A multiple microfossil biochronology for the Miocene
A multiple microfossil biochronology is presented for the Miocene which allows resolution of time approaching 100,000 years. Carbonate stratigraphy is integrated to greatly enhance this resolution. Graphical correlation techniques were applied to over 20 DSDP (Deep Sea Drilling Project) sections to identify 175 planktonic foraminiferal, calcareous nannofossil, radiolarian, and diatom datum levels between 24.0 and 4.3 Ma which show the most consistent (isochronous) correlations. Ages are estimated for these datum levels through 72 direct correlations to paleomagnetic stratigraphy and extrapolation between the correlation points. The resulting Miocene time scale resembles previously published time scales except for the early Miocene, where recent paleomagnetic correlations result in changes.
The three CENOP (Cenozoic Paleoceanography Project) time slices (~21, 16, and 8 Ma) are characterized biostratigraphically (planktonic foraminifers, calcareous nannofossils, radiolarians, and diatoms) and in terms of carbonate stratigraphy. The ages of the time slices are estimated as follows: the early Miocene time slice (21.2–20.1 Ma; given as 22 Ma in this volume), the late early Miocene time slice (16.4–15.2 Ma), and the late Miocene time slice (8.9–8.2 Ma).
An alternate time scale utilizing a paleomagnetic Anomaly 5-paleomagnetic Chron 11 correlation is also presented. Estimated ages for microfossil zones and datum levels in the late middle and early late Miocene (14–7 Ma) utilizing the alternate time scale are generally younger than those for the more traditional time scale. The late Miocene time slice has an estimated age of 8.0–7.0 Ma.