**2.8 Depth distribution of special Euler's points**

The depth distribution of magnetically disturbing masses is well illustrated by the Euler deconvolution solutions calculated in the Oasis Montaj software. We used a structural index of 1 with a window size of 20 km<sup>2</sup> .

**Figure 3.** *Tracing of axes of magnetic field anomaly, normalized to the pole.*

*The Geomagnetic Field Transformants and Their Complexing with Data of Gravitational… DOI: http://dx.doi.org/10.5772/intechopen.111560*

Clusters of Euler points indicate an increased density of magnetic anomalies and their grouping into ordered lines can be used to trace the depths and contours of anomaly-forming objects or magnetically disturbing masses [7].

The schemes of the distribution of Euler points on depth and density (**Figures 4**–**6**) and the structure diagram of these points in geomagnetic fields (**Figure 7**) convincingly testify in favor of the inhomogeneous magnetization of rocks occurring at different depths, which is also indicated by the previously considered transformants of the geomagnetic fields.

The distribution of magnetically disturbing masses in the study area is sharply differentiated on area and depth. For example, in the depth interval of 6–11 km in the northern part of the Shakhpakhta tectonic step, the Euler points are grouped into NE-trending bands (**Figure 5**).

Their position is not controlled by the fault. From which we can conclude that the faults identified here do not have "deep roots."

At the southern part of the Shakhpakhty tectonic step and at the Assakeaudan depression, Euler points form clouds of variable orientations from sublatitudinal to submeridional (in the depth interval 6–11 km), which call into doubt the tying between the genesis of magnetically disturbing masses and fault tectonics.

An indirectly revealed fact indicates a large total thickness of the rocks of the sedimentary cover and the quasi-platform cover on the Shakhpakhty tectonic step, which in turn indicates this tectonic element as favorable from the point of view of their oil and gas potential.

And finally, at the Central Ustyurt system of dislocations, the Euler points are grouped in the form of a zone of northwest orientation in the depth interval of

**Figure 5.** *Scheme of distribution by depth and density of Euler points (in interval 6–11 km) of the geomagnetic field.*

*The Geomagnetic Field Transformants and Their Complexing with Data of Gravitational… DOI: http://dx.doi.org/10.5772/intechopen.111560*

#### **Figure 7.**

*Graph of the distribution of Euler points by regions in geomagnetic models.*

6–11 km (**Figure 5**). The orientation of the zone of increased density of Euler points is consistent with the direction of deep faults, which is the basis for talking about their paragenetic relationship.

Additionally, the Central Ustyurt system of dislocations revealed the presence of another depth interval (10–15 km) with the highest concentration of Eulerian singular points (**Figure 7**). This finding indirectly suggests that the Karabaur swell has subsided in a northern direction under the North Ustyurt massif, resulting in a "double" crustal effect. However, this assumption needs further serious verification with the construction of three-dimensional geological and geophysical models.

Another feature of the specific Euler points has been revealed in all three regional tectonic structures considered above. A sharp or "jump-like" increase in the density of these points in the depth interval of 6–11 km is observed (**Figure 5**).

Considering the distribution of Euler points at various depths in geomagnetic models, it is possible to preliminarily conclude that the top edge of magnetically disturbing masses within the Central Ustyurt system of dislocations occurs at intervals of 4–6 km and 10–15 km depths, while the Assakeaudan Depression sees such occurrences at a depth of 8–10 km, and the Shakhpakhty tectonic step sees it at a depth of 10–15 км.

Analyzing the distribution density of Euler points in the depth interval up to 6 km (**Figure 4**), it is important to note their minimum values throughout the study region, which form small fields with an implicit orientation. It can be assumed that intrusions of the basic composition into the quasi-platform cover took place here.

And finally, the depth interval is up to 20 km. In the Assakeaudan trough, in the Shakhpakhty step, and in the Central Ustrta system of dislocations, there are no differences in the distribution density and orientations of the Euler points, which in turn indicates the basement of these tectonic elements (**Figure 6**).

#### **2.9 Distribution of Euler points based on gravimetry data**

The geological informativeness of the models built on the basis of the data of magnetically disturbing masses would be insufficient without the involvement of data about the depths of occurrence of gravity-disturbing objects.

The special Euler points, calculated in the Geosoft Oasis Montaj software using the algorithm of three-dimensional deconvolution [8], are concentrated near the edges of the anomalies, and correspond to the position and depth of anomaly-forming or gravitationally-disturbing bodies [9].

The regional structural elements are reliably identified with the distribution of density inhomogeneities in depth based on the distribution of Euler points, as well as with the involvement of other transformants of the gravitational field. Theoretical calculations show that even if the Euler points do not form dense clusters near anomalous bodies, at least in their vicinity, the distribution density of these points becomes the highest.

The scheme (**Figure 8**) and the table (**Table 2**) of the location of Euler singular points in the depth range from 0.6 to 8.0 km, as well as the graph of the distribution of these points in the vertical geological section (**Figure 9**) convincingly testify in favor of the density differentiation of rocks according to their depth.

The geological orientation of gravity-disturbing objects at the South Ustyurt is drastically differentiated by area. For example, in the 2–8 km depth interval in the northern part of the Shakhpakhty step, Euler points are grouped into bands of northeastern geological strike (**Figure 9**).

In the Central Ustyurt dislocation system, special Euler points are concentrated in swathes of predominantly northwestern geological orientation.

In the south of the Shakhpakhty tectonic step and in the Assakaudan depression, these points form a cloud extending in a submeridional direction.

