Permian and Triassic Floras of the Beardmore Glacier Area: Icehouse or Greenhouse?

点击翻译按钮获取中文摘要

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for research to investigate fossil plants from the central Transantarctic Mountains toward an understanding of plant diversity and evolution as well as an improved understanding of the paleoenvironmental conditions. The terrestrial rocks of the central Transantarctic Mountains have been a source of outstanding plant fossil discoveries over the last 30 years, including Permian and Triassic permineralized peat, fossil forests silicified in growth position, and compression floras with cuticular preservation. The rare juxtaposition of sites that include many different types of plant preservation (permineralization, compression/impression, in situ forests, mummified wood), the exceptional quality of the plant preservation, and the richness of the sites make this area unique in the world. This project centers on the collection of Permian and Triassic plant megafossils from the Beardmore Glacier area. Fieldwork is anticipated in the 2003-2004 field season as part of a mini-camp with other researchers. Collections would include compression floras, especially those from Graphite Peak, and permineralized peats from Skaar Ridge and Fremouw Peak, both in the vicinity of Walcott Neve. These permineralizations represent the rarest form of plant fossil preservation. Since they preserve a three-dimensional record of the flora, they are important in understanding the basic morphology and anatomy of fossil plants, as well as detailing relationships among groups. The additional data provided by the juxtaposition of plant fossils preserved both as permineralizations and compressions have already contributed a great deal to our understanding of late Paleozoic-early Mesozoic plant evolution. This project will address several important phylogenetic hypotheses through further collection of material, coupled with material already processed. The Permian and Triassic represent an important time in plant evolution, and one about which we still know relatively little, especially in the southern hemisphere. The glossopterid seed ferns in the Permian (leaf type, Glossopteris), and the corystosperms in the Triassic (leaf type, Dicroidium) were the dominant plant groups in Gondwana. Since both of these groups bore seeds which were enclosed in some manner, they have been proposed at one time or another as possible ancestors of the flowering plants, and have figured prominently in phylogenetic analyses of seed plants. Only through a combination of permineralizations and compressions is it possible to reveal a complete picture of the form and structure of fossil plants, but more importantly, to understand the position of these plant groups in seed plant evolution. Plants and silicified logs will be collected from the section at Graphite Peak, which is believed to contain the Permian/Triassic boundary. These plant fossils will be used to test several hypotheses concerning the floral and paleoclimate changes that may have occurred across this boundary. These include: How early in the Triassic does the Dicroidium flora appear? Does Glossopteris occur with Dicroidium as it does in several other Gondwana floras? Is there any evidence of a megaflora dominated by lycopods, as some of the palynological evidence suggests? Silicified logs have been noted in the lower Buckley Formation (mid-Permian?) at this site and these will be collected and examined for paleoclimate data from tree rings. These can also be compared with tree rings in Late Permian wood (upper Buckley) from nearby Mt. Achernar. The Late Permian has been assumed to be much warmer than Early-Middle Permian and this should be reflected in differences in the width and structure of the tree rings.This project is expected to lead to significant improvements in understanding of both plant evolution and paleoenvironmental conditions during the critical Permian to Triassic interval.