Tjörnes – Pliocene and Pleistocene sediments and faunas

Abstract

On the western side of the Tjornes Peninsula in North Iceland a longsequence of fossiliferous marine sediments, basalts, and diamicititesrecords the climatic history of the North Atlantic during the Plioceneand Lower Pleistocene. The Pliocene Tjornes beds are divided in threebiozones; the Tapes Zone (oldest), the Mactra Zone, and the SerripesZone (youngest). The Tjornes beds consist mainly of marine silt- andsandstones but there art, also several fossiliferous terrestrial beds inthe lower part. The marine faunas in the Tapes and Mactra Zones aremainly boreal, but during the deposition of the Serripes Zone the faunagreatly diversified with immigration of Pacific molluscan species withmore arctic elements. They reached the North Atlantic at 3.6 Ma aftermigration through the Bering Strait coeval with closing of the CentralAmerican Seaway. Marine molluscs of Pacific ancestry it? the Tapes andMactra Zones post-date also the first opening of the Bering Strait. Inthe Breioavik Group, diamictite beds alternate with volcaniclasticmudrocks and sandstones, and basaltic lava flows. Fourteen lithologicalcycles are identified in the Breidavik Group each one starting with adiamictite interpreted as lodgement tillite and ending with terrestrialsediments and lava flows. Interbedded marine fossiliferous mudrocks andsandstones contain arctic to boreal faunal assemblages. The oldest cyclein the Breioavik group was probably deposited about 2.5 Ma, just afterthe Gauss/Matuyama polarity reversal.