Cretaceous-tertiary extinctions: alternative models.
Cretaceous-tertiary extinctions: alternative models.
复制标题
白垩纪-第三次灭绝：替代模型。
DOI：
10.1126/science.230.4731.1292
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发表时间：
1985
期刊：
影响因子：
56.9
通讯作者：
F. Kyte
中科院分区：
文献类型：
--
作者：
J. Smit;F. Kyte
Officer and Drake (1) appear to pre-sent a valid alternative to the large impact model for the Cretaceous-Tertiary extinctions. Their basic premise is that the distribution of iridium (Ir) in some sections can only be explained by an event of relatively long duration. This proposal is supported by a model which suggests that Ir distribution extending beyond an interval expected by bioturbation requires a noninstantaneous source for the siderophiles. They further suggest that evidence favors a mantle (volcanic) origin for these elements. We find that (i) the bioturbation model is inaccurately applied and inadequately explains possible sedimentary effects for any given section,(ii) there is no evidence of prolonged Ir sedimentation at any site, and (iii) the volcanic model, although not positively excluded by the data, is not easily reconciled with the data and remains at best a very low probability alternative to the impact hypothesis. The bioturbation interval of 11 cm (5 to 6 cm after compaction) used by Officer and Drake applies only to the homogenization interval for surface sediments. As deposition (and burial) proceeds, old-er sediments continue to be mixed upward. Sediments that are deposited in-stantaneously (like microtektites or ash) can be spread over tens of centimeters (2). Table 1 shows the observed distribution of microtektites (3), which are spread over a minimum of 35 cm and an average of 59 cm. Bioturbation is only one process that will affect Ir distribution after a presumed impact. Other poten-tially important processes include diagenetic mobilization, secondary deposition after transport by bottom currents, and
