Late Quaternary sedimentation on the Mid-Atlantic Reykjanes Ridge: clay mineral assemblages and depositional environment

• Published in: Geologische Rundschau
• Main Authors: Gehrke, B., Lackschewitz, Klas, Wallrabe-Adams, H. -J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 1996
• Subjects: Reykjanes; Iceland; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/31229/; https://oceanrep.geomar.de/id/eprint/31229/1/art_10.1007_BF02369007.pdf; https://doi.org/10.1007/BF02369007

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 ...