Methane seeps on the U.S. Atlantic margin: An updated inventory and interpretative framework

IF 2.6 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Marine Geology Pub Date : 2024-04-09 DOI:10.1016/j.margeo.2024.107287
C.D. Ruppel , A.D. Skarke , N.C. Miller , M.W. Kidiwela , J. Kluesner , W. Baldwin
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Abstract

Since the discovery of >570 methane flares on the northern U.S. Atlantic margin between Cape Hatteras and Georges Bank in the last decade, the acquisition of thousands of kilometers of additional water column imaging data has provided greater coverage at water depths between the outer continental shelf and the lower continental slope. The additional high-resolution data reveal >1400 gas flares, but the removal of probable duplicates from the combined database of new flares and those recognized in 2014 yields ∼1139 unique sites. Most of these sites occur in clusters of 5 or more seeps, leaving about 275 unique locations (including 47 clusters) for seepage along the margin. As a function of depth, seep distribution is heavily skewed toward the upper continental slope at water depths shallower than 400 m on the southern New England margin and ∼ 550 m in the Mid-Atlantic Bight, with additional seeps clustered at ∼1100 m and just deeper than ∼1400 m in both sectors. Despite little ongoing tectonic deformation or active faulting on this passive margin, a variety of processes driven from below the seafloor (e.g., migration of fluids along faults or through permeable strata, seepage above diapirs or other pre-existing structures) and from above (e.g., erosion, sapping, unroofing) contribute to the development of seeps in different settings along the margin. In addition, the prevalence of seeps on promontories overlooking shelf-breaking canyons may be directly related to the three-dimensional nature of the hydrate stability zone in these locations. As a function of depth, the parts of the slope at the contemporary landward limit of gas hydrate stability are devoid of seeps, and the upper slope zones with the most concentrated seepage were not within the gas hydrate stability zone even during the Last Glacial Maximum. Thus, if the large number of upper slope seeps is at least partially sourced in gas hydrate degradation, the gas emitted at these seeps must have migrated there from greater depths on the continental slope.

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美国大西洋边缘的甲烷渗漏:最新清单和解释框架
自过去十年在哈特拉斯角和乔治斯滩之间的美国北部大西洋边缘发现570个甲烷燃烧点以来,数千公里的额外水柱成像数据的获取扩大了在外大陆架和下大陆坡之间水深的覆盖范围。新增的高分辨率数据揭示了 1400 个气体耀斑,但从新耀斑和 2014 年确认的耀斑合并数据库中去除可能的重复数据后,得到了 1139 个独特的地点。这些地点大多由 5 个或更多渗漏点组成,因此边缘地带的渗漏点约有 275 个(包括 47 个渗漏点)。作为水深的函数,在新英格兰南部边缘水深浅于 400 米和大西洋中部海湾水深 550 米处,渗漏分布严重偏向大陆坡上部,在这两个区域,还有一些渗漏聚集在水深 1100 米和水深 1400 米处。尽管在这一被动边缘上几乎没有持续的构造变形或活动断层,但来自海底下部(如流体沿断层或通过渗透性地层的迁移、在断裂带或其他已存在的结构上的渗流)和上部(如侵蚀、抽吸、解顶)的各种过程促使了边缘不同环境中渗流的发展。此外,在俯瞰陆架断裂峡谷的岬角上渗流的普遍性可能与这些地方水合物稳定区的三维性质直接相关。作为深度的函数,处于当代天然气水合物稳定向陆极限的斜坡部分没有渗漏,而渗漏最集中的斜坡上部区域即使在末次冰川极盛时期也不在天然气水合物稳定区范围内。因此,如果上坡的大量渗漏至少部分源于天然气水合物的降解,那么这些渗漏所释放的天然气一定是从大陆坡的更深处迁移到这里的。
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来源期刊
Marine Geology
Marine Geology 地学-地球科学综合
CiteScore
6.10
自引率
6.90%
发文量
175
审稿时长
21.9 weeks
期刊介绍: Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.
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