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PhD project in Historical Geology and Palaeontology: Origin of Proterozoic-Cambrian photosynthetic microbiota

Plant microfossils are extracted from strata of Upper Devonian age occurring at two previously uninvestigated localities in Eastern Canada and in the Canadian Arctic. The extraction procedure includes a new permanent palynological mounting technique using corn syrup and Permount, a synthetic resin. In addition, a method of eliminating by-product in residues after hydrofluoric acid, is also described. A number of miospore and acritarch form species are described and figured; nine new form species of miospores are proposed. The miospore species recovered from both localities indicate a geological age of early Upper Devonian (Frasnian) for the enclosing strata. A new way of assessing qualitative, regional palaeofloristic changes is provided by tabulation of morphological characteristics of individual miospores. The use of miospore species in defining Upper Devonian microfloral provinces and Upper Devonian-Lower Carboniferous migration of parent forms is demonstrated. / Thesis / Master of Science (MSc)

<p>The only direct evidence of past life is provided by fossils. Fossils tell us about the evolution of life on Earth and they give us clues concerning ancient environments. The Ediacaran Period (roughly 635-542 million years ago) is characterised by the appearance and diversification of various microbiota and also the diversification of metazoans. Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran sedimentary successions in the Officer Basin in South Australia. Acritarch assemblages from the Giles 1 and Murnaroo 1 drillcores show a wide morphological disparity and are taxonomically diverse. Assemblages change over short stratigraphic intervals which enables the recognition of different biozones. The presence of taxa common between Australia, Siberia, Baltica and China provides a means for global correlation of the Ediacaran System. Examination of the wall ultrastructure of several acritarch specimens by use of transmission electron microscopy reveals a complexity in the cell wall that is not seen in prokaryotes but is indicative in some cases of particular clades of microalgae. Wall ultrastructures range from single-layered to three- and four-layered and from homogeneous to porous. The wall ultrastructure can be used to assess biological affinities and the affinities of the studied taxa in relation to green algae, dinoflagellates and metazoans are discussed. However, before taxonomic interpretations can be made with confidence, an understanding of taphonomic degradation of microorganisms is required. With focus on illustrated specimens, one part of this thesis explains what happens to an acritarch as it undergoes various types of degradation and why an understanding of these processes is important for taxonomic identification. A meteorite impact in South Australia spread an ejecta layer over a 550 km radius area. This ejecta layer is recognised in subsurface drillcores and provides an independent stratigraphic marker horizon that supports an acritarch-based correlation.</p>

In this study diatom distribution within the lower Save River, Mozambique, has been identified from surface sediments, surface water, mangrove cortex and buried sediments. Sandy units, bracketing a geographically extensive clay layer, have been dated with optical stimulated luminescence (OSL). Diatom analysis has been used to interpret the spatial salinity gradient and to discuss taphonomic processes within the delta. Previously, one study has been performed in the investigated area and it is of great importance to continue to identify diatom distributions since siliceous microfossils are widely used for paleoenvironmental research. Two diatom taxa, which were not possible to classify to species level have been identified; Cyclotella sp. and Diploneis sp. It is suggested that these represent species not earlier described; however they are assigned a brackish water affinity. Diatom analysis from surface water, surface sediments and mangrove cortex indicate a transition from ocean water to a dominance of freshwater taxa c. 10 km upstream the delta front. Further, ratios between marine/brackish taxa for samples from surface water and surface sediments do not correspond. It is therefore suggested that diatoms in surface sediments underestimate prevailing salinity conditions in water. In the investigated area extensive taphonomic processes seem to have large impact on diatom frustules in sediments and may bias interpretations. Therefore it is recommended to carefully investigate geology, geomorphology and vegetation before diatom analysis is applied in studies of delta paleoenvironments.

