Sedimentology and Diagenesis of Upper Triassic Sandstones, with Emphasis on the Snadd-Fruholmen Transition, Barents Sea

Abstract

Triassic and Jurassic sediments from two cores in the Nordkapp Basin, Barents Sea, were analyzed by sedimentological, petrographic, SEM and XRD methods. The objective of the study was to gain better understanding of the depositional environments of the Upper Triassic-Jurassic, Snadd-, Fruholmen- and Stø formations with emphasis a mineralogical shift in the transition between the Snadd and Fruholmen formations, and try to relate the differences to depositional environment, climatic changes and diagenesis.The studied sediments of the Snadd and Fruholmen formations represent a transition from tidal flat, shoreline and inner shelf deposits. And the Stø Formation mainly represents inner shelf deposits, with exception of some fluvial deposits due to a local variation in one of the cores. The deposits represent an overall transgressive trend.The diagenetic processes differ in the three formations due to dissimilar depositional environment. In the Snadd Formation rhizocretions have been observed in combination with rootlets,and high levels of iron and manganese indicate influence by fresh-water. XRD analyses of mudstones showed no great compositional differences the Snadd and Fruholmen formations supporting observations from sandstone compositions of similar provenance and environment above and below the formation boundary.The largest compositional variation is seen between the Fruholmen and Stø formations, this is in accordance with other studies conducted in the Nordkapp Basin. The distinct increase in maturity may be due to extensive reworking connected with a regional transgression and sea-level rise.