Evidence of fire in Australian Cenozoic rainforests
Introduction
Australia's remarkable arid-adapted modern flora stands in stark contrast to its Cenozoic record, which is dominated by warm and ever-wet rainforest communities (Macphail et al., 1994; Martin, 2006). The timing of this major climatic transition and the origin of Australia's dryland flora within a rainforest-dominated continent remain contentious (Crisp et al., 2004; Hill, 2004). Traditionally, the onset of aridity, and the associated increased frequency of burning, was suggested to commence in the mid-late Miocene (Martin, 1990; Kershaw et al., 1994; Martin, 2006) in southeastern Australia, with evidence (i.e., charcoal abundance) derived from studies on the Yallourn brown coals of the Latrobe Group (Blackburn and Sluiter, 1994). The onset of aridity reportedly terminated coal deposition in the Gippsland Basin (Sluiter and Kershaw, 1982) and limited Late Miocene sedimentation in the region (Kershaw et al., 1994). Recent evidence does however suggest that the Australian scleromorphic angiosperm vegetation may be older (Carpenter et al., 2015) and more persistent through the Eocene (Carpenter et al., 2014) in other parts of Australia.
This Cenozoic history of wet climates is also reflected in Australia's (particularly southeastern Australia's) geological record, with a long and semi-continuous record of forested peatland environments in regions such as the Gippsland Basin. Throughout the world, large peatlands and coal-forming systems are restricted to regions of very high rainfall and/or humidity (Stach et al., 1982), and in the Gippsland Basin, coals are deposited throughout the early Cenozoic, persisting into the Middle Miocene (Korasidis et al., 2018). The widespread occurrence of coals and coaly sediments in many of southeastern Australia's basins up to the mid-Miocene (Holdgate, 2003) is further suggestive that a wet climatic regime existed in the region well into the Neogene. Several authors however, suggest that seasonally drying climates were present in the mid-Miocene of the Gippsland Basin (e.g., Blackburn and Sluiter, 1994; Holdgate et al., 2007), while others propose that the onset of aridification and drying in Australia occurred during the late Neogene, as late as 1.5 Ma (McLaren and Wallace, 2010). In this study, we use new quantitative palynological, charcoal and colourimetry analysis to determine if the Latrobe Group peatlands record any evidence of fire and climatic drying from the Middle Eocene to Middle Miocene. The evolution of floral successions represented by the extensive brown coal lithotype cycles of the Latrobe Group through the Early Oligocene and Middle Miocene are also investigated in this study.
Section snippets
Geological setting
The Latrobe Valley of Australia (Fig. 1) contains Eocene to Miocene low ash (<5%) brown coals, with individual seams > 100 m thick and vertical multi-seam levels without parallel globally (e.g. up to 700 m thick) (George and Mackay, 1991; Holdgate et al., 1995). The Traralgon, Morwell and Yallourn formations are the main coal-bearing sequences, which within the Gippsland Basin are further subdivided into individual seams. In order of decreasing age, these are the T2, T1, T0, M2C, M2B, M2A, M1B,
Methodology
Six hundred and eighty four (684) new samples collected from the Loy Yang and Yallourn Open Cut Mines were quantitatively analysed using colourimetry measurements as outlined in Holdgate et al. (2014). New quantitative colourimetry analysis was completed on the upper M1B seam (78 samples), M1A seam (314 samples) and Y seam (292 samples). This new colourimetry analysis was completed because every palynology sample processed could then be accurately assigned to a particular lithotype based on its
Colourimetry analysis
The stratigraphic sections of the M2A, M1B, M1A and Y seams consist of a series of lithotype cycles (Fig. 3) of variable thickness (5–30 m). The lithotypes are cyclic on a coarse scale and exhibit oscillations on a fine scale. Overall lithotype cycles lighten upwards (see Supplementary material 1), as supported by statistical analyses conducted by Mackay et al. (1985). Cycle boundaries are characterised by light or pale coals of the underlying cycle being overlain abruptly by laminated dark or
Depositional environments of the Latrobe Group lithotypes
New palynological and charcoal data confirms that each brown coal lithotype has a distinct floral component that is controlled by the peat-forming environment (Holdgate et al., 2014; Korasidis et al., 2016, Korasidis et al., 2017a). The laminated dark lithotypes of the Early Oligocene to Middle Miocene Morwell and Yallourn brown coal seams are characterised by high but fluctuating relative abundances of Cyatheaceae and Gleicheniaceae fern spores and of Banksieaeidites spp., Cyperaceae,
Conclusions
New palynological analysis of the Latrobe Group coals of the Gippsland Basin in Australia suggests that the distribution of charcoal and fire-adapted flora within brown coals is entirely controlled by facies and the paleoenvironments within the peatland, and does not result from drier climates as has been previously suggested. Charcoal and fire-tolerant floras are closely associated with emergent and meadow marsh environments that produced darker lithotypes. The low-nutrient and fire-prone
Acknowledgments
AGL Loy Yang and GHD are gratefully acknowledged for enabling the sampling of the M2A, M1B and M1A seams from the Loy Yang Open Cut Mine. Energy Australia is also gratefully acknowledged for enabling the sampling of the Yallourn seam from the Yallourn Open Cut Mine. We are also grateful to Dr. Alan Partridge for his insights into the identification of palynomorphs. The contributions of John Korasidis to the processing of colourimetry samples are also appreciated. This work was supported by an
References (63)
- et al.
