Сбор, диагностика и обработка палеонтологических материалов при проведении учебных геологических практик. Учебное пособие на модульной основе

1. Types of preservation of fossil organisms and their significance

(see Fig. 250). The term “organic-walled” can also be extended to macrofossils.

Many eufossils retain information not only about the soft parts of the body and its functional systems, such as circulatory, reproductive, conducting bundles of plants, etc., but also about lifestyle and biogeochemical processes.

Ichnofossils (Greek: ichnos – trace) are represented by traces of the vital activity of fossil organisms. Most often they are preserved in the form of prints, less often in the form of lowvolume formations. Ichnofossils include traces of crawling and burying of arthropods, worms, bivalves; traces of eating, mink, passages and traces of drilling of sponges, bivalves, arthropods; traces of movement of vertebrates.

Coprophossilia (Greek: kopros – droppings, manure) consist of waste products of fossil organisms. They have a voluminous character, being preserved in the form of rollers, nodules, mounds, columns and even formation bodies. The term “coprophossilia” was proposed in 1989 in the textbook “General Paleontology”. It is based on the name “coprolites”, introduced into the scientific literature over 150 years ago and denoting “petrified animal excrement” (Paleontological Dictionary, 1965).

The most typical coprofossils include the final products of digestion of mud-eaters and vertebrates; in the second group of coprophossilia, undigested remains of other animals and plants can be preserved. The coprophossils of the mud-eaters are represented by rollers and ribbons, which, at first glance, do not seem to differ from the surrounding stones. But after passing through the intestines of the mud-eater, the sediment is enriched with calcium, iron, magnesium, potassium and phosphorus. As a result, the coprophossils of the mud-eaters acquire a lighter or, conversely, a darker, often reddish hue, which distinguishes them from the surrounding stones. The process of sludge processing by mud-eaters and biofilters is called bioturbation. Most sedimentary deposits of the present and the past undergo bioturbation. The end products of bioturbation and traces of vital activity are sometimes called bioglyphs.

11

1. Types of preservation of fossil organisms and their significance

Chemofossils (Greek: chemie – chemistry) include organic fossil biomolecules of bacterial, cyanobiont, plant and animal origin. Chemofossils store the chemical composition of biomolecules, which allows to determine the systematic position of the original organism, but not its morphology. The study of the chemical and taxonomic diversity of сhemofossils is closely related to the problems of the origin and development of life, as well as the origin of fossil fuels, especially oil. The biological factor in the formation of oil has long been denied, considering it only chemogenic. Advances in the study of chemophossilia prove the opposite. Chemophossils are the object of study of biochemistry and molecular paleontology.

Sometimes fossils form pseudofossils (Greek: pseudos – lies). False forms that are not peculiar to the mineral substance. Pseudofossils, or false fossils, owe their origin to various mechanical, physical and chemical processes that affected sedimentary rock during its formation, diagenesis or weathering. In the latter case, harder mineral formations stand out sharply against the background of soft rock. Pseudofossils are mainly associated with concretions (Latin concreto – concentration; the process consisting in the fact that mineral solutions, when deposited, form irregular lenticular, spherical or nodular aggregates), infiltration (infiltration of dissolved substances and cementation of rocks by them) and with the influence of weathering processes.

Geologists and paleontologists quite often have to deal with objects whose systematic affiliation to a particular group of organisms is unclear and, moreover, it is not even always provable at all that they belong to the remains of organisms. All such remains are called problematic. There are, however, several different understandings of this term. Most paleontologists understand by problems any remains of organisms for which it is impossible to indicate the exact belonging to a particular class or even type.These may be single, completely incomprehensible forms, sometimes parts of the skeleton that do not give a complete picture of the whole skeleton; individual genus,

12

1. Types of preservation of fossil organisms and their significance

sometimes groups of genus, conditionally united into families and even orders of unknown systematic position. With this understanding of the problem, it also includes various traces of the vital activity of organisms (traces of crawling, mink, etc.). This understanding has become so widely accepted in science that even entire collections containing descriptions of various groups of organisms with the word “problematics” in their names are published – for example, “Paleozoic and Mesozoic Problematics” and “Phanerozoic Problematics” (Drushchits, 1974, et al.).

