Chemical composition of zeolites in sandstones at DSDP Sites 445 and 446

Andesitic volcaniclastic sandstones of Middle Eocene age recovered from DSDP Sites 445 and 446, a back-arc basin, contain clinoptilolite, heulandite and analcite as a pore-filling cement. Clinoptilolite and heulandite at Sites 445 and 446 contain different chemical composition from other deep-sea clinoptilolites and heulandites. The dominant cation of both clinoptilolite and heulandite is Na+ ion activity in pore water was greater at the time of their formation. Volcanic glass has acted as a precursor for both clinoptilolite and heulandite at Sites 445 and 446. Biogenic silica is also suggested as a precursor. […]