Oligocene strontium isotope stratigraphy of Indian Ocean sediments

Strontium isotope (87Sr/86Sr) ages have been established for Oligocene samples of Leg 119 Site 744, Leg 120 Sites 747 and 748, and Leg 121 Sites 756 and 757. Ages were determined using the strontium isotope age equation of Miller et al. (1988) and preliminary correlations have been made with available nannofossil biostratigraphy. The strontium isotope ages calculated here augment biostratigraphy, which for the Oligocene is characterized by long biozones, and provide additional detail where the paleomagnetic record is not clear (Sites 756 and 757). Results from the lower latitude Ninetyeast Ridge sites where standard calcareous nannofossil datums are present are compared to those of the higher latitude Kerguelen Plateau sites in order to examine biostratigraphic events across latitude in the Indian Ocean. The 87Sr/86Sr determined ages are used here as a tool for correlation.

本研究已为第119航次（Leg 119）744站位、第120航次（Leg 120）747与748站位，以及第121航次（Leg 121）756与757站位的渐新世（Oligocene）样品建立了锶同位素（87Sr/86Sr）年龄数据。年龄计算采用Miller等人（1988）提出的锶同位素年龄计算公式，并结合现有钙质超微化石（nannofossil）生物地层学资料完成了初步地层对比。本次计算得到的锶同位素年龄可补充渐新世以长生物地层带为典型特征的生物地层学研究，同时可在古地磁记录（paleomagnetic record）不够清晰的756与757站位提供更为精细的年代学细节。为探究印度洋（Indian Ocean）跨纬度的生物地层学事件，本研究将已获取标准钙质超微化石标定基准面（datum）的低纬度九十东海岭（Ninetyeast Ridge）站位结果，与高纬度凯尔盖朗高原（Kerguelen Plateau）站位的相关结果进行了对比分析。本次研究将测得的87Sr/86Sr年龄作为地层对比工具加以应用。