Hansen et al
Abstract:
Three successive marine habitats and their benthic macrofossil communities have been recognized and assessed in the uppermost Maastrichtian chalk of Stevns Klint, Denmark. The mound-bedded lower Sigerslev Member was deposited below the photic zone under the influence of persistent, non-erosive bottom currents. It is draped by the upper Sigerslev Member, which was laid down in deeper water than any other chalk known from onshore Denmark. Deposition took place under quiet conditions, apparently not influenced by bottom currents. The sparse level-bottom community lived on a seafloor with low nutrient supply. It was characterized by recumbent brachiopods and bivalves, sponges and some spatulate, long-spined echinoids, which were able to traverse the soft substrate. The top part of the Maastrichtian assigned to the Højerup Member, consists of low biogenic chalk mounds formed mainly by profuse growth of small-sized bryozoans governed by nutrient-rich currents from the south. The macrofauna of this member is of very high density and richness, yet species composition is similar to that of the mound-bedded lower Sigerslev Member. The bryozoan thickets of the two members are accompanied by a rich fauna of bivalves, echinoids, polychaetes, gastropods and brachiopods. Attached forms were dependent on hard, mainly small substrates provided largely by dead bryozoans, and on a steady nutrient supply. The bivalve fauna is richer and occurs in slightly higher densities in the Højerup Member than in the similarly mound-bedded lower Sigerslev Member. The number of polychaete species is also greater in the Højerup Member. The faunal differences reflect the shallower-water setting and a higher influx of food during deposition of the latter unit. The final Maastrichtian benthic macrofossil community at Stevns Klint represented by the Højerup Member thus shows the greatest faunal richness and density in the Upper Cretaceous chalk in the Danish Basin. There is no evidence of faunal impoverishment at the end of the Cretaceous in the Stevns Klint succession, which is complete across the Cretaceous–Paleogene boundary, and the study thereby corroborates the increasingly dominant view of a very abrupt faunal turnover at the K/Pg boundary.
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