Barzok Cave of Kashan is one of the active karst formations west of central Iran. This karst formation is located in parts of shale and limestones of the Shemshak formation (Jurassic) and mainly in Cretaceous limestones (Coniacian to Santonian). The systems affecting the Barzok cave karst network are considered based on the combined processes of tectonic forces, reverse fault activity, and chemical dissolution. Barzok Cave has various forms of special stones in the cave, including stalagmites, stalactites, flowstones, draperies, rim stones, popcorn, and stars. The initial stage of the formation of this karst cave began with reverse fault activity, and compressional forces extending northeast-southwest caused the displacement of Cretaceous limestone layers along the fault plane. Erosion regimes have caused the formation of numerous joints and cracks, all of which follow the aforementioned fault movements, and in these limestones, have increased the porosity and secondary permeability of the rock mass. Then, chemical dissolution by carbonic acid and organic acids caused the formation of karst deposits on the limestone masses and the emergence of the Barzok Cave karst network.
Introductions
Despite extensive research on caving, the role of hydrogeochemistry in cave development in interaction with an active tectonic substrate is not well understood. According to the definition, any empty natural space in the rock that can be suitable for human entry is called a cave. It should be noted that the above definition is a little different from what hydrologists have about caves. The karst formations of Barzok Cave are mainly developed in upper Cretaceous limestones (Coniacian to Santonian) and limestone and shale layers of the Shemshak Formation of the Jurassic age. The Barzok Karst Cave is affected by phenomena of tectonic origin, fault movements, and chemical dissolution, and erosional regimes over a relatively long period have caused the deposition of karst forms in this cave.
Despite the historical and geological importance of Barzok Cave, no significant study has been conducted on it due to its difficult access, very narrow and long entrances, and dangerous traffic routes. This research deals with the role of tectonic and hydrochemical factors and the relationship of sedimentary deposits inside the cave on the emergence and development of its morphology.
Materials and Methods
The research method was based on field visits, including the study of rock and strata units in the area, topographic features, linear structures, including joints and fault systems, and collecting rock samples to prepare thin sections, laboratory studies, and remote sensing studies.
Geographical location of Barzok Cave
The Barzok region of Kashan is located in the west of the Central Iran zone, 45 kilometers southwest of Kashan and on the Kashan-Golpaygan Road.
The karst formation of Barzok Cave was formed based on faulting events, with the displacement of Coniacian-Santonian limestone layers and limestone and shale layers of the Shemshak Formation of Jurassic age, followed by chemical dissolution.
Discussion and Results
In general, the karst formation of Barzok Cave was formed based on tectonic and fault activity during different geological times and the dissolution of limestone layers in atmospheric waters with significant acidity. This cave was formed in limestone rocks of Jurassic age in the Shemshak Formation and Upper Cretaceous from the Coniacian to Santonian. Considering that the primary factor of the emergence of the Barzok Karst Cave was reverse fault activities, it is possible to show the role of the dissimilarity of the Coniacian to Santonian limestone layers and Jurassic limestones in the formation of this cave, considering the shape that indicates a similar process.
Numerous tectonic forces during different geological times, predominantly in a northwest-to-southeast trend with an azimuth of N268 ͦ, have been very effective in creating the cave.
The deposits inside the cave are divided into two main groups: destructive and chemical. Stalagmite, Stalactite, Flowstone, Drapery, Rimstone, Popcorn or Coralloids, Stars, and Helictite are the major chemical deposits of Barzok Cave, which have different ages. The mechanism of these limestones is that empty spaces are formed inside the limestones due to the dripping of water into the cave. Barzok Cave is one of the active caves. Examining the cave rocks can also help determine past climate. Various forms of dissolution and sedimentation change with different colors and shapes in the form of cauliflower and crystallized sedimentary rocks have been shown in the Barzok Cave.
Chemical dissolution by carbonic acid and organic acids has caused the formation of karst deposits on limestone masses and the emergence of the karst network of Barzok Cave.
Conclusion
The karst formation of Barzok Cave, in the northwest of central Iran, was formed based on tectonic, faulting and dissolution activities of limestone layers in atmospheric waters with significant acidity. The role of temperature is also significant in the development of this karst. Considering the proximity of this cave to numerous travertine formations of the Oligocene-Miocene Qom Formation and the fact that the region was affected by Eocene volcanic activity and the presence of temperature changes of karst waters and relatively severe climatic and temperature changes during the periods of the emergence and development of the cave, it can be concluded that the expansion of this cave occurred in numerous and irregular periods and the diversity of karst features formed in this cave can also confirm this issue. The compressive force required for the rupture of the reverse fault and the displacement of the layers can be attributed to tectonic forces and recent orogenic phases. Given the relatively high purity of Coniacian-Santonian limestones and the crystallization of these limestones, the starting point of chemical dissolution can be considered to be the points of morphological-crystalline disturbance and their discontinuity boundaries. The logarithmic constant K can indicate the difference in the occurrence of various karst phenomena in Barzok Cave.