ABSTRACT Early diagenetic chert in the upper Kotuikan and Yusmastakh formations, northeastern Siberia, preserves an exceptional record of carbonate textures and microfossils in an early Mesoproterozoic peritidal carbonate platform. Silicified lithologies include carbonate precipitates that formed at or near the sediment-water interface, as well as micritic event laminae that appear to have lithified more slowly. Precipitated textures include (1) radial-fibrous laminae nucleated on organic horizons and locally forming botryoids that stack vertically to produce microdigitate structures; and (2) micron-scale carbonate laminae. Both radial-fibrous carbonates and microlaminites contain abundant microfossils, some of which are preserved as uncompressed casts and molds that retain cellular detail. These indicate that lithification preceded microbial decay; actualistic taphonomy experiments on filamentous cyanobacteria suggest that lithification occurred on a timescale of days to weeks. In other silicified textures, microfossils show evidence of extensive post-mortem decay and compression, suggesting less rapid lithification. Papier-mâché carbonate sedimentation, characterized by essentially instantaneous lithification, appears to have been locally common in restricted tidal-flat environments during the Mesoproterozoic and earlier eras but uncommon in Neoproterozoic and later times.