**2. Results of the geological interpretation of the geomagnetic field transformants**

#### **2.1 Structure of the observed geomagnetic field**

The poleward geomagnetic field in the study region is represented by linearly elongated ΔТа anomalies of both signs and is characterized by a northwest trend (**Figure 1A**).

The Karabaur swell is characterized by high values of the geomagnetic field intensity (+240 + 360 nT, in places up to +520 + 800 nT) with maximum values on the northern periphery of this swell, which indirectly indicates its dipping in the northern direction under the North Ustyurt massif.

The southern periphery of the Central Ustyurt system of dislocations is marked by a drastic decrease in the magnetization of rocks, which is demonstrated by the minimum values of the geomagnetic field intensity (up to 50 nT).

The boundary separating the Shakhpakhty step and the Central Ustyurt system of dislocations (Kolsai trough and Koskudyk swell) is distinguished by the minimum values of ΔTa anomalies (from +46 nT to +14 nT).

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

#### **Figure 1.**

*(A) Anomalous magnetic field reduced-to-the-pole; (B): Vertical derivative of the anomalous magnetic field reduced-to-the-pole. The dashed black lines indicate major faults along V reflecting horizon. Dashed pink lines indicate major tectonic break highlighted on a set of completed research (gravity exploration, magnetic prospecting, thermal fields, and ground surface).*

The northern part of the Shakhpakhty tectonic step is characterized by a negative anomalous geomagnetic field (up to 50-100 nT) on the local structures Utezhan, Koskudyk, Kozhantai, Northern Kozhantai, and Otynshy (**Figure 1A**).

This circumstance indicates the formation of an anomalous geomagnetic field at the northern part of the Shakhpakhty step at a different time than at the Central Ustyurt fault system of dislocation and the Assakeaudan depression.

At the southern part of the Shakhpakhty step, another reversal of the geomagnetic field was revealed. Here, a high-gradient zone of positive anomalies ΔTa manifests itself with quantitative values up to +100 + 120 nT (**Figure 1A**).

At the Assakeaudan depression, large anomalies of the geomagnetic field of northwestern orientation with an intensity of up to +300 nT have been established (**Figure 1**).

#### **2.2 Vertical gradient of the geomagnetic field**

The tectonic boundaries between the Central Ustyurt system of dislocation, the northern and southern parts of the Shakhpakhty tectonic step, and the Assakeaudan trough show themselves sharply and rather contrastingly in the transformant (dZ) of the geomagnetic field (**Figure 1B**).

The Assakeaudan depression is characterized by minimal variations in this transformant (0.002 + 0.006 nT/m), while the Shakhpakhty step exhibits intermediate values (0 to 0.006 nT/m). The maximum values are observed at the Central Ustyurt system of dislocations (0.01 + 0.01 nT/m) (**Table 1**).

The vertical gradient of the geomagnetic field localizes anomalies, reveals the block structure of magnetic and non-magnetic rocks, emphasizes the high-frequency component, and makes it possible to see more clearly the structural and tectonic features along the chains of anomalies when mapping faults. Presumably, some of them were

migration of hydrocarbons in the presence of favorable structural and tectonic conditions.

If traps were encountered along the paths of migrating hydrocarbons, then the possibility of their filling is not excluded. In these cases, changes in the redox environment above the field are possible, leading to the formation of such ferromagnets as magnetite, hematite, pyrrhotite, which could be reflected in the structure of the highfrequency component of the geomagnetic field in the form of dissected and broken isodynamic lines.

Presumably, such processes occurred on the Utezhan, Kozhantai, Northern Kozhantai local structures, which is confirmed in the field of negative values of this transformant. However, this geological phenomenon needs further study.
