Foraminifera in late quaternary deposits from the Oslofjord area.

Abstract

Approximately 2500 core samples from 130 borings, 4 m to 40 m deep, in Late Quaternary (latest Allerød through Sub-Atlantic) clay deposits in the Oslofjord area in southeastern Norway were investigated micropaleontologically. In addition some samples from clay pits and excavations for foundation purposes were examined. 180 species, subspecies, and forms, of Foraminifera, belonging to 76 genera and 23 families of the superfamilies Astrorhizoidea, Lituoloidea, Milioloidea, Nodosarioidea, Bulliminoidea, Spirillinoidea, and Rotalioidea occurred. Only one of the species was planktonic. A subdivisional of the deposits were undertaken, based upon foraminiferal zonation, 7 zones from A to G, and 10 subzones were recognized. The zones and subzones were ecologically interpreted, on the basis of comparison with Recent faunas from environments assumed to be similar to those of the fossil faunas, and by radiocarbon datings. They were correlated with substages of the recession of the land ice through the area and, as far as possible, with units of a previously established stratigraphy for the Oslofjord area. Subzone Am (A-middle), was found to be of Younger Dryas age, deposited during the formation of the large glacial marginal ridge called the Ra.