Marine Plio-Pleistocene of Iceland and problems of Its Correlation

Abstract

The marine Pliocene-Pleistocene sequence of Iceland contains four main assemblages of mollusks: (1) Venerupis rhomboides et al., (2) Serripes groenlandicus et al., (3) Portlandia arctica et al., and (4) recent species. Analysis of the stratigraphic distribution of 100 species shows that the percentage of extinct species in the assemblages decreases from 40% in the oldest to 4–8% in the youngest. There is also a change from south boreal affinities in the oldest assemblage to north boreal in the youngest. The molluskan assemblages of Iceland can be correlated with Pliocene-Pleistocene assemblages of England and North Europe: (1) Coralline Crag, (2) Red Crag—lower part of the Icenian strata, (3) upper part of the Icenian-Cromerian strata. The upper boundaries of the Pliocene and Eopleistocene are defined by paleomagnetic data and radiological dating. The upper boundary of the Pliocene presumably should be established in the basalts lying between the Tjörnes and the Breidavik deposits by changes between the second and third mollusk assemblages and by the Gilsa paleomagnetic event.

Climatic effects of reduced Arctic sea ice limits in the Giss II General Circulation Model

“…Furthermore, the subsidence of the Bering land bridge, and the initiation of flow through the Bering Straits, occurred early in the late Pliocene. A major dispersal of Pacific fauna into the Atlantic Ocean suggests that the Bering seaway was permanently established by about 3.0 Ma [Hopkins, 1967;Gladenkov, 1981]. Similarly, the formation of the Panamanian isthmus could also have significantly influenced oceanic heat transport to the high-latitude North Atlantic and potentially the Arctic Ocean [Maier-Reimer et al, this issue] but this occurred in the mid-Pliocene [Keigwin, 1982].…”

Engineering-geologic maps of northern Alaska, Harrison Bay quadrangle

“…The lower Breidavik beds contain mollusk faunas of a more arctic aspect and are interbedded with tillites. According to Gladenkov (1981, Table 2) the base of the Breidavik beds occurs just above the Olduvai Chron (referred to by him as the Gilsa event) and the top of the Tjornes deposits is about 2 Ma. Thus both the mollusks and the marine vertebrate fauna suggest that the Fishcreekian transgression occurred prior to the Olduvai Chron, which began about 1.87 Ma.…”

“…The fauna includes taxa of Pacific origin and thus post-dates the opening of Bering Strait, which occurred between 3 and 3.5 m.y. ago (Hopkins, 1972;Gladenkov, 1981). The Colvillian transgression may correlate with Hopkins 1 (1967) Beringian transgression as defined for the type locality at Nome.…”

Pliocene paleoecologic reconstructions based on ostracode assemblages from the Sagavanirktok and Gubik formations, Alaskan North Slope

“…Pliocene marine sediments throughout the Northern Hemisphere provide evidence of oceanographic and climatic changes that impacted the Arctic Basin, including (1) changes in North Atlantic circulation between 3-5 Ma caused by the final closure of the Isthmus of Panama and the consequent strengthening of the Gulf Stream (Keigwin, 1978;Jones and Hasson, 1985), (2) the opening of Bering Strait between 3 and 4 Ma (Gladenkov, 1981;Einarsson and Albertsson, 1988;Gladenkov and others, 1991), allowing the first exchange of Pacific faunas and water masses since the late Cretaceous (Marincovich and others, 1990), (3) progressive cooling of the Arctic Ocean beginning about 4 Ma (Herman and Hopkins, 1980;Clark, 1990), and (4) the first significant development at about 2.4 Ma of greatly increased ice rafting and iceberg delivery to lower latitudes of the North Atlantic (Shackleton and others, 1984;Raymo and others, 1989; Jansen and Sjoholm, 1991).…”

“…The effects of these climatic and oceanographic changes can be seen in Arctic Ocean shallowwater faunas and include the first appearance of North Pacific forms in the Arctic and North Atlantic beginning about 3 Ma (Durham and MacNeil, 1967;Gladenkov, 1981;Gladenkov and others, 1980;Fyles and others, 1991)…”