April 28th 2017

Dating the age of landscape formation

Ivö: Weathered bedrock at Ivö in southern Sweden.
An international research team led by the Geological Survey of Norway (NGU) has just published a research article in the prestigious journal Nature Communications.

Here the authors describe results from the dating of illite clay formed during the chemical weathering of rock using the K/Ar (Potassium-Argon) geochronological dating method. The K/Ar dating method has long been used by geologists to date the formation of rocks, or strictly speaking to date when molten lava cools and becomes solid rock. However, the methodological advances described in the paper allow for dating of extremely fine-grained material such as the clay mineral illite. This has barely been tested before and is thus a scientific breakthrough with interesting geoscientific implications. Clays form as secondary minerals when rock weathers through chemical interaction with water. Rock weathering is a fundamental part of the geological rock cycle, disintegrating bedrock and  producing sediments. It is also a critical concept in geomorphology - the study of the origin and evolution of Earth's surface topography and landforms - where chemical weathering is an important landscape-forming agent creating so-called etch surfaces. With these advances it is now possible to estimate/determine the age of rock weathering and landscape formation.

The new method was first tested at two locations with a known age of chemical weathering. The authors then applied the method on the so-called strandflat, a coastal landscape in western Norway, where they mapped and sampled weathering profiles. The strandflat is a very low relief rock landscape close to the present sea level that is common along much of the Norwegian coast and some other high latitude areas.
The age and origin of the strandflat has been debated by scholars for more than a century, among others by famous researchers like Hans H. Reusch and Fridtjof Nansen.

The new results in this study show that formation of the strandflat landscape in western Norway originated in a tropical climate during the Mesozoic (about 200 million years ago). The strandflat was subsequently covered by younger sedimentary rocks, and has only recently been exposed again as a relict landscape from times long past.

During the course of the project a state-of-the-art K-Ar laboratory has been built at the Geological Survey of Norway in Trondheim, with the unique capability to separate, characterize and date fine- grained material such as illite clay. This laboratory facility can help solve geochronological problems in the fields of for example geomorphology, structural geology, sedimentology and hydrocarbon reservoir research.

Ref:: The inheritance of a Mesozoic landscape in western Scandinavia. Authors: Ola Fredin, Giulio Viola, Horst Zwingmann, Ronald Sørlie, Marco Brönner, Jan-Erik Lie, Else Margrethe Grandal, Axel Müller, Annina Margreth, Christoph Vogt og Jochen Knies. Nature Communications (DOI: 10.1038/ncomms14879)

Bömlo: Geologist Ola Fredin investigates a narrow zone of weathered bedrock at Bømlo, southwestern Norway.

Relaterte prosjekter

"Basement fracturing and weathering on- and offshore Norway - Genesis, age, and landscape development" (BASE).