High-Resolution Late Devonian Magnetostratigraphy From the Canning Basin, Western Australia: A Re-Evaluation

Theodore Green,Peter W Haines,Paul Montgomery,Joseph L Kirschvink,Plinio Jaqueto,Timothy D Raub,Roger M Hocking,Eric Tohver,Sarah P Slotznick,Ted E Playton

doi:10.3389/feart.2021.757749

Abstract

Late Devonian time was a period of rapid upheaval in the Earth system, including climate change, sea level changes, widespread ocean anoxia, and the Frasnian-Famennian mass extinction; the cause(s) of these changes remain(s) uncertain. The Lennard Shelf of the Canning Basin in Western Australia contains carbonate reef sections spanning much of the Late Devonian Epoch and has been sampled for paleomagnetic analysis with studies by Hansma and colleagues in 2015 and Playton and colleagues in 2016. However, previous paleomagnetic directions were scattered and their use for magnetostratigraphy has been questioned. Here, rock magnetic data and magnetostratigraphy for a late Devonian drill-core from the Lennard Shelf were analyzed. Three magnetostratigraphic interpretations were made using different paleopoles that showed good correlation with each other and the earlier interpretations by Playton and colleagues in 2016. Additionally, the rock magnetic data revealed the samples contain various mixtures of detrital and diagenetic minerals, the former of which should be viable recorders of primary magnetic signatures. Even in samples with these detrital phases, paleomagnetic data were often noisy and produced ambiguous polarity assignments, likely due to the anomalously weak Devonian field. Because of this ambiguity and the absence of a robust paleopole, broader correlations for this critical time-period will be difficult without additional paleomagnetic data from the late Devonian Period. Expanded data for this interval could eventually shed light on the timing, causes, and rates of the Frasnian-Famennian mass extinction and other environmental shifts in the late Devonian Epoch.

Highlights

The Devonian Period had expansive reefs that contributed to abundant carbonate production and the greatest marine diversity of the Paleozoic Era, including the appearance and diversification of aquatic tetrapods (e.g., Becker et al, 2020; Bambach et al, 2002; Kiessling et al, 2003)
Magnetic directions were determined for each sample using principle component analysis (Kirschvink, 1980) and the PmagPy software (Tauxe et al, 2016). Following these rock magnetic protocols, the derivative of the isothermal remanent magnetization (IRM) demagnetization was used to determine the coercivity of remanence and fit using the MAX UnMix web application (Maxbauer et al, 2016) to identify the ferromagnetic minerals present in each sample (Figure 2; Peters and Dekkers, 2003)
Concerns have been raised about prior paleomagnetic analyses of the Canning Basin and their potential to be used for magnetostratigraphy (Bilardello, 2019; van der Boon et al, 2021, in review); this study provides an internal consistency check as this same set of MR1 samples was interpreted as part of the Playton et al (2016) analysis of the Canning Basin

Summary

Introduction

The Devonian Period had expansive reefs that contributed to abundant carbonate production and the greatest marine diversity of the Paleozoic Era, including the appearance and diversification of aquatic tetrapods (e.g., Becker et al, 2020; Bambach et al, 2002; Kiessling et al, 2003). Despite overall high Devonian marine diversity, a protracted mass extinction event occurred during the Frasnian and Famennian stages that greatly decreased the abundance of marine and terrestrial life before and continuing into the Carboniferous Period (Percival et al, 2018). The FrasnianFamennian mass extinction was especially destructive to the widespread Devonian reef systems and stromatoporoids (Percival et al, 2018) but, in the aftermath, lead to diversification of organisms like tetrapods, actinopterygians, and chondrichthyans that had previously comprised a less significant part of the biotic system (Sallan and Coates, 2010). The eruption of the Viluy or Kola-Dnieper Large Igneous Provinces, marine anoxia, orbital forcings, and extraterrestrial impact events have all been suggested as causes of the extinction (Ernst and Youbi, 2017; Percival et al, 2018; Lu et al, 2021), but poorly constrained Devonian chronostratigraphy and imprecise dating of the causal mechanisms have led to continued debate (e.g., Ricci et al, 2013; Ma et al, 2016; Percival et al, 2018; Lu et al, 2021)

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Conclusion