Characteristics of Authigenic Minerals around the Sulfate-Methane Transition Zone in the Methane-Rich Sediments of the Northern South China Sea: Inorganic Geochemical Evidence
Characteristics of Authigenic Minerals around the Sulfate-Methane Transition Zone in the Methane-Rich Sediments of the Northern South China Sea: Inorganic Geochemical Evidence
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DOI：
10.3390/ijerph16132299
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发表时间：
2019-06
影响因子：
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通讯作者：
Daidai Wu;Tiantian Sun;R. Xie;Mengdi Pan;Xuegang Chen;Y. Ye;Lihua Liu;N. Wu
中科院分区：
文献类型：
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作者：
Daidai Wu;Tiantian Sun;R. Xie;Mengdi Pan;Xuegang Chen;Y. Ye;Lihua Liu;N. Wu
海洋冷渗区的沉积物提供了过去流体流动的潜在档案，有助于深入了解过去甲烷渗流活动的演变。然而，由于几个因素，特别是洪水和浊积沉积，甲烷厌氧氧化（AOM）的信号可能在冷渗环境下的大块沉积物中被掩盖。本研究收集了全面的无机数据，以探索冷渗漏相关记录的可用性，并为过去甲烷渗漏活动的演变提供见解。对南海北坡台南盆地974 -4站点沉积物的总碳硫、总有机碳δ13C值（δ13CTIC）、铬还原硫δ34S值（δ34SCRS）和有孔虫氧碳同位素进行了表征。结果证实了自生矿物的形成与AOM有很强的相关性。此外，海底以下619 ~ 900 cm的硫酸盐-甲烷过渡带（SMTZ）自生硫化物中34S的富集和丰富的铬还原硫（CRS）含量反映了过去在持续甲烷渗流支持下的高甲烷通量。浮游有孔虫的岩性分布和AMS（加速器质谱）14C测年表明，浊积岩（~35.14 ka）与有孔虫富层段（Unit II: 440-619 cmbsf）有关，在末次盛冰期（LGM）碳酸盐生产力增加。第二单元Mo和U富集，营养金属（Al、Ti、V、Ni、Fe、Mn和Cu）含量较低。冷渗沉积物富有孔虫层段（Unit II）可能与浊积岩导致的沉积序列不连续现象有关，导致Fe、Mn和Ba缺乏富集。ⅲ单元未富集U，只富集Mo，这可能与甲烷渗流过程中AOM产生H2S有关。根据上述结果，可以推测该地区经历了多次甲烷渗漏事件。对AOM的进一步探索应重点关注快速沉积的风险，特别是浊度流对沉积物的影响。
Sediments at marine cold seep areas provide potential archives of past fluid flow, which allow insights into the evolution of past methane seepage activities. However, signals for anaerobic oxidation of methane (AOM) might be obscured in bulk sediments in cold-seep settings due to several factors, especially flood and turbidite deposition. Comprehensive inorganic data were gathered in this study to explore the availability of related records at cold seeps and to provide insights into the evolution of past methane seepage activities. Sediments collected from the site 973-4 in the Taixinan Basin on the northern slope of the South China Sea were characterized in terms of total carbon and sulfur, δ13C values of total organic carbon (δ13CTIC), δ34S values of chromium reducible sulfur (δ34SCRS), and foraminiferal oxygen and carbon isotopes. The results confirmed a strong correlation between formation of authigenic minerals and AOM. Moreover, the 34S enrichments and abundant chromium reducible sulfur (CRS) contents in the authigenic sulfides in the sulfate–methane transition zone (SMTZ) within 619–900 cm below seafloor (cmbsf) reflected past high methane fluxes supported by constant methane seepages. Lithological distribution and AMS (Accelerator Mass Spectra) 14C dating of planktonic foraminifera show that the turbidite (~35.14 ka) was related to a foraminifera-rich interval (Unit II: 440-619 cmbsf) and increased carbonate productivity during the last glacial maximum (LGM). Enrichment of Mo and U was observed accompanied by low contents of nutrient metals (Al, Ti, V, Ni, Fe, Mn, and Cu) in Unit II. The foraminifera-rich interval (Unit II) of cold seep sediments was probably linked to the phenomenon of inconsecutive sedimentary sequence due to the turbidites, which resulted in the lack of Fe, Mn, and Ba enrichment. There is no U enrichment but only Mo enrichment within Unit III, which might be related to H2S produced by AOM during the methane seepages. Based on the above results, it can be speculated that this area has experienced multiple-episodes of methane seep events. Further exploration of AOM should focus on the risks of rapid deposition, especially the impact of turbidity current on sediments.