Macrofossils as indicators of Plio-Pleistocene climates in Tasmania and Antarctica

Abstract

7001.Plant macrofossils can be used as proxy palaeoclimatic indicators, since both the taxa present at a site and the form ofleaves depend on the climate, and macrofossils are rarely transported far. In the simple case of the Sirius Group Nothofagus leaves and wood in Antarctica, the fossils provide data on climate that suggest temperatures at the time of deposition were in the order of> 10°C warmer than at present. While the age of the fossils is still debated, the climatic signal is not. However, in more subtle cases, where the climatic differences are smaller and the fossil evidence is more complex, it is critical to interpret the evidence cautiously. Mactofossils from Pleistocene localities in Tasmania provide a clear signal on temperature and rainfall that is sometimes at odds with pollen-based reconstructions, but the former is inherently likely to be more accurate.

Early Eocene estuary at Strahan, Tasmania

“…In all four localities the Tertiary sediments are overlain unconformably by cobble/boulder gravel of Pleistocene age (Jordan et al 1995;Hill & Jordan 1996;Jordan 1997).…”

Contrasts between the Climatic Ranges of Fossil and Extant Taxa: Causes and Consequences for Palaeoclimatic Estimates

“…The presence of some of these taxa, notably Lauraceae, has been used to infer warm climates in the Tertiary. While the climate at the time of deposition of the RPU2 sediments may have been warmer than it is now, the most parsimonious solution is that the climate was no warmer than it is now (Hill and Jordan 1996), and a number of 'Tertiary' taxa were quite cold-tolerant. These taxa probably became extinct during Pleistocene glacial periods, but would have been quite viable in climates as cool as modern Tasmania.…”

“…Some of the climatic data in this work are also presented by Hill and Jordan (1996). Climatic ranges of Australian taxa were calculated using monthly precipitation and mean maximum and minimum temperatures estimated by ESOCLIM (H. A. Nix, J. P. Busby, M. F. Hutchinson and J. P. McMahon, unpublished data;Hutchinson 1991) for a large data set of compiled point distribution data (Floyd 1990; Environmental Resources Information Network, Department of Environment and Land Management, Tasmania; Tasmanian Herbarium; Australian National Herbarium; Australian National Botanic Gardens Herbarium).…”

“…For most fossil deposits there was a clear region of overlap of the climatic envelopes of most NLRs. This is assumed to provide reasonable limits on the estimates of palaeoclimate at the time of deposition (see Hill and Jordan 1996). The climatic ranges of some NLRs fall outside this envelope, and such taxa are identified as anomalies.…”

“…The upper limit of the temperature range is not increased significantly without considerable further relaxation of the parsimony. Thus, allowing for errors in the estimates, then the most parsimonious solution is that the climate was no warmer than it is now, and perhaps cooler by about 3°C (see Hill and Jordan 1996).…”