Taphonomy of the Juvenile Valves of Organophosphate Brachiopods in Mudstones of the Shumnine Formation (Botomian and Toyonian Stages, Lower Cambrian), North-West of the Siberian Platform (Borehole XC-1)

The core samples derive from the XC-1 borehole (1012-1013 m), Shumnine Formation, Botomian-Toyonian stages, Lower Cambrian, Siberian platform. The samples are represented by thin laminated bituminous mudstone. The imprints of phosphate brachiopod (lingulids and acrotretids) valves and casts of the valves occur on the bedding surface of the samples. One sample bare a cluster of small fossils (60-220 µm) probably belonging to embryos or brephic valves of these brachiopods. Chemical analysis has revealed that the originally organic material of the valves was replaced by pyrite most likely after their death. At the same time, the fragments of the valves of the adult lingulate are composed of calcium phosphate.