Sapropel (a contraction of Ancient Greek words sapros and pelos, meaning putrefaction and mud (or clay), 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 wt.% in weight.
The term sapropel events may also refer to cyclic oceanic anoxic event (OAE), in particular those affecting the Mediterranean Sea with a periodicity of about 21,000 years.