Small carbonaceous fossil
Small carbonaceous fossils (SCFs) are sub-millimetric organic remains of organisms preserved in sedimentary strata. This category of fossils has traditionally included robust or thick-walled entities such as plant spores, acritarchs and chitinozoa, but the term 'SCFs' is usually applied to more fragile remnants of animals that can only be extracted through a delicate maceration technique.
Source: Wikipedia — Small carbonaceous fossil (CC BY-SA 4.0)