Systematic Overview of the Pliocene Molluscs and Barnacles of the Barmur Group on Tjörnes, North Iceland

Timing and Consequences of Bering Strait Opening: New Insights From40Ar/39Ar Dating of the Barmur Group (Tjörnes Beds), Northern Iceland

“…The difference in age range between the faunal events in Iceland and Alaska could reflect a period of several hundred thousand years for molluscs to cross the Arctic, and it could also reflect site‐specific limitations on the occurrence of molluscs. Presence of sparse Pacific‐type mollusc fauna within the Tapes and Mactra biozones of the Barmur Group (Símonarson & Eiríksson, 2021b) is in line with the hypothesis that the molluscs crossed the Arctic quickly after first gateway opening, but the first appearance of abundant Pacific‐type molluscs in Iceland was moderated by site‐specific conditions. Thus, the most parsimonious explanation for the available faunal exchange data is that first opening of the Bering Strait in the latest Miocene (c. 5.5 Ma) was soon followed by marine faunal exchange in both directions.…”

“…Marincovich (2000) proposed an age of 3.6 Ma for the Pacific‐to‐Atlantic faunal exchange event by correlating the reported first appearance of the Pacific bivalve Mya arenaria at the Mactra / Serripes boundary in the Barmur Group, Iceland (Figure 5a), with its first appearances in the supposedly correlative Coralline Crag Formation of England and Rushmere Member (Yorktown Formation) of the eastern USA (Campbell, 1993; MacNeil, 1965). However, Símonarson and Eiríksson (2021a, 2021b) conducted a comprehensive study of the genus Mya and showed that the reports of Mya arenaria in the Barmur Group were mistaken; the specimens were actually Mya schwarzbachi . Furthermore, the Coralline Crag Formation has now been dated as 4.4–3.8 Ma (De Schepper et al., 2009) and the base of the Rushmere Member as 3.3 Ma (Dowsett et al., 2021), so first appearances of any fauna at these locations compared with the Barmur Group must be diachronous.…”

“…The boundary between the Mactra / Serripes biozones is of key importance to our study because it represents the sudden arrival of abundant Pacific‐type fauna in Iceland. A few Pacific‐type molluscs appear in the Barmur Group below the Serripes biozone (Símonarson & Eiríksson, 2021b). The abrupt appearance of at least 24 new Pacific‐type mollusc species in shell bed 13 that were not present in bed 12 or lower defines the base of the Serripes biozone, and this bioevent is the widely used signal of the first opening of the Bering Strait oceanic gateway (Buchardt & Sı́monarson, 2003; Símonarson & Eiríksson, 2008, 2021a; Verhoeven et al., 2011).…”

“…The first post‐Cretaceous opening of an oceanic gateway is signaled by the appearance of Atlantic molluscs in the Pacific, and vice versa (Gladenkov & Gladenkov, 2004; Gladenkov et al., 2002). The Barmur Group contains a plentiful and well‐studied molluscan fauna (Durham & MacNeil, 1967; Símonarson & Eiríksson, 2021b; Strauch, 1963, 1972a, 1972b). The arrival of abundant Pacific bivalve molluscs defines the boundary between the Mactra and Serripes biozones (Figure 2).…”