Campanian/Maastrichtian stage boundary in southern California: Resolution and implications for large-scale depositional patterns

Abstract

Detailed paleomagnetic study of Upper Cretaceous, predominantly deep-sea fan deposits from the Point Loma Formation (San Diego, California), situated within the allochthonous Peninsular Ranges terrane, has produced a magnetic polarity stratigraphy with one reversed magnetozone. Foraminiferal and megafossil (primarily molluscan) occurrences demonstrate that these strata are late Campanian to early Maastrichtian in age, and that the reversed magnetozone is almost certainly basal Maastrichtian Chron 32r. Recognition of this chron provides a direct correlation of the North Pacific province biostratigraphic zonations to the standard Cretaceous stages in Europe. The identification of Chron 32r indicates that for the available biostratigraphic zonations the Pacific slope megafossil Campanian/Maastrichtian stage boundary shows the best accord with the standard European stage boundary. Improved age relations for these strata suggest that their large-scale depositional patterns were strongly influenced by both local active-plate-margin tectonics and global eustatic factors during the Late Cretaceous.