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Published May 2012 | public
Journal Article

Integration of macrofossil biostratigraphy and magnetostratigraphy for the Pacific Coast Upper Cretaceous (Campanian–Maastrichtian) of North America and implications for correlation with the Western Interior and Tethys


New biostratigraphic data obtained from measured stratigraphic sections of Santonian through Maastrichtian age located along the west coast of North America necessitate changes to the currently accepted chronostratigraphic framework for this region of the North Pacific biotic province. We recognize and/or define 12 molluscan zones over this interval of the Upper Cretaceous and propose revisions to the currently accepted integration of ammonite zones with global Upper Cretaceous magnetochrons. Our findings demonstrate that there was significantly more faunal interchange between the North American Pacific Coast and both the Western Interior and Gulf Coast regions of North America during the Late Cretaceous than has previously been recognized, and because of this, novel and direct biostratigraphic correlations can be made. These new faunal correlations are augmented with the magnetostratigraphic record from Pacific Coast localities to arrive at better interregional correlation for the Upper Cretaceous globally. The new integration of the global polarity time scale with the local, west coast ammonite zonation now allows better correlation between sections both within the North Pacific province (but geographically far from our study areas) as well as to sections outside of the province itself. However, we note here that previous correlations between biostratigraphy and the top and bottom of magnetochron 33r in west coast North American sections appear to have been in error due to unrecognized, modern-day normal-field overprint of originally reversed polarity in Upper Cretaceous sections. We reinterpret the position of this chron based on this new information.

Additional Information

© 2012 Geological Society of America. Received 16 April 2009; Revision received 13 December 2010; Accepted 17 December 2010. This study would not have been possible without the kind help of numerous individuals and institutions. Foremost, we want to thank W.A. Cobban of the U.S. Geological Survey, Denver, for identifications and loan of comparative material of Western Interior Baculites species. LouElla Saul also generously allowed us to photograph and study material in the Natural History Museum of Los Angeles County, and provided much information about the stratigraphy at Santa Catarina Landing, Mexico. W.J. Kennedy helped with some identifications and allowed study of material then at the Oxford Museum. Neil Larson of Black Hills Institute read an earlier draft of the manuscript, loaned us important specimens, and shared much of his copious knowledge of the ammonite faunas from the Western Interior. Similarly, Graham Beard, of Qualicum Beach, British Columbia, loaned us many specimens over the years and shared selflessly of his knowledge of Vancouver Island ammonites. Many students helped in field work over the years, and we would especially like to thank David Backus, Jennifer Zweible, and Ken MacLeod in this regard, as well as Bruce Crowley , Rod Bartlett, and Cory Brimblecombe for fossil preparation, and Jennifer Zweible and David Backus for strontium analyses. We would also like to thank two plainclothes Royal Canadian Mounted Police who released several of us after extensive interrogation about suspected sabotage in the Gulf Islands of Canada while we were sampling for magnetostratigraphy. We also extend our thanks to two local residents of Colonet, Baja California, Mexico, who pulled our vehicle out of deep sand at San Antonio del Mar.

Additional details

August 19, 2023
October 17, 2023