Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate‐Bearing Sediments in the Eastern Nankai Trough
Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate‐Bearing Sediments in the Eastern Nankai Trough
复制标题
南海海槽东部含天然气水合物沉积物的岩性、生物地层学和磁力地层学
DOI：
10.1111/j.1751-3928.2004.tb00184.x
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发表时间：
2004
期刊：
影响因子：
1.4
通讯作者：
R. Matsumoto
中科院分区：
文献类型：
--
作者：
Y. Hiroki;Kazue Watanabe;R. Matsumoto
摘要：在日本御前崎附近60 km的南海海槽向陆坡上钻探的BH-1井沉积物中，研究了地层对天然气水合物形成和分布的控制作用。在250 m厚的沉积物序列中识别出三个岩性单元：单元1（0-70 mbsf）由石灰质淤泥和粘土组成，带有薄火山灰层，2号机组（70-150 mbsf）由石灰质粉土和粘土以及火山灰和薄砂层组成，单元3（150-250 mbsf）由弱固结钙质粉土和粘土组成，砂层厚且频繁。沉积物中的糊状结构和气泡表明在40和130 mbsf之间和低于195 mbsf的两个水合物区的存在。超微化石生物地层学和磁性地层学表明，在BH-1井恢复的层序大部分是连续的，代表0至1.5 Ma的沉积物。沉降速率的计算揭示了65和90 mbsf之间的浓缩部分。BH-1井中天然气水合物的推断分布似乎受到沉积物的地层学和岩性的强烈控制。3号机组中厚的缓倾斜砂层为来自较深区域的气体迁移提供了通道，并被认为是195 mbsf以下水合物带形成的原因。在较浅的水平，薄的，轻轻倾斜的砂层也被认为是允许气体的迁移，导致40和130 mbsf之间的上部水合物区的形成。冷凝段上覆的近水平粉砂和粘土截断了下伏的缓倾斜砂和粉砂/粘土层，可为通过砂层供应的气体提供有效的圈闭，进一步促进上部水合物带的水合物形成。
Abstract: Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH‐1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m‐thick sequence of sediments: Unit 1 (0–70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70–150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150–250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH‐1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH‐1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub‐horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.