Origin of hydrocarbons in the Green Tuff region of Japan: 129I results from oil field brines and hot springs in the Akita and Niigata Basins
Origin of hydrocarbons in the Green Tuff region of Japan: 129I results from oil field brines and hot springs in the Akita and Niigata Basins
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DOI：
10.1016/j.chemgeo.2009.03.008
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发表时间：
2009-06
期刊：
影响因子：
3.9
通讯作者：
H. Tomaru;Zunli Lu;U. Fehn;Y. Muramatsu
中科院分区：
文献类型：
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作者：
H. Tomaru;Zunli Lu;U. Fehn;Y. Muramatsu
秋田盆地和新泻盆地是日本本州绿色凝灰岩地区的一部分，该地区拥有主要的石油和天然气以及热液硫化物-硫酸盐黑矿矿床。绿色凝灰岩建造与日本海的开放有关，该开放发生在早中新世，并伴随着大规模的火山活动。我们测量了油气田卤水和温泉中的卤素浓度和129 I/I比值，以确定碘的来源，并间接确定该地区烃的来源及其与日本岛弧形成过程中地质作用的关系。根据碘的浓度，这些样品分为三类：A型（I>190 μM）、B型（150 μM>I>90 μM）和C型（I<50 μM）。A型和B型样品主要来自油气田，129 I/I比值低于300×10−15，基本上对应于始新世的年龄。相反，C型样品通常来自温泉，129 I/I比值大于400×10−15，对应于渐新世至中新世的年龄。C型的物源层是在日本海活跃打开期间积累的，然而，A型和B型的物源层可能是富含有机质的始新世沉积物或早于与日本岛弧后扩张相关的火山岩建造的更老的基底岩石。石油和天然气主要存在于中新世中期至晚期的储层中，这表明这些盐水的流动与日本海开放期间的构造和火山/热液活动有关，这也导致了同一地区Kuroko矿床的形成。C型温泉样品最直接地反映了这些过程。由于碘与甲烷和其他碳氢化合物密切相关，因此绿色凝灰岩地区的石油和天然气可能也来自比当前储层形成时间更早的来源。
The Akita and Niigata Basins are part of the Green Tuff region of Honshu, Japan, which hosts major occurrences of oil and gas and of hydrothermal sulfide-sulfate Kuroko Deposits. The Green Tuff formation is associated with the opening of the Japan Sea, which occurred in the Early Miocene and was accompanied by large-scale volcanic activities. We measured halogen concentrations and129I/I ratios in oil and gas field brines and hot springs in order to determine the origin of iodine and, indirectly, of hydrocarbons in this area and their association with geological processes during the formation of the Japanese Island Arc. Based on the concentration of iodine, these samples fall into three categories: Type A (I>190 μM), Type B (150 μM>I>90 μM), and Type C (I<50 μM). Samples in Types A and B come predominantly from oil/gas fields and have129I/I ratios below 300×10−15, corresponding to ages essentially in the Eocene epoch. In contrast, samples in Type C are generally from hot springs and have129I/I ratios above 400×10−15, corresponding to Oligocene to Miocene ages. Source formations for Type C were accumulated during the active opening of the Japan Sea, however, those for Types A and B probably are organic-rich Eocene sediments or older basement rocks which predate the volcanic formations associated with the backarc spreading of the Japanese Island. The observation that oil and gas is predominantly found in reservoir formations of middle to late Miocene age suggests mobilization of these brines in association with the tectonic and volcanic/hydrothermal activities during the opening of the Japan Sea which also led to the formation of the Kuroko Deposits in the same area. The hot spring samples of Type C reflect these processes most directly. Because of the close association of iodine with methane and other hydrocarbons, oil and gas in the Green Tuff area probably is also derived from sources considerably older than the current reservoir formations.