ABSTRACT

Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100–2600 m. Pockmarks are most concentrated at 400–850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes – (1) large (>0.5 km² area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (∼100–200 m diameter; ∼0.008–0.03 km² area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic.

摘要

封闭的凹陷，称为麻点，是广泛存在的海底形态，通常与流体渗漏有关。这项研究首次详细记录了新西兰奥特亚罗阿南岛/蒂怀普纳穆的南韦斯特兰边缘附近的麻点。通过在 100–2600 米的水深中手动和半自动选择，从多波束测深（25 米网格）识别麻点。麻点最集中在海底峡谷间大陆坡区水深400～850 m处。麻点形态的连续体包括 - (1)部分填充通道上方的大（>0.5 km ^{2区域）和不规则形状的麻点；}(2) 小而圆形的麻点（直径约 100-200 米；约 0.008-0.03 公里²区）发生在峡谷之间；(3) 细长和中等大小的麻点，通常沿斜坡方向，通常出现在埋藏的沉积物波之上。细长的麻点似乎已被近海底海洋学和/或浊流改变。麻点特征出现在 Aotearoa 周围的许多地方，包括东部和西部边缘。在这些不同的构造、沉积和海洋环境中发现了一些相似的麻点形态，这表明形成机制可能存在一些相似之处，但导致其形成的明确机制仍然是个谜。