R. Farley Fleming
Douglas J. Nichols
1990
<p><span>Shortly after the introduction of the extraterrestrial-impact hypothesis of the </span>terminal<span> </span>Cretaceous<span> </span>event<span> (TCE), </span>plant<span> microfossils, which had been used to locate the </span>Cretaceous<span>/Tertiary (K/T) boundary </span>in<span> nonmarine rocks, became critical to its precise identification; they continue to serve </span>in<span> this capacity. The K/T boundary </span>in<span> nonmarine rocks from New Mexico to Alberta is identified by the coincidence of a palynological extinction horizon and an iridium abundance anomaly. </span>Plant<span> microfossils provide evidence of the effects of the TCE and place constraints on theories of its cause. Changes </span>in<span> </span>plant<span> </span>microfossil<span> assemblages within intervals spanning the K/T boundary are evidence of abrupt and permanent changes </span>in<span> terrestrial, floras that were a consequence of the TCE; these changes are essentially independent of lithofacies. Extinction levels varied among major groups of plants (angiosperms, gymnosperms, and pteridophytes), but simultaneously affected different </span>plant<span> communities throughout the region. The abrupt nature of the extinction across </span>western<span> North America is consistent with the impact hypothesis; it is inconsistent with progressive change </span>in<span> paleoclimate possibly being the cause of the </span>terminal<span> </span>Cretaceous<span> extinctions. By causing the extinction of a significant portion of the Late </span>Cretaceous<span> flora of the region, the TCE influenced the development of the modern flora, but its effects appear to have been concentrated </span>in<span> </span>western<span> North America.</span></p>
application/pdf
10.1130/SPE247-p445
en
Geological Society of America
Plant microfossil record of the terminal cretaceous event in the western United States and Canada
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