Analyses of hydrocarbon gases and sulphate in sediments from the King George Basin, Antarctica

Thermogenic hydrocarbons, formed by the thermal alteration of organic matter, are encountered in several piston core stations in the King George Basin, Anatarctica. These hemipelagic sediments are being deposited in an area of active hydrothermalism, associated with the back-arc spreading in the Bransfield Strait. The lateral extent of sediments infiltrated by the hydrothermally influenced interstitial fluids is characterized by basalt diapiric intrusions and is delineated by an acoustically turbid zone in the sediments of the eastern part of the basin. Iron-sulphide-bearing veins and fractures cut across the sediment in several cores; they appear to be conduits for flow of hydrothermally altered fluids. These zones have the highest C2+ and ethene contents. The thermogenic hydrocarbons have molecular C1/(C2 + C3) ratios typically < 50 and delta13CH4 values between -38‰ and -48‰, indicating an organic source which has undergone strong thermal stress. Several sediment cores also have mixed gas signatures, which indicate the presence of substantial amounts of bacterial gas, predominantly methane. Hydrocarbon generation in the King George Basin is thought to be a local phenomenon, resulting from submarine volcanism with temperatures in the range 70-150°C. There are no apparent seepages of hydrocarbons into the water column, and it is not believed that significant accumulation of thermogenic hydrocarbons reside in the basin.

热成因烃类（thermogenic hydrocarbons）由有机质热蚀变形成，在南极乔治王盆地（King George Basin, Antarctica）的多个活塞取芯站位（piston core stations）均有检出。此类半远洋沉积物沉积于与布兰斯菲尔德海峡（Bransfield Strait）弧后扩张（back-arc spreading）相关的活跃热液活动（active hydrothermalism）区域。受热液影响的孔隙流体（interstitial fluids）渗透的沉积物横向分布范围以玄武岩底辟侵入体（basalt diapiric intrusions）为特征，并在盆地东部沉积物中以声学浑浊带（acoustically turbid zone）圈定。多个岩芯中可见含铁硫化物脉（iron-sulphide-bearing veins）及裂隙切割沉积物，这些结构似乎是热液蚀变流体运移的通道。此类区域的C2+烃类及乙烯（ethene）含量最高。热成因烃类的分子比值C1/(C2+C3)通常小于50，甲烷碳同位素δ13CH4值介于-38‰至-48‰之间，表明其有机质源岩经历了强烈热应力作用。部分沉积岩芯还呈现混合气体特征，显示存在大量以甲烷为主的细菌成因气（bacterial gas）。学界认为乔治王盆地的烃类生成属于局部现象，由温度介于70-150℃的海底火山作用（submarine volcanism）所致。目前未发现烃类向水柱（water column）发生明显渗漏，且该盆地中不存在显著的热成因烃类聚集。