区相文,邬黛黛,谢瑞,等. 南海北部神狐海域沉积物Fe-P-S元素地球化学特征及对甲烷渗漏的指示[J]. 海洋地质与第四纪地质,2022,42(1): 96-110. doi: 10.16562/j.cnki.0256-1492.2021080501
引用本文: 区相文,邬黛黛,谢瑞,等. 南海北部神狐海域沉积物Fe-P-S元素地球化学特征及对甲烷渗漏的指示[J]. 海洋地质与第四纪地质,2022,42(1): 96-110. doi: 10.16562/j.cnki.0256-1492.2021080501
OU Xiangwen,WU Daidai,XIE Rui,et al. Fe-P-S geochemical characteristics of sediments in the Shenhu area of northern South China Sea and their implications for methane leakage[J]. Marine Geology & Quaternary Geology,2022,42(1):96-110. doi: 10.16562/j.cnki.0256-1492.2021080501
Citation: OU Xiangwen,WU Daidai,XIE Rui,et al. Fe-P-S geochemical characteristics of sediments in the Shenhu area of northern South China Sea and their implications for methane leakage[J]. Marine Geology & Quaternary Geology,2022,42(1):96-110. doi: 10.16562/j.cnki.0256-1492.2021080501

南海北部神狐海域沉积物Fe-P-S元素地球化学特征及对甲烷渗漏的指示

Fe-P-S geochemical characteristics of sediments in the Shenhu area of northern South China Sea and their implications for methane leakage

  • 摘要: 神狐海域是我国天然气水合物勘探试采的重点区域,在甲烷渗漏过程中会形成黄铁矿和蓝铁矿等具有指示意义的矿物,这些矿物和Fe、P、S等元素密切相关,通过Fe-P-S等元素地球化学特征来研究该区域的甲烷渗漏对进一步了解南海水合物的成藏状况有重要意义。本研究选取南海北部神狐海域Site 2A柱状沉积物为研究对象,通过对其主微量元素、铁结合磷、自生磷灰石态磷、碳酸盐铁、磁铁矿铁、还原性铁、铬还原硫、硫同位素以及总有机碳(TOC)等数据分析,研究该地区的Fe、P和S等元素之间的关系以及对甲烷渗漏的指示。研究发现,在600 cmbsf(centimeter below sea floor)深度以下的初级生产力水平随深度增加而略有升高。在600 cmbsf深度以下,沉积物中可指示黄铁矿的铬还原硫含量增加,其硫同位素明显正偏,说明可能存在甲烷厌氧氧化作用,根据沉积物中指示富镁方解石和文石的Mg/Ca和Sr/Ca、与自生碳酸盐有关的Sr/Ti和Ba/Ti均在600 cmbsf出现了峰值,以及铁结合磷和自生磷灰石态磷含量的增加,可推测600 cmbsf左右为硫酸盐—甲烷转换带(SMTZ)的上界。另外,铁结合磷的含量在SMTZ带明显增加,黄铁矿中的铬还原硫以及δ34S可以指示黄铁矿的含量,从而可以利用不同形态的Fe、P和S元素地球化学特征指示和识别甲烷渗漏。

     

    Abstract: The Shenhu area is a key area in China for gas hydrate exploration and trial production. Research results suggest that such elements as Fe-P-S, are easily affected by the anaerobic oxidation of the methane (AOM) to form the minerals of pyrite and viviante. To study the methane seep intensity and hydrate accumulation potential of the area through Fe-P-S and other elements and their geochemical characteristics has reference significance for further understanding the gas hydrate accumulation mechanisms. In this paper, the core sediments from the Site 2A of the Shenhu area in the north of South China Sea are selected as the research target. Upon the basis of previous studies, the relationship among Fe, P, S and their implications for methane leakage are studied with the analysis data of major and trace elements, iron-bound phosphorus, authigenic apatite phosphorus, carbonate iron, magnetite iron, reducing iron, chromium-reduced sulfur (CRS), sulfur isotopes, and total organic carbon (TOC). All the data of TOC, P/Ti, Al/Ti, Ba/Ti, high active iron (FeHR) and other productivity indicators from the Site 2A station indicate a medium level of primary productivity. The primary productivity below 600 cmbsf (centimeter below sea floor) in water depth increases slightly deepwards. CRS content increases below 600 cmbsf and its sulfur isotope is obviously positive, which indicates the existence of AOM. The Mg/Ca and Sr/Ca are indicators of high magnesium calcite and aragonite in sediments, and Sr/Ti and Ba/Ti contents related to authigenic carbonate. They all leave peaks at 600 cmbsf, and the water around this depth, the contents of Iron-bound phosphorus and Authigenic apatite phosphorus are also high. Therefore, we speculate that the depth of 600 cmbsf is most probably the upper boundary of Sulfate Methane Transition Zone (SMTZ). The research further suggests that the content of iron-bound phosphorus increases significantly in the SMTZ, CRS and δ34S in pyrite and may indicate the content of pyrite, so that methane seep can be recognized by different forms of Fe, P and S elements.

     

/

返回文章
返回