Quaternary Geochronology

U-series and U-Pb capability for carbonate geochronology has been developed at NIGL to support NERC climate research, benefitting from extensive knowledge transfer from NIGL's U-Th-Pb geochronology facility. U-series (specifically 230Th/234U) geochronology projects currently in progress and recently completed include studies of speleothems, warm and cold water corals, terrestrial deposits (tufa), and lake sediments, as well as 234U/238U as a groundwater tracer work. Samples dated thus far have ranged in age from c. 450 ka to recent. Sample preparation takes place in NIGL's clean chemistry laboratories which are equipped with an ESI/New Wave Research micromill for microsampling, Evapoclean unit for total sample dissolution involving perchloric acid if necessary, and in-house ultrapure acid production. Samples are routinely analysed on a Neptune Plus MC-ICP-MS, although if required, U samples can be measured on NIGL's U-Pb geochronology Triton TIMS instrument.The Neptune is fitted with a variety of Faraday amplifier boards that would permit very high precision 234U/238U analysis if required by particular applications. Highly enriched mixed 229Th/236U tracers are used at NIGL and have been calibrated against gravimetric solutions prepared from high purity U and Th metals.

In addition to solution-mode U series analysis, NIGL has developed high-spatial resolution laser ablation ICP-MS techniques and characterised in-house carbonate materials by both ICP-MS and TIMS as standards, all specifically suited for U-Pb carbonate dating and rapid carbonate U-Th-Pb reconnaissance screening. Carbonate dating is done using the very fast scanning AttoM (Nu instruments) SF-ICP-MS, while screening is performed using either NIG's AttoM or NuHR MC-ICP-MS, both employing an ESI-New Wave Instruments 193 nm short UV laser microprobe for sampling. These techniques have been applied to a variety of projects including dating of >1 Myr old hominid fossils and >700 ka speleothems whose antiquity precludes analysis by the U-Th chronometer. Screening for U, Th and Pb concentrations and 207Pb/206Pb isotope ratio is routinely applied at NIGL to carbonates to determine sample suitability and aid refined sample selection for U-series or U-Pb chronology.

Some current projects

  • U-Pb dating of speleothems to constrain Plio-Pleistocene uplift rates in north west Borneo
  • Holocene climatic and cultural change in Cappadocia, Turkey
  • High resolution isotope analysis of Iberian speleothem deposits
  • Growth history of Mingulay Reef: uranium-series dating of cold-Wwter corals
  • Carbonates from Olduvai Gorge, Tanzania — palaeoenvironments and geochronology
  • Climate change and associated human responses in the Cuatro Cienegas Basin, north east Mexico, from the Late Pleistocene to the present
  • Dating landslip in the Cotswolds
  • Inferring the extent of scarp retreat and valley incision; evidence from the Ogof Draenen cave system, south Wales
  • U-Th-Pb Chronology of fracture filling carbonates in crystalline rocks