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 wrinkles that cannot be ironed out?
Geology keeps a lot of amazing questions and even more amazing answers to them. Anyone who is sure that his house will not stagger and “crawl” in the near future may not be interested in rocks at all.
What breeds are mountain? And where did they lie down?
Occurrence of rocks is called the location, shape and relationship to each other of fairly clearly defined fragments of the earth's crust. Moreover, they are composed of one (or close) breeds of common origin and similar age.
Their spatial location relative to the horizon plane, cardinal points and how they are connected with other rocks around are taken into account.
Sedimentary and some volcanic havelayered form of rock formation. The primary occurrence here is gently sloping. But various processes in the earth's crust change and disrupt it.
What is interesting about rocks? Their occurrence forms are numerous. According to them, scientists recreate the geographical and geological picture of the past of our planet.
Rocks are messengers of the past
Paleography is the study of the conditions of nature, which distinguished the most ancient geological epochs.
This scientific discipline explores 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.
Palaeographers compile both paleographic and lithofacies maps. Subdivisions of paleography are paleoecology, paleobiogeography, paleoclimatology. She has several more directions:
- terrigenous-mineralogical,
- geochemical,
- paleotectonic,
- paleondrological,
- paleogeomorphological,
- paleovolcanological,
- paleomagnetic and others.
Mountains can only be better… well-studied mountains
Rock occurrences, shapes, types and types are the subject of study of many other disciplines of geology.
| Name of disciplines | What exactly are they studying |
| Geology andplanetology, 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 | Actually the earth's crust (firmament of the earth) - the outer solid part of the lithosphere, the shell of the Earth. |
And if you consider that natural gases, oil and even water in the broadest sense 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 arose in the process of formation of this particular rock. And the secondary ones are those formed by the deformation that the primary ones were subjected to over time.
The secondary form of occurrence is called dislocation. What they are - inseparable (folded) or discontinuous - depends on what types of tectonic influences the rock has undergone.
The first are layers - flat bodies of sedimentary rock. They are usually distinguished by a large area extending horizontally for tens of meters or even kilometers. Their appearance is often incorrect. Some layers sometimes become thinner and disappear altogether, others, on the contrary, become thicker.
Studying the order of occurrence of rocks, they call the place of thinning of the layer "pinching" if it then again reaches the same or large size. If the stratification thins to the point of complete disappearance, the form of occurrence is called "wedging out".
Lenticular occurrence (simply - a lens) occurs if the layer is wedged out at a small distance from its center. There are also interlayers (thickness - small, abundance - very large), interlayers (proliferation - limited, thickness - small).
Depending on how exactly they are formed, primary occurrences are divided into:
- deep (the second name is intrusive) – these include sills and batholiths, lopolites and stocks, laccoliths and dikes;
- outflow (or effusive) are extrusions, as well as covers and flows.
Unbroken and broken
By type of occurrence, rocks can be:
- horizontal,
- monocline,
- pleated.
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, it is said to be horizontal.
Time and tectonic activity take their toll. As a result, in one place or another, the layered sedimentary rock tilts in a certain direction.
If the layers are inclined in a common direction, and the distance between them is large enough,the angle of inclination is general and they do not repeat in the section; then we are talking about a disturbed monoclinal occurrence.
These creases can't be ironed out
Sometimes the breed seems to be wrinkled with characteristic folds. Such plastic deformation of the strata indicates the presence of a folded type of occurrence.
Select multiple pleat elements:
- vault (aka castle),
- wings,
- angle.
Morphological classification of folds is based on:
- on the shape of the lock;
- on the position of the axial surface of the fold;
- on the ratio of the wings to each other;
- on the ratio of the width and length of the fold.
Diapiric folds stand out in a special way. They are obtained when plastic masses are embedded in the denser rocks that surround them. Vivid examples of them are clay diapirs and s alt domes.
According to its type, folding can be:
- full,
- intermittent,
- interim.
Geological maps reflect features of folds. On platforms they are mostly domed. There are also folds that are long and elongated, straight, inclined, overturned, recumbent, diving. According to the angle, they are divided into blunt, sharp, fan-shaped, stamped.
Power is equal to the distance from the sole to the roof
This formula is used to find such an important value as reservoir thickness.
Sedimentary rock is divided intolayers of the so-called bedding surface. The lower one is the sole, and the upper one is the roof of the formation. Accordingly (if the occurrence of rock layers is considered in packs), the roof of the lower one serves as the sole of the upper one.
The distance (moreover, the smallest) between them will just be the thickness of the reservoir.
Types of rock occurrences
Rocks, called sedimentary, are formed at the bottom in a horizontal direction or with a slight slope. And each upper layer will be younger than the one that is underlying it. If the situation with precipitation is relatively stable, the stratified surfaces will lie in parallel (in terms of terms - according to). In this case, the cut is represented by continuous layers.
However, even in this case, there may be an unconformity in the occurrence of layers. It is called parallel or stratigraphic and is fixed if the strata are historically inconsistent. This phenomenon occurs when the earth's crust oscillates.
Angular and tectonic unconformity are also violations of the original bedding. In the first case, layers of different ages deviate by no means in one direction.
All described unconformities give erosional boundaries separating 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 rock formation.
Whenconstruction, the most favorable places are selected, namely those where the rocks lie horizontally. A good sign is also considered to be a large thickness of the layers and a homogeneous composition of the rock is desirable.
If structures and buildings have a foundation located in a homogeneous soil, then the weight of the structure will create a uniform compressibility of the layers. Accordingly, the stability of the building increases.
But in the presence of a dislocation (that is, a secondary form of rock deposits), the uniformity of all soils at 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 also for everyone else, it is important which 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.
