Stable carbon and oxygen istotope ratios of Oligocene foraminifera from ODP Hole 121-758A of the northern Ninetyeast Ridge, Indian Ocean (Appendix 1)@en
收藏资源简介：
An Oligocene-basal Miocene (Zones P19-P22/N4) oxygen and carbon isotope stratigraphy is presented based on mixed benthic foraminiferal faunas and different species of planktic foraminifers from Eastem Indian Ocean ODP Hole 758A. Lack of covariance in planktic and benthic delta18O ratios indicates that many Oligocene sea level fluctuations, including the major fall at 30 Ma, are not of glacio-eustatic origin. Delta18O values suggest that test morphology is a poor indicator of preferred depth habitat of Oligocene planktic foraminifers. Also, some groups show considerable shifts in preferred depth habitat. Reconstructed surface water temperature was nearly constant during the investigated period, but even assuming a large Antarctic icecap, values are unrealistically low, 18°-20°C. Most likely, water masses with markedly different oxygen isotopic composition existed, this poses great problems for quantitative temperature reconstructions. […]
本研究报道了渐新世-中新世早期（P19-P22/N4生物地层带）的氧碳同位素地层序列，数据源自东印度洋大洋钻探计划（Ocean Drilling Program, ODP）758A井的混合底栖有孔虫组合与不同属种浮游有孔虫。浮游与底栖有孔虫的δ¹⁸O比值无协变关系，表明诸多渐新世海平面波动事件（包括30 Ma时的大规模海平面下降）并非冰川海面升降成因。δ¹⁸O数值显示，壳体形态并非渐新世浮游有孔虫偏好栖息深度的可靠指示指标，且部分类群的偏好栖息深度存在显著偏移。研究时段内重建的表层海水温度近乎恒定，但即便假设存在大规模南极冰盖，该温度数值仍处于不合理的低位区间（18℃-20℃）。最合理的推测是，当时存在同位素组成差异显著的水团，这为定量温度重建带来了极大挑战。[…]
