Coccoliths and discoasters from adriatic bottom sediments

The presence of coccoliths and discoasters in Adriatic bottom sediments is established. Both recent and fossil or allochthonous forms can be distinguished. The grab samples are located in sections across the sea. A consistent decrease of land-derived forms and an increase of recent forms can be observed in the composition of the species in the samples at increasing distances from the Italian coast. It is thought that these land derived forms are allochthonous, originating from the mountains of the Italian peninsula and brought down by rivers to the sea-shore from where they were swept out to the open sea by currents. These forms are indicative of Upper Cretaceous and Tertiary sediments and many are shown in polarized light to be in a recrystallized state. The supply of material from the eastern or Yugoslavian side of the sea turned out to be negligible. A relation was found between the composition of the samples and the pattern of sea currents. It was concluded, however, that their strong tendency to be reworked resulting from easy transportation over great distances, together with their little effect of solution, must be considered a serious drawback in stratigraphic use. As a result the reworked forms can not easily be distinguished from those in situ. The study further includes a systematic description of some of the more common forms. The techniques used are shortly mentioned and the technical difficulties when using both light and electron microscopes are briefly discussed.