COLLABORATIVE RESEARCH: Towards a Milankovitch-Scale Stable Isotope Stratigraphy of the Late Oligocene to early Miocene

本文拟利用大洋钻探计划（ODP）第154段至西赤道大西洋Ceara Rise收集的岩心，建立首个天文校正的晚渐新世至早中新世（21-27.5 Ma）稳定同位素时间序列。这个时间序列将是一个复合记录，由Ceara Rise上三个孔（926、928和929）的底栖有孔虫的碳和氧同位素记录组成。通过剪接，该组合物将在6.5米长的间隔内具有地层连续性。因此，它将成为有史以来最长的高分辨率同位素时间序列之一。初步工作已经证明了所建议的方法的可行性。事实上，目前正在努力调整磁化率和现有的稳定同位素记录，以适应这个区间的轨道光谱（与N.J.沙克尔顿合作）。利用天文校正的同位素记录，我们将能够(1)估计渐新世/中新世边界的相对年龄，(18O最大值Oi2a， Mi1, Mi1a（以及所有小事件），(2)以前所未有的细节表征晚渐新世/早中新世气候变率（冰量/温度）的演变。这项调查的结果将带来几个重要的好处。首先，提出的天文校正同位素时间序列将作为全球标准参考剖面，与所有其他晚渐新世-早中新世海相序列进行比较。利用稳定同位素地层学，将沉积剖面的长段或短段与这一记录相关联并进行校准，从而显著提高年龄模型的准确性，这是可能的。更为重要的是，调整后的海陆上升同位素记录为重建气候、深海环流和化学变化提供了框架，将极大地加强这一区间的古海洋学和古气候研究。总之，提出的米兰科维奇尺度记录将代表着新生代地层学和地球史的重大进展。

9725789 Zachos We propose to develop the first astronomically tuned stable isotope time series for the late Oligocene to early Miocene (21-27.5 Ma) with cores collected during Ocean Drilling Program (ODP) Leg 154 to Ceara Rise, western Equatorial Atlantic. This time series will be a composite record, constructed with the carbon and oxygen isotope records of benthic foraminifers from three Holes on Ceara Rise (Sites 926, 928, and 929). Through splicing, the composite will be stratigraphically continuous over a 6.5 m.y long interval. As such, it will be one of the single longest high-resolution isotope time series ever assembled. Preliminary work has demonstrated the feasibility of the proposed approach. In fact, efforts are now underway to tune the magnetic susceptibility and existing stable isotope records to orbital spectra for this interval (in collaboration with N.J. Shackleton). With the astronomically tuned isotope record we will be able to (1) estimate the relative ages of the Oligocene/Miocene boundary, (18O maxima Oi2a, Mi1, Mi1a (as well as all minor events), and (2) characterize in unprecedented detail the evolution of late Oligocene/early Miocene climate variability (ice-volume/temperature). Several important benefits will be derived from the results of this investigation. For one, the proposed astronomically tuned isotope time series will serve as a global standard reference section by which all other late Oligocene-early Miocene marine sequences are compared. It will be possible, using stable isotope stratigraphies, to correlate and calibrate either long or short segments of sedimentary sections to this record, thereby significantly improving the accuracy of age models. More importantly, by providing the framework for reconstructing changes in climate, deep ocean circulation and chemistry, the tuned Ceara Rise isotope records should greatly enhance paleoceanographic and paleoclimatic research on this interval. In sum, the proposed Milankovitch-scale records will rep resent a significant advance in Cenozoic stratigraphy and Earth history.