Biotic Responses to the Mjølnir Meteorite Impact, Barents Sea: Evidence from a Core Drilled within the Crater

Abstract

The Mjølnir meteorite crater in the Barents Sea was formed at the Juassic/Cretaceous (Volgian-Ryazanian) boundary. The meteorite impacted the organic-rich clays assigned to the Hekkingen Formation (Volgian-Ryazanian age) and penetrated into underlying Middle Jurassic to Triassic rocks. Studies of macro- and microfossil assemblages from core 7329/03-U-01 drilled at the edge of the crater’s central high have revealed the following: 1) a lower unit consisting of strongly disturbed crater fill deposits with a microfossil content similar to that found in the Wilhelmøya Subgroup (Svalbard) and microfloral assemblage similar to those from the Sassendalen Group (Botneheia Formation) and the Storfjorden and Wilhelmøya subgroups on Svalbard; 2) a series of gravity flow deposits containing a mixture of reworked microfloras and -faunas of Middle Triassic/Middle Jurassic origin, and dinoflagellates of Volgian-Ryazanian age; 3) post-impact sediments of the Hekkingen Formation showing anomalous biotal features. In the lowermost post-impact sediments a conspicuous acme of Leiosphaeridia combined with an influx of abundant juvenile freshwater algae (Botryococcus) occurs. This points to brackish surface water conditions. In the same interval, only a few foraminiferids are found while the bivalve Buchia are frequent. High freshwater supply, stratified water-masses and high influx of released nutrients are considered as main factors acting on the post-impact depositional environment. Open marine conditions were restored in the Early Ryazanian.