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B. Gehrke K. S. Lackschewitz H. -J. Wallrabe-Adams 《International Journal of Earth Sciences》1996,85(3):525-535
Sediment samples from the Mid-Atlantic Reykjanes Ridge (59°N) were taken to get information about sediment genesis and to
identify different sources during the late Quaternary. Samples were investigated by X-ray diffraction and grain-size analyses.
The clay mineral assemblages in sediments of the Reykjanes Ridge reflect paleoceanographic changes during the late Quaternary.
Holocene sediments are characterized by high contents of smectite, mainly of less developed crystallinity. In the spatial
distribution of clay minerals high smectite concentrations on the eastern flank and slightly decreasing concentrations on
the western flank of the Reykjanes Ridge indicate the action of bottom-water transport. The smectite originates mainly from
the volcanogenous Icelandic shelf and reflects the influence of Iceland-Scotland Overflow Water (ISOW). Stratigraphic variability
in the clay mineral composition reflects predominantly the influence of different sources, resulting from oceanographic and
glacial transport processes. During glacial time sediment transport is due mainly to input by icebergs. Increasing amounts
of illite, chlorite, and kaolinite characterize ice-rafted sediments of the “Heinrich layers”. In these sediments smectite
crystallinity is well developed. In contrast, several other ice-rafted layers contain smectite with low crystallographic order,
similar to smectites of Holocene age. The icelandic source was proved by distinct amounts of basaltic glass in the coarse-grained
sediment. At approximately 55 ka increasing amounts of chlorite and kaolinite suggest an enhanced influx of warm North Atlantic
surface waters. This hypothesis is supported by a high carbonate shell production at this time. Relative low concentrations
and the well-developed crystallinity of smectite minerals characterize the Last Glacial Maximum (LGM; 18–16 ka), indicating
a reduced supply of fine icelandic material. Shortly after the LGM, at the beginning of termination IA, a distinct increase
in fine-grained quartz (<2μm) and smectite are visible, which are proposed to reflect a supply of fine-grained ice-rafted
material. At 13 ka linear increasing smectite concentrations of lower crystallographic order indicate increasing supply of
fine-grained material from Iceland, linked to reinitiation of bottom currents of the ISOW. Full reinitiation is indicated
at around 10 ka, where a strong increase in smectite of low crystallographic order is detected. 相似文献
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Ice-raft debris layers in the North Atlantic sediments of IRD belt characterize abrupt climate variability, corresponding to Heinrich events during the Last Glacial and Heinrich(-like) events beyond the Last Glacial. During Heinrich/(-like) events, the Earth's atmosphere, hydrosphere and cryosphere interacted strongly on the millennial-scale and had a profound impact on the global climate. In more than 30 years of continuous research on Heinrich/(-like) events and their remote response, the results have been more focused on the trigger mechanism and the new distinguished proxies of Heinrich/(-like) events. The first occurrence of Heinrich/(-like) events in IRD belt during MIS 16 was the initiation of a major landmark climate mechanism after MPT. The research on Heinrich/(-like) events may require a new ice sheet dynamics model related to the large ice sheet and the long-term ice age, which is forming a new hot topic. 相似文献
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Nigel R. Larkin Jonathan R. Lee E. Rodger Connell 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(3):445-454
Erratic clasts with a mass of up to 15 kg are described from preglacial shallow marine and coastal deposits (Wroxham Crag Formation) in northeast Norfolk. Detailed examination of their petrology has enabled them to be provenanced to northern Britain and southern Norway. Their clustered occurrence in coastal sediments in Norfolk is believed to be the product of ice-rafting from glacier incursions into the North Sea from eastern Scotland and southern Norway, and their subsequent grounding and melting within coastal areas of what is now north Norfolk. The precise timing of these restricted glaciations is difficult to determine. However, the relationship of the erratics to the biostratigraphic record and the first major expansion of ice into the North Sea suggest these events occurred during at least one glaciation between the late Early Pleistocene and early Middle Pleistocene (c. 1.1–0.6 Ma). In contrast to the late Middle (Anglian) and Late Pleistocene (Last Glacial Maximum) glaciations, where the North Sea was largely devoid of extensive marine conditions, the presence of far-travelled ice-rafted materials implies that earlier cold stage sea-levels were considerably higher. 相似文献
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