Strontium-isotope stratigraphy and oxygen- and carbon-isotope variation during the Middle Jurassic–Early Cretaceous of the Falkland Plateau, South Atlantic
Strontium-isotope stratigraphy and oxygen- and carbon-isotope variation during the Middle Jurassic–Early Cretaceous of the Falkland Plateau, South Atlantic
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南大西洋福克兰高原中侏罗世-早白垩世的锶同位素地层学以及氧和碳同位素变化
DOI：
10.1016/s0031-0182(01)00486-2
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
D. Gröcke
中科院分区：
文献类型：
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作者：
G. Price;D. Gröcke
87 Sr/86 Sr数据的碧流岩从中侏罗世-早白垩世继承福克兰高原（深海钻探项目站点511和330），沉积在一个周期性缺氧，半封闭的浅水盆地。成岩筛选的锶同位素值为0.706789上升到0.707044，然后急剧增加到0.707428在采样序列的最上部。与公布的锶校准曲线的比较表明，最古老的样品是Calovian到Oxfordian的年龄，而其余的侏罗纪部分的继承组成的Kimmeridgian和早期提东时代的沉积物。超微化石，甲藻和软体动物组合提供了可比的年龄测定。最年轻的箭石的锶同位素分析点的Hauterivian-Barremian年龄，而年龄解释的基础上的动物群提供了广泛的年龄范围从Barremian早期Albian。因此，锶同位素地层学的这一系列提供了更高的年龄分辨率，提供有关的数据已记录在整个南大西洋盆地的底层水缺氧事件的时间。保存完好的箭石标本显示氧同位素范围在+0.08至-2.22 ‰之间（PDB，Peedee Belemnite国际标准），碳同位素范围在+2.35至-1.33 ‰之间（PDB）。δ 13 C值在晚侏罗世-早白垩世逐渐变负，与87 Sr/86 Sr数据一致，揭示了风化和侵蚀程度增加的趋势。氧同位素数据，如果解释的古温度是一致的温暖的古温度在Kimmeridgian和稍冷的温度为蒂托和早白垩世的继承部分。因此，建议的相对Kimmeridgian温暖（基于锶同位素年龄分配）与其他已发表的古温度记录吻合得很好。
87Sr/86Sr data of belemnites are presented from a Middle Jurassic–Early Cretaceous succession from the Falkland Plateau (Deep Sea Drilling Project Sites 511 and 330) that was deposited in a periodically anoxic, semi-enclosed shallow water basin. Diagenetically screened strontium-isotope values of 0.706789 rise to 0.707044 before increasing sharply to 0.707428 in the uppermost part of the sampled succession. Comparison with published strontium calibration curves suggests that the oldest samples were Callovian to Oxfordian in age, whilst the remainder of the Jurassic part of the succession consisted of Kimmeridgian and Early Tithonian age sediments. The nannofossil, dinoflagellate and molluscan assemblages provide comparable age determinations. The strontium-isotope analysis of the youngest belemnites points to a Hauterivian–Barremian age, whilst age interpretations based upon the fauna provide a wide age range from the Barremian to early Albian. Strontium-isotope stratigraphy of this succession hence offers increased age resolution providing data regarding the timing of episodes of bottom water anoxia which have been recorded throughout the South Atlantic Basin. Well-preserved belemnite specimens display an oxygen-isotope range between +0.08 and −2.22‰ (PDB, Peedee belemnite international standard) and a carbon-isotope range from +2.35 to −1.33‰ (PDB). δ13C values become increasingly negative through the Late Jurassic–Early Cretaceous and in concert with the87Sr/86Sr data reveal a trend that could be accounted for by increasing levels of weathering and erosion. The oxygen-isotope data if interpreted in terms of palaeotemperature are consistent with warm palaeotemperatures in the Kimmeridgian and slightly cooler temperatures for the Tithonian and Early Cretaceous parts of the succession. The proposed relative Kimmeridgian warmth (based upon strontium-isotope age assignments) is thus in good agreement with other published palaeotemperature records.