## 2 Geological Settings  
The geodynamic development of the Western Carpathians significantly influenced the structure and tectonic development of the Humenne Unit. The position of the Humenne Unit as the easternmost segment of the Inner Western Carpathians is the result of the Alpine orogenic cycle [23]. The unit was deformed and modified several times, which has been reflected in its tectonic as well as lithological structure. Like all the Paleoalpine units of the Western Carpathians, the Humenne Unit was thrust northward during the Upper Cretaceous. However, no fragments of this Upper Cretaceous deformation stage are preserved in the current structure. Based on the lithological composition, the unit as a whole was detached from the base of the Middle Triassic Gutenstein limestones. The older members of the unit (Lower Triassic) remained in the dorsal part of the nappe. It is indisputable that the most significant tectonic impact in the Humenne Unit occurred during the Neogene development, when the unit was repeatedly (southwardly) overthrusted and broken up into blocks [24]. In the present, the unit is situated over the buried Inacovo-Kricevo Unit and overlaid by Paleogene/Neogene sedimentary sequences and Neogene volcanics. The internal structure consists of Mesozoic sediments (Middle Triassic-Middle Cretaceous) which are represented as an eastward continuation of the Western Carpathians (Figure 2). Lithologically, the Middle Triassic limestones are characterized by intensive shallow-water carbonate sedimentation (Gutenstein limestones, Ramsau dolomites, and pale limestones) with thickness up to 250 m. The overlying Jurassic marly-sandy shales, shallow-water crinoidal limestones, and marly limestones are only partially represented. The Jurassic formations are conformally overlain by the Lower-Middle Cretaceous limestones with chert stone nodules and dark grey sandy limestones. The estimated thickness of the Cretaceous sediments is about 300 to 400 m. The Humenne Unit is overlain by transgressive Paleogene sedimentary sequences such as conglomerates and breccias as well as Neogene volcanic sedimentary complexes (where andesites and marks dominate). The Humenne Unit's deformation had an impact on layer thickness and geophysical rock properties [24; 25]. Strong rock failure and an imbricate structure with alternating carbonates and peitic rocks are also reflected in the hydrogeological conditions of the area. The flow and accumulation of groundwater in the Humenske Mountains are affected by their imbricate structure. They are also affected by a fault system that divides the Mesozoic blocks into partial structures which are either elevated or depressed. These depressed or elevated depositions of Triassic carbonates are collectors of thermal waters. The infiltration area of the geothermal waters of the Humenne Unit is represented by the Humenske Mountains and neovolancis of the Vihorlatske Mountains. Much of the groundwater crosses into the Quaternary and Neogene sediments. Part of the intermediate and regional groundwater flow, which occurs in lava flows and tectonic faults, contributes to the formation of geothermal waters. Likewise, part of the groundwater from Neogene sediments can transfer to the Mesozoic collector under favorable geological-tectonic conditions [26]. The geothermal aquifer in the Humenne Unit has a fracture and a fracture-karstic permeability and contains two chemical groundwater types. The first type is hydrogen carbonate groundwater with TDS 0.83-0.84 g\(\cdot\)L\({}^{-1}\), which is tied to the southeastern edge of the unit. The aquifer is made up of Triassic carbonates with carbonate to carbonate-sulfatogenic mineralization, with a limited marinogenic mineralization effect. Carbonate coefficient values rHCO\({}_{3}\)/rCl = 6.90r confirm an open hydrogeological structure. The second type is groundwater containing chlorides and sulfates with TDS 10-13 g\(\cdot\)L\({}^{-1}\). This type shows significant impact from marinogenic mineralization.