Late Weichselian deglaciation and early Holocene development of a cold-water coral reef along the Lopphavet shelf (Northern Norway) recorded by benthic foraminifera and ostracoda

摘要

Cold-water coral (CWC) settlement in northern Norway is strongly related to the outlet-glaciers of the Fennoscandian Ice-sheet, and dating of known CWC structures show clearly post-glacial ages. Two gravity cores (POS391559/2,277 cm long and POS391559/3,282 cm long) were recovered on a CWC reef in the area of Lopphavet, northern Norway. Detailed investigations on lithology (sediment structures and composition), micropaleontology (foraminifera and ostracoda) and AMS ~(14)C dating on the epibenthic foraminifera Discanomalina coronata were performed on the two cores. Phosphorus analyses were performed only on core POS391559/3. Results indicate that the whole core POS391559/2 is representative of a CWC reef environment. The base of the core is dated at 10,600 ±120 cal. yr BP, thus representing one of the oldest ages of a Norwegian coral reef. Core POS391559/3 documents the passage from a proximal glacier environment characterized by fine silty sediments with intercalation of several dropstone layers to a CWC ecosystem. The transition from the glacial to the interglacial stage is dated as old as 10,725 ± 205 cal. yr BP, whereas the base of the core is dated to an age of 15,300 ± 550 cal. yr BP. Diversity of benthic foraminifera is higher within the CWC, especially in the intervals containing coral framework. Five clusters are identified based on the Bray-Curtis Similarity Term Analyses and the interpretation of data shows that they are related to different ecological settings, e.g., fluctuations of the sea-ice cover; influence of the warmer and more saline Atlantic water masses; transitional to a fully interglacial environment; well oxygenated, nutrient-rich and high current setting being conducive to CWC. Ostracod assemblages show that these crustaceans may be also used to characterize sedimentary facies on CWC reefs.