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84 NCKRI Special Paper No. 1 Synopsis Several general points can be derived from the above regional overview. 1) Hypogenic speleogenesis is much more widespread that previously assumed. It is identified in various lithologies and geological and tectonic settings. Despite these variations, the resultant caves demonstrate a remarkable similarity in their patterns and mesomorphology, which suggests that the hydrogeologic settings were broadly identical in their formation. The morphologic suites of rising flow with buoyancy components are clearly identifiable in most of these caves. 2) In many areas more than one dissolutional process, such as CO2-driven hydrothermal dissolution and H2S (sulfuric acid) dissolution, is recognized to form hypogenic caves. They operated either simultaneously or sequentially, and it is often difficult to discriminate between their respective speleogenetic effects. 3) The great majority of accessible hypogenic caves are relict. Many of them bear signs of overprint by epigenetic processes. However, many active (in the sense of continued hypogenic development) caves are documented, either directly or indirectly. Active hypogenic caves are found in various current hydrogeologic environments: at the water table, at depth in presently unconfined aquifers (rising flow through them indicates vertical head gradient from still deeper aquifers and the hypogenic component), and in currently confined conditions. In many cases these settings (with regard to cave-hosting formations) occur proximal to each other in the same region, suggesting a speleogenetic evolutionary sequence in response to uplift and erosional lowering/entrenchment. 4) Many maturely developed hypogenic caves with type morphological characteristics are unambiguously shown to develop under confined conditions. None of the morphologically mature caves presently active at a water table were unambiguously shown to form in the respective contemporaneous settings. This suggests that confined settings are the principal hydrogeologic environment for hypogenic speleogenesis, which is in agreement with the broad analysis of hydrogeological evolution and the ascending transverse speleogenetic model. However, hypogenic caves may experience substantial modification under subsequent unconfined stages, especially when H2S dissolution mechanisms are involved. 5) Whether or not water table/subaerial dissolution can be a major mechanism in also creating features that occur by hypogenenic processes remains an open debate and requires more research. 4.6 Comparison of confined versus unconfined conduit porosity The distinctions between hypogenic (confined) and epigenic (unconfined) speleogenesis can be illustrated by the analysis of morphometric parameters of typical cave patterns. Klimchouk (2003b) compared two representative samples of typical cave systems formed in these two settings. The sample that represents unconfined speleogenesis consists solely of limestone caves, characteristically displaying branchwork patterns. Gypsum caves of this type tend to be less dendritic. The sample that represents hypogenic-confined speleogenesis consists of both limestone and gypsum caves that have network maze patterns. Passage network density (the ratio of the cave length to the area of the cave field, km/km 2 ) is one order of magnitude greater in confined settings than in unconfined (average 167.3 km/km 2 versus 16.6 km/km 2 ). Similarly, an order of magnitude difference is observed in cave porosity (the fraction of the volume of a cave block occupied by mapped cavities; 5.0% versus 0.4%). This illustrates that storage in maturely karstified confined aquifers is generally much greater than in unconfined aquifers. Average areal coverage (a fraction of the area of the cave field occupied by passages in a plan view) is about 5 times greater in confined settings than in unconfined (29.7% versus 6.4%). This means that conduit permeability in confined aquifers is appreciably easier to target with drilling than the widely spaced conduits in unconfined aquifers. The results in Tables 1 and 2 clearly demonstrate that there are considerable differences