A 1.16 Ma record of carbon accumulation in western European peatland during the Oligocene from the Ballymoney lignite, Northern Ireland
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The Oligocene Ballymoney lignite in Northern Ireland is one of the thickest lignites in Europe and provides the potential for comparing Holocene and pre-Holocene peatland evolution and its response to long-term climate change on time scales much greater than 10 ka. Samples were collected from 50 m of lignite and analysed for δ13C. Spectral analysis of the δ13C record reveals that the record contains significant frequencies at 0.21 m−1 and 1.12 m−1. These cycles are interpreted as the c. 100 ka eccentricity and 20 ka precession cycles, respectively. These cycles were then tuned and the duration was determined as 1.16 Ma with a carbon accumulation rate of 27 g C m−2 a−1. If long-term changes in lignite δ13C are related to changes in the δ13C of the exogenic carbon reservoir, and if the lignite Chattian age is accepted, then the lignite probably formed between 24.6 and 25.8 Ma. Comparison of the estimated carbon accumulation rate with other Cenozoic peatland carbon accumulation rates indicates that this rate appears to be insensitive to changes in the concentration of atmospheric CO2.