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Western Bornholm

Theme: Tectonically controled Mesozoic coast 

Locality: Western Bornholm
Description of a Danish GeoSite

Primary identification

1. GeoSite no.:
GS - 8-1.

2. National locality no.:
NGI - 195, 196, 198.

3. GeoSite name:
Mesozoicum of Western Bornholm.

4. Location:
Denmark; Bornholm.

5. Co-ordinates UTM:
System ED50 Zone 32:
x=865841, y=6132512; x=866118*, y=6121952;
x=865233, y=6121842; x=867389, y=6119409;
x=867223, y=6118801.

6. Type of locality:
Coastal cliffs and inland quarries.

Primary geological features

7. Main topic:
Coastal deposition along an active fault zone.

8. Geo(morpho)logy:
Upper Triassic to Upper Cretaceous freshwater and marine deposits from the coastal zone.
The Fennoscandian Border Zone was activated several times during the Mesozoic rift phase (Triassic-Jurassic). This rifting resulted in differential subsidence of the R�nne Graben which, in combination with eustatic sea-level variations, controlled deposition at Bornholm onshore and offshore during this period.
Deposition started in the Late Triassic when red and green clays and coarse-grained sands of the Riseb�k Member were formed on a featureless river plain area near the shoreline.
After a period of block faulting, uplift and erosion, sedimentation began in the early Jurassic and continued without interruption until the Middle Jurassic.
In the Early Jurassic, the R�nne Formation was deposited in lakes and rivers, where multicoloured clays and sands were laid down. Later sands, clays and coal were deposited on a delta plain, followed by tidal sands and beach sands during the continued transgression. In the Late Sinemurian, a tidal environment prevailed with sandy and muddy flats and tidal channels with coal-bearing marshes.
The Lower Pliensbachian Hasle Formation was deposited close to a fault-controlled shoreline under fully marine conditions. The formation consists mainly of hummocky cross-bedded, fine-grained sandstones with silt and gravel and subordinate claystones.
The environmental conditions changed during the Late Pliensbachian, and from this time to the end of the Bathonian, the continental Bag� Formation was laid down on a delta plain in channels, levees and swamps. The sediments were dominantly coals, clays and sands with subordinate gravels. Conglomerates were resedimented into the basin from nearby fault scarps, testifying to tectonic activity.
During the Bathonian to Berriasian (earliest Cretaceous) faulting, uplift and erosion took place. Early Cretaceous deposition resumed with fluvial sand and gravels of the Lower Berriasian Rabekke Formation, which was succeeded by black clays with coal and wood deposited in near-coast swamps. In the Late Berriasian, sedimentation continued with barrier, beach and tidal, fine-grained quarts sands of the Robbedale Formation, which was followed by medium to coarse-grained quarts sands of high-energy barrier island origin. The Upper Berriasian to Valanginian Jydeg�rd Formation was deposited in a large lagoon-lake complex, dominated by clayey sediments, which to the south was bordered by sandy and clayey back-barrier sediments, wash-over sands, small meandering channels and tidal channels. Deposition of the Robbedale and the Jydeg�red Formations was influenced strongly by tectonic activity.
Above the Jydeg�rd Formation there is a hiatus that accounts for the Hauterivian, Barremian and Aptian Stages. In the Albian, fully marine deposition returned to the area during a number of transgressions, but the former Albian deposits were largely removed by intra-Cretaceous erosion. Clasts derived by erosion from the Albian are, however, found within the lower Middle Cenomanian conglomerate of the Arnager Greensand Formation.
Three periods of marine sedimentation interrupted by non-deposition or erosion are then characteristic of the Late Cretaceous.
The Lower-Middle Cenomanian Arnager Greensand Formation starts with the above mentioned conglomerate containing reworked Albian deposits. The successive fine-grained, strongly glauconitic sands and silts were deposited on a shallow shelf.
After a period of non-deposition, the Lower-Middle Coniacian Arnager Limestone Formation was laid down on low mud-mounds on a shallow shelf. The formation consists of clayey silica-rich chalk. The basal bed of the formation is a thin conglomerate, interpreted as a hard ground, composed of glauconized and phosphatized chalk pebbles with burrows,.
During the Late Coniacian to early Santonian, the Bavnodde Greensand Formation was deposited on a shallow shelf, often dominated by storm conditions. This formation is composed of clayey, fine-grained, strongly glauconitic quarts sands containing abundant erosive storm beds.
Deposition from the latest part of the Late Cretaceous and the Pleistocene are not known from Bornholm.

9. Frame / context:
Sedimentology, stratigraphy.

10. Chronostratigraphy:
Late Triassic to Late Cretaceous.

11. Primary value:
The Mesozoic freshwater and marine deposits from the coastal zone in Western Bornholm uniquely illustrate the depositional environment along an active fault zone.

