Retraversing the Highs and Lows of Cenozoic Sea Levels.

We present a sequence-stratigraphically based reappraisal of sea-level variations for the Paleogene, Neogene, and early Quaternary Periods (66.0-1.5 Ma) that is biochronostratigraphically controlled and then fine-tuned through oxygen-isotopic (d18O) calibrations, with a higher-frequency, mostly isotopically calibrated curve for the last 1.5 m.y. of the Quaternary Period. Depositional sequences that form the basis of sea-level curves are largely third-order cycles (~0.5-2.5 m.y. in duration) for the Paleogene-Neogene interval and fourth- and fifth-order cycles (~400-100 k.y.) for the Quaternary. The availability of betterresolved, astronomically tuned Cenozoic chronostratigraphy and new sequence-stratigraphic studies in the past three decades makes this update timely. In this major revision, the ages of the depositional surfaces (i.e., sequence boundaries and maximum flooding surfaces, which form the basis of the sea-level curves) have been calibrated to marine benthic foraminiferal oxygen-isotopic data, thereby improving their chronologic precision. The amplitudes of sea-level highs and lows have been reevaluated based on global averaging of stratigraphic estimates, aided by isotopic data, where we also discuss the many inherent issues that reduce the efficacy of both methodologies. The global-mean data suggest that the shorter-term highs and lows are extremely variable during the Cenozoic Era, ranging from ~150 to a few tens of meters of change. Refined ages of the sequence boundaries and the resultant durations of third-order sequences imply their strong linkage to the longperiod modulations of the obliquity and eccentricity cycles and, thus, to climatic variations. [ABSTRACT FROM AUTHOR]