Reappraisal of Oligocene-Miocene chronostratigraphy and the Mi-1 event: Ocean Drilling Program Site 744, Kerguelen Plateau, southern Indian Ocean

摘要

The Oligocene-Miocene Transition (OMT) is an important interval in Earth's history, with substantial changes in Antarctic ice volume and mean temperature. The OMT is complicated in paleoclimatology, chronostratigraphy, and terminology, and there is a need for additional sites outside of the tropic/subtropics or Atlantic Basin to better understand the cause(s) and consequences of the OMT. Ocean Drilling Program Hole 744A sits on the southern edge of the Kerguelen Plateau, and is thus a sensitive recorder of changes on Antarctica and in the Indian Ocean sector of the Southern Ocean. Previous stratigraphic studies have concluded that the Oligocene/Miocene boundary is contained within a short coring gap (1 m) between Cores 744A-11 and 12. A new benthic foraminiferal stable isotope curve is at odds with the existing age model for the upper similar to 0.5 m of Core 12. A number of different explanations for age models arc discussed, and we find there is only one plausible explanation for the chronostratigraphy through Core 12. We suggest there was a short (similar to 150-200 kyr) hiatus, encompassing the peak Mi-1 excursion, based on interpreted magnetostratigraphy. This hiatus has no obvious lithologic expression.