N. M. Boeva

Decaying of Artemia salina in clay colloids: 14-month experimental formation of subfossils

Abstract. 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 shrimp Artemia 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.

PERSISTENCE OF EXTERNAL ANATOMY OF SMALL CRUSTACEANS IN A LONG TERM TAPHONOMIC EXPERIMENT

Abstract:  Although studied for more than a century, the preservation mechanisms of soft-bodied organisms in Lagerstätten remain disputable. One aspect of this phenomenon, the role of sediments in the decay and preservation of soft tissues, is understudied. We present the results of an 18-month decay experiment that shows the difference between the preservation of the crustacean Artemia salina buried in marine water and inside clay sediment. We found that the decay of the external tissues of A. salina is slower in the sediment than in marine water, while the internal anatomy decays rapidly in both settings. This results in the formation of exuviae-like structures, accounted for not by the recalcitrance of external tissues, but by the burying conditions in the thick marine sediment. The experiment indicates the importance of organic-mineral interactions in the understanding of the taphonomic retarding of soft-tissue decay and the persistence of fine external anatomical features.

Structural-morphological features of kaolinite from clayey rocks subjected to different stages of lithogenesis: Evidence from the Voronezh anteclise

This paper reports the results of precision structural-morphological study of kaolinite from clayey rocks taken in various areas of the Voronezh anteclise subjected to different stages of lithogenesis: primary kaolins of the weathering crust, proluvial-talus and lacustrine secondary kaolins, as well as lacustrine-swampy fireproof and deltaic-lagoonal refractory clays. The clayey material was transported over more than 300 km. The formation of the fireproof and refractory kaolin deposits in the Voronezh anteclise was related to the Devonian and Early Cretaceous stages of the geological evolution of the region. In terms of spatiotemporal and facies features, the studied genetic series of the kaolin clay deposits is unique. It was established that the sequential structural-morphological evolution o kaolinite in the considered deposits was caused by its mechanical disintegration during transport and redeposition. Interrelation between organic and mineral matters in the fireproof clays was revealed for the first time. Experimental studies of the behavior of kaolinite during sequential grinding and heating confirmed the main reasons for its natural degradation. The formation of virtually monomineral kaolin clays was provoked by the “flow-through” diagenesis, which is similar to weathering in trend. Evolution of mineral matter of the considered genetic series in kaolinite clay deposits was accompanied by the increase of δ18O values and their dispersion. Peculiarities identified in the behavior of kaolinite and related oxygen isotope characteristics of different-aged denudation and redeposition products of the Devonian weathering crust can play an indicator role in studying different stages of the lithogenesis of clayey rocks.

The first find of biogenic nanosiderite in oxidized ferrous quartzite of the Lebedinsk deposit, Kursk Magnetic Anomaly

The first data on biogenic nanosiderite originally discovered in oxidized Fe-quartzites from the Lebedinsk deposit of the Kursk Magnetic Anomaly (KMA) are reported. Two generations of siderite with radically different morphology and crystal-chemical and physical properties were identified. The biogenic origin is substantiated for the late generation (nanosized siderite particles). We suggest that the early ores were transformed as a result of the evolution of the atmosphere and biosphere in the area of the KMA in the Phanerozoic. Such significant differences in the properties of biogenic nanosiderite and early rhombohedral siderite may provide evidence for their different origins. The early generation of siderite was most likely formed during an abiogenic process.

Biogenic nanogoethite in the weathering crust of the basalts of Vietnam: Crystal morphology and thermal and magnetic properties

Studies of the mineral substance in the weathering crust (CW) of the basalts of Vietnam have shown that these basalts might be considered as a natural laboratory for the formation of mineral bionanostructures of specific crystal morphology and thermal and magnetic properties. It is suggested that the crystallization of goethite in the cuirass and underlying bauxites of the CW of Vietnam resulted from the coagulation of colloidal particles and of hydrated iron oxide under the impact of bacterial colonies, which determined the specific features.

Interaction of anoxygenic phototrophic bacteria Rhodopseudomonas sp. with kaolinite

The interaction between freshwater nonsulfur purple bacteria Rhodopseudomonas sp. UZ-25p (Uzon caldera, Kamchatka, Russia) and two kaolinite samples (Zhuravlinyi Log, Chelyabinsk oblast) was investigated. Alterations in the chemical composition of the minerals and solutions, the parameters of bacterial growth, and crystal morphology and mineralogy of the kaolinite samples indicated the interactions between all components of the system (minerals, water, growth medium, and bacteria). Bacteria removed some elements from the medium, used them for growth, and promoted their transition into the mineral exchange pool. In the presence of bacteria, kaolinite cation exchange capacity increased and saturation of kaolinites with bases occured. Partial biodegradation of kaolinites, accompanied by ordering of the crystalline structure of their lamellar phase, was the main factor responsible for the increase in cation exchange capacity. For the first time anoxygenic phototrophic bacteria were found to degrade kaolinite with formation of gibbsite. The theoretical and applied significance of the experimental results is discussed.

The role of organic matter in the formation of fireproof clay of the Latnenskoe deposit

634 Organic matter of vegetal and (or) bacterial origin in the Earths crust under the conditions of hypergen� esis carries two functions: destructive, providing decomposition and dissolution of primary minerals, and creative, which controls incorporation of mineral� ized organic remnants in the composition of new hypergene formations. Biomineral interactions and their role in mineral formation are related to one of the most important problems of the twentyfirst century in mineralogy (1, 2). It has become much more evident that bacteria occur in all environments and on all sur� faces and that they actively participate in rock weath� ering, material transportation, sedimentation, and diagenesis. Biofilms and cyan bacterial mats play an important role in the processes of mineral formation as well (3). Additional support for these facts was obtained during study by a scanning (SEM) and trans� mitting (TEM) electron microscopy, thermal analysis, and IRspectroscopy of fireproof clay from the Latn� enskoe deposit; as a result, the interaction between organic and inorganic materials during their forma� tion was originally discovered. The deposit is located in 15 km to the west of Vor� onezh in the Don-Veduga-Devitsa interfluves. Clay composes oval lenses with a width of several hundred meters and a length of a few kilometers; it occurs in the middle part of the section of sand-gravel alluvial deposits of Aptian age. The thickness of productive horizon ranges from n to 40 m; the average thickness of proper fireproof clay is 3-4 m. Clay is mainly com� posed of kaolinite, the concentration of which is 70- 90%. Terrigenous hydromica and quartz, as well as authigenous montmorillonite and gibbsite, usually

Biogenic nanomagnetite in the Lebedinskii deposit: Evidence of biochemical processes in the origin of banded iron formation of KMA

For the first time, biogenic nanomagnetite has been detected in banded iron formation of the Lebedinskii deposit of the KMA and has been demonstrated to be a primary mineral. This finding may imply a key role of metabolic processes in primary deposition of divalent iron with formation of trivalent iron minerals, the precursors of banded iron formation of the KMA.

Biomineralization in Bauxitic Laterites of Modern and Paleotropics of Earth

The top part of a lateritic profile including laterites in sensu stricto, bauxites and even zones of clay minerals (кaolinite, halloysite, montmorillonite), contains plentiful traces and products of interaction of a substratum with live organic substance and mortmasses. The surface of laterites is hidden under the cover of trees and bushes and the dense felt like a film weaved from filamentous fungus, roots of vegetation, and fossilized microorganisms. Dying off, they turned into biofilms, which is replaced with biominerals such as gibbsite-Al (OH)3, goethite-HFeO2, hematite-α-Fe2O3, and halloysite-Al4(OH)10[Si4O8](OH)2 · 4H2O. A zone of a biological pedoturbation is completely processed by the burrowing organisms. Earlier it was represented that they make only mechanical impact on rocks. We revealed that burrowing organisms, including worms, mill all minerals of a substratum, passing it through the digestive path, and satiate it with biochemically active substances. It causes dissolution of all minerals except rutile—TiO2. Gibbsite, when passed through a digestive path, recrystallizes and forms surprisingly beautiful and perfect idiomorphic crystals filling the burrows of the worms and covering their walls. We managed to find the paradoxical phenomenon: passing of worms through large (2–4 cm) quartz crystals. The entrances are surrounded with a biofilm similar to slimes and turned into units of crystals of hematite. The described phenomena are established on numerous bauxite deposits of India, Guinea, and Brazil of the modern tropic and on the ancient deposits of Siberia.

The Latnenskoe refractory clay deposit (Central Russia)

This paper reports the results of our recent studies and generalizes previously known data on the geology, mineralogy, geochemistry, and genesis of the Russia’s largest Latnenskoe refractory clay deposit. It is shown that conditions of its localization were defined by regional and local factors. The regional factors controlled the distribution of the clay raw material in the region, while the local factors were responsible for the genesis and composition of refractory clays of the Latnenskoe deposit. Our studies showed that the formation of refractory clays is not only related to terrigenous but also to authigenic processes of sedimentation. The terrigenous component of clays was formed by the erosion of kaolin weathering crusts of the Voronezh anteclise crystalline basement and Paleozoic sedimentary hydromica–kaolinite rocks. Authigenic processes were significantly contributed by organic matter, which determined the environmental pH and Eh parameters. It is established that the mineral matter of clays of the deposit is represented by three morphological modifications (crystalline, amorphous, and biomorphic), which were formed subsequently and (or) simultaneously and could be transformed into each other. Application of a complex of modern precision methods allowed us to reveal a previously unknown biomorphic modification of kaolinite, the major rock-forming mineral, as well as mixed-layer kaolinite-smectite in the clays. It is shown that the distribution of major and trace elements and the sulfur isotope composition in different technological types of clay depend mainly on the facies conditions of their formation. Technological properties of clay raw material are considered.