Chemistry, radiocarbon ages, and development of a subtropical acid peat in Queensland, Australia

Abstract

A subtropical peat, developed on a costal plain in southern Queensland, has been studied with respect to its morphology, radiocarbon (¹⁴C) age, total organic carbon (C) content, stable C isotopic (δ¹³C) values, and spectroscopic characteristics (¹³C-NMR and FTIR). The combination of techniques allowed for an interpretation of changes in peat development over time, an assessment of paleoclimatic changes that apparently occurred during peat growth, and a comparison with perched lake sediments on Fraser Island.

Geochemical data from the peat showed a relative increase in abundance of aromatic C (which may include charcoal) from the Pleistocene to the early Holocene and much decreased abundances of aromatic C thereafter. This trend may be due to changes in fire frequency from the Pleistocene–early Holocene (high fire frequency) to the early and middle Holocene (relatively low fire frequency). This interpretation is consistent with other published data from this area, showing increased aridity, increased fire frequency and dominance of sclerophyll forest during the late Pleistocene–early Holocene.

Another significant geochemical change in the acid peat occurred within the middle to late Holocene. This period is characterised by highly ¹³C-depleted organic matter and a comparably high alkyl C (lipid) content. These data are interpreted as indicating wetter and year-round waterlogged conditions, possibly associated with poor drainage during the Holocene sea level maximum c. 5500–3000 years BP. By comparison, abundance of alkyl C decreased and δ¹³C values increased in the latest Holocene. The geochemical data from the acid peat point to the occurrence of a dry phase during the late Pleistocene to early Holocene and a wet phase in the middle to late Holocene, followed by another dry phase. These data correspond well with published data of 2 phases of dune formation (dry periods) in the early to middle Holocene and in the latest Holocene for North Queensland.