(Table 1) Interstitial water chemistry at DSDP Leg 78A Holes

Studies of interstitial water carried out during Deep Sea Drilling Project Leg 78A (Sites 541, 542, and 543) have revealed that alteration of volcanic material dispersed in the sediments is largely responsible for increased concentrations of dissolved calcium and decreased concentrations of dissolved magnesium and potassium. This conclusion is supported by studies of the 87Sr/86Sr ratio of dissolved strontium, as well as by studies of the oxygen isotopic composition of interstitial waters. At Site 543 a large part of the d18O decrease in the interstitial waters must result from diffusive exchange with underlying basement rocks. Data from studies of interstitial water do not indicate upward advection of fluids at Sites 541 and 542.