Plant Macrofossils

An important source of palaeoclimate information on land comes from fossil plants (both macro- and microfossils) (Fig. 8.7). The fossil plant record suggests that during the Late Palaeocene to Early Eocene moist, cool temperate rainforests were present, similar to modern low to mid-altitude Valdivian rainforests in southern Chile. These forests were dominated by Nothofagus and conifer trees, with ferns, horsetails and some less-prominent angiosperm groups. Assemblages of Eocene fossil plants and palynomorphs signal a generally warm climate during the Early Eocene but conditions deteriorated throughout the Antarctic Peninsula through the latter part of the Eocene when cold, seasonal climates developed (Francis, 1991; Francis and Poole, 2002; Francis et al., 2004, 2008; Poole et al., 2005).

Fossil plant assemblages of younger age have been found in glacial sediments in the Transantarctic Mountains, representing vegetation that grew on Antarctica under icehouse conditions. These include the Sirius Group flora from the Transantarctic Mountains (the age of which is problematic, Francis and Hill, 1996; Wilson et al., 1998a,b; Askin et al., 1999), and a new flora of Miocene age discovered in the Dry Valleys (Ashworth et al., 2008). Surprisingly, leaf fossils, although single leaves, have also been discovered in drill cores within Oligocene and Miocene glacial sequences. The early glacial world of Antarctica was clearly not totally barren of vegetation.

Palaeogene fossil plants have been discovered from around the Antarctic margin in outcrop, in sea-floor cores and in glacial erratic boulders from the Antarctic Peninsula (King George Island and Seymour Island) and Ross Sea (McMurdo Sound and Minna Bluff) regions. The collections consist of compressions, impressions and petrifactions of leaves, seeds, flowers and wood indicating a high southern latitude flora of variable diversity but dominated by fossils comparable to modern Nothofagus (the southern beech) and conifer trees. Ferns, horsetails and additional significant Southern

On s

Stratigraphie age

Flora

Composition

Vegetation model

Modern analogue

Inferred palaeoclimate

King George Island. South Shetland Islands:

Late Eocene

Nothofagus-type (mostly small) and other dicotyledon types ?Podocarpaceae

Nothofagus forest with well-developed undergrowth, where ferns (including tree

Recent fern-bush communities of southern oceanic islands, e.g. Gough

Moist

Petrified Forest Creek

Fagus-Nothofagus Araucaria

ferns) are important

and Auckland Islands

(MAP 1220-3225mm)1

Late

Palaeocene-

MiddJe

Eocene

Several Nothofagus spp. (microphyllous leaves) and a few other angiosperms Podocarpaceae

Nothofagus-Podocarpus dominated communities

Patagonian-Magellanic rainforests, Chile

Cool temperate (MAT 5-8°C)

Moist (600-4300mm)

Dragon Glacier Moraine

Equisetum Ferns

Angiosperms (dominated by Nothofagus spp.) Conifers (Araucariaceae, Cupressaceae, Podocarpaceae)

Temperate rainforest

Valdivian rainforests, Chile

MAT c. 10°C MAP c. 1000mm

1 Although the small leaves suggest this may be too warm (Francis, 1999).

1 Although the small leaves suggest this may be too warm (Francis, 1999).

Figure 8.7: Antarctic Peninsula Late Palaeocene-Late Eocene fossil floras: composition, modern analogue vegetation and palaeoclimate interpretations. Refer to text for relevant references. MAT: mean annual temperature; MAP: mean annual precipitation.

Stratigraphic Flora J>£<L_

Composition

Vegetation model Modern analogue Inferredpalaeoclimate

Late

Palaeocene-Middle Eocene ( continued )

Fossil Hill 40 taxa:

Ferns

Mixed broadleaf angiosperms (dominated by Nothofagus spp.) Conifers (podocarp, araucarian, cupressacean)

Rainforest - mixed neotropical and subantarctic elements2

Tropical Latin America and southern South American rainforests

Collins Glacier

Seymour Island, James Ross Basin:

Ferns

Angiosperms (including

Nothofagoxylon spp.,

Weinmannioxylon euctyphioides,

Myceugenelloxylon ontorcticus Conifers (Aroucorio, Cup res sin oxylon, Podocarpoxylon filde sense)

Cool temperate rainforest

Low-mid altitude Valdivian rainforests, Chile

Temperate - warm temperate3 Slightly above 10 C with a low annual temperature range (MAT c.9 C), Abundant precipitation

Cool temperate

Early-latest La Meseta Fm. Ferns, angiosperms and conifers Late Eocene including: Nothofagus spp.

(notophyllous at older Middle Eocene locality ), Dilleniaceae, Myricaceae, Myrtaceae, Lauraceae, Proteaceae, _Podocarpaceae, Araucariaceae

Cool - cold temperate rainforest

Valdivian and Magellanic rainforests, Chile

Cool to cold temperate (MAT 11-13°C or 10.8°C) with abundant rainfall (MAP 1000-3000mm) Seasonal.

" Perhaps altitude related?

3 The Nothofagus leaves in the Fossil Hill flora are much bigger than their modern relatives suggesting a warmer and more humid climate during the Middle Eocene.

Figure 8.7: (Continued).

Hemisphere angiosperm families, including the Proteaceae, Myrtaceae and Lauraceae, are also represented. The macrofossil record has largely been described from isolated collections, even of single leaves in cores, and although reasonably dated as a whole, a comprehensive understanding of stratigraphic relationships between the floras, particularly in the Antarctic Peninsula region, is at present hampered by differing stratigraphic interpretations.

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