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

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

of pectinids and ostreids, which have sharply inequivalve shells, is noted.

At the end of the transformation of sediment into rock, the remains of organisms buried in it do not remain unchanged. They can be completely destroyed by the action of a wide variety of factors: pressure, temperature, dissolution, etc. On the other hand, in the course of diagenesis, the structure can be compacted or the primary skeletal substance (calcium carbonates, calcium phosphate, etc.) can be replaced by more stable minerals. The most common are silicification, phosphatization, pyritization, etc.; the transition of the unstable polymorphic difference of CaCO3 – aragonite – into its stable form – calcite is very important. There may be other processes that favor fossilization. Often fossils are preserved in nodules (siderite, phosphate, etc.) and at the same time are completely absent in the host rocks.

3.2. Search and field collection of fossil organisms

The remains of organisms, which are called fossils, or petrified remains, are found mainly in sedimentary rocks. And within the limits of the SFedU training ground, fossil remains are found only in rocks of sedimentary genesis (Byakov et al.).

The form of their preservation may be different. From vertebrates, individual bones, spinal bones, teeth are usually preserved, less often entire skeletons and imprints of individual body parts. In exceptional cases (in asphalt, in permafrost conditions), soft parts of the body are also preserved. The form of preservation of invertebrates is more diverse. The most valuable are the remains of skeletons: shells of mollusks and brachiopods, their individual valves and parts (aptychs of ammonites, rostra of belemnites, etc.), shells and spines of sea urchins, thecal plates and joint of stalks of sea lilies, etc. etc.

The cores are quite common, among which there are external and internal ones. The first of them, which are casts (formings) of the outer surface of the organic remains, are formed when the mineral substance fills the void that has arisen in the rock

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

as a result of the dissolution of the organism remains. The inner cores are casts (formings) of the internal cavity of the skeleton (most often mollusk shells). They are formed when such a cavity is filled with sediment and the subsequent dissolution of the skeleton itself. The cores are often phosphatized or pyritized. Imprints are impressions of the skeleton or soft parts of the body of an animal in the rock. The remains of plants that can be detected with the naked eye are represented mainly by imprints of leaves and stems; pieces of wood, fruits and seeds are also preserved. Plant remains are usually highly mineralized (most often silicified) or charred. Much more often in the sedimentary strata there are the smallest plant remains – spores and pollen, the presence of which is established after the use of special methods for their extraction from the rock and with the help of a binocular or microscope.

Often, not only the remains of animals are preserved in the fossil state, but also traces of their vital activity: traces of crawling, passages, burrows, drilling. Coprolites (fossilized excrement). Burrows and drilling are clearly visible in the vertical walls of outcrops, often they are filled with the rock of the overlying layer. The moves of mud-eating animals are very common in carbonate rocks. Traces of crawling are found on the surfaces of the stratification. It is necessary to distinguish the “positive” prints left by an organism crawling on the surface of a soft sediment from the “negative” ones representing casts of such traces on the sole of the overlying layer.

The drilling left by various organisms (worms, bryozoans, sponges, barnacles, gastropods and even fungi and algae) in the skeletons of other organisms is very interesting. They are common in the shells of gastropods and pelecypods, in the rostra of belemnites; some of these borings can be detected only under a magnifying glass or with the help of binoculars.

Only in exceptional cases, along with traces of vital activity, the remains of those organisms to which these traces belong are preserved. In the overwhelming majority of cases, the organisms that left such traces are either completely unknown or have been

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

established presumably. Such traces of vital activity belong to the so-called problematic remains or problematics.

To be successful in the search and collection of fossils, it is important to know the morphological features of fossil organisms, their lifestyle and habitat conditions, to have an idea of the conditions of burial of the remains and finally, to understand the possible ways of fossilization. To guide the search for possible locations of fossil organic remains, a geologist and a paleontologist should have an idea of the geological structure of the area, the stratigraphic sequence and the lithological composition of the rocks composing it.

The overall objective of the study largely determines the nature of the collection. Organic remains are used in stratigraphic work, they can provide very valuable information necessary to clarify the physical and geographical situation of the past, and finally, they are collected for special paleontological study.

