Deciphering the geological history of the Forlandsundet Graben and its implications for Arctic-Atlantic connectivity

The Fram Strait, located between Svalbard and Northeast Greenland, is the only deep oceanic passage linking the Arctic and Atlantic Oceans. Water exchange through the strait is crucial for the Atlantic Meridional Overturning Circulation, controlling global climate. Increased water exchange between the Arctic and Atlantic Oceans might have been one of the main factors driving global climate into an icehouse state at the Eocene-Oligocene Transition, around 34 million years ago. However, proxy evidence is scarce due to limited sedimentary archives from the region.

The <20 km-wide Forlandsundet Graben located on the western Svalbard margin is a pull-apart basin formed during the early Paleogene. It may represent a precursor to the Fram Strait, potentially allowing water exchange already during the Paleogene. The thickness and age of the graben fill are poorly constrained, necessitating a better stratigraphic framework to understand the events leading to the seaway’s opening and deep-water connection between the Atlantic to the Arctic Ocean.

Vintage 2D seismic data suggest the sedimentary succession in the graben may exceed 4 km. A petroleum exploration well (7811/5-1) drilled onshore at Sarstangen in 1974 reached metamorphic basement rocks at a depth of 1046 m, penetrating over 1 km of mostly marine mudstones and sandstones, initially dated as possibly Eocene and Oligocene.

To refine the stratigraphy and estimate paleo-environments and maturity of the sedimentary succession, we investigated three cored intervals of the 7811/5-1 well. Combined dinocyst and foraminifera assemblages suggest a middle Eocene age for the lowermost core interval and an upper Eocene to early Oligocene age for the uppermost core interval. Foraminifera indicate outer neritic to upper bathyal water depths (100-500 m) in the Eocene. Pollen and spores are more common than marine dinocysts, and the uppermost core yields coal fragments. TOC, Tmax, and HI suggest inert kerogen of mixed origin, classified as type III/IV.

These findings enhance our understanding of the Forlandsundet Graben's stratigraphy and its role in Arctic-Atlantic water exchange during the Paleogene, providing crucial insights into the geological history and paleo-environments of the region.