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- Claybourn, Thomas M., 1989-
(author)
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Biostratigraphy and Systematics of Cambrian Small Shelly Fossils from East Antarctica and South Australia
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The remote lower Cambrian Byrd group of sedimentary rocks from East Antarctica has been studied intermittently since its discovery over a century ago. Previous insights into the trilobites and archaeocyaths indicated a close correlation to the sedimentary sequences of South Australia. The lowest unit of the Byrd Group is the fossiliferous Shackleton Limestone which overlies the Neoproterozoic metamorphic rocks of the Beardmore Group and is representative of a long period of carbonate shelf formation on a passive margin with the palaeo-Pacific. This was truncated by marine transgression and the deposition of the deeper-water calcareous siltstones of the fossiliferous Holyoake Formation. This is overlain by the Starshot Formation and all three units are cross-cut by the Douglas Conglomerate, marking the start of a collisional tectonic regime between the East Gondwana and palaeo-Pacific plates. The first systematically sampled and analysed sections through the carbonate Shackleton Limestone and argillaceous Holyoake Formation has yielded a new fauna of small primarily phosphatic and secondarily phosphatised shelly fossils. The abundant molluscs, brachiopods and tommotiids are reported here. These findings are ideal for correlating this section to the fossil biozones of South Australia, including the Dailyatia odyssei small shelly fossil Zone and the Pararaia janeae trilobite Zone. Chemostratigraphic data from three sections preserve the profiles of two major stable carbon isotope excursions: the Mingxinsi Carbon Isotope Excursion and the Archaeocyathid Extinction Carbon isotope Excursion. The combination of these two lines of evidence are a strong indicator for Cambrian Series 2, early-mid Stage 4. This is corroborated by newly described D. odyssei-P. janeae Zone small shelly fossils from the carbonate clasts from the Cambrian Stage 4 White Point Conglomerate of South Australia which bear strong similarity to the fauna of the Shackleton Limestone. Palaeobiogeographically the fauna recovered from the Byrd Group is similar to the East Gondwanan region of South Australia, with similar brachiopod assemblages to those recovered from the Xinji Formation of North China and similar molluscan assemblages to the Bastion Formation of North-East Greenland.
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| 2. |
- Claybourn, Thomas, 1989-
(author)
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Cambrian Series 2 (Stages 3-4) Small Shelly Fossils from East Antarctica
- 2017
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Licentiate thesis (other academic/artistic)abstract
- An assemblage of Cambrian Series 2, Stages 3-4 small shelly fossils has been recovered from the Shackleton Limestone and Holyoake Formations of East Antarctica. Small shelly fossils from the early Cambrian are an important window into the world of Cambrian palaeobiology, biostratigraphy and biogeography. The aim of this thesis is to add this view the previously under-described fauna from East Antarctica. The molluscs from the Shackleton Limestone prove important in biostratigraphic correlation to South Australia, North-East Greenland, North China and South China. Morphometric analysis of these has also yielded insights into inter- and intraspecific variation in the helcionelloid mollusc Mackinnonia. The remaining fauna contains certain key taxa for biostratigraphic comparison, such as the tommotiid Dailyatia odyssei, the bradoriid arthropod Spinospitella coronata and the brachiopod Karathele yokensis. This allows for direct correlation with the Cambrian Series 2 Stages 3-4 Dailyatia odyssei Zone of South Australia, further strengthening an already recognised close relationship between the faunas of East Antarctica and South Australia.