The collection of fossils in order to use them for dissection and comparison of sections must necessarily be carried out in layers, with careful linking of finds to the section. All remains of organisms should be collected, but special attention should be paid to the collection of fossils, which are the guide forms for sediments of this age. For marine strata of the Mesozoic, such fossils are brachiopods, ammonites, belemnites, some bivalves (for chalk inocerams, rudites, etc.), echinoderms (sea urchins and sea lilies), dinosaurs from vertebrates, for Cenozoic marine sediments – large foraminifera (nummulites, dislocyclins, etc.), brachiopods, bivalves and gastropods and others (Krumbigel, Walter, 1984).

Not all fossils within the SFedU students’ practice area are equivalent for determining the geological age of rocks. And therefore, first of all it is necessary to pay attention to representatives of orthogroups, especially ammonites (Byakov A. S., 1995).

The amount of organic remains, their distribution, systematic composition and the nature of their presence in the rock are of great importance for the restoration of paleogeographic

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

conditions. It is important to establish, first of all, whether these remains are in a lifetime position or have experienced transfer and re-deposition. More complete information is provided, of course, by paleo biocoenosis, but postmortem accumulations can also be valuable witnesses to the situation of the past. For example, according to the orientation of skeletal elements of elongated shape (rhabdosomes of graptolites, shells of endoceratids and orthoceratids, rostrums of belemnites, etc.), it is possible to restore the direction and nature of the movement of sea waters (along – coastal and tidal currents, waves, etc.) and thus approach the determination of the depth of the basin and its coastline.

For a special paleontological study of any group of fossils, mass collections of representatives of this group are necessary. Naturally, well-preserved specimens are of the greatest value. However, fragments of skeletons should not be neglected either, since important details of the structure, destroyed on whole valves or shells, can be preserved on them. It is also important to collect the remains of associated organisms, this can provide very important information about the relationships of the studied group.

It is necessary to strive to extract organic remains directly from the rock. However, talus material can also be very useful. It happens that the specimens from the talus are the only ones found in this outcrop. Often skeletal remains that have been on the daytime surface for a long time are more easily extracted from the host rock. It is advisable to start the search for fossils with an inspection of the talus, because a much larger surface of the rock is usually available for observation in them. In all cases, it is necessary to strictly distinguish the specimens that were in the root occurrence (in situ) and collected in the talus.

Fossils extracted from the rock or pieces of rock enclosing them must be carefully packed directly on the out crop. Hard cores and prints, strong skeletons (for example, shells of thick-walled astroids) are tightly wrapped in wrapping paper.

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

Individual specimens or pieces of rock with organic remains should not come into contact with each other. Thinner-walled mollusk shells, cores and prints. The supporting elements of a thin sculpture, etc., must be wrapped in cotton wool, and only then wrapped in paper. If it is intended to determine the collected material in the field at the base, it can be packed not in paper, but in bags. Fragile remains (colonies of bryozoans, very thin mollusk shells, leaf prints, etc.) must be placed in boxes with cotton wool. Sometimes loose and brittle remains (for example, vertebrate bones) have to be impregnated with special strengthening solutions directly on the outcrop.

Each sample must necessarily be provided with a label written here on the outcrop.

3.3. Primary processing of paleontological material

Fossils collected in routes from various outcrops are laid out in trays or racks along stratigraphic horizons. Within each horizon, the material is placed in systematic groups. If representatives of different groups were included in the sample, then their separation should be carried out; at the same time, labels should be repeated.

Only a few fossils (ammonite cores; pelecipod shucks) are suitable for subsequent determination without prior preparation. Most often the collected material needs to be dissected, that is, release from the host rock.

In the process of preparation, organic residues are extracted completely, or some parts of them necessary for determination are cleaned from the rock. Various methods of preparation are used: mechanical (the sample is processed with tools), chemical (the host rock is dissolved by acids or alkalis), thermal (the rock is destroyed by heating and rapid cooling). The choice of the preparation method is determined by the composition of the host rock and the characteristics of organic remains.

