Lithostratigraphy of the Tjörnes Sequence in Barmur and Höskuldsvík on the West Coast of Tjörnes, North Iceland

New data on the stratigraphy of Tjornes Peninsula, North Iceland, are presented. Over 25 stratigraphic sections have been measured, lithological units defined and sampled for macro- and microfauna, forming the basis of a new lithostratigraphic classification scheme for the Miocene to Pliocene part of the Tjornes sequence. Three group units are identified: the Kaldakvisl, the Barmur, and the Hoskuldsvik Groups. Geological maps reveal new details of the geological structure including right-lateral transcurrent faults at the southern margin of the Tjornes Fracture Zone, which is split up in west-northwest east-southeast trending blocks. Early subsidence and transgression towards the end of the Miocene has led to the development of a north-south trending graben structure. During the Pliocene, the axis of subsidence shifted eastward and a new graben became active east of the initial one and a Pleistocene depression in Breiðavik developed. Vertical facies changes within the Barmur Group are cyclic and repeated transgressions and regressions are inferred. Sedimentation took place in coastal and shallow-marine environments. The lowest part of the Barmur Group sediments has been preserved on laterally dislocated basement blocks, so that lithological units cannot be correlated across the separating faults. Paleontological data provide constraints on the stratigraphy.