|Victoria Poutans, Lev Merklin, Ivar Murdmaa|
Sediment Filling of the Jan Mayen Fracture Zone Trough and the Extinct Aegir Rift Valley, Norwegian Sea
Victoria Poutans (Russia State Geological Prospecting University; Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia) Lev Merklin and Ivar Murdmaa, (Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia) In deep (3600-3800m) central part of Norway Sea (Fig. 1), the detailed seismoacoustic profiling by Parasound-DS1 was carried out in 90s (3d cruise of RV "Akademik Ioffe", 12th and 16th cruises of RV "Akademik Sergey Vavilov"). This research aimed investigation of fine structure of bottom sediments and sedimentation processes during late Quaternary glaciations.
At the junction of the Jan Mayen Fracture Zone (FZ) with the extinct Aegir spreading ridge axis (Fig. 2) seismoacoustic Parasound records revealed abnormal sedimentary pattern (Fig. 8). The subhorizontally bedded sediment body, up to 80-90 m thick, overlies acoustic basement in the depressions, and wedges out against the bordering ridge slopes covered with thin discontinuous pelagic sediments. Three concordant seismostratigraphic units are distinguished in the infilling sediments: (A) the upper transparent unit, up to 20-25 m thick (Fig.4); (B) the middle strongly stratified unit, 5-20 m thick (Fig. 5); and (C) the lower transparent unit, up to 40-50 m thick in depocenters (Fig. 6).
Sediment age of Layer C basement is limited by extinction time of the spreading ridge in the Late Miocene, but a major part of sediments likely accumulated during the Late Quaternary glaciations, under direct or indirect influence of the Fennoscandinavian ice sheet. Unfortunately, direct coring data on the sediment composition and age is absent, but we can keep tabs on boundary A-B by the slope (Fig.10) up to Voring Plateau with a coring data of Vavilov-16 (2002) which gives boundary A-B age of H1 - first Heinrich event.
Acoustic transparency of Layers A and C tells about thin disperce sediments without stratifications. The regional sedimentological setting  suggests that units likely consist of rapidly accumulated homogeneous clay and ooze originally derived from the glacier meltwater. The acoustically stratified unit presumably comprises a series of denser interbeds which consist of alternating terrigenious sediments with coarse debris (IRD) and tefras correlated with Last Deglaciation.
Transporting and accumulation mechanisms are not quite clear because of known low accumulation speed in central part of the sea. Although our huge sediment body was deposited very fast – layer A (20m) by 8 kyr, such a velocity could be explained by resuspending by sliding on Norwegian (and Greenland?) continental slopes including by Storegga Slide (7000 Y), for example. As it seemed from hydroacoustic data ,  the Storegga Slide sediment material reached the Jan-Majen trough exactly (Fig. 12). Similarity of sedimentary patterns in Greenland fjords  (Fig. 9) with ours allows to suppose their identical origin – transporting by near-bottom suspension flows (Fig. 11). In the same time there are no acoustically transparent layers on the Voring Plateau and Scandinavian continental slope.
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