## 2 Geological Setting  
The Kovagoszolos Sandstone Formation and the Boda Claystone Formation are part of the 4000-5000 m thick Palaeozoic-Triassic sedimentary sequence of the Western Mecsek Mountains in SW Hungary (Figure 1) [8]. The KSF was deposited in continental (fluvial and paludinal) facies in a hot, semi-arid climate [10; 11]. Due to the uneven subsidence of the depositional environment, the fluvial basin, the known thickness of the formation varies between 150 and 1400 m [12]. Based on sporomorphs the uppermost part of the KSF can be dated to the Triassic. The Permian-Triassic boundary can be drawn within the formation [13]. The KSF consists of a rhythmic succession of coarse- and fine-grained beds. The major sedimentary cycle begins with conglomerates, and the middle part consists of relatively fine-grained sandstone layers. The upper part of the formation becomes coarser again, and the uppermost part ends with coarse sandstone with pebbles, which could be related to regression [14]. Based on the predominant colour of the sandstone layers, the formation could be divided into three heterotopic members: the deepest member is the varied sandstone (Bakonya varied sandstone), followed by the grey sandstone (Kovagottottos Sandstone) and the red sandstone (Cserkuit Red Sandstone) at the top [11; 14]. At the boundary between the grey and red sandstones, a layer of green sandstone could be separated (Kajdacs volgy Sandstone), with which significant uranium ore enrichment is associated [11]. Figure 1: (**A**) Map of Hungary with the location of the Mecsek Mountains. (**B**) Geological map of the Mecsek Mountains with the distribution of the Kovagoszolős Sandstone Formation and the Boda Claystone Formation; modified after [9]. Legend: 1—Neogene sediments; 2—Jurassic and Cretaceous sediments and Cretaceous volcanic rocks; 3—Triassic sediments (sandstones, carbonates and evaporites); 4—Upper Permian–Triassic Kovagoszolős Sandstone Fm; 5—Upper Permian Boda Claystone Fm; 6—Palaeozoic; 7—fault; 8—strike-slip fault; 9—thrust fault; 10—syncline and anticline; 11—well site. The underlying formation of the KSF is the Boda Claystone Formation, a reddish-brown formation composed of claystone, siltstone, alibitolite with dolomite and fine sandstone interbeds [15; 16]. Due to its extent (150 km\({}^{2}\)), thickness (700-900 m) and impermeable properties, it is suitable for the proposed repository for high-level radioactive waste [1]. BCF was deposited in a lacustrine environment, in an alkaline lake on a periodically drying playa mudflat in an arid to semi-arid climate [15; 17; 18; 19; 20]. The study area is within the subcritical profile of well BAF-3, which intersected both formations in a considerable thickness. The borehole is 845 m deep, quaternary sediments are located in the uppermost 2.76 m, the Kovagottottos member (grey sandstone) of the KSF is found between 2.76 and 112.46 m, and the Bakonya member (variegated sandstone) of the KSF is located below it, between 112.46 and 343.08 m. The boundary of the two formations is at 343.08 m, below that BCF is located. Between 691.2 and 695.6, there is a reductive layer in the BCF, which has been documented in several other boreholes as well (Figure 2) [21]. Numerous successive tectonic phases characterise the tectonic evolution of the area. In the Late Cretaceous, a significant NE-SW shortening is documented [22]. The main tectonic events in the Neogene are related to the formation of the Pannonian Basin. In the early Miocene, tensional stresses [23; 24; 25] and in the late Miocene, compression [26] led to deformation in this area. This event was followed by thermal subsidence of the basin during the Pannonian [27; 28]. The most recent significant event is the ongoing tectonic inversion of the basin [9].