Carbon cycle dynamics linked with Karoo-Ferrar volcanism and astronomical cycles during Pliensbachian-Toarcian (Early Jurassic)
Carbon cycle dynamics linked with Karoo-Ferrar volcanism and astronomical cycles during Pliensbachian-Toarcian (Early Jurassic)
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DOI：
10.1016/j.gloplacha.2018.08.012
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发表时间：
2018-11-01
影响因子：
3.9
通讯作者：
Yamada, Kazuyoshi
中科院分区：
文献类型：
--
作者：
Ikeda, Masayuki;Hori, Rie S.;Yamada, Kazuyoshi
中生代最深刻的环境变化之一发生在Pl/To时间间隔，包括Pl/To边界的大量黑色页岩沉积和早期Toarcian海洋缺氧事件（T-OAE）。这些事件与负碳同位素偏移（CIE），但其时间与C-12丰富的碳注入，可能与Karoo-Ferrar火山作用和碳循环反馈，如陆地甲烷生成和甲烷水合物分解，仍有争议。在这里，我们提出了一个新的化学地层学的有机质的碳同位素比（三角洲C-13（org））从Pl/到深海继承，结合生物天体年代学。深海层序位于日本犬山地区的胜山和坂保木露头处，包含两个黑色层状燧石层段，分别命名为T-BBC 1和2，其天体年代学年龄分别为183.25-183.01 +/- 0.2 Ma和183.55-182.80 +/- 0.2 Ma。T-BBC 1和2的基底上分别识别出类似于千分之2和千分之5的负CIE，这与基于生物地层学的浅海剖面中的Pl/To边界和经典T-OAE相关。T-BBC 1和T-BBC 2爆发的天体年代学年龄分别在Karoo和Ferrar LIP最古老的高精度U-Pb年龄的误差范围内。这些时间关系表明，与卡鲁和Ferrar火山活动相关的C-12富碳注入，以及与广泛的黑色页岩沉积在整个Pl/To和T-OAE，分别CIE之间的联系。经典T-OAE CIE的倾斜周期可能与高纬度地区的陆地甲烷生成和甲烷水合物分解有关，而T-CIE和T-BBCs沉积终止的405-kyr节奏可能与较弱季风强度下化学风化和营养供应减少有关，并可能在Pl/To和T-OAE周期终止时抑制甲烷循环。
One of the most profound environmental changes in the Mesozoic occurred during the Pliensbachian-Toarcian (Pl/To) time interval, including massive black shale deposition across Pl/To boundary and early Toarcian Oceanic Anoxic Event (T-OAE). These events are associated with negative carbon isotope excursions (CIEs), but their temporal link with C-12-rich carbon injection, possibly related with Karoo-Ferrar volcanisms and carbon cycle feedbacks, such as terrestrial methanogenesis and methane hydrate dissociation, is still debated. Here we present a new chemostratigraphy of the carbon isotopic ratio of organic matter (delta C-13(org)) from Pl/To deep-sea successions, in conjunction with bio-astrochronology. The deep-sea successions are located at the Katsuyama and Sakahogi outcrops in the Inuyama area, Japan, and contain two black bedded chert intervals named T-BBCs 1 and 2, which have astrochronologic ages of 183.25-183.01 +/- 0.2 Ma and 183.55-182.80 +/- 0.2 Ma. Negative CIEs of similar to 2 parts per thousand and similar to 5 parts per thousand are recognized across the base of T-BBCs 1 and 2, respectively, which are correlated with Pl/To boundary and classical T-OAE in shallow marine sections based on biostratigraphy. Astrochronologic ages of the onset of T-BBCs 1 and 2 are within the errors of the oldest high-precision U-Pb ages of Karoo and Ferrar LIPs, respectively. These temporal relations suggest a link between the C-12-rich carbon injection associated with Karoo and Ferrar volcanism, and CIEs associated with widespread black shale deposition across the Pl/To and T-OAE, respectively. Obliquity cycles in classic T-OAE CIE could have linked with terrestrial methanogenesis and methane hydrate dissociation in high-latitudes areas, whereas 405-kyr pacing of termination of T-CIE and T-BBCs deposition would be related with decreased chemical weathering and nutrient supply under weaker monsoon intensity, and possibly suppressed methane cycle across the termination of Pl/To and T-OAE periods.