Hemipelagic deposits on the Mendeleev and northwestern Alpha submarine Ridges in the Arctic Ocean: acoustic stratigraphy,depositional environment and an inter-ridge correlation calibrated by the ACEX results |
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Authors: | Vibeke Bruvoll Yngve Kristoffersen Bernard J Coakley John R Hopper |
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Institution: | 1.Department of Earth Science,University of Bergen,Bergen,Norway;2.Geophysical Institute,University of Alaska, Fairbanks,Fairbanks,USA;3.Geological Survey of Denmark and Greenland,?ster Voldgade 10,Copenhagen K,Denmark |
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Abstract: | The first high resolution multichannel seismic data from the Mendeleev and Alpha Ridges in the Arctic Ocean have been used
to investigate the depositional history, and compare acoustic stratigraphies of the three main sub-marine ridges (Mendeleev,
Alpha and Lomonosov) in the polar ocean. Acoustic basement on the Mendeleev Ridge is covered by a ~0.6–0.8 s thick sediment
drape over highs and up to 1.8 s within grabens. A pronounced angular discordance at 0.18–0.23 s below the seafloor along
the middle to upper slopes divides the succession into an upper, undisturbed, uniformly thick, hemipelagic drape (Unit M1)
and a partially truncated lower unit (Unit M2) characterized by strong reflection bands. Unit M2 is thicker in intra-ridge
grabens and includes three sub-units with abundant debris flows in the uppermost subunit (M2a). The discordance between Units
M1 and M2 most likely relates to instability along the middle to upper slopes and mass wasting, triggered by tectonic activity.
The scars were further smoothed by bottom current erosion. We observe comparable acoustic stratigraphy and discordant relationships
on the investigated northwestern part of Alpha Ridge. Similarly, on the central Lomonosov Ridge, Paleocene and younger sediments
sampled by scientific drilling include an uppermost ~0.2 s thick drape overlying, highly reflective deposits with an angular
unconformity confined to the upper slope on both sides of the ridge. Sediment instability on the three main ridges was most
likely generated by a brief phase of tectonic activity (~14.5–22 Ma), coinciding with enhanced bottom circulation. These events
are coeval with the initial opening of the Fram Strait. The age of the oldest sediments above acoustic basement on the Mendeleev-
and west-central Alpha Ridges is estimated to be 70–75 Ma. |
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