The preservation of organisms and their significance in geology are influenced by the characteristics of the chemical composition and their rock-forming and relief-forming significance.

Rock-forming fossils are those that make up 30–40 % or more of the total volume of sediments. Both skeletal remains and waste products, i. e. eufossils and coprofossils, take part in the formation of an organogenic rock. Sometimes such rocks are called bioliths. An indispensable condition for rock formation is the “crowded” nature of the habitat of organisms.

The composition of fossil skeletons can be mineral, mineralorganic and organic. Among the mineral skeletons, the most common are calcareous, flint and phosphate, forming rocks corresponding in composition. There are especially many organogenic rocks of calcareous (carbonate) composition (CaCО3): limestones, marls, writing chalk stone, primary and secondary dolomites. (Mikhailova, 1997, etc.) For the name of organogenic rocks, in contrast to chemogenic, an adjective is used from the Latin (Greek) name of the group of organisms that is the main rockforming agent. Among the organogenic limestones and marbles formed by animal skeletons, the most common are foraminiferous, coral, stromatopore, archaeocyte, spongy, serpulite, gastropod (pteropod, spiratellous, etc.), cephalopod, ostracod, bryozoans, brachiopod and crinoid. Calcareous rocks consisting of clusters of bivalve shells are usually called shell rocks (coquina), oyster horizons, rudist limestones (Bogoyavlenskaya, 1990).

Clusters of vertebrate bones and skeletons are called neutrally – “bone layers”. Plants with carbonate skeletons give

13

1. Types of preservation of fossil organisms and their significance

rise to limestones – algal, lithotamnium, charophytes and coccolith (writing chalk stone). Organogenic limestones can also occur as end products of cyanobionts and bacteria. They leave stratified interbedding, nodular, columnar, concentric and “figured” formations – stromatolites, oncolites and catagraphs (Bondarenko, Mikhailova, 1984).

Organic skeletons are built mainly with carbohydrates, proteins and fats. Among organic skeletons, chitinous, chitinlike, silk-like (spongin), corneous and cellulose are the most common. They form the shells of bacteria and cyanobionts, shells, crusts and skeletons of animals, as well as tissues, spore vessels and pollen of plants. Higher plants play the biggest role in organic rock formation. Their massive accumulations during certain burial processes lead to the emergence of fossil fuels (caustobiolites), such as peat, coal, oil shale, oil and gas. The origin of oil and gas is associated with the deep destruction of the primary organic composition caused by both the vital activity of bacteria and cyanobionts and geological processes. Due to the vital activity of higher plants, resins (amber) are formed.

It is also necessary to note the relief-forming role of fossils and modern organisms that create reef structures of various types: coastal and barrier reefs, atolls, biostromes, bioherms, etc. Reef buildings have a complex structure. They consist of a complex of substituting calcareous rocks: organogenic, bioclastic and chemogenic.

14

2. THE PRINCIPLE OF USING PALEONTOLOGICAL

INFORMATION

The method is based on the determination of the species composition of fossils of ancient organisms and the idea of the evolutionary development of the organic world, according to which the remains of simple organisms are found in ancient sediments, and in younger ones – organisms of complex structure. This feature is used to determine the age of rocks (Krumbiegel, Walter, 1980).

For geologists, an important point is that evolutionary changes in organisms and the appearance of new species occur in a certain period of time. The boundaries of evolutionary transformations are the boundaries of the geological time of accumulation of sedimentary layers and horizons.

Fossil organisms are divided into 2 types. The first includes those that have existed for a long time without much change and are found in several layers of sedimentary strata. The second type is organisms that lived in a narrow period of time and are found in separate layers of sedimentary rocks. They are called guide fossils or guide forms. Guide forms should: occur frequently and in large quantities in the layer and be easily recognized; have a narrow age (or vertical) distribution interval, but a wide horizontal distribution so that distant sections can be compared.