Macrofossils, i. e. fossils discernible to the naked eye, are extracted from soft rocks directly in the field. Previously, they

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

were also extracted from dense rocks in the field using a hammer and chisel. This method is currently considered barbaric. It is better to knock out a monolith, i.e. a piece of rock, and in laboratory conditions, using various chemical and technological techniques, carefully extract them.

The sample is placed on a bag of dense fabric filled with sand during pricking – a preparation pillow. Accidentally dropped fragments of the fossil are attached to the main object with glue. From particles of loose sands and soft clays, the fossils are cleaned using a preparation needle and rinsing with water. In the process of mechanical processing, it is impossible to allow violation of the integrity of the surface of the fossil.

If there are no tools for simple mechanical preparation in the field, then all the collected material is packed for subsequent processing in the laboratory. It is advisable to pack fossils into systematic groups.

Any field collections of fossils are accompanied by a description not only of the sediments in which they are directly found, but also of the entire section, if this location is not isolated. In any case, in the field book and on the label, it is necessary to indicate the administrative and geographical address of the location of the fossils, and, if possible, the degree reference, so that in the future, if interested, it would be possible to repeat the collection. In addition, it is necessary to give a lithological characteristic of the rocks, the thickness of the layer, where the sample was taken from, indicate the geological (geochronological) age, and note in the label who and when (date, month, year) made the collections and from which organization.

The specific features of the field collection of minerals depends on three main factors: 1) what is collected, macrofossils or micro (nano) fossils; 2) for what purpose are collected (biostratigraphic, paleoecological, taphonomic studies, for museum collections, etc.); 3) how much time is allowed for collections and what financial support.

Particular care must be taken in collecting ichnofossils in the field, represented by traces of vital activity, such as traces of

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

movement along the substrate and inside it, burrowing holes, drilling, etc. Micro(nano)fossils, i. e. fossils of microscopic size, in the field are not visible to the naked eye. Nevertheless, it is known that they can be present in any sedimentary rocks, especially in fine and microgranular sediments enriched in calcium carbonate or completely calcareous. Samples on microfossils are taken at each change in lithology, and within a homogeneous layer at intervals of 1–4 m (and even more often, after several centimeters). If the rock is soft or not very strong, then for foraminifera and radiolaria one should take a sample of at least 0.2 kg, for ostracods – from 0.5 to 1 kg, for conodonts – from 1.0 to 10 kg. If the rock is strong, hard, then to make sections with microfossils, it is necessary to take a piece of rock with a volume of at least 5x3x2 cm.

The above described field collections of macroand microfossils are usually considered sufficient for biostratigraphic studies. With the formulation of paleoecological and taphonomic problems, field work on the collection of fossils becomes more complicated. Before collecting fossils, it is necessary to fix (draw, photograph) their position in the rock and relative to each other along the strike (area) along the section.

Heavy liquids and surfactants are also used to extract microand nanofossils. Then they are placed in various chambers or conserving agents such as resins, glycerin, gypsum.

Maceration is one of the options for chemical preparation. It is used for charred plant remains. During maceration, the sample is sequentially placed in various mixtures of acids, salts, alkalis, and then the washed sample is enclosed in some kind of conserving agent as gelatin, Canadian balsam, glycerin, plastic.

When grinding, a series of thin sections is made, less often polished sections. A thin section is a very thin plate with a thickness of not more than tenths of a millimeter, placed between a slide and a cover slip in Canadian or fir resin. Thin sections are examined under a microscope in transmitted light, more rarely in reflected light. Paleontological sections are thicker than

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

petrographic ones; their thickness is set individually in each specific case. Polished section is a smooth surface of the sample, polished to a mirror finish. The study of some groups of fossils is necessarily accompanied by viewing thin sections and polished sections (stromatolites, oncolites, fusulinids, archaeocyathids, coralss, bryozoans, petrified plant stems, bones of vertebrates)

“Etching” is used to obtain a relief from the polished or raw surface of the sample. Etching is carried out with acids, alkalis and salts (chemical etching) or with an inert gas such as argon (physical etching) (Krumbigel, Walter, 1984).

