Additional information comes from the application of small-angle neutron scattering (SANS), on the same specimens, which reveals the presence of mass or surface fractals. Tentatively, this is ascribed at the presence of nanocrystals. Both results pave the way to a re-evaluation of speleothem crystallization and, thus, incorporation of geochemical data when non-classical pathways of nucleation and growth influenced speleothem capture of climate change.
- Subject
- coralloid speleothems; fabrics; calcite; hydroaerosol; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1388215
- Identifier
- uon:32733
- Rights
- Copyright 2018 Valentina Vanghi
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 8 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 337 KB | Adobe Acrobat PDF | View Details Download |