National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)

Chapter: Eocene

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Suggested Citation:"Eocene." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
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Page 166

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THE LATE CRETACEOUS AND CENOZOIC HISTORY OF VEGETATION AND CLIMATE AT NORTHERN AND 166 SOUTHERN HIGH LATITUDES: A COMPARISON taxodiaceous forests. Floras across this region, and in Svalbard and Greenland, suggest a possible thermal maximum for the past 100 m.y. (Heer, 1868; Schweitzer, 1974; Wolfe and Poore, 1982; Francis and McMillan, 1987). During warm intervals of the Middle and Late Eocene, the vegetation of southern Alaska included multistratal rain forest dominated by Palmae, Lauraceae, Menispermaceae, Fagaceae, Theaceae, and other mesothermal families. Further north, the Alaska Eocene vegetation was dominantly broad-leaved deciduous (e.g., Meshik floras). Important elements were Taxodiaceae, "Cercidiphyllum," "Cocculus," Fagus, Quercus, and Juglandaceae (Wolfe, 1966, 1980, 1985; Spicer etal., 1987). These taxa were all derived from lower-latitude ancestors. Oligocene-Miocene-Pliocene Overall diversity decreased into the Early Oligocene, although Pinaceae and Salicaceae increased in diversity and ecological importance. The vegetation included cool temperate, angiosperm-dominated, broad-leaved deciduous forest. Thick coals (at Healey, Alaska) interspersed with very thick conglomerates suggest very high and evenly distributed rainfall (R.A.S., personal observation). Cooling produced a general pattern of southward migrations of particular lineages of closely related species. Salix, which originated in lower latitudes, is diverse in Early Miocene and even more diverse in the later Miocene of the Kenai Group, contrasting with its lower diversity in coeval midlatitude assemblages (Wolfe, 1985). Early Middle Miocene floras on Banks Island (70°-80°N) include Pinus, Picea, Tsuga, and Juglans (Hills et al., 1974). Grasses first became a major component of the pollen flora at about the Miocene-Pliocene transition, and taiga and tundra began to develop on a wide scale (Wolfe, 1985). Taiga appears to develop first in Siberia at about this time (Baranova et al., 1968; Sher et al., 1979) and provides evidence for periglacial conditions. Southern Cenozoic The present ice cover on Antarctica greatly hampers the retrieval of information on Cenozoic (and older) vegetation and climates. Much of our knowledge is derived from careful interpretation of recycled palynomorphs in recent seafloor muds around the coast of Antarctica, with sediment provenance inferred from tracing ice stream paths (Truswell, 1983; Truswell and Drewry, 1984). Only a generalized view of vegetation and climate could be derived from these data, in part because there was no refined age control for many of the (endemic) palynomorphs. This situation should improve as more Antarctic and Subantarctic sediments are drilled and as precise stratigraphic ranges of distinctive palynomorph species are established from these drillholes, and from the rare outcrop localities such as Seymour Island. Paleocene On the Antarctic Peninsula, the southern high latitude lower Paleocene vegetation apparently had decreased diversity (Askin, 1988a). Cuticular evidence suggests that conditions may have been slightly cooler than in the Maastrichtian; however, the composition of dispersed cuticle assemblages and the presence of frost-sensitive epiphyllous fungi preclude severe frost, at least in coastal areas (G. R. Upchurch, University of Colorado, personal communication, 1990). Tree-ring data from conifer and angiosperm wood also suggest cooler conditions through the upper Maastrichtian into the Paleocene (Francis, 1986, 1991). Podocarpaceous conifer-Nothofagus-Proteaceae forest floras continued through the Paleocene. Lagarostrobus remained an important component, and its predominance in Paleocene coals in Australia (Stover and Partridge, 1973; Martin, 1984; Truswell, 1990) and Seymour Island (Fleming and Askin, 1982) highlight its preference for wet habitats. In marginally high latitudes, Cunoniaceae-dominated vine forests with conifers covered the central Australian landscape (Sluiter, 1990), and further south, Nothofagus was becoming more prominent. By the Paleocene, the New Zealand- Campbell Plateau block had separated and was drifting into lower latitudes. Leaf floras from King George Island with Nothofagus, Myrtaceae, various other angiosperms, and ferns, represent a temperate broad-leaved forest with MAT of 10 to 12°C and rainfall of 1000 to 4000 mm/yr (Birkenmajer and Zastawniak, 1989). Seymour Island Paleocene leaf floras are dominated by fern foliage, with microphyllous Nothofagus, other angiosperms (some notophyllous), and conifer foliage, and probably reflect a cool temperate climate (Dusen, 1908; Case, 1988). Evidence for warm, humid conditions in East Antarctica (adjacent to Maud Rise) in the earliest Paleocene is provided by ODP 113 material, with further evidence from subsequent Paleocene lateritic and possible aeolian sediments for warm, semiarid, continental climate in inland East Antarctica (Kennett and Barker, 1990). Eocene The Eocene is marked by diverse floras and a general shift from conifer-dominated forest to Nothofagus-dominated vegetation in the coastal high latitudes. Warmth-loving (frost-sensitive) taxa are present through much of the Eocene, and a warm, moist climate is indicated. Information is available from leaf floras (Dusen, 1908; Case, 1988) and palynomorphs (Zamaloa et al., 1987; Askin et

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What can we expect as global change progresses? Will there be thresholds that trigger sudden shifts in environmental conditions—or that cause catastrophic destruction of life?

Effects of Past Global Change on Life explores what earth scientists are learning about the impact of large-scale environmental changes on ancient life—and how these findings may help us resolve today's environmental controversies.

Leading authorities discuss historical climate trends and what can be learned from the mass extinctions and other critical periods about the rise and fall of plant and animal species in response to global change. The volume develops a picture of how environmental change has closed some evolutionary doors while opening others—including profound effects on the early members of the human family.

An expert panel offers specific recommendations on expanding research and improving investigative tools—and targets historical periods and geological and biological patterns with the most promise of shedding light on future developments.

This readable and informative book will be of special interest to professionals in the earth sciences and the environmental community as well as concerned policymakers.

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