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Orbital tuning and correlation of 1.7 m.y. of continuous carbon storage in an early Miocene peatland

¹ School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK
² Department of Earth Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK
³ Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK

Peatland is an important terrestrial carbon reservoir that contains >25% of soil carbon and accounts for 25%–38% of natural methane emissions. Most of this carbon is contained in postglacial boreal peat. Our understanding of the carbon cycle within this reservoir and its links to the atmosphere is therefore restricted to periods of <10 k.y. A record of the longer-term behavior of the peatland carbon reservoir under nonglacial conditions does, however, exist in thick lignite deposits formed over periods of >1 m.y. Spectral analysis of varying lignite color reveals that 120 m of early Miocene lignite from the Gippsland Basin, Australia, contains a 1.7 m.y. record of orbitally paced climate oscillations dominated by the response to obliquity. Use of the regular orbital signal indicates that the average long-term rate of peatland carbon accumulation recorded in the lignite is 27.5 g·m^–2·yr^–1. This rate is constant over periods of >100 k.y. and is independent of shorter-term, <10 k.y., fluctuations in climate and hydrology. Matching the lignite record to the theoretical insolation curve indicates that the lignite formed between 22.5 and 20.8 Ma. Contemporaneous long-term changes in lignite color and the ¹³C/¹²C ratios of marine foraminifera may relate to changing peatland methane flux and thus point to a link between terrestrial and marine carbon dynamics.

Key Words: Miocene • lignite • carbon cycle • methane • astronomical calibration

This article has been cited by other articles:

				D. J. Large A 1.16 Ma record of carbon accumulation in western European peatland during the Oligocene from the Ballymoney lignite, Northern Ireland Journal of the Geological Society, December 1, 2007; 164(6): 1233 - 1240. [Abstract] [Full Text] [PDF]