The Mesozoic rocks of Andøy, northern Norway.

Abstract

The Jurassic-Lower Cretaceous sediments of Andøy are found in a small, downfaulted area on the north-east coast of the island. The Mezosoic sequence is more than 650 m thick, and rests non-conformably on weathered basement rocks. The lower part of the sequence (about 85 m thick) consists of coarse-grained sandstones interbedded with some siltstones, bituminous shales and a few coal layers. The age of this part is Middle Jurassic or earliest Upper Jurassic. On top of this are micaceous sandstones and siltstones of Upper Jurassic age, with a total thickness of nearly 300 m. The next formation consists of calcareous sandstones and siltstones (about 80 m), inpart Valanginian in age, and this is followed by a formation consisting of fine-grained siltstones and shales, more than 200 m thick and probably of Lower Cretaceous age. The Mesozoic sequences is largely marine, except for a few layers of freshwater and brackish-water deposits in the lowest part. The sediments are part of an onlap sequence which rapidly thins towards the NW. The main basin of deposition probably lay somewhere to the east, the sediments coming in mainly from the north-west. Sedimentation started as a consequence of faulting in Middle Jurassic time. Another period of faulting occurred in early Cretaceous time.