Conceptualisation of speleogenesis in multi-storey artesian systems: a model of transverse speleogenesis

Abstract

Conceptual and respective quantitative models of speleogenesis/karstifi cation developed for unconfi ned aquifers do not adequately represent speleogenesis in confi ned settings. A conceptual model for speleogenesis in confi ned settings is suggested, based on views about hydraulic continuity in artesian basins and close cross-formation communication between aquifers in multi-storey artesian systems. Soluble units sandwiched between insoluble porous/fi ssured formations (common aquifers) initially serve as low permeability beds separating aquifers in a confi ned system. Conduits evolve as result of vertical hydraulic communication between aquifers across the soluble bed ("transverse speleogenesis"). Recharge from the adjacent aquifer is dispersed and uniform, and fl ow paths across the soluble bed are rather short. There is a specifi c hydrogeologic mechanism inherent in artesian transverse speleogenesis (restricted input/output) that suppresses the positive fl ow-dissolution feedback and hence speleogenetic competition in fi ssure networks, and accounts for the development of more pervasive channelling in confi ned settings, of maze patterns where appropriate structural prerequisites exist. This is the fundamental cause for the distinctions between cave morphologies evolving in unconfi ned and confi ned aquifers and for eventual distinctions of karstic permeability, storage characteristics and fl ow system behaviour between the two types of aquifers. Passage network density (the ratio of the cave length to the area of the cave fi eld, km/km2) and cave porosity (a fraction of the volume of a cave block, occupied by mapped cavities) are roughly one order of magnitude greater in confi ned settings than in unconfi ned. Average areal coverage (a fraction of the area of the cave fi eld occupied by passages in a plan view) is about 5 times greater in confi ned settings. Conduit permeability in unconfi ned settings tends to be highly heterogeneous, whereas it is more homogeneous in confi ned settings. The storage characteristics of confi ned karstifi ed aquifers are much greater. Recognition of the differences between origin, organisation and behaviour of karst systems evolved in unconfi ned and confi ned settings can improve effi ciency of exploration and management of various resources in karst regions and adequacy of assessment of karst-related hazards.

Early-stage hypogene karstification in a mountain hydrologic system: A coupled thermohydrochemical model incorporating buoyant convection

“…However, we did not consider some other geologic and hydrogeologic features representative of other reported hypogene karst systems, such as mixed lithologies [e.g., Hobba et al, 1979, Ford and Williams, 2007, Klimchouk, 2009 and cross-formational flow systems [Klimchouk, 2009], which produce transverse speleogenesis in the sense of Klimchouk [2003]. To some extent, this was influenced by the computationally intensive nature of the simulations, which restricted the scope of our study.…”

Aquifer configuration and geostructural links control the groundwater quality in thin-bedded carbonate–siliciclastic alternations of the Hainich CZE, central Germany

“…The spatial correlation of marlstones presumes that basin-centre marlstones are laterally more continuous than shallow water limestones (Aigner, 1985). In accordance with published examples for multi-storey subsurface architecture (Haag and Kaupenjohann, 2001;Heinz and Aigner, 2003;Klimchouk, 2005;Sharp, 2007), we use the term "aquifer storey" to emphasize our conceptualization of the fine-stratified setting by arbitrary definition of intervals that are dominated by fractured limestone beds and confined at the top and base by unfractured or low permeable beds, the latter with an effective minimum thickness of 80 cm. The degree of aggregation is a compromise between increased detail to account for different hydrogeochemical patterns and the necessary well yield for recovering water samples.…”

“…As caprock sinkholes are arranged in lineaments (Fig. 2a) parallel to regionally known fault orientations, it is very likely that they are coupled to the penetration of surface-subsurface water at fracture zones (compare to Smart and Hobbs, 1986;Worthington, 1999;Klimchouk, 2005) that promote preferential recharge (Smart and Hobbs, 1986;Suschka, 2007). Although dissolution of soluble rocks is limited within the target aquifers of this study, it is reasonable that collapse structures are accompanied by enhanced rock fracturing and permeability.…”

“…As hydraulic heads and chemical groundwater compositions of different aquifers at the same sites (H13/14 (cluster 1); H41/42 (clusters 2 and 4); H51/53 (clusters 3 and 5)) are significantly distinct, vertical communication between aquifer storeys is highly reduced. Thus we interpret the thin aquifer beds as confined, "sandwich flow type" aquifers (term: White, 1969;Klimchouk, 2005) which are interbedded with confining aquitards. The assumed lat- Figure 6.…”

Subglacial Maze Origin in Low-Dip Marble Stripe Karst: Examples from Norway

“…The network geometry and the effluent flow function are suggestive of caves of hypogene origin (Klimchouk, 2003(Klimchouk, , 2009). However, this sort of hypogene speleogenesis is characterized by water injection from a porous aquifer below or above the soluble strata, and the presence of impermeable strata in stripe karst makes a hypogene origin implausible.…”