D/H COMPOSITION OF BIOMARKERS IN FRESHWATER SEDIMENTS: STABLE HYDROGEN ISOTOPES AS PALAEOTEMPERATURE INDICATORS

The stable hydrogen isotopic composition (dD) of selected aliphatic biomarkers in torbanites (of similar maturity and with similar biological inputs) from Scotland and Australia, covering the Late Carboniferous to the Late Permian, deposited under glacial, cool-temperate and tropical climate regimes have been determined. dD values were measured on a Micromass (IsoPrime) isotope mass spectrometer.

 

The n-alkanes in two Eastern Australian (Temi) torbanites, deposited during the Early Permian under glacial conditions are significantly depleted in deuterium (ca. 40‰ to 70‰) relative to n-alkanes in a torbanite from Scotland (Torbane Hill), deposited during the Carboniferous under a tropical climate regime. Two other Eastern Australian (Newnes) torbanites, deposited during Late Permian times under cool-temperate conditions, contain n-alkanes with dD values falling in between those of n-alkanes in tropical and glacial sediments. The dD values acquired for n-alkanes are in accordance with the typical dD values of meteoric waters.

 

A saw-toothed profile of dD values obtained for the n-alkanes in the Australian torbanites is attributed to a dual-source system, perhaps a predominant Botryococcus braunii input with a second minor contribution from land plants to odd-carbon-numbered n-alkanes. This finding supports previous work by Boreham et al. (1994) and Grice et al. (2001) who reported a similar but opposite profile of d¹³C values for the n-alkanes in these samples.

 

References

 

Boreham, C.J., Summons, R.E., Roksandic, Z., Dowling, L.M. and Hutton, A.C., 1994, Organic Geochemistry 21, 685-712.

 

Grice, K., Audino, M., Boreham, C.J., Alexander, R. and Kagi, R.I., 2001, Organic Geochemistry 32, 1195-1210.