Hydrocarbon Seepage during the Boreal Base Cretaceous Hot Shale Event

Abstract:

We have identified a number of carbonate bodies interpreted as seep-related from near the Jurassic-Cretaceous boundary in Svalbard, arctic Norway. The paleoseeps discovered so far occur over 50 km along strike, representing a seepage field of considerable extent. Ammonites indicate a base Cretaceous (Late Volgian to Late Ryazanian) age. The carbonate bodies are highly fossiliferous, with a very diverse fauna consisting mainly of normal-marine species but also seep-restricted taxa. Carbonate d¹³C isotopes reach -46‰, which, considering mixture with seawater-derived carbon, is interpreted as indicating a biogenic methane source. It is of interest to note the correlation of this paleoseepage with an episode of extremely high burial of organic matter near the Jurassic-Cretaceous boundary, noted both in Svalbard (top Slottsmøya Member of the Agardhfjellet Formation), in the Barents Sea (Hekkingen Formation) and in the North Sea (Mandal Formation), possibly providing a shallow source for biogenic gas. Together with near contemporaneous events in the Boreal Realm such as ongoing rifting, the base Cretaceous unconformity, the Mjølnir meteorite impact and a possible minor extinction event, these finds contribute to the impression of the Jurassic-Cretaceous boundary as a highly dynamic and interesting time in the North Atlantic area.