45. Clay Mineralogy of the Lower Cretaceous Deep-Sea Fan, Deep Sea Drilling Project Site 603, Lower Continental Rise Off North Carolina

The clay mineralogy of Lower Cretaceous deep-sea fan sediment in the western North Atlantic is dominated by smectite in most intervals, and by illite in samples from intervals of high sand input. Different intervals of higIt'sand input are enriched in kaolinite. Kaolinite and illite levels do not correlate in this sediment, indicating that the input of each clay type was independent and represents either a different provenance or a different depositional mode. The latter hypothesis is preferred because equivalent, continental strata have clay mineral suites dominated in most cases by kaolinite, and in other cases by illite. Only marine strata of eastern North America have expandable clay. Thus under normal conditions in the Early Cretaceous, kaolinite was deposited in continental environments, illite dominated deposition in transitional environments, and smectite was transported to the deep sea. At certain intervals in the Neocomian and Aptian, fine-grained sediment bypassed the shelf and slope and enhanced Lower Cretaceous clay mineral suites in the western North Atlantic. These intervals probably corresponded to turbidity-current activity or continental flooding. Illite-enriched sediment may have been supplied by the outer shelf, whereas kaolinite-enriched intervals may have come from a more nearshore or terrestrial environment.