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Astronomically calibrated timescales from 6 to 2.5 Ma and Benthic Isotope Stratigraphies, sites 1236, 1237, 1239, and 1241 Public Deposited

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  • We present benthic isotope stratigraphies for Sites 1236, 1237, 1239, and 1241 that span the late Miocene–Pliocene time interval from 6 to 2.4 Ma. Orbitally tuned timescales were generated for Sites 1237 and 1241 by correlating the high-frequency variations in gamma ray attenuation density, percent sand of the carbonate fraction, and benthic δ¹³C to variations in Earth’s orbital parameters. The astronomical timescales for Sites 1237 and 1241 are in agreement with the one from Atlantic Site 925/926 (Ocean Drilling Program Leg 154). The comparison of benthic δ¹⁸O and δ¹³C records from the east Pacific sites and Atlantic Site 925/926 revealed a surprising clarity of the “41-k.y. signal” in δ¹³C records and a remarkably good correlation between their δ¹³C records. This suggests that the late Miocene–Pliocene amplitudes of obliquityrelated δ¹³C cycles reflect a magnitude of global response often larger than that provided by obliquity-related δ¹⁸O cycles. At Site 1237, the orbitally derived ages of Pliocene magnetic reversal boundaries between the base of Réunion and the top of Thvera confirm astronomical datings of the generally accepted ATNTS2004 timescale, except for the top of Kaena and the base of Sidufjall. Our astronomical age for the top of Kaena is about one obliquity cycle older. The base of Sidufjall appears to be about one precession cycle younger. The age models of Sites 1236 and 1239 were established by correlating their benthic δ¹⁸O and δ¹³C records directly to the orbitally tuned isotope record of Site 1241.
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  • Tiedemann, R., Sturm, A., Steph, S., Lund, S., & Stoner, J. (2007). Astronomically calibrated timescales from 6 to 2.5 Ma and Benthic Isotope Stratigraphies, sites 1236, 1237, 1239, and 1241. Proceedings of the Ocean Drilling Program, Scientific Results, 202, 1-69.
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