#### **Figure 8.**

*Schematic diagram of the Euler points location in the gravitational field at depths up to 8.0 km (with an interval of 1.0 km). Legend: Black dotted lines represent faults complicating the structure of the V reflecting horizon. Dotted pink lines indicate deep faults identified by a set of geophysical data (gravity survey, magnetic survey, and thermal fields).*

*The Geomagnetic Field Transformants and Their Complexing with Data of Gravitational… DOI: http://dx.doi.org/10.5772/intechopen.111560*


**Table 2.**

*Locations of Euler points in the depth interval of 600–8000 meters.*

#### **Figure 9.**

*Graph of the distribution of special Euler points based on gravimetry data (calculated in the Geosoft Oasis Montaj software).*

At the Assakeaudan depression, the maximum number of Euler points on the surface of gravity-disturbing bodies is concentrated at depths up to 2000 m, in the Central Ustyurt dislocation system at depths up to 5000 m, and in the Shakhpakhty step at depths up to 6000 m (**Table 2**).

**Figure 9** generally demonstrates a similar pattern, revealing significant variations in the depths of occurrence of gravity-disturbing bodies in all three regional structures, even at depths of 6000–7000 m. Deeper, these differences are significantly leveled. It can be assumed that this phenomenon is associated with a general transition from the formations of the quasi-platform cover to the rocks of the consolidated basement.

Considering the correlation of the depths of occurrence of gravitational and magnetically disturbing masses [10], it can be noted that accumulations of magnetically disturbing bodies in the Central Ustyurt dislocation system are observed in the depth intervals of 4000–6000 m. It is important to note that the depths of the occurrence of gravitationally and magnetically disturbing bodies coincide.

Based on CDP-2D seismic data, the depth of the basement surface at the Central Ustyurt dislocation system varies significantly, ranging from 4 to 8 km. The structures identified on this surface are linearly elongated, have a northwestern orientation, and are characterized by a general deepening in a southerly direction. In the area of the Akmechet local structure, the basement surface deepens to 9 km [11].

Consequently, the variations in the depths of the basement according to the CDP-2D seismic data are correlated in depth with the distribution of Euler points according to the gravity data.

It is important to note that in the Assakudan depression a serious discrepancy between the depths of occurrence of gravity-disturbing objects and magnetically disturbed masses was revealed.

The upper edge of the gravity-disturbing masses embeds at depths of 1000– 2000 m and, apparently, reflects the transition from unconsolidated and weakly consolidated Lower Cretaceous rocks to more consolidated and epigenetically altered Upper Jurassic deposits. A similar phenomenon was revealed in some areas of the North Ustyurt region [7].

The upper edge of the magnetically disturbing masses here deepens to 8–10 km, which corresponds to the basement surface composed of rocks of basic and ultrabasic composition.

Interpretation data of the geomagnetic field anomalies are well correlated with the results of interpretation of the seismic CDP-2D data, which indicate that on the northern board of the Assakeaudan depression, the top of basement is deepened in a southerly direction from 7 to 10 km (at the Birinzhik local structure).

In contrast, a trend of uplift in the south-west direction can be observed along the top of the Upper Jurassic sediments (III reflecting horizon) from Kazgurly local structure, where it ranges from 2.6–2.8 km, to Birinzhik and Northern Birinzhik local structures, where it ranges from 1.7–2.0 km [11].

Therefore, we can talk about the correlation of the upper edge of the gravity-disturbing bodies with the top of Upper Jurassic sediments, while the upper edge of the magnetically disturbing masses is distinguished in the interval of depths of the top of basement.

*At the Shakhpakhty step*, a discrepancy was revealed in the position of the upper edges of the magnetic- and gravity-disturbing masses, which are submerged, respectively, to depths of 8–12 km and 6–7 km. The distribution pattern of these features suggests that there are differences in the depths of the basement and the quasi-platform cover.

This conclusion is confirmed by CDP-2D seismic data, based on which the depth of subsidence of the top of the Upper Paleozoic carbonate-terrigenous (quasi-platform cover) deposits varies in a wide range (from 3.8 km on the Tabyn structure, 4.5 km on the Samtyr and Utezhan structures, and up to more than 5.5 km on the Kozhantai and Otynshi structures).

The structures at the top of the Upper Paleozoic carbonate-terrigenous sediments here have polygonal shapes and mosaic character, as well as a general deepening trend in the southeast direction. The exception is the local structure of Tabyn with a northwestern orientation and brachianticlinal forms.

It is difficult to speak about the depth of the top of basement according to CDP seismic data, since this boundary does not have good acoustic rigidity.

Consequently, at the Shakhpakhty step, the upper edges of the gravity- and magnetically disturbing masses are characterized by maximum depth. At the Assakeaudan depression, these physical inhomogeneities have a large spread in depth, while in the Central Ustyurt system of dislocations, they are distinguished by small fluctuations in the depth of occurrence.

Сonclusions obtained as a result of integrated interpretation of magnetometry and gravimetry data are confirmed by airborne gamma ray spectrometer (radiometric) data processed and interpreted by the thorium normalized method [12, 13].

Thus, the Tabyn, Kozhantai, Northern Kozhantai, Utezhan, and Kyzgyrly local structures are recognized as potentially promising for the search and exploration of *The Geomagnetic Field Transformants and Their Complexing with Data of Gravitational… DOI: http://dx.doi.org/10.5772/intechopen.111560*

**Figure 10.** *Zonation of the area according to the RAE (radioactive) parameters (according to the algorithm of A.V. Petrov).*

hydrocarbon deposits based on the data of the interpretation of the anomalous magnetic field and the parameters of potassium and uranium content (**Figure 10**). And further, it is recommended to carry out detailed study of these structures using the seismic CDP-3D and deep drilling.
