流体渗漏强度变化对烟囱状冷泉碳酸盐岩中铁和磷循环的影响  

The impact of change in fluid seepage intensity on iron and phosphorus cycling in chimney-like seep carbonates

作　　者：高宇 刘春阳 胡钰[1] 陈琳莹 梁前勇[2] 冯东 陈多福[1] GAO Yu;LIU Chunyang;HU Yu;CHEN Linying;LIANG Qianyong;FENG Dong;CHEN Duofu(College of Marine Sciences,Shanghai Ocean University,Shanghai 201306,China;MNR Key Laboratory of Marine Mineral Resources,Guangzhou Marine Geological Survey,Guangzhou 510075,China)

机构地区：[1]上海海洋大学海洋科学学院,上海201306 [2]中国海洋地质调查局广州海洋地质调查局,广州510075

出　　处：《海洋地质与第四纪地质》2024年第6期96-104,共9页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金面上项目“南海海马冷泉区硫化环境中蓝铁矿的形成机制及其对海洋磷循环的指示”(42472145)。

摘　　要：冷泉碳酸盐岩形成过程中渗漏流体特征的变化可以改变参与的碳、硫等元素循环的生物地球化学过程,但对铁(Fe)和磷(P)元素循环及相关生物地球化学过程的影响目前还不清楚。本文对南海东沙海域一个冷泉碳酸盐岩烟囱横截面进行了矿物学、碳和硫地球化学及Fe和P组分进行了分析。结果显示,生物成因甲烷的厌氧氧化作用导致了极端13C亏损的自生碳酸盐的形成(δ^(13)C_(VPDB)<-55.5‰),并且形成过程中由于水合物分解,加入了富^(18)O流体,使得烟囱碳酸盐岩表现出异常高的氧同位素组成(5.5‰~5.8‰)。烟囱外层矿物组成以方解石为主,内层以文石为主,内层烟囱样品形成于更强的甲烷渗漏强度条件。样品中最主要的含磷物质是自生磷酸盐(P_(Auth)),并且最高含量出现在烟囱内层。相比外层烟囱样品,内层铁氧化物含量更低,但是铁结合态磷(P_(Fe))含量更高,推测可能是有蓝铁矿的形成。综合上述结果表明,在形成冷泉碳酸盐岩的强渗漏条件下,甲烷渗漏强度的增强会影响P_(Auth)和P_(Fe)的丰度,可能更有利于蓝铁矿和自生磷灰石的形成,从而对冷泉环境中的磷和铁循环产生影响。During the formation of seep carbonates,variations in fluid seepage affect the biogeochemical processes that drive the cycling of various elements,such as carbon and sulfur.However,such an influence on iron(Fe)and phosphorus(P)cycling and related biogeochemical processes remains unclear.In this study,mineral compositions,carbon and sulfur geochemistry,Fe and P component were investigated on a cross section of a chimney-like seep carbonate sample collected from the Dongsha area of the South China Sea.Results reveal that the anaerobic oxidation of biogenic methane led to the formation of the extremely ^(13)C-depleted authigenic carbonate rocks(δ^(13)C_(VPDB)<-55.5‰),and the addition of enriched ^(18)O fluids from the dissociation of gas hydrates results in abnormally high oxygen isotope composition(5.5‰-5.8‰)observed in the chimney carbonates.Combined with the dominant minerals with calcite in the outer layer of the chimney carbonates and aragonite in the inner layer,we inferred that the carbonates in the inner layer were formed at the later stage under stronger methane seepage condition.The most significant P-bearing mineral in the samples is authigenic phosphate(P_(Auth)),and the highest content is in the inner layer of the chimney carbonates.Compared with the outer chimney sample,the inner layer has lower Fe oxide content,but higher Fe-bound P(P_(Fe))content,indicating the formation of vivianite.Therefore,we believe that under a stronger seepage condition during the formation of seep carbonates,an enhanced intensity of methane seepage can affect the abundance of P_(Auth) and P_(Fe),which may favor the formation of vivianite and authigenic phosphates,thereby influencing Fe and P cycling in cold-seep environments.

关 键 词：甲烷渗漏 磷组分 铁组分 磷循环 冷泉碳酸盐岩 

分 类 号：P736.3[天文地球—海洋地质]