Detailed aeromagnetic investigation of the Arctic Basin

Abstract

Systematic low‐level aeromagnetic surveys conducted during 1974–1975 reveal details of the magnetic fabric in two parts of the Arctic Basin. These profiles extend coverage of the Nansen (Gakkel; Mid‐Arctic) Ridge from 85.3°N, 13°E to 86°N, 50°E, where these new data overlap previous Soviet aeromagnetic coverage. Prominent magnetic lineations can be identified despite spreading half‐rates as low as 0.3 cm/yr about 25–35 m.y. B.P. The separation of Lomonosov Ridge from Eurasia occurred at or before anomaly 24 time (55 m.y. B.P.). Although there is ‘room’ for anomalies 25–27 between 24 and the continental margin, a broad magnetic negative exists in their place. Either anomalies 25–27 were suppressed or erased by thick sediment fill or some other process associated with initial rifting, or the associated crust is subsided continental material. All anomalies, particularly the central anomaly, exhibit dramatic variations of amplitude along their strike. It is the low values of amplitude that are anomalous with respect to the Mid‐Atlantic Ridge to the south. Bathymetric data demonstrate that the high central anomaly amplitudes correlate with shallower rift valley floors (3500–4000 m) and higher rift mountains. We propose that the pillow basalt layer (2a) is thicker in the magnetic high amplitude zones. There is no bathymetric evidence for sediment gaining access to the valley floor in the area examined. A second survey was flown across the northern Canada Basin and Alpha Ridge. Complex, but lineated, anomalies of 1500 to 2500 nT relief parallel the crest of Alpha Ridge. A crestal valley, 2500 m deep and 30 km wide, flanked by ridges with crests 1200–1500 m deep, correlates well with magnetic and gravity anomalies; this suggests that prominent Alpha Ridge magnetic anomalies are caused by basement topography of high magnetization (20–30 A/M) and normal polarity. If the Alpha Ridge is floored by an anomalous type of oceanic crust, it probably originated during the long mid‐Cretaceous period of normal polarity. In the northern Canada Basin, several prominent linear anomalies cross the surveyed swath on strikes of 040°T to 065°T, subparallel to the Alpha Cordillera. If these lineations reflect sea‐floor spreading and geomagnetic reversals (possibly during the lower Cretaceous to upper Jurassic), the spreading axis cannot have paralleled either the Canadian continental margin or the Alpha Ridge as has been proposed, but instead, lay parallel to the Northwind Escarpment.

Food Colors and Behavior

“…this and other marine silicoflagellate assemblages in the Arctic area does not -preclude a brief terminal Cretaceous freshening event." These are substantially the same conclusions advanced earlier (8 As to the volume of the latest Cretaceous Arctic Ocean, most reconstructions require the Amerasian Basin to be underlain by very old crust, crust that probably was already in thermal or isostatic equilibrium in latest Cretaceous time (11,12). The very large amount of post-Cretaceous sediment fill, therefore, probably has reduced the volume of the basin.…”

The Cenozoic palaeoenvironment of the Arctic Ocean

“…This led to the hypothesis that the Lomonosov ridge was a continental fragment that broke away from the Eurasian continental margin owing to spreading along the Gakkel ridge. Aeromagnetic surveys support this assumption, and suggest that initiation of Arctic seafloor spreading along the Gakkel ridge began during chron 24, ,57 Myr ago, the time of the Palaeocene/Eocene boundary 5,6 . As rifting progressed, the Lomonosov ridge moved away from the continent, towards the pole, and subsided ,1,200 m, initially at a slow rate in the Palaeogene, followed by more rapid subsidence later ARTICLES in the Neogene.…”

Expanding the Cenozoic paleoceanographic record in the Central Arctic Ocean: IODP Expedition 302 Synthesis

“…The Lomonosov Ridge separates the older Amerasian Basin from the younger Eurasian Basin (Figure 1). This ridge was rifted from the Eurasian margin as a continental margin fragment during the late Paleocene, initiating the formation of the Eurasian Basin [10][11][12][13][14]. The deep basins of the Arctic Ocean are blanketed with thick sediment sequences, 6-10 km in the older Amerasian Basin and 2-3 km in the younger Eurasian Basin [15].…”