Waage Malin, Serov Pavel, Andreassen Karin, Waghorn Kate A, Bünz Stefan
CAGE - Centre for Arctic Gas Hydrate, Environment, and Climate, Department of Geosciences, UiT the Arctic University of Norway, 9037, Tromsø, Norway.
Sci Rep. 2020 May 21;10(1):8450. doi: 10.1038/s41598-020-65018-9.
Active methane seepage occurs congruent with a high density of up to 1 km-wide and 35 m deep seafloor craters (>100 craters within 700 km area) within lithified sedimentary rocks in the northern Barents Sea. The crater origin has been hypothesized to be related to rapid gas hydrate dissociation and methane release around 15-12 ka BP, but the geological setting that enabled and possibly controlled the formation of craters has not yet been addressed. To investigate the geological setting beneath the craters in detail, we acquired high-resolution 3D seismic data. The data reveals that craters occur within ~250-230 Myr old fault zones. Fault intersections and fault planes typically define the crater perimeters. Mapping the seismic stratigraphy and fault displacements beneath the craters we suggest that the craters are fault-bounded collapse structures. The fault pattern controlled the craters occurrences, size and geometry. We propose that this Triassic fault system acted as a suite of methane migration conduits and was the prerequisite step for further seafloor deformations triggered by rapid gas hydrate dissociation some 15-12 ka BP. Similar processes leading to methane releases and fault bounded subsidence (crater-formation) may take place in areas where contemporary ice masses are retreating across faulted bedrocks with underlying shallow carbon reservoirs.
在巴伦支海北部的石化沉积岩中，活跃的甲烷渗漏与高密度的海底火山口同时出现，这些火山口宽达1公里、深35米（在700平方公里的区域内有超过100个火山口）。火山口的成因据推测与约15 - 12千年前快速的天然气水合物分解和甲烷释放有关，但促成并可能控制火山口形成的地质背景尚未得到探讨。为了详细研究火山口下方的地质背景，我们获取了高分辨率的三维地震数据。数据显示，火山口出现在约2.5亿 - 2.3亿年前的断层带内。断层交叉点和断层面通常界定了火山口的周边。通过绘制火山口下方的地震地层和断层位移图，我们认为这些火山口是断层边界的塌陷构造。断层模式控制了火山口的出现、大小和几何形状。我们提出，这个三叠纪断层系统充当了一套甲烷运移通道，并且是约15 - 12千年前快速的天然气水合物分解引发进一步海底变形的前提条件。在当代冰体正在跨越具有浅层碳储层的断层基岩后退的地区，可能会发生导致甲烷释放和断层边界沉降（火山口形成）的类似过程。