The method of determining the relative age of layers using guide fossils is called the guide fossils method. According to this method, layers containing similar guide forms are of the same age. This method became the first paleontological method of determining the age of rocks. On its basis, the stratigraphy of many regions was developed.

To avoid mistakes, along with this method, the method of paleontological complexes is used. In this case, the entire complex of extinct organisms found in the studied rock mass is used. In this case, the following can be highlighted:

1-fossil forms that lived in only one layer; 2-forms that first appeared in the studied layer and pass into the overlying one (the lower boundary of the layer is drawn); 3-forms passing from

15

2. The principle of using paleontological information

the lower layer and ending their existence in the layer under study (surviving forms); 4-forms living in the lower or upper layer, but not encountered in the layer under study (upper and lower boundaries of the layer).

In turn, sedimentary rock strata can be formed over a significant area, while it can be seen how various parameters change within the same age strata or even horizons – this is a change in the composition of rocks, both along the stretch of the strata and from its sole to the roof, the thickness values in the section can fluctuate.

For the first time, such a phenomenon was explained by the Swiss scientist A. Gressley. He introduced the concept of facies (from the French – kind, face, appearance). According to Gressley, this means a section of any layer of the same age rocks that differs from neighboring ones in petrographic composition and fossil remains.

The term facia has become widespread. Different researchers put their own idea and content into it. Among them, we note two extreme views on the definition of facies. In the first case, facies is a part of a layer with its own lithological and paleontological features, which are called facies features. In the second case, facies is the physical and geographical conditions that determine the inorganic and organic processes at a given site at a given time, i.e. facies is a unit of the landscape. The following approach to the definition seems to be the most optimal. Facies is the physical and geographical conditions or conditions reflected in the sediment.

The facies of the geological past are defined by the rocks and the fossils they contain. Hence, the method of restoring paleogeographic environment is called facies analysis. This method is based on the principle of actualism. According to one of its founders, C. Lyell, its essence lies in the fact that modern phenomena are the key to understanding the same processes in past eras. For example, by observing the activity of modern volcanoes, geologists can reconstruct a picture of ancient volcanism. But such an approach can also lead to errors if it is applied mechanically,

16

2. The principle of using paleontological information

without taking into account the evolutionary changes that occurred during the long development of the earth’s crust and its surface. Each historical epoch, along with the general ones, has its own specific features of development. For example, the modern composition of the atmosphere is different from what it was in the early stages. In the process of evolution of the organic world, many modern species have changed significantly compared to their ancestors. And comparing their way of life now and in the past can lead to errors if you do not take into account the characteristics of this past. Considering all this, the principle of actualism is supplemented by a comparative historical method, which considers changes in the nature and results of the processes themselves that took place on Earth over time. One of the most important methods for determining the conditions of the geological past is biofacies analysis. The basis for its implementation are fossil organisms and traces of their vital activity. The main living conditions for organisms in the sea are: 1-salinity, 2-temperature, 3-light, 4-gaseous regime, 5-depth, 6-water movement or hydrodynamics, 7-soil composition. Each of these factors is reflected: in the morphology of the organism (i. e., the size of the shell, its sculpture, thickness, etc.), in the diversity of species, it affects the distribution of organisms over the area of the​ reservoir.

Therefore, in the biofacies analysis, we can determine with a certain degree of certainty many of the listed habitat conditions, and hence the paleogeographic conditions for a certain period of time, based on the appearance of fossil remains.

Biofacies analysis begins with determining the nature of the burial of fossil remains. They are of two types:

1.Fossil biocoenosis – burial in the habitat of the organisms themselves.

2.Thanatocenosis – the burial place is removed from the habitat.

The type of burial is determined by the preservation of organic remains, their orientation, sorting, and species complex. Signs of thanatocenosis during transfer are: destruction of skeletal

17

2. The principle of using paleontological information

elements, sorting of individuals by size and weight, orientation of skeletal elements along the flow, etc. During thanatocenosis, species living in different facies conditions can be in one place (for example, terrestrial or nectonic plants can be found along with the remains of benthos).

