New Paleomagnetic Data Related to the Opening of the Arctic Ocean

Samples for paleomagnetic measurements were collected from the New Siberian Islands (2006) and from further north on Bennett Island in the De Long Terrane (2011). All samples were subjected to multi-stepThermal and/or Alternating Field demagnetization. The Kotel'ny Island samples represent three age groups, Lower Triassic (Induan, 250-245 Ma) uppermost Triassic to lowermost Jurassic (Rhaetian, approx. 208 Ma) and Albian (approx. 100Ma). All the sampling sites had relatively shallow bedding attitudes (0-20°) with little in-site variation. This made in-site fold tests impossible. Variations in the mean vectors between sites showed clear, but small separations between the geographic and stratigraphic reference frames in favor of a post tilting (overprint) magnetization. The combined vector directions and the resultant VGP from all localities in a geographic reference frame are: Dg 52.9, Ig 84.6, N=51, R=50, α95=2.8: VGP lat 78.7, Long 187, α95=5.5°. The mean normal polarity overprint VGP for all of Northeast Russia is: Lat 73, Long 134, N=26, α95=6.8 and is presumed to be related to the long Cretaceous Normal Polarity event (about 120Ma to 80Ma). Six basaltic flow units were sampled on Bennett Island, five from near the base of the section which lies on Cambrian basement, which is exposed close to sea level, and the sixth from the basaltic plateau (207m asl). Samples were also collected from cobbles in a rubble interbed for magnetic stability tests. The age of these basalts has been measured using K-Ar techniques as being between 124Ma and 106Ma by Federov et al., (Doklady Earth Sciences 401, 2005). Samples from the 2011 collection are currently being measured using 40Ar/39Ar methods. The preliminary paleomagnetic measurements on the Bennett Island flows give four flows with Normal magnetizations and one which is Reversed. The cobbles from the interbed give random directions (α95= 85°). The reversed and normal directions pass the reversal test. The preliminary resultant vectors give steep inclinations, very similar to the pervasive overprint seen on Kotel'ny Island and throughout Northeast Russia, however the reversal and "conglomerate" test clearly indicate a primary magnetization. The preliminary results give a vector mean in the stratigraphic reference frame: Ds 125.9, Is 85.4, N=6, R=56.2, α95=9: VGP Lat 70.3, Long 170.1, N=6, α95=17.5. This pole lies close to the mean pole for the Cretaceous still-stand between 130Ma-80Ma. (Lat. 75.5, Long.192.5, N=11, α95=1.2, Kent and Irving, JGR, 2010) which implies that Bennett Island was not significantly displaced from Eurasia.