Calcareous nannofossils of Deep Sea Drilling Project Sites 558 and 563, North Atlantic Ocean: biostratigraphy and the distribution of Oligocene braarudosphaerids.

Abstract

Deep Sea Drilling Project Sites 558 and 563, located on the W flank of the Mid-Atlantic Ridge between 33-37oN latitude, yielded lower Oligocene through Pleistocene nannofossil-bearing sediments. A detailed study of the abundance, preservation, and biostratigraphic distribution of calcareous nannofossils at Sites 558 and 563 shows that preservation ranges from moderate to good and nannofossil assemblages are reasonably diverse. These long, continuously cored sections add substantially to the record of Tertiary nannofossiliferous sediments recovered in the North Atlantic. A hiatus of early Pliocene age is noted in Hole 558A, where the nannofossil Subzones CN10b, CN10c, and CN11a are missing. An increase in the relative abundance of triradiate forms of Discoaster brouweri proved useful in determining the LAD (last appearance datum) of D.brouweri in the presence of considerable reworking. A significant occurrence of abundant braarudosphaerids, along with holococcoliths, was noted in the lower Oligocene section of Hole 563, the first report of abundant Oligocene braarudosphaerids from the central North Atlantic Ocean. Together with Southern Hemipshere occurrences, this North Atlantic occurrence of braarudosphaerids may indicate a bipolar distribution in the maximum abundance of Oligocene Braarudosphaera.-from Authors