Plant assemblages from SW Gondwana: further evidence for high-latitude vegetation in the Devonian of Argentina
D. Edwards, D. G. Poiré, E. M. Morel, C. A. Cingolani, 2009. "Plant assemblages from SW Gondwana: further evidence for high-latitude vegetation in the Devonian of Argentina", Early Palaeozoic Peri-Gondwana Terranes: New Insights from Tectonics and Biogeography, M. G. Bassett
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Plant assemblages are described from the Talacasto and Punta Negra Formations, San Juan Province, the Argentine Precordillera. A detailed facies study involving trace fossil assemblages indicates that the plants were buried in shallow low- to high-energy marine environments, but not in turbidites as previously postulated. Apart from a single specimen resembling Cooksonia from the Lochkovian Talacasto Formation, the abundant compression fossils consist of short lengths of smooth axes, occasional defoliated lycopod stems, and very rare isolated sporangia. It is thus impossible to assign any to existing taxa with confidence nor are there sufficient distinguishing characters to erect new ones. Although the possible age of the formations in the Precordillera remains conjectural, the fossils themselves, even preserved in such fragmentary states, indicate much lower grades of organization than seen in coeval assemblages elsewhere, particularly on the Laurussian and South China palaeocontinents. Palaeocontinental reconstructions of Gondwana indicate that the localities are within 30° of the palaeo South Pole. Thus a global latitudinal gradient in vegetation is postulated for the Early Devonian with decreasing disparity and diversity at higher latitudes. An explanation for the latter is explored in terms of light regime and temperature in highly stressed environments.
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Following the late Neoproterozoic – early Cambrian breakup of the supercontinent Rodinia, Gondwana evolved as one of the principal continental masses on Earth, embracing most of South America, Africa, Australasia, Antarctica, much of western Europe and parts of Asia. Around its margins were various other terranes that had varying tectonic and biogeographical affinities with the main continental block. This book incorporates a series of reviews and multidisciplinary research papers that together explore the tectonic, palaeogeographical and palaeobiogeographical evolution of the elements that made up the peri-Gondwanan collage. The stratigraphical scope of the coverage embraces the late Precambrian through early Devonian, providing a comprehensive overview of structural, stratigraphical and biological evolution through this significant interval of Earth history. Integration of these various processes throughout the volume will be of broad-based interest to a wide range of geoscientists.