PALEOGEOGRAPHIC CYCLES IN SCAGLIA ROSSA LIMESTONES: CAN TRUE POLAR WOBBLES PROVIDE A NEW TIME CALIBRATION APPROACH FOR MAGNETOSTRATIGRAPHY?

We present here a potential technique for continuous global stratigraphic correlation using high-resolution magnetostratigraphy. Magnetostratigraphic sampling at sub-meter resolution of the Scaglia Rossa Limestones reveals ~1-million-year cycles in paleolatitude with amplitudes as great as ~20° during Santonian-Campanian time (ca. 80 Ma). Correlation of these cycles with similar, isochronous declination swings from the Pierre Shale in North America suggests a global paleomagnetic signal. Initial comparison of the pole locations from the Scaglia Rossa and Pierre Shale shows that they agree (after correcting for seafloor spreading), suggesting a common rotation axis for Italy and North America. We interpret these correlated signals as bulk rotations of the solid Earth relative to the spin axis, classically known as True Polar Wander, but here called “True Polar Wobbles” due to their small magnitudes and rapid directional shifts. Due to the global nature of these True Polar Wobbles, the corresponding paleogeographic cycles should be globally isochronous, much like magnetic reversals, allowing for correlations across all continents. The continuous nature of the cycles, however, also allows for stratigraphic tuning, similar to orbital cycles, and allows for magnetostratigraphic correlation between magnetic reversals. In particular, we propose this new magnetostratigraphic correlation may provide a basis for subdivision of the Cretaceous Long Normal (C34N) and even shorter magnetochrons. These Late Cretaceous True Polar Wobbles may also have implications for the Baja-BC hypothesis and the “tiny wiggles” observed in marine magnetic patterns. The identification of True Polar Wobbles provides a potential new means for magnetostratigraphic correlation between magnetic reversals, with particular implications for the Late Cretaceous.