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

Brachiopod shell imprints from the core samples from Borehole XC-1 (1012–1013 m), Shumnaya Formation, Botomian–Toyonian stages, Lower Cambrian, Siberian Platform were examined. The samples are represented by thin laminated bituminous mudstone. Imprints of phosphate brachiopod (lingulids and acrotretids) valves and casts of valves occur on the bedding surfaces of the samples. One sample contains 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 postmortem. At the same time, the fragments of the valves of adult lingulate brachiopods are composed of calcium phosphate.