Forlandsundet Graben – a missing piece of puzzle for understanding the water exchange between the Arctic Ocean and Atlantic Ocean in the late Paleogene (Eocene to Oligocene)

The Fram Strait, located between Svalbard and Northeast Greenland, is today the only deep oceanic passage linking the Arctic and Atlantic Oceans. The water exchange across the Fram Strait plays a key role in the Atlantic Meridional Overturning Circulation, influencing 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 very scarce due to limited sedimentary archives from the region.

The <20 km-wide Forlandsundet Graben, located on the western Svalbard margin, is one of several pull-apart basins formed when the continental plates hosting Greenland and Svalbard began to diverge in the early Paleogene. The Forlandsundet Graben may represent a precursor to the Fram Strait and may have allowed water exchange earlier than previously thought. However, the thickness and age of the graben fill are poorly constrained. A better stratigraphic framework of its sedimentary succession is therefore crucial for understanding the events leading to the seaway’s opening and deep-water connection to the Arctic Ocean.
Vintage seismic data across the graben indicate that the thickness of the sedimentary succession may exceed 4 km. An exploration well (7811/5-1) drilled in 1974 at Sarstangen reached metamorphic basement rocks at 1046 m and penetrated over 1 km of mostly marine mudstones and sandstones, which were initially dated as possibly Eocene and Oligocene.
To improve the stratigraphy and estimate paleo-environments and maturity of the sedimentary succession in the graben, we collected 15 sediment samples from three cored intervals of the 7811/5-1 well (1026.4-1023 m, 912.5-907 m, and 653.4-648.7 m). Combined dinocyst and foraminifera assemblages suggest a middle Eocene age for the lowermost core and an upper Eocene to early Oligocene age for the uppermost core. The foraminifera suggest an outer neritic to upper bathyal water depth of 100-500 m in the Eocene. Pollen and spores are more common than marine dinocysts, and the uppermost core yields coal fragments. TOC values
range from 0.57% to 0.89%. The Tmax values are fairly constant in the range 437 °C to 431 °C. HI values range between 79 and 143. Combined these values suggest overall inert kerogen of mixed origin, classified as type III/IV.