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Cenozoic basin evolution beneath the southern McMurdo Ice Shelf, Antarctica

机译：南极麦克默多冰架下方的新生代盆地演化

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Fifty-two kilometres of multi-channel seismic reflection data were acquired from the southern McMurdo Ice Shelf (SMIS) during potential drill site investigations for the Antarctic Drilling (ANDRILL) program. The survey was acquired atop 110 to 220 m of floating ice and extended across ablation and accumulation zones of the ice shelf. Seismic processing was tailored to the ice shelf environment, including: datum static corrections to account for changes in the thickness and average velocity of the near-surface firn layer, and changes in the surface elevation across the survey area; residual static corrections to account for near-surface ice shelf irregularities; and two-step predictive deconvolution to suppress ice and firn layer multiples. A model for the ice shelf thickness was also incorporated in the interval velocity model during depth conversion to ensure that the ice shelf structure did not impose non-static shifts on the seismic section. The depth converted CMP stacked sections reveal several N to NE trending normal faults, that offset reflective horizons by up to 150 m within the lower part of the section and form a broad east-dipping, half-graben structure. The seafloor possesses trough and arch morphology in parallel with the half-graben structure. These features are interpreted as the southern extension of the Terror Rift. The rift succession comprises a dislocated (?)early-Miocene synrift package and a relatively undeformed (?)late-Miocene post-rift package separated by an erosional unconformity. The post-rift package infills and onlaps the rift topography, and drapes over the graben system, reaching a maximum thickness of 400 m. Throughout the post-rift phase, the basin was also influenced by Neogene volcanism, evidenced by three small volcanic features within the seismic profiles, and associated successions of inferred volcanic material. An angular unconformity within the post-rift succession is interpreted as a flexural horizon related to the load of Mount Discovery and/or Mount Morning. Up to 150 m of flexural moat fill occurs above this surface at -20 km from the load centres. The post-rift succession also includes several glacio-geomorphic features, the orientation and morphology of which indicate an approximately SW to NE ice flow direction during a mid-Miocene grounding event and a SE to NW ice flow direction during Quaternary ice sheet grounding events. The thickness and lower extent of the rift succession was not able to be determined because signal-to-noise ratio and vertical resolution were low at these depths. Strata from an earlier, Paleogene, rift episode may underlie the Terror Rift succession, or it may be directly underlain by acoustic basement. A Paleogene rift episode has previously been proposed based on the occurrence of Eocene fossiliferous erratics around the margin of the SMIS and the structural setting revealed by the SMIS seismic reflection profiles is consistent with this hypothesis.
机译：在对南极钻探（ANDRILL）计划进行潜在钻探现场调查时，从南部的麦克默多冰架（SMIS）获得了52公里的多通道地震反射数据。该调查是在110至220 m的浮冰上进行的，并横跨冰架的消融和积聚区域。地震处理是针对冰架环境量身定制的，包括：基准静态校正，以考虑近表层烧成层的厚度和平均速度的变化，以及整个调查区域中地表高度的变化；残余静校正，以解决近地冰架的不规则性；和两步预测反褶积来抑制冰层和烧成层的倍数。在深度转换过程中，还将冰架厚度模型纳入了层速度模型，以确保冰架结构不会在地震剖面上施加非静态位移。经过深度转换的CMP叠层断面显示出几个N到NE趋势的正断层，这些断层在该断层的下部偏移了最多150 m的反射层，并形成了一个宽广的向东倾斜的半graben结构。海底具有低谷和拱形形态，与半graben结构平行。这些特征被解释为恐怖纵容的南部延伸。裂谷序列包括一个错位的（-）中新世早期的中空包裹和一个相对较不变形的（β）中-中新世后裂谷的包裹，其被侵蚀不整合所分开。裂谷后包裹充填并覆盖裂谷地形，并覆盖在pes住系统上，最大厚度为400 m。在整个裂谷后阶段，该盆地还受到新近纪火山作用的影响，这由地震剖面内的三个小型火山特征以及推断的火山物质的相关演替来证明。裂谷后演替过程中的角度不整合被解释为与Mount Discovery和/或Mount Morning的负荷有关的挠曲层位。距负载中心-20 km处，该表面上方会发生多达150 m的弯曲mo沟填充。裂谷后的演替过程还包括几个冰川-地貌特征，它们的方向和形态指示在中新世中期事件期间大约SW到NE的冰流方向，在第四纪冰盖地面事件期间的SE到NW的冰流方向。由于在这些深度处信噪比和垂直分辨率较低，因此无法确定裂谷演替的厚度和较低程度。距今较早的裂谷事件地层可能是恐怖裂谷演替的基础，也可能是声学基底的直接地下层。以前已经根据SMIS边缘周围始新世化石的不规则性提出了古近纪裂谷事件，SMIS地震反射剖面揭示的构造背景与此假说是一致的。

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