T1. Geochronology

The basic aim of geochronology is to place significant events (geological, climatological and archaeological events) in the Earth’s history within a common and absolute temporal framework. The dating techniques are very varied and can be either relative or absolute. Absolute geochronology, which principals are based on the use of natural radioactive decay, is invaluable for anchoring relative chronologies within an absolute timescale. The principal methods that we are developing are magnetic and isotopic stratigraphies (relative methods), and radio-isotopic methods based on the analysis of uranium and thorium series, ¹⁴C, potassium/argon and argon-argon chronometry (absolute dating methods). These different relative and absolute methods can be applied to investigate and to date climatic archives (ice cores, continental and marine sediments, etc.), for a better understanding of the mechanisms governing our the climate and of serveral environmental processes such as, erosion, particulate and dissolved transfer, soils, groundwater, etc., as well as the dynamics of human settlement and associated cultural transitions. Most of these methods are also well suited to date geological samples (lavas, tephra, speleothems, sediments, corals...).

Sub-themes and associated methods:

T1.1 – Geochronology and Thermochronology

• Dating of continental and oceanic geological archives [K-Ar and ⁴⁰Ar/³⁹Ar, U/Th and ¹⁴C dating]

• Calibration of timescales – Standardisation of timescales [K-Ar and ⁴⁰Ar/³⁹Ar, U/Th and ¹⁴C dating, Archaeomagnetic dating, Magnetostratigraphy]

• ¹⁴C Calibration. Marine and lacustrine reservoir ages [¹⁴C, U/Th, Palaeomagnetism]

• Dynamics of volcanic systems [K-Ar and ⁴⁰Ar/³⁹Ar dating]

• Formation of mountain ranges [Low temperature thermochronology: (U-Th)/He and apatite and/or zircon fission track analysis - K-Ar and ⁴⁰Ar/³⁹Ar dating]

• Filling and inversion of sedimentary basins [Low temperature thermochronology: (U-Th)/He and apatite and/or zircon fission track analysis - K-Ar and ⁴⁰Ar/³⁹Ar dating]

• Evolution of passive margins [Low temperature thermochronology: (U-Th)/He and apatite and/or zircon fission track analysis - K-Ar and ⁴⁰Ar/³⁹Ar dating]

T1.2 - Archaeometry and archaeology

• Chronology of settlements, Evolution of societies [K-Ar and ⁴⁰Ar/³⁹Ar dating] [¹⁴C], [U/Th] etc.

• Emergence and evolution of prehistoric art [¹⁴C] and [U/Th]

• Characterisation of diet [δ¹³C, δ¹⁸O, δ¹⁵N]

• Characterisation of technological choices (organic temper in pottery, textile fibres, etc.) [δ¹³C, δ¹⁵N]

• Transhumance, agropastoralism [δ¹⁸O]; [⁸⁷Sr/⁸⁶Sr]

T1.3 - Dating of climate archives

• Dating of ice cores, forcings and climate variations at orbital and millennial scales [Absolute dating through measurement of ⁴⁰Ar/³⁶Ar and ³⁸Ar/³⁶Ar ratios; Orbital tuning through O₂/N₂ and δ¹⁸O of O₂; Ice age vs gas age relative dating based on the δ¹⁵N of N₂]

• Dating of continental climate transitions and events, at various scales, based on speleothems: history, millennium, climate cycles [U/Th] [¹⁴C]

  Dating of marine archives [U/Th]; [¹⁴C]

• The relationship between climate and volcanism [⁴⁰Ar/³⁹Ar and ⁴⁰Ar/³⁸Ar/³⁶Ar dating]; [δ¹⁸O isotopic stratigraphy]

• Changes in ocean circulation : the relationship between climate and ocean circulation [¹⁴C]; [δ¹⁸O isotopic stratigraphy]; [Palaeomagnetism, Magnetostratigraphy]

• Dating of lacustrine and palustrine records: ¹⁴C for lacustrine records, ostracods and pollen for palustrine records, and marine mollusc shells, Gamma-Ray Spectrometric dating. [¹⁴C ]; [Gamma-ray Spectrometer]

• Dating of loess sequences: Bulk ¹⁴C dating and ¹⁴C dating of specific molecules [¹⁴C]

• Chronology of sedimentary formations, establishment of marine and fluvial terraces, aridification and formation of dune fields, moraines, etc. ¹⁴C dating of macro-remains. [¹⁴C]

• Archaeometry [δ¹³C, δ¹⁵N], [⁸⁷Sr/⁸⁶Sr]

T1.4 – Dating of groundwater

- Evaluation of residence-, transit-, and renewal times [CFCs, SF6]; [¹⁴C].