NJG90-3-02
2010
Morphology and speleogenesis of Okshola, Fauske, northern Norway: example of a multistage network cave in a glacial landscape
90
3
123-139
978-82-92394-64-9

Maze, or labyrinth, caves are high-porosity zones in karst. Reticular networks may arise through different speleogenetic processes. Here, we present and discuss an apparently multi-stage labyrinthal development in a stripe karst setting in the Norwegian Caledonides. Okshola (the upper part of the Okshola-Kristihola cave system at Fauske, Nordland) displays a network of preserved, essentially phreatic tubes intersected by four distinct, vadose inlet passages. The cave developed along a low-angle fracture (thrust) zone, which is sub-parallel with the foliation. Scallops in the walls of phreatic conduits demonstrate that water flow was directed down-dip into the rock mass, and thus that the phreatic network developed during the last active stage as a groundwater recharge zone. This flow function is consistent with the proximal location of the cave with respect to former topographically directed glacial flow. Cyclic and strong fluctuations in the hydraulic regime are evident from cave interior deposits. We suggest that Okshola developed in concert with the glacial erosion of the surface topography and that a process of caprock stripping resulted in progressive lowering of both sink and spring levels. Morphology, together with radiometric datings, indicate that speleogenesis commenced several glacial cycles ago.

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