Geomagnetic Polarity Time Scale

The time scale for marine magnetic anomalies for the Late Cretaceous through Neogene (C-sequence) and Middle Jurassic through Early Cretaceous (M-sequence with deep-tow extension) has been calibrated through magnetostratigraphic studies to biostratigraphy, cycle-stratigraphy and selected radioisotope-dated levels. The majority of the geomagnetic polarity time scale for the past 160 Myr is constructed by fitting spreading rate models to these constraints. The status of the geomagnetic polarity time scale for each geologic period is summarized in the appropriate period chapters. This chapter incorporates some of the discussions from the Geomagnetic Polarity Time Scale chapters in GTS2004 and GTS2012 by J.G. Ogg and A.G. Smith. The derivation of age-models for the C-sequence and the M-sequence of polarity chrons are new to GTS2020.