Bjørn Lundschien, Norwegian Petroleum Directorate (Norway)
Tore Høy, Norwegian Petroleum Directorate (Norway)
Fridtjof Riis, IRIS (Norway)
Atle Mørk, SINTEF (Norway)
Mai Britt Mork, NTNU (Norway)
Interpretation of an extensive data set of shallow stratigraphic cores and deep seismic profiles has resulted in new information about the development of the Middle and Late Triassic succession in the northern Barents Shelf. This information may also have implications for our understanding of the Triassic development of eastern Svalbard. Mapping of seismic clinoforms show that since the late Early Triassic (Olenekian), the western Barents Sea shelf was filled in through a large scale deltaic progradation from sediment sources located to the east-south east. The clinoform belt represents the slope which separated a deep shelf area with deposition of organic rich, phosphatic shales in the west (Botneheia Formation and Steinkobbe Formation) from the delta front area in the east (Kobbe and Snadd Formations). In the time period from the Olenekian to the Carnian, progressively larger areas were covered by shallow shelf and paralic deposits. As a result of this progradation, Middle and Upper Triassic lithological formation boundaries are diachronous, being older in the south-east than in the north-west. Seismic data from the south-western Barents Sea indicate that preceding the Middle-Late Triassic progradation, a southern, Baltoscandian sediment source prevailed in the Early Triassic.
The seismic data imply that reconstructions of the Late Triassic in the northernmost Barents Sea which are based on field data from Svalbard tend to under-estimate the volume of sediments sourced from the east-south east, and over-estimate the importance of sources from the west and north. Seismic interpretation of data east of Svalbard show no indication of a northern provenance area. In our reconstruction, a Triassic shelf area existed in Svalbard and the northernmost Barents Sea until the earliest Carnian. In this time period, sediment input to Svalbard mainly came from the western margin. As a result of further progradation from the east - south east, in the Late Carnian a continuous paralic shelf area extended from the Barents Sea to Svalbard (De Geerdalen Formation in Svalbard, Snadd Formation in the Barents Sea). Based on our data from the northern Barents Sea and on Svalbard field observations, it is suggested that the De Geerdalen Formation would have been influenced by the east - south-east sediment source area in the Late Carnian. It is considered as possible that no northern source area existed for the de Geerdalen sandstones. Studies of petrography and mineralogy on Upper Triassic samples from the offshore coreholes and east Svalbard outcrops show lithic-arkosic sandstone compositions, including some characteristic provenance components of cherty rocks, felsic and mafic igneous/volcanic (and metamorphic) rocks which are similar over the entire area. Further field work, dating and provenance studies will be carried out to test the different hypotheses.