Journal of Conference Abstracts

Blowing Hot and Cold About Palaeoclimatic Records in Terrestrial Carbonates

Julian Andrews (j.andrews@uea.ac.uk)¹, Sarah Dennis¹, Paul Dennis¹, Martyn Pedley² & Richard Preece³

¹ School of Environmental Sciences, University of East Anglia,, Norwich NR4 7TJ, UK

² School of Geography & Earth Resources, University of Hull, Hull, HU6 7RX, UK

³ Department of Zoology, University of Cambridge, Cambridge, CB2 3ER, UK

During the last 30 years, and particularly in the 1990s, is has been quite well established that modern terrestrial carbonates, including microbial crusts, tufas, lacustrine, cave and soil deposits, record information about local environmental conditions. A number of studies have used stable carbon and oxygen isotopes to try and reconstruct climatic variables such as temperature, rainfall regime and climatically-related vegetation changes. In our work during the 1990s we have concentrated on riverine and lacustrine microbial carbonates and tufa deposits. Stable isotope work on these types of modern carbonates (Andrews et al. 1993; Andrews et al. 1996) suggests that in well-flushed environments mean ¹⁸O carbonate values are close to equilibrium values with local rainfall, suggesting that carbonate ¹⁸O can furnish information on water temperature and water isotopic composition. ¹³C values typically reflect the principal carbon source (e.g. soil-zone CO₂, atmospheric CO₂ or aquifer rock dissolution).

Based on these results it is possible that stable isotopic variation in Holocene microbial carbonates records similar climatic and environmental information. Our first attempt to test this was on an early Holocene back-barrage tufa deposit from Alport in Derbyshire, U.K. (Andrews et al. 1994). The results were encouraging and we were able to interpret systematic variation in the oxygen isotopes as reflecting temperature change, possibly associated with a Holocene climatic optimum. The only satisfactory way to test our interpretation was to repeat the coring and isotopic analyses both at Alport, close to our original site, and elsewhere in the UK where similar aged deposits exist. In this oral poster we present new isotopic data from a duplicate core at Alport and from a similar aged and environmentally well-characterized tufa sequence from Wateringbury in Kent. The degree of coherence in isotopic data from the three tufa sequences will demonstrate just how robust the isotopic palaeoclimatic record is in these types of terrestrial carbonate archives.

Andrews, JE, Riding, R & Dennis PF, Sedimentology, 40, 303-314, (1993).

Andrews, JE, Pedley, HM & Dennis PF, The Holocene, 4, 349-355, (1994).

Andrews, JE, Riding, R & Dennis PF, Palaeogeography, Palaeoclimatology, Palaeoecology, 129, 171-189, (1997).

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