The most important for biofacies analysis is the fossil biocoenosis, according to which habitat conditions are restored. Whereas according to thanatocenosis – the environment of the burial. (Bondarenko et al.)

As in paleontology, guide fossils are organisms that lived in a narrow time interval, so in biofacies analysis an important role belongs to organisms – indicators of habitats or ancient climates. Such organisms include those whose existence is due to some specific requirement (for example, only normal salinity of water, temperature interval, etc.).

18

3. METHODS OF FIELD STUDY OF FOSSIL

REMAINS OF ORGANISMS

3.1. Conditions for the conservation of fossil organic remains

Fossils are extremely unevenly distributed in sedimentary strata: in some layers there are many of them, in others they occur singly, and in others they are completely absent. This unevenness is due to a number of factors.

First of all, this may be due to the alternation of epochs favorable and unfavorable for the development of organisms in this area during the accumulation of sediments.

The conditions of their burial have a very significant effect on the preservation of fossils. After the death of organisms (the causes of death can be very diverse), their remains remain in their habitat or are carried away over more or less significant distances. In the first case, we are dealing with paleobiocoenosis, a lifetime community of fossil organisms. An example of such paleobiocoenosis are bryozoan and coral reefs, in which organisms are preserved in their life position (Bondarenko O. B., et al.).

Such lifetime communities in the fossil state, however, are not very common. It should also be borne in mind that due to the inevitable loss of part of the organisms during burial, they never constitute true biocoenosis (complexes of organisms inhabiting this site and are in certain relationships with each other and the external environment). Accumulations of remains of organisms that lived within a certain biotype are more widespread (Greek. topos is the place and buried here in the habitat, but are no longer in a lifetime position. Such accumulations of organic remains are called thanatocenosis (Gerch. thanatos – death) or necrocoenosis (Greek. nekros is dead). Even more often, the remains of organisms are carried away (on land – by wind and water currents; in the aquatic environment – by waves, currents, etc.). At the same time, clusters of remains of organisms that lived in a variety of conditions are formed. Such clusters are called oryctocoenosis (Greek oryctos – fossil). It is clear that the greater the number of individuals represented by such a species

19

3. Methodology for the field study of fossil remains of organisms

and the greater the density of its settlement on a given biotype, the more likely it is that its remains will be preserved in a fossil state. The living conditions of organisms are also important. Thus, benthic forms (attached, burrowing, drilling, etc.) are usually in more favorable conditions for burial than nectonic and planktonic organisms. Organisms inhabiting the land have the most favorable conditions for preservation in the fossil state. Not all the remains fall into the oryctocoenosis. A significant part of them, even represented by solid massive formations, are destroyed even before burial by sediment. The destruction of skeletons often begins during the life of the animal. So, for example, the shells of live mussels attached to the substrate are abraded by solid particles of soil carried by tidal currents or waves when they move in the sediment. Very significant damage to the shell can be caused by boring organisms. The drilling sponges of Cliona settle on living mollusks (eg oysters) and destroy their shells. Hyphae of boring fungi and filaments of algae sometimes literally pierce the skeletons of littoral mollusks and balanids (Krumbigel and Walter, 1980).

The processes of destruction of the body of organisms after their death proceed even more vigorously. Soft tissues are destroyed very quickly as a result of oxidation and the activity of various bacteria and scavenger organisms. Extremely favorable conditions are necessary (first of all, very rapid burial by sediment and the cessation of oxygen supply) in order to preserve the soft tissues of animals in one form or another. The skeletal formations of dead organisms are quickly destroyed: boring organisms continue to operate, processes of biogeochemical destruction proceed intensively, and finally, fragmentation and abrasion of skeletons by waves and currents occur.

During the formation of oryctocenoses during the transfer of organic remains, they are sorted by size and shape. Therefore, different parts of the skeleton of the same individual can be carried away to different distances from the habitat of the organism. For example, the sorting of the left and right valves

20