Groundwater System and Thermal Field has not been Investigated So Far

Subsequently, newly available data were integrated additionally to structurally refine the Tertiary unit (Noack et al., 2013). Figure 1a and b outline the location of the study area and its present-day topographic elevation. The dominantly clastic sedimentary succession of the NEGB resolved in the model ranges from the Permian to Cenozoic and reaches up to 8000 m thick in the central part of the basin (Fig. 2a).

In response to variations in lithologies, four aquitards of regional extent subdivide the sedimentary succession into different aquifer systems (Fig. 2b). These aquitard layers are from bottom to top, the Permian basement forming the lowermost impermeable layer in the model (Fig. 3a), the Upper Permian Zechstein salt (Fig. 3b), the Middle Triassic Muschelkalk limestones (Fig. 3c) and the Tertiary Rupelian clays (Fig. 3d). Model detailed information about the hydrogeological configuration of sedimentary layers of interest is given in Sect. 2.1.

Along the southern margin the basin is dissected by two major fault zones, the Gardelegen and Lausitz escarpments (Fig. 1b), which vertically offset the pre-Permian basement by several km. As a result, the basement is uplifted by about 5 km coming close to the surface south of the Gardelegen Fault (Scheck-Wenderoth et al., 2008) (see also Fig. 3a). The conductive thermal field of the Brandenburg region was first calculated by Noack et al. (2010, 2012). A comparison of the model results with published temperature measurements of 52 wells showed that the model predictions are largely consistent with the observations, indicating predominantly conductive heat transport (Noack et al., 2010, 2012). Local deviations between observations and model results were interpreted to be the result of additional fluid- related processes. Indeed, recent 3-D coupled fluid and heat transport simulations have revealed that the shallow thermal field is influenced by forced convective processes due to hydraulic gradients (Noack et al., 2013). Another aspect that could be responsible for the deviations between observed and predicted temperatures are faults, which may provide pathways for moving fluids and which have been not included in the model (Noack et al., 2012, 2013).

These previous studies have provided deeper insights into the present-day thermal structure of the Brandenburg area. However, the impact that major existing fault zones may have on the groundwater system and thermal field has not been investigated so far. Previous 2-D numerical studies applied to different geological settings showed that faults may significantly influence the hydrothermal field (e.g. Bense et al., 2008; Garven et al., 2001; Lampe and Person, 2002; Magri et al., 2010; Simms and Garven, 2004; Yang et al., 2004a, b).

These investigations demonstrated that along-fault convection may be an important heat transport mechanism in permeable faults and may give rise to significant variations of the thermal field. Results from 3-D studies seem to confirm these conclusions (Alt-Epping and Zhao, 2010; Bächler et al., 2003; Baietto et al., 2008; Cacace et al., 2013; Cherubini et al., 2013; López and Smith, 1995, 1996; Yang, 2006). However, differences between 2-D and 3-D studies have been found, due to the fact that the longitudinal fluid flow and heat transport along the strike of the faults are ignored in 2-D studies (Yang, 2006).