The team found a rich mud, called sapropel in the Marmara.
From the sciencedaily.com
Going upward from this depth level, the organic content of sapropel S1 decreases corresponding to an increasing average oxygen content and concomitant breakdown of the organic material.
From the sciencedaily.com
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Sludge (rich in organic matter) that accumulates at the bottom of lakes or oceans
Sapropel (a contraction of ancient Greek words sapros and pelos, meaning putrefaction and mud, respectively) is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter. Organic carbon concentrations in sapropels commonly exceed 2% in weight.