between confined and unconfined settings in the average characteristics of cave patterns and porosity. The fundamental cause of this difference in conduit porosity is demonstrated to be a specific hydrogeologic mechanism inherent in confined transverse speleogenesis (restricted input/output), which suppresses positive flow-dissolution feedback and speleogenetic competition in fissure networks (Klimchouk, 2000a, 2003a). This mechanism accounts for the development of more pervasive channeling and maze patterns in confined settings where appropriate structural prerequisites exist. In contrast, the positive flowdissolution feedback and competition between alternative flowpaths dominates in unconfined settings to form widely spaced dendritic cave patterns. Table 2 shows no appreciable difference of parameters between gypsum and limestone caves formed in confined settings. However, there are noticeable differences between parameters of particular caves even from the same region (Table 1). For example, compare the characteristics of Jewel and Wind caves, both occurring within the slopes of the structural dome of the Black Hills, or characteristics of the gypsum mazes in the western Ukraine. There are two explanations for such differences. First, one of the implications of the hypogenic transverse speleogenetic model is that virtually all hydrogeologically
HYPOGENIC CAVE FEATURES TABLE 1 Characterization of cave patterns and porosity in unconfined versus confined aquifers Length, Area Cave km of cave, m 2 x10 6 Volume of cave, m 3 x10 6 Area of cave field km 2 Volume of rock, m 3 x10 6 Specific volume, m 3 /m “Common” caves – speleogenesis in unconfined settings Blue Spring Cave, Indiana, USA, Carboniferous limestones Mammoth Cave, Kentucky, USA, Carboniferous limestones Friars Hole System, WV, USA, Carboniferous limestones Krasnaya Cave, Crimea, Ukraine, Jurassic limestones Jewel Cave, South Dakota, USA, Carboniferous limestones Wind Cave, South Dakota, USA, Carboniferous limestones Knock Fell Caverns, N. Pennines, UK, Carboniferous limestones Fuchslabyrinth Cave, Germany, Triassic limestones (Muschelkalk) Moestroff Cave, Luxembourg, Triassic limestones (Muschelkalk) Botovskaya Cave, Siberia, Russia, Lower Ordovician limestones Estremera Cave, Madrid, Spain, Neogene gypsum Optimistychna Cave, W. Ukraine, Neogene gypsum Ozerna Cave, W. Ukraine, Neogene gypsum Mlynki Cave, W. Ukraine, Neogene gypsum Kristalna Cave, W. Ukraine, Neogene gypsum Slavka Cave, W. Ukraine, Neogene gypsum Verteba Cave, W. Ukraine, Neogene gypsum Atlantida Cave, W. Ukraine, Neogene gypsum Ugryn Cave, W. Ukraine, Neogene gypsum Jubilejna Cave, W. Ukraine, Neogene gypsum Passage density, km/km 2 Cave porosity, % 85 Areal coverage, % 32.0 0.146 0.5 2.65 119.34 15.6 12.07 0.42 5.5 (0.08) (1.1) 550.0 1.386 8.0 36.78 3310.2 14.5 14.95 0.24 3.77 (0.09) (1.4) 70.0 0.3 2.7 4.37 349.92 38.6 16.00 0.77 6.86 (0.28) (2.5) 17.3 0.064 0.27 0.74 37.0 15.5 23.23 0.15 8.55 Maze caves – speleogenesis in confined settings 148.01 0.67 1.49 3.01 135.63 10.00.0 49.11 1.10 22.20 143.2 0.43 1.13 1.36 61.0 7.9 105.68 1.86 31.73 4.0 0.006 0.012 0.02 0.12 3.0 170.94 10.26 25.64 6.4 0.0058 0.007 0.03 0.15 1.1 217.61 4.80 19.55 4.0 0.004 0.0035 0.01 0.05 0.9 406.09 7.14 40.61 23.0 0.067 0.104 0.11 1.37 4.5 201.75 7.62 58.51 3.5 0.008 0.064 0.06 0.71 18.3 59.32 9.04 13.56 188.0 0.26 0.52 1.48 26.03 2.8 127.03 2.00 17.57 111.0 0.33 0.665 0.74 13.2 6.0 150.00 5.04 44.59 24.0 0.047 0.08 0.17 2.38 3.3 141.18 3.36 27.65 22.0 0.038 0.11 0.13 1.82 5.0 169.23 6.04 29.23 9.0 0.019 0.034 0.07 0.98 3.7 139.14 3.47 29.05 7.8 0.023 0.047 0.07 0.66 6.0 117.82 12.00 34.74 2.52 0.0045 0.0114 0.02 0.29 4.5 168.00 4.00 30.00 2.12 0.004 0.008 0.01 0.14 3.8 176.67 5.71 33.33 1.5 0.002 0.0035 0.01 0.08 2.3 277.78 4.00 37.04
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Hypogene Speleogenesis: Hydrogeolog
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Published and distributed by Nation
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Foreword In 1998, the National Cave
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Figure 33. Maze caves in Siberia: B
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