Strontium isotopes in Early Jurassic seawater
Strontium isotopes in Early Jurassic seawater
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DOI：
10.1016/0016-7037(94)90382-4
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发表时间：
1994-02
影响因子：
5
通讯作者：
C. E. Jones;H. Jenkyns;S. Hesselbo
中科院分区：
文献类型：
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作者：
C. E. Jones;H. Jenkyns;S. Hesselbo
对英国侏罗纪保存完好、年代确定的箭石和牡蛎的分析得出了早侏罗世约束良好、详细的海水锶同位素曲线。用Mn、Fe、δ 13 C和δ 18 O等指标对低镁方解石化石的保存进行了监测。铁是最有用的指标，约75%的样品含有超过150 ppm的铁显示87锶-86锶比升高相对于相邻点的曲线。高Mn浓度与87 Sr-86 Sr比值升高的相关性较低;但是，在此情况下，低锰（< 25 ppm Mn）始终与明显良好的-δ 13 C和δ 18 O对成岩作用不敏感，因为它们影响87 Sr 86 Sr。锶同位素曲线的主要特征包括在100 ℃时上升到约0.70772，三叠纪晚期和侏罗纪早期（Hettangian）。从Hettangian开始，曲线开始大致线性下降，通过Sinemurian和Pliensbachian。在Pliensbachian晚期出现小幅平稳和上升之后，曲线福尔斯迅速下降到早侏罗世的最低值0.70706。然后，它在Toarcian逐渐增加，直到falciferum带，在那里它明显地突然增加到0.70719，然后在Aalenian-Bajocian（中侏罗世）继续缓慢增加到0.70728。这种在Sinemurian和Pliensbachian建立的下降趋势的逆转以前没有被发现。曲线的Sinemurian和Pliensbachian部分可能允许在1或2个菊石亚带（±0.5至1 Ma）内进行对比和定年。
The analysis of well-preserved, well-dated belemnites and oysters from the Jurassic of Great Britain has resulted in a well-constrained, detailed seawater strontium isotope curve for the Early Jurassic. The preservation of fossil low-Mg calcite was monitored using Mn, Fe, δ 13 C, and δ 18 O. Iron was the most useful indicator, with about 75% of the samples containing more than 150 ppm Fe showing 87 Sr 86 Sr ratios elevated relative to adjacent points on the curve. High Mn concentrations less often correlated with elevated 87 Sr 86 Sr ratios; however, low Mn concentrations (< 25 ppm Mn) were consistently associated with apparently well-preserved 87 Sr 86 Sr. δ 13 C and δ 18 O proved to be insensitive to diagenesis as it affects 87 Sr 86 Sr. The principal features of the strontium isotope curve include a rise to about 0.70772 in the latest Triassic and earliest Jurassic (Hettangian). From the Hettangian, the curve begins a roughly linear descent through the Sinemurian and Pliensbachian. Following a small levelling off and increase in the late Pliensbachian, the curve falls rapidly to its Early Jurassic minimum of 0.70706. It then gently increases through the Toarcian until the falciferum zone, where it shows an apparently abrupt increase to 0.70719 before continuing its slow increase to 0.70728 in the Aalenian-Bajocian (Middle Jurassic). This reversal of the downwards trend established in the Sinemurian and Pliensbachian had not been previously identified. The Sinemurian and Pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones (±0.5 to 1 Ma).