Earliest known Cambrian calcimicrobial reefs occur in the Gobi-Altai, western Mongolia: Intriguing geobiological products immediately after the Ediacaran–Cambrian boundary

A dramatic shift in microbial reefs occurred around the Ediacaran–Cambrian boundary. Here we describe changes composition, construction, and texture of Zavkhan Terrane Gobi-Altai Province, western Mongolia, during late Ediacaran early Cambrian. Stromatolites consisting peloids, micritic clots, homogeneous lime mud without calcified microbes (calcimicrobes) are characteristic upper (units 9 16A Zuun-Arts Formation). In contrast, abundant thrombolites with stromatolites occur lowest Terreneuvian 17A 17 Bayan Gol These Cambrian made up clots close association calcimicrobes including Korilophyton, Renalcis, Tarthinia. The calcimicrobial studied herein directly stratigraphically above strata that record a strong negative δ13C values dominated by small shelly fossils; these earliest known reef representatives Phanerozoic. changed almost simultaneously drastic fluctuations environmental conditions (e.g., seawater chemistry, Ca concentration, carbonate saturation, oxygen level). would have been influenced evolution skeletal metazoans across present work provides crucial geobiological information on substantial shifts at boundary how related textures appeared tandem innovation biomineralisation.