At Tjörnes peninsula are abundance of marine sediments older than the Ice Age (the oldest about 5 million years) and the total thickness of these layers is no less than 500 meters. In these layers remains of different marine animal communities have been discovered and nowhere else have more species of marine animals been found in Icelandic sediments. The molluscs, crustaceans and forams are most common, but there are also remains of fish and marine mammals, that is seals, walrus and whales. The layers can be divided into three belts by which type of shell is the most dominant in each layer. The lowest and oldest is the Venerupis zone or Tapes zone, in the middle is the Mactra zone and at the top and youngest is the Serripes zone.