GEOMAGNETIC FIELD STRENGTH AND IMPLICATIONS FOR ENVIRONMENTAL CHANGE DURING THE DIVERSIFICATION OF EDIACARAN FAUNA

Paleomagnetic studies of the Ediacaran Period indicate that the geomagnetic field was highly unusual, exhibiting a hyper reversal frequency (Bazhenov et al., 2016), high secular variation (Bono and Tarduno, 2015) and an ultralow field intensity (Bono et al., 2019). This magnetic field behavior is intriguing because it co-occurs with the Ediacaran diversification of macroscopic life, but the nature of a linkage, if any, remains unclear. Herein, we review the available data and present new analyses to further define geomagnetic field history to better understand the potential uniqueness of the Ediacaran dynamo. Ultimately, we seek to determine if the geomagnetic field affected the Ediacaran environment, including oxygenation, through changes in magnetospheric processes. Previous data suggest that Earth’s magnetic field was up to 10 times weaker at 565 Ma compared to the present (Bono et al., 2019). These data, and numerical models (Driscoll, 2016) suggest that these ultralow fields mark the onset of inner core nucleation (ICN). Soon after ICN the field should rebound in strength because new energy sources become available to power the dynamo. Such a renewal is supported by higher field strengths in the early Cambrian at 532 Ma as reported by Zhou et al. (2022). What has been unknown is when the period of low to ultralow fields intensities started. To fill this gap, we have sampled the latest Cryogenian/earliest Ediacaran Santa Teresa anorthosite of Brazil and we further apply the single crystal paleointensity technique (Tarduno et al., 2006). First order reversal curve data indicate that feldspars from this anorthosite contain single domain magnetic mineral inclusions capable of preserving high fidelity magnetic records. Thermal demagnetization experiments utilizing CO₂ demagnetization (Tarduno et al., 2007) suggest the inclusions have a titanomagnetite composition. Initial total thermal remanent magnetization and Thellier paleointensity analyses, before anisotropy and cooling rate corrections, suggest fields substantially lower than the present-day. Further results of our ongoing studies will be discussed.