The late Mesozoic-Cenozoic was a time of profound tectonic activity in the Arctic, with incipient spreading in the Arctic Ocean, Baffin Bay-Labrador Sea and North Atlantic, as well as the northward movement of the Greenland microplate leading to collision and deformation in Greenland, Arctic Canada and Svalbard (Eurekan Orogeny). It is, however, still unclear, how northern Svalbard, situated at the northwestern edge of the Barents Shelf, was affected by these processes. Furthermore, northern Svalbard has been proposed to have been a Cretaceous-Cenozoic sediment source to surrounding regions because it lacks a post-Devonian sedimentary cover. When erosion took place and how that related to the tectonic history of the Arctic, is yet unresolved. In order to reconstruct the erosion history of northern Svalbard, we constrained its thermal evolution using apatite fission track (AFT) thermochronology. Our data reveal AFT ages between 62 +/- 5 and 214 +/- 10 Ma, recording late Mesozoic-early Paleogene exhumation. Our data show that northern Svalbard was emergent and experienced erosion from the Early Jurassic and presumably through the Cenozoic, although total exhumation was restricted to similar to 6 km. Pronounced exhumation took place during Jurassic-Cretaceous time, probably linked to the extensional tectonics during the opening of the Amerasian Basin (Arctic Ocean). In contrast, Cenozoic ocean basin formation and the Eurekan deformation did not cause significant erosion of northem Svalbard. Nonetheless, AFT data show that Late Cretaceous-Early Paleocene fault-related exhumation affected some parts of northern Svalbard. Fault zones were reactivated due to the reorganization of Arctic landmasses during an early phase of the Eurekan deformation, which implies that this episode commenced similar to 20 m.y. earlier in Svalbard than previously understood.

Seismic profiles across the Lomonosov Ridge, Marvin Spur and adjacent basins, acquired near the North Pole by the drifting ice-station NP-28, provide a reflection image of the upper parts of the Ridge that is readily correlatable with those acquired by the Alfred Wegner Institute closer to the Siberian margin. A prominent flat-lying composite reflection package is seen in most parts of the Ridge at a few hundred meters below the sea bottom. Underlying reflections are variable in intensity and also in dip. The base of this reflection package is often accompanied by a sharp increase in P-velocity and defines a major angular discontinuity, referred to here as the Lomonosov Unconformity. The Arctic Coring Expedition (ACEX) cored the first c. 430 in section on the Lomonosov Ridge near the North Pole, in 2004 defining the deeper water character of the Neogene and the shallower water Paleogene sediments. These boreholes penetrated the composite reflection package towards the base of the hole and identified sediments (our Unit III) of late Paleocene and early Eocene age. Campanian beds at the very base of the hole were thought to be representative of the units below the Lomonosov Unconformity, but the P-velocity data suggest that this is unlikely. Correlation of the lithologies along the top of the Lomonosov Ridge and to the Marvin Spur indicates that the Marvin Spur is a sliver of continental crust closely related to, and rifted off the Ridge. This narrow (50 km wide) linear basement high can be followed into, beneath and across the Makarov Basin, supporting the interpretation that this Basin is partly resting on thinned continental crust. In the Makarov Basin, the Paleogene succession is much thicker than on the Ridge. Thus, the condensed, shallow water succession (with hiati) was deposited on the Ridge during rapid Eocene to Miocene subsidence of the Basin. In the Amundsen Basin, adjacent to the Lomonosov Ridge, the sedimentary successions thicken towards the Canadian margin and the reflections on the Ridge are not readily identifiable. The approximate ages of the sedimentary units are inferred from their relationships to the linear magnetic anomalies in the Basin. Lomonosov acoustic basement dips gently into the Basin over a distance of about 100 km and the linear negative anomaly, previously thought to be chron 25. is probably related to a rift-related mafic intrusive complex. (C) 2008 Elsevier B.V. All rights reserved.