PP21B-2237
Towards an Accurate Orbital Calibration of Late Miocene Climate Events: Insights From a High-Resolution Chemo- and Magnetostratigraphy (8-6 Ma) from Equatorial Pacific IODP Sites U1337 and U1338

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Anna Joy Drury1, Thomas Westerhold1, Thomas Frederichs2, Roy Wilkens3, James E T Channell4, Helen F Evans5, David A Hodell6, Cedric M John7, Mitchell W Lyle8, Ursula Roehl1 and Jun Tian9, (1)MARUM - University of Bremen, Bremen, Germany, (2)University of Bremen, Department of Geosciences, Bremen, Germany, (3)University of Hawaii at Manoa, School of Ocean and Earth Science and Technology (SOEST), Honolulu, HI, United States, (4)University of Florida, Ft Walton Beach, FL, United States, (5)Integrated Ocean Drilling Program, College Station, TX, United States, (6)University of Cambridge, Cambridge, United Kingdom, (7)Imperial College London, London, United Kingdom, (8)Texas A&M University, College Station, TX, United States, (9)Tongji University, State Key Laboratory, Shanghai, China
Abstract:
In the 8-6 Ma interval, the late Miocene is characterised by a long-term –0.3 ‰ reduction in benthic foraminiferal δ18O and distinctive short-term δ18O cycles, possibly related to dynamic Antarctic ice sheet variability. In addition, the late Miocene carbon isotope shift (LMCIS) marks a permanent long-term –1 ‰ shift in oceanic δ13CDIC, which is the largest, long-term perturbation in the global marine carbon cycle since the mid Miocene Monterey excursion.

Accurate age control is crucial to investigate the origin of the δ18O cyclicity and determine the precise onset of the LMCIS. The current Geological Time Scale in the 8-6 Ma interval is constructed using astronomical tuning of sedimentary cycles in Mediterranean outcrops. However, outside of the Mediterranean, a comparable high-resolution chemo-, magneto-, and cyclostratigraphy at a single DSDP/ODP/IODP site does not exist. Generating an accurate astronomically-calibrated chemo- and magneto-stratigraphy in the 8-6 Ma interval became possible with retrieval of equatorial Pacific IODP Sites U1337 and U1338, as both sites have sedimentation rates ~2 cm/kyr, high biogenic carbonate content, and magnetic polarity stratigraphies.

Here we present high-resolution correlation of Sites U1337 and U1338 using Milankovitch-related cycles in core images and X-ray fluorescence core scanning data. By combining inclination and declination data from ~400 new discrete samples with shipboard measurements, we are able to identify 14 polarity reversals at Site U1337 from the young end of Chron C3An.1n (~6.03 Ma) to the onset of Chron C4n.2n (~8.11 Ma). New high-resolution (<1.5 kyr) stable isotope records from Site U1337 correlate highly with Site U1338 records, enabling construction of a high-resolution stack. Initial orbital tuning of the U1337-U1338 records show that the δ18O cyclicity is obliquity driven, indicating high-latitude climate forcing. The LMCIS starts ~7.55 Ma and is anchored in Chron C4n.1n, which is comparable to the north and equatorial Atlantic.

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