ABSTRACT

The clay mineralogy and grain-size distribution of quartz silt in approximately 100 pelagic Deep Sea Drilling Project sediment samples has been examined to outline the history of dust supply to the North Atlantic. Samples were taken from eight time planes between Early Cretaceous and Late Miocene. With the exception of a few samples, the quartz is generally fine grained (means 9.00-7.34, 2-6 µm), moderate to well sorted and negatively skewed. By comparing the grain-size distributions with those of airborne dust, and by attempting to eliminate other processes through careful sample selection, it is concluded that most of the sampled quartz is eolian. By elimination of other processes and by association with the quartz, the cla minerals in the samples are also presumed mainly wind-blown throughout the Tertiary and Cretaceous, though an apparently diagenetic assemblage prevails in the Eocene samples. The clay mineralogy differs between one side of the Atlantic and the other, and on several time planes the quartz becomes coarser towards both the African and American continents. Eolian input from both continents is tentatively suggested. Furthermore, the zone of maximum dust input appears to have remained in latitudes 20-30° since the Early Cretaceous.