Original paper
Magnetostratigraphy of the Upper Paleocene-Lower Eocene deposits in Denmark
Beyer, Claus; Heilmann-Clausen, Claus; Abrahamsen, Niels
published: 12/19/2001
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ArtNo.: ESP026003901001
Abstract
A palaeomagnetic study of the clayey fades of the Upper Paleocene-Lower Eocene sediments in Denmark has been carried out on material from two clay pits at Olst and a cored borehole from Store Bælt (the Great Belt). The studied sections constitute a nearly complete stratigraphic record of this time period. The clay pits at Olst form the type locality for the Olst Formation which is approximately equivalent to the transitional Paleocene/Eocene Sele and Balder Formations in the North Sea Basin. In addition, there are exposures of the uppermost part of the Paleocene Holmehus Formation in the clay pits. The palaeomagnetic data were interpreted in relation to the existing biostratigraphy. The study shows that the whole Olst Formation has an age equivalent to magnetic chron C24r. A major hiatus is present between the base of this formation and the Holmehus Formation. In the latter the chrons 26n and 26r are registered. Chrons C25n and C25r are missing at the hiatus, which thus corresponds to a time gap of some 1.7-2.0 m.y. A core from the Osterrende in Store Bælt contains sediment representing the time interval missing at Olst. The ten meter long sequence contains the informal units "Osterrende Clay" and "Glauconitic Silt". This interval shows the presence of one reverse and one normal magnetic polarity zone, which on biostratigraphical grounds are assigned to chrons C25r and C25n. This is the first documentation of the time chron C25n in Denmark. A notable increase in sedimentation rate from estimated 5 mm/1000 y (Holmehus Fm.) to at least 240 mm/1000 y (Haslund Mb.) occurred during the deposition of the succession. Four short normal anomalies occurring in the sequence may be recordings of cryptochrons. One of them is present at the same stratigraphic level in both the Osterrende core and at Olst. Variations in the magnetic susceptibility throughout the sequence are related to the content of volcanic ash.