HIGH PRECISION DTM-LASER-1M SURVEY AND ITS POTENTIAL APPLICATION FOR STRAIN ESTIMATION IN SEDIMENTARY ROCKS: EXAMPLE IN THE JURA MOUNTAIN OF SWITZERLAND

Balanced cross-sections of detachment folds are mainly based on information from geologic maps or seismic data. In most cases, strain accommodated at small scale, below the resolution of the current documents (typically 10-3 to 10 m-scale), is either ignored or qualified as “requisite strain” that includes sub-resolution structures and errors in the cross-section construction. Strain at microscale (millimeter to centimeter) can be locally estimated from hand specimens and thin-sections but strain accommodated by decametric structures, larger than the dimension of current outcrops but too small to be represented on a map or a cross section, is difficult to grasp.

The use of high precision Digital Terrain Model (1-2 points per square meter) can help to fill this information gap. The test area is located in the Jura Mountain of Switzerland, on the crest of a kilometer-size detachment anticline. The bedding of folded Mesozoic sedimentary rocks is clearly outlined by erosion and individual meter thick beds can be easily followed on the DTM, commonly over a few kilometers, even through slightly forested areas. This leads to an unmatched precise mapping of metric to decametric tectonic structures like small strike-slip faults and hinges of second-order folds. This new information, coupled with conventional structural analysis, greatly increases precision of the geologic map up to a point where strain accommodated by decametric structures can be estimated.