Making replicas is reduced to removing thin prints on transparent films from the sample surface. To obtain a replica, the sample is polished to a mirror finish, then etched with acid, then an impression is taken from the etched surface using a transparent photographic film or a gradually hardening varnish.

Casts are obtained by filling various cavities left from fossils or located in the fossils themselves. For example, cavities preserved after leaching of gastropod shells are filled with lead, cellulose, a special paste or a rubber-like compound – latex; after hardening, bulk copies are obtained.

After the preparation of the samples, the scientific study of fossils begins, but even here it is not complete without the use of technological tools: ordinary and binocular magnifiers, microscopes – light, polarization and electronic scanning (raster), cameras, X-ray devices, as well as microanalyzers for determining the chemical composition of fossils. Radiography gives good results in the study of malacoid organisms, as well as the remains of a malacoid body (tentacles and ink sacs of cephalopods, imprints of jellyfish, worms and arthropods) (Krumbigel, Walter 1984).

The identification of fossils is accompanied by an analysis of variability, geochronological interval and ecological-geographical distribution, which is necessary, first of all, to establish the geological age of sediments and reconstruct the habitat.

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

3.4.Preliminary determination of organic remains.

The speed of evolutionary variability of organisms or the limited vertical distribution of their remains in the section is one of the mandatory requirements for guide fossils. It is also important that these fossils have a wide geographical distribution, are often found in rocks, and are fairly well preserved.

Paleontological material makes it possible to draw stratigraphic boundaries in sections in various ways. One can be guided by the appearance of new forms, the disappearance of old ones and the flourishing of organisms, as indicated by the abundance of their remains in sediments. In all cases, it should be borne in mind that these stages of development usually do not coincide in different groups.

The definition of fossils is understood as the establishment of their systematic or taxonomic affiliation (Bondarenko, Mikhailova, et al.). The animal kingdom is divided into the following taxonomic units – taxons (from large to small):

Type Phylum

Class Classis

Order Ordo

Family Familia

Genus Genus

Species Species.

The basic taxonomic unit is the species. Some species have two or more subspecies. Similar, genetically related species form genera, genera are combined into families, families into orders, orders into classes, and finally classes into types. Intermediate taxonomic units are often used – superclasses, subclasses, etc.

All taxonomic divisions up to and including the genus have a name consisting of one Latin word (Bondarenko, Mikhailova, Drushchits, etc.). For example:

Mollusks type Phylum Mollusca Cephalopods class Classis Cephalopoda Ammonites subclass Subclassis Ammonoidea

Ammonitids order Ordo Ammonitida

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

Family Familia Neocomitidae Spath Genus Genus Leopoldia Mayer – Eymar.

After the name of the family and genus, the name of the researcher who first established them is put. In monographic works, the year of publication of the work, in which its first description is given, is added to the name of taxons from the family and below, after the author’s surname. The specific name is composed of two Latin words, of which the first (noun) is the name of the genus to which the species belongs, and the second (adjective) is the specific name. Generic names are written with a capital letter, and the names of animal species, even those derived from proper names, with a lowercase letter. For example:

Jnoceramus lamarcki.

This method of naming organisms, first used by K. Liney, is called binary nomenclature (Drushchits, 1974).

If several species belonging to the same genus are listed, then the full name of the genus is indicated only for the first species, and for the rest it is abbreviated. For example: Parahoplites melchioris Anth., P. Subcampischei Sinz., P. maximus Sinz.

In the same way, the genus can be abbreviated in the further description. The abbreviations of the names of the genus and the names of the authors must be the same throughout the text and graphic appendices.

The definition of a fossil consists in establishing its identity with known, previously described forms that are recognized as typical for a given taxon. Its position in the system of the animal or plant world is established sequentially from the highest to the lowest taxa. The assignment of the remainder to large systematic units, up to and including the order, usually presents no difficulty and is carried out according to the principle of macrodescription. To determine families and genera, one has to turn to paleontological reference books.

The genera and species affiliation of the remains of organisms is established according to special works devoted to the description of individual groups of fossils of a certain stratigraphic interval and a specific region.

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