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西北冰洋北风海盆的碎屑流沉积
Debris flows deposition in the Northwind Basin, western Arctic Ocean
极地区域大陆边缘广泛发育水下碎屑流沉积,其中很多是冰川成因,是冰盖到达陆架边缘的产物。位于北冰洋楚科奇陆缘的北风海盆,其西侧陆缘已识别出大量碎屑流事件,而对北风海盆内部碎屑流的研究却几乎没有开展。该文利用高分辨率的浅地层剖面数据,勾勒出了北风海盆上部地层的碎屑流平面展布,且进行了期次划分;并结合周边的大型冰川线理(MSGL)的分布及走向,对所有识别出的碎屑流进行了成因推断。结果表明研究区内的碎屑流主要分布在西部次海盆的西南斜坡和中北部斜坡、东部次海盆的东南部以及部分海山/陡崖之下,其来源包括周边陆架、海脊高地和盆内海山。绝大多数碎屑流与MSGL伴生存在,推测为冰川成因,其中以西南斜坡最为发育,发现了超过9期的冰川碎屑流事件,代表了在其西南的冰蚀槽(宽水深槽)内曾发生超过9次的冰流事件,这一数据远大于前人所推测的冰流事件次数(3~5次)。同时也发现部分碎屑流邻近的海山/高地上不发育MSGL等冰川触地地貌,推测其为非冰川成因,邻近区域的冰盖/冰架触地或构造活动所引发的震动可能是这类碎屑流的触发因素。
Subaqueous debris flows are widely developed on polar continental margins, many of which are glacigenic, representing the products of ice sheets reaching the shelf edge. In the western Arctic Ocean, a large number of debris flows have been identified at the continental margin west of the Northwind Basin, however research on debris flows within this basin has hardly been carried out. In this study, the distribution of debris flows was outlined and their formation ages were determined using the high-resolution sub-bottom profiler data. Then the mega-scale glacial lineations (MSGL) was used as the judgment indicators to infer the origin of these debris flows. It is found that the debris flows in the study area are mainly distributed on the southwestern and northern-central slope of the western sub-basin, in the southeastern part of the eastern sub-basin, and on the slopes of some seamounts and cliffs. They are from the surrounding continental shelf, ridges and seamounts. Most debris flows coexist with MSGL and are presumed to be glacigenic. More than 9 glacigenic debris flows have been found on the southwestern slope, which may indicate more than 9 ice streams advances through the Broad Bathymetric Trough. The number of ice streams advances are much more than the previous speculation (3-5). There are also some debris flows with no ice-grounding landforms (e.g. MSGL) have been found in the nearby seamounts and are presumed to be non-glacigenic. The shock caused by the grounding of the ice sheets/shelves in the nearby area or tectonic movement may be the trigger factors for this kind of debris flows.
北风海盆 / 楚科奇边缘地 / 冰川碎屑流 / 大型冰川线理
Northwind Basin / Chukchi Borderland / glacigenic debris flows / MSGL
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鲜本忠, 安思奇, 施文华. 水下碎屑流沉积:深水沉积研究热点与进展[J]. 地质论评, 2014, 60(1):39-51.
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At least two episodes of glacial erosion of the Chukchi margin at water depths to ∼ 450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ18O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ18O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide meltwater pulse at the Younger Dryas onset. The Bering Strait opening is also marked in the composition of late deglacial Chukchi sediments.
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Multibeam bathymetry and 3.5-kHz sub-bottom profiler data collected from the US icebreaker Healy in 2003 provide convincing evidence for grounded ice on the Chukchi Borderland off the northern Alaskan margin, Arctic Ocean. The data show parallel, glacially induced seafloor scours, or grooves, and intervening ridges that reach widths of 1000 m (rim to rim) and as much as 40 m relief. Following previous authors, we refer to these features as “megascale glacial lineations (MSGLs).” Additional support for ice grounding is apparent from stratigraphic unconformities, interpreted to have been caused by ice-induced erosion. Most likely, the observed sea-floor features represent evidence for massive ice-shelf grounding. The general ESE/WNW direction of the MSGLs, together with sediment, evidently bulldozed off the Chukchi Plateau, that is mapped on the western (Siberian) side of the plateau, suggests ice flow from the Canada Basin side of Chukchi Borderland. Two separate generations of glacially derived MSGLs are identified on the Chukchi Borderland from the Healy geophysical data. The deepest and oldest extensive MSGLs appear to be draped by sediments less than 5 m thick, whereas no sediment drape can be distinguished within the resolution of the sub-bottom profiles on the younger generation.
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Surface Related Multiple Elimination (SRME) usually suffers the issue of either over-attenuation that damages the primaries or under-attenuation that leaves strong residual multiples. This dilemma happens commonly when SRME is combined with least-squares subtraction. Here we introduce a more sophisticated subtraction approach that facilitates better separation of multiples from primaries. Curvelet-domain subtraction transforms both the data and the multiple model into the curvelet domain, where different frequency bands (scales) and event directions (orientations) are represented by a finite number of curvelet coefficients. When combined with adaptive subtraction in the time–space domain, this method can handle model prediction errors to achieve effective subtraction. We demonstrate this method on two 2D surveys from the TAiwan Integrated GEodynamics Research (TAIGER) project. With a careful parameter determination flow, our result shows curvelet-domain subtraction outperforms least-squares subtraction in all geological settings. We also present one failed case where specific geological condition hinders proper multiple subtraction. We further demonstrate that even for data acquired with short cables, curvelet-domain subtraction can still provide better results than least-squares subtraction. We recommend this method as the standard processing flow for multi-channel seismic data.
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Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet.
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Multibeam report for HLY1603[R/OL]. [2022-05-02]. https://www.ngdc.noaa.gov/ships/healy/HLY1603_mb.html.
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感谢中国第11次北极科学考察“雪龙2”号船长赵炎平及全体船员。
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