2.3. Design of the taphonomic (burial) experiments.
Our taphonomic experiments (Table 1) imitate rapid burial of SBO under a sediment layer, which is believed to be a common condition for the Cambrian Lagerstätten formation. The experimental design was described in our earlier works (Naimark et al., 2016a, b, 2018 a, b). The homogeneously mixed clay suspensions were poured into high glass tubes (50-70 cm in height, 1.0-1.5 cm in diameter; as we observed in multiple experiments, this variation did not affect preservation). 200-300 mg of dead nauplii of Artemia salina were put on top of the suspension in each tube, and then the carcasses and mineral particles were allowed to settle together. The nauplii accumulated in the middle or in the upper part of the kaolinite sediment. In silica, the nauplii sank approximately with the same speed as the smallest particles, so the carcasses were deposited within the thin top layer of the sediment. In clinochlore and chamosite, the particles sank faster than the dead nauplii, so the majority of the nauplii were concentrated in the topmost layer and at the surface of the sediment. To cover them on top, we added a portion of the respective sediment (clinochlore or chamosite, according to the type of experiment). Montmorillonite formed a thin colloidal solution which was gradually settling down throughout the 5-year experiment. Carcasses were distributed in the middle and lower parts of the colloid; their concentration gradually increased from top to bottom. The bright orange coloration of the nauplii was clearly visible in all sediments. We used the same sediments without nauplii as controls; there was also a sediment-free control (nauplii in the ASW).
All tubes were sealed by one layer of Parafilm, which decreases evaporation and gas exchange but does not block these processes completely. Then the tubes stayed undisturbed in the dark at room temperature (25-28oC). After 1 year (5 years for the montmorillonite) they were opened and analyzed.
There were 15 replicate tubes for the kaolinite, which were used to demonstrate the robustness of the decay pattern (Naimark et al., 2018a). There were also three replicate experiments (tubes) for the clinochlore, and two for the clinochlore control and the chamosite. Other experiments had no replication. All replications demonstrated the same decay pattern and very similar pH changes and degree of preservation of the carcasses (Naimark et al., 2018 a, b).