Bio- and magnetostratigraphy of Rupelian–mid Chattian deposits from the Danish land area

Abstract

The age of the lithostratigraphic units in the Oligocene succession of Denmark is not well known. In order to remedy this situation, an integrated bio-magnetostratigraphical study of the Rupelian–mid Chattian deposits was carried out on six key sections situated in central Jutland. The studied sections include all previously known lithostratigraphical units (i.e., the Grundfør and Viborg Clay Members of the Viborg Formation, Linde Clay, Hvorslev Clay, Branden Clay) and a new, informal Unit X.The biostratigraphical part of the paper critically discusses the differences in ranges of some dinoflagellate cysts in relation to the two most commonly applied dinocyst zonations, the D- and NSO-zonation. The local calcareous nannofossil zonation of the upper NP23–lower NP25 interval in the studied sections is correlated to the standard NP zonation via the Contessa Barbetti Road section in central Italy. The correlation shows that an interval of the range of the dinoflagellate cyst Svalbardella recognized within the lower Chattian Asterigerina guerichi guerichi Zone in Denmark and Belgium is coeval with the global Oi2b cooling event.The identified magnetic polarity intervals have been correlated with the global polarity time scale on the basis of the biostratigraphy. The Viborg Formation is thus referred to Chron C13n and the lowermost part of C12r; the Linde Clay is referred to lower Chron C12r; and the Hvorslev Clay is referred to Chron C11n, C10 and C9r, or only the C11n.1n–C10r interval. The Branden Clay is referred to Chron C9r, C9n and C8r. Unit X is referred to Chron C8n.