sapropel
An aquatic sludge-like sediment rich in organic matter formed in oxygen-free areas at the bottom of lakes, seas etc.
countable, uncountable
Another instance in which Mediterranean sapropels have provided clues about events deep within the African continent is the ‘greening’ of the Sahara about 120,000 years ago.
Where it comes from
From German Sapropel, corresponding to sapro- + Ancient Greek πηλός (pēlós, “mud, clay”).
Adapted from the Wiktionary entry sapropel (CC BY-SA 4.0).