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Integrated absolute dating approach for terrestrial records of past climate using trapped charge methods

Periodic Reporting for period 3 - INTERTRAP (Integrated absolute dating approach for terrestrial records of past climate using trapped charge methods)

Reporting period: 2019-04-01 to 2020-09-30

The practice of tuning different climate proxies prevents the observation of regional response times of terrestrial archives to global changes. Thus, it is imperative to develop correlation protocols based on absolute chronologies. Loess-palaeosol deposits are continental archives of Quaternary paleoclimates and loess is generally considered an ideal material for the application of luminescence dating. The agreement obtained for 10-20 ka ages using different techniques has given us confidence in using the state of the art measurement protocols for young deposits, as confirmed by comparison with independent age control. INTERTRAP proposes detailed investigations of loess samples collected in close proximity to the transition to the recent soil, with the purpose of obtaining a temporal quantification of the ending of the Late Tardiglacial and the beginning of the Holocene on three continents. However, a series of recent luminescence investigations carried out on quartz of different grain sizes extracted from loess yielded severe age discrepancies for ages >~40 ka. While the cause of this observation is hitherto not fully explained, our studies prove that it is a general effect, potentially affecting deposits worldwide, and raising doubts on previous chronologies. Methodological studies within INTERTRAP will develop an integrated approach using luminescence and electron spin resonance investigations. This part of the study aims at unraveling the mechanism responsible for the observed discrepancies and developing innovative trapped charge dating measurement protocols based on quartz that will yield reliable ages for and beyond the last interglacial glacial cycle.
• INTERTRAP lead to the development of a unique combined luminescence and electron spin resonance research laboratory.
• Our luminescence dating studies on loess paleosol sequences question the practice of directly correlating rapid climate events identified for different archives in the absence of age control.
• Work was carried out for dating of the Pleistocene/Holocene boundary in loess-paleosol deposits over three continents. Extensive sampling campaigns have been carried out by INTERTRAP team members in Central and Eastern Europe, China and United States of America. We have shown that SAR-OSL dating of fine (4-11 µm) and coarse (˃63 µm) quartz provide consistent ages for the transition from the last glacial loess to the modern soil in the loess-paleosol sites. Preliminary results available show that the magnetic susceptibility reflects a gradual transition from the Last Glacial towards the Holocene, indicating that the onset of the magnetic signal enhancement produced by pedogenesis started around Termination 1 (~17 ka in the North Atlantic) as observed in radiocarbon-dated regional benthic δ18O stacks, but before the stratigraphic Pleistocene/ Holocene transition dated at 11.7 ka in ice core records (Constantin et al., 2018).
• Methodological studies carried out so far in the framework of INTERTRAP in luminescence and electron spin resonance dating using quartz show that an extended SAR laboratory dose response curve does not necessarily enable high doses to be recorded accurately, or provide a corresponding extended age range and infer that coarse grains (> 63 µm) give more reliable ages than fine (4-11μm) grains.
• Further work is in progress for better understanding the charge trapping sites and mechanisms of TL/OSL production in quartz grains for extending the applicable age range of quartz based luminescence dating.