The Top Oligocene Unconformity in the Arctic Ocean

Anne Hegewald

Based on multi-channel seismic lines as well as seismic wide-angle reflection and refraction data, acquired in the northern Chukchi region during the RV Polarstern ARK-XXIII/3 summer expedition in 2008, we were able to date sediment horizons within the research area. For dating, the age control of five exploration wells drilled near the coast of Alaska in combination with additional seismic reflection lines located on the Chukchi Shelf were used. In total, six sediment horizons with ages between Barremian/Hauterivian and the Top Miocene were identified. Especially the Top Oligocene horizon forms an erosional surface on the Chukchi Plateau and on the southern Mendeleev Ridge flanks. This special flank erosion was prior reported from the northern Mendeleev Ridge, the Alpha Ridge as well as the Lomonosov Ridge, unfortunately without any age control. In general, the Top Oligocene horizon separates two modes of sedimentation: (1) undulated reflectors with high impedance contrasts below the horizon and (2) continuous, undisturbed reflectors with low impedance contrasts above the horizon. At the same time (Late Oligocene/Early Miocene) we observed that the relative sea level of the Arctic Ocean fell dramatically by around 400 m and significant erosion occurred on the shelf areas. These facts lead to the conclusion that the origin of the Top Oligocene unconformity was a regional, tectonic event. The opening of the Fram Strait in the Late Oligocene/Early Miocene indicates a significant change in the Arctic Ocean current system and therefore, in the mode of sedimentation. This reconnection of the Arctic Ocean with the global ocean, especially the Atlantic Ocean, led to the drainage of Arctic Ocean water into the Atlantic Ocean and a fall of the Arctic relative sea level.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013