Magnetostratigraphy of ODP Site 177-1092 (Table 1)

Ocean Drilling Program (ODP) Site 1092 from the sub-Antarctic South Atlantic produced a clear magnetic stratigraphy for the Late Miocene [Evans et al., 2003, doi:10.1046/j.1365-246X.2003.01916.x]. Three short intervals of reverse polarity were identified within the long (~1 Myr) normal polarity subchron C5n.2n. These excursion chrons were tentatively correlated to the three "cryptochrons" identified within subchron C5n.2n from NE Pacific marine magnetic anomaly data. New oxygen isotope data from ODP Site 1092 have allowed astronomical calibration of eight polarity chron boundaries in the interval between C4Ar.1n and C5r.1n (9.3-11.2 Ma) as well as calibration of the three excursion chrons identified within C5n.2n. The new polarity chron ages in the C4Ar.1n-C5r.1n interval differ from a current (2004) timescale by up to 48 kyr. The astrochronology yields durations in the 3-4 kyr range for the three excursion chrons in C5n.2n. The relative paleointensity record from Site 1092, and hence the three excursion chrons, can be correlated to the deep-tow magnetic anomaly record from 19°S on the East Pacific Rise (EPR). Based on published correlation of the EPR deep-tow record with the sea-surface magnetic anomaly stack from the NE Pacific, the three excursion chrons do not correspond to the "cryptochrons" recognized in the NE Pacific stack.采自亚南极南大西洋的大洋钻探计划（Ocean Drilling Program, ODP）1092站位，为晚中新世地层提供了清晰的磁地层学记录[埃文斯等人, 2003, doi:10.1046/j.1365-246X.2003.01916.x]。研究人员在时长约1百万年的正极性亚时（subchron）C5n.2n内部，识别出3段短暂的反向极性间隔。研究人员初步将这些极性漂移亚时（excursion chrons）与东北太平洋海洋磁异常数据中，于C5n.2n亚时内部识别出的3处隐伏亚时"cryptochrons"进行了关联对比。依托大洋钻探计划1092站位获取的新氧同位素数据，研究人员得以对C4Ar.1n至C5r.1n（9.3~11.2百万年）层位内的8处极性时边界开展天文校准，同时完成了C5n.2n内部识别出的3处极性漂移亚时的校准工作。C4Ar.1n至C5r.1n层位内的新极性时年龄数据，与当前（2004年）使用的地质年代标尺的最大偏差可达48千年。天文年代学分析结果显示，C5n.2n内部的3处极性漂移亚时的持续时长介于3~4千年之间。1092站位的相对古强度记录，连同其内部识别出的3处极性漂移亚时，可与东太平洋海隆（East Pacific Rise, EPR）南纬19°处的深拖磁异常记录进行对比关联。结合已发表的东太平洋海隆深拖磁异常记录与东北太平洋海面磁异常堆叠数据的对比结果，这3处极性漂移亚时并不对应东北太平洋磁异常堆叠数据中识别出的隐伏亚时"cryptochrons"。