4th Swiss Geoscience Meeting, Bern 2006 Astronomical time scales for the Swiss and French Jura Mountains (Middle Oxfordian to Late Kimmeridgian)

Ever since Earth Sciences exist there has been a quest for measuring geological time. Relative time scales have been established through biostratigraphy and are constantly being refined. Radiometric dating furnishes absolute ages but error margins may still be large. Astronomical time scales use the sedimentary or geochemical record of insolation changes and are directly linked to orbital periodicities with known durations. Except for the Quaternary where other dating methods give yearly, decadal, or centennial time resolutions, astronomical time scales offer the highest resolution available for the geologic past. If the sedimentary systems were sensitive enough to record orbitally induced climate changes, and if the general time frame is constrained by radiometric dating, then a time resolution of 20’000 years (corresponding to the cycle of the precession of the equinoxes) can optimally be obtained. The Oxfordian and Kimmeridgian sediments of the Swiss Jura Mountains has been studied extensively since the 19th century (e.g., Heer 1865). Lithology and biostratigraphy of these mostly shallow-water carbonates are well known (e.g.