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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 426 (2003), S. 822-826 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Earth's most severe glaciations are thought to have occurred about 600 million years ago, in the late Neoproterozoic era. A puzzling feature of glacial deposits from this interval is that they are overlain by 1–5-m-thick ‘cap carbonates’ (particulate deep-water marine ...
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Key words Atmospheric inputs ; Ecosystem development ; Hawaii ; Metrosideros polymorpha ; Rock weathering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We used isotopes of Sr to quantify weathering versus atmospheric sources of foliar Sr in 34 Hawaiian forests on young volcanic soils. The forests varied widely in climate, and in lava flow age and texture. Weathering supplied most of the Sr in most of the sites, but atmospheric deposition contributed 30–50% of foliar Sr in the wettest rainforests. A stepwise multiple regression using annual precipitation, distance from the ocean, and texture of the underlying lava explained 76% of the variation in Sr isotope ratios across the sites. Substrate age did not contribute significantly to variation in Sr isotope ratios in the range of ages evaluated here (11–3000 years), although atmospheric sources eventually dominate pools of biologically available Sr in Hawaiian rainforests in older substrates (≥150,000 years).
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  • 3
    Publication Date: 2011-04-01
    Description: Neoproterozoic deglacial stratigraphy is commonly characterized by a sharp contact separating glacial sediments from laminated capping carbonates. This stratigraphic relation is generally assumed to have time significance and to reflect an abrupt shift from icehouse to greenhouse conditions. In contrast to this, sequence stratigraphic field studies of an Ediacaran (ca. 635 Ma) glacial to postglacial transition in the Amadeus Basin of central Australia reveal a complex deglacial stratigraphy, in which more than 175 m of conglomerate, sandstone, marl, and carbonate at the basin margin, and portions of four unconformity-bounded sequences, pass basinward into no more than 3 m of laminated dolomicrite of typical cap carbonate facies. The unconformities, which are characterized by as much as several tens of meters of erosional relief (oblique sections of incised valleys), separate intervals of contrasting sediment provenance, and are confidently mapped on the basis of both criteria. Comparable unconformities are absent in the overlying Neoproterozoic succession, which is 〉2 km thick and encompasses many tens of millions of years. The Amadeus Basin cap carbonate was thus deposited during a protracted interval of multiphase (cyclical) transgression more similar to Phanerozoic cyclical sea-level rise than to the single catastrophic deglaciation and instantaneous precipitation invoked by popular current models to explain the classic cap carbonate. The superposition of carbonate on glacial facies in distal sections evidently records condensation in the absence of siliciclastic sediment rather than abrupt shifts between glacial and tropical conditions. Facies lithologically similar to cap carbonates may be less obvious in Phanerozoic successions because of a secular change in carbonate composition to reefal and deep-sea pelagic deposits.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 4
    Publication Date: 2011-06-01
    Description: Here we describe the oldest evidence of non-marine animals from the early Cambrian Wood Canyon Formation, California, evidence created by metazoans of a variety of sizes and behaviors. Millimeter-sized vertical trace fossils, including the U-shaped burrow Arenicolites and the vertical burrow Skolithos, as well as a centimeter-scale horizontal trace fossil, occur in conglomerate and gritty arkosic sandstone bed tops within fluvial channels. These fossils demonstrate that animals were dwelling in this habitat coincident with, or possibly predating, the first trilobites, and extend the freshwater record of animals back at least 80 m.y. The development of a functioning terrestrial ecosystem was concurrent with the early Cambrian marine radiation and suggests that freshwater environments were populated early by metazoans and that ecological opportunity likely played a determining role in metazoan exploitation of non-marine habitats versus commonly assumed influences from physiological or nonbiological barriers.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 5
    Publication Date: 2012-04-01
    Description: Kula et al. (2012) reanalyze our sequence stratigraphic interpretation and carbon isotope data for the younger Neoproterozoic cap carbonate interval in the northeastern Amadeus Basin of central Australia (Kennedy and Christie-Blick, 2011), and conclude that they are incompatible. This conclusion is unwarranted.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 6
    Publication Date: 2012-06-01
    Description: Davies and Gibling (2012) raise concerns that sediments hosting trace fossils in the early Cambrian middle member of the Wood Canyon Formation, which we have interpreted as fluvial, may be marine in origin. They suggest that in the absence of body fossils or specific minerals, it may not be possible to separate marine and fluvial sediments. They point out that there is no single diagnostic sedimentary structure unique to fluvial environments, and that the presence of mudstones and the trace fossils themselves are sufficient evidence for interpreting a marine environment for the middle member of the Wood Canyon Formation. In a second comment, McIlroy (2012) suggests that while the morphology of the trace fossils is different from those recognized in marine members of the Wood Canyon Formation, they are consistent with juvenile traces and those occurring in stressed environments in younger marine sediments, and thus do not uniquely identify a fluvial environment.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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