QUATERNARY GEOLOGY
POSTER

The distribution and chronology of post glacial intertidal deposits around Ringkøping Fjord, Western Jutland, Denmark

Peter Roll Jakobsen
Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen K, Denmark.
Email: prj@geus.dk

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Abstract

The circumjacent deposits of Ringkøbing Fjord are post-glacial marine deposits. The Western delineation of Ringkøbing Fjord is build up of marine sediments deposited in a high energy coastal environment, and along the eastern coast of Ringkøbing Fjord intertidal deposits prevail along with beach ridges (Jakobsen et al., 2003).

Towards the west the straight and narrow spit of Holmsland Klit separates Ringkøbing Fjord from the North Sea. Holmsland Klit grew from the north, probably starting about 3500 to 4000 years ago, contemporaneously with spit development in the Jyske Bank area (Leth, 1996). The southern part of the spit was formed as late as the 18th century, leading to the closure of the former mouth of Ringkøbing Fjord at Nyminde Gab. The presence of oyster banks in Ringkøbing Fjord as late as in the 18th century indicates fully marine conditions until then.

In the concave eastern surrounding of Ringkøbing Fjord the marine deposits consist of marine sand and intertidal marine clay, delineated by gravelly beach ridges towards Ringkøbing Fjord. The beach ridges sheltered the tidal flats, and thicker deposits of intertidal marine clay are often seen right behind them. The marine deposits are observed up to 1.5 m above present sea level.

The intertidal marine clay is often deposited upon freshwater peat. Wood trunks from the peat have been 14C dated and the youngest dated trunk was about 4200 years old, and the marine deposits are consequently younger.

The peninsula Tipperne in the southernmost part of Ringkøbing Fjord consists of very young marine deposits, deposited as the mouth of Ringkøbing Fjord moved southwards after the 18th century. Tipperne consist of marine sandy deposits covered with intertidally deposited marine clay and silt, and in the southwest part of Tipperne dunes cover the marine deposits.

References

Jakobsen, P. R., Pedersen, S.A.S. & Petersen, K.S., 2003. Geological Map of Denmark, 1:50 000, Copenhagen: Geological Survey of Denmark and Greenland

Leth, J.O., 1996. Late Quaternary geological development of the Jutland Bank and the initiation Jutland Current, NE North Sea. Geological Survey of Norway. Bulletin 430, 25-34