Organic carbon accumulation in the Holocene sapropel of the Black Sea

The modern laminated coccolith marl (unit 1) of the Black Sea containing 2–6 wt% organic carbon overlies a finely laminated sapropel (unit 2) containing 5–20 wt% organic carbon. However, the accumulation rate of organic carbon in the sapropel is not significantly different from that in unit 1. In contrast, the accumulation rates of either CaCO₃ or lithogenous matter (clay) are significantly lower in the sapropel compared with unit 1. Thus, the sapropel has very high organic carbon contents because of lesser dilution of the organic fraction by the other bulk components. Because the accumulation rate of organic carbon in the sapropel is similar to that in unit 1, which is not significantly different from accumulation rates in oxygenated environments in similar settings, the Black Sea sapropel is not necessarily characteristic of anoxic basins.