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).