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

9725789 Zachos我们计划开发第一个天文调谐的稳定同位素时间序列，用于晚渐新世至早中新世(21-27.5 Ma)，取芯于大洋钻探计划第154航段至西赤道大西洋的塞拉隆起。这一时间序列将是一个综合记录，由塞拉隆起(926、928和929)三个洞中海底有孔虫的碳和氧同位素记录构成。通过拼接，复合材料将在6.5英里长的间隔内在地层上连续。因此，这将是有史以来最长的高分辨率同位素时间序列之一。初步工作证明了该方法的可行性。事实上，目前正在努力调整磁化率和现有稳定的同位素记录，以适应这一区间的轨道光谱(与N.J.沙克尔顿合作)。利用天文调谐的同位素记录，我们将能够(1)估计渐新世/中新世界线的相对年龄(180O Maxima Oi2a，Mi1，Mi1a(以及所有小事件))，以及(2)前所未有地详细描述晚渐新世/早中新世气候变异性(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，建议的天文调谐同位素时间序列将作为全球标准参考剖面，用来比较所有其他晚渐新世-早中新世海相层序。将有可能利用稳定的同位素地层学，将沉积剖面的长段或短段与这一记录进行关联和校准，从而显著提高年龄模型的准确性。更重要的是，通过提供重建气候、深海环流和化学变化的框架，调谐的塞拉隆起同位素记录应该会极大地加强这一区间的古海洋和古气候研究。总之，拟议的米兰科维奇尺度记录将代表着新生代地层学和地球历史的重大进步。

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.