Main geology
THE GEOPARK'S GEOLOGICAL HISTORY
Nature's history book lies far outside of the living room door, and in order to read and understand the story, one needs some background knowledge. The Geopark's geology tells an exciting story that spans a period of 1500 millions years.
The landscape was completely different; there were no plants, no large animals as far as we know, and Grenland was part of a continent located south of the equator.
The Geopark's geological history.
Nature's history book lies far outside of the living room door, and in order to read and understand the story, one needs some background knowledge.
The Geopark's geology tells an exciting story that spans a period of 1500 millions years.
To the west (pink) we find the oldest rock types, from the earth's Precambrian Era. These old rocks are mostly metamorphic; earlier they were sandstones, mudstones, granites and volcanic rocks. Through this long time period including much movement in the earth's crust, they have been altered to gneisses, quartzites, amphibolites and many other types.
The little green area to the north of all the pink denotes the quite characteristic Fensfeltet volcanic province. Here, a quite distinctive volcanic activity took place 580 million years ago. Out of the Fen volcano flowed lava that has solidified to become volcanic limestones - a curiosity of world class.
Over 500 million years ago the land was flooded by water. The sea that eventually covered the land was teeming with life, and the remains of this life, and the sand and clay from the earlier sea floor, have become the rock types shown in blue and yellow. The striped rock cuts that are so typical for the Grenland area are fossil-rich limestones, sandstones and slates from the period known as Cambro-Silurian (for the most part from the Ordovician and Silurian Periods, ca. 490 to 420 million years ago).
300 million years ago the Geopark was the centre of violent geological forces. The landscape became fractured and faulted and there was great volcanic activity and many earthquakes. The brown, red and purple areas all represent different magmatic rock types that intruded upwards through the earth's crust at this time. The result was the world renowned Oslo-Rift, with its rare rock types like rhombeporphyry, larvikite and many special minerals.
Luckily for us, the fracturing stopped there. The Geopark entered into a quieter time, and we know of no other dramatic occurrences until the big Ice Age began. During the last 2.6 million years, our country has been covered by ice many times. This ice has eroded and shaped our country, deposited sand, gravel and boulders, and contributed to the formation of our soils. Many places over the whole Geopark we see signs of the ice, as pebbles on Mølen and on Jomfruland, the bare rock faces along the whole coast, and as potholes and sandpits at Eidanger and Geiteryggen.
Signs from the ice age
Many places over the whole Geopark we see signs of the ice, as pebbles on Mølen and on Jomfruland, the bare rock faces along the whole coast, and as potholes and sandpits at Eidanger and Geiteryggen.