2.1. Sediments used in taphonomic experiments with Artemia
salina.
We buried A. salina in five different fine-grained sediments
(four clays and artificial silica) in order to assess the relative
importance of different components and properties of the sediment for
the preservation of SBO. Sediments of similar mineralogy are common in
Lagerstätten (Anderson et al., 2018). However, we made no attempt to
model real sediment types involved in Lagerstätten formation; rather, we
sought to better understand the general principles of SBO fossilization.
The main criterion for choosing sediments was the purity of the
available samples which was crucial for the subsequent analysis and
interpretation.
The initial chemical composition of the sediments, measured by X-ray
fluorescent analysis, is shown in Table 2. The kaolin came from the
Polog deposit (Ukraine) and contained 97% of kaolinite in the purified
sample (see Naimark et al., 2016a for details). The clinochlore
originated from the Akhmetievskoe deposit (Ural mountains) and was given
to us from the collection of Fersman Mineralogical Museum (Moscow). The
chamosite originated from the Kursk Magnetic Anomaly, the collection
stored in the museum of the Institute of Geology of Ore Deposits,
Petrography, Mineralogy and Geochemistry (Moscow). The montmorillonite
was from Tikhmenievskoe deposit (Sakhalin), from the collection of one
of the authors (N.B.). Artificial silica was precipitated from perlite
by thermal decomposition (150o C) with NaOH and
consequent neutralization by sulfuric acid yielding porous, amorphous
siliceous particles. We did not use glass beads or sand as a model for
siliceous sediment (like in Newman et al., 2019) because glass beads and
sand are chemically highly inert.
Non-sterile artificial sea water (ASW; brand “Tetra”) was prepared
according to the instructions for this brand. We checked its pH
(7.4-7.8) and salinity (24‰); the chemical composition was assessed by
X-ray fluorescent analysis (Table 2). For the freshwater experiment with
montmorillonite we took tap water and kept it open under non-sterile
conditions in a glass jar for a week to obtain a stable microbial
consortium.
To prepare the sediments, all samples of minerals were ground finely in
an agate mortar. Next, they were mixed in settled tap water and
equilibrated for half a minute, allowing large and/or heavy particles to
gravitate to the bottom. Then the upper portion (approximately 2/3 of
the suspension) was decanted. This upper portion was dried, ground again
and mixed in ASW (or tap water in the case of montmorillonite) in
proportion of 3g/100 ml. The resulting suspensions were actively mixed
with bubbling from an air pump for 48 hours to remove clay pellets.