863 resultados para Betula alleghaniensis


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Neogene palynofloras of southern California have been all too infrequently studied. Previous investigations of Pacific Coast sediments have been largely restricted to Pacific Northwest locales. Some important studies include those by Gray (1964), Wolfe, Hopkins, and Leopold (1966), Wolfe and Leopold (1967), Hopkins (1968), Piel (1969, 1977), Ballog, Sparks, and Waloweek (1972), and Musich (1973). The only published study of southern California materials is that of Heusser (1978) on Holocene sediments of the Santa Barbara basin. Most of these studies are concerned with the microflora from a particular formation; thus they have limited stratigraphic value and in most cases involve nonmarine to marginal marine rocks where no planktonic zonation was available. Musich's (1973) study was the first attempt at tying pollen assemblages to a planktonic zonation over an extended stratigraphic interval (Miocene to Pleistocene).Its location in the southern California Borderland and the sedimentary sections sampled make Leg 63 extremely valuable in deciphering the palynologic history of the Pacific Coast Neogene. Site 467 was chosen for our initial detailed study, because the relatively slow sedimentation rate provides an almost complete Neogene sequence of mainly terrigenous sediments and reliable planktonic age control is available.The goals of this study were to: (1) establish a reference section of Neogene palynomorph assemblages; (2) develop biostratigraphic criteria for use in correlation with other localities; (3) correlate the palynologic assemblages with the planktonic zonations; and (4) study the paleoenvironmental history in the southern California Neogene.

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Pollen, plant macrofossil, loss-on-ignition and radiocarbon analyses of a 1.4-m section in thermokarst topography from Faddeyevskiy Island (75°20'N, 143°50'E, 30 m elevation) provides new information on Late Pleistocene interstadial environmental history of this high Arctic region. Conventional radiocarbon dates (25,700 ± 1000, 32,780 ± 500, 35,200 ± 650 yr BP) and two AMS dates (29,950 ± 660 and 42,990 ± 1280 yr BP) indicate that the deposits accumulated during the Kargian (Boutellier) interval. Numerous mammoth (Mammuthus primigenius) remains that have been collected in vicinity of the site in this study were radio-carbon dated to 36,700-18,500 yr BP. Rare bison (Bison priscus) bones were dated to 32,200 ± 600 and 33,100 ± 320 yr BP. Poaceae, Cyperaceae, and Artemisia pollen dominate the spectra with some Ranunculaceae, Caryophyllaceae, Rosaceae, and Asteraceae. The pollen spectra reflect steppe-like (tundra-steppe) vegetation, which was dominant on the exposed shelf of the Arctic Ocean. Numerous Carex macrofossils suggest that the summer climate was at least 2°C warmer than today. The productivity of the local vegetation during the Kargian interstadial was high enough to feed the population of grazing mammals.