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21/11/16 Seminaire Européen. David Harper (Durham University)

Titre: On the cusp of animal domination: Cambrian bodies in the Sirius Pass, North Greenland (a l'ENS, amphi L)
Quand ? Le 10/10/2016,
de 14:00 à 15:00
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On the cusp of animal domination: Cambrian bodies in the Sirius Pass, North Greenland    

    The early Cambrian exceptionally-preserved biotas provide critical evidence for the initial construction of animal-based communities, the early diversification and relationships of the metazoans, the environmental constraints on the appearance of modern ecosystems. The Sirius Passet fossil biota is the most remote and least well known of all the Cambrian Lagerstätten. Following its serendipitous discovery in 1984 by the geological Survey of Greenland, the locality in the Buen Formation, Peary Land, North Greenland, has been visited a number of times, most recently in 2009 and 2011 by multidisciplinary and multinational groups, led by the Natural History Museum of Denmark. The Sirius Passet Lagerstätte occurs in black slates deposited at or just below storm wave base, deposited by low-density sediment gravity flows. The formation is c. 516.5-519 Ma and contemporary with or possibly older than the Chengjiang Lagerstätte from the Yangtze platform in South China. It thus represents the earliest Cambrian microbial mat community with exceptional preservation, predating the Burgess Shale by 10 million years. Here we have an opportunity to observe a very major turning point in the history of life.
    The Sirius Passet fauna is broadly similar to that of the Burgess Shale, but to date only comprises ca. 50 species including trilobites, sponges, worms, halkieriids, lobopods, and non-trilobite bivalved arthropods. The fauna is one of the earliest examples of high-fidelity, soft-tissue preservation in the Cambrian. The remarkable siliceous death mask preservation of its very abundant trilobite fauna opens a new window on the environment and location of the Cambrian Explosion. This window closed with the appearance of abundant mat grazers later as the Cambrian Explosion intensified.
    Geochemical clues of early Cambrian oceanic conditions primarily stem from sections on the Yangtze platform, suggesting a low-oxygen ocean with possibly oxygen minimum conditions. Additional information from Sirius Passet significantly extends the geographic spread of our understanding of ocean chemistry at this critical time and provides an indication of possible drivers for the early stages of the Cambrian Explosion.



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Département ENS
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    Stéphane Labrosse
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