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21.
Submarine push moraine formation during the early Fennoscandian Ice Sheet deglaciation 总被引：2，自引：0，他引：2
The glacial history in the topographically confined paleo-ice stream drainage route of Vestfjorden, North Norway, was analysed based on bathymetric data, high-resolution seismology and 14C AMS-dated gravity cores. The inner part of the fjord is characterised by axial-parallel mega-scale lineations whereas the outer part is dominated by two marginal morainal bank systems. The Værøy (inner) and Røst (outer) marginal moraine systems comprise several transverse, zigzag-shaped ridges. Seismic records show thrusted and folded sediment blocks within the ridges. The landforms are inferred to reflect basal processes and the transition from warm-based (inner fjord) to cold-based (outer fjord) conditions, i.e. fast flow followed by basal freeze-on, sediment deformation and morainal bank formation. The moraines formed during the final part of two paleo-ice sheet re-advances. 14C AMS dating indicates a maximum age of 13.7 14C ka BP (16.2 cal ka BP) for the Røst system whereas the Værøy system is inferred to be slightly older than 12.5 14C ka BP (14.5 cal ka BP). This demonstrates that the northern part of the Fennoscandian Ice Sheet behaved in a much more dynamic way during the early deglaciation than previously assumed. 相似文献
22.
J. S. Laberg M. Strasser T. M. Alves S. Gao K. Kawamura A. Kopf G. F. Moore 《Landslides》2017,14(3):849-860
The processes of flow deformation of marine mass-transport sediments, including their ability to affect the underlying substrate and add mass during sediment flow events, are addressed based on sedimentological analyses of strata from the distal part of a ～61-m-thick mass-transport deposit (MTD 6) drilled during Integrated Ocean Drilling Program (IODP) Expedition 333. Our analyses, supported by 3D seismic data, show a cohesive density flow deformed by folding, faulting and shear, except for its lowermost part (～7 m), where no deformation and sediment entrainment was identified. While the lowermost part moved as rigid sediment, the underlying sand layer acted as the basal shear zone for this part of the distal MTD 6. This shear zone was restricted to the sand, not involving the overlying sediments. From this, the studied part of MTD 6 was found to represent a case where the flow behaviour at least partly depended on the location and properties of the underlying sand layer, a situation that so far has received little attention in studies of marine flows. Our results also show that shear-induced mixing, located by the initial layering, is an important process in the flow transformation from cohesive slumps to mud flows and that this may occur over short distances (<4 km) without involving disintegration into blocks, probably due to only moderate prefailure consolidation of the sediments involved. In conclusion, we find that the bulk part of the flow was self-contained from a mass balance point of view and that that the overall amount of entrainment was limited. 相似文献