Jurassic-cretaceous boundary ammonite blanfordiceras (Mollusca: Cephalopoda) from Fortissimo-1 wildcat well, Browse Basin, northwest shelf, Australia

Jeffrey Stilwell, Matthew Dixon, Benedikt Lehner, Silvia Gamarra

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    Jurassic-Cretaceous ammonites are particularly robust fossil tools in global stratigraphy and correlation. The successive evolution and extinction of these cephalopod mollusks was so rapid that many ammonite zones are no more than one million years in duration. A well-preserved ammonite specimen from the Fortissimo-1 core, Browse Basin, NW Australia is assignable to the widespread latest Jurassic dimorphic berriaselline genus, Blanfordiceras Cossmann, recorded previously from the Spiti area, Nepal, Tibet, Madagascar, Papua-New Guinea, Antarctica, and southern South America. This is the first report of ammonites of this age in the Australian region. The evolute shell of an estimated 90-100 mm diameter (when extrapolated) and pronounced ornamentation of variably bifurcating, curvilinear and flexuous ribs, intercalated with simple, non-bifurcating ribs, is consistent with Blanfordiceras wallichi (Gray, 1832), which has traditionally been restricted to the uppermost Tithonian Stage, ca. 146.5-145.5 Ma, but may well have survived into the earliest part of the Berriasian. The first recorded occurrence of this ammonite in Australia fills an anomalous absence in the paleobiogeographic distribution of Jurassic-Cretaceous boundary ammonites in the Indo-SW Pacific Subrealm with important implications for the calibration of offshore rocks and wells in Australia
    Original languageEnglish
    Pages (from-to)549 - 552
    Number of pages4
    JournalJournal of Paleontology
    Issue number3
    Publication statusPublished - 2011

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