MC-ICPMS U-series dating
An important and central part of my work is U-series dating by MC-ICPMS. Highly precise
and accurate U and Th isotope measurements are very important for establishing
the timing of events and determining the rates of a wide variety of natural
processes in earth and planetary sciences or archaeology. I work with a ThermoFinnigan Neptune MC-ICPMS.
Details of my setup and procedures are published in various papers: Hoffmann et al. (2007), International Journal of Mass Spectrometry 264, 97-109;
Hoffmann (2008), International Journal of Mass Spectrometry 275, 75-79; Hoffmann et al. (2009), Chemical Geology 259, 253-261.
However, since then I have improved the setup by implementing three different Th isotope solutions for Th mesurements and four mixed 229Th/236U spikes with different Th/U ratios. My philosophy in MC-ICPMS U-series measurements is basically: quality over quantity, always double check setup and results and there is always something to improve.
U-series measurements are important to a wide range of applications in Earth Sciences, e.g. palaeoclimate research, or archaeology. My main field of interest is U-series dating with a focus on speleothems. more
Speleothem based palaeoclimate research
I am working on speleothems (e.g. stalagmites, flowstones, stalactites) from various parts of the world to investigate
climate conditions at the time of formation. Speleothems record fast, direct responses to local climate and provide
rich archives of climate change that are dateable at very high precision back to approximately 600ka BP using the U-Th technique.
The chronology of speleothem growth itself already provides important information about palaeoclimatic conditions.
For example, speleothem growth is related to the climatic conditions above the cave and depends on water availability in the epikarst system
which in turn depends on precipitation and evaporation. Speleothems found in desert areas which are currently too dry for speleothem
formation indicate substantially different climate conditions in the past. Or speleothems from currently submerged
caves can be used to constrain past sea levels. Changes of the speleothem growth rates are often related to changes in
precipitation intensity, temperature or vegetation cover above the cave. Speleothems are also archives for palaeoclimate
proxies such as stable oxygen and carbon isotopes or trace element (e.g. Mg, Sr, P) concentrations. Multiproxy studies on
stalagmites, involving combinations of stable isotopes and trace elements have enormous potential in identifying
process controls of speleothem formation in palaeoenvironmental studies. more
U-series dating of rock art
I am involved in an international team that works on a project to date Palaeolithic cave art of the Iberian Peninsula
by U-series techniques. My recent progress on minimising sample sizes needed
for U-Th dating makes it possible to date small amounts of carbonate taken from
deposits overlying (and in some cases underlying) cave art to constrain the age of the painting itself.
We work on many palaeolithic rock art sites including Altamira or Cuevas del Monte Castillo.
First results were published in 2012 pushing early cave art back to a minimum age of 40800 years (more).
Recently we published new results which show that Neandertals were cave artists.
U-series dating of archaeological sites and artefacts
In some cases archaeological sites are situated within karstic environments and stratigraphically related to secondary
calcite (or aragonite) formations. For example, in a cave calcite forms from percolating waters entering the cave. This results in
stalagmites, stalagtites or flowstones. Sometimes, calcite forms on top of archaeological remains such as bones or artefacts, or these
are found within sediments that overly / underly flowstones or stalagmites. U-Th dating can be used for the calcite and provides maximum
or minimum age constraints. My work on the Almonda cave system helped to constrain the age of the Aroeira cranium.
U-Th dating can also be applied to travertine or tufa formations. These are usually forming where spring waters reach the surface, areas which are attractive for humans and animals. Archaeological remains are found in such travertine and dating the formation of the travertine also provides an age for the archaeological remains. For example, human footprints were found embedded in travertine in the Tibetan Plateau and were dated to an age range between 8,000 and 12,000 years footprints.
Together with Denis Scholz (University of Mainz) I developed an algorithm to construct distance - age models for speleothems based on U-series dating results.
The algorithm uses U-series ages and the corresponding errors for modelling and also includes stratigraphic information in order to further constrain and improve the age model.
The algorithm provides a high degree of reproducibility and comparability and is designed for application by the general, non-expert user and has no adjustable free parameters.
This work has recently been published in Quaternary Geochronology. The algorithm can be obtained here free of charge.
I worked with David Richards and Pete Smart (University of Bristol) and Warren Beck (University of Arizona) on a project funded by NERC, where we analysed stalagmites from a submerged cave on Grand Bahamas. Sample GB-89-25-3 formed during the last glacial period between 44 ka and 28 ka. A robust chronology is based on 42 U-Th analyses and we analysed the sample for 14C. This allows to calculate the initial (atmospheric) 14C between 44 and 28 ka B.P. Our results are included in the IntCal13 calibration curve.