![]() The assemblage is considered to be of early Maastrichtian age on the basis of ammonite occurrences and has been dated to the lower Maastrichtian biozone CF 7 by planktic foraminifera. A total of 23 species referred to 18 genera are described, in addition to the possible coleoid Naefia neogaeia. Sediments of the Méndez Formation near Cerralvo, north-eastern Mexico, yield an abundant and diverse Maastrichtian ammonite assemblage. We re-interpret the position of this chron based on this new information. 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-fi eld overprint of originally reversed polarity in Upper Cretaceous sections. 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 Pacifi c province (but geographically far from our study areas) as well as to sections outside of the province itself. These new faunal correla tions are augmented with the magneto stratigraphic record from Pacifi c Coast localities to arrive at better interregional correlation for the Upper Cretaceous globally. Our fi ndings demonstrate that there was signifi cantly more faunal interchange between the North Ameri-can Pacifi c 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. We recognize and/or defi ne 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. 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 chrono-stratigraphic framework for this region of the North Pacifi c biotic province. ![]()
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