What is "sapropel"

n. (context geology English) An aquatic sludge-like sediment rich in organic matter formed in oxygen-free areas at the bottom of lakes, seas etc.

n. 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.