Cheilostome Bryozoa in the Danian Deposits of East Denmark

Abstract

In the present work the results are presented of some investigations into the paleontology and distribution of the Cheilostome Bryozoa within the Danian deposits in East Denmark.

In the Introduction an account is given of the extent and development of these investigations.

The following chapter includes descriptions of localities, a short survey being made of situation, literature, lithology, stratigraphy, and material for each of the localities treated: Stevns, Kagstrup, Thorslunde, Faxe, Saltholm, Copenhagen, Herfølge, and Klintholm.

The paleontological chapter is introduced by a section on the systematic classification. Next, a few remarks for the reader's guidance are offered concerning the descriptions of species, thus as regards measurements, material, types, and distribution. A terminological section includes definitions of the morphological terms used in descriptions of species, while the following section comprises a chronological survey of papers in which Cheilostome Bryozoa in Danian deposits from Denmark, Sweden, or North Germany are described, pictured, or mentioned. In the systematic part 117 Cheilostome species and subspecies are described, 42 of which have not previously been treated. The species examined are pictured on 28 plates at the end of the work.

The stratigraphical chapter is introduced by a section about the purpose of the stratigraphical investigations. First of all it has been the author's aim to obtain a more reliable standard of comparison than the one existing, by taking fresh samples from the localities selected. Next, the task has been to elucidate the extent to which the Bryozoa have participated in the formation of the various cretaceous rocks, partly to learn the composition of the Bryozoan assemblages within the various zones of the Danian - with due reference to the possible influence of conditions of environments.

In the lithological section the analyses made are discussed in more detail. These investigations have shown that the share of the Bryozoa in the formation of rocks is smaller than has so far been supposed. The contents of Bryozoa do not exceed 40 per cent. in any of the samples examined; in most of the samples the Bryozoa constitute a considerably smaller percentage. Furthermore it proves that Cyclostome Bryozoa have contributed to the formation of rocks to a greater extent than the Cheilostome species.

In the Paleoecological section it has been tried to estimate conditions of bottom, depth, temperature, and current, the supply of nutrients, and the salinity in the sea in which the Danian Bryozoa lived. The measurements of zooecia, etc., have been discussed in some detail in the same section. The character forms of the localities and biozones are treated in a special section, after which, in conclusion of the stratigraphical chapter a biostratigraphical evaluation of the Bryozoan material is made. The species naturally are distributed on four groups, corresponding to the four Tylocidaris zones. The stratigraphical grouping of the localities on the basis of the occurrence of the Bryozoa is in agreement with the experiences won through the study of the distribution of other animal groups, with one exception, viz. Saltholm. If the limestone on Saltholm should be placed in the stratigraphical diagram on the basis of the Bryozoa alone, both Bryozoan Limestone and Sandy-limestone should be referred to the T. brünnichi zone.

This deviation from the current view has made it necessary to go through the faunistic and lithological arguments applied in the documentation of the reference of Sandy-limestone to the T. vexillifera zone. Such a revision is made in the last chapter of the work. The conclusion of these investigations was that there is no information in the geological literature about Saltholm which decidedly goes against referring the Sandy-limestone on Saltholm to the T. brünnichi zone.