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Integrated chronostratigraphy of the lower Cambrian Byrd Group, Transantarctic Mountains
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Antarctica and Australia were sutured together straddling the equator during the major pulse of animal biodiversification associated with the Cambrian radiation. However, lack of detailed systematic sampling of lower Cambrian sedimentary packages from Antarctica has significantly impeded precise age determination and correlation with other Cambrian paleocontinents, especially with other parts of East Gondwana. Here were present new, integrated biostratigraphic and chemostratigraphic (δ13C isotopes) data from three stratigraphic sections measured through autochthonous shallow water carbonates (including archaeocyath-microbial bioherms) from the lower Cambrian Byrd Group in the Transantarctic Mountains. Recovered shelly fossil assemblages (brachiopods, tommotiids, molluscs, trilobites) from the Holyoake and Churchill Ranges include conspecific taxa previously described from Hawker Group rocks in the Arrowie Basin of South Australia facilitating direct correlation with the upper Dailyatia odyssei biozone. Synchronous chemostratigraphic data capture a distinctive positive 𝛿13C excursion in the Churchill Range interpreted as the global Mingxinsi Carbon Isotope Excursion (MICE) peak. A succeeding gradual negative 𝛿13C excursion captured in the Churchill and Holyoake sections is interpreted as the global Archaeocyathid Extinction Carbon Isotope Excursion (AECE) event. There is no chemostratigraphic evidence for the large Redlichiid-Olenellid Extinction Carbon Isotope Excursion (ROECE) negative event that straddles and defines the Cambrian Stage 4 – Miaolingian boundary. Hence, the integrated faunal and new chemostratigraphic data presented herein strongly support a Cambrian Stage 4 age for the upper Shackleton Limestone – Holyoake Formation – Starshot Formation succession of the Byrd Group.

Keywords [en]
Cambrian Series 2, East Antarctica, Biostratigraphy, Chemostratigraphy, Carbon Isotopes
National Category
Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-405194OAI: oai:DiVA.org:uu-405194DiVA, id: diva2:1396873
Available from: 2020-02-26 Created: 2020-02-26 Last updated: 2020-02-26
In thesis
1. Biostratigraphy and Systematics of Cambrian Small Shelly Fossils from East Antarctica and South Australia
Open this publication in new window or tab >>Biostratigraphy and Systematics of Cambrian Small Shelly Fossils from East Antarctica and South Australia
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2021. p. 63
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1907
Keywords
Cambrian, Biostratigraphy, Systematics, East Antarctica, Small Shelly Fossils
National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-405216 (URN)978-91-513-0880-7 (ISBN)
Public defence
2021-02-26, Hambergsalen, Geocentrum, Villavägen 16,, 752 36 Uppsala, 10:00 (English)
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Supervisors
Available from: 2021-01-29 Created: 2020-02-26 Last updated: 2021-03-04

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Citation style
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