Seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the Toarcian (Early Jurassic) in Central and Northern Spain. Comparison with other European sections
Seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the Toarcian (Early Jurassic) in Central and Northern Spain. Comparison with other European sections
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DOI：
10.1016/j.palaeo.2007.11.005
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发表时间：
2008-02
期刊：
影响因子：
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通讯作者：
J. J. Gómez-J.;A. Goy;M. L. Canales
中科院分区：
文献类型：
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作者：
J. J. Gómez-J.;A. Goy;M. L. Canales
早期Toarcian大灭绝标志着地球历史上的关键事件之一。其中许多事件都与重大的气候变化有关。在西班牙中部和北方研究了显示高分辨率菊石生物地层学的Toarcian剖面。基于对192个成岩筛选的箭石方解石和41个块状碳酸盐岩的分析，稳定同位素数据集允许构建δ 13 C曲线和基于δ 18 O的古温度。与欧洲和北方非洲其他剖面的灭绝模式比较表明，早期Toarcian大规模灭绝边界发生在细鳞-蛇纹过渡带，与大洋性南极事件相关的富有机质相和相关的负δ 13 C漂移具有穿时性。从最新的普林斯巴赫期冷却间隔开始，海水温度的第一次平均上升约为4.5 °C，开始于普林斯巴赫期-托阿尔期边界附近，并在最早的托阿尔期细骨节生物时期发展，标志着主要灭绝间隔的开始。从细鳞鱼-蛇形鱼过渡期到生物时湾，记录到海水温度平均上升5.7 °C至7.8 °C。这一变暖间隔期开始得很快，至少在西欧似乎是同步的，被认为是造成大规模灭绝的主要因素之一。对于一些作者来说，这种快速变暖可能是由于大量的温室气体注入大气层，但它似乎并没有记录在箭石方解石中，这些可能的气体的起源在文献中有很大的争议。额外的同位素漂移被发现在研究的部分在西班牙在中东和晚Toarcian。在最新的Bifrons Biochron中记录到负的δ 13 Cbel偏移。在这一偏移之上，代表2-3 °C ΔT的Illustris-Vitiosa分区热峰可能与卡鲁盆地记录的构造岩浆活动峰之一有关。在西北欧和西特提斯，菊石和腕足动物群的更新与这种气候变化相一致。一个有趣的热峰也被检测到的标志分区的箭石。ΔT约为3 °C，在这两个剖面中，热峰都包含在δ 13 C bel-1. 5 ‰的负偏移中。卡鲁主要岩浆活动年龄（178-180 Ma）与新年龄的相对同步性表明，δ 13 C负异常和变暖间隔可能是由火山成因温室气体释放引起的。在这一短时间内，观察到西北欧和特提斯几个动物群中记录的组合的丰度和多样性发生了显著变化。最高的Levesquei分区热峰仅在位于西班牙中部的剖面的沉积物中被识别，并且与正δ 13 C偏移相一致。
The Early Toarcian mass extinction marks one of the critical events in the history of the Earth. Many of these events have been linked to important climate changes. Two sections of the Toarcian showing high-resolution ammonite-based biostratigraphy are studied in Central and Northern Spain. Stable isotope datasets, based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates, allowed the construction of δ13C curves and a δ18O-based palaeotemperature. Comparison of the extinction pattern with other sections in Europe and northern Africa shows that the Early Toarcian mass extinction boundary occurred at the Tenuicostatum–Serpentinum transition, and that the organic-rich facies linked to the Oceanic Anoxic Event and the associated negative δ13C excursion are diachronous. From a latest Pliensbachian cooling interval, a first increment of seawater temperature averaging about 4.5 °C, started around the Pliensbachian–Toarcian boundary and developed during the earliest Toarcian Tenuicostatum Biochron, marking the beginning of the main extinction interval. From the Tenuicostatum–Serpentinum transition up to the Bifrons Biochron, a rise in seawater temperature averaging 5.7 °C to 7.8 °C was recorded. This warming interval, which started rapidly and which seems to be synchronous at least in Western Europe, is considered one of the main factors responsible for mass extinction. For some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere, but it does not seem to be recorded in belemnite calcite, and the origin of these possible gases is largely debated in the literature. Additional isotope excursions were found in the studied sections in Spain during the Middle and Late Toarcian. A negative δ13Cbelexcursion has been recorded at the latest Bifrons Biochron. Above this shift, the Illustris–Vitiosa subzones thermal peak, which represents a 2–3 °C ΔT, could be linked to one of the tectonomagmatic activity peaks recorded in the Karoo Basin. A renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in NW Europe and Western Tethys. An interesting thermal peak has also been detected in belemnites of the Insigne Subzone. ΔT is in the order of 3 °C, and in both sections the thermal peak is included into a δ13Cbelnegative excursion of about −1.5‰. Relative synchrony with the new age for the Karoo main magmatic activity (178–180 Ma) indicates that the δ13C negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases. At this short interval, noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of NW Europe and Tethys are observed. The uppermost Levesquei Subzone thermal peak has only been recognized in the deposits of the section located in Central Spain and coincides with a positive δ13C excursion.