Late Cretaceous true polar oscillation artifact: further evidence for Earth’s long-term rotational stability

Determining Earth’s stability with respect to the spin axis sets boundary conditions for understanding the planet’s deep mantle and interpreting records of past climate. Analyses of global paleomagnetic data sets have suggested very limited polar wander since the Mid-Cretaceous (Cottrell and Tarduno, 2000; Tarduno and Smirnov, 2001). However, this conclusion has been challenged by calls for a Late Cretaceous true polar oscillation whereby the entire solid Earth rotated by 12 degrees, and then rotated back, 86 to 78 million years ago (Mitchell et al., 2021). This posit is based on paleomagnetic data from a dense sampling (approximately 1000 limestone samples) and automated magnetic measurements yielding data from magnetic polarity chrons 34 to 32n in the Italian Apennines. Herein, we analyze these data and find that the oscillation signal across magnetic chrons polarity 33r to 33n exceeds the maximum speed constrained by mantle viscosity (2.4 degrees/myr; Tsai and Stevenson, 2007) and is thus physically implausible. When considered in the light of prior paleomagnetic and rock magnetic studies on these rocks, the data point to an unrecognized overprint magnetization carried by authigenic hematite. This overprint has a differential angular effect on the normal and reversed polarity primary remanences, creating biased magnetic directions and attendant false polar wander. This artifact serves as a cautionary tale with respect to paleomagnetic analyses, but also further highlights the remarkable stability of Earth relative to the axis since at least the mid-Cretaceous which sets the planet apart from smaller planetary bodies which may have experienced polar wander. Principal differences are that external forces since the lunar forming impact are too small to drive such motion, and Earth’s mantle viscosity structure which dampens any potential motion driven by changes in its mass heterogeneities.