Astronomical Pacing of Middle Eocene Sea‐Level Fluctuations: Inferences From Shallow‐Water Carbonate Ramp Deposits

Abstract

Astrochronologically calibrated deep‐sea records document the Cenozoic (66–0 Ma) global climatic cooling in great detail, but the magnitude of sea‐level fluctuations of the middle Eocene Warmhouse state (47.8–37.7 Ma) and the ∼40.3 Ma warming event of the Middle Eocene Climatic Optimum (MECO) is not well constrained. Here, we present a sequence stratigraphic classification of a shallow marine mixed carbonate—clastic ramp system for this time interval in Paris basin, France. Based on sedimentologic, paleogeographic and biostratigraphic data, we hypothesize that the 22 elementary sequences recognized each correspond to the long cycle of orbital eccentricity (0.405 Myr). With the exception of the MECO, the shoreline trajectory of superimposed, third‐order depositional sequences evolved in phase with the very long cycles of orbital eccentricity (2.4 Myr), suggesting significant polar ice build‐up leading to sea level lowstands during nodes of the very long eccentricity cycle. Inferred from Fischer Plot methodology, Lutetian third‐order eustasy was in the order of 5–10 m and during the MECO 30 m or more. Furthermore, the shallow‐water record implies that third order sea‐level changes were astronomically paced in the middle Eocene Warmhouse climate state, but a decoupling occurred during the transient MECO warming.