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Ratio mass-spectrometry
Botryococcus-braunii
Pyrolysis
Oil
D/h
Biomarkers
Sediments
Bitumen
Kerogen
Shale
Abstract:
We measured the stable hydrogen isotopic composition (deltaD) of selected aliphatic compounds in torbanites from Scotland and Australia, covering the Late Carboniferous to the Late Permian. The torbanites contain organic matter predominantly from a single algal source, Botryococcus braunii, and are of similar thermal maturity. The deltaD values of n-alkanes in the extracts appear to reflect the depositional palaeoclimate of each torbanite, in response to the typical deltaD values of meteoric waters. The deltaD values of n-alkanes in torbanites deposited at high latitude under glacial conditions are depleted in deuterium by up to 70parts per thousand relative to n-alkanes in a torbanite deposited at low latitude under a tropical climate regime. Torbanites deposited in mid-latitude regions under cool-temperature conditions contain n-alkanes with deltaD values between those of n-alkanes in tropical and glacial sediments. A saw-toothed profile of deltaD values obtained for the n-alkanes in the Australian torbanites is attributed to a dual-source system, perhaps a predominant B. braunii input with a second minor contribution from land plants. Pristane and phytane from two Australian torbanites are significantly depleted in deuterium relative to n-alkanes in the same samples and a significant difference between the deltaD values of pristane and phytane is suggested to be caused by different sources for the two isoprenoids, or isotope effects associated with their derivation from a common phytol precursor. The offset between the deltaD of values of n-alkanes and isoprenoids is similar to that found in modern biological samples, indicating that their indigenous deltaD signatures may have been preserved for at least 260-280 million years. (C) 2003 Elsevier Ltd. All rights reserved. [References: 37]
