Theme: Coastal washover fans
Description of Danish GeoSite
Photo: Gravel of terrestrial origin over marine sand, Boerup, by E. Skovbjerg Rasmussen
1. GeoSite no.:
GS - 7-1
2. National locality no.:
NGI - 97.
3. GeoSite name:
Denmark; Lillebaelt, Eastern Jutland.
5. Co-ordinates UTM:
System ED50 Zone 32, x=542649, y=6153796.
6. Type of locality:
Primary geological features
7. Main topic:
Shoreface and backbarrier deposits.
The cliff exposes a Lower Miocene succession equivalent to the Ribe and Arnum Formations. The deposits are composed of white sand and gravel.
In the lower part of the section there are 0.1 m to 0.5 m thick, fine- to medium-grained sandbeds. The sandbeds are homogeneous to planar laminated and capped by wave ripples. There are occasional bioturbated layers. These sandbeds are succeeded by planar laminated, medium to coarse-grained sand and trough cross-stratified sand. Over the sandbeds there are two erosive gravel layers, at the base of which there is a hiatus. The gravel layers are up to 1m thick, and have a local grain size up to 3 cm at the base of the lowermost gravel layer. The gravels are overlain by organic-rich, clayey silt with some intercalated sandbeds.
9. Frame / context:
Miocene; Aquitanian and Burdigalian.
11. Primary value:
The section is characteristic for sand and lagoonal mud along the coastline of the Miocene North Sea. The section further is an excellent example of a sequence boundary that was formed during a major regression of the shoreline. The regression which formed a hiatus between Aquitanian and Burdigalian deposits lasted for at least 3.5 million years.
12. Comparative evaluation:
The outcrop at Boerup and the other outcrops at Lillebælt: Hindsgavl, Hagenoer and Roenshoved show the development and lateral variations within a shoreface and backbarrier setting. At Hindsgavl examples of different storm deposits, i.e. hummocky and swaley cross-stratified sands, are exposed. The lateral development of the shoreface and back-barrier deposits is illustrated through the outcrops at Roenshoved, Hagenoer and the upper part of the Boerup section. The southern locality (Roenshoved) is dominated by lower and upper shoreface sedimentation and at Hagenoer and Boerup, lagoonal mud occasionally interbedded with sandy washover deposits crop out. The formation of different sedimentological structures due to grain size variation during a storm is illustrated through hummocky cross-stratification developed in fine-grained sand at Roenshoved and cross-grained wave ripples formed at Hagenoer.
13. Comparable GeoSites:
In Denmark: None.
Supplementary data in support of the locality
14. Delineation on a map:
15. Higth of the GeoSite:
The exposed profile is ca. 8 m high.
16. Area of the GeoSite:
Ca. 0,1 km2.
17. Subordinate geological interests:
18. "Non"-geo interests:
Dybkjær, K. & Rasmussen, E.S., 2000: Palynological dating of the Oligocene-Miocene succession in the Lille Bælt area, Denmark. Bull. geol. Soc. Demn., 47, 87-103.
Friis, H., Mikkelsen, J. & Sandersen, P., 1998: Depositional environment of the Vejle Fjord formation of the Upper Oligocene-Lower Miocene of Denmark: a back island/barrier-protected depositional complex. Sedimentary Geology 17, 221-244.
Radwanski, A., Friis, H. & Larsen, G., 1975: The Miocene Hagenør-Børup sequence at Lillebelt (Denmark): its biogenic structures and depositional environment. Bull. geol. Soc. Denm., 24, 229-260.
Rasmussen, E.S., 2001: Tertiære grundvandsmagasiner. Geologi; Nyt fra GEUS, 7-9.
Rasmussen, E.S. and Dybkjær, K. (2005): Sequence stratigraphy of the Upper Oligocene – lower Miocene of eastern Jylland, Denmark: role of structural relief and variable sediment supply in controlling sequence development. Sedimentology 52, 25-63.
20. Data sources, collections:
23. Description by:
A Danish GeoSite.
26. Supplementary description: