G. T. Ushatinskaya

Origin and dispersal of the earliest brachiopods

Brachiopods first appeared at the very beginning of the Phanerozoic together with the first skeletal organisms. Most brachiopod taxa that arose in the first half of the Cambrian had a short temporal range and became completely extinct by the middle of the Middle Cambrian. Rigid articulation of the valves of brachiopods was provided by various structures, which also appeared in the Early Cambrian. This fact points to the importance of this feature for the formation of the whole group and at the same time testifies to the high variability of rigid articulation at the early stages of brachiopod evolution. This is a typical manifestation of archaic diversity in this animal phylum, which appeared very early in the Phanerozoic. Another important property of the archaic diversity of the early brachiopods was the large number of centers of diversification. As for the majority of groups, climatic zonality was the main factor determining the distribution of brachiopods at the beginning of the Phanerozoic. The main ecological types of brachiopods also appeared in the Early Cambrian.

Laboratory simulations of cyanobacterial mats of the alkaline geochemical barrier

The goal of this work was to illustrate a possible interaction between the “soda continent” and the ocean. A laboratory simulation was undertaken of the development of alkaliphilic mat with calcium carbonate and calcium phosphate interlayers in the zone where ocean waters, containing calcium and manganese, come into contact with carbonate- and phosphate-rich alkaline waters. The macrostructure of the layered cyanobacterial mat turned out to be little dependent on the chemical conditions causing sediment formation. The chemical composition of freshly formed mineral interlayers of the mat was found to vary with the medium composition. The mineralogical composition of the sediment is determined by diagenesis conditions in its depth, which can cause mineral phase conversions.

The role of cyanobacteria in crystallization of magnesium calcites

Laboratory experiments showed the effect of the cyanobacterium Microcoleus chthonoplastes on the formation of magnesium calcites, using model solutions (2.14M MgCl2-0.05M CaCl2-0.6M NaCl-0.18M NaHCO3). The conditions of existence of cyanobacteria in such solutions in light or darkness significantly alter the structure of the sediment and the shape and size of the carbonate crystals. Cyanobacteria slow down crystallization due to the formation of exometabolites with a chelating effect, which leads to the precipitation of high-magnesium calcites. In the photosynthetic environment the presence of huntite (CaMg3(CO3)4), possible forerunner of dolomite, is prominent.

Revision of the Early-Middle Cambrian Lingulida (Brachiopoda) from the Siberian Platform

Based on Yu.L. Pelman’s lingulid collection and our own material, the Early-Middle Cambrian genus Eoobolus, which was widespread on the Siberian Platform, is revised. The Siberian members of this genus have previously been assigned to Lingulella. Two out of these six members are recognized as valid species: Eoobolus siniellus (Pelman) and E. variabilis (Pelman). Lingulella acuta Pelman and L. linguata Pelman are considered here to be junior synonyms of E. priscus (Poulsen, 1932). The valid species are redescribed and their stratigraphic and geographic ranges are given. A new species, E. pelmani sp. nov., is described. New data on the Eoobolus microornamentation and shell structure are provided.

Stratigraphic and geographic distribution of acrotretids (Brachiopoda, Lingulata) in the Middle and Late Cambrian

The analysis of the taxonomic composition and distribution of acrotretids (Brachiopoda) in the Middle Cambrian and early Late Cambrian shows that, in the later half of the Cambrian, the order Acrotretida was the most abundant brachiopod order and many of its representatives were cosmopolites. The structure, mode of life, and biological features of acrotretids, along with the arrangement of continents with epicontinental seasmostly in the low latitudes, promoted the wide dispersal of this group on the Earth in the Cambrian.

Preservation of living organic structures in unicellular and multicellular organisms in the fossil state

It is known that early postmortem mineralization is a phenomenon underlying the preservation of organic structures such as bacterial cells, biofilms, soft bodies, cells, vessels, and slightly mineralized integuments of multicellular animals in the fossil state. Bacteria, the activity of which creates conditions for mineralization of organic matter, are a driving force behind this process. The most widely known types of postmortem mineralization that are mediated by bacteria are phosphatization, silicification, pyritization, carbonatization, iron-manganese mineralization, and the formation of clay minerals, which either replace organic structures or cover them with thin films.

Find of Tremadocian ostracodes in cherts of Kazakhstan

First late Tremadocian (Early Ordovician) ostracodes were found in cherts of the Burubaital Formation near the “Burultas” deposit in southern Kazakhstan. The preservation of carbonate ostracode shellshells in siliceous environment is discussed. The monotypic ostracode assemblage includes the newly described form, Burultalina nikitinae gen. et sp. nov.

[Transformation of carbonate minerals in a cyano-bacterial mat in the course of laboratory modeling].

A laboratory model of a cyano-bacterial mat with mineral layers of carbonates was used to examine the dynamics of the transformation of calcium-magnesium carbonate under the conditions of a soda lake. The activity of various organisms of the cyanobacterial community results in conditions under which the Ca-Mg carbonate precipitate undergoes changes. The crystal lattice of the initial carbonate is restructured; its mineralogical composition changes depending on the conditions of the mat. In magnesium calcites, which are formed under such low-temperature conditions, a rudimentary cation adjustment can occur with the formation of dolomite domains. These experiments confirm the hypothesis that the dolomite found in stromatolites is of a secondary origin and can be formed in the course of transformation of Ca-Mg carbonates under alkaline conditions in an alkaliphilic cyanobacterial community.

Significance of bacteria in natural and experimental sedimentation of carbonates, phosphates, and silicates

The role of bacteria in sedimentation of phosphorites, siliceous and carbonate rocks is discussed. Preservation of bacterial bodies in fossil condition, even in very ancient deposits, is connected with their very early mineralization. A series of laboratory experiments allowed conditions to be reproduced that could have led to mineralization of cyanobacteria and their preservation in sedimentary deposits. The experiments have also shown the important role of cyanobacteria and their metabolic products in the formation of some carbonate minerals, as well as in the accumulation of stromatolites.

Protegulum and brephic shell of the earliest organophosphatic brachiopods

Early development stages imprinted on the shells of Cambrian brachiopods from the class Linguliformea (orders Paterinida, Lingulida, Acrotretida) were studied with scanning electron microscope based on a large collection from the Siberian Platform. Some specimens of all three orders preserved protegulum (embryonic shell); their brephic (juvenile) shells, also were studied. Many of them might lack larval development stage as it is known for the recent representatives of the family Lingulidae. But unlike recent lingulids, the surface of the juvenile dorsal valves of all studied linguliformeans bore two (rarely three) pairs of gentle elevations accommodating bundles of setae, which sometime preserve as groups of fine imprints along their margins. Recent Lingula and Glottidia lack setae in this stage. On the other hand, recent classes Craniformea and Rhynchonelliformea have setae, but they develop in the larval stage. Most of brachiopod groups have the setae in the adult stage but these setae have different origin, are short, located on the lateral and anterior ends of the shell, and grow from the marginal cells of the mantle.