Geophysical and geochemical evidence of large scale fluid flow within shallow sediments in the eastern Gulf of Mexico, offshore Louisiana
Geophysical and geochemical evidence of large scale fluid flow within shallow sediments in the eastern Gulf of Mexico, offshore Louisiana
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DOI：
10.1111/j.1468-8123.2010.00304.x
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发表时间：
2011-02
期刊：
影响因子：
1.7
通讯作者：
Y. Takano;W. Gilhooly;C. Berndt;K. Heeschen;N. Suzuki;Shunsuke Saegusa;F. Nakagawa;U. Tsunogai;Shaoyong Jiang;M. Lopez
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文献类型：
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作者：
Y. Takano;W. Gilhooly;C. Berndt;K. Heeschen;N. Suzuki;Shunsuke Saegusa;F. Nakagawa;U. Tsunogai;Shaoyong Jiang;M. Lopez
我们分析了现代密西西比峡谷东部堤坝上沉积物内的流体流动状况，使用三维地震数据和井下测井数据在站点U1322和U1324在2005年综合大洋钻探计划（IODP）远征308在墨西哥湾。孔隙水中的硫酸盐和甲烷浓度表明，硫酸盐-甲烷过渡区位于海底以下74米和94米处，是沉积盆地中发现的最深处之一。这部分是由于在一个埋藏的浊流通道（蓝色单位，1000 mbsf），它分隔位于该单位下方和上方的沉积隔间，阻止正常向上的甲烷通量到海底盆地内的流体流动。下隔室的超压导致流体通过绕过上隔室的深导管进行间歇性和集中性的迁移，在海底形成泥火山。这也可能有利于海水循环，我们解释深硫酸盐-甲烷过渡区的高向下硫酸盐通量来自海水，约5-10倍以上，在其他盆地测量的结果。结果表明，火星-乌尔萨盆地浅层沉积物中的地球化学反应主要受海水下降流的控制，而其他盆地则是由上升流控制甲烷相关反应。这意味着地下天然气水合物的存在，是埋藏沉积物和水柱之间活动联系的证据。
We analyse the fluid flow regime within sediments on the Eastern levee of the modern Mississippi Canyon using 3D seismic data and downhole logging data acquired at Sites U1322 and U1324 during the 2005 Integrated Ocean Drilling Program (IODP) Expedition 308 in the Gulf of Mexico. Sulphate and methane concentrations in pore water show that sulphate–methane transition zone, at 74 and 94 m below seafloor, are amongst the deepest ever found in a sedimentary basin. This is in part due to a basinward fluid flow in a buried turbiditic channel (Blue Unit, 1000 mbsf), which separates sedimentary compartments located below and above this unit, preventing normal upward methane flux to the seafloor. Overpressure in the lower compartment leads to episodic and focused fluid migration through deep conduits that bypass the upper compartment, forming mud volcanoes at the seabed. This may also favour seawater circulation and we interpret the deep sulphate–methane transition zones as a result of high downward sulphate fluxes coming from seawater that are about 5–10 times above those measured in other basins. The results show that geochemical reactions within shallow sediments are dominated by seawater downwelling in the Mars-Ursa basin, compared to other basins in which the upward fluid flux is controlling methane-related reactions. This has implications for the occurrence of gas hydrates in the subsurface and is evidence of the active connection between buried sediments and the water column.