Major drainage reorganization at the Triassic – Jurassic transition and the implications for reservoir development on the Western Barents Shelf

At the Triassic – Jurassic transition on the Barents Shelf, thick, mud?dominated intervals containing sands with variable reservoir properties gave way to thin sand-dominated intervals with favourable reservoir qualities. Consensus has yet to be reached regarding the mechanisms causing these sedimentological and mineralogical changes. Climatic and tectonic forcing, leading to depositional environment and provenance shifts have been suggested, but resultant models are conflicting. A multi?proxy sedimentary provenance study has aimed to refine and improve these models. The analyses reveal that a distinct and rapid provenance change followed an early Norian maximum flooding surface. This is seen by an increase in grain size, compositional maturity and proportion of stable heavy minerals.

These data are interpreted to reflect an episode of major drainage reorganisation prompted bytectonism on Novaya Zemlya. Uplift of the Finnmark Platform and Central Barents Arch choked incoming sediment from the Uralian Orogen whilst hinterland rejuvenation resulted in extensive recycling of pre?Norian units and an influx of material originating from crystalline basement.

Following the transition, detrital zircon age spectra are dominated by Proterozoic ages that are difficult to interpret. However, through complementary heavy mineral analysis and chemical/age data from rutile and K feldspar in particular, west and east Caledonian sand types have been delineated. These can be used to help predict the location and quality of reservoir intervals within the Realgrunnen Subgroup.