Reconstructing the Paleoenvironments of the Quaternary Tjörnes Basin, North Iceland

Environmental history of the Breiðavik Group on Tjornes, North Iceland, is reconstructed based on sedimentary facies, foraminifera, and molluscs. The lithological record is characterized by repeated diamictites reflecting advances of glacial ice over the region, and during the early Pleistocene, accumulation of volcanics and sediments deposited close to sea level. The Breiðavik Group contains a unique record of Cainozoic glacier variations in the North Atlantic reflected in lithological variations where marine and terrestrial sediments are intercalated between lava flows and pyroclastic rocks. As a detailed example of the development from a full glaciation through deglaciation and interglacial conditions, we present the 1.5 Ma old Svarthamar Member which shows a lithological cycle from glacial to proglacial and then to shallow marine sedimentation coinciding with a faunal succession reflecting a change from arctic to boreal-arctic or even boreal conditions in the sea north of Iceland. The age model for the sequence indicates that this occurred just after the Olduvai event of the Matuyama chron. The amplitude of this climatic cycle is comparable to the Late Pleistocene glacial-interglacial cycles in the North Atlantic. Most of the upper part of the Breiðavik Group accumulated in a terrestrial environment.