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Pollen and spores in marine Cretaceous/Tertiary boundary sediments at mid‐Waipara River, North Canterbury, New Zealand

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New Zealand Journal of Geology and Geophysics

Informa UK Limited

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      Most cited references 53

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      Extraterrestrial cause for the cretaceous-tertiary extinction.

       H Michel,  F Asaro,  W Alvarez (1980)
      Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rock; a fraction of this dust would stay in the stratosphere for several years and be distributed worldwide. The resulting darkness would suppress photosynthesis, and the expected biological consequences match quite closely the extinctions observed in the paleontological record. One prediction of this hypothesis has been verified: the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 +/- 4 kilometers.
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        The development of paleoseaways around Antarctica

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          Fossil in situ spores and pollen grains: an annotated catalogue

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            Author and article information

            Journal
            New Zealand Journal of Geology and Geophysics
            New Zealand Journal of Geology and Geophysics
            Informa UK Limited
            0028-8306
            1175-8791
            June 2003
            June 2003
            : 46
            : 2
            : 255-273
            10.1080/00288306.2003.9515008
            © 2003

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