Download PDF - Speleogenesis
Download PDF - Speleogenesis
Download PDF - Speleogenesis
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8<br />
NCKRI Special Paper No.1<br />
2. Karst in the context of the systematized and hierarchical<br />
nature of regional groundwater flow<br />
Artesian basins are principal hydrogeologic structures<br />
at regional scales in predominantly layered sedimentary<br />
rocks (sedimentary basins) that contain stratiform<br />
groundwater bodies (layered aquifers); and<br />
hydrogeological massifs are tectonic block-faulted<br />
groundwater bodies with an overwhelming dominance of<br />
crosscutting fissure-conduit permeability (Zaitzev and<br />
Tolstikhin, 1971; Pinneker, 1977). Transitional types<br />
include disrupted basins and layered massifs. In cratonic<br />
regions and their passive margins, large artesian basins<br />
predominate, with subordinated hydrogeological massifs.<br />
Folded orogenic regions are characterized by the<br />
dominance of hydrogeological massifs, although small<br />
artesian basins are also common. Basins and massifs are<br />
commonly hydraulically connected, with massifs playing<br />
the role of marginal recharge areas.<br />
Broad understanding of karst processes as a<br />
geological agent, one of the most powerful and universal<br />
illustrations of groundwater as a geological agent, is<br />
based on the growing recognition in mainstream<br />
hydrogeology of hydraulic continuity, the systematized<br />
nature and hierarchical organization of regional flow, and<br />
the great role of cross-formational communication in<br />
multiple-aquifer (multi-story) confined systems (e.g.<br />
Pinneker, 1982; Sharp and Kyle, 1988; Shestopalov,<br />
1981, 1989; Tóth, 1995, 1999). Principal categories of<br />
karst-forming environments and resultant karst/<br />
speleogenetic styles can be adequately understood and<br />
classified only within the context of regional groundwater<br />
flow systems, as they are regularly associated with<br />
distinct segments and evolutionary states of these<br />
systems. The works of Tóth (1995, 1999) provide a<br />
particularly useful and inspiring synopsis of the nature of<br />
the system, hierarchical organization, and the geologic<br />
role of regional groundwater flow systems.<br />
<strong>Speleogenesis</strong>, like other natural effects produced by<br />
groundwater flow systems, is a result of interaction<br />
between groundwater and its environment, driven by the<br />
various components and attributes of the two respective<br />
systems seeking equilibration (Tóth, 1999). To cause<br />
speleogenetic development, dissolution effects of<br />
disequilibria have to accumulate over sufficiently long<br />
periods of time and/or to concentrate within relatively<br />
small rock volumes or areas. The systematic transport and<br />
distribution mechanism capable of producing and<br />
maintaining the required disequilibrium conditions is the<br />
groundwater flow system (Tóth, 1999). This is the single<br />
fundamental reason why the principal categories of karst<br />
and speleogenetic environments should be distinguished<br />
primarily on the basis of hydrogeologic considerations,<br />
rather than by the particular dissolutional mechanisms<br />
involved.<br />
The development of groundwater circulation is<br />
broadly cyclic. The hydrogeologic cycle begins with<br />
marine sedimentation that is succeeded by tectonic<br />
subsidence and the formation of connate waters. It then<br />
encompasses uplift, with denudation and progressive<br />
invasion of meteoric waters into the reservoir. It may<br />
include the intrusion of magma with release of juvenile<br />
waters. It closes with a new marine transgression.<br />
Groundwater circulation in a basin adjusts to the<br />
pattern of maximum and minimum fluid potentials.<br />
Large-scale groundwater flow in sedimentary basins can<br />
be driven by several forces, such as sediment compaction<br />
due to burial or tectonic compression, dehydration of<br />
minerals, continental landscape topography gradients, and<br />
density gradients due to temperature or solute variations.<br />
Following uplift and establishment of the continental<br />
regime and topography, gravity-driven flow systems of<br />
meteoric groundwater increasingly flush out connate and<br />
resurgent waters from a basin, although compaction-