Derry L A, Keto L S, Jacobsen S B, Knoll A H, Swett K
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
Geochim Cosmochim Acta. 1989;53:2331-9. doi: 10.1016/0016-7037(89)90355-4.
We report initial 87Sr/86Sr values from an Upper Proterozoic carbonate succession from Svalbard and East Greenland. This succession, now tectonically separated into three sequences, is thick, relatively continuous, and well preserved. The relative ages of the samples from within the basin are well constrained by litho-, bio-, and chemostratigraphic techniques. The data from this study and related data from the literature are used to construct a curve of 87Sr/86Sr for Upper Proterozoic seawater. The new data reported in this study substantially improve the isotopic record of Sr in seawater for the period between 650 and 800 Ma. The data indicate that delta 87Sr values of seawater were variable but low (delta 87Sr approximately -500 to -250) between 900 and 650 Ma, and rose rapidly to approximately +30 by 600 Ma. The range of variation of delta 87Sr in seawater during the Riphean-Vendian exceeds the entire range of delta 87Sr in seawater during the Phanerozoic. While variation in the average isotopic composition of Sr delivered to the oceans by rivers can account for some of the observed range, changes in the ratio of submarine hydrothermal flux to river water (continental) flux are responsible for the large variation in seawater Sr isotopic composition. Changes in the continental flux of Sr to the oceans can be related to tectonic factors. Large changes in the hydrothermal flux to river water flux ratio indicated by the data could have significant consequences for the chemistry of the ocean-atmosphere system.
我们报告了来自斯瓦尔巴群岛和东格陵兰上元古界碳酸盐岩序列的初始87Sr/86Sr值。该序列目前在构造上被分隔为三个层序，厚度大、相对连续且保存完好。盆地内样品的相对年龄通过岩性地层学、生物地层学和化学地层学技术得到了很好的限定。本研究的数据以及文献中的相关数据被用于构建上元古界海水的87Sr/86Sr曲线。本研究报告的新数据显著改善了650至800百万年前海水锶同位素记录。数据表明，900至650百万年前海水的δ87Sr值变化不定但较低（δ87Sr约为-500至-250），到600百万年前迅速上升至约+30。里菲纪-文德纪期间海水δ87Sr的变化范围超过了显生宙期间海水δ87Sr的整个变化范围。虽然河流输送到海洋的锶平均同位素组成的变化可以解释部分观测到的范围，但海底热液通量与河水（大陆）通量之比的变化是海水锶同位素组成大幅变化的原因。大陆向海洋输送锶通量的变化可能与构造因素有关。数据表明的热液通量与河水通量之比的大幅变化可能对海洋-大气系统的化学性质产生重大影响。
