(Table 1) Interstitial water chemistry at DSDP Leg 65 Holes

Studies of the chemical composition of interstitial waters obtained at Sites 482, 483, 484, and 485 on DSPP Leg 65 have revealed the following: (1) Early diagenetic processes in these rapidly deposited sediments led to large decreases in dissolved sulfate and concomitant increases in dissolved ammonia and bicarbonate (alkalinity). Associated with these processes of biodegradation of organic matter are carbonate-precipitation reactions leading to minima in dissolved calcium. (2) In Sites 482, 483, and 485 a flux of dissolved calcium from the basalts of Layer 2 into the sediments is implied. This flux is diffusive in nature, and in none of the sites, drilled on very young oceanic crust, is there any evidence for convective motion of pore fluids in the sediment column. (3) As a result of elevated temperatures in the sediments (caused by relatively high heat flow on young oceanic crust), silica diagenesis occurs at a relatively early stage. This diagenesis is associated with processes involving the alteration of volcanic matter in the sediments (low dissolved 87Sr/86Sr), which results in decreases in dissolved silica, magnesium, and potassium, and increases in dissolved calcium, lithium, and strontium.