(Table 1) Interstitial water chemistry at DSDP Leg 63 Holes

Interstitial water studies of drill sites off the California Continental Borderland (Sites 467, 468, 469) reveal that fresh water can penetrate through the sediments as far as the San Miguel Gap (Site 467). In the rapidly deposited sediments of Site 467, decreases in magnesium concentrations can be related to the formation of dolomite in the claystone unit of the sediment column. Decreases in magnesium and increases in calcium at Site 469 at the base of the Patton Escarpment are probably the result of alteration of volcanic matter in the sediments and/or the underlying basalts.
Studies of the gradients of calcium, magnesium, potassium, strontium, and lithium at Site 471 indicate that a 150-meter-thick porcellanite-claystone-limestone complex acts as an almost complete barrier to diffusive exchange with the underlying sediments. Uptake reactions involving potassium and magnesium may still occur in the Porcellanite complex.
At all sites, with the exception of Site 467, gradients of calcium show concentration increases with depth and simultaneous decreases in dissolved magnesium - a pattern commonly observed in open-ocean environments.