Carbonate buildup flank deposits: an example from the Permian (Barents Sea, northern Norway) challenges classical facies models

Abstract

Mounds seen on seismic in the Barents Sea, offshore northern Norway, occur in the upper Palaeozoic of the Finnmark Platform. A 160-m-long cored section from such a mound, dated as unspecified Asselian-Artinskian (Lower Permian), documents a carbonate buildup of microbial origin and rich in Stromatactis fabric. The cored section of a buildup where depositional dip angles vary from a few degrees to about 45°. Approximately 2/3 of the flank consists of in-situ microbial boundstone with abundant Stromatactis and, in the upper part, bryozoan—cement framestone. The remainder is gravity flow sediment deposited on the flank and at the toe of the buildup consisting of argillaceous sediment alternating with crinoid grainstones. Modal thin-section analysis indicates that biogenic particles make up 38% of the buildup flank, diagenetic products such as early, fibrous cement, microcrystalline cement and late, blocky calcite 46%, and lime mud, including that interpreted as microbially induced, 16%. The studied core interval shows that steeply inclined buildup flanks can be largely in-situ deposits rather than allochthonous as predicted in classical facies models.