An Age Model for the Miocene to Pleistocene Tjörnes Sequence, North Iceland

According to a new revised age model which is consistent with published paleomagnetic and radiometric data, marine sedimentation in the Tjornes Basin started close to the Miocene-Pliocene boundary. The oldest part of the north-west dipping sedimentary sequence, the Tapes Zone, is not a continuous, conformable sequence, but has been dislocated laterally within the Tjorne Fracture Zone. Its basal age was previously determined by dinoflagellate stratigraphy. Above the boundary between the Tapes and Mactra Zones the sequence is continuous, but the development of a graben to the east of the present coastline changed the focus of accumulation. An erosional surface developed to the west of this graben, resulting in a gap in the presently exposed coastal section. The uppermost part of the Mactra Zone is correlated to a level within the uppermost Gilbert reversed polarity chron with an estimated age of 3.8 Ma. Serripes Zone sediments span the interval 3.8–3.2 Ma, and the lowest tillite bed of the Tjornes sequence in the Furuvik creek is dated to the Gauss-Matuyama boundary at 2.58 Ma. Volcanic units both in the coastal sections on east Tjornes and in the Grasafjall and Burfell mountains in central Tjornes expose Matuyama-Brunhes chron boundary at 0.78 Ma.