A Geochemical Comparison of Southern African Stromatolites and Stromatolite Pools
- Authors: Dodd, Carla
- Date: 2020
- Subjects: Stromatolites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48235 , vital:40527
- Description: Microbialite accretion takes place via either mineral precipitation, the trapping and binding of mineral and sediment grains, or a combination of the two. Recently, the geochemistry of carbonate deposits, including microbialites, has been used to reconstruct palaeoenvironments and infer biogenicity. Numerous modern stromatolite (layered microbialites) systems are located on the southern African coastline and are formed predominantly by mineral precipitation with minor detrital input. In order to better understand the environmental and biological processes influencing the formation of microbialites, the geochemistry of southern African coastalstromatolites is examined. This is done by a spatial comparison of the hydrochemistry as well as the major and trace element geochemistry of various coastal stromatolite systems. The influence of the underlying geology on the composition of the stromatolites forms a particular focus of the study. In addition, the effect of metazoans on the micro-fabrics and sediment incorporation into the stromatolite matrix is assessed. Finally, the trace element geochemistry of active, inactive, and ancient stromatolites is compared with a speleothem sample in order to test the validity of using trace elements as a means to determine biogenicity of deposition. Results show that the bulk geochemistry of the South African stromatolites is not a simple function of the associated bedrock lithologies, although certain parallels do exist. It was found that metazoans indirectly influence sediment incorporation by increasing porosity and thereby accommodation space for detrital input. Furthermore, trace element signatures could not be directly attributed to microbial influence in the deposition of the carbonates. Ultimately, this study provides valuable insights into the formation processes of the active South African stromatolites and the use of trace elements as a geochemical tool to investigate the evolution of life and determine past environmental conditions.
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- Date Issued: 2020
Microhabitat and biotic structure of stromatolite formations
- Authors: Weston, Ross-Lynne Alida
- Date: 2018
- Subjects: Stromatolites , Microbial mats Sedimentary structures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/17493 , vital:28358
- Description: Stromatolites are among the oldest types of microbial formations. In contrast to their ancient counterparts, many modern marine stromatolites have a coarser internal structure and host a diverse eukaryotic community. Different mesofabric structures are found within stromatolite formations which may provide microhabitat opportunities for organisms. Therefore, the first aim of this study was to investigate how the microalgal (including Bacillariophyta, Chlorophyta and cyanobacteria) community contributes towards the differences observed amongst mesofabric structures in terms of depth profiles and layering at representative stromatolites forming along the Port Elizabeth coastline in South Africa. The second aim was to investigate how the invertebrate community changes between mesofabric types. This was achieved by comparing the proportional abundances of each of the major microalgal classes between the different mesofabric types and depth profiles. Additionally, the invertebrates found within samples collected were identified and counted. These were related to site and environmental characteristics using multivariate modelling. Clear variability in terms of proportional abundance was apparent between microhabitats and with depth. Coarser, more-bioturbated types had a higher bacillariophyte biomass than smoother types. Invertebrate abundance was generally higher in coarser mats. However, one of the finer, well-laminated types had surprisingly more invertebrates than expected, but only in summer. The changes in microalgal and invertebrate community distribution varied seasonally. More microalgae were found in summer and more invertebrates were found in winter. Microalgae distribution was driven by mesofabric features whereas invertebrate distribution was attributed to resource changes. The implications of this study are in terms of the role of microalgae as ecosystem engineers in driving microhabitat differences. The microhabitats provide opportunities for colonisation by invertebrates.
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- Date Issued: 2018