31. THE STRONTIUM ISOTOPIC COMPOSITION OF PORE WATERS FROM LEG 133: NORTHEAST AUSTRALIAN MARGIN1

Data are reported for strontium isotopic compositions of approximately 100 samples of pore waters recovered from the sediments of Ocean Drilling Program (ODP) Sites 812, 813, 814, 815, 817, 818, 823, and 824. Two types of pattern were found: 1. Sites 812 through 814 and 824 reflect a zoned system with the uppermost pore waters under diffusive control and with Sr concentrations and isotopic compositions controlled principally by dissolution of aragonite and the deeper pore waters affected by fluid flow with both Sr concentrations and 87Sr/8°Sr ratios close to modern seawater values despite the Miocene age of the host sediment. It is possible that the fluid flow at depth is associated with a hardground between Pliocene/Pleistocene and Miocene/Pliocene sediments. 2. Pore waters from Sites 815,817,818, and 823 show increasing salinities/chloride with depth, which may reflect the presence of evaporites beneath the drilled sections. At Site 823, where porewater Sr concentrations reach nearly 3 mM, upward transport of Sr may be recognized from porewater 87Sr/86Sr ratios.