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| 3. |
- Bassett-Butt, Lewis, 1990-
(author)
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The Cambrian lophotrochozoans of the Transantarctic Mountains, Antarctica
- 2015
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Licentiate thesis (other academic/artistic)abstract
- The origin of many lophotrochozoan groups can be traced to “small shelly fossil” (SSF) faunas of the Early Cambrian. Antarctica is a key region of study, due to the continent’s known close geographical proximity to well-studied Australian and Indian basins in in the Cambrian. Few studies have focused on this region however, due to a paucity of data. Re-examination of camenellan sclerites from the Early Cambrian Shackleton Limestone of the Churchill Mountains of Antarctica has revealed a previously unidentified species of Dailyatia in the formation, co-occurring alongside previously described Dailyatia odyssei Evans and Rowell, 1990, as in the Arrowie Basin of Australia. Re-examination of material previously described as Kennardia sp. A and Kennardia sp. B has indicated that these taxa can likely be synonymized as a second species of Dailyatia. Dailyatia sclerites were also found in the temporally equivalent “Schneider Hills Limestone” formation, which cropsout in the Argentina Range of Antarctica. These specimens appear to belongto a third species of Dailyatia, suggesting that the spatial distribution of tommotiids in the Early Cambrian was more complex than previously recognized, and that the group may be useful in future biostratigraphic studies. A study ofthe Middle Cambrian (Drumian Stage) Nelson Limestone Formation of the Neptune Range, Antarctica has revealed a moderately diverse brachiopod and trilobite fauna. The brachiopods have strong faunal links to taxa from South Australia and India, as well as other parts of the Antarctic province, fitting independent strong evidence for a united East Gondwanan region in the Middle Cambrian. An unidentified camenellan tommotiid sclerite is also described from the Nelson Limestone. This extends the worldwide temporal range of the tommotiid clade into the Drumian Stage, and suggests that more basal members of the brachiopod stem-group survived to form part of a more diverse Middle Cambrian fauna.
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| 4. |
- Larsson, Cecilia M
(author)
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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
- 2012
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Doctoral thesis (other academic/artistic)abstract
- The emergence and radiation of metazoan body plans around the Precambrian/Cambrian boundary, some 500-600 million years ago, seems to be concordant with the appearance and diversification of preservable hard parts. Several Precambrian soft-bodied, multicellular organisms most likely represent stem-group bilaterians, but their fossil record is rather sparse. In contrast, the Cambrian fossil record is comparably rich – comprising hard part, trace fossil and delicate soft tissue preservation – and most animal phyla that we know of today had evolved by the end of the Cambrian. Consequently, this time represents an important period in the early evolution of metazoan life forms. Most skeletal remnants of invertebrate organisms from this period are preserved in incomplete, disarticulated sclerite assemblages, and the true architecture of the original skeletal structure, the scleritome, may therefore be hard to discern. Many scleritomous taxa have been suggested to be members of the lophotrochozoan clade, while their exact position within this group remains unclear. Such taxa are often referred to as Problematica. This thesis deals with some problematic scleritomous early Cambrian lophotrochozoans, and as such also addresses the dilemmas of scleritome reconstructions. In the first part, completely disarticulated calcareous sclerites from the lower Cambrian of North Greenland are described as Trachyplax arctica. Hypothetical scleritome reconstruction alternatives and comparisons to other scleritome-bearing taxa are discussed, but the lack of articulated material obscures any satisfactory conclusions regarding phylogenetic affinities and the original morphology of the organism. The other part of the thesis focuses on some minute, organophosphatic scleritomous metazoans, tommotiids, found in lower Cambrian limestone successions in South Australia – Paterimitra pyramidalis and Kulparina rostrata – their scleritome architecture and their phylogenetic relationship with paterinid brachiopods. The oldest brachiopod from South Australia, Askepasma saproconcha, and the slightly younger Askepasma toddense are also described and discussed. Based on articulated specimens, recently described partial scleritomes of the tommotiid Eccentrotheca helenia and similarities in shell ultrastructure with both Eccentrotheca and Askepasma, Paterimitra is interpreted as a stem-group brachiopod and reconstructed as a bilaterally symmetrical, sessile, filter feeder with a tubular/conical scleritome. The morphological similarities with Paterimitra point in the same direction for the slightly older Kulparina.
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