The Tjörnes Peninsula contains sediments rich in fossils from the Pliocene and Pleistocene Epochs. These sediments, known as the Tjörnes, Furuvík and Breiða beds, contain a record of climatic change in the North Atlantic and are therefore uniquely important in the geological history of Iceland.
Tjörnes is also remarkable because it shows evidence of horizontal transfer of approximately 100 km, when compared to the land south of the Húsavík fault zone, and thus geologically delineates Tjörnes to the south.
The Tjörnes sediments are exposed in banks dozens of metres high, along a 5 km section called Barmur. The sediments were mostly formed in shallow water close to land and lignite beds are to be found interspersed within them. The Tjörnes sediments extend some distance inland where they gradually thin out. The overall dip of the sequence is 10° to the north-west. The marine fauna of the Tjörnes beds indicates cooling of the ocean during the Pliocene, culminating in glacial temperatures after their formation was complete and lavas covered the area. In the uppermost biozone of the Tjörnes beds (which is called the Serripes Zone), one can find extinct species of molluscs.