Deciphering the origin of high carbon shales: the Amungee organofacies conundrum, Velkerri Formation, Greater McArthur Basin
Date
2023
Authors
Edwards, L. E.
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Abstract
The Mesoproterozoic (1.4 Ga) Velkerri Formation of the McArthur Basin contains a number of intervals rich in organic matter (with TOC values locally >10wt%). These have been used as supporting evidence for a transient middle Mesoproterozoic global oxygenation event. New geochemical data collected from Urapunga-4 were compiled with previously published data to;
a) illuminate the origin of these organofacies and to particularly understand why the shale preserved such large fluctuations in TOC over short stratigraphic distances, and to
b) address the competing hypotheses.
The relationship between TOC and δ13C(org) shows that the TOC peaks in all three high organic shales (A, B, and C shales) in the Amungee Member are interpreted to be caused by primary production. However, the A shale was also interpreted to possibly be due to sediment input outpacing the increased carbon production. The B shale was interpreted to be a result of a small organic bloom that was immediately followed by an increased sediment supply that was likely from a storm event.
In addition, organic geochemical data and detrital U-Pb zircon and novel laser Rb-Sr dating from newly accessible core samples in the Beetaloo Sub-basin, combined with detailed sedimentology, were used, along with previously published data from Urapunga-4, to verify whether this new core (ELT002) intersects the Velkerri Formation.
The depositional age of the new core and the difference in sedimentology and geochemistry between Urapunga-4 well indicate that this new core likely intersects the Kyalla Formation rather than the Velkerri Formation.
School/Discipline
School of Physical Sciences
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Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR
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