zircon; orbital parameters; Early solar system; Milankovic cycles; sedimentary cycles; Proterozoic; geochronology; vocanic ash beds; U-Pb dating
Percival L. M. E., Davies J. H. F. L., Schaltegger U., De Vleeschouwer D., Da Silva A.-C., Föllmi K. B. (2018), Precisely dating the Frasnian–Famennian boundary: implications for the cause of the Late Devonian mass extinction, in Scientific Reports
, 8(1), 9578-9578.
Davies Joshua H. F. L., Sheldrake Tom E., Reimink Jesse R., Wotzlaw Jörn-Frederik, Moeck Christian, Finlay Alex (2018), Investigating Complex Isochron Data Using Mixture Models, in Geochemistry, Geophysics, Geosystems
Farina Federico, Dini Andrea, Davies Joshua H.F.L., Ovtcharova Maria, Greber Nicolas D., Bouvier Anne-Sophie, Baumgartner Lukas, Ulianov Alexey, Schaltegger Urs (2018), Zircon petrochronology reveals the timescale and mechanism of anatectic magma formation, in Earth and Planetary Science Letters
, 495, 213-223.
Davies J.H.F.L., Stern R.A., Heaman L.M., Moser D.E., Walton E.L., Vennemann T. (2018), Evaluating baddeleyite oxygen isotope analysis by secondary ion mass spectrometry (SIMS), in Chemical Geology
, 479, 113-122.
The interactions between the Sun, the Earth, the Moon and the other planets of our solar system have manifold influences on the environment. The combination of the eccentricity of Earth's orbit as well as the precession and obliquity of its spin axis produce cyclic changes in the insolation curve at a given spot on Earth, known as Milankovic cycles (Milankovic, 1941), and are the major driver of the cyclic changes of our climate. These cycles can be reconstructed back in time from bedded sedimentary deposits that record the orbital parameters through strongly climate-dependent input into a sedimentary basin. A second type of interaction between the solar system and processes on Earth is caused by the Earth-Moon tidal friction (transfer of energy and angular momentum of Earth's rotation to Moon's orbital motion), which is slowing down Earth's rotation as well as causing the recession of the Moon from the Earth. These interactions are recorded in the sedimentary record by rhythmically layered tidalites in delta settings, where they represent semi-diurnal or diurnal tidal cycles. Very astonishingly (and fortuitous for us), some of these cyclic and rhythmic sedimentary features are still preserved in Paleo- to Neoprotoerozoic sedimentary rocks and can be counted in order to determine the length of days, months and years in the deep geological past (Williams, 2000). This project plans to make a novel contribution to the knowledge of the orbital parameters of our solar system in the Proterozoic by direct dating of volcanic ash beds occurring as layers in rhythmic and cyclic sedimentary rocks, by applying high-precision U-Pb dating techniques using the mineral zircon. Combining these highly precise U-Pb dates and sophisticated Bayesian depositional rate models with orbital tuning (recognition of orbitally forced sedimentary cycles) in chemical and clastic depositional environments, we will determine the length of sedimentary cycles, assign them to orbital parameters (eccentricity, obliquity, precession) and directly determine their durations. We have identified undisturbed and spectacularly well-preserved Proterozoic sedimentary sequences in Western Australia (Hamersley basin), in the Northwestern Territories in Canada (Slave province), and in Eastern Brazil (Diamantina basin). Our precise age determinations on zircon in interbedded ash layers will be used to establish age models based on Bayesian probabilistic statistics (Parnell et al., 2008) and calculate durations of presumed orbital cycles. The data will finally be integrated in numerical models of orbital mechanics of early solar system.In conclusion, the project will potentially create the following new knowledge:•Establish quantitative age models through high-precision U-Pb and probabilistic age modelling for Paleo- and Mesoproterozoic sedimentary sequences on three continents and demonstrate that they are orbitally forced.•Calculate the durations of these cycles and compare them to modern astronomical solutions (Laskar et al. 2011).•Calculate orbital parameters for the solar system 2.5, 1.9 and 1.4 Ga ago. The results will possibly give independent information on the orbital mechanics of the solar system in deep time.