The integration of classical paleontological methods and "absolute" radiometric methods for the establishment of the time parameter for geologic processes during the Paleozoic Era has been barely initiated. Sufficient preliminary radiometric data have been obtained on stratigraphically assignable materials to give approximate time interval assignments to the Paleozoic Era and its constituent periods. Yet there are fewer than half a dozen correlation points which begin to possess the documentation from both approaches that is necessary and feasible.

For each of the various Paleozoic systems it is a reasonable estimate that 20 ± 10 resolvable faunal zones can be distinguished consistently. Accepting present estimates for the duration of the Paleozoic in absolute time, this could provide the corresponding average resolving power of ± 2-3 m.y. if the faunal zones were successfully calibrated. Utilizing optimal geological materials and adequate sampling and analytical procedures, it should be possible to establish radiometric ages with precisions of ± 5 to ± 2 m.y. from the beginning to the end of the Paleozoic. Discrepancies in radioactive decay constants can be normalized to ^lgr U²³⁸, adequately, for such purposes. Thus the potential resolving power of the radiometric and paleontologic methods is com arable.

A successful effort at cross-calibration could provide the basis for the determination of the important time constants for the great host of significant geologic processes ranging from faunal evolution to orogeny recorded for the Paleozoic interval. The keys to such an effort are: (1) a careful geologic search for the definitive sampling sites; (2) realistic evaluation of stratigraphic assignments using as many independent faunal elements as possible; and (3) persistent application of several radiometric methods to materials whose geologic context at the sample site has been established by careful mapping and petrologic study. A preliminary evaluation suggests that numerous sites containing intraformational tuffs, intercalated volcanic rocks, and stratigraphically assigned plutonic ro ks exist in North America and Europe. A coordinated interlaboratory effort should be a major geological objective in the next 5 years.

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