A review and reinterpretation of evidence concerning the origin of Victorian Brown Coal
Int. J. Coal Geol.
(1990) - et al.
Sequence stratigraphic analysis and the origins of Tertiary brown coal lithotypes, Latrobe Valley, Gippsland Basin, Australia
Int. J. Coal Geol.
(1995) - et al.
A review of the Traralgon Formation in the Gippsland Basin—a world class brown coal resource
Int. J. Coal Geol.
(2000) - et al.
The Middle Miocene Yallourn coal seam—the last coal in Australia
Int. J. Coal Geol.
(2007) - et al.
Was the Oligocene–Miocene a time of fire and rain? Insights from brown coals of the southeastern Australia Gippsland Basin
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2014) - et al.
The origin of lithotype cycles in Oligo-Miocene brown coals from Australia and Germany
Int. J. Coal Geol.
(2016) - et al.
The nature and evolution of lithotypes in the Tertiary brown coals of the Latrobe Valley, southeastern Australia
Int. J. Coal Geol.
(1991) - et al.
Cyclic floral succession and fire in a Cenozoic wetland/peatland system
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2016) - et al.
Oligo-Miocene peatland ecosystems of the Gippsland Basin and modern analogues
Glob. Planet. Chang.
(2017) - et al.
New age controls on Oligocene and Miocene sediments in southeastern Australia
Rev. Palaeobot. Palynol.
(2018)
The origin of pale and dark layers in Pliocene lignite deposits from Yunnan Province, Southwest China, based on coal petrological and organic geochemical analyses
Int. J. Coal Geol.
Tertiary climate and phytogeography in southeastern Australia
Rev. Palaeobot. Palynol.
Cenozoic climatic change and the development of the arid vegetation in Australia
J. Arid Environ.
Plio-Pleistocene climate change and the onset of aridity in southeastern Australia
Glob. Planet. Chang.
Biogeographic, ecological and stratigraphic relationships of the Miocene brown coal floras, Latrobe Valley, Victoria, Australia
Int. J. Coal Geol.
The Oligo–Miocene coal floras of south-eastern Australia
Fire and the angiosperm revolutions
Int. J. Plant Sci.
What limits the spread of fire-dependent vegetation? Evidence from geographic variation of serotiny in a New Zealand shrub
Glob. Ecol. Biogeogr.
Early evidence of xeromorphy in angiosperms: stomatal encryption in a new Eocene species of Banksia (Proteaceae) from Western Australia
Am. J. Bot.
Fossil evidence for open, Proteaceae-dominated heathlands and fire in the Late Cretaceous of Australia
Am. J. Bot.
Radiation of the Australian flora: what can comparisons of molecular phylogenies across multiple taxa tell us about the evolution of diversity in present–day communities?
Philos. Trans. R. Soc. Lond. B
Flammable biomes dominated by eucalypts originated at the Cretaceous–Palaeogene boundary
Nat. Commun.
History of Australian aridity: chronology in the evolution of arid landscapes
Geol. Soc. Lond. Spec. Publ.
Petrology. The Science of Victorian Brown Coal: Structure, Properties and Consequences for Utilization
Fire and the Australian flora: a review
Aust. For.
The Snapper development, Gippsland Basin
Aust. Pet. Explor. Assoc. J.
The Geologic Time Scale 2012. 2-Volume Set
New species of Banksieaeformis and a Banksia ‘cone’ (Proteaceae) from the tertiary of central Australia
Aust. Syst. Bot.
Banksia born to burn
New Phytol.
Fossil evidence for the onset of xeromorphy and scleromorphy in Australian Proteaceae
Aust. Syst. Bot.
Origins of the southeastern Australian vegetation
Philos. Trans. R. Soc. Lond. B
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Gleichenia nagalingumiae sp. nov., a remarkably well-preserved fossil species with in situ spores from the Miocene of Australia
2023, Review of Palaeobotany and PalynologyCitation Excerpt :It has been reported that the Yallourn Seam of Middle Miocene age (16.4 to 14.5 Ma, C. bellus zone; Holdgate et al., 2007) has an abundance of rhizomes, pinnae, pinnules and spores, and the plant producing these remains is considered close to Gleichenia dicarpa (Blackburn and Sluiter, 1994). This taxon is most abundant in dark coals with high charcoal content indicating a relationship with fire and disturbance (Korasidis et al., 2016, 2019). The only fertile material described to date comes from late Pleistocene deposits in Tasmania where pinnules have been referred to the extant Gleichenia dicarpa based on the presence of two sori per pinnule (Jordan et al., 1991).
Petrology of the A and B Seams, Ermelo Coalfield (South Africa): Indications for changing palaeoenvironmental and sedimentary conditions
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2020, International Journal of Coal GeologyCitation Excerpt :Each environment produces distinct lithotypes and lightening-upwards cycles are interpreted as terrestrialization cycles. The observed colour change, from darker to lighter lithotypes, results from the environment evolving from anaerobic/inundated to less anaerobic/less moist settings via peatland aggradation (Korasidis et al., 2016, 2017a, 2019a). Floral successions in coal were also observed in the palynological studies by Anderson and Muller (1975) on the late Miocene Berakas coal in Brunei, and by Demchuck and Moore (1993) in Kalimantan, Indonesia.