EVOLUTION OF EARLY TO MIDDLE JURASSIC REDOX CONDITIONS WITHIN THE VIKING CORRIDOR, NORTH SEA BASIN

The Early Jurassic Toarcian Oceanic Anoxic Event (TOAE; ~183 Ma) was a warming episode associated with a perturbation of the carbon cycle marked by a negative δ¹³C isotopic excursion (CIE). The event is linked to the release of CO₂ from the Karoo-Ferrar Large Igneous Province (KF-LIP) resulting in anoxic marine conditions aiding in the global deposition of organic-rich shales. Despite extensive work on the TOAE, these records are: 1) from the NW European epicontinental shelf; 2) solely based on δ¹³C; 3) low-resolution; or 4) spans short intervals. There is also a scarcity of records providing a broader context of the event, specifically during Early-Middle (186-169 Ma) Jurassic.

We present new δ¹³C_org, redox-sensitive elements (RSE), and mercury (Hg) data from the Viking Corridor to provide insight on the spatial and temporal evolution of redox conditions between Early-Middle Jurassic. We assess a global and regional event—the TOAE and the localized uplift of the North Sea Dome (NSD; ~182-170 Ma), respectively. The NSD is the domal uplift of the North Sea that acted as a barrier to heat flow patterns in the region.

The expression of the TOAE in the NCS is not well understood. Moreover, while we understand the role that the NSD played in the tectonostratigraphic configuration of the NCS, the impact on redox conditions during its onset and evolution remains elusive. We confirm the TOAE presence with a negative CIE that coincides with the onset of KF-LIP along with elevated Hg and RSE. Our data shows a spatial Hg trend across a basinal transect, where proximal settings are elevated in Hg and RSE. Temporally, in proximal settings, post-TOAE successions are Hg-enriched across the Early-Middle Jurassic, possibly linked to the NSD. Alternatively, enhanced weathering may have a role in bringing terrestrially-derived Hg into the marine system. RSE enrichment factors suggest a particulate shuttle mechanism acting beneath an oxygen-minimum zone. Distal settings, however, have punctuated peaks of slightly elevated mercury during Aalenian, suggesting a NSD signal. Together, this work provides insights on the interplay between TOAE, LIP, and Hg-RSE systems during an important transition in the Earth’s biogeochemical history.

This work has been financed by Gassco and Equinor. Gassco is the operator for the Norwegian gas transport system and of several gas processing and receiving terminals in Norway and in Europe. Equinor is an energy company with substantial international activities and the operator of a large part of Norwegian oil and gas production.