Panoply - Themes presentation

T1. Geochronology

2017-06-29T12:44:10+00:00

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].

T2. Geochemistry and transfer of water and contaminants in the environment

2015-12-15T08:47:52+00:00

T2. Geochemistry and transfer of water and contaminants in the environment

The object of this theme is the reconstruction, using geochemical methods, of flows of water and of particulate or dissolved constituents, both within various environmental compartments (soils, surface water, groundwater, etc.) and between compartments. It seeks to evaluate the chemical quality of solutions and solids, to trace the origins of this quality by identifying the sources, and, finally, to evaluate the dynamics by using indicators of residence-, transit and renewal times.

Sub-themes and associated methods

The approach is based on three complementary aspects:

T2.1 Chemical quality of solutions and solids

Chemical quality of solutions (including the particulate phase) and solids (e.g. soils, sediments), which allow us to reveal the potential presence of contaminants in the broadest sense since we may be dealing with compounds that are toxic at low doses for humans and/or the environment (e.g. certain metals) or compounds that become problematic at high concentrations (e.g. water potability criteria: practically all elements are concerned).
[Chemical analyses of major-, minor- and trace elements]

T2.2 Tracing the origin of water and elements/compounds in continental hydrosystems.

This is carried out by comparing their geochemical and isotopic signatures with those of potential sources. This step allows us to construct a conceptual model of the transfers and to quantify exchanges between the different reservoirs present in the system under investigation.
[Chemical analyses of major-, minor- and trace elements] [ Isotopic analysis of O, H, C, He, Sr, B, metal] [¹⁴C ]

T2.3 Quantification of the dynamics of continental hydrosystems.

This is carried out by establishing time constraints that can be obtained from geochemical and isotopic records and by measuring the concentrations of radioactive- (decay) and radiogenic- (accumulation) elements, as well as the concentration of elements whose introduction chronology in the system is known (anthropogenic). Clearly this temporal information is invaluable for identifying the impacts (quantitative and qualitative) of climate change and human activity on resources (water, soils) and for evaluating current and future vulnerability of these resources.
[Measurement of ³H, ³He, ⁴He, CFCs, and SF6]; [¹⁴C]

T3. Palaeoclimatology and palaeoceanography

2015-12-15T08:47:52+00:00

T3. Palaeoclimatology and palaeoceanography

Palaeoclimatology is the science of past climates, which are studied on time scales that vary from a few thousand years to several million years. The deciphering of climate conditions and their natural variability is based on the study of natural archives from the earth’s principal compartment: the hydrosphere, cryosphere, atmosphere, lithosphere and biosphere. Today, the emergence of new analytical techniques allows a better-defined geochemical reading in terms of temporal and spatial resolution, through the use of in situ analysis and new climate proxies respectively.

Sub-themes and associated methods:

The four principal research axes developed at the LSCE and GEOPS are as follows:

T3.1 - Understanding the processes by which environmental parameters are recorded within the climate archives

Understanding the processes by which environmental parameters (T°, salinity, alkalinity, seawater pH, isotopic composition of precipitation, etc.) are recorded within the climate archives, which are mainly of sedimentary or biogenic origin.

T3.2 – Atmospheric water cycle dynamics.

Using water isotopes to trace the current origin of water vapour and the processes involved so as to characterise past climate variations from the archives.

T3.3 – Oceanic circulation dynamics

Oceanic circulation dynamics (palaeoceanography) and its role in climate variability and in the linkages between climate, the carbon cycle and acidification.

T3.4 – Reconstruction of continental palaeoenvironments

Reconstruction of continental palaeoenvironments using isotopes of hydrogen, oxygen, carbon and nitrogen in calcareous lacustrine organisms, speleothems, tree rings and loess organic matter so as to characterise variations in lake levels, temperature and precipitation.

In order to answer these scientific questions, the following analytical techniques are used:

IRMS (Isotope Ratio Mass Spectrometry) of (bio) carbonates for C and O isotopes (A2, A3, A5, A6)), and IRMS of clumped isotopes (D47) (A2, A3, A5, A6)
Continuous-flow IRMS for the DIC and O-C of seawater (A2)
IRMS (Isotope Ratio Mass Spectrometry) of water isotopes trapped within fluid inclusions (A6).
IRMS, ¹⁷O and ¹⁸O of ice (A1)
IRMS, ¹³C and ¹⁸O of tree rings (A4)
EA-IRMS for ¹³C and ¹⁵N in sediments and soils (T3.1, T3.2, T3.3)
Picarro D/H CRDS (water) (A1)
Laser granulometry (A2, A3)
Cryogenic magnetometers, Micromag (AGM2900), Curie scale (A2, A3)
Magnetic susceptibility (A2, A3, A6)
X-ray diffractometry (A2, A3)
MC-ICP-MS Actinides Pa/Th, U/Th (A2, A3, A5, A6) ; lanthanides (A2, A3, A5), stable Li and B isotopes (A5); Sr isotopes (A2, A3, A5, A6); Nd isotopes (A2, A3, A5)
ICP-AES measurements of Mg/Ca trace elements (A2, A3, A5, A6)
ICP-QMS measurements of B/Ca, Li/Mg, Sr/Ca, REE, U and major- and trace elements (A5, A6)
ICPMS-HR measurements of B/Ca, Li/Mg, Sr/Ca, REE, U and major- and trace elements (A5, A6)
ECHoMICADAS (A2, A3, A5, A6)

