Jurassic stratigraphy of the Western Barents sea region: A review

Abstract

The Jurassic succession of the western Barents Sea Region comprises Hettangian to Bathonian marginal to openmarine sandy and shaly sequences, and Callovian to Volgian open marine dominantly shale and claystone deposits. In overall character and development the Jurassic sequences on the Barents Shelf are related to those found on the Svalbard archipelago. However, since Svalbard emerged in Late Bajocian - Bathonian time, strata of Hettangian - Aalenian age on Spitsbergen occur mainly as thin erosional remnants, while Bajocian to Middle Bathonian deposits apparently are missing. Contemporaneously, thick clastic sequences were deposited in depressions in the present offshore Troms area. On Svalbard the Hettangian - Aalenian sequences are assigned to the Wilhelmøya Formation (Kap Toscana Group), while the Bathonian to Volgian sequences comprise the Brentskardhaugen Beds and the Agardhfjellet Formation (Janusfjellet Subgroup). In the offshore Troms area, contemporaneous deposits to the Wilhelmya Formation are represented by the Tubaen, Nordmela and lower Stø Formations (Realgrunnen Group). The Late Middle and Late Jurassic Fuglen and Hekkingen Formations (Teistgrunnen Group) of offshore Troms are time-equivalent to the Janusfjellet Subgroup on Svalbard. In these Jurassic to lowermost Cretaceous successions, important TR cycles boundaries are recognized at the base of the Pliensbachian and in the early Toarcian, Late Toarcian/?Aalenian, Late Bathonian and Early Oxfordian; also at the base of the Valanginian. The Jurassic ammonite record of the western Barents Sea Region is still incomplete, but faunas which allow a subdivision at zonal level are found in the Toarcian - Aalenian, Upper Bathonian - Callovian, Oxfordian, Kimmeridgian and Middle Volgian. Microfossils are well documented and provide a good mean for correlations of the Middle and Upper Jurassic sequences. Formal biostratigraphic zonations have been proposed for the Callovian to lowermost Cretaceous based on foraminifera and for the Toarcian to lower Oxfordian based on dinoflagellates.