12. Comparative evaluation:
The area is a.o. used for comparison to analogue, but deep-seated facies in the North Sea Basin.

13. Comparable GeoSites:
In Denmark: None.
In Sweden: Fyledalen (and others).

Supplementary data in support of the locality

14. Delineation on a map:

15. Higth of the GeoSite:
0-40 m a.s.l.

16. Area of the GeoSite:
Localities along a 10 km long coastline.

17. Subordinate geological interests:
Biostratigraphy, Palaeoecology for Late Cretaceous animal groups, Early Jurassic palaeosoils.

18. "Non"-geo interests:
Tourism, bathing, fishing.

19. References:
Arndorff, L. 1993: Lateral relations of deltaic palaeosols from the Lower Jurassic R�nne Formation on the island of Bornholm, Denmark. Palaeogeo., Palaeoclim., Palaeoeco., 100. 235-250.
Gravesen, P. 1996: Geologisk set - Bornholm. Red. Andersen, S., Skov- og Naturstyrelsen, Geografforlaget & Milj�ministeriet, 208pp.
Gravesen, P., Rolle, F. & Surlyk, F. 1984: Lithostratigraphy and sedimentary evolution of the Triassic, Jurassic and Lower Cretaceous of Bornholm, Denmark.
Kennedy, W.J., Hankock, J.M. & Christensen, W.K. 1981: Albian and Cenomanian ammonites from the island of Bornholm (Denmark). Bull. Geol. Soc. Denmark, 29, 203-244.
Koppelhus, E.B. & Nielsen, L:H: 1994: Palynostratigraphy and palaeoenvironment of the Lower to Middle Jurassic Bag� Formation on Bornholm, Denmark. Palynology, 18. 139-194.
Larsen, O.H. & Friis, H. 1991: Petrology, diagenesis and pore-water evolution of a shallow marine sandstone (Hasle Formation, Lower Jurassic, Bornholm, Denmark). Sedimentary geology, 72, 269-284.
Noe-Nygaard, N. & Surlyk, F. 1985: Mound bedding in a sponge-rich Coniacian chalk, Bornholm, Denmark. Bull. Geol. Soc. Denmark, 34. 237-249.
Noe-Nygaard, N.& Surlyk, F. 1988: Washower fans and brachish bay sedimentation in the Berriasian-Valanginian of Bornholm, Denmark. Sedimentology 35. 197-217.
Noe-Nygaard, N, Surlyk, F. & Piasecki, S. 1987: Bivalve mass mortality caused by toxic dinoflagellate blooms in a Berrisian-Valanginian lagoon, Bornholm, Denmark. Palaios, 2. 263-273.
Sch�iler, P. 1992: Dinoflagellate cysts from the Arnager Limestone Formation (Ciniacian, Late Cretaceous), Bornholm, Denmark. Rev. Palaeobotany and Palynology, 72, 1-25.
Sellwood, B. 1972: Tidal-flat sedimentation in the Lower Jurassic of Bornholm, Denmark. Palaeoecol. 11. 93-106.
Surlyk, F., Arndorff, L., Hamann, N-E., Hamberg, L., Johannessen, P.N., Koppelhus, E.B., Nielsen, L.H., Noe-Nygaard, N., Pedersen, G.K. & Petersen, H.I. 1995: High-resolution sequence stratigraphy of a Hettangian-Sinemurian paralic succession, Bornholm, Denmark. Sedimentology, 42, 2. 323-354.
Surlyk, F. & Noe-Nygaard, N. 1986: Hummocky cross-stratification from the Lower Jurassic Hasle Formation of Bornholm, Denmark. Sedimentary Geology, 46. 259-273.
Tr�ger, K-A. & Christensen, W.K. 1991: Upper Cretaceous (Cenomanian-Santonian) inoceramid bivalve faunas from the island of Bornholm, Denmark. Danm. Geol. Unders., Ser. A, 28, 28pp.

20. Data sources, collections:

21. Illustrations:

22. Proposers:
Dansk Geologisk Forening & Det Kongelige Danske Geografiske Selskab.

23. Description by:
Compiled from various sources.

24. Recommandation:
All subsites constitute �ne GeoSite all together.

Sub-localities are coastal cliffs at Hasle and in between R�nne and Riseb�k, and further the quarries at Bag�, R�nne and Robbedale. All sub-localities should be considered one GeoSite entirety regardless of age.

26. Supplementary description:

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List of localities
The Bornholm region

Theme: Tectonnically controled Mesozoic coast
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Last modified : Sunday 07. Jan. 2007 Erik Nygaard
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