Cyclostratigraphy and eccentricity tuning of the early Oligocene through early Miocene (30.1-17.1 Ma): Cibicides mundulus stable oxygen and carbon isotope records from Walvis Ridge Site 1264

摘要

Few astronomically calibrated high-resolution (<= 5 kyr) climate records exist that span the Oligocene-Miocene time interval. Notably, available proxy records show responses varying in amplitude at frequencies related to astronomical forcing, and the main pacemakers of global change on astronomical time-scales remain debated. Here we present newly generated X-ray fluorescence core scanning and benthic foraminiferal stable oxygen and carbon isotope records from Ocean Drilling Program Site 1264 (Walvis Ridge, southeastern Atlantic Ocean). Complemented by data from nearby Site 1265, the Site 1264 benthic stable isotope records span a continuous similar to 13-Myr interval of the Oligo-Miocene (30.1-17.1 Ma) at high resolution (similar to 3.0 kyr). Spectral analyses in the stratigraphic depth domain indicate that the largest amplitude variability of all proxy records is associated with periods of similar to 3.4 m and similar to 0.9 m, which correspond to 405- and similar to 110-kyr eccentricity, using a magnetobiostratigraphic age model. Maxima in CaCO3 content, delta O-18 and delta C-13 are interpreted to coincide with similar to 110 kyr eccentricity minima. The strong expression of these cycles in combination with the weakness of the precession- and obliquity-related signals allow construction of an astronomical age model that is solely based on tuning the CaCO3 content to the nominal (La2011_ecc3L) eccentricity solution. Very long-period eccentricity maxima (similar to 2.4-Myr) are marked by recurrent episodes of high-amplitude similar to 110-kyr delta O-18 cycles at Walvis Ridge, indicating greater sensitivity of the climate/cryosphere system to short eccentricity modulation of climatic precession. In contrast, the responses of the global (high-latitude) climate system, cryosphere, and carbon cycle to the 405-kyr cycle, as expressed in benthic delta O-18 and especially delta C-13 signals, are more pronounced during similar to 2.4-Myr minima. The relationship between the recurrent episodes of high-amplitude similar to 110-kyr delta O-18 cycles and the similar to 1.2-Myr amplitude modulation of obliquity is not consistent through the Oligo-Miocene. Identification of these recurrent episodes at Walvis Ridge, and their pacing by the similar to 2.4-Myr eccentricity cycle, revises the current understanding of the main climate events of the Oligo-Miocene. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.