Compression and expansion index and void ratio of samples from Lomonosov Ridge and Yermak Plateau@en

With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (~ 790-950 thousand years ago - ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf.借助北冰洋破冰船开展的多波束条带测深（multibeam swath bathymetry）、高分辨率浅地层剖面探测与沉积物取芯联合观测，学界对现今水深小于1000米的诸多地形高地广泛发育第四纪冰接地事件的认知正不断深化。在罗蒙诺索夫海岭（Lomonosov Ridge）与叶尔马克高原（Yermak Plateau）等区域，通过钻探或取芯获取的超固结沉积物（overconsolidated sediments），赋存于冰川成因的地震成像不整合面之下。然而，目前尚未有针对这类沉积物岩土工程特性的综合分析，也未明确其推断应力状态与不同冰川作用过程或冰荷载类型之间的关联。本研究整合了罗蒙诺索夫海岭与叶尔马克高原的地球物理、地层学及岩土工程测量数据，探讨了超固结沉积物的冰川地质意义。基于孔隙度与抗剪强度测定得到的超固结程度，证实其源于冰接地条件下的固结及/或变形；除罗蒙诺索夫海岭的单个区域外，该超固结程度无法用上覆沉积物的侵蚀作用解释。研究表明，叶尔马克高原中更新世（约79万~95万年前，ka）冰接地事件引发的孔隙度损失量与损失深度，与冰盖或冰隆作用下的沉积物固结过程相契合。与之相反，两个区域晚更新世冰接地事件（经独立定年为海洋同位素阶段（Marine Isotope Stage, MIS）6）下方沉积物的岩土工程特性，则显示其为更短暂的事件，与冰架崩解产生的平顶冰山过境过程相符。