Antarctic Peninsula King George Island

Many macrofloras have been discovered on King George Island in the South Shetland Island group, north of the Bransfield Strait in the Antarctic Peninsula region, currently dated between Late Palaeocene and Late Eocene in age. The floras may have lived at a palaeolatitude of ~62°S, similar to its present-day location (Lawver et al., 1992). The stratigraphy is complex because Birkenmajer (1981, 1989, 1990) and Birkenmajer et al. (1986) erected many local formations in comparison to a simpler scheme created by Smellie et al. (1984). No single stratigraphic scheme exists and so the relationship between the floras is confusing. The stratigraphic framework used here includes both schemes (also reviewed by Hunt, 2001). Leaf macrofloras, currently understood to be of Late Palaeocene to Middle Eocene in age, have been described in varying completeness from the Admiralty Bay and Fildes Peninsula areas of the island.

In the Admiralty Bay area, the Middle Eocene Mt. Wawel Formation (Point Hennequin Group) contains the macroflora deposits collectively known as the Point Hennequin Flora with individual localities named Mount Wawel and Dragon Glacier Moraine floras (Zastawniak et al., 1985; Birkenmajer and Zastawniak, 1989a; Askin, 1992; Hunt, 2001; Hunt and Poole, 2003). The Mount Wawel flora comprises macrofossils of Equisetum (horsetail), ferns and several Nothofagus species as microphyllous leaves (a leaf-size category of 2.5-7.5cm long), in addition to a few other angiosperms and Podocarpaceae. The Dragon Glacier Moraine flora is similar, the angiosperm leaves being dominated by Nothofagus and the conifers including Araucariaceae and Cupressaceae, in addition to Podo-carpaceae. The Middle Eocene Petrified Forest Creek flora from the Arctowski Cove Formation and the Late Eocene Cytadela flora from the Point Thomas Formation are both within the Ezcurra Inlet Group. The former is a wood flora requiring revision, but intermediate Fagus-Nothofagus-type species are recorded. The Cytadela leaf flora includes ferns (including a Blechnum-affinity species), mostly small Nothofagus-type leaves with pinnately veined leaves of other dicotyledonous types and possible Podocarpaceae (Birkenmajer and Zastawniak, 1989a; Askin, 1992; Birkenmajer, 1997). Birkenmajer and Zastawniak (1989a) considered this flora to be E/O boundary in age.

In this region, therefore, Nothfagus-dominated forests were the norm in the Middle to Late Eocene with ferns and tree ferns becoming increasingly important. Estimated mean annual temperatures of 5-8°C are slightly cooler than those on Seymour Island to the east during the Middle Eocene, and the vegetation was similar to the southernmost Patagonian-Magellanic forests of southern Chile (Zastawniak et al., 1985; Birkenmajer and Zastawniak, 1989a; Askin, 1992; Hunt, 2001). By the Late Eocene, vegetation was more comparable to the recent fern-bush communities of southern oceanic islands (e.g. the Auckland Islands), interpreted from the Cytadela and Petrified Forest Creek floras (Birkenmajer and Zastawniak, 1989a; Askin, 1992; Birkenmajer, 1997). However, mean annual temperature estimates of 11.7-15°C appear too high, especially considering the small-sized leaves (Francis, 1999).

In the Fildes Peninsula area in the southwest of King George Island, the Fildes Peninsula Group contains the contemporary Middle Eocene Collins Glacier and Rocky Cove floras within the Fildes Formation, and the diverse Late Palaeocene-Middle Eocene Fossil Hill flora (Fossil Hill Formation). The latter is a leaf flora containing 40 recognized taxa, including mixed broadleaf angiosperms (with large-leaved Nothofagus species), conifers (podocarp, araucarian and cupressacean) and ferns (Birkenmajer and Zastawniak, 1989a,b; Li, 1992; Haomin, 1994; Francis, 1999; Reguero et al., 2002). Neotropical and sub-Antarctic elements appear to be mixed perhaps indicating a collection derived from communities at different altitudes (Li, 1992), although this mixed signature may be a feature of early Tertiary polar vegetation (Francis et al., 2004). The Nothofagus leaves are much larger than their modern relatives, suggesting a warmer and more humid climate during the early part of the Eocene. Estimates of mean annual temperature suggest >10 °C (from 40% entire-margined leaves) and a small annual temperature range (Li, 1992).

Fossil leaves remain undescribed from the Rocky Cove flora; however, wood from this locality has been identified as Nothofagoxylon antarcticus (Shen, 1994; Hunt, 2001). The Collins Glacier deposit is primarily a wood flora that includes wood of both coniferous (Cupressinoxylon sp. and Podocarpoxylon fildesense) and angiospermous (Nothofagoxylon spp., Weinmannioxylon eucryphioides (Cunoniaceae) and Myceugenelloxylon antarcticus (Myrtaceae)) affinity (Hunt, 2001; Poole et al., 2001, 2005). The mean annual temperature had dropped to 9°C by the Middle Eocene and precipitation appears to have increased; however, the latter is probably due to changes in the environmental setting rather than climate change because of no immediate change in angiosperm wood from a semi-ring to ring porous condition (Poole et al., 2005).

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