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The new lithostratigraphic table of Switzerland – where do we stand?
Alain Morard

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-05 02:00 PM – 02:30 PM
Last modified: 2018-11-23

Abstract


A harmonised lithostratigraphic scheme and nomenclature for Switzerland has been developed by the Swiss Geological Survey, in close collaboration with the Swiss Committee for Stratigraphy (Strasky et al., 2013). This new scheme now serves as a standardised master legend for the Geological Atlas of Switzerland 1:25000 (GA25) and is currently being implemented in vector datasets of already published map sheets, that are stepwise integrated into the geological viewer of the Swiss Confederation (www.map.geo.admin.ch > Geocatalog > Nature and Environment > Geology > GeoCover). In parallel, valid units are briefly described in an online lexicon (www.strati.ch), that also links the old terminology with the new lithostratigraphic nomenclature.

However, this first step in the countrywide harmonisation of lithostratigraphy does not yet involve any geometrical modifications where cartographic mismatches occur, as this would imply a thorough revision of the individual geological maps, only achievable on the mid- to long-term. As a corollary, quite a large number of informal, no longer recognised unit assemblages (or parallel subdivisions) still have to be maintained, at least locally, as long as a new delimitation has been drawn (resp. provisional units have to be introduced until a formal definition is elaborated). Last but not least, many cartographic units are not – strictly speaking – of stratigraphic nature. This is particularly the case for tectonites, gangue rocks and purely petrographic map units, especially in crystalline basement but also for some sedimentary lithologies (e.g., characteristic facies recurring vertically or changing laterally without a clear stratigraphic succession within a formation, such as shell sandstone beds of the molasse). The present day state of work will be sketched based on the situation around the Jurassic/Cretaceous boundary.

In conclusion, in the transitional phase between the transposition of the harmonised lithostratigraphic master legend and the geometrical revision of the vector datasets, it is important that the remaining cartographic discrepancies be clearly documented, so that the end-user knows what is the validity and revision status of the different elements of the map he looks at. This is achieved through the use of a specific attribute highlitghting in which cases the mapped objects are truly up-to-date and – if not – what kind of inconstistency still remains to be resolved.