Orbitally tuned timescale and astronomical forcing in the middle Eocene to early Oligocene

摘要

Deciphering the driving mechanisms of Earth system processes, including theclimate dynamics expressed as paleoceanographic events, requires a complete,continuous, and high-resolution stratigraphy that is very accurately dated.In this study, a robust astronomically calibrated age model was constructedfor the middle Eocene to early Oligocene interval (31–43 Ma) inorder to permit more detailed study of the exceptional climatic events thatoccurred during this time, including the middle Eocene climate optimum andthe Eocene–Oligocene transition. A goal of this effort is to accurately datethe middle Eocene to early Oligocene composite section cored during thePacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphicframework for the new timescale is based on the identification of the stablelong eccentricity cycle in published and new high-resolution recordsencompassing bulk and benthic stable isotope, calibrated XRF core scanning,and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218,and 207-1260 as well as IODP Sites 320-U1333, and 320-U1334 spanning magneticpolarity Chrons C12n to C20n. Subsequently orbital tuning of the records tothe La2011 orbital solution was conducted. The resulting new timescalerevises and refines the existing orbitally tuned age model and thegeomagnetic polarity timescale from 31 to 43 Ma. The newly definedabsolute age for the Eocene–Oligocene boundary validates the astronomicaltuned age of 33.89 Ma identified at the Massignano, Italy, globalstratotype section and point. The compilation of geochemical records ofclimate-controlled variability in sedimentation through the middle-to-lateEocene and early Oligocene demonstrates strong power in the eccentricity bandthat is readily tuned to the latest astronomical solution. Obliquity drivencyclicity is only apparent during 2.4 myr eccentricity cycle minimaaround 35.5, 38.3, and 40.1 Ma.