Terrestrial Early Eocene Volcanic Paleoenvironment of the Skoll High, Mid-Norwegian Margin, Based on New High-Resolution 3D Seismic Geomorphology

Extensive magmatism during the NE Atlantic break-up generated about 6-10 million cubic kilometers of magma in the Paleogene. Magmatic degassing and explosive discharge of thermogenic gases by contact metamorphism is implicated in triggering the Paleocene-Eocene Thermal Maximum (PETM; 56 Ma). In 2022, the CAGE22-5 research cruise collected high-resolution seismic, sub-bottom profiler, and multibeam data across the central and northern Vøring Plateau to tie IODP Expedition 396 Sites U1571 to U1574. One high-resolution P-Cable 3D seismic cube (10.3 by 1.8 km) was collected on the Skoll High, covering both sites U1571 and U1572. The data were fast-track processed with a bin size of 6.1 x 6.1 m. Four Cenozoic sedimentary horizons and the Top Basalt horizon were subsequently interpreted, followed by horizon attribute analyses. The Top Basalt horizon reveals unprecedented details of the nature of the volcanic paleosurface. A faulted and eroded lava horizon characterizes the southeastern part of the cube at 150-250 m below sea floor (bsf) around the U1571 site location. In contrast, in the northwestern part of the cube, the Top Basalt attribute maps reveal a pitted surface and lobate structures with linear ridges with characteristic inter-ridge spacings of a few tens of meters. The pitted basalt surface is mapped in an area of about 5.5 km2 at depths of 250-350 m bsf and drilled by Site U1572. About 270 individual pits have been mapped with radius ranging from about six meters, within the horizontal resolution of the data, to about 50 meters with a mean radius of c. 16 meters. The holes are interpreted as rootless cones, which comprise volcanic craters resulting from the explosive reaction between lava flows which flow over water-saturated sediments. The dimensions of the rootless cones in the Skoll 3D survey are comparable with the field analogue of rootless cones mapped in the Myvatn lake area of NE Iceland. Unlike at Myvatn and at other field analogues, the Skoll3D data allow unique 3D imaging of the rootless cones revealing internal structures and geometries including the base of the cone structures. The cone depths vary from meters to a few tens of meters. The lobate structures are interpreted as separate subaerial lava flows with compressional ridges. These lava flows are similar to outcrop analogue lava flows and compressional ridges imaged by elevation model ISN2016 with a 2x2 m resolution near the Myvatn lake. In conclusion, the interpreted patterns of the basaltic pitted surface within the Skoll3D suggest a wet terrestrial paleoenvironment during effusive volcanism. Unlike in the eastern faulted area of the survey, the extremely well imaged pitted basalt surface of the Skoll3D area did not experience significant erosion, suggesting rapid subsidence and drowning of the paleo-land surface in a low-energy coastal environment. This study demonstrates the unprecedented detail that is possible when high resolution 3D seismic data acquisition is applied to buried volcanic landscapes and opens the potential for unique associated insights in the Northeast Atlantic and further afield.