Where did the rocks lie? What message do they carry from the prehistoric past, and who is able to decipher it? How many scientists study the earth? What soles are hidden in it? What are the creases that cannot be ironed out?
A lot of amazing questions and even more amazing answers are kept by geology. Those who are sure that his house is not staggering and will not “creep” in the near future, he may not be interested in rocks at all.
Which rocks are mountainous? And where did they lie?
The occurrence of rocks is the location, shape, and relation to each other of fairly clearly defined fragments of the earth's crust. Moreover, they are composed of one (or close) rocks of common origin and of similar age.
They take into account their spatial location relative to the horizon, the cardinal points and how they are connected with other rocks around.
Sedimentary and some volcanic have a bed-like form of rock. The primary occurrence here is shallow. But various processes in the earth's crust change and violate it.
What are the rocks interesting for? Their occurrence forms are numerous. According to them, scientists recreate the geographical and geological pictures of the past of our planet.
Rocks - messengers of the past
The study of natural conditions, which distinguished the most ancient geological eras, is engaged in paleography.
This scientific discipline examines the composition, conditions and forms of occurrence of rocks, analyzes strata of the same age, and subjects the remains of organisms found in them to paleoecological studies.
Paleographers compose both paleographic maps and lithological-facies ones. The divisions of paleography are paleoecology, paleobiogeography, paleoclimatology. She has several more areas:
- terrigenous mineralogical,
- geochemical
- paleotectonic
- paleo-neurological,
- paleogeomorphological,
- paleovolcanological,
- paleomagnetic and others.
Only mountains can be better than mountains ... well-studied mountains!
The occurrence of rocks, forms, types and types are the subject of study and many other disciplines of geology.
Discipline Name | What exactly are studying |
Geology and planetology, paleography and paleoecology | Earth as a whole and the impact of space on it. The history of the planet. |
Volcanology and stratigraphy, geotectonics and seismology, geochemistry and regional geology, dynamic geology and petrology, engineering geology and petrography, mineralogy and lithology | The earth’s crust itself (earth’s solidity) is the outer solid part of the lithosphere, the shell of the Earth. |
And if we take into account that natural gases, oil, and even water in the broad sense of the understanding are also considered rocks, then this list can be continued for a long time.
Which are primary and which are secondary?
The primary forms of occurrence of rocks include those that occurred during the formation of this particular rock. And secondary ones are those formed by deformation, which the primary ones underwent over time.
The secondary form of occurrence is called dislocation. Whether they are inextricable (folded) or explosive depends on what types of tectonic influences the rock has undergone.
The first include layers - flat bodies of sedimentary rock. They usually have a large area, extending horizontally for tens of meters, or even kilometers. Their appearance is often incorrect. Some layers, it happens, become thinner and completely disappear, while others, on the contrary, become thicker.
Students studying the bedding order of rocks refer to the place of thinning of the layer as “pinch” if it then again reaches the previous or large sizes. If the bedding is thinned to complete disappearance, the bedding form is called “wedging”.
Lenticular bedding (simply a lens) occurs if the wedging of the layer occurred at a small distance from its center. Interlayers are also distinguished (power - small, prevalence - very large), interlayers (prevalence - limited, power - small).
Depending on how they are formed, the primary occurrence is divided into:
- deep (second name - intrusive) - these include sills and batholiths, lapolites and stocks, laccoliths and dikes;
- spilled (or effusive) - this is extrusion, as well as covers and flows.
Undisturbed and disturbed
According to the type of occurrence, rocks can be:
- horizontal
- monoclinal,
- folded.
The earth's crust, namely its upper part, is formed by layered strata of sedimentary origin, which were deposited in water for a long time.
The place where they accumulated was overwhelmingly the horizontal bottom of the lagoons and seas of antiquity. Therefore, when sedimentary rocks of this type of primary undisturbed occurrence occur, they say that it is horizontal.
Time and tectonic activity do their job. As a result, in one place or another, the layered sedimentary rock tilts in a certain direction.
If the layers are tilted in the general direction, and the distance between them is large enough, the angle of inclination is general and in the section they are not repeated; this is a disturbed monoclinic bed.
You cannot iron these folds.
Sometimes the breed seems to wrinkle with characteristic folds. Such plastic deformation of the strata indicates the presence of a folded type of occurrence.
There are several elements of the fold:
- vault (aka castle),
- wings,
- angle.
The morphological classification of folds is based on:
- on the shape of a castle;
- on what position the axial surface of the fold occupies;
- on the relationship of the wings to each other;
- on the ratio of the width and length of the fold.
Diapir folds stand out in a special way. They are obtained when plastic masses are introduced into the denser rocks that surround them. Their striking examples are clay diapirs and salt domes.
The type of folding can be:
- complete
- intermittent
- intermediate.
Geological maps show the features of folds. On platforms, they are mainly domed. There are also folds long and elongated, straight, oblique, overturned, lying, diving. By angle, they are divided into blunt, sharp, fan-shaped, stamped.
Power is the distance from the sole to the roof
According to this formula, such an important quantity as reservoir thickness is found.
Sedimentary rock is divided into layers by the so-called bedding surface. The bottom is the sole, and the top is the roof of the formation. Accordingly (if bedding of rocks is considered in batches), the roof of the lower serves as the sole of the upper.
The distance (and the smallest) between them will be just the thickness of the reservoir.
Types of occurrence of rocks
Rocks called sedimentary are formed at the bottom in a horizontal direction or with a slight slope. And each top layer will be younger than the one that is underlying to him. If the situation with precipitation is relatively stable in this case, the deposited surfaces will fall in parallel (in the language of terms - according to). In this case, the incision is represented by continuous layers.
However, even in this case, disagreement can be observed in the bedding of the layers. It is called parallel or stratigraphic and is fixed if the strata are inconsistent historically. This phenomenon occurs when the earth's crust fluctuates.
Angular and tectonic disagreement is also a violation of the initial occurrence of the beds. In the first case, layers of different ages deviate by no means in one direction.
All the described disagreements give erosion boundaries dividing fragments of rocks of different ages.
Rock study is important for the future
In engineering geology, great importance is attached to data on the sequence of occurrence of rocks.
During construction, the most favorable places are chosen, namely those where the rocks lie horizontally. A high thickness of the layers is also considered a good sign and a uniform rock composition is desirable.
If structures and buildings have a foundation located in a homogeneous soil, then the weight of the structure will create uniform compressibility of the layers. Accordingly, the stability of the building increases.
But if there is a dislocation (that is, a secondary form of rock bedding), the homogeneity of all the soils in the base will most likely be violated. This will greatly complicate the construction.
So the narrow specificity of the topic of rocks and, in particular, their occurrence under a person’s feet, is only apparent. In fact, not only for geologists, but for everyone else, it is important what land to walk on, what will happen to it in the near future. It also matters on what foundation to build a house so that it stands indestructible for many years.