WHY SOME MEDITERRANEAN SAPROPELS SURVIVED BURN-DOWN (AND OTHERS DID NOT)

We have evaluated, using a numerical model, the burn-down depth (depth of post-depositional oxygenation) of organic matter-rich sapropels un der aerobic conditions at the seafloor. The model suggests that saprop els may be erased by burn-down to depths of at least 5 cm after 10 kyr of bottom-water reoxygenation. A test of the sensitivity shows that t he parameters exerting a major control over the burn-down process are the flux of freshly sedimenting organic carbon, the oxygen Concentrati on of the bottom water, the amount of organic matter in the sapropel, and the sedimentation rate. In comparison, bioturbation is of minor im portance. The result implies that burial of elevated concentrations of non-refractory organic carbon is generally improbable when the sedime ntation rate is lower than 1-2 cm kyr(-1). The record of sapropel depo sition in the Mediterranean Sea and elsewhere may thus be biased towar ds depositional environments where the sedimentation rate is large eno ugh to shield the organic-rich layer from oxygenation. (C) 1997 Elsevi er Science B.V.