Climate archives analysed:

A1/ Ice
A2/ Marine sediments
A3/ Continental sediments
A4/ Tree rings
A5/ Biocarbonates
A6/ Speleothems

T4. Sedimentary transfers, diagenesis and resources

2017-06-14T09:59:20+00:00

T4. Sedimentary transfers, diagenesis and resources

The object of this theme is the reconstruction of soil erosion, the transfer of sediments and contaminants at the earth’s surface, their transport to sedimentary basins and all of the transformations that occur during their burial. The methodological approach adopted is varied and includes sedimentology, geochemistry, magnetic properties, measurement of radioactive tracers, etc. This approach allows us to extract significant information, at various time scales from different types of natural samples (sediments, water, rocks, minerals, etc.). The information retrieved throws light on the formation conditions (deposition conditions, sedimentary environment, hydrolysis conditions, etc.), on export conditions (erosion, percolation, fracturing, burial, etc.) and on long-term transformations (burial diagenesis, modification of petro-physical properties, fluid-rock interactions, etc.) The studies focus on current environments (transfer of particles and contaminants, evolution of carbon in the soil and in aquatic environments, etc.) and past environments, landscape evolution, palaeoclimate and the accumulation of resources within reservoirs (hydrocarbons, metals, materials).

Sub-themes and associated methods:

T4.1 – Erosion, chemical alteration and sedimentary dynamics in the past

Climate changes and sedimentary dynamics [Laser granulometry, X-ray diffractometry, SEM, Environmental magnetism, Cathodoluminescence microscopy]
Clay sedimentology [X-ray diffractometry]
Reconstruction of marine currents [Laser granulometry, X-ray diffractometry, SEM, Environmental magnetism]

T4.2 Diagenetic evolution of sediments. [X-ray diffractometry, SEM, Cathodoluminescence microscopy, Water porosimeter, Optical microscopes]

Characterisation of fluid-mineral interactions [X-ray diffractometry, SEM, Cathodoluminescence microscopy, Water porosimeter, Optical microscopes]
Characterisation of mineralogical transformations [X-ray diffractometry, SEM, Cathodoluminescence microscopy, Optical microscopes]
Characterisation of the transformations of organic matter [EA-IRMS]
Relationships between deposition environments and diagenetic evolution [X-ray diffractometry, SEM, Cathodoluminescence microscopy, Optical microscopes]

T4.3 Study of the mechanisms and chronology of the physico-chemical processes leading to the formation of exploitable deposits [X-ray diffractometry, SEM, Cathodoluminescence microscopy, Water porosimeter, Optical microscopes]

Dating of newly-formed phases [SEM, Cathodoluminescence microscopy, Optical microscopes, LA-ICPMS-HR]
Characterisation of the geometry of sedimentary bodies and the link with porosity and permeability properties. [SEM, Cathodoluminescence microscopy, Optical microscopes]

T4.4 – Current soil erosion – transfer of particles and contaminants - Dynamics of environmental change

Chronological reconstruction of pollution and sedimentation [Gamma-Ray spectrometry, ICP-QMS]
Radio-isotopic chronometry of particle transfer processes [Gamma-Ray spectrometry]
Soil carbon dynamics and vulnerability [¹⁴C, ¹³C, ¹⁵N]
The dynamics and fate of organic matter in aquatic environments (rivers, seas and oceans) [¹⁴C, Tritium, ¹³C]
Landscape geomorphology and evolution (valley formation, etc.) [Gamma-Ray spectrometry, ICP-QMS]
Fate and persistence of artificial ¹⁴C emissions. [¹⁴C]
The dynamics of natural and anthropogenic magnetic particles in river systems [Environmental magnetism]
Analytical tools (associated themes):
Lithological thin-section workshop (preparation of thin-sections of rock and unconsolidated sediments) (T4.2, T4.3)
Métromesures impregnation cell (T4.2, T4.3)
Optical microscopes (T4.2, T4.3)
Cathodoluminescence microscopy (T4.1, T4.2, T4.3)
X-ray diffractometry (clay-, rock-, and sediment mineralogy) (T4.1, T4.2, T4.3)
Wet-phase laser granulometry (T4.1)
Scanning electron microscope equipped with an EDS sensor (T4.1, T4.2, T4.3)
Cryogenic magnetometers, Magnetic susceptibility test bench, Micromag (AGM2900), Curie scale (T4.1, T4.4)
Low-background gamma spectrometry (T4.4)
EA-IRMS (T4.2, T4.4)
Trace and major element ICP-QMS (T4.4)
MC-ICPMS of Sr isotopes (T4.4)
ECHoMICADAS ¹⁴C (T4.4)