Paleoenvironmental implications of Permo-Triassic geographic shift in oxygen stable isotope (δ18Op) from tetrapod bone in the South African Karoo Basin

Kevin Rey, Romain Amiot, François Fourel, Julie Luyt, Frédéric Fluteau, Christophe Lécuyer

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Abstract

The Beaufort Group of the Main Karoo Basin of South Africa provides an uninterrupted record of fluvio-lacustrine
sedimentation from the Middle Permian to the Middle Triassic and covers an area of approximately 200,000 km2,
about 20% of the country’s surface area. A diverse range of vertebrate taxa including fish, therapsids, amphibians,
archosauromorphs and parareptiles, has been recovered from this rock succession and provides an ideal
sampleset to investigate temporal and geographical variations of local hydrology using stable isotopes. Questions
relating to temporal and biological variations in oxygen stable isotope ratios of apatite phosphate (δ18Op) in
Beaufort tetrapod taxa have previously been addressed, but geographic variation of bioapatite-recorded δ18Op
across the Permo-Triassic of South Africa has not yet been studied. Here we highlight variations in δ18Op
recorded over a large geographic spread in the Karoo basin for four Permo-Triassic vertebrate assemblage zones
(AZ). Tetrapods, mainly therapsids, were sampled from two Permian (Cistecephalus AZ and Daptocephalus AZ) and
two Triassic biozones (Lystrosaurus declivis AZ and Cynognathus AZ). For each of these biozones, fossils were
sampled from several localities and their δ18Op values compared. Results from the Permian data showed no
isotopic difference in apatite from localities divided by longitude 24◦. Isotopic differences seem to appear further
east in the Basin. Most of the Permian localities (restricted to the south-western part of the Basin) were under the
influence of a water system originating from the southern mountainous source terrain. Oxygen isotope compositions
of vertebrates from the Lystrosaurus declivis AZ show a significant latitudinal gradient interpreted as an
evaporation effect from a southern source in the mountains running toward the north. The Basin during the
Cynognathus AZ was under a similar pattern with an evaporation effect highlighted with lower δ18O values in the
south and higher in the north.
Original languageEnglish
Article number104999
Pages (from-to)1-10
Number of pages10
JournalJournal of African Earth Sciences
Volume205
DOIs
Publication statusPublished - Sep 2023

Bibliographical note

Funding Information:
The authors thank the South African Heritage Resources Agency (SAHRA) for their authorization to sample the fossils, and export sub-samples for stable isotope analysis of phosphate (PermitID: 2790 and 2841). Marion Bamford, Bernhard Zipfel and Sifelani Jirah are acknowledged for access to the Karoo fossil collections of the ESI and for sanction to sample the tetrapod fossils. We also thank both anonymous reviewers for their constructive and helpful comments. This work was supported by the Palaeontological Scientific Trust (PAST) and its Scatterlings of Africa programmes, National Research Foundation (NRF) African Origins Platform of South Africa and DST/NRF Centre of Excellence in Palaeosciences .

Funding Information:
The authors would greatly thank Prof. Bruce Rubidge for his expertise on the Permo-Triassic Main Karoo Basin and its fauna, which greatly improved this manuscript. Dr. Hannah F. James is acknowledged for language editing. The authors thank the South African Heritage Resources Agency (SAHRA) for their authorization to sample the fossils, and export sub-samples for stable isotope analysis of phosphate (PermitID: 2790 and 2841). Marion Bamford, Bernhard Zipfel and Sifelani Jirah are acknowledged for access to the Karoo fossil collections of the ESI and for sanction to sample the tetrapod fossils. We also thank both anonymous reviewers for their constructive and helpful comments. This work was supported by the Palaeontological Scientific Trust (PAST) and its Scatterlings of Africa programmes, National Research Foundation (NRF) African Origins Platform of South Africa and DST/NRF Centre of Excellence in Palaeosciences.

Publisher Copyright:
© 2023 Elsevier Ltd

Keywords

  • Late Permian
  • Middle Triassic
  • Stable isotopes
  • Climate
  • Therapsids

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