The Stability of the Earth Relative to its Spin Axis Across the K-Pg Boundary Tested by Skewness Analysis of Marine Magnetic Anomaly C27r

Recent work on the Pacific plate apparent polar wander path has demonstrated two potential reorientations of the Earth relative to its spin axis, i.e. True Polar Wander (TPW), since 60 Ma with a mostly stable Earth spin axis orientation between events (Woodworth et al. This Session, Seidman et al. 2019, Woodworth & Gordon 2018). A stable configuration between 56 and 66 Ma is inferred mainly from high-precision paleomagnetic poles determined by skewness analysis of marine magnetic anomalies. The oldest pole defining this stable configuration is determined from anomalies C27r-C31, which covers a wide age window of 62.5 to 69.3 Ma, spanning the K-Pg boundary (Acton & Gordon 1991, Gradstein et al. 2012). This pole differs significantly and is displaced ~6.4° in the Pacific hotspot reference frame from the C32 (71.4-74.3 Ma) pole of Petronotis et al. 1994 suggesting TPW.

The impact event associated with the K-Pg boundary could have had the capacity to cause a reorientation of the Earth relative to its spin axis during the interval spanned by the Acton and Gordon 1991 result, potentially explaining the offset relative to the Petronotis et al. 1994 pole. Understanding the effect the K-Pg impact may have had on the relative orientation of the Earth and its spin axis by altering the non-hydrostatic moment of inertia tensor is crucial to interpreting the resulting effect on life at the time. In particular, a rapid shift in latitudinal position of landmasses caused by TPW has the potential to alter the magnitude and duration of global climatic change associated with the impact.

To test the hypothesis that the Earth was fixed relative to its spin axis during this time at a position roughly defined by the C26r (59.2-62.2 Ma) skewness pole ~10° from its current location and to refine our age resolution during this critical period of Earth's history, here we present the results of an investigation of the skewness of marine magnetic anomaly C27r. C27r spans 62.5 to 63.5 Ma shortly after the K-Pg boundary at 66 Ma, improving our temporal resolution seven fold over Acton and Gordon 1991 result. This forms the first result in a larger body of work more closely examining the skewness of Pacific marine magnetic anomalies around the K-Pg boundary.