COLLABORATIVE RESEARCH: Towards a Milankovitch-Scale Stable Isotope Stratigraphy of the Late Oligocene to early Miocene

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9725789 Zachos We propose to develop the first astronomically tuned stable isotope time series for the late Oligocene to early Miocene (21-27.5 Ma) with cores collected during Ocean Drilling Program (ODP) Leg 154 to Ceara Rise, western Equatorial Atlantic. This time series will be a composite record, constructed with the carbon and oxygen isotope records of benthic foraminifers from three Holes on Ceara Rise (Sites 926, 928, and 929). Through splicing, the composite will be stratigraphically continuous over a 6.5 m.y long interval. As such, it will be one of the single longest high-resolution isotope time series ever assembled. Preliminary work has demonstrated the feasibility of the proposed approach. In fact, efforts are now underway to tune the magnetic susceptibility and existing stable isotope records to orbital spectra for this interval (in collaboration with N.J. Shackleton). With the astronomically tuned isotope record we will be able to (1) estimate the relative ages of the Oligocene/Miocene boundary, (18O maxima Oi2a, Mi1, Mi1a (as well as all minor events), and (2) characterize in unprecedented detail the evolution of late Oligocene/early Miocene climate variability (ice-volume/temperature). Several important benefits will be derived from the results of this investigation. For one, the proposed astronomically tuned isotope time series will serve as a global standard reference section by which all other late Oligocene-early Miocene marine sequences are compared. It will be possible, using stable isotope stratigraphies, to correlate and calibrate either long or short segments of sedimentary sections to this record, thereby significantly improving the accuracy of age models. More importantly, by providing the framework for reconstructing changes in climate, deep ocean circulation and chemistry, the tuned Ceara Rise isotope records should greatly enhance paleoceanographic and paleoclimatic research on this interval. In sum, the proposed Milankovitch-scale records will rep resent a significant advance in Cenozoic stratigraphy and Earth history.