Limestone columns at the Hirsholmene

Theme: Limestone columns  

Locality: Kattegat (Hirsholmene)
Description of a Danish GeoSite

Photo: Karsten Dahl. To of limestone column with epifauna.

Primary identification

1. GeoSite no.:
GS - 12-1.

2. National locality no.:
N.a.

3. GeoSite name:
Hirsholmene.

4. Location:
Denmark; Kattegat; Several locations in the Kattegat Sea from Frederikshavn (Strandby) to Hirsholmene, L�s� and Anholt.

5. Co-ordinates UTM:
System ED50 Zone 32, x=, y=

6. Type of locality:
Submarine sandstone columns, slabs and pavements.

Primary geological features

7. Main topic:
Submarine carbonate-cemented sandstone columns.

8. Geo(morpho)logy:
Methane-derived submarine carbonate-cemented marine sandstones at several locations in the Kattegat. The carbonate-cemented sandstones occur as individual slabs or more widely distributed lithified pavements. In some areas, the sandstones take the form of large, spectacular, vertical columns and mushroom-like bodies, which protrude from the seafloor. The cementation took place within the sea bed, the sandy material of which has thereafter been removed by submarine erosion, leaving the columnal residuals. The highest concentrations of sandstone columns are observed at Hirsholmene but they have a widespread occurence from the near-coastal at Frederikshavn to the deep water environment at L�s� and Anholt. The carbonate cement consists of aragonite, high-magnesium calcite and calcian dolomite. Isotope geochemical investigations indicate that the carbonate precipitation is the result of methane oxidation by sulphate reducing bacteria.
The carbonate-cemented sandstones consitute an unique geochemical environment induced by seepage of methane from Eemian - Early Weichselian marine deposits. The linear allignment of cemented sandstone occurrences indicates that they are structurally controlled.

9. Frame / context:
Diagenesis.

10. Chronostratigraphy:
Postglacial to Recent.

11. Primary value:
Carbonate-cemented sandstone caused by submarine methane seeps, most likely structurally controlled.

12. Comparative evaluation:
Methane-derived carbonate cementation of marine sediments have been reported from shelf seas worldwide, but the Danish occurrences are unique due to the spectacular exposures on the seafloor as the result of subsequent submarine large-scale erosion.

13. Comparable GeoSites:
In Denmark: None.

Supplementary data in support of the locality

14. Delineation on a map:
...

15. Higth of the GeoSite:
N.a.

16. Area of the GeoSite:
...

17. Subordinate geological interests:
Sedimentology, Geochemistry.

18. "Non"-geo interests:
The exposed carbonate-cemented sandstones form a unique biotope for a rich sessile fauna and flora. SCUBA diving.

19. References:
Jensen, P and Fenchel, T., 1991: De boblende rev; Et nyt havbundslandskab af sandsten med et rigt plante- og dyreliv. Ny Carlsberg Fondet, �rsskrift 1991, Rhodos, s 22-27.
Jensen, P., Aagaard, I., Burke, R.A., Dando, P.R., J�rgensen, N.O., Kuijpers, A., Laier, T., O'Hara, S.C.M. and Schmaljohann, R., 1992: Bubbling reefs in the Kattegat: Carbonate-cemented rocks support a diverse ecosystem at methane seeps. Marine Ecology Progress Series 83, 103-112.
J�rgensen, N.O., 1976: Recent high magnesian calcite/aragonite cementation of beach and submarine sediments from Denmark. Journ. Sed. Petrology 46, 940-951.
J�rgensen, N.O., 1979: Magnesium incorporation in Recent marine calcite cement from Denmark. Journ. Sed. Petrol.49, 945-950.
J�rgensen, N.O., 1979: Kalkh�rdnede marine sedimenter fra Kattegat. Ingeni�ren 20, 36-37.
J�rgensen, N.O., 1980: Gypsum formation in Recent submarine sediments from Kattegat, Denmark. Chemical Geology 28, 349-353.
J�rgensen, N.O., 1981: Authigenic K-feldspar in Recent submarine gypsum concretions from Denmark. Marine Geology 39, M21-M25.
J�rgensen, N.O., 1989: Holocene methane-derived dolomite cemented sandstone pillars from Kattegat, Denmark. Marine Geology 88, 71-81.
J�rgensen, N.O., Laier, T., Buchardt, B. and Cederberg, T., 1990: Shallow hydrocarbon gas in the northern Jutland-Kattegat region, Denmark. Bull. geol. Soc. Denmark 38, 69-76.
J�rgensen, N.O., 1992: Methane-derived carbonate cementation of marine sediments from Kattegat, Denmark - Geochemical and geological evidences. Marine Geology 103, 1-13.
J�rgensen, N.O., 1992: Methane-derived cementation of marine sediments from Kattegat. Continental Shelf Research 12, 1209-1218.

20. Data sources, collections:
...

21. Illustrations:
Photo:

22. Proposers:
Dansk Geologisk Forening & Det Kongelige Danske Geografiske Selskab/Poul Erik Nielsen.

23. Description by:
N.Oluf J�rgensen.

24. Recommandation:
A GeoSites.

25. Comments:
...

26. Supplementary description:
...