Final Report Summary - GTSNEXT (Towards the next generation of the Geological Time Scale for the last 100 million years – the European contribution to EARTHTIME)
Towards the next generation of the Geological Time Scale for the last 100 million years - the European contribution to EARTHTIME
GTSnext forms the European contribution to the EARTHTIME initiative. GTSnext is a Marie Curie Initial Training Network aimed at improving accuracy, precision and stability of the Geological Time Scale (GTS) and as a next step application of this time scale to outstanding research questions in Earth Sciences. For that purpose we trained a next generation of geologists equipped to apply and integrate numerical dating techniques.
The standard GTS is crucial for reconstructing Earth history, tracing mineral resources and predicting future climate. It shapes our awareness of deep (or geological) time and how accurately we can measure it. The principal scientific objective of GTSnext is to contribute to the next generation GTS for the last 100 million years. The projected time scale will both be stable and have an unprecedented accuracy, precision and resolution through integration and inter¬calibration of independent state-of-the-art numerical dating techniques. To achieve this, we selected the three most important techniques (40Ar/39Ar, U/Pb, astronomical tuning) and applied these methods in an integrated way to three successive time intervals (Neogene, 0-24 million years (Ma); Paleo¬gene, 66-24 Ma; and Late Cretaceous; 100-66 Ma). At the same time, we improved the methods and applied the new time scale to solve fundamental research questions. Below, we summarize the main scientific results of GTSnext.
Intercalibration of dating techniques
For the projected time scale, it is essential that different methods yield the same age when the same event is dated. Thus intercalibration of the three independent dating techniques stood at the base of - the success of - GTSnext. In particular, we focused on the age of the mineral sanidine from the Fish Canyon tuff (FCs), as this is the most widely used standard in 40Ar/39Ar dating and plays a crucial role in the construction of the standard GTS. Intercalibration with astronomical dating had provided an age of 28.201 ± 0.046 Ma (Kuiper et al., 2008). But this age has been challenged, resulting in age differences of more than one million years for the Cretaceous-Paleogene (K/Pg) boundary when dinosaurs became extinct as a consequence of asteroid impact. However, studies within the framework of GTSnext have confirmed the astronomically calibrated age of 28.201 Ma, providing an age of 28.172 ± 0.028 Ma (Rivera et al., 2011). Moreover, single crystal U/Pb zircon dating of two samples from the FC tuff itself produced eruptive ages of 28.183 ± 0.035 Ma and 28.196 ± 0.0018 Ma, again in excellent agreement with our FCs age (Wotzlaw et al., subm.). The FCs age of 28.201 Ma was adopted in GTS2012, the new standard time scale of Gradstein et al. (2012), as calibration model for all 40Ar/39Ar ages (Schmitz, 2012).
Extension of the Astronomical Time Scale
The standard geological time scale for the Neogene, i.e. the last 23 million of years of Earth history, was already largely based on astronomical dating in 2004 (GTS2004: Gradstein et al., 2004). Time was ripe to extend this astronomical time scale back into the Paleogene and late Cretaceous, and the astronomically calibrated age of the FCs standard played a crucial role in this attempt. Cyclic deep marine sections in Spain proved perfectly suitable for constructing an ATS for the Paleocene (Kuiper et al., 2008; Hilgen et al., 2010) and the Maas¬trichtian, the youngest stage of the Cretaceous (Batenburg et al., 2012). Two options are presented for the Maastrichtian, based on selected ages of 65.95 and 65.68 for the K/Pg boundary, but only the former is consistent with our preferred age of the FCs. The older age is further supported by youngest single crystal U/Pb zircon ages for an ash layer intercalated slightly above the K/Pg boundary in a continental section in Canada (Heredia et al., in prep.). The astronomical time scale for the Early Paleogene has been incorporated in the Paleogene chapter in GTS2012 (Vandenberghe et al., 2012), although a competing time scale with a much younger age for the K/Pg boundary has been published by Westerhold et al. (2012). The latter, however, is inconsistent with the results of GTSnext. Furthermore, the major discrepancy between ages for the Eocene-Oligocene (E/O) boundary around 34 million years ago (Ma) has been significantly reduced by new improved radio-isotope dates of ash layers in continental sections in North America (Sahy et al., in prep.).
