Detection of Late Cretaceous eustatic signatures using quantitative biostratigraphy

This study tested the potential for high-resolution quantitative biostratigraphic methods to distinguish tectonic from supposedly eustatic sequences. The study employed automated multidimensional graphic correlation using constrained optimization (program CONOP). Our analysis was based on 15 onshore sections in eastern New Zealand spanning the Coniacian to Maastrichtian stages (Upper Cretaceous), and 398 well-constrained lowest- or highest-occurrence records derived from 245 dinoflagellate species. The age of the resulting composite section was calibrated using six dated bioevents; two of these events were tied to geochemical or paleomagnetic datums. Following calibration, the composite section had an average relative temporal resolution of less than 130 k.y. through the study interval, although the succession of events was not dated to this level of precision in an absolute sense. Although the CONOP composite will not resolve unconformities or condensed intervals that occur across all studied sections, such 'global' unconformities can be identified using clusters of events that are placed at a single composite level. Fifteen major event clusters were identified, 10 of which coincided closely with sequence boundaries identified in the Northern Hemisphere; the probability of this coincidence arising by chance alone is ~8%. Although these results must be regarded as provisional, they suggest that high-resolution quantitative stratigraphy can provide a potent tool for the identification and correlation of stratigraphic sequences. Furthermore, our findings add significant support for recent studies that have argued for the presence of Late Cretaceous eustasy. Keywords: biostratigraphy, correlation, eustasy, Late Cretaceous, New Zealand, quantitative analysis, sequence stratigraphy, unconformities.