Speleogenesis and karst landform development in central Scandinavia: An overview

Category Geomorphology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Lauritzen, Stein-Erik
Holding Date 08 September 2008

Karstification of the Caledonian metacarbonates in Scandinavia developed in pace with a landscape that was heavily eroded during the Quaternary glaciations. Caledonian nappe tectonics sealed and removed all porosity (bedding planes, cross-joints, etc., which normally are loci for speleogenesis in unmetamorphosed karst rocks), leaving marble with hydrogeologic properties resembling granite. Rifting, doming and unloading through erosion and glaciation left a structural template of inclined bands (marble stripe karst) penetrated by tectonic fractures. Incipient water flow was controlled by in situ stress and unloading.
Paleo- and hypogean karst is unknown; endokarst development is confined to the time-space between primary (paleic) surface and the present-day landscape. Most of the relief developed during Quaternary, accelerating during the last 800 kyr. Karstification occurred during ice cover (subglacial speleogenesis) and ice-free periods. Stadial water supply was dictated by the thermal conditions within ice-sheets. Clear-cut examples of subglacial corrosive flow are up-gradient, reversed flow with paragenesis and phreatic caves guided by (young) unloading valley fractures. Subglacial enlargement of pre-existing caves was efficient, cave passages enlarged under low-gradient flow. Chemical constraints made subglacial generation of proto-conduits from fractures (speleogenesis sensu stricto) inefficient. ’Cave inception’ most probably operated on unloading- and glaciotectonically reactivated fractures during subsequent interglacials when corrosion was more intense. Late-glacial stagnant (lacustrine) clays and silts demonstrate that many passages remained inactivated. Deglaciations provided high flow regimes yielding rapidly deposited gravel fills (even jøkulhlaups), resulting in a typical, upwards coarsening sedimentary cycle. Ice-dammed lakes were too transient to generate distinct speleogen phases, but did control clastic sedimentation.
Small karst forms were easily erased by glaciers, large landforms survived because they became surrounded by dry-based, stagnant ice. Relict caves in the present landscape may be explained by cycles of both interglacial and subglacial evolution phases. U-series dating of speleothems covers some 750 kyr, but are by their nature only minimum dates of the caves. Modeling suggests that only few, very large cave fragments may represent pre-glacial (Tertiary) speleogenesis. Pre-glacial cave fills are yet to be found. The region is characterized by a mélange of deranged subglacial and interglacial karst, leaving only remnants of ’true’ epikarst and truncated caves. Caves are polycyclic and polygenetic. Present (interglacial) processes are intense, creating lapies and large caves at optimum velocity.