The Evolution of the Tjörnes Sedimentary Basin in Relation to the Tjörnes Fracture Zone and the Geological Structure of Iceland

The Tjornes Fracture Zone (TFZ) connects the Kolbeinsey Ridge spreading axis north of Iceland and the Northern Volcanic Zone in Iceland. North-south trending ridges and basins are arranged along the 75 km wide west-northwest east-southeast trending TFZ. Major faults mark the southern boundary. Thick sediments and volcanics (the Tjornes sequence) have accumulated within the Tjornes Basin (TB) in the eastern part of the TFZ. The oldest sediments of the Tjornes sequence were deposited on a Miocene alluvial/lava plain. Marine and terrestrial fossiliferous sediments and volcanics then accumulated in a coastal to shallow-marine setting during the Pliocene. Littoral and sublittoral sandstones with abundant marine fossils were deposited during periods of transgression, while peats and lacustrine mudrocks accumulated in regressive sequences. The Quaternary sediments contain diamictites and conglomerates, with marine fossiliferous deposits. The sediments are intercalated with lava sequences and tuff beds reflecting increased volcanic activity in the vicinity and within the TFZ. The minimum age of the present configuration is five million years, which is the age of the oldest sedimentary units found in a TFZ basin. An eastward shift of the most active subsidence during the Miocene was followed by a Late Pliocene and Quaternary reversal to uplift.