The limestones in the Lower Cretaceous of Greenland – and their associated fossils

The Geological Survey of Denmark and Greenland (GEUS); 2Dept. of Geosciences,Ruhr-University Bochum

The Mesozoic in Greenland is an almost exclusively siliciclastic sedimentary succession. The Cretaceous is dominated by dark-grey, silty mudstones low in organic carbon and fossils – and has thus been considered boring and of little interest.

We present three Early Cretaceous exceptions with “carbonate” deposition.

1) Vividly-coloured, fauna- and flora-rich Ryazanian–Valanginian mudstone deposits on structural highs. They were considered ‘the first representative of limestone deposition’ since the Late Permian in Greenland, when first described by the early mapping geologist in the 1930-40’ies. However, the amount of carbonate, originating from calcareous nannofossils (CN), only qualify the unit as calcareous mudstones. Calcareous nanofossils as well as various ammonites, belemnites and brachiopods are partly of Tethyan origin and reflect major palaeoceanographic changes.

2) The re-discovery of the mid-1930’ies fauna-rich Hühnerbjerg locality represent pure carbonates that largely originate from inoceramid prisms. The setting was an isolated basement horst submerged in earliest Cretaceous (Valanginian–Hauterivian) and constituted a seamount, protected from siliciclastic input and hosted a rich fauna: brachiopods, in particular, ammonites, nautiloids, belemnites, bivalves, gastropods, crinoids, echinoids, serpulids, corals and crustaceans – and barren of calcareous nannofossils. The mount top carbonates were swept of the sides of the mount and transported in debris flows down the flanks and deposited as packstones and grainstones.

3) Imbedded in dark Barremian mudstones are methane seep carbonates. The seep mounds attracted a rich and diverse fauna and provide a rare preservation window to the otherwise almost barren Barremian marine succession.