ATLANTIC

Sediment samples obtained by deep-sea drilling at DSDP Sites 382, 385, and 386 in the western North Atlantic contain limited concentrations of phillipsite and clinoptilolite, the concentrations of which are controlled apparently by bulk sediment content. Quanti¬ tative estimates of zeolite mineral concentrations determined by X-ray diffraction reveal that phillipsite is the dominant zeolite in volcanogenic and montmorillonite-rich sediments. Zeolite minerals in siliceous and feldspathic sediments are dominated by clinoptilo¬ lite. High carbonate content appears to promote zeolite dissolution. As volcanogenic sediments dominate the sedimentary section on seamounts as at Sites 382 and 385, phillipsite tends to be the dominant zeolite mineral appearing on such topographic features. The remaining North Atlantic reflects the high silica and alkali feldspar content of the sea-floor sediments, as clinoptilolite domi¬ nates the zeolites of these beds. The major element composition of selected zeolites reflects their mineralogy, but not the environment of their genesis. No systematic chemical variation is observed among analyses of a zeolite mineral from various types of sedimentary beds, save a tendency for sedimentary phillipsites to be slightly more silicic and potassic than their volcanogenic counterparts. Trace elements show greater variability, but insufficient data are available to evaluate their variation