Microbially induced sedimentary structure
Microbially induced sedimentary structures (MISS) are primary sedimentary structures formed by the interaction of microbes with sediment and physical agents of erosion, deposition, and transportation. The structures commonly form when microbial mats (which may comprise bacteria, fungi, protozoans, archaea or algae) are preserved in the sedimentary geological record.
Source: Wikipedia — Microbially induced sedimentary structure (CC BY-SA 4.0)