Carbon and oxygen isotope records from the southern Eurasian Seaway following the Triassic-Jurassic boundary: Parallel long-term enhanced carbon burial and seawater warming
Carbon and oxygen isotope records from the southern Eurasian Seaway following the Triassic-Jurassic boundary: Parallel long-term enhanced carbon burial and seawater warming
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三叠纪-侏罗纪边界欧亚海道南部的碳和氧同位素记录：平行的长期增强碳埋藏和海水变暖
DOI：
10.1016/j.earscirev.2020.103131
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发表时间：
2020
影响因子：
12.1
通讯作者：
Anders L. Ebbesen
中科院分区：
文献类型：
--
作者：
S. Hesselbo;C. Korte;C. Ullmann;Anders L. Ebbesen
底栖生物和底栖动物的化石贝壳已被证明是海水碳、氧同位素地球化学的忠实记录，因此也有助于追踪碳循环与古温度的关系。在这项研究中，我们提供了一个广泛的数据集，来自下侏罗统(赫堂统和下中国统)软体动物和腕足类硬体动物部分，这些硬化石来自生物地层学很好地校准的英国沿海露头(布里斯托尔海峡和赫布里底盆地)。这些盆地的古地理位置位于连接特提斯海和北冰洋的劳亚海南部。所有样品都根据元素组成、光学显微镜和扫描电子显微镜观察进行了成岩作用的筛选。在赫布里底盆地内的一些地方，古近纪侵入体周围的热液系统的蚀变导致了碳酸盐氧同位素的重新设定，但贝壳的原始碳同位素值基本保持不变。在紧邻三叠系-侏罗系(T-J)界线(在菱镁铀矿生物带中)发生的显著的、明显短暂的~3/milδ13C碳正同位素漂移之上，显著的负碳同位素漂移(所谓的主要负碳同位素漂移)横跨整个赫堂期。在赫堂期-震旦纪界线，穿过震旦纪下部，骨骼碳酸盐的碳同位素值再次趋于更多的正值，但代表了数百万年的时间。最重的δ13C碳值约为+4.3mil/mil，在下西穆尔统顶部很明显，与从日耳曼带和下托阿尔西统观察到的值相当，后者在侏罗纪更高。这一长期积极的驼峰证实了从大量有机质碳同位素记录得出的趋势，支持了长期加强有机碳埋藏的证据，据推测，在中大西洋岩浆省侵位后，广泛的湖泊和海洋裂谷系统穿越了支离破碎的联合古陆。与之平行的是，骨架型碳酸盐岩的氧同位素值从赫堂统下部(平面双峰带~−1/milδ18OCarb)到西穆尔统下部(高峰带~−2.5/milδ18OCarb)呈持续下降的趋势。氧同位素值可解释为由于古温度的逐渐升高和(或)大气或冰冻圈水成分的增加；在劳亚海的情况下，古海洋学和古生态考虑指向一个占主导地位的古温度信号。因此，通过逐步增加δ13C碳值并假设硅酸盐风化汇恒定，大气二氧化碳对全球古温度的任何下降效应，在海道中都被导致底层水温显著变暖的区域过程所抵消。
Fossil shells of benthos and nektobenthos have been shown to be faithful recorders of seawater carbon- and oxygen-isotope geochemistry, and thus also useful to track the relationship between carbon cycle and palaeotemperature. In this study we present an extensive dataset from Lower Jurassic (Hettangian and lower Sinemurian) mollusc and brachiopod hard parts collected from biostratigraphically well-calibrated UK coastal outcrops (Bristol Channel and Hebrides basins). These basins lay palaeogeographically in the southern part of the Laurasian Seaway that connected the Tethys and Boreal oceans. All samples have been subject to screening for diagenesis on the basis of elemental composition, light microscopy, and SEM observations. In the case of some localities within the Hebrides Basin, alteration by hydrothermal systems around Paleogene intrusions has led to re-setting of carbonate oxygen isotopes, but the original carbon isotope values from the shells are largely preserved. Above the prominent and apparently short-lived, ~3 per mil δ13Ccarbamplitude positive carbon-isotope excursion (CIE) that occurs immediately above the Triassic-Jurasic (T-J) boundary (in thetilmanniammonite biozone), a pronounced negative CIE (the so-called Main Negative CIE) spans the entire Hettangian Stage. At the Hettangian-Sinemurian boundary, and through the lower Sinemurian, the carbon-isotope values of the skeletal carbonate again trend towards progressively more positive values, but representing a time of several million years. The heaviest δ13Ccarbvalues of about +4.3 per mil are evident towards the top of the lower Sinemurian, and are comparable with values observed from thetilmanniZone, and from the lower Toarcian, higher in the Jurassic. This long-term positive hump, which confirms trends derived from bulk organic matter carbon-isotope records, is supporting evidence of prolonged enhanced organic carbon burial that is inferred to have occurred in the extensive system of lacustrine and marine rifts that traversed a fragmenting Pangaea after emplacement of the Central Atlantic Magmatic Province. In parallel, oxygen-isotope values of the skeletal carbonate show a continuous downward trend from the lower part of the Hettangian (~ −1 per mil δ18Ocarbin theplanorbisZone) to the top of the lower Sinemurian (~ −2.5 per mil δ18Ocarbin the higherturneriZone). Oxygen-isotope values may be interpreted as due to gradually increasing palaeotemperature, and/or addition of a meteoric or cryospheric water component; in the case of the Laurasian Seaway, palaeoceanographic and palaeoecological considerations point towards a dominant palaeotemperature signal. Consequently, any atmospheric carbon-dioxide drawdown effect on global palaeotemperatures, as suggested by progressively increasing δ13Ccarbvalues, and assuming a constant silicate weathering sink, was more than counterbalanced in the seaway by regional processes that led to significantly warmer bottom water temperatures.
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影响因子：
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作者：
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影响因子：
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影响因子：
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影响因子：
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作者：
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