Karstbase Bibliography Database
Karstbase Bibliography Database
This is the first comprehensive study of cave inception and development in metacarbonate rocks. The main study area is a 40000km2 region in central Scandinavia that contains over 1000 individual metacarbonate outcrops, and has nearly 1000 recorded karst caves (with passage lengths up to 5.6km). The area, which was repeatedly glaciated in the late Cenozoic, comprises a suite of nappes in the Cambro–Silurian Caledonides, a paleic range of mountains with terranes presently occurring on both sides of the northern Atlantic. Information about the stripe karst and non-stripe karst outcrops and their contained caves was assembled into computer-based databases, enabling relationships between the internal attributes of the caves and their external geological and geomorphological environments to be analysed. A rather consistent pattern emerged. For example, karst hydrological system distances are invariably shorter than 3.5km, and cave passages are positioned randomly in a vertical dimension, whilst commonly remaining within 50m of the overlying surface. This consistency is suggestive that the relevant cave inception, development and removal processes operated at a regional scale, and over long timescales. A consequence of the epigean association of caves with the landscape is that cave development can only be understood in the context of the geomorphological evolution of the host region. A review of the latest knowledge of the inception and development of caves in sedimentary limestones concluded that the speleogenesis of the central Scandinavian caves cannot be explained by these ideas. Five new inter-related conceptual models are constructed to explain cave development in metacarbonate rocks in the various Caledonide terranes. These are:
1. The tectonic inception model - this shows that it is only open fracture routes, primarily created by the seismic shocks that accompany deglaciation, which can provide the opportunity for dissolution of metalimestone rocks that have negligible primary porosity.
2. The external model of cave development - this black-box approach reveals how the formation, development and destruction of the karst caves are related to the evolution of their local landscape. During the Pleistocene, these processes were dominated by the cycle of glaciation, leading to cyclic speleogenesis, and the development of ever-longer and deeper systems, where the maximum distance to the surface commonly remains within one-eighth of the extent of change in local relief.
3. The hydrogeological model - this demonstrates that the caves developed to their mapped dimensions in timescales compatible with the first two models, within the constraints imposed by the physics and chemistry of calcite dissolution and erosion, primarily in almost pure water. Relict caves were predominantly formed in phreatic conditions beneath active deglacial ice-dammed lakes, with asymmetric distributions on east- and west-facing slopes. Mainly vadose caves developed during the present interglacial, primarily vadose, conditions, with maximum dimensions determined by catchment area. Combination caves developed during both deglacial and interglacial stages. The cross-sections of phreatic passages obey a non-fractal distribution, because they enlarged at maximum rates in similar timescales. Phreatic cave entrances could be enlarged at high altitudes by freeze / thaw processes at the surface of ice-dammed lakes, and at low altitudes by marine activity during isostatic uplift.
4. The internal static and dynamic model of cave development - this white-box approach demonstrates that many caves have ‘upside-down’ morphology, with relict phreatic passages overlying a single, primarily vadose, streamway. Both types of passage are guided along inception surfaces that follow the structural geology and fractures of the carbonate outcrops. Dynamically, the caves developed in a ‘Top-Down, Middle-Outwards’ (TDMO) sequence that may have extended over several glacial cycles, and passages in the older multi-cycle caves were removed downwards and inwards by glacial erosion.
5. The Caledonide model - this shows that the same processes (with some refinements) applied to cave development in most of the other (non-central Scandinavian) Caledonide areas. The prime influences on cave dimensions were the thicknesses of the successive northern Atlantic glacial icesheets and the positions of the caves relative to deglacial ice-dammed lakes and to local topography. Other influences included contact metamorphism, proximity to major thrusts, and marine incursions. With knowledge of these influences for each area, mean cave dimensions can be predicted.
The thesis provides the opportunity for the five models to be extended, so that cave development in other glaciated metamorphic and sedimentary limestones can be better understood, and to be inverted, so that landscape evolution can be derived from cave data.