FLUID-FLOW IN DEEP-SEA CARBONATES - ESTIMATES BASED ON POREWATER SR

Fluid flow of up to 200 m/myr is documented in thick (about 500 m) dee p-sea carbonate sections by numerical modeling of the porewater Sr2+ a nd Sr-87/Sr-86 profiles at DSDP Sites 572, 573 and 574. These sites we re selected as likely candidates for significant fluid flow in the sed imentary part of the section because it had already been shown that th ey are underlain by rapidly flowing fresh seawater in the basaltic bas ement. The nature of the exercise is to fit the porewater Sr propertie s at these sites by finding a common rate of Sr exchange as a function of sediment age and a local rate of vertical fluid flow. The flow rat es determined in this way are 20 m/myr upwards at Site 574, 20 m/myr d ownwards at Site 573 and 200 m/myr downwards at Site 572. Because of u ncertainties of about a factor of 2 in the assumption of a common rate of Sr exchange at all sites, and trade-offs between the Sr exchange a nd fluid flow in determining the shape of Sr2+ and Sr-87/Sr-86 profile s at a given site, the precision of the method is of the order of 10 m /myr. Thus at least at Site 572, the Sr properties of the interstitial waters provide a convincing measure of vertical fluid flow through a thick carbonate section.