Minerals at DSDP Leg 78A Holes

The main constituents are quartz, feldspar, clinoptilolite, opal-CT, calcite, and clay minerals (kaolinite, illite, smectite, and palygorskite). Minor components (generally less than 10% of the total) include amphibole, dolomite, rhodochrosite, chlorite, and mixed-layer clays.

Amorphous clays, volcanic glass, and biogenic silica are also present. Calcite in the form of microfossils is a major component of the Cretaceous and post-Miocene sediment: during the Paleocene to Miocene the sites were below the calcite compensation depth (CCD). Detrital quartz and feldspar increase upsection, recording the passage of the area from ridge crest, through open ocean, to the vicinity of a volcanic arc.