Botryococcus braunii is a microscopic, colonial green alga that may be found in fresh and brackish waters throughout the globe. B. braunii is unique in that it constitutively synthesises and secretes copious amounts of various long-chain (C23-C40) hydrocarbons, generically termed “botryococcenes”. Botryococcanes, the hydrogenated forms of botryococcenes, comprise 1% of the fossil hydrocarbons found in petroleum deposits and in oil-shales. Microfossils identified as Botryococcus by optical and scanning electron microscopy are also abundant in these strata, but the actual identity and precise relationship between these microfossils and extant Botryococcus species is not known. In this investigation, the relationship between living Botryococcus algae and microfossils identified as Botryococcus using traditional palaeontological analysis and light-microscopy was investigated by analysis of ancient DNA (aDNA). The material used was identified in sediments from Boswell Lake (British Columbia, Canada), a Holocene lake that had remained undisturbed since the glacial retreat. New flow-cytometry methods were developed to rapidly purify enough of the relevant microfossils, from which aDNA was extracted and sequenced. Pollen grains were purified using the same flow-cytometry method and from the same horizons as the Botryococcus microfossils and used to age the sedimentary horizons by 14C radiocarbon dating. Samples of the purified microfossils were imaged by scanning electron microscopy for comparison with published images of fossils identified as Botryococcus from kerogens. In addition, metaDNA from the relevant horizons was extracted and sequenced by NGS, and a chemical analysis for botryococcene derivatives performed using two-dimensional gas chromatography (2D-GC). The genomic analyses show that the sub-fossils identified in Boswell Lake are likely to be representatives of B. braunii, race B. The geochemical analysis identified hydrocarbons that migrate as botryococcenes on 2D-GC in the strata whence the sub-fossils were purified. The SEM images indicate that the microfossils purified from Boswell Lake have similar morphologies to those found in kerogens. Taken together, these data strongly support the proposition that petroleum and kerogen deposits are unusually rich in B. braunii and that these algae have a lineage potentially dating 500 million years. The metagenomic analysis enabled similar conclusions to be reached regarding the presence of B. braunii within the sediment, without the need for targeted microfossil purification. While this analysis was less precise due to the under-representation of algal genomes in the public sequence databases, the metagenomics approach employed was particularly well suited to the temporal analysis of prokaryotic microcosms within Lake Boswell, the succession of which could be associated with periods of climatic variation. The analytical methods described herein are generally applicable to understanding microbial systems over geological periods, and may be used to generate important insights into the cause and effect relationships between microbial populations and environmental perturbation.

The only direct evidence of past life is provided by fossils. Fossils tell us about the evolution of life on Earth and they give us clues concerning ancient environments. The Ediacaran Period (roughly 635-542 million years ago) is characterised by the appearance and diversification of various microbiota and also the diversification of metazoans. Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran sedimentary successions in the Officer Basin in South Australia. Acritarch assemblages from the Giles 1 and Murnaroo 1 drillcores show a wide morphological disparity and are taxonomically diverse. Assemblages change over short stratigraphic intervals which enables the recognition of different biozones. The presence of taxa common between Australia, Siberia, Baltica and China provides a means for global correlation of the Ediacaran System. Examination of the wall ultrastructure of several acritarch specimens by use of transmission electron microscopy reveals a complexity in the cell wall that is not seen in prokaryotes but is indicative in some cases of particular clades of microalgae. Wall ultrastructures range from single-layered to three- and four-layered and from homogeneous to porous. The wall ultrastructure can be used to assess biological affinities and the affinities of the studied taxa in relation to green algae, dinoflagellates and metazoans are discussed. However, before taxonomic interpretations can be made with confidence, an understanding of taphonomic degradation of microorganisms is required. With focus on illustrated specimens, one part of this thesis explains what happens to an acritarch as it undergoes various types of degradation and why an understanding of these processes is important for taxonomic identification. A meteorite impact in South Australia spread an ejecta layer over a 550 km radius area. This ejecta layer is recognised in subsurface drillcores and provides an independent stratigraphic marker horizon that supports an acritarch-based correlation.

Past earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great AD 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here, we infer heterogeneous slip for the Cascadia margin in AD 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3-D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extents, the more precise subsidence estimates are best explained by a model with along-strike slip heterogeneity, with multiple patches of high moment release separated by areas of low moment release. For example, in AD 1700 there was very little slip near Alsea Bay, Oregon (~ 44.5°N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for precise, high-quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47°N), southernmost Oregon, and northern California (south of 43°N), where slip distributions of prehistoric earthquakes are poorly constrained. / Graduate

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