The mechanism that guides the formation of exceptionally preserved fossils with soft tissues variously displayed is a paramount challenge to paleontology. The key question for exceptional preservation is the nature of the slowdown of decay and acceleration of soft tissue mineralization. Here we report the experimental formation of subfossils of the brine shrimpArtemia salina(Crustacea, Branchiopoda), which were produced during 14 months of aging in a kaolinite clay sediment. EDS/SEM elemental analyses showed that the subfossils were preserved as thin clay-organic replicas that displayed fine anatomical details. Decomposition in the clay-colloidal solution established highly heterogeneous acidic conditions, with the lowest pH typically found in the vicinity of the buried organisms, and visually manifested in patchy coloration of the sediment. Elevated acidity is likely what ultimately slowed the decay. An acidic environment increases the rate of clay destruction and, consequently, the diffusion rate decline. As a result, the acidic products quickly accumulate around a buried body; this in turn inhibits bacterial proliferation, accelerates the acidic hydrolysis of clay and, accordingly, the release of tanning and mineralizing agents. The subfossils remained stable under experimental high pressure and temperature. These model subfossils exhibit features that are typical of some Lagerstätten fossils preserved in fine-grained sediments.

Cambrian Lagerstätten host rocks are frequently composed of kaolinite and chlorite in varying amounts; accordingly, our goal was to study the preservation potential of crustaceans in these two clays. We conducted long-term experiments (12–18 months, the longest duration of actualistic taphonomy experiments from published literature) on the decay of Artemia salina in these clay sediments. The degree of preservation, transformed mineralogical composition of the sediments, and the elemental composition of the nauplial remains were examined. We demonstrate that the kaolinite and chlorite sediment enhanced the preservation (in the kaolinite the effect was considerably higher than in the chlorite) compared with the sediment-free control. pH inside the sediments dropped to 6.5–7.1 and was even lower (<4) around the buried carcasses, facilitating the dissolution of clays. This phenomenon was confirmed by mineralogical analyses of the experimental sediments, which showed mineralogical signatures of such dissolution and new mineral phases. According to the variations in the dissolved minerals in the sediments, different cations entered the buried remains as was shown by the multiple energy dispersive X-ray analyses. An increased level of Mg was detected in the carcasses buried in chlorite, whereas Al and Si concentrations were higher in the kaolinite; in both cases, Ca rapidly entered the decaying tissues from marine water. Bacteria underwent similar mineralization as the macroremains and apparently had no direct effect on the mineralization. The results confirmed an important role of dissolved Al ions in preservation of soft-bodied organisms in clay-dominated sediments and explained wide variation in chemical composition of their fossils.

The structure, chemical composition, and properties of palygorskites from several deposits in the Russian Federation, Ukraine, Uzbekistan, and Slovakia have been investigated by transmission electron microscopy, microanalysis, X-ray diffraction, IR spectroscopy, and thermal analysis. It is shown that the palygorskites formed under different physicochemical conditions may significantly differ in chemical composition, morphology, and defect structure. Depending on the formation conditions, palygorskites decompose differently upon heating.

The study of a large amount of factual material about the formation conditions of gibbsite or boehmite and their mutual transformations in lateritic bauxites allowed us to solve the problem of boehmite formation and its spatial and genetic relationship to gibbsite. The boehmite formation occurred only during the formation of sedimentary-lateritic bauxites from alluvial and lacustrine sediments that underwent bleaching and resilification at the stage of sediment flooding, as well as on bleached bedrock under sedimentary-lateritic bauxites. The most intense boehmite formation occurred at a depth of 20–30 m from the surface and was accompanied by an alumina input, which was realized here in the form of boehmite along with the gibbsite formation due to the hydrolytic decomposition of kaolinite and partially due to the input alumina. In the upper profiles, the recrystallization of bauxites occurs with the replacement of dissolving boehmite with gibbsite, with a decrease in the total Al₂O₃ content and an increase in the amount of crystallization water. In classic lateritic bauxites, the boehmite content is highly insignificant; that is, its formation in them practically does not occur or is very much inhibited.