Jurassic ammonite faunas from Nepal and their bearing on the palaeobiogeography of the Himalayan belt |
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| Authors: | Raymond Enay Elie Cariou |
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| Institution: | 1. Higher Marsh Farm, Marsh Lane, Henstridge, Somerset BA8 0TQ, UK;2. Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK;3. Institute of Geology, Mineralogy and Geophysics, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany |
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| Abstract: | From the Upper Bathonian up to the Tithonian–Berriasian, six main faunas and twelve basic faunal assemblages within them are distinguished in Nepal. The successive faunas show (1) low taxonomic diversity and (2) the dominance of a small number of genera and the subordinate place of the associated taxa.The assemblages include: (1) strictly Tethyan (e.g., Mediterranean or European Tethyan) species and/or genera, very few in number and occurring as isolated individuals or discontinuous faunal horizons; (2) Indo-Malagasian components, some scattered, others with a wide occurrence in the SW Pacific, some as far as Antarctica and/or Patagonia; (3) indigenous genera endemic for the Himalayas and the SW Pacific region. Faunas of the same age for the Sula Islands, Papua-New Guinea, Australia, New Zealand, Antarctica and South America are also considered.In spite of common components, the Himalayan faunas contrast with the relatively higher diversity of the Indo-Malagasian faunas. Low diversity and dominance of indigenous genera mean that the faunas extending from the Himalayas to Antarctica and Patagonia represent an actual biogeographical unit, the Indo Pacific (faunas and) Realm.Indo Pacific and Tethyan faunas show a less marked contrast than the Tethyan and Boreal. Transitional or mixed faunas of subaustral type developed in the Indo-Malagasian and Andean regions. This is explained by the absence of a geographical trap comparable to the land-locked palaeogeography of the Arctic Basin. The palaeogeography of the Arctic amplified the role of the other environmental factors. Among these the high latitude seasonal effects are likely to have resulted in environmental instability, controlling trophic resources and therefore the structure of the ecosystems, for instance low diversity and high density of the high latitude ammonite faunas. |
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| Keywords: | Ammonites Jurassic Himalayas Nepal Palaeobiogeography Indo Pacific Austral fauna |
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