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Figure 7.39 Palynostratigraphy of the K-T boundary interval on the North Slope of Alaska (from Frederiksen et al. 1998). Horizontal line marks position of the K-T boundary. Reprinted by permission.

diversity of Maastrichtian taxa (including some interpreted as reworked) dropped to a fraction of Cretaceous values, and where there is also a distinct drop in the ratio of strictly Maastrichtian specimens to specimens of species most common in the Paleocene. The location of the boundary was uncertain because it was bracketed within a sandy interval that may include a small disconformity. Despite rapid turnover of pollen taxa in the upper Maastrichtian (which Frederiksen et al. 1998 attributed to climatic deterioration), taxonomic diversity is constant until 15-30 m below the chosen boundary level. In the last 15-30 m below the boundary, last appearances of taxa are more numerous than first appearances. Nonetheless, most Maastrichtian taxa range to the top of the Cretaceous or nearly so (Figure 7.39). Frederiksen et al. (1998) discussed the influence of the Signor-Lipps effect (see Section 1.3) on the pattern of diversity in the uppermost Cretaceous and concluded

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