Application of the Geological Time Scale
The next generation GTS is critical to understand Earth history. But even the Neogene time scale is hampered by uncertainties in tuning of the Early Miocene and values fir tidal dissipation and dynamical ellipticity in the astronomical solution; the latter is key for reconstructing climate response to orbital forcing in the Miocene. Deep-sea cores were used to construct an astronomical tuning to eccentricity for the interval between 20 and 24 Ma; this includes the Oligocene/Miocene (O/M) boundary marked by a major glaciation (Liebrand et al., 2011; in prep.). The Monte dei Corvi section in Italy and deep-sea cores in the equatorial Atlantic were instrumental in solving the tidal dissipation/dynamical ellipticity issue, allowing phase relations between orbital forcing and climate response in the Miocene to be calculated for the first time (Zeeden et al., 2012; in prep.). The Paleogene time scale is critical to understand the role of astronomical climate forcing or other processes during hyperthermals, i.e. short periods of extreme warming that may provide clues for future climate change as a consequence of present-day greenhouse warming. Similarly, solving the time scale problems around the E-O boundary will help to address why Antarctic ice sheets expanded dramatically at the transition from Greenhouse to Ice House world.
Improving the numerical dating methods
Apart from contributions to the next generation GTS directly, a special task was carried out by ERs to improve the numerical dating methods themselves. Regarding the astronomical dating method, we contributed to the understanding of the chaotic behaviour of the main asteroids and the effect this has on the stability of the astronomical solution on the long term (Laskar et al., 2011a). This solution is now potentially accurate back to 54 Ma (Laskar et al., 2011b). We also published a revised 238U/235U ratio for terrestrial zircons (Hiess et al., 2012), which has fundamental implications for uranium-lead geochronology and cosmochronology (Stirling, 2012). In 40Ar/39Ar dating, Morgan et al. (2011) discuss the theoretical approach and technical design of a gas delivery system to precisely measure 40Ar concentrations necessary to accurately determine ages of mineral dating standards and, hence, improve the independent standard age determination by the K-Ar decay system.
Summarizing, GTSnext made a significant contribution to the next generation GTS for the last 100 Myr. This was achieved by improving both the current time scale as well as the underlying numerical dating methods. Part of the results has been incorporated in GTS2012 (Gradstein et al., 2012). We also applied the new time scale to address fundamental problems in Earth Sciences, such as the phase relations between climate response and orbital forcing (Zeeden et al., in prep.). A much improved GTS that will not undergo any significant changes is of great benefit for the entire Earth Science community, industry and academia alike.
Website: www.gtsnext.eu / Contact: Dr. F.J. Hilgen (fhilgen@geo.uu.nl) or Dr. K.F. Kuiper (k.f.kuiper@vu.nl)
References: Batenburg, S.J. et al., (in press) Cyclostratigraphy and astronomical tuning of the Late Maastrichtian at Zumaia (Basque country, Northern Spain). Earth Planet. Sci. Lett. / Gradstein, F.M. et al. (2012). The Geologic Time Scale 2012. Elsevier Publ. Comp, 1176p. / Kuiper, K.F. et al. (2008). Synchronizing Rock Clocks of Earth History. Science 320, 500-504. / Morgan, L.E. et al. (2011). A metrological approach to measuring 40Ar* concentrations in geological materials. Geochemistry, Geophysics, Geosystems, 12, A0AA20, 17p. / Rivera, T.A. et al. (2011). A Refined Astronomically Calibrated 40Ar/39Ar Age for Fish Canyon Sanidine. Earth Planet. Sci. Lett., 311, 420-426. / Schmitz, M.D. (2012). Radiogenic isotope geochronology. In: Gradstein, F.M. et al., eds., The Geologic Time Scale 2012. Elsevier Publ.Comp pp. 115-126. / Hiess J. et al., (2012) 238U/235U Systematics in Terrestrial Uranium-Bearing Minerals. Science 335, 1610-1614. / Laskar, J. et al. (2011a) Strong chaos induced by close encounters with Ceres and Vesta”, A&A 532, L4. / Laskar, J. et al. (2011b). La2010: a new orbital solutionfor the long-term motion of the Earth. A&A 532, A89. / Liebrand, D. et al. (2011) Antarctic ice-sheet and oceanographic response to eccentricity forcing during the early Miocene. Climate of the Past, 7, 869-880. / Stirling C.H. (2012) Keeping Time with Earth’s Heaviest Element. Perspective in Science 335, 1585-1586. / Vandenberghe, N. et al. (2012). The Paleogene Period. In: Gradstein, F.M. et al., eds., The Geologic Time Scale 2012. Elsevier Publ.Comp pp. 879-946. / Westerhold, T. et al. (2012). Time scale controversy: accurate orbital calibration of the early Paleogene. G., Geochem. Geophys. Geosyst., 13, Q06015. / Wotzlaw, J.-F. et al. (submitted). Tracking the evolution of a giant magmatic system from assembly to supereruption. / Zeeden, C. et al. (in press) Revised Miocene splice, astronomical tuning and calcareous plankton biochronology of ODP Site 926 between 5 and 14.4 Ma. Palaeogeography, Palaeoclimatology, Palaeoecology.
Note: a 2 page publishable summary is also attached as annex.