Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation, Flin Flon Belt, Canada
Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation, Flin Flon Belt, Canada
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加拿大弗林弗伦带1.84 Ga Embury Lake组沉积环境的地球化学约束
DOI：
10.1111/iar.12343
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发表时间：
2020
期刊：
影响因子：
1.5
通讯作者：
Sano Yuji
中科院分区：
文献类型：
--
作者：
Motomura Kento;Kiyokawa Shoichi;Ikehara Minoru;Tanaka Kentaro;Sano Yuji
加拿大弗林-弗隆带含有与哈德逊造山带有关的古元古代火山-沉积序列。层序包括被陆下沉积岩不整合覆盖的岛弧火山岩和火山碎屑岩(阿米斯克群)，以及较年轻的深相沉积。在弗林弗隆地区，几条南北走向的断裂将层序划分为块体，掩盖了深相沉积的沉积环境。在本地，在弗林弗隆地区，恩伯里湖组与阿米斯克和米西群的岛弧火山-沉积序列处于断层接触中。为了确定恩伯里湖组的沉积环境，我们使用了岩石学和地球化学法。在这里，我们报告了有机质碳同位素(δ13Corg)和硫同位素(δ34S)，以及地层中黑色页岩的总有机碳和总硫的测量结果。样品取自一个含有交替的砂岩和黑色页岩带的钻芯。黑色页岩中的黄铁矿分为四种结构类型：真面体结构、脉状结构、椭圆形结构和微晶结构。微晶黄铁矿通常是由微生物介导的硫酸盐还原作用产生的。极低的S/C比率(平均值)=0.04)与湖相沉积相一致。δ13Corg(−36‰到−27‰)和δ34S(+3.0‰到+7.7‰)的范围可以用细菌光合作用来解释，细菌光合作用涉及卡尔文循环和乙酰辅酶A途径，以及低硫酸盐环境中的硫酸盐还原。考虑到之前在<； 1.84 Ga研究中报告的沉积年龄，恩伯里湖组很可能是在横贯哈德逊造山期的湖相环境中侵位的。
The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ13Corg) and sulfur isotopes (δ34S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ13Corg(−36 ‰ to −27 ‰) and δ34S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.