Exploring the impact of stalagmite microstructures on climate proxies using combined imaging and element mapping techniques
This Master's project was designed for Kristian Bergh who started the Master's program in Earth sciences, UiB, fall 2024. The Master's project is given by the research group Quaternary geology & paleo climate.
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Project description
Background: Cave stalagmites are well-established archives providing crucial information about climate changes in the past, with excellent age control from radiometric dating methods. In the last decades, a wide range of techniques has been developed to analyse speleothems and derive proxies for paleoclimate reconstructions. Among these methods, trace element distributions are known to be related to several physical and biological factors, offering proxies for paleohydrological and environmental conditions. Stalagmite crystal fabrics can vary over time dependent on growth conditions and are expected to both influence trace element distributions and be affected by them (e.g., via defects in the mineral structure). Understanding these relationships is vital for improving proxy interpretation in speleothems. This master project aims to investigate the relationship between stalagmite microstructures and trace element distributions by using a novel combination of Scanning Electron Microscope CathodoLuminescence (SEM-CL) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).
SEM-CL is commonly used to investigate cementation and diagenesis processes, analyse growth and dissolution features, and find defect microstructures in rocks and minerals. LA-ICP-MS permits the fast mapping of trace element distributions on surfaces at micron-scale, hence potentially allowing annual growth layer resolution, and with detection limits down to ppb levels. By combining these techniques for the first time, this project aims to identify different types of microstructures in stalagmites and constrain their origins and relationships with the trace element distribution. The results will contribute to a deeper understanding of how these factors might influence trace elements in stalagmites, but also other classically employed proxies.
Research questions:
-What are the spatial relationships between CL features and trace element distribution in stalagmites?
-What is the origin of the observed microstructures and of the trace element distributions?
-How do the results affect our interpretations of the data obtained from commonly used techniques like stable isotope analyses, U-Th dating, and microthermometry on fluid inclusions?
Work plan:
The plan for this project starts with the selection of the samples among a collection of worldwide stalagmites (e.g. Borneo, South Africa, etc.) and with sample preparation in polished thick sections. These samples will be characterized through optical microscope and SEM (ELMILAB) in order to select the best areas where to perform the following analyses. Finally, the student will perform SEM-CL and LA-ICP-MS. The results from both techniques will be processed with a statistical approach and compared to other data from the literature.
CL picture of a stalagmite from Borneo
Proposed course plan during the master's degree (60 ECTS)
Fall semester:
GEOV222 (10P)
GEOV217 (10P)
GEOV324 (5P)
Spring semester:
GEOV302 (10P)
GEOV316 (10P)
GEOV342 (10P)
Fall semester:
GEOV300 (5P)
Field-, lab- and analysis work
Lab work ~ 4-6 months, including sample preparation, optical microscope analysis, SEM CL analysis and LA ICP MS
analysis.